Investigation of the complex reaction coordinate of acid catalyzed amide hydrolysis from molecular dynamics simulations

International Nuclear Information System (INIS)

Zahn, Dirk

2004-01-01

The rate-determining step of acid catalyzed peptide hydrolysis is the nucleophilic attack of a water molecule to the carbon atom of the amide group. Therein the addition of the hydroxyl group to the amide carbon atom involves the association of a water molecule transferring one of its protons to an adjacent water molecule. The protonation of the amide nitrogen atom follows as a separate reaction step. Since the nucleophilic attack involves the breaking and formation of several bonds, the underlying reaction coordinate is rather complex. We investigate this reaction step from path sampling Car-Parrinello molecular dynamics simulations. This approach does not require the predefinition of reaction coordinates and is thus particularly suited for investigating reaction mechanisms. From our simulations the most relevant components of the reaction coordinate are elaborated. Though the C···O distance of the oxygen atom of the water molecule performing the nucleophilic attack and the corresponding amide carbon atom is a descriptor of the reaction progress, a complete picture of the reaction coordinate must include all three molecules taking part in the reaction. Moreover, the proton transfer is found to depend on favorable solvent configurations. Thus, also the arrangement of non-reacting, i.e. solvent water molecules needs to be considered in the reaction coordinate

Degradation of Perfluorooctanoic Acid and Perfluoroctane Sulfonate by Enzyme Catalyzed Oxidative Humification Reactions

Science.gov (United States)

Huang, Q.

2016-12-01

Poly- and perfluoroalkyl substances (PFASs) are alkyl based chemicals having multiple or all hydrogens replaced by fluorine atoms, and thus exhibit high thermal and chemical stability and other unusual characteristics. PFASs have been widely used in a wide variety of industrial and consumer products, and tend to be environmentally persistent. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two representative PFASs that have drawn particular attention because of their ubiquitous presence in the environment, resistance to degradation and toxicity to animals. This study examined the decomposition of PFOA and PFOS in enzyme catalyzed oxidative humification reactions (ECOHR), a class of reactions that are ubiquitous in the environment involved in natural organic humification. Reaction rates and influential factors were examined, and high-resolution mass spectrometry was used to identify possible products. Fluorides and partially fluorinated compounds were identified as likely products from PFOA and PFOS degradation, which were possibly formed via a combination of free radical decomposition, rearrangements and coupling processes. The findings suggest that PFOA and PFOS may be transformed during humification, and ECOHR can potentially be used for the remediation of these chemicals.

Visible-Light Photoredox-Catalyzed Giese Reaction: Decarboxylative Addition of Amino Acid Derived α-Amino Radicals to Electron-Deficient Olefins

KAUST Repository

Millet, Anthony

2016-06-20

A tin- and halide-free, visible-light photoredox-catalyzed Giese reaction was developed. Primary and secondary α-amino radicals were generated readily from amino acids in the presence of catalytic amounts of an iridium photocatalyst. The reactivity of the α-amino radicals has been evaluated for the functionalization of a variety of activated olefins. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Visible-Light Photoredox-Catalyzed Giese Reaction: Decarboxylative Addition of Amino Acid Derived α-Amino Radicals to Electron-Deficient Olefins

KAUST Repository

Millet, Anthony; Lefebvre, Quentin; Rueping, Magnus

2016-01-01

A tin- and halide-free, visible-light photoredox-catalyzed Giese reaction was developed. Primary and secondary α-amino radicals were generated readily from amino acids in the presence of catalytic amounts of an iridium photocatalyst. The reactivity of the α-amino radicals has been evaluated for the functionalization of a variety of activated olefins. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Base catalyzed transesterification of acid treated vegetable oil blend for biodiesel production

Energy Technology Data Exchange (ETDEWEB)

Yusup, Suzana; Khan, Modhar Ali [Chemical Engineering Department, Universiti Teknologi PETRONAS, Seri Iskandar, Tronoh, Perak 31750 (Malaysia)

2010-10-15

Biodiesel can be produced from low cost non-edible oils and fats. However, most of these sources are of high free fatty acid content which requires two stage transesterification to reduce the acid value and produce biodiesel. The acid treatment step is usually followed by base transesterification since the latter can yield higher conversions of methyl esters at shorter reaction time when compared with acid catalyzed reaction. In the current study, base transesterification in the second stage of biodiesel synthesis is studied for a blend of crude palm/crude rubber seed oil that had been characterized and treated with acid esterification. Optimum conditions for the reaction were established and effect of each variable was investigated. The base catalyzed transesterification favored a temperature of 55 C with methanol/oil molar ratio of 8/1 and potassium hydroxide at 2% (ww{sup -1}) (oil basis). The conversion of methyl esters exceeded 98% after 5 h and the product quality was verified to match that for biodiesel with international standards. (author)

An efficient synthesis of isocoumarins via a CuI catalyzed cascade reaction process

Institute of Scientific and Technical Information of China (English)

无

2009-01-01

3-Alkyl isocoumarins are provided by CuI/amino acid-catalyzed Sonogashira coupling reaction of o-bromo benzoic acids and terminal alkynes and the subsequent additive cyclization. This cascade process allows synthesis of diverse isocoumarins by varying both coupling partners bearing a wide range of functional groups.

Gold-Catalyzed Formal C-C Bond Insertion Reaction of 2-Aryl-2-diazoesters with 1,3-Diketones.

Science.gov (United States)

Ren, Yuan-Yuan; Chen, Mo; Li, Ke; Zhu, Shou-Fei

2018-06-29

The transition-metal-catalyzed formal C-C bond insertion reaction of diazo compounds with monocarbonyl compounds is well established, but the related reaction of 1,3-diketones instead gives C-H bond insertion products. Herein, we report a protocol for a gold-catalyzed formal C-C bond insertion reaction of 2-aryl-2-diazoesters with 1,3-diketones, which provides efficient access to polycarbonyl compounds with an all-carbon quaternary center. The aryl ester moiety plays a crucial role in the unusual chemoselectivity, and the addition of a Brønsted acid to the reaction mixture improves the yield of the C-C bond insertion product. A reaction mechanism involving cyclopropanation of a gold carbenoid with an enolate and ring-opening of the resulting donor-acceptor-type cyclopropane intermediate is proposed. This mechanism differs from that of the traditional Lewis-acid-catalyzed C-C bond insertion reaction of diazo compounds with monocarbonyl compounds, which involves a rearrangement of a zwitterion intermediate as a key step. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of 2-monoacylglycerols and structured triacylglycerols rich in polyunsaturated fatty acids by enzyme catalyzed reactions.

Science.gov (United States)

Rodríguez, Alicia; Esteban, Luis; Martín, Lorena; Jiménez, María José; Hita, Estrella; Castillo, Beatriz; González, Pedro A; Robles, Alfonso

2012-08-10

This paper studies the synthesis of structured triacylglycerols (STAGs) by a four-step process: (i) obtaining 2-monoacylglycerols (2-MAGs) by alcoholysis of cod liver oil with several alcohols, catalyzed by lipases Novozym 435, from Candida antartica and DF, from Rhizopus oryzae, (ii) purification of 2-MAGs, (iii) formation of STAGs by esterification of 2-MAGs with caprylic acid catalyzed by lipase DF, from R. oryzae, and (iv) purification of these STAGs. For the alcoholysis of cod liver oil, absolute ethanol, ethanol 96% (v/v) and 1-butanol were compared; the conditions with ethanol 96% were then optimized and 2-MAG yields of around 54-57% were attained using Novozym 435. In these 2-MAGs, DHA accounted for 24-31% of total fatty acids. In the operational conditions this lipase maintained a stable level of activity over at least 11 uses. These results were compared with those obtained with lipase DF, which deactivated after only three uses. The alcoholysis of cod liver oil and ethanol 96% catalyzed by Novozym 435 was scaled up by multiplying the reactant amounts 100-fold and maintaining the intensity of treatment constant (IOT=3g lipase h/g oil). In these conditions, the 2-MAG yield attained was about 67%; these 2-MAGs contained 36.6% DHA. The synthesized 2-MAGs were separated and purified from the alcoholysis reaction products by solvent extraction using solvents of low toxicity (ethanol and hexane); 2-MAG recovery yield and purity of the target product were approximately 96.4% and 83.9%, respectively. These 2-MAGs were transformed to STAGs using the optimal conditions obtained in a previous work. After synthesis and purification, 93% pure STAGs were obtained, containing 38% DHA at sn-2 position and 60% caprylic acid (CA) at sn-1,3 positions (of total fatty acids at these positions), i.e. the major TAG is the STAG with the structure CA-DHA-CA. Copyright © 2012 Elsevier Inc. All rights reserved.

Efficient Synthesis of Spirobarbiturates and Spirothiobarbiturates Bearing Cyclopropane Rings by Rhodium(II)-Catalyzed Reactions of Cyclic Diazo Compounds

International Nuclear Information System (INIS)

Wang, Xue; Lee, Yong Rok

2013-01-01

Rhodium(II)-catalyzed reactions of cyclic diazo compounds derived from barbituric acid and thiobarbituric acid with a variety of styrene moieties were examined. These reactions provide rapid synthetic routes to the preparations of spirobarbiturates and spirothiobarbiturates bearing cyclopropane rings

Efficient Synthesis of Spirobarbiturates and Spirothiobarbiturates Bearing Cyclopropane Rings by Rhodium(II)-Catalyzed Reactions of Cyclic Diazo Compounds

Energy Technology Data Exchange (ETDEWEB)

Wang, Xue; Lee, Yong Rok [Yeungnam Univ., Gyeongsan (Korea, Republic of)

2013-06-15

Rhodium(II)-catalyzed reactions of cyclic diazo compounds derived from barbituric acid and thiobarbituric acid with a variety of styrene moieties were examined. These reactions provide rapid synthetic routes to the preparations of spirobarbiturates and spirothiobarbiturates bearing cyclopropane rings.

Decomposition of peracetic acid catalyzed by vanadium complexes

International Nuclear Information System (INIS)

Makarov, A.P.; Gekhman, A.E.; Moiseev, I.I.; Polotryuk, O.Y.

1986-01-01

This paper studies the decomposition of peracetic acid (AcOOH) in acetic acid (AcOH) catalyzed by vanadium complexes. It is shown that peractic acid in acetic acid solutions of ammonium anadate decomposes with the predominant formation of 0 2 and small amounts of CO 2 , the yield of which increases with increasing temperature and peracetic acid concentration. Both reactions proceed without the formation of free radicals in amounts detectable by ESR spectroscopy. The rate of oxygen release under conditions in which the formation of CO 2 is insignificant obeys a kinetic equation indicating the intermediate formation of a complex between V 5+ ions and peracetic acid and the slow conversion of this complex into the observed products

Diazo compounds and N-tosylhydrazones: novel cross-coupling partners in transition-metal-catalyzed reactions.

Science.gov (United States)

Xiao, Qing; Zhang, Yan; Wang, Jianbo

2013-02-19

Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo

Theoretical Study on the Aza-Diels-Alder Reaction Catalyzed by PHCl2 Lewis Acid via Pnicogen Bonding.

Science.gov (United States)

Yaghoobi, Fereshteh; Sohrabi Mahboub, Mahdi

2018-03-15

The reaction mechanism of the Aza-Diels-Alder (A-D-A) cycloaddition reaction between X 2 C═NNH 2 , where X = H, F, Cl, Br, and 1,3-butadiene catalyzed by a PHCl 2 Lewis acid was characterized using density functional theory calculations. The influences of various substituents of X on the studied reaction were analyzed using the activation strain model (ASM), which is also termed as the distortion-interaction model. Calculations showed that the smallest and largest values of the activation energies belong to the substituents of F and Br, respectively. The activation energy of the studied reactions was decreased within 8.6 kcal·mol -1 in the presence of PHCl 2 catalyst. Investigations showed that the pnicogen bonding is adequately capable of activating the A-D-A reaction. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were implemented to understand the nature of C 4,Cbut ···C XIm and C 1,Cbut ···N XIm bonds at the TS structures. Additionally, the energy decomposition analysis (EDA) based on the ETS-NOCV scheme was used to characterize the nature of C 4,Cbut ···C XIm and C 1,Cbut ···N XIm bond. The results of the study mirror the fact that the PHCl 2 Lewis acid may be suggested as a simple suitable catalyst for experimental studies on the A-D-A reactions.

Desaturation reactions catalyzed by soluble methane monooxygenase.

Science.gov (United States)

Jin, Y; Lipscomb, J D

2001-09-01

Soluble methane monooxygenase (MMO) is shown to be capable of catalyzing desaturation reactions in addition to the usual hydroxylation and epoxidation reactions. Dehydrogenated products are generated from MMO-catalyzed oxidation of certain substrates including ethylbenzene and cyclohexadienes. In the reaction of ethylbenzene, desaturation of ethyl C-H occurred along with the conventional hydroxvlations of ethyl and phenyl C-Hs. As a result, styrene is formed together with ethylphenols and phenylethanols. Similarly, when 1,3- and 1,4-cyclohexadienes were used as substrates, benzene was detected as a product in addition to the corresponding alcohols and epoxides. In all cases, reaction conditions were found to significantly affect the distribution among the different products. This new activity of MMO is postulated to be associated with the chemical properties of the substrates rather than fundamental changes in the nature of the oxygen and C-H activation chemistries. The formation of the desaturated products is rationalized by formation of a substrate cationic intermediate, possibly via a radical precursor. The cationic species is then proposed to partition between recombination (alcohol formation) and elimination (alkene production) pathways. This novel function of MMO indicates close mechanistic kinship between the hydroxylation and desaturation reactions catalyzed by the nonheme diiron clusters.

Lewis acid catalysis of a Diels-Alder reaction in water

NARCIS (Netherlands)

Otto, S; Bertoncin, F; Engberts, JBFN

1996-01-01

Here we report the first detailed study of a Diels-Alder (DA) reaction that is catalyzed by Lewis acids in water. The effect of Co2+, Ni2+, Cu2+ and Zn2+ ions as Lewis acid catalysts on the rate and endo-exo selectivity of the DA reaction between the bidentate dienophiles

Amino acid-catalyzed conversion of citral : cis-trans isomerization and its conversion into 6-methyl-5-hepten-2-one and acetaldehyde

NARCIS (Netherlands)

Wolken, W.A.M.; Have, R. ten; Werf, M.J. van der

2000-01-01

Under alkaline conditions, amino acids or proteins catalyze the deacetylation of citral, a major aroma component, resulting in methylheptenone and acetaldehyde formation. 3-Hydroxycitronellal is an intermediate in this reaction. Amino acids also catalyze the cis-trans isomerization of the pure

Kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid

NARCIS (Netherlands)

Girisuta, B.; Janssen, L. P. B. M.; Heeres, H. J.

2007-01-01

A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of cellulose. An interesting example is levulinic acid, a versatile precursor for fuel additives, polymers, and resins. A detailed kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid is

Cyclodextrin-Catalyzed Organic Synthesis: Reactions, Mechanisms, and Applications

Directory of Open Access Journals (Sweden)

Chang Cai Bai

2017-09-01

Full Text Available Cyclodextrins are well-known macrocyclic oligosaccharides that consist of α-(1,4 linked glucose units and have been widely used as artificial enzymes, chiral separators, chemical sensors, and drug excipients, owing to their hydrophobic and chiral interiors. Due to their remarkable inclusion capabilities with small organic molecules, more recent interests focus on organic reactions catalyzed by cyclodextrins. This contribution outlines the current progress in cyclodextrin-catalyzed organic reactions. Particular emphases are given to the organic reaction mechanisms and their applications. In the end, the future directions of research in this field are proposed.

A two-step acid-catalyzed process for the production of biodiesel from rice bran oil

Energy Technology Data Exchange (ETDEWEB)

Zullaikah, S.; Lai, Chao Chin; Vali, S.R.; Ju, Yi Hsu [National Taiwan Univ. of Science and Technology, Taipei (China). Dept. of Chemical Engineering

2005-11-15

A study was undertaken to examine the effect of temperature, moisture and storage time on the accumulation of free fatty acid in the rice bran. Rice bran stored at room temperature showed that most triacylglyceride was hydrolyzed and free fatty acid (FFA) content was raised up to 76% in six months. A two-step acid-catalyzed methanolysis process was employed for the efficient conversion of rice bran oil into fatty acid methyl ester (FAME). The first step was carried out at 60 {sup o}C. Depending on the initial FFA content of oil, 55-90% FAME content in the reaction product was obtained. More than 98% FFA and less than 35% of TG were reacted in 2 h. The organic phase of the first step reaction product was used as the substrate for a second acid-catalyzed methanolysis at 100 {sup o}C. By this two-step methanolysis reaction, more than 98% FAME in the product can be obtained in less than 8 h. Distillation of reaction product gave 99.8% FAME (biodiesel) with recovery of more than 96%. The residue contains enriched nutraceuticals such as {gamma}-oryzanol (16-18%), mixture of phytosterol, tocol and steryl ester (19-21%). (author)

Biodiesel Production from Spent Fish Frying Oil Through Acid-Base Catalyzed Transesterification

Directory of Open Access Journals (Sweden)

Abdalrahman B. Fadhil

2012-06-01

Full Text Available Biodiesel fuels were prepared from a special type of frying oil namely spent fish frying oil through two step transesterification viz. acid-base catalyzed transesterification. Hydrochloric acid and potassium hydroxide with methanol were used for this purpose. The oil was pre-treated with (1.0 wt% HCl and methanol to reduce free fatty acids content of the oil. Then, conditions of the base catalyzed step such as base concentration, reaction temperature, methanol to oil molar ratio and reaction time were optimized. The study raveled that, 0.50% KOH w/w of oil; a 6:1 methanol to oil molar ratio; a reaction temperature of 60°C and a duration of 1h were the optimal conditions because they resulted in high biodiesel yield. Fuel properties of the products were assessed and found better than those of the parent oil. Furthermore, they met the specified limits according to the ASTM standards. Thin layer chromatography was used as a simple technique to monitor the transesterification of the oil. Blending of the optimal biodiesel sample with petro diesel using specified volume percentages was done as well. The results indicated that biodiesel had slight effect on the values of the assessed properties.

Acid base catalyzed transesterification kinetics of waste cooking oil

Energy Technology Data Exchange (ETDEWEB)

Jain, Siddharth; Sharma, M.P.; Rajvanshi, Shalini [Alternate Hydro Energy Centre, Indian Institute of Technology, Roorkee (India)

2011-01-15

The present study reports the results of kinetics study of acid base catalyzed two step transesterification process of waste cooking oil, carried out at pre-determined optimum temperature of 65 C and 50 C for esterification and transesterification process respectively under the optimum condition of methanol to oil ratio of 3:7 (v/v), catalyst concentration 1%(w/w) for H{sub 2}SO{sub 4} and NaOH and 400 rpm of stirring. The optimum temperature was determined based on the yield of ME at different temperature. Simply, the optimum concentration of H{sub 2}SO{sub 4} and NaOH was determined with respect to ME Yield. The results indicated that both esterification and transesterification reaction are of first order rate reaction with reaction rate constant of 0.0031 min{sup -1} and 0.0078 min{sup -1} respectively showing that the former is a slower process than the later. The maximum yield of 21.50% of ME during esterification and 90.6% from transesterification of pretreated WCO has been obtained. This is the first study of its kind which deals with simplified kinetics of two step acid-base catalyzed transesterification process carried under the above optimum conditions and took about 6 h for complete conversion of TG to ME with least amount of activation energy. Also various parameters related to experiments are optimized with respect to ME yield. (author)

Development of Fluorous Lewis Acid-Catalyzed Reactions

Directory of Open Access Journals (Sweden)

Joji Nishikido

2006-08-01

Full Text Available Organic synthetic methodology in the 21st century aims to conform to the principles of green sustainable chemistry (GSC and we may expect that in the future, the realization of GSC will be an important objective for chemical industries. An important aim of synthetic organic chemistry is to implement waste-free and environmentally-benign industrial processes using Lewis acids as versatile as aluminum choride. A key technological objective of our work in this area has been to achieve a “catalyst recycling system that utilizes the high activity and structural features of fluorous Lewis acid catalysts”. Thus, we have developed a series of novel fluorous Lewis acid catalysts, namely the ytterbium(III, scandium(III, tin(IV or hafnium(IV bis(perfluoroalkanesulfonylamides or tris(perfluoro- alkanesulfonylmethides. Our catalysts are recyclable and effective for acylations of alcohols and aromatics, Baeyer-Villiger reactions, direct esterifications and transesterifications in a fluorous biphasic system (FBS, in supercritical carbon dioxide and on fluorous silica gel supports.

Hydrogen-bonded intermediates and transition states during spontaneous and acid-catalyzed hydrolysis of the carcinogen (+)-anti-BPDE.

Science.gov (United States)

Palenik, Mark C; Rodriguez, Jorge H

2014-07-07

Understanding mechanisms of (+)-anti-BPDE detoxification is crucial for combating its mutagenic and potent carcinogenic action. However, energetic-structural correlations of reaction intermediates and transition states during detoxification via hydrolysis are poorly understood. To gain mechanistic insight we have computationally characterized intermediate and transition species associated with spontaneous and general-acid catalyzed hydrolysis of (+)-anti-BPDE. We studied the role of cacodylic acid as a proton donor in the rate limiting step. The computed activation energy (ΔG‡) is in agreement with the experimental value for hydrolysis in a sodium cacodylate buffer. Both types of, spontaneous and acid catalyzed, BPDE hydrolysis can proceed through low-entropy hydrogen bonded intermediates prior to formation of transition states whose energies determine reaction activation barriers and rates.

Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation

Directory of Open Access Journals (Sweden)

Marcio J. da Silva

2008-09-01

Full Text Available The production of biodiesel from low-cost raw materials which generally contain high amounts of free fatty acids (FFAs is a valuable alternative that would make their production costs more competitive than petroleum-derived fuel. Currently, the production of biodiesel from this kind of raw materials comprises a two-stage process, which requires an initial acid-catalyzed esterification of the FFA, followed by a basecatalyzed transesterification of the triglycerides. Commonly, the acid H2SO4 is the catalyst on the first step of this process. It must be said, however, that major drawbacks such as substantial reactor corrosion and the great generation of wastes, including the salts formed due to neutralization of the mineral acid, are negative and virtually unsurmountable aspects of this protocol. In this paper, tin(II chloride dihydrate (SnCl2·2H2O, an inexpensive Lewis acid, was evaluated as catalyst on the ethanolysis of oleic acid, which is the major component of several fat and vegetable oils feedstocks. Tin chloride efficiently promoted the conversion of oleic acid into ethyl oleate in ethanol solution and in soybean oil samples, under mild reaction conditions. The SnCl2 catalyst was shown to be as active as the mineral acid H2SO4. Its use has relevant advantages in comparison to mineral acids catalysts, such as less corrosion of the reactors and as well as avoiding the unnecessary neutralization of products. Herein, the effect of the principal parameters of reaction on the yield and rate of ethyl oleate production has been investigated. Kinetic measurements revealed that the esterification of oleic acid catalyzed by SnCl2·2H2O is first-order in relation to both FFAs and catalyst concentration. Experimentally, it was verified that the energy of activation of the esterification reaction of oleic acid catalyzed by SnCl2 was very close those reported for H2SO4.

Palladium-catalyzed domino C,N-coupling/carbonylation/Suzuki coupling reaction: an efficient synthesis of 2-aroyl-/heteroaroylindoles.

Science.gov (United States)

Arthuis, Martin; Pontikis, Renée; Florent, Jean-Claude

2009-10-15

A convenient one-pot synthesis of 2-aroylindoles using a domino palladium-catalyzed C,N-coupling/carbonylation/C,C-coupling sequence is described. The reaction involved easily prepared 2-gem-dibromovinylanilines and boronic acids under carbon monoxide. Optimized reaction conditions allowed the construction of a wide variety of highly functionalized 2-aroyl-/heteroaroylindoles in satisfactory yields.

Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

Science.gov (United States)

Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

2016-02-01

Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines.

Science.gov (United States)

Unhale, Rajshekhar A; Sadhu, Milon M; Ray, Sumit K; Biswas, Rayhan G; Singh, Vinod K

2018-04-03

A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-hydroxyisoindolinones has been demonstrated in this communication. A variety of isoindolinone-based α-amino diazo esters bearing a quaternary stereogenic center were afforded in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). Furthermore, the synthetic utility of the products has been depicted by the hydrogenation of the diazo moiety of adducts.

Production of Biodiesel from High Acid Value Waste Cooking Oil Using an Optimized Lipase Enzyme/Acid-Catalyzed Hybrid Process

Directory of Open Access Journals (Sweden)

N. Saifuddin

2009-01-01

Full Text Available The present study is aimed at developing an enzymatic/acid-catalyzed hybrid process for biodiesel production using waste cooking oil with high acid value (poor quality as feedstock. Tuned enzyme was prepared using a rapid drying technique of microwave dehydration (time required around 15 minutes. Further enhancement was achieved by three phase partitioning (TPP method. The results on the lipase enzyme which was subjected to pH tuning and TPP, indicated remarkable increase in the initial rate of transesterification by 3.8 times. Microwave irradiation was found to increase the initial reaction rates by further 1.6 times, hence giving a combined increase in activity of about 5.4 times. The optimized enzyme was used for hydrolysis and 88% of the oil taken initially was hydrolyzed by the lipase. The hydrolysate was further used in acid-catalyzed esterification for biodiesel production. By using a feedstock to methanol molar ratio of 1:15 and a sulphuric acid concentration of 2.5%, a biodiesel conversion of 88% was obtained at 50 °C for an hour reaction time. This hybrid process may open a way for biodiesel production using unrefined and used oil with high acid value as feedstock.

Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels-Alder Reaction of Styrene-ynes.

Science.gov (United States)

Mun, Hyeon Jin; Seong, Eun Young; Ahn, Kwang-Hyun; Kang, Eun Joo

2018-02-02

The intramolecular didehydro-Diels-Alder reaction of styrene-ynes was catalyzed by Fe(II) and Fe(III) to produce various naphthalene derivatives under microwave heating conditions. Mechanistic calculations found that the Fe(II) catalyst activates the styrenyl diene in an inverse-electron-demand Diels-Alder reaction, and the consecutive dehydrogenation reaction can be promoted by either Fe(II)-catalyzed direct dehydrogenation or an Fe(III)-catalyzed rearomatization/dehydrogenation pathway.

Noble metal catalyzed hydrogen generation from formic acid in nitrite-containing simulated nuclear waste media

International Nuclear Information System (INIS)

King, R.B.; Bhattacharyya, N.K.; Wiemers, K.D.

1994-08-01

Simulants for the Hanford Waste Vitrification Plant (HWVP) feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO 3 2- , NO 3 -, and NO 2 - were used as media to evaluate the stability of formic acid towards hydrogen evolution by the reaction HCO 2 H → H 2 + CO 2 catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Small scale experiments using 40-50 mL of feed simulant in closed glass reactors (250-550 mL total volume) at 80-100 degree C were used to study the effect of nitrite and nitrate ion on the catalytic activities of the noble metals for formic acid decomposition. Reactions were monitored using gas chromatography to analyze the CO 2 , H 2 , NO, and N 2 O in the gas phase as a function of time. Rhodium, which was introduced as soluble RhCl 3 ·3H 2 O, was found to be the most active catalyst for hydrogen generation from formic acid above ∼80 degree C in the presence of nitrite ion in accord with earlier observations. The inherent homogeneous nature of the nitrite-promoted Rh-catalyzed formic acid decomposition is suggested by the approximate pseudo first-order dependence of the hydrogen production rate on Rh concentration. Titration of the typical feed simulants containing carbonate and nitrite with formic acid in the presence of rhodium at the reaction temperature (∼90 degree C) indicates that the nitrite-promoted Rh-catalyzed decomposition of formic acid occurs only after formic acid has reacted with all of the carbonate and nitrite present to form CO 2 and NO/N 2 O, respectively. The catalytic activities of Ru and Pd towards hydrogen generation from formic acid are quite different than those of Rh in that they are inhibited rather than promoted by the presence of nitrite ion

Transition-Metal-Catalyzed Decarbonylative Coupling Reactions: Concepts, Classifications, and Applications

KAUST Repository

Guo, Lin; Rueping, Magnus

2018-01-01

Transition metal‐catalyzed decarbonylative coupling reactions have emerged as a powerful alternative to conventional cross‐coupling protocols due to the advantages associated with the use of carbonyl‐containing functionalities as coupling electrophiles instead of commonly used organohalides or sulfates. A wide variety of novel transformations based on this concept have been successfully achieved, including decarbonylative carbon–carbon and carbon–heteroatom bond forming reactions. In this Review, we summarize the recent progress in this field and present a comprehensive overview of metal‐catalyzed decarbonylative coupling reactions with carbonyl derivatives.

Transition-Metal-Catalyzed Decarbonylative Coupling Reactions: Concepts, Classifications, and Applications

KAUST Repository

Guo, Lin

2018-05-14

Transition metal‐catalyzed decarbonylative coupling reactions have emerged as a powerful alternative to conventional cross‐coupling protocols due to the advantages associated with the use of carbonyl‐containing functionalities as coupling electrophiles instead of commonly used organohalides or sulfates. A wide variety of novel transformations based on this concept have been successfully achieved, including decarbonylative carbon–carbon and carbon–heteroatom bond forming reactions. In this Review, we summarize the recent progress in this field and present a comprehensive overview of metal‐catalyzed decarbonylative coupling reactions with carbonyl derivatives.

Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds**

Science.gov (United States)

Best, Daniel; Burns, David J; Lam, Hon Wai

2015-01-01

A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N—H groups are tolerated on the barbituric acid, with no complications arising from N—H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. PMID:25959544

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review.

Science.gov (United States)

He, Jie; Yang, Xiaofang; Men, Bin; Wang, Dongsheng

2016-01-01

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals (OH) from reactions between recyclable solid catalysts and H2O2 at acidic or even circumneutral pH. Hence, it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology. Due to the complex reaction system, the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating, and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies. Iron-based materials usually possess high catalytic activity, low cost, negligible toxicity and easy recovery, and are a superior type of heterogeneous Fenton catalysts. Therefore, this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials. OH, hydroperoxyl radicals/superoxide anions (HO2/O2(-)) and high-valent iron are the three main types of reactive oxygen species (ROS), with different oxidation reactivity and selectivity. Based on the mechanisms of ROS generation, the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron, the heterogeneous catalysis mechanism, and the heterogeneous reaction-induced homogeneous mechanism. Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed. Finally, related future research directions are also suggested. Copyright © 2015. Published by Elsevier B.V.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions.

Science.gov (United States)

Ruiz-Castillo, Paula; Buchwald, Stephen L

2016-10-12

Pd-catalyzed cross-coupling reactions that form C-N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C-N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

Energy Technology Data Exchange (ETDEWEB)

Klobukowski, Erik [Iowa State Univ., Ames, IA (United States)

2011-01-01

conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and

Precision Synthesis of Functional Polysaccharide Materials by Phosphorylase-Catalyzed Enzymatic Reactions

Directory of Open Access Journals (Sweden)

Jun-ichi Kadokawa

2016-04-01

Full Text Available In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the synthesis of pure amylose with a precisely controlled structure. Similarly, using a phosphorylase-catalyzed enzymatic polymerization, the chemoenzymatic synthesis of amylose-grafted heteropolysaccharides containing different main-chain polysaccharide structures (e.g., chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose was achieved. Amylose-based block, star, and branched polymeric materials have also been prepared using this enzymatic polymerization. Since phosphorylase shows a loose specificity for the recognition of substrates, different sugar residues have been introduced to the non-reducing ends of maltooligosaccharides by phosphorylase-catalyzed glycosylations using analog substrates such as α-d-glucuronic acid and α-d-glucosamine 1-phosphates. By means of such reactions, an amphoteric glycogen and its corresponding hydrogel were successfully prepared. Thermostable phosphorylase was able to tolerate a greater variance in the substrate structures with respect to recognition than potato phosphorylase, and as a result, the enzymatic polymerization of α-d-glucosamine 1-phosphate to produce a chitosan stereoisomer was carried out using this enzyme catalyst, which was then subsequently converted to the chitin stereoisomer by N-acetylation. Amylose supramolecular inclusion complexes with polymeric guests were obtained when the phosphorylase-catalyzed enzymatic polymerization was conducted in the presence of the guest polymers. Since the structure of this polymeric system is similar to the way that a plant vine twines around a rod, this polymerization system has been named �

A computational study on Lewis acid-catalyzed diastereoselective acyclic radical allylation reactions with unusual selectivity dependence on temperature and epimer precursor.

Science.gov (United States)

Georgieva, Miglena K; Santos, A Gil

2014-12-05

In stereoselective radical reactions, it is accepted that the configuration of the radical precursor has no impact on the levels of stereoinduction, as a prochiral radical intermediate is planar, with two identical faces, independently of its origin. However, Sibi and Rheault (J. Am. Chem. Soc. 2000, 122, 8873-8879) remarkably obtained different selectivities in the trapping of radicals originated from two epimeric bromides, catalyzed by chelating Lewis acids. The selectivity rationalization was made on the basis of different conformational properties of each epimer. However, in this paper we show that the two epimers have similar conformational properties, which implies that the literature proposal is unable to explain the experimental results. We propose an alternative mechanism, in which the final selectivity is dependent on different reaction rates for radical formation from each epimer. By introducing a different perspective of the reaction mechanism, our model also allows the rationalization of different chemical yields obtained from each epimer, a result not rationalized by the previous model. Adaptation to other radical systems, under different reaction conditions, is also possible.

Titanocene(III)-Catalyzed Three-Component Reaction of Secondary Amides, Aldehydes, and Electrophilic Alkenes.

Science.gov (United States)

Zheng, Xiao; He, Jiang; Li, Heng-Hui; Wang, Ao; Dai, Xi-Jie; Wang, Ai-E; Huang, Pei-Qiang

2015-11-09

An umpolung Mannich-type reaction of secondary amides, aliphatic aldehydes, and electrophilic alkenes has been disclosed. This reaction features the one-pot formation of C-N and C-C bonds by a titanocene-catalyzed radical coupling of the condensation products, from secondary amides and aldehydes, with electrophilic alkenes. N-substituted γ-amido-acid derivatives and γ-amido ketones can be efficiently prepared by the current method. Extension to the reaction between ketoamides and electrophilic alkenes allows rapid assembly of piperidine skeletons with α-amino quaternary carbon centers. Its synthetic utility has been demonstrated by a facile construction of the tricyclic core of marine alkaloids such as cylindricine C and polycitorol A. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed Decarboxylative γ-Olefination of 2,5-Cyclohexadiene-1-carboxylic Acid Derivatives with Vinyl Halides.

Science.gov (United States)

Chang, Chi-Hao; Chou, Chih-Ming

2018-04-06

This study explores a Pd-catalyzed decarboxylative Heck-type Csp 3 -Csp 2 coupling reaction of 2,5-cyclohexadiene-1-carboxylic acid derivatives with vinyl halides to provide γ-olefination products. The olefinated 1,3-cyclohexadienes can be further oxidized to produce meta-alkylated stilbene derivatives. Additionally, the conjugated diene products can also undergo a Diels-Alder reaction to produce a bicyclo[2.2.2]octadiene framework.

Graphene oxide for acid catalyzed-reactions: Effect of drying process

Science.gov (United States)

Gong, H. P.; Hua, W. M.; Yue, Y. H.; Gao, Z.

2017-03-01

Graphene oxides (GOs) were prepared by Hummers method through various drying processes, and characterized by XRD, SEM, FTIR, XPS and N2 adsorption. Their acidities were measured using potentiometric titration and acid-base titration. The catalytic properties were investigated in the alkylation of anisole with benzyl alcohol and transesterification of triacetin with methanol. GOs are active catalysts for both reaction, whose activity is greatly affected by their drying processes. Vacuum drying GO exhibits the best performance in transesterification while freezing drying GO is most active for alkylation. The excellent catalytic behavior comes from abundant surface acid sites as well as proper surface functional groups, which can be obtained by selecting appropriate drying process.

Synthesis of heterocycles via transition-metal-catalyzed hydroarylation of alkynes.

Science.gov (United States)

Yamamoto, Yoshihiko

2014-03-07

Transition-metal (TM)-catalyzed hydroarylation reactions of alkynes have received much attention, because they enable the net insertion of alkyne C-C triple bonds into C-H bonds of aromatic precursors, resulting in regio- and stereo-selective formation of synthetically useful arylalkenes. Taking advantage of this feature, TM-catalyzed alkyne hydroarylations have been successfully used for the synthesis of heterocycles. TM-catalyzed alkyne hydroarylations can be classified into three major categories depending on the type of reaction and precursors involved: (1) palladium-catalyzed reductive Heck reactions of alkynes with aryl halides, (2) TM-catalyzed conjugate arylation reactions of activated alkynes with arylboronic acids, and (3) TM-catalyzed aromatic C-H alkenylations with alkynes. This review surveys heterocycle synthesis via TM-catalyzed hydroarylation of alkynes according to the above classification, with an emphasis on the scope and limitations, as well as the underlying mechanisms.

catalyzed oxidation of some amino acids by acid bromate

African Journals Online (AJOL)

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ABSTRACT: Kinetic investigations on Pd(II) catalyzed oxidation of dl-serine and dl- ... A suitable mechanism in agreement with observed kinetics has been ..... In acidic solution of potassium bromate quick .... Annual Review of Biochemistry.

Au-Cu core-shell nanocube-catalyzed click reactions for efficient synthesis of diverse triazoles.

Science.gov (United States)

Madasu, Mahesh; Hsia, Chi-Fu; Huang, Michael H

2017-06-01

Au-Cu core-shell nanocubes and octahedra synthesized in aqueous solution were employed to catalyze a 1,3-dipolar cycloaddition reaction between phenylacetylene and benzyl azide in water at 50 °C for 3 h. Interestingly, the nanocubes were far more efficient in catalyzing this reaction, giving 91% yield of a regioselective 1,4-triazole product, while octahedra only recorded 46% yield. The Au-Cu nanocubes were subsequently employed to catalyze the click reaction between benzyl azide and a broad range of aromatic and aliphatic alkynes. The product yields ranged from 78 to 99%. Clearly the Au-Cu cubes exposing {100} surfaces are an excellent and green catalyst for click reactions.

1-Butyl-3-methylimidazolium hydrogen sulfate catalyzed in-situ transesterification of Nannochloropsis to fatty acid methyl esters

International Nuclear Information System (INIS)

Sun, Yingqiang; Cooke, Peter; Reddy, Harvind K.; Muppaneni, Tapaswy; Wang, Jun; Zeng, Zheling; Deng, Shuguang

2017-01-01

Highlights: • [Bmim][HSO_4] catalyzed in-situ transesterification of wet algae. • [Bmim][HSO_4] served as both effective solvent and excellent acid catalyst. • Proposed a mechanism for [Bmim][HSO_4] catalyzed in-situ transesterification. • Identified cell walls and lipid droplets in algae using confocal imaging tests. • Obtained crude biodiesel yield about 95% in 30 min at 200 °C. - Abstract: 1-Butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO_4]) is used as a solvent and an acid catalyst for in-situ extractive transesterification of wet Nannochloropsis with methanol. The reaction is supposed to be a five-step process: (1) wet algae cell wall dissolves in ionic liquid at reaction temperatures; (2) hydrogen ions and sulfate ions release from the ionization of HSO_4"−. The hydrogen ions (H"+) act as catalysts for accelerating the reactive extraction of triglyceride from wet Nannochloropsis; (3) hydrogen ions and methanol molecules transfer from bulk to active site of cells without passing through cell wall that is dissolved by ionic liquid; (4) in-situ transesterification of lipid (mainly triglycerides) with methanol; and (5) products transfer from inside of algae cells to outside of cells. The crude biodiesel yield of [Bmim][HSO_4] catalyzed in-situ transesterification is about 95.28% at reaction temperature of 200 °C, reaction time of 30 min, mass ratio of [Bmim][HSO_4] to wet Nannochloropsis of 0.9:1, and a mass ratio of methanol to wet algae of 3:1. It decreases to 81.23% after [Bmim][HSO_4] is recycled for 4 times, which indicates that [Bmim][HSO_4] catalyzed in-situ transesterification is an economic approach for biodiesel production from wet algae.

First Novozym 435 lipase-catalyzed Morita-Baylis-Hillman reaction in the presence of amides.

Science.gov (United States)

Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

2016-03-01

The first Novozym 435 lipase-catalyzed Morita-Baylis-Hillman (MBH) reaction with amides as co-catalyst was realized. Results showed that neither Novozym 435 nor amide can independently catalyze the reaction. This co-catalytic system that used a catalytic amount of Novozym 435 with a corresponding amount of amide was established and optimized. The MBH reaction strongly depended on the structure of aldehyde substrate, amide co-catalyst, and reaction additives. The optimized reaction yield (43.4%) was achieved in the Novozym 435-catalyzed MBH reaction of 2, 4-dinitrobenzaldehyde and cyclohexenone with isonicotinamide as co-catalyst and β-cyclodextrin as additive only in 2 days. Although enantioselectivity of Novozym 435 was not found, the results were still significant because an MBH reaction using lipase as biocatalyst was realized for the first time. Copyright © 2015 Elsevier Inc. All rights reserved.

Nucleic Acid Templated Reactions for Chemical Biology.

Science.gov (United States)

Di Pisa, Margherita; Seitz, Oliver

2017-06-21

Nucleic acid directed bioorthogonal reactions offer the fascinating opportunity to unveil and redirect a plethora of intracellular mechanisms. Nano- to picomolar amounts of specific RNA molecules serve as templates and catalyze the selective formation of molecules that 1) exert biological effects, or 2) provide measurable signals for RNA detection. Turnover of reactants on the template is a valuable asset when concentrations of RNA templates are low. The idea is to use RNA-templated reactions to fully control the biodistribution of drugs and to push the detection limits of DNA or RNA analytes to extraordinary sensitivities. Herein we review recent and instructive examples of conditional synthesis or release of compounds for in cellulo protein interference and intracellular nucleic acid imaging. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Transition Metal Catalyzed Synthesis of Carboxylic Acids, Imines, and Biaryls

DEFF Research Database (Denmark)

Santilli, Carola; Madsen, Robert

the carboxylate.  Manganese catalyzed radical Kumada-type reaction between aryl halidesand aryl Grignard reagents. The reaction between aryl halides and aryl Grignard reagents catalyzed by MnCl2 has been extended to several methyl-substituted aryl iodide reagents byperforming the reaction at 120 ˚C in a microwave...... oven (Scheme ii). A limitation of the heterocoupling process is the concomitant dehalogenation of the aryl halide and homocoupling of the Grignard reagent leading low to moderate yields of the desired heterocoupling product. The mechanism of the cross-coupling process was investigated by performing two...

Catalytic Asymmetric Piancatelli Rearrangement: Brønsted Acid Catalyzed 4π Electrocyclization for the Synthesis of Multisubstituted Cyclopentenones

KAUST Repository

Cai, Yunfei; Tang, Yurong; Atodiresei, Iuliana; Rueping, Magnus

2016-01-01

The first catalytic asymmetric Piancatelli reaction is reported. Catalyzed by a chiral Brønsted acid, the rearrangement of a wide range of furylcarbinols with a series of aniline derivatives provides valuable aminocyclopentenones in high yields

Copper-catalyzed oxidative Heck reactions between alkyltrifluoroborates and vinyl arenes.

Science.gov (United States)

Liwosz, Timothy W; Chemler, Sherry R

2013-06-21

We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification, and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented.

Asymmetric Synthesis of Hydrocarbazoles Catalyzed by an Octahedral Chiral-at-Rhodium Lewis Acid.

Science.gov (United States)

Huang, Yong; Song, Liangliang; Gong, Lei; Meggers, Eric

2015-12-01

A bis-cyclometalated chiral-at-metal rhodium complex catalyzes the Diels-Alder reaction between N-Boc-protected 3-vinylindoles (Boc = tert-butyloxycarbonyl) and β-carboxylic ester-substituted α,β-unsaturated 2-acyl imidazoles with good-to-excellent regioselectivity (up to 99:1) and excellent diastereoselectivity (>50:1 d.r.) as well as enantioselectivity (92-99% ee) under optimized conditions. The rhodium catalyst serves as a chiral Lewis acid to activate the 2-acyl imidazole dienophile by two-point binding and overrules the preferred regioselectivity of the uncatalyzed reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective Formation of Secondary Amides via the Copper-Catalyzed Cross-Coupling of Alkylboronic Acids with Primary Amides

Science.gov (United States)

Rossi, Steven A.; Shimkin, Kirk W.; Xu, Qun; Mori-Quiroz, Luis M.; Watson, Donald A.

2014-01-01

For the first time, a general catalytic procedure for the cross coupling of primary amides and alkylboronic acids is demonstrated. The key to the success of this reaction was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the mono-alkylation of amides. PMID:23611591

Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.

Science.gov (United States)

Jain, Siddharth; Sharma, M P

2010-10-01

Out of various non-edible oil resources, Jatropha curcas oil (JCO) is considered as future feedstock for biodiesel production in India. Limited work is reported on the kinetics of transesterification of high free fatty acids containing oil. The present study reports the results of kinetic study of two-step acid base catalyzed transesterification process carried out at an optimum temperature of 65 °C and 50 °C for esterification and transesterification respectively under the optimum methanol to oil ratio of 3:7 (v/v), catalyst concentration 1% (w/w) for H₂SO₄ and NaOH. The yield of methyl ester (ME) has been used to study the effect of different parameters. The results indicate that both esterification and transesterification reaction are of first order with reaction rate constant of 0.0031 min⁻¹ and 0.008 min⁻¹ respectively. The maximum yield of 21.2% of ME during esterification and 90.1% from transesterification of pretreated JCO has been obtained. Copyright © 2010 Elsevier Ltd. All rights reserved.

Optimization of reaction parameters for enzymatic glyceride synthesis from fish oil: Ethyl esters versus free fatty acids

DEFF Research Database (Denmark)

Ravn, Helle Christine; Damstrup, Marianne L.; Meyer, Anne S.

2012-01-01

Enzymatic conversion of fish oil free fatty acids (FFA) or fatty acid ethyl esters (FAE) into glycerides via esterification or transesterification was examined. The reactions catalyzed by Lipozyme™ 435, a Candida antarctica lipase, were optimized. Influence on conversion yields of fatty acid chain...... length, saturation degree, temperature, enzyme dosage, molar ratio glycerol:fatty acids, acyl source composition (w/w ratio FFA:FAE), and reaction time was evaluated collectively by multiple linear regression. All reaction variables influenced the conversion into glycerides. Transesterification of FAE...

Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds.

Science.gov (United States)

Best, Daniel; Burns, David J; Lam, Hon Wai

2015-06-15

A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N-H groups are tolerated on the barbituric acid, with no complications arising from N-H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Noble metal-catalyzed homogeneous and heterogeneous processes in treating simulated nuclear waste media with formic acid

International Nuclear Information System (INIS)

King, R.B.; Bhattacharyya, N.K.; Smith, H.D.

1995-09-01

Simulants for the Hanford Waste Vitrification Plant feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO 3 2 -, NO 3 -, and NO 2 - were used to study reactions of formic acid at 90 degrees C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the CO 2 , H 2 , NO, and N 2 O in the gas phase and a microammonia electrode to analyze the NH 4 +/NH 3 in the liquid phase as a function of time. The following reactions have been studied in these systems since they are undesirable side reactions in nuclear waste processing: (1) Decomposition of formic acid to CO 2 + H 2 is undesirable because of the potential fire and explosion hazard of H 2 . Rhodium, which was introduced as soluble RhCl 3 -3H 2 O, was found to be the most active catalyst for H 2 generation from formic acid above ∼ 80 degrees C in the presence of nitrite ion. The H 2 production rate has an approximate pseudo first-order dependence on the Rh concentration, (2) Generation of NH 3 from the formic acid reduction of nitrate and/or nitrite is undesirable because of a possible explosion hazard from NH 4 NO 3 accumulation in a waste processing plant off-gas system. The Rh-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was found to exhibit the following features: (a) Nitrate rather than nitrite is the principal source of NH 3 . (b) Ammonia production occurs at the expense of hydrogen production. (c) Supported rhodium metal catalysts are more active than rhodium in any other form, suggesting that ammonia production involves heterogeneous rather than homogeneous catalysis

(Salen)Ti(Ⅳ)-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

Institute of Scientific and Technical Information of China (English)

Zheng Hong ZHOU; Zhao Ming LI; Bing LIU; Kang Ying LI; Li Xin WANG; Guo Feng ZHAO; Qi Lin ZHOU; Chu Chi TANG

2006-01-01

The asymmetric ring-opening of epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(Ⅳ) complex formed in situ from the reaction of Ti(OPr-i)4 and the chiral Schiff base derived from (1R,2R)-(+)-diaminocyclohexane was realized. The resulting products were obtained with low to good enantioselectivity (up to 73% ee).

Transition metal-catalyzed carboxylation reactions with carbon dioxide.

Science.gov (United States)

Martin, Ruben; Tortajada, Andreu; Juliá-Hernández, Francisco; Borjesson, Marino; Moragas, Toni

2018-05-03

Driven by the inherent synthetic potential of CO2 as an abundant, inexpensive and renewable C1 chemical feedstock, the recent years have witnessed renewed interest in devising catalytic CO2 fixations into organic matter. Although the formation of C-C bonds via catalytic CO2 fixation remained rather limited for a long period of time, a close look into the recent literature data indicates that catalytic carboxylation reactions have entered a new era of exponential growth, evolving into a mature discipline that allows for streamlining the synthesis of carboxylic acids, building blocks of utmost relevance in industrial endeavours. These strategies have generally proven broadly applicability and convenient to perform. However, substantial challenges still need to be addressed reinforcing the need to cover metal-catalyzed carboxylation arena in a conceptual and concise manner, delineating the underlying new principles that are slowly emerging in this vibrant area of expertise. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Asymmetric synthesis of allylic sulfonic acids: enantio- and regioselective iridium-catalyzed allylations of Na2SO3.

Science.gov (United States)

Liu, Wei; Zhao, Xiao-ming; Zhang, Hong-bo; Zhang, Liang; Zhao, Ming-zhu

2014-12-15

An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combined cross-linked enzyme aggregates of horseradish peroxidase and glucose oxidase for catalyzing cascade chemical reactions.

Science.gov (United States)

Nguyen, Le Truc; Yang, Kun-Lin

2017-05-01

Cascade reactions involved unstable intermediates are often encountered in biological systems. In this study, we developed combined cross-linked enzyme aggregates (combi-CLEA) to catalyze a cascade reaction which involves unstable hydrogen peroxide as an intermediate. The combi-CLEA contains two enzymes̶ glucose oxidase (GOx) and horseradish peroxidase (HRP) which are cross-linked together as solid aggregates. The first enzyme GOx catalyzes the oxidation of glucose and produces hydrogen peroxide, which is used by the second enzyme HRP to oxidize 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The apparent reaction rate of the cascade reaction reaches 10.5±0.5μM/min when the enzyme ratio is 150:1 (GOx:HRP). Interestingly, even in the presence of catalase, an enzyme that quickly decomposes hydrogen peroxide, the reaction rate only decreases by 18.7% to 8.3±0.3μM/min. This result suggests that the intermediate hydrogen peroxide is not decomposed by catalase due to a short diffusion distance between GOx and HRP in the combi-CLEA. Scanning electron microscopy images suggest that combi-CLEA particles are hollow spheres and have an average diameter around 250nm. Because of their size, combi-CLEA particles can be entrapped inside a nylon membrane for detecting glucose by using the cascade reaction. Copyright © 2017 Elsevier Inc. All rights reserved.

Ru (III) Catalyzed Oxidation of Aliphatic Ketones by N-Bromosuccinimide in Aqueous Acetic Acid: A Kinetic Study

Science.gov (United States)

Giridhar Reddy, P.; Ramesh, K.; Shylaja, S.; Rajanna, K. C.; Kandlikar, S.

2012-01-01

Kinetics of Ru (III) catalyzed oxidation of aliphatic ketones such as acetone, ethyl methyl ketone, diethyl ketone, iso-butylmethyl ketone by N-bromosuccinimide in the presence of Hg(II) acetate have been studied in aqueous acid medium. The order of [N-bromosuccinimide] was found to be zero both in catalyzed as well as uncatalyzed reactions. However, the order of [ketone] changed from unity to a fractional one in the presence of Ru (III). On the basis of kinetic features, the probable mechanisms are discussed and individual rate parameters evaluated. PMID:22654610

Pd(II)-Catalyzed Hydroxyl-Directed C–H Olefination Enabled by Mono-Protected Amino Acid Ligands

Science.gov (United States)

Lu, Yi; Wang, Dong-Hui; Engle, Keary M.

2010-01-01

A novel Pd(II)-catalyzed ortho-C–H olefination protocol has been developed using spatially remote, unprotected tertiary, secondary, and primary alcohols as the directing groups. Mono-N-protected amino acid ligands were found to promote the reaction, and an array of olefin coupling partners could be used. When electron-deficient alkenes were used, the resulting olefinated intermediates underwent subsequent Pd(II)-catalyzed oxidative intramolecular cyclization to give the corresponding pyran products, which could be converted into ortho-alkylated alcohols under hydrogenolysis conditions. The mechanistic details of the oxidative cyclization step are discussed and situated in the context of the overall catalytic cycle. PMID:20359184

β-Secondary and solvent deuterium kinetic isotope effects and the mechanisms of base- and acid-catalyzed hydrolysis of penicillanic acid

International Nuclear Information System (INIS)

Deraniyagala, S.A.; Adediran, S.A.; Pratt, R.F.

1995-01-01

β-Secondary and solvent deuterium kinetic isotope effects have been determined at 25 degrees C for the alkaline and acid-catalyzed hydrolysis of penicillanic acid. In order to determine the former isotope effect, [6,6- 2 H 2 ]dideuteriopenicillanic acid has been synthesized. In alkaline solution, the former isotope effect was found to be 0.95 ± 0.01. These values support the B AC 2 mechanism of hydrolysis with rate-determining formation of the tetrahedral intermediate that has been proposed for other β-lactams. The measured β-secondary kinetic isotope for the acid-catalyzed reaction was 1.00 ± 0.01. The data indicates that a likely pathway of acid-catalyzed hydrolysis would be that of an A AC 1 mechanism with an intermediate acylium ion. If this were so, the calculated β-secondary isotope effect per hydrogen coplanar with the breaking C-N bond and corrected for the inductive effect of deuterium would be 1.06 ± 0.01. This suggests an early A AC 1 transition state, which would be reasonable in this case because of destabilization of the N-protonated amide with respect to the acylium ion because of ring strain. The absence of specific participation by solvent in the transition state, as would be expected of an A AC 1 but not an associative mechanism, is supported by the strongly inverse solvent deuterium kinetic isotope effect of 0.25 ± 0.00 in 1 M HCl and 0.22 ± 0.01 in 33.3 wt % H 2 SO 4 . 1 fig., 3 tabs

Process limitations of a whole-cell P450 catalyzed reaction using a CYP153A-CPR fusion construct expressed in Escherichia coli

DEFF Research Database (Denmark)

Lundemo, M. T.; Notonier, S.; Striedner, G.

2016-01-01

fatty acids at the terminal position. ω-Hydroxylated fatty acids can be used in the field of high-end polymers and in the cosmetic and fragrance industry. Here, we have identified the limitations for implementation of a whole-cell P450-catalyzed reaction by characterizing the chosen biocatalyst as well......Cytochrome P450s are interesting biocatalysts due to their ability to hydroxylate non-activated hydrocarbons in a selective manner. However, to date only a few P450-catalyzed processes have been implemented in industry due to the difficulty of developing economically feasible processes...

Steroid hydroxylations: A paradigm for cytochrome P450 catalyzed mammalian monooxygenation reactions

International Nuclear Information System (INIS)

Estabrook, Ronald W.

2005-01-01

The present article reviews the history of research on the hydroxylation of steroid hormones as catalyzed by enzymes present in mammalian tissues. The report describes how studies of steroid hormone synthesis have played a central role in the discovery of the monooxygenase functions of the cytochrome P450s. Studies of steroid hydroxylation reactions can be credited with showing that: (a) the adrenal mitochondrial enzyme catalyzing the 11β-hydroxylation of deoxycorticosterone was the first mammalian enzyme shown by O 18 studies to be an oxygenase; (b) the adrenal microsomal enzyme catalyzing the 21-hydroxylation of steroids was the first mammalian enzyme to show experimentally the proposed 1:1:1 stoichiometry (substrate:oxygen:reduced pyridine nucleotide) of a monooxygenase reaction; (c) application of the photochemical action spectrum technique for reversal of carbon monoxide inhibition of the 21-hydroxylation of 17α-OH progesterone was the first demonstration that cytochrome P450 was an oxygenase; (d) spectrophotometric studies of the binding of 17α-OH progesterone to bovine adrenal microsomal P450 revealed the first step in the cyclic reaction scheme of P450, as it catalyzes the 'activation' of oxygen in a monooxygenase reaction; (e) purified adrenodoxin was shown to function as an electron transport component of the adrenal mitochondrial monooxygenase system required for the activity of the 11β-hydroxylase reaction. Adrenodoxin was the first iron-sulfur protein isolated and purified from mammalian tissues and the first soluble protein identified as a reductase of a P450; (f) fractionation of adrenal mitochondrial P450 and incubation with adrenodoxin and a cytosolic (flavoprotein) fraction were the first demonstration of the reconstitution of a mammalian P450 monooxygenase reaction

Kinetics of Maleic Acid and Aluminum Chloride Catalyzed Dehydration and Degradation of Glucose

Energy Technology Data Exchange (ETDEWEB)

Zhang, Ximing; Hewetson, Barron B.; Mosier, Nathan S.

2015-04-16

We report the positive effect of maleic acid, a dicarboxylic acid, on the selectivity of hexose dehydration to 5-hydroxymethyfurfural (HMF) and subsequent hydrolysis to levulinic and formic acids. We also describe the kinetic analysis of a Lewis acid (AlCl3) alone and in combination with HCl or maleic acid to catalyze the isomerization of glucose to fructose, dehydration of fructose to HMF, hydration of HMF to levulinic and formic acids, and degradation of these compounds to humins. The results show that AlCl3 significantly enhances the rate of glucose conversion to HMF and levulinic acid in the presence of both maleic acid and HCl. In addition, the degradation of HMF to humins, rather than levulinic and formic acids, is reduced by 50% in the presence of maleic acid and AlCl3 compared to HCl combined with AlCl3. The results suggest different reaction mechanisms for the dehydration of glucose and rehydration of HMF between maleic acid and HCl.

Enzyme-catalyzed and binding reaction kinetics determined by titration calorimetry.

Science.gov (United States)

Hansen, Lee D; Transtrum, Mark K; Quinn, Colette; Demarse, Neil

2016-05-01

Isothermal calorimetry allows monitoring of reaction rates via direct measurement of the rate of heat produced by the reaction. Calorimetry is one of very few techniques that can be used to measure rates without taking a derivative of the primary data. Because heat is a universal indicator of chemical reactions, calorimetry can be used to measure kinetics in opaque solutions, suspensions, and multiple phase systems and does not require chemical labeling. The only significant limitation of calorimetry for kinetic measurements is that the time constant of the reaction must be greater than the time constant of the calorimeter which can range from a few seconds to a few minutes. Calorimetry has the unique ability to provide both kinetic and thermodynamic data. This article describes the calorimetric methodology for determining reaction kinetics and reviews examples from recent literature that demonstrate applications of titration calorimetry to determine kinetics of enzyme-catalyzed and ligand binding reactions. A complete model for the temperature dependence of enzyme activity is presented. A previous method commonly used for blank corrections in determinations of equilibrium constants and enthalpy changes for binding reactions is shown to be subject to significant systematic error. Methods for determination of the kinetics of enzyme-catalyzed reactions and for simultaneous determination of thermodynamics and kinetics of ligand binding reactions are reviewed. Copyright © 2015 Elsevier B.V. All rights reserved.

Cobalt catalyzed peroxymonosulfate oxidation of tetrabromobisphenol A: Kinetics, reaction pathways, and formation of brominated by-products

Energy Technology Data Exchange (ETDEWEB)

Ji, Yuefei [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China); Kong, Deyang [Nanjing Institute of Environmental Science, Ministry of Environmental Protection of PRC, Nanjing 210042 (China); Lu, Junhe, E-mail: jhlu@njau.edu.cn [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China); Jin, Hao; Kang, Fuxing; Yin, Xiaoming; Zhou, Quansuo [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China)

2016-08-05

Highlights: • Cobalt catalyzed peroxymonosulfate oxidation of tetrabromobisphenol A. • Phenolic moiety was the reactive site for sulfate radical attack. • Pathways include β-scission, oxidation, debromination and coupling reactions. • Brominated disinfection by-products were found during TBBPA degradation. • Humic acid inhibited TBBPA degradation but promoted DBPs formation. - Abstract: Degradation of tetrabromobisphenol A (TBBPA), a flame retardant widely spread in the environment, in Co(II) catalyzed peroxymonosulfate (PMS) oxidation process was systematically explored. The second-order-rate constant for reaction of sulfate radical (SO{sub 4}{sup ·−}) with TBBPA was determined to be 5.27 × 10{sup 10} M{sup −1} s{sup −1}. Apparently, degradation of TBBPA showed first-order kinetics to the concentrations of both Co(II) and PMS. The presence of humic acid (HA) and bicarbonate inhibited TBBPA degradation, most likely due to their competition for SO{sub 4}{sup ·−}. Degradation of TBBPA was initiated by an electron abstraction from one of the phenolic rings. Detailed transformation pathways were proposed, including β-scission of isopropyl bridge, phenolic ring oxidation, debromination and coupling reactions. Further oxidative degradation of intermediates in Co(II)/PMS process yielded brominated disinfection by-products (Br-DBPs) such as bromoform and brominated acetic acids. Evolution profile of Br-DBPs showed an initially increasing and then decreasing pattern with maximum concentrations occurring around 6–10 h. The presence of HA enhanced the formation of Br-DBPs significantly. These findings reveal potentially important, but previously unrecognized, formation of Br-DBPs during sulfate radical-based oxidation of bromide-containing organic compounds that may pose toxicological risks to human health.

Lipase-Catalyzed Esterification of Ferulic Acid with Oleyl Alcohol in Ionic Liquid/Isooctane Binary Systems

DEFF Research Database (Denmark)

Chen, Bilian; Liu, Huanzhen; Guo, Zheng

2011-01-01

Lipase-catalyzed synthesis of ferulic acid oleyl alcohol ester in an ionic liquid (IL)/isooctane system was investigated. Considerable bioconversion and volumetric productivity were achieved in inexpensive 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]) and 1-methyl-3-octylimidazolium....... Variations of the ratios of IL/isooctane and concentrations of oleyl alcohol also profoundly affected the volumetric productivity. To a higher extent, [Hmim][PF6]/isooctane and [Omim][PF6]/isooctane show similar reaction behaviors. Under the optimized reaction conditions (60 °C, 150 mg of Novozym 435 and 100...

SOLVENT EFFECTS IN THE LIQUID-PHASE HYDRATION OF CYCLOHEXENE CATALYZED BY A MACROPOROUS STRONG ACID ION-EXCHANGE RESIN

NARCIS (Netherlands)

PANNEMAN, HJ; BEENACKERS, AACM

1992-01-01

The liquid-phase hydration of cyclohexene, a pseudo first order reversible reaction catalyzed by a strong acid ion exchange resin, macroporous Amberlite XE 307, was investigated in solvent mixtures of water and sulfolane. A decrease by a factor of 3 and 6 is observed in the experimentally measured

Heterogeneously Catalyzed Oxidation Reactions Using Molecular Oxygen

DEFF Research Database (Denmark)

Beier, Matthias Josef

Heterogeneously catalyzed selective oxidation reactions have attracted a lot of attention in recent time. The first part of the present thesis provides an overview over heterogeneous copper and silver catalysts for selective oxidations in the liquid phase and compared the performance and catalytic...... that both copper and silver can function as complementary catalyst materials to gold showing different catalytic properties and being more suitable for hydrocarbon oxidation reactions. Potential opportunities for future research were outlined. In an experimental study, the potential of silver as a catalyst...... revealed that all catalysts were more active in combination with ceria nanoparticles and that under the tested reaction conditions silver was equally or even more efficient than the gold catalysts. Calcination at 900 °C of silver on silica prepared by impregnation afforded a catalyst which was used...

Stability and dynamics of reactors with heterogeneously catalyzed reactions

Energy Technology Data Exchange (ETDEWEB)

Eigenberger, G [BASF A.G., Ludwigshafen am Rhein (Germany, F.R.)

1978-12-01

Our knowledge of causes and consequences of problems arising from instability and dynamic effects in reactors with heterogeneously catalyzed reactions has increased remarkably in recent years. Especially thermal effects, caused by the self-acceleration of an exothermic reaction in combination with heat and mass transport, are now well understood. In addition, kinetic effects, i.e. phenomena which have to be explained by the kinetic peculiarities of surface reactions, have attracted increasing interest. For both cases the state of the art will be reviewed, highlighting the physical and chemical causes of the observed phenomena.

Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Five-, Six-, and Seven-Membered β-Substituted Cyclic Enones: Enantioselective Construction of All-Carbon Quaternary Stereocenters

KAUST Repository

Kikushima, Kotaro; Holder, Jeffrey C.; Gatti, Michele; Stoltz, Brian M.

2011-01-01

The first enantioselective Pd-catalyzed construction of all-carbon quaternary stereocenters via 1,4-addition of arylboronic acids to β-substituted cyclic enones is reported. Reaction of a wide range of arylboronic acids and cyclic enones using a

Primary and secondary kinetic isotope effects in the acid-catalyzed dehydration of 1,1'-diadamantylmethylcarbinol in aqueous acetic acid

International Nuclear Information System (INIS)

Lomas, J.S.

1981-01-01

The sulfuric acid catalyzed dehydration of 1,1'-diadamantyl-methylcarbinol in anhydrous acetic acid proceeds exclusively to 1,1'-bis(1-adamantyl)ethylene. The secondary deuterium isotope effect of 1.32 found for this reaction shows that carbonium ion formation from the protonated alcohol is rate determining. In the presence of water, however, capture of the carbonium ion competes with deprotonation, introducing a primary isotope effect. Consequently, the overall KIE rises, reaching 3.18 for 80% aqueous acetic acid. Analysis of the KIE for 80 to 100% aqueous acetic acid is consistent with a simple classical mechanism involving reversible formation of the intermediate carbonium ion. The primary isotope effect upon deprotonation is at the most 2.98, indicative of an asymmetric transition state close to the carbonium ion

Convenient synthesis of benzothiazoles and benzimidazoles through Brønsted acid catalyzed cyclization of 2-amino thiophenols/anilines with β-diketones.

Science.gov (United States)

Mayo, Muhammad Shareef; Yu, Xiaoqiang; Zhou, Xiaoyu; Feng, Xiujuan; Yamamoto, Yoshinori; Bao, Ming

2014-02-07

Brønsted acid catalyzed cyclization reactions of 2-amino thiophenols/anilines with β-diketones under oxidant-, metal-, and radiation-free conditions are described. Various 2-substituted benzothiazoles/benzimidazoles are obtained in satisfactory to excellent yields. Different groups such as methyl, chloro, nitro, and methoxy linked on benzene rings were tolerated under the optimized reaction conditions.

The Arabidopsis aldehyde oxidase 3 (AA03) gene product catalyzes the final step in abscisic acid biosynthesis in leaves

NARCIS (Netherlands)

Seo, M.; Peeters, A.J.M.; Koiwai, H.; Oritani, T.; Marion-Poll, A.; Zeevaart, J.A.D.; Koornneef, M.; Kamiya, Y.; Koshiba, T.

2000-01-01

Abscisic acid (ABA) is a plant hormone involved in seed development and germination and in responses to various environmental stresses. The last step of ABA biosynthesis involves oxidation of abscisic aldehyde, and aldehyde oxidase (EC 1.2.3.1) is thought to catalyze this reaction. An aldehyde

Cooperative Effects Between Arginine and Glutamic Acid in the Amino Acid-Catalyzed Aldol Reaction.

Science.gov (United States)

Valero, Guillem; Moyano, Albert

2016-08-01

Catalysis of the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde by mixtures of L-Arg and of L-Glu in wet dimethyl sulfoxide (DMSO) takes place with higher enantioselectivity (up to a 7-fold enhancement in the anti-aldol for the 1:1 mixture) than that observed when either L-Glu or L-Arg alone are used as the catalysts. These results can be explained by the formation of a catalytically active hydrogen-bonded complex between both amino acids, and demonstrate the possibility of positive cooperative effects in catalysis by two different α-amino acids. Chirality 28:599-605, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

UDP-glucuronyltransferase-catalyzed deconjugation of bilirubin monoglucuronide

NARCIS (Netherlands)

Cuypers, H. T.; ter Haar, E. M.; Jansen, P. L.

1984-01-01

Bilirubin monoglucuronide is rapidly deconjugated when incubated with UDP and rat liver microsomal preparations at pH 5.1. The following evidence was found that this reaction is catalyzed by UDP-glucuronyltransferase: (i) unconjugated bilirubin and UDP-glucuronic acid were identified as the reaction

Synthesis of structured triacylglycerols containing caproic acid by lipase-catalyzed acidolysis: Optimization by response surface methodology

DEFF Research Database (Denmark)

Zhou, D.Q.; Xu, Xuebing; Mu, Huiling

2001-01-01

Production in a batch reactor with a solvent-free system of structured triacylglycerols containing short-chain fatty acids by Lipozyme RM IM-catalyzed acidolysis between rapeseed oil and caproic acid was optimized using response surface methodology (RSM). Reaction time (t(r)), substrate ratio (S......-r = 2-6 mol/mol; and W-c = 2-12 wt %. The biocatalyst was Lipozyme RM IM, in which Rhizomucor miehei lipase is immobilized on a resin. The incorporation of caproic acid into rapeseed oil was the main monitoring response. In addition, the contents of mono-incorporated structured triacylglycerols and di......-incorporated structured triacylglycerols were also evaluated. The optimal reaction conditions for the incorporation of caproic acid and the content of di-incorporated structured triacylglycerols were as follows: t(r) = 17 h; 8, = 5; E-1 = 14 wt %; W-c = 10 wt %; T-e = 65 degreesC. At these conditions, products with 55...

A kinetic mechanistic study of acid-catalyzed alkylation of isobutane with C4-olefins at low temperatures

Energy Technology Data Exchange (ETDEWEB)

Doshi, B.M.

1978-01-01

A kinetic and mechanistic study of sulfuric acid-catalyzed alkylation of isobutane with C/sub 4/-Olefins at Low Temperatures(-20/sup 0/ to 0/sup 0/C) was based on a new two-step reaction sequence in which the desired first-step reactions are between acid and olefin to form sulfates and the desired second-step reactions are between sulfates and isobutane to form mostly trimethylpentanes. Linear butenes formed stable sulfates that formed alkylates of exceptionally high quality, up to 100 Research octane, whereas isobutylene and trimethylpentene mainly polymerized during the first step, and the alkylate produced had only 90 Research octane. Trimethylpentanes and dimethylhexanes, when contacted with concentrated sulfuric acid at -10/sup 0/ to +25/sup 0/C, degraded and isomerized to form C/sub 4/-C/sub 9/ and higher isoparaffins and acid-soluble hydrocarbons (conjunct polymers). For the two-step process and the degradation and isomerization reactions, kinetic models based on reaction at the interface were developed; but for isoolefins, a polymerization-cracking sequence (via C/sub 12/- and even C/sub 16/-olefins) is the preferred route. Commercial applications of the results are proposed.

Efficient Lewis Acid Ionic Liquid-Catalyzed Synthesis of the Key Intermediate of Coenzyme Q10 under Microwave Irradiation

Directory of Open Access Journals (Sweden)

Thomas Efferth

2010-12-01

Full Text Available An efficient synthesis of a valuable intermediate of coenzyme Q10 by microwave-assisted Lewis acidic ionic liquid (IL-catalyzed Friedel-Crafts alkylation is reported. The acidity of six [Etpy]BF4-based ionic liquids was characterized by means of the FT-IR technique using acetonitrile as a molecular probe. The catalytic activities of these ionic liquids were correlated with their Lewis acidity. With increasing Lewis acid strength of the ionic liquids, their catalytic activity in the Friedel-Crafts reaction increased, except for [Etpy]BF4-AlCl3. The effects of the reaction system, the molar fraction of Lewis acid in the Lewis acid ILs and heating techniques were also investigated. Among the six Lewis acid ionic liquids tested [Etpy]BF4-ZnCl2 showed the best catalytic activity, with a yield of 89% after a very short reaction time (150 seconds. This procedure has the advantages of higher efficiency, better reusability of ILs, energy conservation and eco-friendliness. The method has practical value for preparation of CoQ10 on an industrial scale.

Ion-exchange Resin Catalyzed Esterification of Lactic Acid with Isopropanol: a Kinetic Study

Directory of Open Access Journals (Sweden)

Amrit P. Toor

2011-05-01

Full Text Available The kinetic behavior of esterification of lactic acid with isopropanol over an acidic cation exchange resin, Amberlyst 15, was studied under isothermal condition. Isopropyl lactate synthesized in this reaction is an important pharmaceutical intermediate. The experiments were carried out in a stirred batch reactor in the temperature range of 323.15 to 353.15 K. The effect of various parameters such as temperature, molar ratio and catalyst loading was studied. Variation in parameters on rate of reaction demonstrated that the reaction was intrinsically controlled. Kinetic modeling was performed using Eley-Rideal model which acceptably fits the experimental data. The activation energy was found to be 22.007 kJ/mol and frequency factor was 0.036809 l2 g-1 mol-1 min-1 for forward reaction. The value of entropy for the forward reaction was found to be 182.317 J K-1 mol-1 . © 2011 BCREC UNDIP. All rights reserved(Received: 19th January 2011, Revised: 16th March 2011; Accepted: 16th March 2011[How to Cite: A.P. Toor, M. Sharma, S. Thakur, and R. K. Wanchoo. (2011. Ion-exchange Resin Catalyzed Esterification of Lactic Acid with Isopropanol: a Kinetic Study. Bulletin of Chemical Reaction Engineering and Catalysis, 6(1: 39-45. doi:10.9767/bcrec.6.1.791.39-45][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.6.1.791.39-45 || or local:  http://ejournal.undip.ac.id/index.php/bcrec/article/view/791 ] | View in  

Macrocyclic bis-thioureas catalyze stereospecific glycosylation reactions.

Science.gov (United States)

Park, Yongho; Harper, Kaid C; Kuhl, Nadine; Kwan, Eugene E; Liu, Richard Y; Jacobsen, Eric N

2017-01-13

Carbohydrates are involved in nearly all aspects of biochemistry, but their complex chemical structures present long-standing practical challenges to their synthesis. In particular, stereochemical outcomes in glycosylation reactions are highly dependent on the steric and electronic properties of coupling partners; thus, carbohydrate synthesis is not easily predictable. Here we report the discovery of a macrocyclic bis-thiourea derivative that catalyzes stereospecific invertive substitution pathways of glycosyl chlorides. The utility of the catalyst is demonstrated in the synthesis of trans-1,2-, cis-1,2-, and 2-deoxy-β-glycosides. Mechanistic studies are consistent with a cooperative mechanism in which an electrophile and a nucleophile are simultaneously activated to effect a stereospecific substitution reaction. Copyright © 2017, American Association for the Advancement of Science.

Stochastic simulation of enzyme-catalyzed reactions with disparate timescales.

Science.gov (United States)

Barik, Debashis; Paul, Mark R; Baumann, William T; Cao, Yang; Tyson, John J

2008-10-01

Many physiological characteristics of living cells are regulated by protein interaction networks. Because the total numbers of these protein species can be small, molecular noise can have significant effects on the dynamical properties of a regulatory network. Computing these stochastic effects is made difficult by the large timescale separations typical of protein interactions (e.g., complex formation may occur in fractions of a second, whereas catalytic conversions may take minutes). Exact stochastic simulation may be very inefficient under these circumstances, and methods for speeding up the simulation without sacrificing accuracy have been widely studied. We show that the "total quasi-steady-state approximation" for enzyme-catalyzed reactions provides a useful framework for efficient and accurate stochastic simulations. The method is applied to three examples: a simple enzyme-catalyzed reaction where enzyme and substrate have comparable abundances, a Goldbeter-Koshland switch, where a kinase and phosphatase regulate the phosphorylation state of a common substrate, and coupled Goldbeter-Koshland switches that exhibit bistability. Simulations based on the total quasi-steady-state approximation accurately capture the steady-state probability distributions of all components of these reaction networks. In many respects, the approximation also faithfully reproduces time-dependent aspects of the fluctuations. The method is accurate even under conditions of poor timescale separation.

CU(II): catalyzed hydrazine reduction of ferric nitrate

International Nuclear Information System (INIS)

Karraker, D.G.

1981-11-01

A method is described for producing ferrous nitrate solutions by the cupric ion-catalyzed reduction of ferric nitrate with hydrazine. The reaction is complete in about 1.5 hours at 40 0 C. Hydrazoic acid is also produced in substantial quantities as a reaction byproduct

Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

Science.gov (United States)

Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

2016-05-17

Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

Influence of hydroxylamine conformation on stereocontrol in Pd-catalyzed isoxazolidine-forming reactions.

Science.gov (United States)

Lemen, Georgia S; Giampietro, Natalie C; Hay, Michael B; Wolfe, John P

2009-03-20

Palladium-catalyzed carboamination reactions between N-Boc-O-(but-3-enyl)hydroxylamine derivatives and aryl or alkenyl bromides afford cis-3,5- and trans-4,5-disubstituted isoxazolidines in good yield with up to >20:1 dr. The diastereoselectivity observed in the formation of cis-3,5-disubstituted isoxazolidines is superior to selectivities typically obtained in other transformations, such as 1,3-dipolar cycloaddition reactions, that provide these products. In addition, the stereocontrol in the C-N bond-forming Pd-catalyzed carboamination reactions of N-Boc-O-(but-3-enyl)hydroxylamines is significantly higher than that of related C-O bond-forming carboetherification reactions of N-benzyl-N-(but-3-enyl)hydroxylamine derivatives. This is likely due to a stereoelectronic preference for cyclization via transition states in which the Boc group is placed in a perpendicular orientation relative to the plane of the developing ring, which derives from the conformational equilibria of substituted hydroxylamines.

N-Boc Amines to Oxazolidinones via Pd(II)/Bis-sulfoxide/Brønsted Acid Co-Catalyzed Allylic C–H Oxidation

Science.gov (United States)

2015-01-01

A Pd(II)/bis-sulfoxide/Brønsted acid catalyzed allylic C–H oxidation reaction for the synthesis of oxazolidinones from simple N-Boc amines is reported. A range of oxazolidinones are furnished in good yields (avg 63%) and excellent diastereoselectivities (avg 15:1) to furnish products regioisomeric from those previously obtained using allylic C–H amination reactions. Mechanistic studies suggest the role of the phosphoric acid is to furnish a Pd(II)bis-sulfoxide phosphate catalyst that promotes allylic C–H cleavage and π-allylPd functionalization with a weak, aprotic oxygen nucleophile and to assist in catalyst regeneration. PMID:24999765

N-Boc amines to oxazolidinones via Pd(II)/bis-sulfoxide/Brønsted acid co-catalyzed allylic C-H oxidation.

Science.gov (United States)

Osberger, Thomas J; White, M Christina

2014-08-06

A Pd(II)/bis-sulfoxide/Brønsted acid catalyzed allylic C-H oxidation reaction for the synthesis of oxazolidinones from simple N-Boc amines is reported. A range of oxazolidinones are furnished in good yields (avg 63%) and excellent diastereoselectivities (avg 15:1) to furnish products regioisomeric from those previously obtained using allylic C-H amination reactions. Mechanistic studies suggest the role of the phosphoric acid is to furnish a Pd(II)bis-sulfoxide phosphate catalyst that promotes allylic C-H cleavage and π-allylPd functionalization with a weak, aprotic oxygen nucleophile and to assist in catalyst regeneration.

Reactions of CH-acids with α,β-unsaturated aldehydes in ionic liquids

DEFF Research Database (Denmark)

Kryshtal, G. V.; Zhdankina, G. M.; Astakhova, Irina Kira

2004-01-01

Metal carbonate-catalyzed reactions of CH-acids (diethyl malonate, ethyl acetoacetate, ethyl cyanoacetate, and ethyl 2-acetyl- and 2-ethoxycarbonyl-5,9- dimethyldeca-4,8-dienoates) with α,β-unsaturated aldehydes (acrolein, crotonaldehyde, citral) were studied in an ionic liquid, 1-butyl-3......- methylimidazolium hexafluorophosphate [bmim][PF 6], and in a 1-butyl-3-methylimidazolium bromide ([bmim][Br]) - benzene system. The reactions with acrolein and crotonaldehyde afforded Michael addition products, those with citral resulted in Knoevenagel addition products. Sonication increased the yields...

Enantioconvergent synthesis by sequential asymmetric Horner-Wadsworth-Emmons and palladium-catalyzed allylic substitution reactions

DEFF Research Database (Denmark)

Pedersen, Torben Møller; Hansen, E. Louise; Kane, John

2001-01-01

A new method for enantioconvergent synthesis has been developed. The strategy relies on the combination of an asymmetric Horner-Wadsworth-Emmons (HWE) reaction and a palladium-catalyzed allylic substitution. Different $alpha@-oxygen-substituted, racemic aldehydes were initially transformed by asy...... the allylic stereocenter and the alkene geometry. Thus, a single $gamma@-substituted ester was obtained as the overall product, in high isomeric purity. The method was applied to a synthesis of a subunit of the iejimalides, a group of cytotoxic macrolides.......A new method for enantioconvergent synthesis has been developed. The strategy relies on the combination of an asymmetric Horner-Wadsworth-Emmons (HWE) reaction and a palladium-catalyzed allylic substitution. Different $alpha@-oxygen-substituted, racemic aldehydes were initially transformed...... by asymmetric HWE reactions into mixtures of two major $alpha@,$beta@-unsaturated esters, possessing opposite configurations at their allylic stereocenters as well as opposite alkene geometry. Subsequently, these isomeric mixtures of alkenes could be subjected to palladium-catalyzed allylic substitution...

Role of keto–enol tautomerization in a chiral phosphoric acid catalyzed asymmetric thiocarboxylysis of meso-epoxide: a DFT study

KAUST Repository

Ajitha, Manjaly John; Huang, Kuo-Wei

2015-01-01

The mechanism of a chiral phosphoric acid catalyzed thiocarboxylysis of meso-epoxide was investigated by density functional theory (DFT) calculations (M06-2X). The nucleophilic ring opening of epoxide by thiobenzoic acid was found to proceed via a concerted termolecular transition state with a simultaneous dual proton transfer to yield the β-hydroxy thioester product. Electrostatic interactions together with the steric environment inside the chiral catalyst play an important role in determining the enantioselectivity of the reaction.

Role of keto–enol tautomerization in a chiral phosphoric acid catalyzed asymmetric thiocarboxylysis of meso-epoxide: a DFT study

KAUST Repository

Ajitha, Manjaly John

2015-09-15

The mechanism of a chiral phosphoric acid catalyzed thiocarboxylysis of meso-epoxide was investigated by density functional theory (DFT) calculations (M06-2X). The nucleophilic ring opening of epoxide by thiobenzoic acid was found to proceed via a concerted termolecular transition state with a simultaneous dual proton transfer to yield the β-hydroxy thioester product. Electrostatic interactions together with the steric environment inside the chiral catalyst play an important role in determining the enantioselectivity of the reaction.

Three-component reactions of kojic acid: Efficient synthesis of Dihydropyrano[3,2-b]chromenediones and aminopyranopyrans catalyzed with Nano-Bi2O3-ZnO and Nano-ZnO

Directory of Open Access Journals (Sweden)

Maryam Zirak

2017-05-01

Full Text Available Synthesis of pyrano-chromenes and pyrano-pyrans was developed by three-component reactions of kojic acid and aromatic aldehydes with dimethone and malononitrile, catalyzed with nano-Bi2O3-ZnO and nano-ZnO, respectively. Reactions proceeded smoothly and the corresponding heterocyclic products were obtained in good to high yields. Nano ZnO and nano Bi2O3-ZnO were prepared by sol-gel method and characterized by X-ray diffraction (XRD, energy-dispersive X-ray analysis (EDX, Fourier transform infrared (FT-IR, scanning electron microscopy (SEM, and transmission electron microscopy (TEM techniques. Supporting Bi3+ on ZnO nanoparticles as Bi2O3, is the main novelty of this work. The simple reaction procedure, easy separation of products, low catalyst loading, reusability of the catalyst are some advantageous of this protocol.

The Formation of Pyrroline and Tetrahydropyridine Rings in Amino Acids Catalyzed by Pyrrolysine Synthase (PylD)

KAUST Repository

Quitterer, Felix

2014-06-10

The dehydrogenase PylD catalyzes the ultimate step of the pyrrolysine pathway by converting the isopeptide L-lysine-Nε-3R-methyl-D-ornithine to the 22nd proteinogenic amino acid. In this study, we demonstrate how PylD can be harnessed to oxidize various isopeptides to novel amino acids by combining chemical synthesis with enzyme kinetics and X-ray crystallography. The data enable a detailed description of the PylD reaction trajectory for the biosynthesis of pyrroline and tetrahydropyridine rings as constituents of pyrrolysine analogues. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pd-Catalyzed Cross-Coupling Reactions of Amides and Aryl Mesylates

Science.gov (United States)

Dooleweerdt, Karin; Fors, Brett P.; Buchwald, Stephen L.

2010-01-01

A catalyst, based on a biarylphosphine ligand, for the Pd-catalyzed cross-coupling reactions of amides and aryl mesylates is described. This system allows an array of aryl and heteroaryl mesylates to be transformed into the corresponding N-arylamides in moderate to excellent yields. PMID:20420379

Acid-Catalyzed Preparation of Biodiesel from Waste Vegetable Oil: An Experiment for the Undergraduate Organic Chemistry Laboratory

Science.gov (United States)

Bladt, Don; Murray, Steve; Gitch, Brittany; Trout, Haylee; Liberko, Charles

2011-01-01

This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when…

Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes

Science.gov (United States)

Kondoh, Azusa; Jamison, Timothy F.

2010-01-01

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki-Miyaura cross-coupling applications are also presented. PMID:20107646

Sequential Au(I-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

Directory of Open Access Journals (Sweden)

Jianbo Wang

2011-05-01

Full Text Available The gold(I-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in good yields. The reaction follows a catalytic sequence of gold carbene formation/water O–H insertion/alcohol-alkyne cyclization. The gold(I complex is the only catalyst in each of these steps.

Structural characterization of tartrate dehydrogenase: a versatile enzyme catalyzing multiple reactions

International Nuclear Information System (INIS)

Malik, Radhika; Viola, Ronald E.

2010-01-01

The first structure of an NAD-dependent tartrate dehydrogenase (TDH) has been solved to 2 (angstrom) resolution by single anomalous diffraction (SAD) phasing as a complex with the intermediate analog oxalate, Mg 2+ and NADH. This TDH structure from Pseudomonas putida has a similar overall fold and domain organization to other structurally characterized members of the hydroxy-acid dehydrogenase family. However, there are considerable differences between TDH and these functionally related enzymes in the regions connecting the core secondary structure and in the relative positioning of important loops and helices. The active site in these complexes is highly ordered, allowing the identification of the substrate-binding and cofactor-binding groups and the ligands to the metal ions. Residues from the adjacent subunit are involved in both the substrate and divalent metal ion binding sites, establishing a dimer as the functional unit and providing structural support for an alternating-site reaction mechanism. The divalent metal ion plays a prominent role in substrate binding and orientation, together with several active-site arginines. Functional groups from both subunits form the cofactor-binding site and the ammonium ion aids in the orientation of the nicotinamide ring of the cofactor. A lysyl amino group (Lys192) is the base responsible for the water-mediated proton abstraction from the C2 hydroxyl group of the substrate that begins the catalytic reaction, followed by hydride transfer to NAD. A tyrosyl hydroxyl group (Tyr141) functions as a general acid to protonate the enolate intermediate. Each substrate undergoes the initial hydride transfer, but differences in substrate orientation are proposed to account for the different reactions catalyzed by TDH.

The conversion of dimethyl ether over Pt/H-ZSM5. A bifunctional catalyzed reaction

NARCIS (Netherlands)

Engelen, C.W.R.; Wolthuizen, J.P.; Hooff, van J.H.C.; Imelik, B.; Naccache, C.; Coudurier, G.

1985-01-01

At low temperatures dimethylether mixed with hydrogen reacts over a platinum loaded H-ZSM5 catalyst selectivity to methane. Two successive steps can be distinguished; first the acid-catalyzed formation of a trimethyloxoniumion, followed by a metal-catalyzed hydrogenation to methane. Experiments with

A Highly Stereocontrolled, One-Pot Approach toward Pyrrolobenzoxazinones and Pyrroloquinazolinones through a Lewis Acid-Catalyzed [3 + 2]-Cycloannulation Process.

Science.gov (United States)

Boomhoff, Michael; Ukis, Rostyslav; Schneider, Christoph

2015-08-21

We report herein a stereocontrolled [3 + 2]-cycloheteroannulation of bis-silyl dienediolate 1 with 2-aminobenzoic acid- and 2-aminobenzamide-derived imines to furnish highly substituted pyrrolo[1,2-a]benzoxazinones 3 and pyrrolo[1,2-a]quinazolinones 4, respectively, in good overall yields. This one-pot process rapidly generates molecular complexity and comprises a Lewis acid-catalyzed, vinylogous Mannich reaction of 1 followed by an intramolecular N,O-acetal- and N,N-aminal formation, respectively, which proceeds with good to excellent stereocontrol.

SOLVENT EFFECTS ON THE HYDRATION OF CYCLOHEXENE CATALYZED BY A STRONG ACID ION-EXCHANGE RESIN .3. EFFECT OF SULFOLANE ON THE EQUILIBRIUM CONVERSION

NARCIS (Netherlands)

PANNEMAN, HJ; BEENACKERS, AACM

The liquid-phase hydration of cyclohexene, a pseudo-first-order reversible reaction catalyzed by a strong acid ion-exchange resin, was investigated in solvent mixtures of water and sulfolane. Macroporous Amberlite XE 307 was used because of its superior catalytic activity. Chemical equilibrium

Synthesis of 5-hydroxymethylfurfural (HMF) by acid catalyzed dehydration of glucose-fructose mixtures

DEFF Research Database (Denmark)

Pedersen, Asbjørn Toftgaard; Ringborg, Rolf Hoffmeyer; Grotkjær, Thomas

2015-01-01

allowing the use of the cheapest available source of fructose: high fructose corn syrup. The dehydration was catalyzed by hydrochloric acid and conducted in acetone-water mixtures, which ensured good selectivity towards HMF and eliminated precipitation of polymer by-products (insoluble humins). Through......Synthesis of 5-hydroxymethylfurfural (HMF) from hexoses has been studied extensively in the scientific literature. However, a process has yet to be implemented at industrial scale. In this paper the simultaneous dehydration of glucose and fructose was investigated, in order to develop a process......-products: soluble humins, glucose dimers, anhydroglucose, and formic acid. The reaction conditions in four different reactor configurations were optimized and compared using the kinetic model. It was found that a recirculating reactor setup is preferable, where the equilibrium controlled by-products (anhydroglucose...

Behaviors of glucose decomposition during acid-catalyzed hydrothermal hydrolysis of pretreated Gelidium amansii.

Science.gov (United States)

Jeong, Tae Su; Choi, Chang Ho; Lee, Ji Ye; Oh, Kyeong Keun

2012-07-01

Acid-catalyzed hydrothermal hydrolysis is one path to cellulosic glucose and subsequently to its dehydration end products such as hydroxymethyl furfural (HMF), formic acid and levulinic acid. The effect of sugar decomposition not only lowers the yield of fermentable sugars but also forms decomposition products that inhibit subsequent fermentation. The present experiments were conducted with four different acid catalysts (H(2)SO(4), HNO(3), HCl, and H(3)PO(4)) at various acid normalities (0.5-2.1N) in batch reactors at 180-210 °C. From the results, H(2)SO(4) was the most suitable catalyst for glucose production, but glucose decomposition occurred during the hydrolysis. The glucose production was maximized at 160.7 °C, 2.0% (w/v) H(2)SO(4), and 40 min, but resulted in a low glucan yield of 33.05% due to the decomposition reactions, which generated formic acid and levulinic acid. The highest concentration of levulinic acid, 7.82 g/L, was obtained at 181.2 °C, 2.0% (w/v) H(2)SO(4), and 40 min. Copyright © 2012 Elsevier Ltd. All rights reserved.

Mild and Efficient Nickel-Catalyzed Heck Reactions with Electron-Rich Olefins

DEFF Research Database (Denmark)

Gøgsig, Thomas; Kleimark, Jonatan; Lill, Sten O. Nilsson

2012-01-01

proved compatible, and the corresponding aryl methyl ketone could be secured after hydrolysis in yields approaching quantitative. Good functional group tolerance was observed matching the characteristics of the analogous Pd-catalyzed Heck reaction. The high levels of catalytic activity were explained...

Investigation of transition metal-catalyzed nitrene transfer reactions in water.

Science.gov (United States)

Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

2018-04-11

Transition metal-catalyzed nitrene transfer is a powerful method for incorporating new CN bonds into relatively unfunctionalized scaffolds. In this communication, we report the first examples of site- and chemoselective CH bond amination reactions in aqueous media. The unexpected ability to employ water as the solvent in these reactions is advantageous in that it eliminates toxic solvent use and enables reactions to be run at increased concentrations with lower oxidant loadings. Using water as the reaction medium has potential to expand the scope of nitrene transfer to encompass a variety of biomolecules and highly polar substrates, as well as enable pH control over the site-selectivity of CH bond amination. Copyright © 2018 Elsevier Ltd. All rights reserved.

Pd(II)-Catalyzed Enantioselective C-H Olefination of Diphenylacetic Acids

Science.gov (United States)

Shi, Bing-Feng; Zhang, Yang-Hui; Lam, Jonathan K.; Wang, Dong-Hui; Yu, Jin-Quan

2009-01-01

Pd(II)-catalyzed enantioselective C-H olefination of diphenylacetic acid substrates has been achieved through the use of mono-protected chiral amino acid ligands. The absolute configuration of the resulting olefinated products is consistent with that of a proposed C-H insertion intermediate. PMID:20017549

Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

Directory of Open Access Journals (Sweden)

Katrina Tait

2016-10-01

Full Text Available Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases.

Copper-Catalyzed Oxidative Reaction of β-Keto Sulfones with Alcohols via C-S Bond Cleavage: Reaction Development and Mechanism Study.

Science.gov (United States)

Du, Bingnan; Wang, Wenmin; Wang, Yang; Qi, Zhenghang; Tian, Jiaqi; Zhou, Jie; Wang, Xiaochen; Han, Jianlin; Ma, Jing; Pan, Yi

2018-02-16

A Cu-catalyzed cascade oxidative radical process of β-keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β-keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C-S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four-coordinated Cu II intermediate, O-O bond homolysis induced C-S bond cleavage and Cu-catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C-S bond cleavage and transformations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation of biodiesel from waste cooking oil via two-step catalyzed process

International Nuclear Information System (INIS)

Wang Yong; Liu Pengzhan; Ou Shiyi; Zhang Zhisen

2007-01-01

Waste cooking oils (WCO), which contain large amounts of free fatty acids produced in restaurants, are collected by the environmental protection agency in the main cities of China and should be disposed in a suitable way. In this research, a two step catalyzed process was adopted to prepare biodiesel from waste cooking oil whose acid value was 75.92 ± 0.036 mgKOH/g. The free fatty acids of WCO were esterified with methanol catalyzed by ferric sulfate in the first step, and the triglycerides (TGs) in WCO were transesterified with methanol catalyzed by potassium hydroxide in the second step. The results showed that ferric sulfate had high activity to catalyze the esterification of free fatty acids (FFA) with methanol, The conversion rate of FFA reached 97.22% when 2 wt% of ferric sulfate was added to the reaction system containing methanol to TG in10:1 (mole ratio) composition and reacted at 95 deg. C for 4 h. The methanol was vacuum evaporated, and transesterification of the remained triglycerides was performed at 65 deg. C for 1 h in a reaction system containing 1 wt% of potassium hydroxide and 6:1 mole ratio of methanol to TG. The final product with 97.02% of biodiesel, obtained after the two step catalyzed process, was analyzed by gas chromatography. This new process has many advantages compared with the old processes, such as no acidic waste water, high efficiency, low equipment cost and easy recovery of the catalyst

Investigation of emulsified, acid and acid-alkali catalyzed mesoporous bioactive glass microspheres for bone regeneration and drug delivery

Energy Technology Data Exchange (ETDEWEB)

Miao, Guohou [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641 China (China); National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou 510006 China (China); Guangdong Province Key Laboratory of Biomedical Engineering, South China University of Technology, Guangzhou 510006 China (China); Chen, Xiaofeng, E-mail: chenxf@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641 China (China); National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou 510006 China (China); Guangdong Province Key Laboratory of Biomedical Engineering, South China University of Technology, Guangzhou 510006 China (China); Dong, Hua [National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou 510006 China (China); Guangdong Province Key Laboratory of Biomedical Engineering, South China University of Technology, Guangzhou 510006 China (China); School of Biological Science and Engineering, South China University of Technology, Guangzhou 510006 (China); Fang, Liming; Mao, Cong; Li, Yuli; Li, Zhengmao; Hu, Qing [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641 China (China); National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou 510006 China (China); Guangdong Province Key Laboratory of Biomedical Engineering, South China University of Technology, Guangzhou 510006 China (China)

2013-10-15

Acid-catalyzed mesoporous bioactive glass microspheres (MBGMs-A) and acid-alkali co-catalyzed mesoporous bioactive glass microspheres (MBGMs-B) were successfully synthesized via combination of sol-gel and water-in-oil (W/O) micro-emulsion methods. The structural, morphological and textural properties of mesoporous bioactive glass microspheres (MBGMs) were characterized by various techniques. Results show that both MBGMs-A and MBGMs-B exhibit regularly spherical shape but with different internal porous structures, i.e., a dense microstructure for MBGMs-A and internally porous structure for MBGMs-B. {sup 29}Si NMR data reveal that MGBMs have low polymerization degree of silica network. The in vitro bioactivity tests indicate that the apatite formation rate of MBGMs-B was faster than that of MBGMs-A after soaking in simulated body fluid (SBF) solution. Furthermore, the two kinds of MBGMs have similar storage capacity of alendronate (AL), and the release behaviors of AL could be controlled due to their unique porous structure. In conclusion, the microspheres are shown to be promising candidates as bone-related drug carriers and filling materials of composite scaffold for bone repair. - Graphical abstract: The morphologies and microstructures of acid-catalyzed mesoporous bioactive glass microspheres (MBGMs-A) and acid-alkali co-catalyzed mesoporous bioactive glass microspheres (MBGMs-B) were observed by scanning electron microscope and transmission electron microscope. MBGMs-A exhibits a dense structure and a porous can be observed in MBGMs-B. The microspheres have a quick inducing-apatite formation ability and show a sustained release of alendronate (AL). Highlights: • A rapid method was reported to prepare mesoporous bioactive glass microspheres. • The addition of ammonia significantly shortens the preparation time. • Acid and acid-alkali co-catalyzed microspheres were studied for the first time. • The materials exhibited excellent in vitro bioactivity and

Theoretical insights into the sites and mechanisms for base catalyzed esterification and aldol condensation reactions over Cu.

Science.gov (United States)

Neurock, Matthew; Tao, Zhiyuan; Chemburkar, Ashwin; Hibbitts, David D; Iglesia, Enrique

2017-04-28

Condensation and esterification are important catalytic routes in the conversion of polyols and oxygenates derived from biomass to fuels and chemical intermediates. Previous experimental studies show that alkanal, alkanol and hydrogen mixtures equilibrate over Cu/SiO 2 and form surface alkoxides and alkanals that subsequently promote condensation and esterification reactions. First-principle density functional theory (DFT) calculations were carried out herein to elucidate the elementary paths and the corresponding energetics for the interconversion of propanal + H 2 to propanol and the subsequent C-C and C-O bond formation paths involved in aldol condensation and esterification of these mixtures over model Cu surfaces. Propanal and hydrogen readily equilibrate with propanol via C-H and O-H addition steps to form surface propoxide intermediates and equilibrated propanal/propanol mixtures. Surface propoxides readily form via low energy paths involving a hydrogen addition to the electrophilic carbon center of the carbonyl of propanal or via a proton transfer from an adsorbed propanol to a vicinal propanal. The resulting propoxide withdraws electron density from the surface and behaves as a base catalyzing the activation of propanal and subsequent esterification and condensation reactions. These basic propoxides can readily abstract the acidic C α -H of propanal to produce the CH 3 CH (-) CH 2 O* enolate, thus initiating aldol condensation. The enolate can subsequently react with a second adsorbed propanal to form a C-C bond and a β-alkoxide alkanal intermediate. The β-alkoxide alkanal can subsequently undergo facile hydride transfer to form the 2-formyl-3-pentanone intermediate that decarbonylates to give the 3-pentanone product. Cu is unique in that it rapidly catalyzes the decarbonylation of the C 2n intermediates to form C 2n-1 3-pentanone as the major product with very small yields of C 2n products. This is likely due to the absence of Brønsted acid sites

Characterization and optimization of carboxylesterase-catalyzed esterification between capric acid and glycerol for the production of 1-monocaprin in reversed micellar system.

Science.gov (United States)

Park, Kyung Min; Kwon, Oh Taek; Ahn, Seon Min; Lee, JaeHwan; Chang, Pahn-Shick

2010-02-28

Calotropis procera R. Br. carboxylesterase (EC 3.1.1.1) solubilized in reversed micellar glycerol droplets containing a very small amount of water (less than 5ppm) and stabilized by a surfactant effectively catalyzed the esterification between glycerol and capric acid to produce 1-monocaprin. Reaction variables including surfactant types, organic solvent media, reaction time, G-value ([glycerol]/[capric acid]), R-value ([water]/[surfactant]), pH, temperature, and types of metal ion inhibitors on the carboxylesterase-catalyzed esterification were characterized and optimized to efficiently produce 1-monocaprin. Bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and isooctane were the most effective surfactant and organic solvent medium, respectively, for 1-monocaprin formation in reversed micelles. The optimum G- and R-values were 3.0 and 0.05, respectively, and the optimum pH and temperature were determined to be 10.0 and 60 degrees C, respectively. K(m,app.) and V(max,app.) were calculated from a Hanes-Woolf plot, and the values were 9.64 mM and 2.45 microM/min mg protein, respectively. Among various metal ions, Cu(2+) and Fe(2+) severely inhibited carboxylesterase-catalyzed esterification activity (less than 6.0% of relative activity). Copyright 2009 Elsevier B.V. All rights reserved.

Investigation of acetic acid-catalyzed hydrothermal pretreatment on corn stover

DEFF Research Database (Denmark)

Xu, Jian; Thomsen, Mette Hedegaard; Thomsen, Anne Belinda

2010-01-01

Acetic acid (AA)-catalyzed liquid hot water (LHW) pretreatments on raw corn stover (RCS) were carried out at 195 °C at 15 min with the acetic acid concentrations between 0 and 400 g/kg RCS. After pretreatment, the liquor fractions and water-insoluble solids (WIS) were collected separately...

An N-Linked Bidentate Phosphoramidite Ligand (N-Me-BIPAM for Rhodium-Catalyzed Asymmetric 1,4-Addition of Arylboronic Acids to α,β-Unsaturated Ketones

Directory of Open Access Journals (Sweden)

Norio Miyaura

2012-12-01

Full Text Available A new bidentate phosphoramidite (N-Me-BIPAM based on Shibasaki’s N-linked BINOL was synthesized. This ligand appears to be highly effective for rhodium-catalyzed asymmetric conjugated addition of arylboronic acids to α,β-unsaturated enones. The reaction of ortho-substituted arylboronic acid with acyclic and cyclic enones provides the corresponding products in good yields and enantioselectivities.

Synthesis of 2-vinylic indoles and derivatives via a Pd-catalyzed tandem coupling reaction.

Science.gov (United States)

Fayol, Aude; Fang, Yuan-Qing; Lautens, Mark

2006-09-14

A novel one-step synthesis of valuable 2-vinylic indoles and their tricycle derivatives is described. This reaction, which utilizes a gem-dibromovinyl unit as a readily available starting material, occurs via an efficient Pd-catalyzed tandem Buchwald-Hartwig/Heck reaction.

Selectivity control in pd-catalyzed c-h functionalization reactions

OpenAIRE

Flores Gaspar, Areli

2013-01-01

Benzocyclobutenones are an intriguing four-membered ring ketone. In the present thesis, we have developed a new protocol for selectively preparing benzocyclobutenones through intramolecular acylation of aryl bromides via palladium catalyzed C-H bond functionalization reactions based on rac-BINAP ligand. We also found that a subtle modification on the ligand backbone lead to a new catalytic manifold for preparing configurationally-pure styrene derivatives, when using dcpp (bis-dicyclohexylphos...

Catalytic Asymmetric Piancatelli Rearrangement: Brønsted Acid Catalyzed 4π Electrocyclization for the Synthesis of Multisubstituted Cyclopentenones

KAUST Repository

Cai, Yunfei

2016-10-13

The first catalytic asymmetric Piancatelli reaction is reported. Catalyzed by a chiral Brønsted acid, the rearrangement of a wide range of furylcarbinols with a series of aniline derivatives provides valuable aminocyclopentenones in high yields as well as excellent enantioselectivities and diastereoselectivities. The high value of the aza-Piancatelli rearrangement was demonstrated by the synthesis of a cyclopentane-based hNK1 antagonist analogue.

Hydrodeoxygenation of fatty acid esters catalyzed by Ni on nano-sized MFI type zeolites

Energy Technology Data Exchange (ETDEWEB)

Schreiber, Moritz W.; Rodriguez-Niño, Daniella; Gutiérrez, Oliver Y.; Lercher, Johannes A.

2016-01-01

The impact of support morphology and composition on the intrinsic activity of Ni supported on MFI-type zeolite was explored in the hydrodeoxygenation of methyl stearate, tristearate, and algae oil (mixture of triglycerides). The nano-sized structure of the support (self-pillared nanosheets) is beneficial for the activity of the catalysts. Higher Ni dispersion and concomitant higher reaction rates were obtained on nano-structured supports than on zeolite with conventional morphology. Rates normalized to accessible Ni atoms (TOF), however, varied little with support morphology. Acidity of the support increases the rate of Ni-catalyzed C-O hydrogenolysis per surface metal site.

The acid-catalyzed hydrolysis of an α-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact

Science.gov (United States)

Rindelaub, Joel D.; Borca, Carlos H.; Hostetler, Matthew A.; Slade, Jonathan H.; Lipton, Mark A.; Slipchenko, Lyudmila V.; Shepson, Paul B.

2016-12-01

The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO + NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long-range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, the hydrolysis mechanism and rate constants were elucidated for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the tertiary APN lifetime ranging from 8.3 min at acidic pH (0.25) to 8.8 h at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant

Lewis acid tuned facial stereodivergent HDA reactions using beta-substituted N-vinyloxazolidinones.

Science.gov (United States)

Gohier, Frédéric; Bouhadjera, Keltoum; Faye, Djibril; Gaulon, Catherine; Maisonneuve, Vincent; Dujardin, Gilles; Dhal, Robert

2007-01-18

The [4 + 2] acido-catalyzed heterocycloaddition between new beta-substituted N-vinyl-1,3-oxazolidin-2-ones (with R' = Me, Ar, CH2 Ar) and beta,gamma-unsaturated alpha-ketoesters (R = Ar) afforded heteroadducts with high levels of endo and facial selectivities. A complete reversal of facial differentiation was achieved by varying the Lewis acid, leading to the stereoselective formation of either endo-alpha or endo-beta adducts. [reaction: see text].

Ruthenium Hydride/Brønsted Acid-Catalyzed Tandem Isomerization/N-Acyliminium Cyclization Sequence for the Synthesis of Tetrahydro-β-carbolines

DEFF Research Database (Denmark)

Hansen, Casper Lykke; Clausen, Janie Regitse Waël; Ohm, Ragnhild Gaard

2013-01-01

This paper describes an efficient tandem sequence for the synthesis of 1,2,3,4-tetrahydro-β-carbolines (THBCs) relying on a ruthenium hydride/Brønsted acid- catalyzed isomerization of allylic amides to N-acyliminium ion intermediates which are trapped by a tethered indolenucleophile. The methodol...... the Suzuki cross-coupling reaction to the isomerization/N-acyliminium cyclization sequence. Finally, diastereo- and enantioselective versions of the title reaction have been examined using substrate control (with dr >15: 1) and asymmetric catalysis (ee up to 57%), respectively...

Integrated Production of Xylonic Acid and Bioethanol from Acid-Catalyzed Steam-Exploded Corn Stover.

Science.gov (United States)

Zhu, Junjun; Rong, Yayun; Yang, Jinlong; Zhou, Xin; Xu, Yong; Zhang, Lingling; Chen, Jiahui; Yong, Qiang; Yu, Shiyuan

2015-07-01

High-efficiency xylose utilization is one of the restrictive factors of bioethanol industrialization. However, xylonic acid (XA) as a new bio-based platform chemical can be produced by oxidation of xylose with microbial. So, an applicable technology of XA bioconversion was integrated into the process of bioethanol production. After corn stover was pretreated with acid-catalyzed steam-explosion, solid and liquid fractions were obtained. The liquid fraction, also named as acid-catalyzed steam-exploded corn stover (ASC) prehydrolyzate (mainly containing xylose), was catalyzed with Gluconobacter oxydans NL71 to prepare XA. After 72 h of bioconversion of concentrated ASC prehydrolyzate (containing 55.0 g/L of xylose), the XA concentration reached a peak value of 54.97 g/L, the sugar utilization ratio and XA yield were 94.08 and 95.45 %, respectively. The solid fraction was hydrolyzed to produce glucose with cellulase and then fermented with Saccharomyces cerevisiae NL22 to produce ethanol. After 18 h of fermentation of concentrated enzymatic hydrolyzate (containing 86.22 g/L of glucose), the ethanol concentration reached its highest value of 41.48 g/L, the sugar utilization ratio and ethanol yield were 98.72 and 95.25 %, respectively. The mass balance showed that 1 t ethanol and 1.3 t XA were produced from 7.8 t oven dry corn stover.

Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

Energy Technology Data Exchange (ETDEWEB)

Zhu, Z.; Espenson, H. [Iowa State Univ., Ames, IA (United States)

1995-11-03

Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

Cationic Pd(II-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

Directory of Open Access Journals (Sweden)

Takashi Nishikata

2016-05-01

Full Text Available Cationic palladium(II complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN4](BF42 or a nitrile-free cationic palladium(II complex generated in situ from the reaction of Pd(OAc2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1 C–H activation to generate a cationic palladacycle; (2 reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3 regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied.

Esterification with ethanol to produce biodiesel from high acidity raw materials. Kinetic studies and analysis of secondary reactions

Energy Technology Data Exchange (ETDEWEB)

Pisarello, M.L.; Dalla Costa, B.; Mendow, G.; Querini, C.A. [Instituto de Investigaciones en Catalisis y Petroquimica (INCAPE)-(FIQ-UNL, CONICET), Santiago del Estero 2654-Santa Fe, S3000AOJ (Argentina)

2010-09-15

In this work, the esterification reaction of free fatty acids (FFA) in sunflower oil, coconut oil and concentrated FFA, with ethanol, methanol and ethanol 96%, using homogeneous acid catalysts to produce biodiesel is studied. Kinetic parameters are estimated with a simplified model, and then used to predict the reaction behavior. Reactions other than the reversible esterification are considered to explain the behavior that this system displays. Such reactions are the triglycerides conversion by acid catalyzed transesterification and hydrolysis. In addition, we include kinetic studies of the reaction that occur between the sulphuric acid and methanol (or ethanol), forming mono and dialkylsulphates. This reaction produces water and consumes methanol (or ethanol), and consequently has a direct impact in the esterification reaction rate and equilibrium conversion. The concentration of sulphuric acid decreases to less than 50% of the initial value due to the reaction with the alcohol. A minimum in the acidity due to the free fatty acids as a function of time was clearly observed during the reaction, which has not been reported earlier. This behavior is related to the consecutive reactions that take place during the esterification of FFA in the presence of triglycerides. The phase separation due to the presence of water, which is generated during the reaction, is also studied. (author)

Modeling the reactions catalyzed by coenzyme B12-dependent enzymes.

Science.gov (United States)

Sandala, Gregory M; Smith, David M; Radom, Leo

2010-05-18

Enzymes accelerate chemical reactions with an exceptional selectivity that makes life itself possible. Understanding the factors responsible for this efficient catalysis is of utmost importance in our quest to harness the tremendous power of enzymes. Computational chemistry has emerged as an important adjunct to experimental chemistry and biochemistry in this regard, because it provides detailed insights into the relationship between structure and function in a systematic and straightforward manner. In this Account, we highlight our recent high-level theoretical investigations toward this end in studying the radical-based reactions catalyzed by enzymes dependent on coenzyme B(12) (or adenosylcobalamin, AdoCbl). In addition to their fundamental position in biology, the AdoCbl-dependent enzymes represent a valuable framework within which to understand Nature's method of efficiently handling high-energy species to execute very specific reactions. The AdoCbl-mediated reactions are characterized by the interchange of a hydrogen atom and a functional group on adjacent carbon atoms. Our calculations are consistent with the conclusion that the main role of AdoCbl is to provide a source of radicals, thus moving the 1,2-rearrangements onto the radical potential energy surface. Our studies also show that the radical rearrangement step is facilitated by partial proton transfer involving the substrate. Specifically, we observe that the energy requirements for radical rearrangement are reduced dramatically with appropriate partial protonation or partial deprotonation or sometimes (synergistically) both. Such interactions are particularly relevant to enzyme catalysis, because it is likely that the local amino acid environment in the active site of an enzyme can function in this capacity through hydrogen bonding. Finally, our calculations indicate that the intervention of a very stable radical along the reaction pathway may inactivate the enzyme, demonstrating that sustained

Rhenium and Manganese-Catalyzed Selective Alkenylation of Indoles

KAUST Repository

Wang, Chengming

2018-04-06

An efficient rhenium‐catalyzed regioselective C‐H bond alkenylation of indoles is reported. The protocol operates well for internal as well as terminal alkynes, affording products in good to excellent yields. Furthermore, a manganese catalyzed, acid free, regioselective C2‐alkenylation of indoles with internal alkynes is described. The directing groups can be easily removed after the reaction and the resulting products can be used as valuable building blocks for the synthesis of diverse heterocyclic compounds.

Rhenium and Manganese-Catalyzed Selective Alkenylation of Indoles

KAUST Repository

Wang, Chengming; Rueping, Magnus

2018-01-01

An efficient rhenium‐catalyzed regioselective C‐H bond alkenylation of indoles is reported. The protocol operates well for internal as well as terminal alkynes, affording products in good to excellent yields. Furthermore, a manganese catalyzed, acid free, regioselective C2‐alkenylation of indoles with internal alkynes is described. The directing groups can be easily removed after the reaction and the resulting products can be used as valuable building blocks for the synthesis of diverse heterocyclic compounds.

Formation of Broensted acids sites in the reaction of cyclohexanol on NaCeY zeolites

International Nuclear Information System (INIS)

Vogt, O.; Nattich, M.; Datka, J.; Gil, B.

2002-01-01

This study was undertaken to elucidate why the catalytic activity of NaCeY in cyclohexanol reactions carried out in a pulse reactor increases with the pulse number. We studied therefore the effect of cyclohexanol and also of ethanol and water on catalytic activity NaCeY (of exchange degrees 36 and 72%) in cyclohexanol reactions: isomerization and disproportionation. We also studied the reaction of cyclohexanol and water with NaCeY zeolite by IR spectroscopy. Our results evidenced that new Broensted acid sites were formed by the reaction of cyclohexanol and water. This was shown by IR spectroscopy: the increase of Si-O 1 H-Al band 3638 cm -1 and in increase of ammonium ions band (upon ammonia adsorption). The new sites were formed by hydrolysis of Ce 3+ ions with water introduced in a pulse, or produced by dehydration of cyclohexanol catalyzed by acid sites. Formation of new Broensted acid sites resulted in an increase of catalytic activity of NaCeY in cyclohexane reaction as observed in this study and also in cyclohexanol reactions. (author)

Grape skins (Vitis vinifera L.) catalyze the in vitro enzymatic hydroxylation of p-coumaric acid to caffeic acid

DEFF Research Database (Denmark)

Arnous, Anis; Meyer, Anne S.

2009-01-01

The ability of grape skins to catalyze in vitro conversion of p-coumaric acid to the more potent antioxidant caffeic acid was studied. Addition of different concentrations of p-coumaric to red grape skins (Cabernet Sauvignon) resulted in formation of caffeic acid. This caffeic acid formation (Y...

Glutathiolactaldehyde as a probe of the overall stereochemical course of glyoxalase-I catalyzed reactions

International Nuclear Information System (INIS)

Brush, E.J.; Kozarich, J.W.

1986-01-01

The overall stereochemical course of the reactions catalyzed by glyoxalase-I (GX-I) has remained elusive as the substrates are equilibrium mixtures of rapidly interconverting diastereomeric thiohemiacetals. However, with the discovery of inverse substrate processing by Kozarich and coworkers, it is possible to design GX-I substrate analogs that are intrinsically more stable than the thiohemiacetals. Hence, Chari and Kozarich reported that glutathiohydroxyacetone (GHA, GSCH 2 COCH 2 OH) undergoes GX-I catalyzed exchange of the pro-S hydroxymethyl proton with solvent deuterium. Their data suggest that GX-I processes a single diastereomeric thiohemiacetal, and are consistent with a cis-enediol intermediate. To test this hypothesis and to follow the overall stereochemistry on a single substrate, they have prepared glutathiolactaldehyde (GLA, GSCH 2 CHOHCHO) as a potential inverse substrate. Human erythrocyte GX-I catalyzes the isomerization of GLA to GHA as evidenced by UV and NMR spectra of the product. Solvent deuterium is incorporated into the hydroxymethyl position, and NMR data suggest that incorporation is stereospecific. Furthermore, 50% of the expected amount of GHA is produced indicating that only one diastereomer of GLA is processed by GX-I. Identification of the absolute stereochemistry of the substrate diastereomer will lead to a clarification of the overall stereochemical and mechanistic course of GX-I catalyzed reactions

Kinetic Study of Esterification of Acetic Acid with n-butanol and isobutanol Catalyzed by Ion Exchange Resin

Directory of Open Access Journals (Sweden)

Amrit Pal Toor

2011-05-01

Full Text Available Esters are an important pharmaceutical intermediates and very useful perfumery agents. In this study the esterification of acetic acid with n-butanol and iso-butanol over an acidic cation exchange resin, Amberlyst 15 were carried out. The effects of certain parameters such as temperature, catalyst loading, initial molar ratio between reactants on the rate of reaction were studied. The experiments were conducted in a stirred batch reactor in the temperature range of 351.15 K to 366.15K.Variation of parameters on rate of reaction demonstrated that the reaction was intrinsically controlled.The activation energy for the esterification of acetic acid with n-butanol and iso butanol is found to be 28.45 k J/mol and 23.29 kJ/mol respectively. ©2011 BCREC UNDIP. All rights reserved.(Received: 16th December 2010, Revised: 19th March 2011; Accepted: 7th April 2011[How to Cite: A.P. Toor, M. Sharma, G. Kumar, and R. K. Wanchoo. (2011. Kinetic Study of Esterification of Acetic Acid with n-butanol and isobutanol Catalyzed by Ion Exchange Resin. Bulletin of Chemical Reaction Engineering and Catalysis, 6(1: 23-30. doi:10.9767/bcrec.6.1.665.23-30][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.6.1.665.23-30 || or local: http://ejournal.undip.ac.id/index.php/bcrec/article/view/665 ] | View in 

The Manganese-Catalyzed Cross-Coupling Reaction and the Influence of Trace Metals

DEFF Research Database (Denmark)

Santilli, Carola; Beigbaghlou, Somayyeh Sarvi; Ahlburg, Andreas

2017-01-01

The substrate scope of the MnCl2-catalyzed cross-coupling between aryl halides and Grignard reagents has been extended to several methyl-substituted aryl iodides by performing the reaction at elevated temperature in a microwave oven. A radical clock experiment revealed the presence of an aryl...

Kinetic Studies on Enzyme-Catalyzed Reactions: Oxidation of Glucose, Decomposition of Hydrogen Peroxide and Their Combination

Science.gov (United States)

Tao, Zhimin; Raffel, Ryan A.; Souid, Abdul-Kader; Goodisman, Jerry

2009-01-01

The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 ± 0.7) ×104 M−1s−1 at 37°C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37°C and well above unity at 25°C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s−1 and 0.090 s−1 respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain. PMID:19348778

Pd(II)/Bipyridine-Catalyzed Conjugate Addition of Arylboronic Acids to α,β-Unsaturated Carboxylic Acids. Synthesis of β-Quaternary Carbons Substituted Carboxylic Acids.

Science.gov (United States)

Liu, Rui; Yang, Zhenyu; Ni, Yuxin; Song, Kaixuan; Shen, Kai; Lin, Shaohui; Pan, Qinmin

2017-08-04

Pd(II)/bipyridine-catalyzed conjugate addition of arylboronic acids to α,β-unsaturated carboxylic acids (including β,β-disubstituted acrylic acids) was developed and optimized, which provided a mild and convenient method for the highly challenging synthesis of β-quaternary carbons substituted carboxylic acids.

An Efficient Synthesis of 3,4-Dihydropyrimidin-2(1H-Ones and Thiones Catalyzed by a Novel Brønsted Acidic Ionic Liquid under Solvent-Free Conditions

Directory of Open Access Journals (Sweden)

Yonghong Zhang

2015-02-01

Full Text Available We report here an efficient and green method for Biginelli condensation reaction of aldehydes, β-ketoesters and urea or thiourea catalyzed by Brønsted acidic ionic liquid [Btto][p-TSA] under solvent-free conditions. Compared to the classical Biginelli reaction conditions, the present method has the advantages of giving good yields, short reaction times, near room temperature conditions and the avoidance of the use of organic solvents and metal catalyst.

Reactions of alkylnitrosoureas in aqueous solution

International Nuclear Information System (INIS)

Snyder, J.K.; Stock, L.M.

1980-01-01

The acid- and base-catalyzed decompositions of N-methyl-,N,N'-dimethyl-, and N,N',N'-trimethyl-N-nitrosourea in aqueous solution have been studied. Below pH 2, the N-methyl compound undergoes both denitrosation and hydrolysis to yield methylurea, nitrous acid, methylamine, nitrogen, and carbon dioxide. The acid-catalyzed denitrosation and hydrolysis of the trimethylnitrosourea are somewhat more rapid than the corresponding reactions of N-methyl-N-nitrosourea. The solvent isotope effect, k/sub H 2 O//k/sub D 2 O/ = 1.3, and the absence of chloride ion catalysis suggest that the denitrosation reaction proceeds by a rate-determining proton transfer which is followed by the rapid loss of the nitroso group. The results for the hydrolysis reaction are compatible with a formulation in which a hydrate of the nitrosourea is protonated in a rate-determining step to form a tetrahedral intermediate which subsequently decomposes to yield methyldiazonium hydroxide and a carbamic acid derivative. The base-catalyzed reactions of the mono, di-, and trimethylnitrosoureas are first order in hydroxide ion over a broad pH range. The hydrolysis of N-methyl-N-nitrosourea yields methanol and derivatives of carbamic acid. Salt effects on the reaction rate are negligible except for the influence of lithium ion. The rate constants for the hydrolysis of the mono- and dimethyl compounds depend upon the buffer concentrationat pH 9.5. The rate constants for the hydrolysis of the trimethyl compound also depend upon the buffer concentration, but a limiting value is not achieved. The solvent isotope effect for the base-catalyzed reaction, the exchange reaction of water- 18 O with the carbonyl group of the urea, and the fact that N-methyl-N-nitrosourea is hydrolyzed about 2.2 x 10 4 times more rapidly than N,N',N'-trimethyl-N-nitrosourea suggest that the hydrolysis occurs by a mechanism in which a tetrahedral intermediate is formed

Insights into the formation of carlactone from in-depth analysis of the CCD8-catalyzed reactions

KAUST Repository

Bruno, Mark; Vermathen, Martina; Alder, Adrian; Wü st, Florian; Schaub, Patrick; van der Steen, Rob; Beyer, Peter; Ghisla, Sandro; Al-Babili, Salim

2017-01-01

Strigolactones (SLs) are a new class of phytohormones synthesized from carotenoids via carlactone. The complex structure of carlactone is not easily deducible from its precursor, a cis-configured β-carotene cleavage product, and is thus formed via a poorly understood series of reactions and molecular rearrangements, all catalyzed by only one enzyme, the carotenoid cleavage dioxygenase 8 (CCD8). Moreover, the reactions leading to carlactone are expected to form a second, yet unidentified product. In this study, we used (13) C and (18) O-labelling to shed light on the reactions catalyzed by CCD8. The characterization of the resulting carlactone by LC-MS and NMR, and the identification of the assumed, less accessible second product allowed us to formulate a minimal reaction mechanism for carlactone generation. This article is protected by copyright. All rights reserved.

Insights into the formation of carlactone from in-depth analysis of the CCD8-catalyzed reactions

KAUST Repository

Bruno, Mark

2017-02-10

Strigolactones (SLs) are a new class of phytohormones synthesized from carotenoids via carlactone. The complex structure of carlactone is not easily deducible from its precursor, a cis-configured β-carotene cleavage product, and is thus formed via a poorly understood series of reactions and molecular rearrangements, all catalyzed by only one enzyme, the carotenoid cleavage dioxygenase 8 (CCD8). Moreover, the reactions leading to carlactone are expected to form a second, yet unidentified product. In this study, we used (13) C and (18) O-labelling to shed light on the reactions catalyzed by CCD8. The characterization of the resulting carlactone by LC-MS and NMR, and the identification of the assumed, less accessible second product allowed us to formulate a minimal reaction mechanism for carlactone generation. This article is protected by copyright. All rights reserved.

Ruthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 C-H bond and Lewis acid catalysis.

Science.gov (United States)

Wang, Ming-Zhong; Zhou, Cong-Ying; Wong, Man-Kin; Che, Chi-Ming

2010-05-17

Ruthenium porphyrins (particularly [Ru(2,6-Cl(2)tpp)CO]; tpp=tetraphenylporphinato) and RuCl(3) can act as oxidation and/or Lewis acid catalysts for direct C-3 alkylation of indoles, giving the desired products in high yields (up to 82% based on 60-95% substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron-withdrawing or electron-donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N-arylindoles to 3-{[(N-aryl-N-alkyl)amino]methyl}indoles (yield: up to 82%, conversion: up to 95%) and the alkylation of N-alkyl or N-H indoles to 3-[p-(dialkylamino)benzyl]indoles (yield: up to 73%, conversion: up to 92%). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp(3) C-H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N-arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three-component coupling reaction of the in situ generated formaldehyde with an N-alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium-labeling experiments are consistent with the alkylation of N-alkylindoles via pathway B. The relative reaction rates of [Ru(2,6-Cl(2)tpp)CO]-catalyzed oxidative coupling reactions of 4-X-substituted N,N-dimethylanilines with N-phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants sigma (R(2)=0.989), giving a rho value of -1.09. This rho value and the magnitudes of the intra- and intermolecular deuterium isotope effects (k(H)/k(D)) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4-X-substituted N,N-dimethylanilines. Ruthenium-catalyzed three-component reaction of N-alkyl/N-H indoles

Triosephosphate isomerase: energetics of the reaction catalyzed by the yeast enzyme expressed in Escherichia coli

International Nuclear Information System (INIS)

Nickbarg, E.B.; Knowles, J.R.

1988-01-01

Triosephosphate isomerase from bakers' yeast, expressed in Escherichia coli strain DF502(p12), has been purified to homogeneity. The kinetics of the reaction in each direction have been determined at pH 7.5 and 30 degrees C. Deuterium substitution at the C-2 position of substrate (R)-glyceraldehyde phosphate and at the 1-pro-R position of substrate dihydroxyacetone phosphate results in kinetic isotope effects on kcat of 1.6 and 3.4, respectively. The extent of transfer of tritium from [1(R)- 3 H]dihydroxyacetone phosphate to product (R)-glyceraldehyde phosphate during the catalyzed reaction is only 3% after 66% conversion to product, indicating that the enzymic base that mediates proton transfer is in rapid exchange with solvent protons. When the isomerase-catalyzed reaction is run in tritiated water in each direction, radioactivity is incorporated both into the remaining substrate and into the product. In the exchange-conversion experiment with dihydroxyacetone phosphate as substrate, the specific radioactivity of remaining dihydroxyacetone phosphate rises as a function of the extent of reaction with a slope of about 0.3, while the specific radioactivity of the products is 54% that of the solvent. In the reverse direction with (R)-glyceraldehyde phosphate as substrate, the specific radioactivity of the product formed is only 11% that of the solvent, while the radioactivity incorporated into the remaining substrate (R)-glyceraldehyde phosphate also rises as a function of the extent of reaction with a slope of 0.3. These results have been analyzed according to the protocol described earlier to yield the free energy profile of the reaction catalyzed by the yeast isomerase

Silver-catalyzed formal inverse electron-demand Diels-Alder reaction of 1,2-diazines and siloxy alkynes.

Science.gov (United States)

Türkmen, Yunus E; Montavon, Timothy J; Kozmin, Sergey A; Rawal, Viresh H

2012-06-06

A highly effective silver-catalyzed formal inverse electron-demand Diels-Alder reaction of 1,2-diazines and siloxy alkynes has been developed. The reactions provide ready access to a wide range of siloxy naphthalenes and anthracenes, which are formed in good to high yields, under mild reaction conditions, using low catalyst loadings.

Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions

DEFF Research Database (Denmark)

Ishøy, Mette; Nielsen, Thomas Eiland

2014-01-01

of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. A sea of opportunities! Transition-metal-catalyzed isomerization of N- and O-allylic compounds provides a mild, selective and synthetically...... versatile method to form iminium and oxocarbenium ions. Given the number of reactions involving these highly electrophilic intermediates, this concept provides a sea of opportunities for heterocycle synthesis, (see scheme; Nu=nucleophile). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim....

Lewis Acid Catalyzed Asymmetric Three-Component Coupling Reaction: Facile Synthesis of α-Fluoromethylated Tertiary Alcohols.

Science.gov (United States)

Aikawa, Kohsuke; Kondo, Daisuke; Honda, Kazuya; Mikami, Koichi

2015-12-01

A chiral dicationic palladium complex is found to be an efficient Lewis acid catalyst for the synthesis of α-fluoromethyl-substituted tertiary alcohols using a three-component coupling reaction. The reaction transforms three simple and readily available components (terminal alkyne, arene, and fluoromethylpyruvate) to valuable chiral organofluorine compounds. This strategy is completely atom-economical and results in perfect regioselectivities and high enantioselectivities of the corresponding tertiary allylic alcohols in good to excellent yields. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetics of an acid-base catalyzed reaction (aspartame degradation) as affected by polyol-induced changes in buffer pH and pK values.

Science.gov (United States)

Chuy, S; Bell, L N

2009-01-01

The kinetics of an acid-base catalyzed reaction, aspartame degradation, were examined as affected by the changes in pH and pK(a) values caused by adding polyols (sucrose, glycerol) to phosphate buffer. Sucrose-containing phosphate buffer solutions had a lower pH than that of phosphate buffer alone, which contributed, in part, to reduced aspartame reactivity. A kinetic model was introduced for aspartame degradation that encompassed pH and buffer salt concentrations, both of which change with a shift in the apparent pK(a) value. Aspartame degradation rate constants in sucrose-containing solutions were successfully predicted using this model when corrections (that is, lower pH, lower apparent pK(a) value, buffer dilution from the polyol) were applied. The change in buffer properties (pH, pK(a)) from adding sucrose to phosphate buffer does impact food chemical stability. These effects can be successfully incorporated into predictive kinetic models. Therefore, pH and pK(a) changes from adding polyols to buffer should be considered during food product development.

Asymmetric Diels-Alder Reaction of α,β-Unsaturated Oxazolidin-2-one Derivatives Catalyzed by a Chiral Fe(III)-Bipyridine Diol Complex.

Science.gov (United States)

Li, Mao; Carreras, Virginie; Jalba, Angela; Ollevier, Thierry

2018-02-16

An asymmetric Fe III -bipyridine diol catalyzed Diels-Alder reaction of α,β-unsaturated oxazolidin-2-ones has been developed. Among various Fe II /Fe III salts, Fe(ClO 4 ) 3 ·6H 2 O was selected as the Lewis acid of choice. The use of a low catalyst loading (2 mol % of Fe(ClO 4 ) 3 ·6H 2 O and 2.4 mol % of Bolm's ligand) afforded high yields (up to 99%) and high enantiomeric excesses (up to 98%) of endo-cycloadducts for the Diels-Alder reaction between cyclopentadiene and substituted acryloyloxazolidin-2-ones. Other noncyclic dienes led to decreased enantioselectivities. A proposed model supports the observed stereoinduction.

Low-temperature superacid catalysis: Reactions of n - butane and propane catalyzed by iron- and manganese-promoted sulfated zirconia

Energy Technology Data Exchange (ETDEWEB)

Tsz-Keung, Cheung; d`Itri, J.L.; Lange, F.C.; Gates, B.C. [Univ. of California, Davis, CA (United States)

1995-12-31

The primary goal of this project is to evaluate the potential value of solid superacid catalysts of the sulfated zirconia type for light hydrocarbon conversion. The key experiments catalytic testing of the performance of such catalysts in a flow reactor fed with streams containing, for example, n-butane or propane. Fe- and Mn-promoted sulfated zirconia was used to catalyze the conversion of n-butane at atmospheric pressure, 225-450{degrees}C, and n-butane partial pressures in the range of 0.0025-0.01 atm. At temperatures <225{degrees}C, these reactions were accompanied by cracking; at temperatures >350{degrees}C, cracking and isomerization occurred. Catalyst deactivation, resulting at least in part from coke formation, was rapid. The primary cracking products were methane, ethane, ethylene, and propylene. The observation of these products along with an ethane/ethylene molar ratio of nearly 1 at 450{degrees}C is consistent with cracking occurring, at least in part, by the Haag-Dessau mechanism, whereby the strongly acidic catalyst protonates n-butane to give carbonium ions. The rate of methane formation from n-butane cracking catalyzed by Fe- and Mn-promoted sulfated zirconia at 450{degrees}C was about 3 x 10{sup -8} mol/(g of catalyst {center_dot}s). The observation of butanes, pentanes, and methane as products is consistent with Olah superacid chemistry, whereby propane is first protonated by a very strong acid to form a carbonium ion. The carbonium ion then decomposes into methane and an ethyl cation which undergoes oligocondensation reactions with propane to form higher molecular weight alkanes. The results are consistent with the identification of iron- and manganese-promoted sulfated zirconia as a superacid.

Copper-Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions: Simultaneous Generation and Trapping of Copper-Triazoles and -Ketenimines for the Synthesis of Triazolopyrimidines.

Science.gov (United States)

Nallagangula, Madhu; Namitharan, Kayambu

2017-07-07

First simultaneous generation and utilization of both copper-triazole and -ketenimine intermediates in copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions is achieved for the one-pot synthesis of triazolopyrimidines via a novel copper-catalyzed multicomponent cascade of sulfonyl azides, alkynes, and azirines. Significantly, the reaction proceeds under very mild conditions in good yields.

SYNTHESIS OF FLAVANONE-6-CARBOXYLIC ACID DERIVATIVES FROM SALICYLIC ACID DERIVATIVE

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Muhammad Idham Darussalam Mardjan

2012-02-01

Full Text Available Synthesis of flavanone-6-carboxylic acid derivatives had been conducted via the route of chalcone. The synthesis was carried out from salicylic acid derivative, i.e. 4-hydroxybenzoic acid, via esterification, Fries rearrangement, Claisen-Schmidt condensation and 1,4-nucleophilic addition reactions. Structure elucidation of products was performed using FT-IR, 1H-NMR, GC-MS and UV-Vis spectrometers. Reaction of 4-hydroxybenzoic acid with methanol catalyzed with sulfuric acid produced methyl 4-hydroxybenzoate in 87% yield. The acid-catalyzed-acetylation of the product using acetic anhydride gave methyl 4-acetoxybenzoate in 75% yield. Furthermore, solvent-free Fries rearrangement of methyl 4-acetoxybenzoate in the presence of AlCl3 produced 3-acetyl-4-hydroxybenzoic acid as the acetophenone derivatives in 67% yield. Then, Claisen-Schmidt condensation of the acetophenone and benzaldehyde derivatives of p-anisaldehyde and veratraldehyde in basic condition gave 2'-hydroxychalcone-5'-carboxylic acid derivatives  in 81 and 71 % yield, respectively. Finally, the ring closure reaction of the chalcone yielded the corresponding flavanone-6-carboxylic acids in 67 and 59% yield, respectively.

SOLVENT EFFECTS ON THE HYDRATION OF CYCLOHEXENE CATALYZED BY A STRONG ACID ION-EXCHANGE RESIN .2. EFFECT OF SULFOLANE ON THE REACTION-KINETICS

NARCIS (Netherlands)

PANNEMAN, HJ; BEENACKERS, AACM

The kinetics of the' hydration of cyclohexene, catalyzed by a strong acid ion-exchange resin, have been studied in a packed bed reactor at temperatures between 353 and 413 K and a pressure of 20 bar. The kinetic rate constants were measured as a function of temperature and solvent composition (0-90

Structural Determinants of Alkyne Reactivity in Copper-Catalyzed Azide-Alkyne Cycloadditions

Directory of Open Access Journals (Sweden)

Xiaoguang Zhang

2016-12-01

Full Text Available This work represents our initial effort in identifying azide/alkyne pairs for optimal reactivity in copper-catalyzed azide-alkyne cycloaddition (CuAAC reactions. In previous works, we have identified chelating azides, in particular 2-picolyl azide, as “privileged” azide substrates with high CuAAC reactivity. In the current work, two types of alkynes are shown to undergo rapid CuAAC reactions under both copper(II- (via an induction period and copper(I-catalyzed conditions. The first type of the alkynes bears relatively acidic ethynyl C-H bonds, while the second type contains an N-(triazolylmethylpropargylic moiety that produces a self-accelerating effect. The rankings of reactivity under both copper(II- and copper(I-catalyzed conditions are provided. The observations on how other reaction parameters such as accelerating ligand, reducing agent, or identity of azide alter the relative reactivity of alkynes are described and, to the best of our ability, explained.

High Pressure Diels Alder Reactions of 1-Vinyl-2,2,6-trimethylcyclohexene Catalyzed by Chiral Lewis Acids; An Enantioselective Route to a Drimane Sesquiterpene Precursor.

NARCIS (Netherlands)

Knol, Joop; Meetsma, Auke; Feringa, Bernard

1995-01-01

The Diels Alder reaction of 1-vinyl-2,2,6-trimethylcyclohexene and 3-((E)-3-(methoxycarbonyl)propenoyl)-1,3-oxazolidin-2-one under high pressure, catalyzed by a chiral bis-imine copper(II) complex, yields a drimane sesquiterpene precursor in a highly regio- and diastereoselective manner with

S,O-Ligand-Promoted Palladium-Catalyzed C-H Functionalization Reactions of Nondirected Arenes

NARCIS (Netherlands)

Naksomboon, K.; Valderas, C.; Gomez-Martinez, M.; Alvarez-Casao, Y.; Fernández Ibáñez, M.A.

Pd(II)-catalyzed C-H functionalization of non directed arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is

State of the art and prospective of lipase-catalyzed transesterification reaction for biodiesel production

International Nuclear Information System (INIS)

Amini, Zeynab; Ilham, Zul; Ong, Hwai Chyuan; Mazaheri, Hoora; Chen, Wei-Hsin

2017-01-01

Highlights: • Enzymatic transesterification process is less energy intensive and robust. • Nano-materials are promising immobilization supports for lipase. • Packed-bed reactors are appropriate for scale-up use. • Potential recombinant, whole cell and recombinant whole cell lipases were enlisted. • Genetic engineering is a promising prospect in biodiesel area. - Abstract: The world demand for fuel as energy sources have arisen the need for generating alternatives such as biofuel. Biodiesel is a renewable fuel used particularly in diesel engines. Currently, biodiesel is mainly produced through transesterification reactions catalyzed by chemical catalysts, which produces higher fatty acid alkyl esters in shorter reaction time. Although extensive investigations on enzymatic transesterification by downstream processing were carried out, enzymatic transesterification has yet to be used in scale-up since commercial lipases are chiefly limited to the cost as well as long reaction time. While numerous lipases were studied and proven to have the high catalytic capacity, still enzymatic reaction requires more investigation. To fill this gap, finding optimal conditions for the reaction such as alcohol and oil choice, water content, reaction time and temperature through proper reaction modelling and simulations as well as the appropriate design and use of reactors for large scale production are crucial issues that need to be accurately addressed. Furthermore, lipase concentration, alternative lipase resources through whole cell technology and genetic engineering, recent immobilizing materials including nanoparticles, and the capacity of enzyme to be reused are important criteria to be neatly investigated. The present work reviews the current biodiesel feedstock, catalysis, general and novel immobilizing materials, bioreactors for enzymatic transesterification, potential lipase resources, intensification technics, and process modelling for enzymatic

Molecular Design of a Chiral Brønsted Acid with Two Different Acidic Sites: Regio-, Diastereo-, and Enantioselective Hetero-Diels-Alder Reaction of Azopyridinecarboxylate with Amidodienes Catalyzed by Chiral Carboxylic Acid-Monophosphoric Acid.

Science.gov (United States)

Momiyama, Norie; Tabuse, Hideaki; Noda, Hirofumi; Yamanaka, Masahiro; Fujinami, Takeshi; Yamanishi, Katsunori; Izumiseki, Atsuto; Funayama, Kosuke; Egawa, Fuyuki; Okada, Shino; Adachi, Hiroaki; Terada, Masahiro

2016-09-07

A chiral Brønsted acid containing two different acidic sites, chiral carboxylic acid-monophosphoric acid 1a, was designed to be a new and effective concept in catalytic asymmetric hetero-Diels-Alder reactions of azopyridinecarboxylate with amidodienes. The multipoint hydrogen-bonding interactions among the carboxylic acid, monophosphoric acid, azopyridinecarboxylate, and amidodiene achieved high catalytic and chiral efficiency, producing substituted 1,2,3,6-tetrahydropyridazines with excellent stereocontrol in a single step. This constitutes the first example of regio-, diastereo-, and enantioselective azo-hetero-Diels-Alder reactions by chiral Brønsted acid catalysis.

Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

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Pedro Almendros

2011-09-01

Full Text Available The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium.

On the Effect of Microwave Energy on Lipase-Catalyzed Polycondensation Reactions

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Alessandro Pellis

2016-09-01

Full Text Available Microwave energy (MWe is, nowadays, widely used as a clean synthesis tool to improve several chemical reactions, such as drug molecule synthesis, carbohydrate conversion and biomass pyrolysis. On the other hand, its exploitation in enzymatic reactions has only been fleetingly investigated and, hence, further study of MWe is required to reach a precise understanding of its potential in this field. Starting from the authors’ experience in clean synthesis and biocatalyzed reactions, this study sheds light on the possibility of using MWe for enhancing enzyme-catalyzed polycondensation reactions and pre-polymer formation. Several systems and set ups were investigated involving bulk and organic media (solution phase reactions, different enzymatic preparations and various starting bio-based monomers. Results show that MWe enables the biocatalyzed synthesis of polyesters and pre-polymers in a similar way to that reported using conventional heating with an oil bath, but in a few cases, notably bulk phase polycondensations under intense microwave irradiation, MWe leads to a rapid enzyme deactivation.

[Study of Reaction Dynamics between Bovine Serum Albumin and Folic Acid by Stopped-Flow/Fluorescence].

Science.gov (United States)

Ye, San-xian; Luo, Yun-jing; Qiao, Shu-liang; Li, Li; Liu, Cai-hong; Shi, Jian-long; An, Xue-jing

2016-01-01

As a kind of coenzyme of one-carbon enzymes in vivo, folic acid belongs to B vitamins, which can interact with other vitamins and has great significance for converting among amino acids, dividing growth of cells and protein synthesis reactions. Half-life, concentration and reaction rate constant of drugs are important parameters in pharmacokinetic study. In this paper, by utilizing fluorescence spectrophotometer and stopped-flow spectrum analyzer, reaction kinetic parameters between bovine serum albumin(BSA) and folic acid in a bionic system have been investigated, which provide references for parameters of drug metabolism related to folic acid. By using Stern-Volmer equation dealing with fluorescence quenching experiments data, we concluded that under 25, 30, and 37 degrees C, the static quenching constants of folic acid to intrinsic fluorescence from bovine serum albumin were 2.455 x 10(10), 4.900 x 10(10) and 6.427 x 10(10) L x mol(-1) x s(-1) respectively; The results of kinetic reaction rate have shown that the reaction rate of BSA and folic acid are greater than 100 mol x L(-1) x s(-1) at different temperatures, pH and buffering media, illustrating that the quenching mechanism between BSA and folic acid is to form composite static quenching process. Reaction concentration of bovine serum albumin and its initial concentration were equal to the secondary reaction formula, and the correlation coefficient was 0.998 7, while the half-life (t1/2) was 0.059 s at physiological temperature. With the increase of folic acid concentration, the apparent rate constant of this reaction had a linear increasing trend, the BSA fluorescence quenching rate constant catalyzed by folic acid was 3.174 x 10(5) mol x L(-1) x s(-1). Furthermore, with different buffer, the apparent rate constant and reaction rate constant of BSA interacting with folic acid were detected to explore the influence on the reaction under physiological medium, which is of great significance to determine the

Kinetics and mechanism of aquation and formation reactions of carbonato complexes. XII. Deuterium solvent isotope effect on the rate of acid-catalyzed decarboxylation of the carbonatobis (ethylenediamine) cobalt(III) complex ion. A mechanistic reappraisal

International Nuclear Information System (INIS)

Harris, G.M.; Hyde, K.E.

1978-01-01

A recent study of the acid-catalyzed decarboxylation of the carbonatotetrakis(pyridine)cobalt(III) complex ion showed there to be rate acceleration in D 2 O solvent, consistent with a proton-preequilibration mechanism. This observation directly contradicts the results of a similar study made some years ago of the analogous ion, carbonatobis(ethylenediamine)cobalt(III), for which there appeared to be deceleration in D 2 O solvent. A reinvestigation of the latter reaction over a much wider acidity range has now shown the earlier work to be in error. The previously proposed generalized mechanism for aquation of chelated carbonato complex ions of the form CoN 4 CO 3 + (N 4 identical with various tetramine ligand groupings of uni-, bi-, or quadridentate type) has thus been revised to include a proton equilibration step. An unexpected complication arises in the interpretation of the data for the bis(ethylenediamine) complex ion in the acidity range 0.1 + ] + ] term, overtakes and exceeds the true first-order rate constant for CO 2 release. The interesting implications of this unusual first-order successive reaction system are fully explored in the context of the present study

Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Five-, Six-, and Seven-Membered β-Substituted Cyclic Enones: Enantioselective Construction of All-Carbon Quaternary Stereocenters

KAUST Repository

Kikushima, Kotaro

2011-05-11

The first enantioselective Pd-catalyzed construction of all-carbon quaternary stereocenters via 1,4-addition of arylboronic acids to β-substituted cyclic enones is reported. Reaction of a wide range of arylboronic acids and cyclic enones using a catalyst prepared from Pd(OCOCF(3))(2) and a chiral pyridinooxazoline ligand yields enantioenriched products bearing benzylic stereocenters. Notably, this transformation is tolerant to air and moisture, providing a practical and operationally simple method of synthesizing enantioenriched all-carbon quaternary stereocenters.

The three transglycosylation reactions catalyzed by cyclodextrin glycosyltransferase from Bacillus circulans (strain 251) proceed via different kinetic mechanisms

NARCIS (Netherlands)

Veen, Bart A. van der; Alebeek, Gert-Jan W.M. van; Uitdehaag, Joost C.M.; Dijkstra, Bauke W.; Dijkhuizen, Lubbert

Cyclodextrin glycosyltransferase (CGTase) catalyzes three transglycosylation reactions via a double displacement mechanism involving a covalent enzyme-intermediate complex (substituted-enzyme intermediate). Characterization of the three transglycosylation reactions, however, revealed that they

Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

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Ohgi Takahashi

2015-01-01

Full Text Available Succinimide formation from aspartic acid (Asp residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe as a model compound, we propose the possibility that acetic acid (AA, which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

Acetic acid can catalyze succinimide formation from aspartic acid residues by a concerted bond reorganization mechanism: a computational study.

Science.gov (United States)

Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

2015-01-12

Succinimide formation from aspartic acid (Asp) residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe) as a model compound, we propose the possibility that acetic acid (AA), which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition) to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds) occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

Palladium-catalyzed aryl C-H olefination with unactivated, aliphatic alkenes.

Science.gov (United States)

Deb, Arghya; Bag, Sukdev; Kancherla, Rajesh; Maiti, Debabrata

2014-10-01

Palladium-catalyzed coupling between aryl halides and alkenes (Mizoroki-Heck reaction) is one of the most popular reactions for synthesizing complex organic molecules. The limited availability, problematic synthesis, and higher cost of aryl halide precursors (or their equivalents) have encouraged exploration of direct olefination of aryl carbon-hydrogen (C-H) bonds (Fujiwara-Moritani reaction). Despite significant progress, the restricted substrate scope, in particular noncompliance of unactivated aliphatic olefins, has discouraged the use of this greener alternative. Overcoming this serious limitation, we report here a palladium-catalyzed chelation-assisted ortho C-H bond olefination of phenylacetic acid derivatives with unactivated, aliphatic alkenes in good to excellent yields with high regio- and stereoselectivities. The versatility of this operationally simple method has been demonstrated through drug diversification and sequential C-H olefination for synthesizing divinylbenzene derivatives.

Laccase-catalyzed removal of the antimicrobials chlorophene and dichlorophen from water: Reaction kinetics, pathway and toxicity evaluation.

Science.gov (United States)

Shi, Huanhuan; Peng, Jianbiao; Li, Jianhua; Mao, Liang; Wang, Zunyao; Gao, Shixiang

2016-11-05

As active agents in cleaning and disinfecting products, antimicrobials have been widely spread in the environment and have drawn extensive attention as potential threats to the ecological system and human health. In this study, the laccase-catalyzed removal of two emerging antimicrobials, chlorophene (CP) and dichlorophen (DCP), was investigated under simulated environmental conditions. Intrinsic reaction kinetics showed that the removal of CP and DCP followed second-order reaction kinetics, first-order with respect to both the enzyme and the substrate concentration. It was also found that fulvic acid could suppress the transformation of CP and DCP by reversing the oxidation reactions through its action as a scavenger of the free radical intermediates produced from reactions between laccase and the substrates. Several reaction products were identified by a quadrupole time-of-flight mass spectrometer, and detailed reaction pathways were proposed. For both CP and DCP, direct polymerization was the principal pathway, and the coupling patterns were further corroborated based on molecular modeling. The nucleophilic substitution of chlorine by the hydroxyl group was observed, and further oxidation products capable of coupling with each other were also found. Additionally, toxicity evaluation tests using Scenedesmus obliquus confirmed that the toxicity of CP and DCP was effectively eliminated during the reaction processes. Copyright © 2016 Elsevier B.V. All rights reserved.

Development of melamine modified urea formaldehyde resins based o nstrong acidic pH catalyzed urea formaldehyde polymer

Science.gov (United States)

Chung-Yun Hse

2009-01-01

To upgrade the performance of urea-formaldehyde (UF) resin bonded particleboards, melamine modified urea-formaldehyde (MUF) resins based on strong acidic pH catalyzed UF polymers were investigated. The study was conducted in a series of two experiments: 1) formulation of MUF resins based on a UF polymer catalyzed with strong acidic pH and 2) determination of the...

A 11-Steps Total Synthesis of Magellanine through a Gold(I)-Catalyzed Dehydro Diels-Alder Reaction.

Science.gov (United States)

McGee, Philippe; Bétournay, Geneviève; Barabé, Francis; Barriault, Louis

2017-05-22

We have developed an innovative strategy for the formation of angular carbocycles via a gold(I)-catalyzed dehydro Diels-Alder reaction. This transformation provides rapid access to a variety of complex angular cores in excellent diastereoselectivities and high yields. The usefulness of this Au I -catalyzed cycloaddition was further demonstrated by accomplishing a 11-steps total synthesis of (±)-magellanine. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetics and mechanism of OsOsub(4) catalyzed oxidation of chalcones by Cesub(4) in aqueous acetic sulfuric acid media

International Nuclear Information System (INIS)

Srinivasulu, P.V.; Adinarayana, M.; Sethuram, B.; Rao, T.N.

1985-01-01

Kinetics of OsOsub(4) catalyzed oxidation of chalcones by Cesup(4+) was studied in aqueous acetic-sulfuric acid medium in the temperature range 313 to 338 K. The order in oxidant is zero while the order with respect to substrate and catalyst are each fractional. The rate of the reaction decreased with increase in percentage of acetic acid while [Hsup(+)] had practically no effect on the rate. The rates of various substituted chalcones are given. A mechanism in which formation of a cyclic ester between chalcone and OsOsub(4) in a fast step followed by its decomposition in a rate-determining step is envisaged. (author)

Redox potential monitoring as a method to control unwanted noble metal-catalyzed hydrogen generation from formic acid treatment of simulated nuclear waste media

International Nuclear Information System (INIS)

King, R.B.; Bhattacharyya, N.K.

1998-01-01

Simulants for the Hanford Waste Vitrification Plant feed containing the major nonradioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO 3 2- , NO 3 - , and NO 2 - were used to study redox potential changes in reactions of formic acid at 90 C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the CO 2 , H 2 , NO, and N 2 O in the gas phase and a redox electrode to follow redox potential changes as a function of time. In the initial phase of formic acid addition to nitrite-containing feed simulants, the redox potential of the reaction mixture rises typically to +400 mV relative to the Al/AgCl electrode because of the generation of the moderately strongly oxidizing nitrous acid. No H 2 production occurs at this stage of the reaction as long as free nitrous acid is present. After all of the nitrous acid has been destroyed by reduction to N 2 O and NO and disproportionation to NO/NO 3 - , the redox potential of the reaction mixture becomes more negative than the Ag/AgCl electrode. The experiments outlined in this paper suggest the feasibility of controlling the production of H 2 by limiting the amount of formic acid used and monitoring the redox potential during formic acid treatment

Mechanistic Implications for the Ni(I-Catalyzed Kumada Cross-Coupling Reaction

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Linda Iffland

2017-11-01

Full Text Available Herein we report on the cross-coupling reaction of phenylmagnesium bromide with aryl halides using the well-defined tetrahedral Ni(I complex, [(TriphosNiICl] (Triphos = 1,1,1-tris(diphenylphosphinomethylethane. In the presence of 0.5 mol % [(TriphosNiICl], good to excellent yields (75–97% of the respective coupling products within a reaction time of only 2.5 h at room temperature were achieved. Likewise, the tripodal Ni(IIcomplexes [(κ2-TriphosNiIICl2] and [(κ3-TriphosNiIICl](X (X = ClO4, BF4 were tested as potential pre-catalysts for the Kumada cross-coupling reaction. While the Ni(II complexes also afford the coupling products in comparable yields, mechanistic investigations by UV/Vis and electron paramagnetic resonance (EPR spectroscopy indicate a Ni(I intermediate as the catalytically active species in the Kumada cross-coupling reaction. Based on experimental findings and density functional theory (DFT calculations, a plausible Ni(I-catalyzed reaction mechanism for the Kumada cross-coupling reaction is presented.

Acidic ionic liquids for n-alkane isomerization in a liquid-liquid or slurry-phase reaction mode

Energy Technology Data Exchange (ETDEWEB)

Meyer, C.; Hager, V.; Geburtig, D.; Kohr, C.; Wasserscheid, P. [Erlangen-Nuernberg Univ. (Germany). Lehrstuhl fuer Chemische Reaktionstechnik; Haumann, M. [Chemical Reaction Engineering, FAU Busan Campus, Korea (Korea, Republic of)

2011-07-01

Highly acidic ionic liquid (IL) catalysts offer the opportunity to convert n-alkanes at very low reaction temperatures. The results of IL catalyzed isomerization and cracking reactions of pure n-octane are presented. Influence of IL composition, [C{sub 4}C{sub 1}Im]Cl / AlCl{sub 3} / H{sub 2}SO{sub 4} and [C{sub 4}C{sub 1}Im]Cl / AlCl{sub 3} / 1-chlorooctane, on catalyst activity and selectivities to branched alkanes was investigated. Acidic chloroaluminate IL catalysts form liquid-liquid biphasic systems with unpolar organic product mixtures. Thus, recycling of the acidic IL is enabled by simple phase separation in the liquid-liquid biphasic reaction mode or the IL can be immobilized on an inorganic support with a large specific surface area. These supported ionic liquid phase (SILP) catalysts offer the advantage to get a macroscopically heterogeneous system while still preserving all benefits of the homogeneous catalyst which can be used for the slurry-phase n-alkane isomerization. The interaction of the solid support and acidic IL influences strongly the catalytic activity. (orig.)

Lecithin-cholesterol acyltransferase (LCAT) catalyzes transacylation of intact cholesteryl esters. Evidence for the partial reversal of the forward LCAT reaction

International Nuclear Information System (INIS)

Sorci-Thomas, M.; Babiak, J.; Rudel, L.L.

1990-01-01

Lecithin-cholesterol acyltransferase (LCAT) catalyzes the intravascular synthesis of lipoprotein cholesteryl esters by converting cholesterol and lecithin to cholesteryl ester and lysolecithin. LCAT is unique in that it catalyzes sequential reactions within a single polypeptide sequence. In this report we find that LCAT mediates a partial reverse reaction, the transacylation of lipoprotein cholesteryl oleate, in whole plasma and in a purified, reconstituted system. As a result of the reverse transacylation reaction, a linear accumulation of [3H]cholesterol occurred during incubations of plasma containing high density lipoprotein labeled with [3H]cholesteryl oleate. When high density lipoprotein labeled with cholesteryl [14C]oleate was also included in the incubation the labeled fatty acyl moiety remained in the cholesteryl [14C]oleate pool showing that the formation of labeled cholesterol did not result from hydrolysis of the doubly labeled cholesteryl esters. The rate of release of [3H]cholesterol was only about 10% of the forward rate of esterification of cholesterol using partially purified human LCAT and was approximately 7% in whole monkey plasma. Therefore, net production of cholesterol via the reverse LCAT reaction would not occur. [3H]Cholesterol production from [3H]cholesteryl oleate was almost completely inhibited by a final concentration of 1.4 mM 5,5'-dithiobis(nitrobenzoic acid) during incubation with either purified LCAT or whole plasma. Addition of excess lysolecithin to the incubation system did not result in the formation of [14C]oleate-labeled lecithin, showing that the reverse reaction found here for LCAT was limited to the last step of the reaction. To explain these results we hypothesize that LCAT forms a [14C]oleate enzyme thioester intermediate after its attack on the cholesteryl oleate molecule

Myeloperoxidase-catalyzed incorporation of amines into proteins: role of hypochlorous acid and dichloramines.

Science.gov (United States)

Thomas, E L; Jefferson, M M; Grisham, M B

1982-11-23

Myeloperoxidase-catalyzed oxidation of chloride (Cl-) to hypochlorous acid (HOCl) resulted in formation of mono- and dichloramine derivatives (RNHCl and RNCl2) of primary amines. The RNCl2 derivatives could undergo a reaction that resulted in incorporation of the R moiety into proteins. The probable mechanism was attack of RNCl2 or an intermediate formed in the decomposition of RNCl2 on histidine, tyrosine, and cystine residues and on lysine residues at high pH. Incorporation of radioactivity from labeled amines into stable, high molecular weight derivatives of proteins was measured by acid or acetone precipitation and by gel chromatography and electrophoresis. Whereas formation of RNCl2 was favored at low pH, the subsequent incorporation reaction was favored at high pH. Up to several hours were required for the maximum amount of incorporation, which was less than 10% of the label in RNCl2. For the amines tested, incorporation was in the order histamine greater than 1,2-diaminoethane greater than putrescine greater than taurine greater than lysine greater than glucosamine greater than leucine greater than methylamine. Initiation of the reaction required HOCl, and oxidized forms of bromide, iodide, or thiocyanate did not substitute. Inhibitors of incorporation fell into three classes. First, ammonia or amines competed with the labeled amine for reaction with HOCl, so that larger amounts of HOCl were required. Second, readily oxidized substances such as sulfhydryl or diketo compounds or thioethers (methionine) reduced RNCl2. Third, certain compounds competed with protein as the acceptor for the incorporation reaction. The amount required to block incorporation into protein depended on protein concentration. Among these inhibitors were imidazole compounds (histidine), phenols (tyrosine), and disulfides (glutathione disulfide, GSSG). Low yields of derivatives of histidine, tyrosine, and GSSG were detected by thin-layer chromatography. Acid-precipitable derivatives were

Effect of acid catalysts and accelerated aging on the reaction of methanol with hydroxy-acetaldehyde in bio-oil

Directory of Open Access Journals (Sweden)

Bhattacharya, P.

2010-05-01

Full Text Available Bio-oil is a promising alternative source of energy produced from fast pyrolysis of biomass. Increasing the viscosity of bio-oil during storage is a major problem that can be controlled by the addition of methanol or other alcohols. This paper reports the results of our investigation of the reactions of short chain alcohols with aldehydes and acids in bio-oil. The reaction of methanol with hydroxyacetaldehyde (HA to form the acetal was catalyzed by the addition of 7 x 10-4 M strong acids such as sulfuric, hydrochloric, p-toluene sulfonic acid, and methanesulfonic acid. HA formed 2,2-dimethoxyethanol (DME, and at 60 oC the equilibrium was reached in less than one hour. Smaller amounts of DME were formed in the absence of strong acid. HA, acetaldehyde, and propanal formed their corresponding acetals when reacted with methanol, ethanol, 1-propanol or 1-butanol. Esters of acetic acid and hydroxyacetic acid were observed from reactions with these same four alcohols. Other acetals and esters were observed by GC/MS analysis of the reaction products. The results from accelerated aging experiments at 90 oC suggest that the presence of methanol slows polymerization by formation of acetals and esters from low molecular weight aldehydes and organic acids.

Noncanonical Reactions of Flavoenzymes

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Pablo Sobrado

2012-11-01

Full Text Available Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates.

Mechanism of Cytochrome P450 17A1-Catalyzed Hydroxylase and Lyase Reactions

DEFF Research Database (Denmark)

Bonomo, Silvia; Jorgensen, Flemming Steen; Olsen, Lars

2017-01-01

Cytochrome P450 17A1 (CYP17A1) catalyzes C17 hydroxylation of pregnenolone and progesterone and the subsequent C17–C20 bond cleavage (lyase reaction) to form androgen precursors. Compound I (Cpd I) and peroxo anion (POA) are the heme-reactive species underlying the two reactions. We have characte...... the concept that the selectivity of the steroidogenic CYPs is ruled by direct interactions with the enzyme, in contrast to the selectivity of drug-metabolizing CYPs, where the reactivity of the substrates dominates....... characterized the reaction path for both the hydroxylase and lyase reactions using density functional theory (DFT) calculations and the enzyme–substrate interactions by molecular dynamics (MD) simulations. Activation barriers for positions subject to hydroxylase reaction have values close to each other and span...

Crystal structure of a trapped phosphate intermediate in vanadium apochloroperoxidase catalyzing a dephosphorylation reaction

NARCIS (Netherlands)

de Macedo-Ribeiro, S.; Renirie, R.; Wever, R.; Messerschmidt, A.

2008-01-01

The crystal structure of the apo form of vanadium chloroperoxidase from Curvularia inaequalis reacted with para-nitrophenylphosphate was determined at a resolution of 1.5 Å. The aim of this study was to solve structural details of the dephosphorylation reaction catalyzed by this enzyme. Since the

An experimental and theoretical study of reaction steps relevant to the methanol-to-hydrocarbons reaction

Energy Technology Data Exchange (ETDEWEB)

Svelle, Stian

2004-07-01

The primary objective of the present work is to obtain new insight into the reaction mechanism of the zeolite catalyzed methanol-to-hydrocarbons (MTH) reaction. It was decided to use both experimental and computational techniques to reach this goal. An investigation of the n-butene + methanol system was therefore initiated. Over time, it became apparent that it was possible to determine the rate for the methylation of n-butene by methanol. The ethene and propene systems were therefore reexamined in order to collect kinetic information also for those cases. With the development of user-friendly quantum chemistry programs such as the Gaussian suite of programs, the possibility of applying quantum chemical methods to many types of problems has become readily available even for non-experts. When performing mechanistic studies, there is quite often a considerable synergy effect when combining experimental and computational approaches. The methylation reactions mentioned above turned out to be an issue well suited for quantum chemical investigations. The incentive for examining the halomethane reactivity was the clear analogy to the MTH reaction system. Alkene dimerization was also a reaction readily examined with quantum chemistry. As discussed in the introduction of this thesis, polymethylbenzenes, or their cationic counterparts, are suspected to be key intermediates in the MTH reaction. It was therefore decided to investigate the intrinsic reactivity of these species in the gas-phase by employing sophisticated mass spectrometric (MS) techniques in collaboration with the MS group at the Department of Chemistry, University of Oslo The data thus obtained will also be compared with results from an ongoing computational study on gas phase polymethylbenzenium reactivity. 6 papers presenting various studies are included. The titles are: 1) A Theoretical Investigation of the Methylation of Alkenes with Methanol over Acidic Zeolites. 2) A Theoretical Investigation of the

Aspergillus niger whole-cell catalyzed synthesis of caffeic acid phenethyl ester in ionic liquids.

Science.gov (United States)

Rajapriya, Govindaraju; Morya, Vivek Kumar; Mai, Ngoc Lan; Koo, Yoon-Mo

2018-04-01

Synthesis of caffeic acid ester essentially requires an efficient esterification process to produce various kinds of medicinally important ester derivatives. In the present study, a comprehensive and comparative analysis of whole-cell catalyzed caffeic acid esters production in ionic liquids (ILs) media was performed. Olive oil induced mycelial mass of halotolerant Aspergillus niger (A.niger) EXF 4321 was freeze dried and used as a catalyst. To ensure maximum solubilization of caffeic acid for highest substrate loading several ILs were screened and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf 2 N]) was found to have the maximum solubility and favoured for enzymatic activity of freeze dried mycelia. The whole-cell catalyzed synthesis of caffeic acid phenethyl ester (CAPE) conditions were optimized and bioconversion up to 84% was achieved at a substrate molar ratio of 1:20 (caffeic acid:2-phenyl ethanol), 30°C for 12h. Results obtained during this study were encouraging and helpful to design a bioreactor system to produce caffeic acid derived esters. Copyright © 2017 Elsevier Inc. All rights reserved.

Carbon Isotope Measurements of Experimentally-Derived Hydrothermal Mineral-Catalyzed Organic Products by Pyrolysis-Isotope Ratio Mass Spectrometry

Science.gov (United States)

Socki, Richard A.; Fu, Qi; Niles, Paul B.

2011-01-01

We report results of experiments to measure the C isotope composition of mineral catalyzed organic compounds derived from high temperature and high pressure synthesis. These experiments make use of an innovative pyrolysis technique designed to extract and measure C isotopes. To date, our experiments have focused on the pyrolysis and C isotope ratio measurements of low-molecular weight intermediary hydrocarbons (organic acids and alcohols) and serve as a proof of concept for making C and H isotope measurements on more complicated mixtures of solid-phase hydrocarbons and intermediary products produced during high temperature and high pressure synthesis on mineral-catalyzed surfaces. The impetus for this work stems from recently reported observations of methane detected within the Martian atmosphere [1-4], coupled with evidence showing extensive water-rock interaction during Martian history [5-7]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization reactions [8,9]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [10-12]. Further, recent experiments by Fu et al. [13] focus on examining detailed C isotope measurements of hydrocarbons produced by surface-catalyzed mineral reactions. Work described in this paper details the experimental techniques used to measure intermediary organic reaction products (alcohols and organic acids).

Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides

Science.gov (United States)

An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production.

On the Brønsted acid-catalyzed homogeneous hydrolysis of furans.

Science.gov (United States)

Nikbin, Nima; Caratzoulas, Stavros; Vlachos, Dionisios G

2013-11-01

Furan affairs: Electronic structure calculations of the homogeneous Brønsted acid-catalyzed hydrolysis of 2,5-dimethylfuran show that proton transfer to the β-position is rate-limiting and provides support that the hydrolysis follows general acid catalysis. By means of projected Fukui indices, we show this to be the case for unsubstituted, 2-, and 2,5-substituted furans with electron-donating groups. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective coupling reaction between 2,6-diiodoanisoles and terminal alkynes catalyzed by Pd(PPh32Cl2 and CuI

Directory of Open Access Journals (Sweden)

Allan F. C. Rossini

2012-06-01

Full Text Available The cross-coupling reaction between aryl halides and terminal alkynes, catalyzed by palladium complexes and copper (I salts, consists in an efficient synthetic tool for the formation of C-C bonds, resulting in disubstituted acetylenic compounds. Accordingly, in this work we present our preliminary results involving the selective cross-coupling reaction between 2,6-diiodoanisoles and terminal alkynes, catalyzed by Pd(PPh32Cl2 and CuI, in the formation of 2-iodo-alkynylanisoles (scheme 1.

An Efficient One-Pot Synthesis of Pyrano[3,2-c]quinolin-2,5-dione Derivatives Catalyzed by L-Proline

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Jing Wang

2012-11-01

Full Text Available A series of 4-aryl-6-methyl-3,4-dihydro-2H-pyrano[3,2-c]quinolin-2,5(6H-diones were synthesized via the three-component reactions of aromatic aldehydes, 4-hydroxy-1-methylquinolin-2(1H-one, and Meldrum’s acid catalyzed by L-proline. The structures of the products were identified by spectroscopic analysis. A mechanism for this three-component reaction catalyzed by L-proline was proposed.

FeCl3- and GaCl3-Catalyzed Dehydrative Coupling Reaction of Chromone-Derived Morita-Baylis-Hillman Alcohols with Terminal Alkynes%FeCl3- and GaCl3-Catalyzed Dehydrative Coupling Reaction of Chromone-Derived Morita-Baylis-Hillman Alcohols with Terminal Alkynes

Institute of Scientific and Technical Information of China (English)

武陈; 曾皓; 刘哲; 刘利; 王东; 陈拥军

2011-01-01

FeCl3- and GaCl3-catalyzed dehydrative coupling reactions of chromone-derived Morita-Baylis-Hillman （MBH） alcohols with terminal alkynes were developed. The reactions provided exclusively a-regioselective and acetylene-substituted products in good yields.

Metal-Catalyzed Intra- and Intermolecular Addition of Carboxylic Acids to Alkynes in Aqueous Media: A Review

Directory of Open Access Journals (Sweden)

Javier Francos

2017-11-01

Full Text Available The metal-catalyzed addition of carboxylic acids to alkynes is a very effective tool for the synthesis of carboxylate-functionalized olefinic compounds in an atom-economical manner. Thus, a large variety of synthetically useful lactones and enol-esters can be accessed through the intra- or intermolecular versions of this process. In order to reduce the environmental impact of these reactions, considerable efforts have been devoted in recent years to the development of catalytic systems able to operate in aqueous media, which represent a real challenge taking into account the tendency of alkynes to undergo hydration in the presence of transition metals. Despite this, different Pd, Pt, Au, Cu and Ru catalysts capable of promoting the intra- and intermolecular addition of carboxylic acids to alkynes in a selective manner in aqueous environments have appeared in the literature. In this review article, an overview of this chemistry is provided. The synthesis of β-oxo esters by catalytic addition of carboxylic acids to terminal propargylic alcohols in water is also discussed.

Mechanistic insights into the dehalogenation reaction of fluoroacetate/fluoroacetic acid

Science.gov (United States)

Miranda-Rojas, Sebastián; Toro-Labbé, Alejandro

2015-05-01

Fluoroacetate is a toxic compound whose environmental accumulation may represent an important contamination problem, its elimination is therefore a challenging issue. Fluoroacetate dehalogenase catalyzes its degradation through a two step process initiated by an SN2 reaction in which the aspartate residue performs a nucleophilic attack on the carbon bonded to the fluorine; the second step is hydrolysis that releases the product as glycolate. In this paper, we present a study based on density functional theory calculations of the SN2 initiation reaction modeled through the interaction between the substrate and the propionate anion as the nucleophile. Results are analyzed within the framework of the reaction force and using the reaction electronic flux to identify and characterize the electronic activity that drives the reaction. Our results reveal that the selective protonation of the substrate catalyzes the reaction by decreasing the resistance of the structural and electronic reorganization needed to reach the transition state. Finally, the reaction energy is modulated by the degree of stabilization of the fluoride anion formed after the SN2 reaction. In this way, a site-induced partial protonation acts as a chemical switch in a key process that determines the output of the reaction.

Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins

Science.gov (United States)

Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines

2011-01-01

A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The…

Parameters affecting incorporation and by-product formation during the production of structured phospholipids by lipase-catalyzed acidolysis in solvent free system

DEFF Research Database (Denmark)

Vikbjerg, Anders Falk; Mu, Huiling; Xu, Xuebing

2005-01-01

By-product formation is a serious problem in the lipase-catalyzed acyl exchange of phospholipids (PL). By-products are formed due to parallel hydrolysis reactions and acyl migration in the reaction system. A clear elucidation of these side reactions is important for practical operation in order...... to minimize by-products during reaction. In the present study we examined the Lipozyme RM IM-catalyzed acidolysis for the production of structured phospholipids between phosphatidylcholine (PC) and caprylic acid in the solvent free system. A five-factor response surface design was used to evaluate...

Density functional theory analysis of the reaction pathway for methane oxidation to acetic acid catalyzed by Pd2+ in sulfuric acid.

Science.gov (United States)

Chempath, Shaji; Bell, Alexis T

2006-04-12

Density functional theory has been used to investigate the thermodynamics and activation barriers associated with the direct oxidation of methane to acetic acid catalyzed by Pd2+ cation in concentrated sulfuric acid. Pd2+ cations in such solutions are ligated by two bisulfate anions and by one or two molecules of sulfuric acid. Methane oxidation is initiated by the addition of CH4 across one of the Pd-O bonds of a bisulfate ligand to form Pd(HSO4)(CH3)(H2SO4)2. The latter species will react with CO to produce Pd(HSO4)(CH3CO)(H2SO4)2. The most likely path to the final products is found to be via oxidation of Pd(HSO4)(CH3)(H2SO4)2 and Pd(HSO4)(CH3CO)(H2SO4)2 to form Pd(eta2-HSO4)(HSO4)2(CH3)(H2SO4) and Pd(eta2-HSO4)(HSO4)2(CH3CO)(H2SO4), respectively. CH3HSO4 or CH3COHSO4 is then produced by reductive elimination from the latter two species, and CH(3)COOH is then formed by hydrolysis of CH3COHSO4. The loss of Pd2+ from solution to form Pd(0) or Pd-black is predicted to occur via reduction with CO. This process is offset, though, by reoxidation of palladium by either H2SO4 or O2.

Rhodium-catalyzed [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes and CO: reaction design, development, application in natural product synthesis, and inspiration for developing new reactions for synthesis of eight-membered carbocycles.

Science.gov (United States)

Wang, Yi; Yu, Zhi-Xiang

2015-08-18

Practical syntheses of natural products and their analogues with eight-membered carbocyclic skeletons are important for medicinal and biological investigations. However, methods and strategies to construct the eight-membered carbocycles are limited. Therefore, developing new methods to synthesize the eight-membered carbocycles is highly desired. In this Account, we describe our development of three rhodium-catalyzed cycloadditions for the construction of the eight-membered carbocycles, which have great potential in addressing the challenges in the synthesis of medium-sized ring systems. The first reaction described in this Account is our computationally designed rhodium-catalyzed two-component [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes (ene-VCPs) and CO for the diastereoselective construction of bi- and tricyclic cyclooctenones. The design of this reaction is based on the hypothesis that the C(sp(3))-C(sp(3)) reductive elimination of the eight-membered rhodacycle intermediate generated from the rhodium-catalyzed cyclopropane cleavage and alkene insertion, giving Wender's [5 + 2] cycloadduct, is not easy. Under CO atmosphere, CO insertion may occur rapidly, converting the eight-membered rhodacycle into a nine-membered rhodacycle, which then undergoes an easy C(sp(2))-C(sp(3)) reductive elimination process and furnishes the [5 + 2 + 1] product. This hypothesis was supported by our preliminary DFT studies and also served as inspiration for the development of two [7 + 1] cycloadditions: the [7 + 1] cycloaddition of buta-1,3-dienylcyclopropanes (BDCPs) and CO for the construction of cyclooctadienones, and the benzo/[7 + 1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to synthesize the benzocyclooctenones. The efficiency of these rhodium-catalyzed cycloadditions can be revealed by the application in natural product synthesis. Two eight-membered ring-containing natural products, (±)-asterisca-3(15),6-diene and (+)-asteriscanolide, have been

Possibilities and scope of the double isotope effect method in the elucidation of mechanisms of enzyme catalyzed reactions

Energy Technology Data Exchange (ETDEWEB)

Schmidt, H L; Medina, R [Technische Univ. Muenchen, Freising (Germany, F.R.). Lehrstuhl fuer Allgemeine Chemie und Biochemie

1991-01-01

Kinetic isotope effects on enzyme catalyzed reactions are indicative for the first irreversible in a sequence of individual steps. Hints on the relative velocities of other steps can only be obtained from the partitioning factor R and its dependence on external reaction conditions. In general, the experimental data needed are obtained from isotope abundance measurements in a defined position of the substrate or product as a function of turnover. This method does not reveal events dealing with neighbour atoms or preceding the main isotope sensitive step. In the method presented here, the analytical measurement is extended to the second atom involved in a bond fission of formation (Double Isotope Effect Method). It is shown that the additional results obtained support the identification of the main isotopically sensitive step and its relative contribution to the overall reaction rate, the identification of other kinetically significant steps and the differentiation between stepwise and concerted reaction mechanisms. The method and its advantages are demonstrated on reactions comprising C-N-bond splitting (urease and arginase reaction), C-C-bound fission (reactions catalyzed by pyruvate-dehydrogenase, pyruvate-formiate-lyase and lactate-oxidase), C-O-bound formation (ribulose-bisphosphate-oxygenase reaction), and N-O-bond fission (nitrate- and nitrite-reductase reactions). (orig.).

Determination of Free Fatty Acids and Triglycerides by Gas Chromatography Using Selective Esterification Reactions

Energy Technology Data Exchange (ETDEWEB)

Kail, Brian W; Link, Dirk D; Morreale, Bryan D

2012-11-01

A method for selectively determining both free fatty acids (FFA) and triacylglycerides (TAGs) in biological oils was investigated and optimized using gas chromatography after esterification of the target species to their corresponding fatty acid methyl esters (FAMEs). The method used acid catalyzed esterification in methanolic solutions under conditions of varying severity to achieve complete conversion of more reactive FFAs while preserving the concentration of TAGs. Complete conversion of both free acids and glycerides to corresponding FAMEs was found to require more rigorous reaction conditions involving heating to 120°C for up to 2 h. Method validation was provided using gas chromatography–flame ionization detection, gas chromatography–mass spectrometry, and liquid chromatography–mass spectrometry. The method improves on existing methods because it allows the total esterified lipid to be broken down by FAMEs contributed by FFA compared to FAMEs from both FFA and TAGs. Single and mixed-component solutions of pure fatty acids and triglycerides, as well as a sesame oil sample to simulate a complex biological oil, were used to optimize the methodologies. Key parameters that were investigated included: HCl-to-oil ratio, temperature and reaction time. Pure free fatty acids were found to esterify under reasonably mild conditions (10 min at 50°C with a 2.1:1 HCl to fatty acid ratio) with 97.6 ± 2.3% recovery as FAMEs, while triglycerides were largely unaffected under these reaction conditions. The optimized protocol demonstrated that it is possible to use esterification reactions to selectively determine the free acid content, total lipid content, and hence, glyceride content in biological oils. This protocol also allows gas chromatography analysis of FAMEs as a more ideal analyte than glyceride species in their native state.

Mechanistic insight into benzenethiol catalyzed amide bond formations from thioesters and primary amines

DEFF Research Database (Denmark)

Stuhr-Hansen, Nicolai; Bork, Nicolai; Strømgaard, Kristian

2014-01-01

The influence of arylthiols on cysteine-free ligation, i.e. the reaction between an alkyl thioester and a primary amine forming an amide bond, was studied in a polar aprotic solvent. We reacted the ethylthioester of hippuric acid with cyclohexylamine in the absence or presence of various quantities...... of thiophenol (PhSH) in a slurry of disodium hydrogen phosphate in dry DMF. Quantitative conversions into the resulting amide were observed within a few hours in the presence of equimolar amounts of thiophenol. Ab initio calculations showed that the reaction mechanism in DMF is similar to the well-known aqueous...... reaction mechanism. The energy barrier of the catalyzed amidation reaction is approximately 40 kJ mol(-1) lower than the non-catalyzed amidation reaction. At least partially this can be explained by a hydrogen bond from the amine to the π-electrons of the thiophenol, stabilizing the transition state...

Investigations Of Surface-Catalyzed Reactions In A Mars Mixture

Science.gov (United States)

Dougherty, Max; Owens, W.; Meyers, J.; Fletcher, D. G.

2011-05-01

In the design of a thermal protection system (TPS) for a planetary entry vehicle, accurate modeling of the trajectory aero-heating poses a significant challenge owing to large uncertainties in chemical processes taking place at the surface. Even for surface-catalyzed reactions, which have been investigated extensively, there is no consensus on how they should be modeled; or, in some cases, on which reactions are likely to occur. Current TPS designs for Mars missions rely on a super-catalytic boundary condition, which assumes that all dissociated species recombine to the free stream composition.While this is recognized to be the the most conservative approach, discrepancies in aero-heating measurements in ground test facilities preclude less conservative design options, resulting in an increased TPS mass at the expense of scientific pay- load.Using two-photon absorption laser induced fluorescence in a 30 kW inductively coupled plasma torch facility, preliminary studies have been performed to obtain spatially-resolved measurements of the dominant species in a plasma boundary layer for a Martian atmosphere mixture over catalytic and non-catalytic surfaces.

Effect of acidic seed on biogenic secondary organic aerosol growth

Science.gov (United States)

Czoschke, Nadine M.; Jang, Myoseon; Kamens, Richard M.

Secondary organic aerosol (SOA) growth in the presence of acid aerosols was studied in twin 500 l Teflon bags and in a 4 m flow reactor. In Teflon bags, isoprene, acrolein and α-pinene were all made to react individually with ozone and exposed to either acid or non-acid inorganic seed aerosols to determine the effect of acid-catalyzed heterogeneous reactions on SOA growth. α-Pinene and ozone were made to react in a flow reactor to assess the immediate effect of mixing an acid aerosol with SOA at high and low relative humidity levels. In all cases, exposure to acid seed aerosol increased the amount of SOA mass produced. Fourier transform infrared spectra of the SOA in acid systems confirmed the transformation of carbonyl functional groups through acid-catalyzed heterogeneous reactions when SOAs formed in acidic environments or were exposed to acidic aerosols. Organic products initially produced from ozonation in the gas phase partition onto the inorganic seed aerosol and react heterogeneously with an acid catalyst forming low vapor pressure products. These acid-catalyzed heterogeneous reactions are implicated in generating the increased SOA mass observed in acidic aerosol systems as they transform predominantly gas phase compounds of high volatility into low vapor pressure predominantly particle phase products.

Unprecedentedly mild direct Pd-catalyzed arylation of oxazolo[4,5-b]pyridine

DEFF Research Database (Denmark)

Zhuravlev, Fedor

2006-01-01

Pd-catalyzed C-2 arylation of oxazolo[4,5-b]pyridine proceeds efficiently at 30 degrees C and tolerates a variety of aryl halides, including derivatized amino acids for which no racemization was observed during the reaction. Experimental evidence for facile deprotonation of oxazolo[4,5-b...

Vapor-Phase Hydrodeoxygenation of Guaiacol to Aromatics over Pt/HBeta: Identification of the Role of Acid Sites and Metal Sites on the Reaction Pathway

Energy Technology Data Exchange (ETDEWEB)

Nie, Lei [Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 P.R. China; Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Peng, Bo [Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Zhu, Xinli [Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 P.R. China

2018-02-05

Hydrodeoxygenation of guaiacol, a phenolic compound derived from lignin fraction of biomass, over a Pt/HBeta catalyst at 350 °C and atmospheric pressure produces benzene, toluene, xylenes, and C9+ aromatics with yield of 42%, 29%, 12%, and 5%, respectively. Reaction pathways for conversion of two functional groups (hydroxyl and methoxyl) over the bifunctional catalyst were studied. Both guaiacol and intermediate products (catechol and cyclopentanone) were fed onto zeolite HBeta and Pt/SiO2 to identify the individual role of acid site and metal site. Acid sites (mainly Brønsted acid site, BAS) catalyze transalkylation and dehydroxylation reactions in sequence, producing phenol, cresols and xylenols as the major products at high conversion. Pt sites catalyze demethylation reaction resulting in catechol as the primary product, which can either be deoxygenated to phenol followed by phenol to benzene, or decarbonylated to cyclopentanone and further to butane. The close proximity of Pt and BAS in bifunctional Pt/HBeta enables both transalkylation and deoxygenation reactions with inhibited demethylation and decarbonylation reactions, producing aromatics as major final products with a total yield > 85%. Both activity and stability of bifunctional Pt/HBeta during hydrodeoxygenation of guaiacol is improved compared to HBeta and Pt/SiO2. The addition of water to the feed further improves the activity and stability via hydrolysis of O-CH3 bond of guaiacol on BAS and removing coke around Pt.

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations.

Science.gov (United States)

Trost, Barry M; Frederiksen, Mathias U; Rudd, Michael T

2005-10-21

The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

Mechanistic insights into the dehalogenation reaction of fluoroacetate/fluoroacetic acid

International Nuclear Information System (INIS)

Miranda-Rojas, Sebastián; Toro-Labbé, Alejandro

2015-01-01

Fluoroacetate is a toxic compound whose environmental accumulation may represent an important contamination problem, its elimination is therefore a challenging issue. Fluoroacetate dehalogenase catalyzes its degradation through a two step process initiated by an S N 2 reaction in which the aspartate residue performs a nucleophilic attack on the carbon bonded to the fluorine; the second step is hydrolysis that releases the product as glycolate. In this paper, we present a study based on density functional theory calculations of the S N 2 initiation reaction modeled through the interaction between the substrate and the propionate anion as the nucleophile. Results are analyzed within the framework of the reaction force and using the reaction electronic flux to identify and characterize the electronic activity that drives the reaction. Our results reveal that the selective protonation of the substrate catalyzes the reaction by decreasing the resistance of the structural and electronic reorganization needed to reach the transition state. Finally, the reaction energy is modulated by the degree of stabilization of the fluoride anion formed after the S N 2 reaction. In this way, a site-induced partial protonation acts as a chemical switch in a key process that determines the output of the reaction

Mechanistic insights into the dehalogenation reaction of fluoroacetate/fluoroacetic acid

Energy Technology Data Exchange (ETDEWEB)

Miranda-Rojas, Sebastián, E-mail: sebastian.miranda@unab.cl [Chemical Processes and Catalysis (CPC), Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello, Avenida República 275, Santiago (Chile); Toro-Labbé, Alejandro [Laboratorio de Química Teórica Computacional (QTC), Facultad de Química, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, Santiago (Chile)

2015-05-21

Fluoroacetate is a toxic compound whose environmental accumulation may represent an important contamination problem, its elimination is therefore a challenging issue. Fluoroacetate dehalogenase catalyzes its degradation through a two step process initiated by an S{sub N}2 reaction in which the aspartate residue performs a nucleophilic attack on the carbon bonded to the fluorine; the second step is hydrolysis that releases the product as glycolate. In this paper, we present a study based on density functional theory calculations of the S{sub N}2 initiation reaction modeled through the interaction between the substrate and the propionate anion as the nucleophile. Results are analyzed within the framework of the reaction force and using the reaction electronic flux to identify and characterize the electronic activity that drives the reaction. Our results reveal that the selective protonation of the substrate catalyzes the reaction by decreasing the resistance of the structural and electronic reorganization needed to reach the transition state. Finally, the reaction energy is modulated by the degree of stabilization of the fluoride anion formed after the S{sub N}2 reaction. In this way, a site-induced partial protonation acts as a chemical switch in a key process that determines the output of the reaction.

Pilot batch production of specific-structured lipids by lipase-catalyzed interesterification: preliminary study on incorporation and acyl migration

DEFF Research Database (Denmark)

Xu, Xuebing; Balchen, Steen; Høy, Carl-Erik

1998-01-01

Effects of water content, reaction time and their relationships in the production of two types of specific-structured lipids (sn-MLM- and sn-LML-types: L-long chain fatty acids; M-medium chain fatty acids) by lipase-catalyzed interesterification in a solvent-free system were studied...... of two totally position-opposed lipids can be observed. Presumably these are caused by the different chain length of the fatty acids. The relationships between reaction time and water content are inverse and give a quantitative prediction of incorporation and acyl migration in selected reaction...

An experimental and theoretical study of reaction steps relevant to the methanol-to-hydrocarbons reaction

Energy Technology Data Exchange (ETDEWEB)

Svelle, Stian

2004-07-01

The primary objective of the present work is to obtain new insight into the reaction mechanism of the zeolite catalyzed methanol-to-hydrocarbons (MTH) reaction. It was decided to use both experimental and computational techniques to reach this goal. An investigation of the n-butene + methanol system was therefore initiated. Over time, it became apparent that it was possible to determine the rate for the methylation of n-butene by methanol. The ethene and propene systems were therefore reexamined in order to collect kinetic information also for those cases. With the development of user-friendly quantum chemistry programs such as the Gaussian suite of programs, the possibility of applying quantum chemical methods to many types of problems has become readily available even for non-experts. When performing mechanistic studies, there is quite often a considerable synergy effect when combining experimental and computational approaches. The methylation reactions mentioned above turned out to be an issue well suited for quantum chemical investigations. The incentive for examining the halomethane reactivity was the clear analogy to the MTH reaction system. Alkene dimerization was also a reaction readily examined with quantum chemistry. As discussed in the introduction of this thesis, polymethylbenzenes, or their cationic counterparts, are suspected to be key intermediates in the MTH reaction. It was therefore decided to investigate the intrinsic reactivity of these species in the gas-phase by employing sophisticated mass spectrometric (MS) techniques in collaboration with the MS group at the Department of Chemistry, University of Oslo The data thus obtained will also be compared with results from an ongoing computational study on gas phase polymethylbenzenium reactivity. 6 papers presenting various studies are included. The titles are: 1) A Theoretical Investigation of the Methylation of Alkenes with Methanol over Acidic Zeolites. 2) A Theoretical Investigation of the

Structure and Reaction Mechanism of Pyrrolysine Synthase (PylD)

KAUST Repository

Quitterer, Felix; Beck, Philipp; Bacher, Adelbert; Groll, Michael

2013-01-01

The final step in the biosynthesis of the 22nd genetically encoded amino acid, pyrrolysine, is catalyzed by PylD, a structurally and mechanistically unique dehydrogenase. This catalyzed reaction includes an induced-fit mechanism achieved by major structural rearrangements of the N-terminal helix upon substrate binding. Different steps of the reaction trajectory are visualized by complex structures of PylD with substrate and product. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure and Reaction Mechanism of Pyrrolysine Synthase (PylD)

KAUST Repository

Quitterer, Felix

2013-05-29

The final step in the biosynthesis of the 22nd genetically encoded amino acid, pyrrolysine, is catalyzed by PylD, a structurally and mechanistically unique dehydrogenase. This catalyzed reaction includes an induced-fit mechanism achieved by major structural rearrangements of the N-terminal helix upon substrate binding. Different steps of the reaction trajectory are visualized by complex structures of PylD with substrate and product. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Mechanism of Rh-Catalyzed Transformation of Fatty Acids to Linear Alpha olefins

Directory of Open Access Journals (Sweden)

Sondre H. Hopen Eliasson

2017-12-01

Full Text Available Linear alpha olefins (LAOs are key commodity chemicals and petrochemical intermediates that are currently produced from fossil resources. Fatty acids are the obvious renewable starting material for LAOs, which can be obtained via transition-metal-catalyzed decarbonylative dehydration. However, even the best catalysts that have been obtained to date, which are based on palladium, are not active and stable enough for industrial use. To provide insight for design of better catalysts, we here present the first computationally derived mechanism for another attractive transition-metal for this reaction, rhodium. By comparing the calculated mechanisms and free energy profiles for the two metals, Pd and Rh, we single out important factors for a facile, low-barrier reaction and for a stable catalyst. While the olefin formation is rate limiting for both of the metals, the rate-determining intermediate for Rh is, in contrast to Pd, the starting complex, (PPh32Rh(COCl. This complex largely draws its stability from the strength of the Rh(I–CO bond. CO is a much less suitable ligand for the high-oxidation state Rh(III. However, for steric reasons, rhodium dissociates a bulkier triphenylphosphine and keeps the carbonyl during the oxidative addition, which is less favorable than for Pd. When compared to Pd, which dissociates two phosphine ligands at the start of the reaction, the catalytic activity of Rh also appears to be hampered by its preference for high coordination numbers. The remaining ancillary ligands leave less space for the metal to mediate the reaction.

Enantioselective [3+3] atroposelective annulation catalyzed by N-heterocyclic carbenes

KAUST Repository

Zhao, Changgui

2018-02-05

Axially chiral molecules are among the most valuable substrates in organic synthesis. They are typically used as chiral ligands or catalysts in asymmetric reactions. Recent progress for the construction of these chiral molecules is mainly focused on the transition-metal-catalyzed transformations. Here, we report the enantioselective NHC-catalyzed (NHC: N-heterocyclic carbenes) atroposelective annulation of cyclic 1,3-diones with ynals. In the presence of NHC precatalyst, base, Lewis acid and oxidant, a catalytic C–C bond formation occurs, providing axially chiral α-pyrone−aryls in moderate to good yields and with high enantioselectivities. Control experiments indicated that alkynyl acyl azoliums, acting as active intermediates, are employed to atroposelectively assemble chiral biaryls and such a methodology may be creatively applied to other useful NHC-catalyzed asymmetric transformations.

An Efficient Synthesis of Substituted Quinolines via Indium(III) Chloride Catalyzed Reaction of Imines with Alkynes

International Nuclear Information System (INIS)

Zhu, Mei; Fu, Weijun; Xun, Chen; Zou, Guanglong

2012-01-01

An efficient synthetic method for the preparation of quinolines through indium(III) chloride-catalyzed tandem addition-cyclization-oxidation reactions of imines with alkynes was developed. The processes can provide a diverse range of quinoline derivatives in good yields from simple imines and alkynes

Palladium-catalyzed three-component reaction of N-tosyl hydrazones, isonitriles and amines leading to amidines.

Science.gov (United States)

Dai, Qiang; Jiang, Yan; Yu, Jin-Tao; Cheng, Jiang

2015-12-04

A palladium-catalyzed three-component reaction between N-tosyl hydrazones, aryl isonitriles and amines was developed, leading to amidines in moderate to good yields. This procedure features the rapid construction of amidine frameworks with high diversity and complexity. Ketenimines serve as intermediates, which encounter nucleophilic attack by amines to produce amidines.

Rhodium-Catalyzed Insertion Reaction of PhP Group of Pentaphenylcyclopentaphosphine with Acyclic and Cyclic Disulfides.

Science.gov (United States)

Arisawa, Mieko; Sawahata, Kyosuke; Yamada, Tomoki; Sarkar, Debayan; Yamaguchi, Masahiko

2018-02-16

Organophosphorus compounds with a phosphorus atom attached to a phenyl group and two organothio/organoseleno groups were synthesized using the rhodium-catalyzed insertion reaction of the PhP group of pentaphenylcyclopentaphosphine (PhP) 5 with acyclic disulfides and diselenides. The method was applied to the synthesis of heterocyclic compounds containing the S-P-S group by the reaction of (PhP) 5 and cyclic disulfides such as 1,2-dithietes, 1,2-dithiocane, 1,4,5-dithiopane, and 1,2-dithiolanes.

Boron-Catalyzed N-Alkylation of Amines using Carboxylic Acids.

Science.gov (United States)

Fu, Ming-Chen; Shang, Rui; Cheng, Wan-Min; Fu, Yao

2015-07-27

A boron-based catalyst was found to catalyze the straightforward alkylation of amines with readily available carboxylic acids in the presence of silane as the reducing agent. Various types of primary and secondary amines can be smoothly alkylated with good selectivity and good functional-group compatibility. This metal-free amine alkylation was successfully applied to the synthesis of three commercial medicinal compounds, Butenafine, Cinacalcet. and Piribedil, in a one-pot manner without using any metal catalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold-catalyzed tandem hydroamination/formal aza-Diels-Alder reaction of homopropargyl amino esters: a combined computational and experimental mechanistic study.

Science.gov (United States)

Miró, Javier; Sánchez-Roselló, María; González, Javier; del Pozo, Carlos; Fustero, Santos

2015-03-27

A tandem gold-catalyzed hydroamination/formal aza-Diels-Alder reaction is described. This process, which employs quaternary homopropargyl amino ester substrates, leads to the formation of an intrincate tetracyclic framework and involves the generation of four bonds and five stereocenters in a highly diastereoselective manner. Theoretical calculations have allowed us to propose a suitable mechanistic rationalization for the tandem protocol. Additionally, by studying the influence of the ligands on the rate of the gold-catalyzed reactions, it was possible to establish optimum conditions in which to perform the process with a variety of substituents on the amino ester substrates. Notably, the asymmetric version of the tandem reaction was also evaluated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Post-Ugi gold-catalyzed diastereoselective domino cyclization for the synthesis of diversely substituted spiroindolines

Directory of Open Access Journals (Sweden)

Amit Kumar

2013-10-01

Full Text Available An Ugi four-component reaction of propargylamine with 3-formylindole and various acids and isonitriles produces adducts which are subjected to a cationic gold-catalyzed diastereoselective domino cyclization to furnish diversely substituted spiroindolines. All the reactions run via an exo-dig attack in the hydroarylation step followed by an intramolecular diastereoselective trapping of the imminium ion. The whole sequence is atom economic and the application of a multicomponent reaction assures diversity.

Kinetic Investigations on Pd(II) Catalyzed Oxidation of Some Amino ...

African Journals Online (AJOL)

Kinetic investigations on Pd(II) catalyzed oxidation of dl-serine and dl-threonine by acidic solution of potassium bromate in the presence of mercuric acetate, as a scavenger have been made in the temperature range of 30–45°C. The rate shows zero order kinetics in bromate [BrO3‾] and order of reaction is one with respect ...

The Brønsted Acid-Catalyzed, Enantioselective Aza-Diels-Alder Reaction for the Direct Synthesis of Chiral Piperidones.

Science.gov (United States)

Weilbeer, Claudia; Sickert, Marcel; Naumov, Sergei; Schneider, Christoph

2017-01-12

We disclose herein the first enantioselective aza-Diels-Alder reaction of β-alkyl-substituted vinylketene silyl-O,O-acetals and imines furnishing a broad range of optically highly enriched 4-alkyl-substituted 2-piperidones. As a catalyst for this one-pot reaction we employed a chiral phosphoric acid which effects a vinylogous Mannich reaction directly followed by ring-closure to the lactam. Subsequent fully diastereoselective transformations including hydrogenation, enolate alkylation, and lactam alkylation/reduction processes converted the cycloadducts into various highly substituted piperidines of great utility for the synthesis of natural products and medicinally active compounds. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unified mechanism of alkali and alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O

Science.gov (United States)

Chen, S.G.; Yang, R.T.

1997-01-01

From molecular orbital calculations, a unified mechanism is proposed for the gasification reactions of graphite by CO2 and H2O, both uncatalyzed and catalyzed by alkali and alkaline earth catalysts. In this mechanism, there are two types of oxygen intermediates that are bonded to the active edge carbon atoms: an in-plane semiquinone type, Cf(O), and an off-plane oxygen bonded to two saturated carbon atoms that are adjacent to the semiquinone species, C(O)Cf(O). The rate-limiting step is the decomposition of these intermediates by breaking the C-C bonds that are connected to Cf(O). A new rate equation is derived for the uncatalyzed reactions, and that for the catalyzed reactions is readily available from the proposed mechanism. The proposed mechanism can account for several unresolved experimental observations: TPD and TK (transient kinetics) desorption results of the catalyzed systems, the similar activation energies for the uncatalyzed and catalyzed reactions, and the relative activities of the alkali and alkaline earth elements. The net charge of the edge carbon active site is substantially changed by gaining electron density from the alkali or alkaline earth element (by forming C-O-M, where M stands for metal). The relative catalytic activities of these elements can be correlated with their abilities of donating electrons and changing the net charge of the edge carbon atom. As shown previously (Chen, S. G.; Yang, R. T. J. Catal. 1993, 141, 102), only clusters of the alkali compounds are active. This derives from the ability of the clusters to dissociate CO2 and H2O to form O atoms and the mobility of the dissociated O atoms facilitated by the clusters.

A green non-acid-catalyzed process for direct N=N-C group formation: comprehensive study, modeling, and optimization.

Science.gov (United States)

Khakyzadeh, Vahid; Zolfigol, Mohammad Ali; Derakhshan-Panah, Fatemeh; Jafarian, Majid; Miri, Mir Vahid; Gilandoust, Maryam

2018-01-04

The aim of this work is to introduce, model, and optimize a new non-acid-catalyzed system for a direct N[Formula: see text]N-C bond formation. By reacting naphthols or phenol with anilines in the presence of the sodium nitrite as nitrosonium ([Formula: see text] source and triethylammonium acetate (TEAA), a N[Formula: see text]N-C group can be formed in non-acid media. Modeling and optimization of the reaction conditions were investigated by response surface method. Sodium nitrite, TEAA, and water were chosen as variables, and reaction yield was also monitored. Analysis of variance indicates that a second-order polynomial model with F value of 35.7, a P value of 0.0001, and regression coefficient of 0.93 is able to predict the response. Based on the model, the optimum process conditions were introduced as 2.2 mmol sodium nitrite, 2.2 mL of TEAA, and 0.5 mL [Formula: see text] at room temperature. A quadratic (second-order) polynomial model, by analysis of variance, was able to predict the response for a direct N=N-C group formation. Predicted response values were in good agreement with the experimental values. Electrochemistry studies were done to introduce new Michael acceptor moieties. Broad scope, high yields, short reaction time, and mild conditions are some advantages of the presented method.

Catalytic Cracking of Lactide and Poly(Lactic Acid) to Acrylic Acid at Low Temperatures.

Science.gov (United States)

Terrade, Frédéric G; van Krieken, Jan; Verkuijl, Bastiaan J V; Bouwman, Elisabeth

2017-05-09

Despite being a simple dehydration reaction, the industrially relevant conversion of lactic acid to acrylic acid is particularly challenging. For the first time, the catalytic cracking of lactide and poly(lactic acid) to acrylic acid under mild conditions is reported with up to 58 % yield. This transformation is catalyzed by strong acids in the presence of bromide or chloride salts and proceeds through simple S N 2 and elimination reactions. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

-Heterocyclic Carbene Complexes of Mineral Acids

KAUST Repository

Brill, Marcel; Nahra, Fady; Gó mez-Herrera, Alberto; Zinser, Caroline; Cordes, David B.; Slawin, Alexandra M. Z.; Nolan, Steven P.

2016-01-01

We have synthesized and characterized new gold-N-heterocyclic carbene (NHC) complexes derived from the deprotonation of mineral acids. The use of sulfuric acid was a particularly interesting case. These complexes were tested in known gold-catalyzed reactions, such as the hydration of alkynes and the Meyer–Schuster rearrangement. They proved to be highly efficient in both reactions.

-Heterocyclic Carbene Complexes of Mineral Acids

KAUST Repository

Brill, Marcel

2016-11-08

We have synthesized and characterized new gold-N-heterocyclic carbene (NHC) complexes derived from the deprotonation of mineral acids. The use of sulfuric acid was a particularly interesting case. These complexes were tested in known gold-catalyzed reactions, such as the hydration of alkynes and the Meyer–Schuster rearrangement. They proved to be highly efficient in both reactions.

[Study of ATP-independent stages of reaction catalyzed by phage T4 RNA-ligase].

Science.gov (United States)

Zagrebel'nyĭ, S N; Zernov, Iu P

1986-01-01

The isotope exchange between [5'-32P]pAP and A(5')ppAp catalyzed by enzyme was shown not to take place in the absence of the acceptor; i. e. the necessity of the acceptor presence during the second step of the process was demonstrated. The isotope exchange reaction between [5'32P]pAp and (pA)5p was studied. It was demonstrated that acceptor (pA)4, slightly whereas the acceptor (pU)4 completely inhibits the isotope reaction. The isotope reaction exchange between [5'-32P]pAp and (pU)4pAp does not take place. The question of existence of adenylated donor elimination mechanism in the presence of "poor" acceptors is considered on the basis of the data obtained.

Aprotic solvent systems provide mechanistic windows for biomolecular reactions: nucleic acid proton exchange

International Nuclear Information System (INIS)

McConnell, B.; Tan, A.

1986-01-01

Detection of general acid-base catalysis of proton transfer reactions in aqueous cytidine (or adenosine) is completely obscured by the highly reactive endocyclic protonated species of the nucleobase, whose amino proton lifetime is much shorter than that of the neutral form. In aqueous solution, protonation of the nucleobase always accompanies protonation of the buffer catalyzing exchange. However, in DMSO/water mixtures this is not the case; aqueous protonated acetate or chloroacetate can be added to cytidine in DMSO solutions without further dissociation of the buffer or significant protonation of cytidine N-3. Under these conditions general acid catalysis is observed, which involves an H-bonded complex between cytidine (N-3) and the buffer acid. Increased amino proton exchange in response to H-bond donation to C(N-3) is further suggested by increased 1 H NMR saturation-recovery rates with the formation of G-C base-pairs in DMSO and by the inverse dependence of amino proton exchange on nucleoside concentration

Caffeine-catalyzed gels.

Science.gov (United States)

DiCiccio, Angela M; Lee, Young-Ah Lucy; Glettig, Dean L; Walton, Elizabeth S E; de la Serna, Eva L; Montgomery, Veronica A; Grant, Tyler M; Langer, Robert; Traverso, Giovanni

2018-07-01

Covalently cross-linked gels are utilized in a broad range of biomedical applications though their synthesis often compromises easy implementation. Cross-linking reactions commonly utilize catalysts or conditions that can damage biologics and sensitive compounds, producing materials that require extensive post processing to achieve acceptable biocompatibility. As an alternative, we report a batch synthesis platform to produce covalently cross-linked materials appropriate for direct biomedical application enabled by green chemistry and commonly available food grade ingredients. Using caffeine, a mild base, to catalyze anhydrous carboxylate ring-opening of diglycidyl-ether functionalized monomers with citric acid as a tri-functional crosslinking agent we introduce a novel poly(ester-ether) gel synthesis platform. We demonstrate that biocompatible Caffeine Catalyzed Gels (CCGs) exhibit dynamic physical, chemical, and mechanical properties, which can be tailored in shape, surface texture, solvent response, cargo release, shear and tensile strength, among other potential attributes. The demonstrated versatility, low cost and facile synthesis of these CCGs renders them appropriate for a broad range of customized engineering applications including drug delivery constructs, tissue engineering scaffolds, and medical devices. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Thermo-kinetics of lipase-catalyzed synthesis of 6-O-glucosyldecanoate.

Science.gov (United States)

Gumel, A M; Annuar, M S M; Heidelberg, T; Chisti, Y

2011-10-01

Lipase-catalyzed synthesis of 6-O-glucosyldecanoate from d-glucose and decanoic acid was performed in dimethyl sulfoxide (DMSO), a mixture of DMSO and tert-butanol and tert-butanol alone with a decreasing order of polarity. The highest conversion yield (> 65%) of decanoic acid was obtained in the blended solvent of intermediate polarity mainly because it could dissolve relatively large amounts of both the reactants. The reaction obeyed Michaelis-Menten type of kinetics. The affinity of the enzyme towards the limiting substrate (decanoic acid) was not affected by the polarity of the solvent, but increased significantly with temperature. The esterification reaction was endothermic with activation energy in the range of 60-67 kJ mol⁻¹. Based on the Gibbs energy values, in the solvent blend of DMSO and tert-butanol the position of the equilibrium was shifted more towards the products compared to the position in pure solvents. Monoester of glucose was the main product of the reaction. Copyright © 2011 Elsevier Ltd. All rights reserved.

Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

KAUST Repository

Vummaleti, Sai V. C.

2015-11-13

Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

KAUST Repository

Vummaleti, Sai V. C.; Alghamdi, Miasser; Poater, Albert; Falivene, Laura; Scaranto, Jessica; Beetstra, Dirk J.; Morton, Jason G.; Cavallo, Luigi

2015-01-01

Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

Reaction of Aldehydes/Ketones with Electron-Deficient 1,3,5-Triazines Leading to Functionalized Pyrimidines as Diels-Alder/Retro-Diels-Alder Reaction Products: Reaction Development and Mechanistic Studies.

Science.gov (United States)

Yang, Kai; Dang, Qun; Cai, Pei-Jun; Gao, Yang; Yu, Zhi-Xiang; Bai, Xu

2017-03-03

Catalytic inverse electron demand Diels-Alder (IEDDA) reactions of heterocyclic aza-dienes are rarely reported since highly reactive and electron-rich dienophiles are often found not compatible with strong acids such as Lewis acids. Herein, we disclose that TFA-catalyzed reactions of electron-deficient 1,3,5-triazines and electron-deficient aldehydes/ketones can take place. These reactions led to highly functionalized pyrimidines as products in fair to good yields. The reaction mechanism was carefully studied by the combination of experimental and computational studies. The reactions involve a cascade of stepwise inverse electron demand hetero-Diels-Alder (ihDA) reactions, followed by retro-Diels-Alder (rDA) reactions and elimination of water. An acid was required for both ihDA and rDA reactions. This mechanism was further verified by comparing the relative reactivity of aldehydes/ketones and their corresponding vinyl ethers in the current reaction system.

Furfural production from fruit shells by acid-catalyzed hydrolysis

Energy Technology Data Exchange (ETDEWEB)

Demirbas, A. [Selcuk Univ., Konya (Turkey). Dept. of Chemical Engineering

2006-01-21

Pentosans are hydrolyzed to pentoses by dilute mineral acid hydrolysis. The main source of pentosans is hemicelluloses. Furfural can be produced by the acid hydrolysis of pentosan from fruit shells such as hazelnut, sunflower, walnut, and almond of agricultural wastes. Further dehydration reactions of the pentoses yield furfural. The hydrolysis of each shell sample was carried out in dilute sulfuric acid (0.05 to 0.200 mol/l), at high temperature (450-525 K), and short reaction times (from 30 to 600 s). (author)

Pd-catalyzed versus uncatalyzed, PhI(OAc)2-mediated cyclization reactions of N6-([1,1'-biaryl]-2-yl)adenine nucleosides.

Science.gov (United States)

Satishkumar, Sakilam; Poudapally, Suresh; Vuram, Prasanna K; Gurram, Venkateshwarlu; Pottabathini, Narender; Sebastian, Dellamol; Yang, Lijia; Pradhan, Padmanava; Lakshman, Mahesh K

2017-11-09

In this work we have assessed reactions of N 6 -([1,1'-biaryl]-2-yl)adenine nucleosides with Pd(OAc) 2 and PhI(OAc) 2 , via a Pd II /Pd IV redox cycle. The substrates are readily obtained by Pd/Xantphos-catalyzed reaction of adenine nucleosides with 2-bromo-1,1'-biaryls. In PhMe, the N 6 -biarylyl nucleosides gave C6-carbazolyl nucleoside analogues by C-N bond formation with the exocyclic N 6 nitrogen atom. In the solvent screening for the Pd-catalyzed reactions, an uncatalyzed process was found to be operational. It was observed that the carbazolyl products could also be obtained in the absence of a metal catalyst by reaction with PhI(OAc) 2 in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Thus, under Pd catalysis and in HFIP, reactions proceed to provide carbazolyl nucleoside analogues, with some differences. If reactions of N 6 -biarylyl nucleoside substrates were conducted in MeCN, formation of aryl benzimidazopurinyl nucleoside derivatives was observed in many cases by C-N bond formation with the N 1 ring nitrogen atom of the purine (carbazole and benzimidazole isomers are readily separated by chromatography). Whereas Pd II /Pd IV redox is responsible for carbazole formation under the metal-catalyzed conditions, in HFIP and MeCN radical cations and/or nitrenium ions can be intermediates. An extensive set of radical inhibition experiments was conducted and the data are presented.

Hydrolysis of palm oil catalyzed by acid%棕榈油的酸催化水解工艺研究

Institute of Scientific and Technical Information of China (English)

张玲玲; 王晖

2015-01-01

以棕榈油为原料进行常压酸催化水解工艺研究。考察了反应时间、反应温度、催化剂用量、油水质量比及乳化剂用量对棕榈油水解反应的影响,得出棕榈油一次酸催化水解的最佳反应条件：反应时间7 h,反应温度100℃,催化剂浓硫酸用量7.5%,油水质量比1∶1,乳化剂磺酸用量0.5%；在最佳反应条件下棕榈油水解产物酸值(KOH)为192.77 mg/g,水解率达到91.96%。并研究出一套循环水解的工艺流程,实现油脂水解产物的循环利用,提高了水相中甘油的含量。%The hydrolysis of palm oil catalyzed by acid was studied. The effects of reaction time,reaction temperature,catalyst dosage,mass ratio of oil to water and emulsifier dosage on the hydrolysis of palm oil were investigated. The optimal reaction conditions of palm oil hydrolysis were obtained as follows:reaction time 7 h,reaction temperature 100℃,mass ratio of oil to water 1∶1,dosage of sulfonic acid used as emul-sifier 0. 5% and catalyst( concentrated sulfonic acid) dosage 7. 5%. Under the optimal reaction condi-tions,the acid value of the hydrolysates was up to 192. 77 mgKOH/g and the hydrolysis rate of palm oil was 91. 96%. A circulated hydrolysis process was designed, then the recycling of hydrolysates was real-ized,and the content of glycerin in the aqueous phase increased.

Improving fatty acid methyl ester production yield in a lipase-catalyzed process using waste frying oils as feedstock.

Science.gov (United States)

Azócar, Laura; Ciudad, Gustavo; Heipieper, Hermann J; Muñoz, Robinson; Navia, Rodrigo

2010-06-01

The application of waste frying oil (WFO) mixed with rapeseed oil as a feedstock for the effective production of fatty acid methyl esters (FAME) in a lipase-catalyzed process was investigated. The response surface methodology (RSM) was used to optimize the interaction of four variables: the percentage of WFO in the mixed feedstock, the methanol-to-oil ratio, the dosage of Novozym 435 as a catalyst and the temperature. Furthermore, the addition of methanol to the reaction mixture in a second step after 8 h was shown to effectively diminish enzyme inhibition. Using this technique, the model predicted the optimal conditions that would reach 100% FAME, including a methanol-to-oil molar ratio of 3.8:1, 100% (wt) WFO, 15% (wt) Novozym 435 and incubation at 44.5 degrees C for 12 h with agitation at 200 rpm, and verification experiments confirmed the validity of the model. According to the model, the addition of WFO increased FAME production yield, which is largely due to its higher contents of monoacylglycerols, diacylglycerols and free fatty acids (in comparison to rapeseed oil), which are more available substrates for the enzymatic catalysis. Therefore, the replacement of rapeseed oil with WFO in Novozym 435-catalyzed processes could diminish biodiesel production costs since it is a less expensive feedstock that increases the production yield and could be a potential alternative for FAME production on an industrial scale. (c) 2009 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Solvent- and ligand-induced switch of selectivity in gold(I-catalyzed tandem reactions of 3-propargylindoles

Directory of Open Access Journals (Sweden)

Roberto Sanz

2011-06-01

Full Text Available The selectivity of our previously described gold-catalyzed tandem reaction, 1,2-indole migration followed by aura-iso-Nazarov cyclization, of 3-propargylindoles bearing (heteroaromatic substituents at both the propargylic and terminal positions, was reversed by the proper choice of the catalyst and the reaction conditions. Thus, 3-(inden-2-ylindoles, derived from an aura-Nazarov cyclization (instead of an aura-iso-Nazarov cyclization, were obtained in moderate to good yields from a variety of 3-propargylindoles.

Mechanism of iron catalyzed oxidation of SO/sub 2/ in oxygenated solutions

Energy Technology Data Exchange (ETDEWEB)

Freiberg, J

1975-01-01

Previous experimental work concerning the iron catalyzed oxidation of SO/sub 2/ in oxygenated acid solutions failed to provide a consistent reaction mechanism and rate expression. As iron is one of the main constituents of urban atmospheric aerosols, the rate studies of heterogeneous sulphate formation in polluted city air were hampered. The present study develops a new theory for the iron catalyzed oxidation of SO/sub 2/. The resulting new rate expression is general enough to account for the results of previous experimental investigations that were performed in different ranges of SO/sub 2/ and catalyst concentrations.

Mechanisms of reactions of organoaluminium compounds with alkenes and alkynes catalyzed by Zr complexes

International Nuclear Information System (INIS)

Parfenova, L V; Khalilov, Leonard M; Dzhemilev, Usein M

2012-01-01

The results of studies dealing with mechanisms of hydro-, carbo- and cycloalumination of alkenes and alkynes catalyzed by zirconium complexes are generalized and systematized for the first time. Data about the structures of intermediates responsible for the formation of the target compounds are presented and the available data on the effect of the structure of organoaluminium compounds and the electronic and steric factors determining the catalytic activity of metal complexes in these reactions are considered in detail. Much attention is paid to studies of the influence of reaction conditions on the chemo-, regio- and stereoselectivity of the Zr-containing complex catalysts. The bibliography includes 217 references.

Silica metal-oxide vesicles catalyze comprehensive prebiotic chemistry.

Science.gov (United States)

Bizzarri, Bruno Mattia; Botta, Lorenzo; Pérez-Valverde, Maritza Iveth; Saladino, Raffaele; Di Mauro, Ernesto; Garcia Ruiz, Juan Manuel

2018-03-30

It has recently been demonstrated that mineral self-assembled structures catalyzing prebiotic chemical reactions may form in natural waters derived from serpentinization, a geological process widespread in the early stages of Earth-like planets. We have synthesized self-assembled membranes by mixing microdrops of metal solutions with alkaline silicate solutions in the presence of formamide (NH2CHO), a single carbon molecule, at 80ºC. We found that these bilayer membranes, made of amorphous silica and metal oxide-hydroxide nanocrystals, catalyze the condensation of formamide, yielding the four nucleobases of RNA, three aminoacids and several carboxylic acids in a single pot experiment. Besides manganese, iron and magnesium, two abundant elements in the earliest Earth crust that are key in serpentinization reactions, are enough to produce all these biochemical compounds. These results suggest that the transition from inorganic geochemistry to prebiotic organic chemistry is common on a universal scale and, most probably, earlier than ever thought for our planet. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transglutaminase catalyzed cross-linking of sodium caseinate improves oxidative stability of flaxseed oil emulsion.

Science.gov (United States)

Ma, Hairan; Forssell, Pirkko; Kylli, Petri; Lampi, Anna-Maija; Buchert, Johanna; Boer, Harry; Partanen, Riitta

2012-06-20

Sodium caseinate was modified by transglutaminase catalyzed cross-linking reaction prior to the emulsification process in order to study the effect of cross-linking on the oxidative stability of protein stabilized emulsions. The extent of the cross-linking catalyzed by different dosages of transglutaminase was investigated by following the ammonia production during the reaction and using SDS-PAGE gel. O/W emulsions prepared with the cross-linked and non-cross-linked sodium caseinates were stored for 30 days under the same conditions. Peroxide value measurement, oxygen consumption measurement, and headspace gas chromatography analysis were used to study the oxidative stability of the emulsions. The emulsion made of the cross-linked sodium caseinate showed an improved oxidative stability with reduced formation of fatty acid hydroperoxides and volatiles and a longer period of low rate oxygen consumption. The improving effect of transglutaminase catalyzed cross-linking could be most likely attributed to the enhanced physical stability of the interfacial protein layer against competitive adsorption by oil oxidation products.

Radiochemical methods for studying lipase-catalyzed interesterification of lipids

International Nuclear Information System (INIS)

Schuch, R.; Mukherjee, K.D.

1987-01-01

Reactions involving lipase-catalyzed interesterification of lipids, which are of commendable interest in biotechnology, have been monitored and assayed by radiochemical methods using 14 C-labeled substrates. Medium chain (C 12 plus C 14 ) triacylglycerols were reacted in the presence of an immobilized lipase from Mucor miehei and hexane at 45 0 C with methyl [1- 14 C]oleate, [1- 14 C]oleic acid, [carboxyl- 14 C]trioleoylglycerol, [1- 14 C]octadecenyl alcohol, and [U- 14 C]glycerol, each of known specific activity. The reactions were monitored and the rate of interesterification determined by radio thin layer chromatography from the incorporation of radioactivity into acyl moieties of triacylglycerols (from methyl oleate, oleic acid, and trioleoylglycerol), alkyl moieties of wax esters (from octadecenyl alcohol), and into glycerol backbone of monoacylglycerols and diacylglycerols (from glycerol). (orig.)

Oligomerization of glycine and alanine catalyzed by iron oxides: implications for prebiotic chemistry.

Science.gov (United States)

Shanker, Uma; Bhushan, Brij; Bhattacharjee, G; Kamaluddin

2012-02-01

Iron oxide minerals are probable constituents of the sediments present in geothermal regions of the primitive earth. They might have adsorbed different organic monomers (amino acids, nucleotides etc.) and catalyzed polymerization processes leading to the formation of the first living cell. In the present work we tested the catalytic activity of three forms of iron oxides (Goethite, Akaganeite and Hematite) in the intermolecular condensation of each of the amino acids glycine and L-alanine. The effect of zinc oxide and titanium dioxide on the oligomerization has also been studied. Oligomerization studies were performed for 35 days at three different temperatures 50, 90 and 120°C without applying drying/wetting cycling. The products formed were characterized by HPLC and ESI-MS techniques. All three forms of iron oxides catalyzed peptide bond formation (23.2% of gly2 and 10.65% of ala2). The reaction was monitored every 7 days. Formation of peptides was observed to start after 7 days at 50°C. Maximum yield of peptides was found after 35 days at 90°C. Reaction at 120°C favors formation of diketopiperazine derivatives. It is also important to note that after 35 days of reaction, goethite produced dimer and trimer with the highest yield among the oxides tested. We suggest that the activity of goethite could probably be due to its high surface area and surface acidity.

A review on biodiesel production using catalyzed transesterification

Energy Technology Data Exchange (ETDEWEB)

Leung, Dennis Y.C.; Wu, Xuan; Leung, M.K.H. [Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong (China)

2010-04-15

Biodiesel is a low-emissions diesel substitute fuel made from renewable resources and waste lipid. The most common way to produce biodiesel is through transesterification, especially alkali-catalyzed transesterification. When the raw materials (oils or fats) have a high percentage of free fatty acids or water, the alkali catalyst will react with the free fatty acids to form soaps. The water can hydrolyze the triglycerides into diglycerides and form more free fatty acids. Both of the above reactions are undesirable and reduce the yield of the biodiesel product. In this situation, the acidic materials should be pre-treated to inhibit the saponification reaction. This paper reviews the different approaches of reducing free fatty acids in the raw oil and refinement of crude biodiesel that are adopted in the industry. The main factors affecting the yield of biodiesel, i.e. alcohol quantity, reaction time, reaction temperature and catalyst concentration, are discussed. This paper also described other new processes of biodiesel production. For instance, the Biox co-solvent process converts triglycerides to esters through the selection of inert co-solvents that generates a one-phase oil-rich system. The non-catalytic supercritical methanol process is advantageous in terms of shorter reaction time and lesser purification steps but requires high temperature and pressure. For the in situ biodiesel process, the oilseeds are treated directly with methanol in which the catalyst has been preciously dissolved at ambient temperatures and pressure to perform the transesterification of oils in the oilseeds. This process, however, cannot handle waste cooking oils and animal fats. (author)

Investigating Students' Reasoning about Acid-Base Reactions

Science.gov (United States)

Cooper, Melanie M.; Kouyoumdjian, Hovig; Underwood, Sonia M.

2016-01-01

Acid-base chemistry is central to a wide range of reactions. If students are able to understand how and why acid-base reactions occur, it should provide a basis for reasoning about a host of other reactions. Here, we report the development of a method to characterize student reasoning about acid-base reactions based on their description of…

Novel big-bang element synthesis catalyzed by supersymmetric particle stau

International Nuclear Information System (INIS)

Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

2010-01-01

The extremely low isotope ratio of 6 Li had remained as a drawback of the Big-Bang Nucleosynthesis (BBN) until Pospelov proposed the 6 Li synthesis reaction catalyzed by negatively charged electroweak-scale particle X - in 2006. He remarked the catalytic enhancement of 6 Li production by about 10 8 times, as well as the life and initial abundance of X - . The present authors classified BBN catalyzed reaction into six types, i.e. (1) non-resonant transfer, (2) resonant transfer, (3) non-resonant radiative capture, (4) resonant radiative capture, (5) three-body breakup and (6) charge transfer reactions to predict absolute values of cross sections which cannot be observed experimentally. Starting from the three-body treatment for those reactions, 6 Li problems, the life-time and abundance of stau are discussed. Large change of element composition at 'late-time' big bang, generation of 9 Be by stau catalyzed reaction, 7 Li problem and stau catalyzed reactions are also discussed. Finally their relations with the supersymmetry theory and dark matter are mentioned. The basic nuclear calculations are providing quantitative base for the 'effect of nuclear reactions catalyzed by the supersymmetric particle stau on big bang nucleosynthesis'. (S. Funahashi)

Improvement in biodiesel production from soapstock oil by one-stage lipase catalyzed methanolysis

International Nuclear Information System (INIS)

Su, Erzheng; Wei, Dongzhi

2014-01-01

Highlights: • Soapstock is a less expensive feedstock reservoir for biodiesel production. • Addition of tert-alcohol can enhance the yield of fatty acid methyl ester significantly. • One-stage lipase catalyzed methanolysis of soapstock oil was successfully developed. • FAME yield of 95.2% was obtained with low lipase loading in a shorter reaction time. - Abstract: A major obstacle in the commercialization of biodiesel is its cost of manufacturing, primarily the raw material cost. In order to decrease the cost of biodiesel, soapstock oil was investigated as the feedstock for biodiesel production. Because the soapstock oil containing large amounts of free fatty acids (FFAs) cannot be effectively converted to biodiesel, complicated two-stage process (esterification followed by transesterification) was generally adopted. In this study, simple one-stage lipase catalyzed methanolysis of soapstock oil was developed via one-pot esterification and transesterification. Water produced by lipase catalyzed esterification of FFAs affected the lipase catalyzed transesterification of glycerides in the soapstock oil severely. Addition of tert-alcohol could overcome this problem and enhance the fatty acid methyl ester (FAME) yield from 42.8% to 76.4%. The FAME yield was further elevated to 95.2% by optimizing the methanol/oil molar ratio, lipase amount, and water absorbent. The developed process enables the simple, efficient, and green production of biodiesel from soapstock oil, providing with a potential industrial application

Can laccases catalyze bond cleavage in lignin?

DEFF Research Database (Denmark)

Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand

2015-01-01

illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin......-substituted phenols, benzenethiols, polyphenols, and polyamines, which may be oxidized. In addition, the currently available analytical methods that can be used to detect enzyme catalyzed changes in lignin are summarized, and an improved nomenclature for unequivocal interpretation of the action of laccases on lignin...

Flavin-N5 Covalent Intermediate in a Nonredox Dehalogenation Reaction Catalyzed by an Atypical Flavoenzyme.

Science.gov (United States)

Dai, Yumin; Kizjakina, Karina; Campbell, Ashley C; Korasick, David A; Tanner, John J; Sobrado, Pablo

2018-01-04

The flavin-dependent enzyme 2-haloacrylate hydratase (2-HAH) catalyzes the conversion of 2-chloroacrylate, a major component in the manufacture of acrylic polymers, to pyruvate. The enzyme was expressed in Escherichia coli, purified, and characterized. 2-HAH was shown to be monomeric in solution and contained a non-covalent, yet tightly bound, flavin adenine dinucleotide (FAD). Although the catalyzed reaction was redox-neutral, 2-HAH was active only in the reduced state. A covalent flavin-substrate intermediate, consistent with the flavin-acrylate iminium ion, was trapped with cyanoborohydride and characterized by mass spectrometry. Small-angle X-ray scattering was consistent with 2-HAH belonging to the succinate dehydrogenase/fumarate reductase family of flavoproteins. These studies establish 2-HAH as a novel noncanonical flavoenzyme. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent Advances in Recoverable Systems for the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction (CuAAC

Directory of Open Access Journals (Sweden)

Alessandro Mandoli

2016-09-01

Full Text Available The explosively-growing applications of the Cu-catalyzed Huisgen 1,3-dipolar cycloaddition reaction between organic azides and alkynes (CuAAC have stimulated an impressive number of reports, in the last years, focusing on recoverable variants of the homogeneous or quasi-homogeneous catalysts. Recent advances in the field are reviewed, with particular emphasis on systems immobilized onto polymeric organic or inorganic supports.

Rhodium(III)-catalyzed three-component reaction of imines, alkynes, and aldehydes through C-H activation.

Science.gov (United States)

Huang, Ji-Rong; Song, Qiang; Zhu, Yu-Qin; Qin, Liu; Qian, Zhi-Yong; Dong, Lin

2014-12-15

An efficient rhodium(III)-catalyzed tandem three-component reaction of imines, alkynes and aldehydes through CH activation has been developed. High stereo- and regioselectivity, as well as good yields were obtained in most cases. The simple and atom-economical approach offers a broad scope of substrates, providing polycyclic skeletons with potential biological properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetics and optimization on discoloration of dyeing wastewater by schorl-catalyzed fenton-like reaction

Directory of Open Access Journals (Sweden)

Xu Huan-Yan

2014-01-01

Full Text Available Kinetics and optimization on the discoloration of an active commercial dye, Argazol Blue BFBR (ABB by heterogeneous Fenton-like reaction catalyzed by natural schorl were investigated in this study. Kinetic investigations revealed that the first-order kinetic model was more favorable to describe the discoloration of ABB at different reaction conditions than the second-order and Behnajady-Modirshahla-Ghanbery models. The relationship between the reaction rate constant k and reaction temperature T followed the Arrhenius equation, with the apparent activation energy Ea of 51.31kJ•mol-1. The central composite design under the response surface methodology was employed for the experimental design and optimization of the ABB discoloration process. The significance of a second order polynomial model for predicting the optimal values of ABB discoloration was evaluated by the analysis of variance and 3D response surface plots for the interactions between two variables were constructed. Then, the optimum conditions were determined.

The flavoprotein Mcap0476 (RlmFO) catalyzes m5U1939 modification in Mycoplasma capricolum 23S rRNA

DEFF Research Database (Denmark)

Lartigue, Carole; Lebaudy, Anne; Blanchard, Alain

2014-01-01

Efficient protein synthesis in all organisms requires the post-transcriptional methylation of specific ribosomal ribonucleic acid (rRNA) and transfer RNA (tRNA) nucleotides. The methylation reactions are almost invariably catalyzed by enzymes that use S-adenosylmethionine (AdoMet) as the methyl g...... specifically modifies m5U1939 in 23S rRNA, a conserved methylation catalyzed by AdoMet-dependent enzymes in all other characterized bacteria. The Mcap0476 methyltransferase (renamed RlmFO) represents the first folate-dependent flavoprotein seen to modify ribosomal RNA.......Efficient protein synthesis in all organisms requires the post-transcriptional methylation of specific ribosomal ribonucleic acid (rRNA) and transfer RNA (tRNA) nucleotides. The methylation reactions are almost invariably catalyzed by enzymes that use S-adenosylmethionine (AdoMet) as the methyl...... group donor. One noteworthy exception is seen in some bacteria, where the conserved tRNA methylation at m5U54 is added by the enzyme TrmFO using flavin adenine dinucleotide together with N5,N10-methylenetetrahydrofolate as the one-carbon donor. The minimalist bacterium Mycoplasma capricolum possesses...

Facile access to amides and hydroxamic acids directly from nitroarenes.

Science.gov (United States)

Jain, Shreyans K; Aravinda Kumar, K A; Bharate, Sandip B; Vishwakarma, Ram A

2014-09-07

A new method for synthesis of amides and hydroxamic acids from nitroarenes and aldehydes is described. The MnO2 catalyzed thermal deoxygenation of nitrobenzene resulted in formation of a reactive nitroso intermediate which on reaction with aldehydes provided amides and hydroxamic acids. The thermal neat reaction in the presence of 0.01 mmol KOH predominantly led to formation of hydroxamic acid whereas reaction in the presence of 1 mmol acetic acid produced amides as the only product.

The Roles of Acids and Bases in Enzyme Catalysis

Science.gov (United States)

Weiss, Hilton M.

2007-01-01

Many organic reactions are catalyzed by strong acids or bases that protonate or deprotonate neutral reactants leading to reactive cations or anions that proceed to products. In enzyme reactions, only weak acids and bases are available to hydrogen bond to reactants and to transfer protons in response to developing charges. Understanding this…

Theoretical Kinetic Study of the Formic Acid Catalyzed Criegee Intermediate Isomerization: Multistructural Anharmonicity and Atmospheric Implications

KAUST Repository

Monge Palacios, Manuel

2018-01-29

We performed a theoretical study on the double hydrogen shift isomerization reaction of a six carbon atom Criegee intermediate (C6-CI), catalyzed by formic acid (HCOOH), to produce vinylhydroperoxide (VHP), C6-CI+HCOOH→VHP+HCOOH. This Criegee intermediate can serve as a surrogate for larger CIs derived from important volatile organic compounds like monoterpenes, whose reactivity is not well understood and are difficult to handle computationally. The reactant HCOOH exerts a pronounced catalytic effect on the studied reaction by lowering the barrier height, but the kinetic enhancement is hindered by the multistructural anharmonicity. First, the rigid ring-structure adopted by the saddle point to facilitate simultaneous transfer of two atoms does not allow formation of as many conformers as those formed by the reactant C6-CI. And second, the flexible carbon chain of C6-CI facilitates the formation of stabilizing intramolecular C–H···O hydrogen bonds; this stabilizing effect is less pronounced in the saddle point structure due to its tightness and steric effects. Thus, the contribution of the reactant C6-CI conformers to the multistructural partition function is larger than that of the saddle point conformers. The resulting low multistructural anharmonicity factor partially cancels out the catalytic effect of the carboxylic acid, yielding in a moderately large rate coefficient, k(298 K) = 4.9·10-13 cm3 molecule-1 s-1. We show that carboxylic acids may promote the conversion of stabilized Criegee intermediates into vinylhydroperoxides in the atmosphere, which generates OH radicals and leads to secondary organic aerosol, thereby affecting the oxidative capacity of the atmosphere and ultimately the climate.

Biodiesel production from Nannochloropsis gaditana lipids through transesterification catalyzed by Rhizopus oryzae lipase.

Science.gov (United States)

Navarro López, Elvira; Robles Medina, Alfonso; González Moreno, Pedro Antonio; Esteban Cerdán, Luis; Martín Valverde, Lorena; Molina Grima, Emilio

2016-03-01

Biodiesel (fatty acid methyl esters, FAMEs) was produced from saponifiable lipids (SLs) extracted from wet Nannochloropsis gaditana biomass using methanolysis catalyzed by Rhizopus oryzae intracellular lipase. SLs were firstly extracted with ethanol to obtain 31 wt% pure SLs. But this low SL purity also gave a low biodiesel conversion (58%). This conversion increased up to 80% using SLs purified by crystallization in acetone (95 wt% purity). Polar lipids play an important role in decreasing the reaction velocity - using SLs extracted with hexane, which have lower polar lipid content (37.4% versus 49.0% using ethanol), we obtained higher reaction velocities and less FAME conversion decrease when the same lipase batch was reused. 83% of SLs were transformed to biodiesel using a 70 wt% lipase/SL ratio, 11:1 methanol/SL molar ratio, 10 mL t-butanol/g SLs after 72 h. The FAME conversion decreased to 71% after catalyzing three reactions with the same lipase batch. Copyright © 2015 Elsevier Ltd. All rights reserved.

Complex chemical composition of colored surface films formed from reactions of propanal in sulfuric acid at upper troposphere/lower stratosphere aerosol acidities.

Science.gov (United States)

Van Wyngarden, A L; Pérez-Montaño, S; Bui, J V H; Li, E S W; Nelson, T E; Ha, K T; Leong, L; Iraci, L T

Particles in the upper troposphere and lower stratosphere (UT/LS) consist mostly of concentrated sulfuric acid (40-80 wt %) in water. However, airborne measurements have shown that these particles also contain a significant fraction of organic compounds of unknown chemical composition. Acid-catalyzed reactions of carbonyl species are believed to be responsible for significant transfer of gas phase organic species into tropospheric aerosols and are potentially more important at the high acidities characteristic of UT/LS particles. In this study, experiments combining sulfuric acid (H 2 SO 4 ) with propanal and with mixtures of propanal with glyoxal and/or methylglyoxal at acidities typical of UT/LS aerosols produced highly colored surface films (and solutions) that may have implications for aerosol properties. In order to identify the chemical processes responsible for the formation of the surface films, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and 1 H nuclear magnetic resonance (NMR) spectroscopies were used to analyze the chemical composition of the films. Films formed from propanal were a complex mixture of aldol condensation products, acetals and propanal itself. The major aldol condensation products were the dimer (2-methyl-2-pentenal) and 1,3,5-trimethylbenzene that was formed by cyclization of the linear aldol condensation trimer. Additionally, the strong visible absorption of the films indicates that higher-order aldol condensation products must also be present as minor species. The major acetal species were 2,4,6-triethyl-1,3,5-trioxane and longer-chain linear polyacetals which are likely to separate from the aqueous phase. Films formed on mixtures of propanal with glyoxal and/or methylglyoxal also showed evidence of products of cross-reactions. Since cross-reactions would be more likely than self-reactions under atmospheric conditions, similar reactions of aldehydes like propanal with common aerosol organic species like glyoxal

Synthesis of 1,1-Diborylalkenes through a Bronsted Base Catalyzed Reaction between Terminal Alkynes and Bis(pinacolato)diboron

OpenAIRE

Morinaga, Akira; Nagao, Kazunori; Ohmiya, Hirohisa; Sawamura, Masaya

2015-01-01

A method for the synthesis of 1,1-diborylalkenes through a Bronsted base catalyzed reaction between terminal alkynes and bis(pinacolato)diboron has been developed. The procedure allows direct synthesis of functionalized 1,1-diborylalkenes from various terminal alkynes including propiolates, propiolamides, and 2-ethynylazoles.

Gold-Catalyzed Cyclization of Furan-Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels-Alder Reaction with In Situ Generated Allenes.

Science.gov (United States)

Sun, Ning; Xie, Xin; Chen, Haoyi; Liu, Yuanhong

2016-09-26

Gold-catalyzed cyclization of various furan-ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold-catalyzed 3,3-rearrangement of the propargyl carboxylate moiety in furan-yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels-Alder reaction of furan and subsequent ring-opening of the oxa-bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5-furan-yne, the cleavage of the oxa-bridge in the cycloadduct with concomitant 1,2-migration of the R(1) group occurs to furnish anthracen-1(2H)-ones bearing a quaternary carbon center. For 1,4-furan-yne, a facile aromatization of the cycloadduct takes place to give 9-oxygenated anthracene derivatives. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones.

Science.gov (United States)

Takaki, Ken; Hino, Makoto; Ohno, Akira; Komeyama, Kimihiro; Yoshida, Hiroto; Fukuoka, Hiroshi

2017-01-01

Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.

Carbon Isotope Systematics in Mineral-Catalyzed Hydrothermal Organic Synthesis Processes at High Temperature and Pressures

Science.gov (United States)

Fu, Qi; Socki, R. A.; Niles, Paul B.

2011-01-01

Observation of methane in the Martian atmosphere has been reported by different detection techniques. Reduction of CO2 and/or CO during serpentization by mineral surface catalyzed Fischer-Tropsch Type (FTT) synthesis may be one possible process responsible for methane generation on Mars. With the evidence a recent study has discovered for serpentinization in deeply buried carbon rich sediments, and more showing extensive water-rock interaction in Martian history, it seems likely that abiotic methane generation via serpentinization reactions may have been common on Mars. Experiments involving mineral-catalyzed hydrothermal organic synthesis processes were conducted at 750 C and 5.5 Kbars. Alkanes, alcohols and carboxylic acids were identified as organic compounds. No "isotopic reversal" of delta C-13 values was observed for alkanes or carboxylic acids, suggesting a different reaction pathway than polymerization. Alcohols were proposed as intermediaries formed on mineral surfaces at experimental conditions. Carbon isotope data were used in this study to unravel the reaction pathways of abiotic formation of organic compounds in hydrothermal systems at high temperatures and pressures. They are instrumental in constraining the origin and evolution history of organic compounds on Mars and other planets.

Indium-Catalyzed Reductive Dithioacetalization of Carboxylic Acids with Dithiols: Scope, Limitations, and Application to Oxidative Desulfurization.

Science.gov (United States)

Nishino, Kota; Minato, Kohei; Miyazaki, Takahiro; Ogiwara, Yohei; Sakai, Norio

2017-04-07

In this study an InI 3 -TMDS (1,1,3,3-tetramethyldisiloxane) reducing system effectively catalyzed the reductive dithioacetalization of a variety of aromatic and aliphatic carboxylic acids with 1,2-ethanedithiol or 1,3-propanedithiol leading to the one-pot preparation of either 1,3-dithiolane derivatives or a 1,3-dithiane derivative. Also, the intact indium catalyst continuously catalyzed the subsequent oxidative desulfurization of an in situ formed 1,3-dithiolane derivative, which led to the preparation of the corresponding aldehydes.

N-Heterocyclic Carbene-Catalyzed Vinylogous Mukaiyama Aldol Reaction of α-Keto Esters and α-Trifluoromethyl Ketones

KAUST Repository

Du, Guang-Fen; Wang, Ying; Xing, Fen; Xue, Mei; Guo, Xu-Hong; Huang, Kuo-Wei; Dai, Bin

2015-01-01

© Georg Thieme Verlag Stuttgart · New York · Synthesis 2016. N-Heterocyclic carbene (NHC)-catalyzed vinylogous Mukaiyama aldol reaction of ketones was developed. Under the catalysis of 5 mol% NHC, α-keto esters and α-trifluoromethyl ketones reacted with 2-(trimethysilyloxy)furan efficiently to produce γ-substituted butenolides containing adjacent quaternary and tertiary carbon centers in high yields with good diastereoselectivities.

One-step production of biodiesel from rice bran oil catalyzed by chlorosulfonic acid modified zirconia via simultaneous esterification and transesterification.

Science.gov (United States)

Zhang, Yue; Wong, Wing-Tak; Yung, Ka-Fu

2013-11-01

Due to the high content (25-50%) of free fatty acid (FFA), crude rice bran oil usually requires a two steps conversion or one step conversion with very harsh condition for simultaneous esterification and transesterification. In this study, chlorosulfonic acid modified zirconia (HClSO3-ZrO2) with strong acidity and durability is prepared and it shows excellent catalytic activity toward simultaneous esterification and transesterification. Under a relative low reaction temperature of 120 °C, HClSO3-ZrO2 catalyzes a complete conversion of simulated crude rice bran oil (refined oil with 40 wt% FFA) into biodiesel and the conversion yield keep at above 92% for at least three cycles. Further investigation on the tolerance towards FFA and water reveals that it maintains high activity even with the presence of 40 wt% FFA and 3 wt% water. It shows that HClSO3-ZrO2 is a robust and durable catalyst which shows high potential to be commercial catalyst for biodiesel production from low grade feedstock. Copyright © 2013 Elsevier Ltd. All rights reserved.

Micro-coulometric study of bioelectrochemical reaction coupled with TCA cycle.

Science.gov (United States)

Tsujimura, Seiya; Fukuda, Jun; Shirai, Osamu; Kano, Kenji; Sakai, Hideki; Tokita, Yuichi; Hatazawa, Tsuyonobu

2012-04-15

The mediated electro-enzymatic electrolysis systems based on the tricarboxylic acid (TCA) cycle reaction were examined on a micro-bulk electrolytic system. A series of the enzyme-catalyzed reactions in the TCA cycle was coupled with electrode reaction. Electrochemical oxidation of NADH was catalyzed by diaphorase with an aid of a redox mediator with a formal potential of -0.15 V vs. Ag|AgCl. The mediator was also able to shuttle electrons between succinate dehydrogenase and electrode. The charge during the electrolysis increased on each addition of dehydrogenase reaction in a cascade of the TCA cycle. However, the electrolysis efficiencies were close to or less than 90% because of the product inhibition. Lactate oxidation to acetyl-CoA catalyzed by two NAD-dependent dehydrogenases was coupled with the bioelectrochemical TCA cycle reaction to achieve the 12-electron oxidation of lactate to CO(2). The charge passed in the bioelectrocatalytic oxidation of 5 nmol of lactate was 4 mC, which corresponds to 70% of the electrolysis efficiency. Copyright © 2012 Elsevier B.V. All rights reserved.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

Directory of Open Access Journals (Sweden)

Ken Takaki

2017-08-01

Full Text Available Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.

Interesterification of rapeseed oil catalyzed by tin octoate

International Nuclear Information System (INIS)

Galia, Alessandro; Centineo, Alessio; Saracco, Guido; Schiavo, Benedetto; Scialdone, Onofrio

2014-01-01

The interesterification of rapeseed oil was performed for the first time by using tin octoate as Lewis acid homogeneous catalysts and methyl or ethyl acetate as acyl acceptors in a batch reactor, within the temperature range 393–483 K. The yields in fatty acid ethyl esters (FAEE) and triacetin (TA) after 20 h of reaction time increased from 8% and 2%–to 61% and 22%, respectively, when the reaction temperature increased from 423 to 483 K. An optimum value of 40 for the acyl acceptor to oil molar ratio was found to be necessary to match good fatty acid alkyl ester yields with high enough reaction rate. The rate of generation of esters was significantly higher when methyl acetate was used as acyl acceptor instead of its ethyl homologue. The collected results suggest that tin octoate can be used as effective catalyst for the interesterification of rapeseed oil with methyl or ethyl acetate being highly soluble in the reaction system, less expensive than enzymes and allowing the operator to work under milder conditions than supercritical interesterification processes. - Highlights: • We study the interesterification of rapeseed oil catalyzed by tin(II) octoate. • Tin(II) octoate is an effective homogeneous catalyst at 483 K. • The acyl acceptor to oil molar ratio must be optimized. • Higher rate of reaction is obtained with methyl acetate as acyl acceptor

Cross-Coupling of Amides with Alkylboranes via Nickel-Catalyzed C–N Bond Cleavage

KAUST Repository

Liu, Xiangqian; Hsiao, Chien-Chi; Guo, Lin; Rueping, Magnus

2018-01-01

A protocol for the nickel-catalyzed alkylation of amides was established. The use of alkylboranes as nucleophilic partners allowed the use of mild reaction conditions and compatibility of various functional groups with respect to both coupling partners. The catalytic alkylation proceeded selectively at the amides in the presence of other functional groups as well as other carboxylic acid derived moieties.

Cross-Coupling of Amides with Alkylboranes via Nickel-Catalyzed C–N Bond Cleavage

KAUST Repository

Liu, Xiangqian

2018-05-09

A protocol for the nickel-catalyzed alkylation of amides was established. The use of alkylboranes as nucleophilic partners allowed the use of mild reaction conditions and compatibility of various functional groups with respect to both coupling partners. The catalytic alkylation proceeded selectively at the amides in the presence of other functional groups as well as other carboxylic acid derived moieties.

Acid-base catalysis of N-[(morpholine)methylene]daunorubicin.

Science.gov (United States)

Krause, Anna; Jelińska, Anna; Cielecka-Piontek, Judyta; Klawitter, Maria; Zalewski, Przemysław; Oszczapowicz, Irena; Wąsowska, Małgorzata

2012-08-01

The stability of N-[(morpholine)methylene]-daunorubicin hydrochloride (MMD) was investigated in the pH range 0.44-13.54, at 313, 308, 303 and 298 K. The degradation of MMD as a result of hydrolysis is a pseudo-first-order reaction described by the following equation: ln c = ln c(0) - k(obs)• t. In the solutions of hydrochloric acid, sodium hydroxide, borate, acetate and phosphate buffers, k(obs) = k(pH) because general acid-base catalysis was not observed. Specific acid-base catalysis of MMD comprises the following reactions: hydrolysis of the protonated molecules of MMD catalyzed by hydrogen ions (k(1)) and spontaneous hydrolysis of MMD molecules other than the protonated ones (k(2)) under the influence of water. The total rate of the reaction is equal to the sum of partial reactions: k(pH) = k(1) • a(H)+ • f(1) + k(2) • f(2) where: k(1) is the second-order rate constant (mol(-1) l s(-1)) of the specific hydrogen ion-catalyzed degradation of the protonated molecules of MMD; k(2) is the pseudo-first-order rate constant (s(-1)) of the water-catalyzed degradation of MMD molecules other than the protonated ones, f(1) - f(2) are fractions of the compound. MMD is the most stable at approx. pH 2.5.

Ru/Me-BIPAM-Catalyzed Asymmetric Addition of Arylboronic Acids to Aliphatic Aldehydes and α-Ketoesters

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Momoko Watanabe

2011-06-01

Full Text Available A ruthenium-catalyzed asymmetric arylation of aliphatic aldehydes and α-ketoesters with arylboronic acids has been developed, giving chiral alkyl(arylmethanols and α-hydroxy esters in good yields. The use of a chiral bidentate phosphoramidite ligand (Me-BIPAM achieved excellent enantioselectivities.

Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

International Nuclear Information System (INIS)

Martin del Campo, Julia S.; Patino, Rodrigo

2011-01-01

Research highlights: → The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. → A spectrophotometric method is proposed for kinetic and thermodynamic analysis. → The pH and the temperature influences are reported on physical chemical properties. → Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD ox ) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD ox as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, Δ f G o = -1784 ± 5 kJ mol -1 .

Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

Energy Technology Data Exchange (ETDEWEB)

Martin del Campo, Julia S. [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico); Patino, Rodrigo, E-mail: rtarkus@mda.cinvestav.mx [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico)

2011-04-20

Research highlights: {yields} The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. {yields} A spectrophotometric method is proposed for kinetic and thermodynamic analysis. {yields} The pH and the temperature influences are reported on physical chemical properties. {yields} Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD{sub ox}) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD{sub ox} as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, {Delta}{sub f}G{sup o} = -1784 {+-} 5 kJ mol{sup -1}.

Palladium-catalyzed cyclization reactions of 2-vinylthiiranes with heterocumulenes. Regioselective and enantioselective formation of thiazolidine, oxathiolane, and dithiolane derivatives.

Science.gov (United States)

Larksarp, C; Sellier, O; Alper, H

2001-05-18

The first palladium-catalyzed ring-expansion reaction of 2-vinylthiiranes with heterocumulenes to form sulfur-containing five-membered-ring heterocycles is described. This regioselective reaction requires 5 mol % of Pd(2)(dba)(3).CHCl(3) and 10 mol % of bidendate phosphine ligand (dppp, BINAP), at 50-80 degrees C, in THF. The reaction of 2-vinylthiiranes with carbodiimides, isocyanates, and ketenimines affords 1,3-thiazolidine derivatives, whereas the reaction with diphenylketene or isothiocyanates results in the formation of 1,3-oxathiolane or 1,3-dithiolane compounds in good to excellent isolated yields and in up to 78% ee.

Lipase-catalyzed acidolysis of canola oil with caprylic acid to produce medium-, long- and medium-chain-type structured lipids

DEFF Research Database (Denmark)

Wang, Yingyao; Xia, Luan; Xu, Xuebing

2012-01-01

Lipase-catalyzed acidolysis of canola oil with caprylic acid was performed to produce structured lipids (SLs) containing medium-chain fatty acid (M) at position sn-1,3 and long-chain fatty acid (L) at the sn-2 position in a solvent-free system. Six commercial lipases from different sources were...

Enhanced removal of aqueous acetaminophen by a laccase-catalyzed oxidative coupling reaction under a dual-pH optimization strategy.

Science.gov (United States)

Wang, Kaidong; Huang, Ke; Jiang, Guoqiang

2018-03-01

Acetaminophen is one kind of pharmaceutical contaminant that has been detected in municipal water and is hard to digest. A laccase-catalyzed oxidative coupling reaction is a potential method of removing acetaminophen from water. In the present study, the kinetics of radical polymerization combined with precipitation was studied, and the dual-pH optimization strategy (the enzyme solution at pH7.4 being added to the substrate solution at pH4.2) was proposed to enhance the removal efficiency of acetaminophen. The reaction kinetics that consisted of the laccase-catalyzed oxidation, radical polymerization and precipitation were studied by UV in situ, LC-MS and DLS (dynamic light scattering) in situ. The results showed that the laccase-catalyzed oxidation is the rate-limiting step in the whole process. The higher rate of enzyme-catalyzed oxidation under a dual-pH optimization strategy led to much faster formation of the dimer, trimer and tetramer. Similarly, the formation of polymerized products that could precipitate naturally from water was faster. Under the dual-pH optimization strategy, the initial laccase activity was increased approximately 2.9-fold, and the activity remained higher for >250s, during which approximately 63.7% of the total acetaminophen was transformed into biologically inactive polymerized products, and part of these polymerized products precipitated from the water. Laccase belongs to the family of multi-copper oxidases, and the present study provides a universal method to improve the activity of multi-copper oxidases for the high-performance removal of phenol and its derivatives. Copyright © 2017 Elsevier B.V. All rights reserved.

Muon catalyzed fusion under compressive conditions

International Nuclear Information System (INIS)

Cripps, G.; Goel, B.; Harms, A.A.

1991-01-01

The viability of a symbiotic combination of Muon Catalyzed Fusion (μCF) and high density generation processes has been investigated. The muon catalyzed fusion reaction rates are formulated in the temperature and density range found under moderate compressive conditions. Simplified energy gain and power balance calculations indicate that significant energy gain occurs only if standard type deuterium-tritium (dt) fusion is ignited. A computer simulation of the hydrodynamics and fusion kinetics of a spherical deuterium-tritium pellet implosion including muons is performed. Using the muon catalyzed fusion reaction rates formulated and under ideal conditions, the pellet ignites (and thus has a significant energy gain) only if the initial muon concentration is approximately 10 17 cm -3 . The muons need to be delivered to the pellet within a very short-time (≅ 1 ns). The muon pulse required in order to make the high density and temperature muon catalyzed fusion scheme viable is beyond the present technology for muon production. (orig.) [de

Cu catalyzed oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran and 2,5-furandicarboxylic acid under benign reaction conditions

DEFF Research Database (Denmark)

Hansen, Thomas S.; Sádaba, Irantzu; Garcia, Eduardo

2013-01-01

containing promoters (NCPs) to obtain excellent yields. In acetonitrile a 95% DFF yield was obtained after 24h with ambient pressure of dioxygen at room temperature in the presence of different NCPs, which – to our knowledge – is the best result reported thus far for this reaction. The use of NCPs made...... it further possible to apply various traditional solvents, e.g. acetone, methanol and methyl isobutyl ketone for the reaction. The latter can be used as extraction solvent for HMF synthesis in aqueous media and thus integrate the two processes. Additionally, HMF was oxidized to 2,5-furandicarboxylic acid...

Synthesis and characterization of poly(lactic acid)/ montmorillonite nanocomposites by in situ polycondensation catalyzed by non-metal-based compound.

Science.gov (United States)

Kaewprapan, Kulwadee; Phattanarudee, Siriwan

2012-01-01

Poly(lactic acid)/montmorillonite nanocomposites were prepared by using non-toxic catalysts, i.e., phthalic acid and succinimide, via in situ polycondensation in presence of silicate. Concentrations of catalysts and clay were varied in a range of 0-3% wt and 0-0.5% wt, respectively. The reaction condition was controlled at 180 degrees C for 24 hr under a reduced pressure. Viscosity average molecular weight of the synthesized polymers and nanocomposites were characterized and compared using an Ubbelohde viscometer. Pattern of silicate distribution in the composites was investigated by X-ray diffraction to correlate with thermal properties evaluated by differential scanning calorimetry and thermogravimetric analysis. The results showed that the addition of catalysts at 2% wt gave the highest product yield (55-60%). The presence of silicate affected on molecular weight reduction, and the diffracted patterns suggested an intercalated structure. With a small amount of added filler, a significant improvement in thermal property and crystallinity of the resultant composites was obtained compared to those of the catalyzed polymers, in which the composites with succinimide exhibited overall better thermal stability and higher crystallinity than the ones prepared with phthalic acid.

Recent developments in gold-catalyzed cycloaddition reactions

Directory of Open Access Journals (Sweden)

Fernando López

2011-08-01

Full Text Available In the last years there have been extraordinary advances in the development of gold-catalyzed cycloaddition processes. In this review we will summarize some of the most remarkable examples, and present the mechanistic rational underlying the transformations.

Biodiesel production from esterification of free fatty acid over PA/NaY solid catalyst

International Nuclear Information System (INIS)

Liu, Wei; Yin, Ping; Zhang, Jiang; Tang, Qinghua; Qu, Rongjun

2014-01-01

Highlights: • Biodiesel production from esterification of oleic acid was catalyzed by PA/NaY. • The influences of the process operating parameters were studied. • RSM was employed to optimize the experimental conditions. • The kinetic equation of the esterification reaction was investigated. - Abstract: Because of the incitements from increasing petroleum prices, diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum fueled engines, biodiesel has been used as a substitute of the regular diesel in recent years. In this paper, biodiesel production from the esterification of the free fatty oil oleic acid with ethanol catalyzed by PA/NaY (PA = organic phosphonic acid) was investigated, and the effect of reaction conditions such as PA loading, catalyst amount, molar ratio of alcohol to acid, reaction temperature and reaction time on the esterification reaction was examined. The process optimization using response surface methodology (RSM) was performed and the interactions between the operational variables were elucidated. The optimum values for maximum conversion ratio of oleic acid could be obtained by using a Box–Behnken center-united design with a minimum of experimental work. The oleic acid conversion reached 79.51 ± 0.68% with the molar ratio of alcohol to oleic acid being 7:1 and 1.7 g PA/NaY catalyst (20 ml of PA loading) at 105 °C for 7 h. Moreover, a kinetic model for the esterification catalyzed by PA/NaY catalyst was established. By fitting the kinetic model with the experimental results, the reaction order n = 2, activation energy of the positive reaction Ea + = 43.41 kJ/mol and that of the reverse reaction Ea − = 59.74 kJ/mol were obtained

Norcoclaurine Synthase: Mechanism of an Enantioselective Pictet-Spengler Catalyzing Enzyme

Directory of Open Access Journals (Sweden)

Alberto Macone

2010-03-01

Full Text Available The use of bifunctional catalysts in organic synthesis finds inspiration in the selectivity of enzymatic catalysis which arises from the specific interactions between basic and acidic amino acid residues and the substrate itself in order to stabilize developing charges in the transition state. Many enzymes act as bifunctional catalysts using amino acid residues at the active site as Lewis acids and Lewis bases to modify the substrate as required for the given transformation. They bear a clear advantage over non-biological methods for their ability to tackle problems related to the synthesis of enantiopure compounds as chiral building blocks for drugs and agrochemicals. Moreover, enzymatic synthesis may offer the advantage of a clean and green synthetic process in the absence of organic solvents and metal catalysts. In this work the reaction mechanism of norcoclaurine synthase is described. This enzyme catalyzes the Pictet-Spengler condensation of dopamine with 4-hydroxyphenylacetaldehyde (4-HPAA to yield the benzylisoquinoline alkaloids central precursor, (S-norcoclaurine. Kinetic and crystallographic data suggest that the reaction mechanism occurs according to a typical bifunctional catalytic process.

Scavenging of free-radical metabolites of aniline xenobiotics and drugs by amino acid derivatives: toxicological implications of radical-transfer reactions.

Science.gov (United States)

Michail, Karim; Baghdasarian, Argishti; Narwaley, Malyaj; Aljuhani, Naif; Siraki, Arno G

2013-12-16

We investigated a novel scavenging mechanism of arylamine free radicals by poly- and monoaminocarboxylates. Free radicals of arylamine xenobiotics and drugs did not react with oxygen in peroxidase-catalyzed reactions; however, they showed marked oxygen uptake in the presence of an aminocarboxylate. These free-radical intermediates were identified using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and electron paramagnetic resonance (EPR) spectrometry. Diethylenetriaminepentaacetic acid (DTPA), a polyaminocarboxylate, caused a concentration-dependent attenuation of N-centered radicals produced by the peroxidative metabolism of arylamines with the subsequent formation of secondary aliphatic carbon-centered radicals stemming from the cosubstrate molecule. Analogously, N,N-dimethylglycine (DMG) and N-methyliminodiacetate (MIDA), but not iminodiacetic acid (IDA), demonstrated a similar scavenging effect of arylamine-derived free radicals in a horseradish peroxidase/H2O2 system. Using human promyelocytic leukemia (HL-60) cell lysate as a model of human neutrophils, DTPA, MIDA, and DMG readily reduced anilinium cation radicals derived from the arylamines and gave rise to the corresponding carbon radicals. The rate of peroxidase-triggered polymerization of aniline was studied as a measure of nitrogen-radical scavenging. Although, IDA had no effect on the rate of aniline polymerization, this was almost nullified in the presence of DTPA and MIDA at half of the molar concentration of the aniline substrate, whereas a 20 molar excess of DMPO caused only a partial inhibition. Furthermore, the yield of formaldehyde, a specific reaction endproduct of the oxidation of aminocarboxylates by aniline free-radical metabolites, was quantitatively determined. Azobenzene, a specific reaction product of peroxidase-catalyzed free-radical dimerization of aniline, was fully abrogated in the presence of DTPA, as confirmed by GC/MS. Under aerobic conditions, a radical-transfer reaction

Iodine-Catalyzed Isomerization of Dimethyl Muconate

Energy Technology Data Exchange (ETDEWEB)

Settle, Amy E [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Berstis, Laura R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Zhang, Shuting [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Rorrer, Nicholas [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Hu, Haiming [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Richards, Ryan [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Beckham, Gregg T [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Crowley, Michael F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Vardon, Derek R [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2018-04-12

cis,cis-Muconic acid is a platform biobased chemical that can be upgraded to drop-in commodity and novel monomers. Among the possible drop-in products, dimethyl terephthalate can be synthesized via esterification, isomerization, Diels-Alder cycloaddition, and dehydrogenation. The isomerization of cis,cis-dimethyl muconate (ccDMM) to the trans,trans-form (ttDMM) can be catalyzed by iodine; however, studies have yet to address (i) the mechanism and reaction barriers unique to DMM, and (ii) the influence of solvent, potential for catalyst recycle, and recovery of high-purity ttDMM. To address this gap, we apply a joint computational and experimental approach to investigate iodine-catalyzed isomerization of DMM. Density functional theory calculations identified unique regiochemical considerations due to the large number of halogen-diene coordination schemes. Both transition state theory and experiments estimate significant barrier reductions with photodissociated iodine. Solvent selection was critical for rapid kinetics, likely due to solvent complexation with iodine. Under select conditions, ttDMM yields of 95% were achieved in <1 h with methanol, followed by high purity recovery (>98%) with crystallization. Lastly, post-reaction iodine can be recovered and recycled with minimal loss of activity. Overall, these findings provide new insight into the mechanism and conditions necessary for DMM isomerization with iodine to advance the state-of-the-art for biobased chemicals.

Recent advances in the ruthenium(ii)-catalyzed chelation-assisted C-H olefination of substituted aromatics, alkenes and heteroaromatics with alkenes via the deprotonation pathway.

Science.gov (United States)

Manikandan, Rajendran; Jeganmohan, Masilamani

2017-08-08

The transition-metal-catalyzed chelation-assisted alkenylation at the inert C-H bond of aromatics with alkenes is one of the efficient methods to synthesize substituted vinylarenes in a highly regio- and stereoselective manner. Palladium, rhodium and ruthenium complexes are frequently used as catalysts for this type of transformation. The present review describes the recent advances in the ruthenium-catalyzed chelation-assisted alkenylation at the C-H bond of aromatics, alkenes and heteroaromatics with alkenes via the deprotonation pathway. Several directing groups including 2-pyridyl, carbonyl, amidine, amide, amine, imidate, sulphonic acid, triazole, cyano, oxazolidinone and hydontoin are widely used in the reaction. The scope, limitation and mechanistic investigation of the alkenylation reactions are discussed elaborately. This feature article includes all the reported ruthenium-catalyzed alkenylation reactions via the deprotonation pathway until the end of March 2017.

The reaction of (R)-limonene with S-thioacids

International Nuclear Information System (INIS)

Mattos, Marcio C.S. de; Bernini, Rafael Berrelho

2007-01-01

The reaction of (R)-limonene with equimolar amount of S-thioacetic or S-thiobenzoic acids in refluxing toluene proceeded regioselectively in anti-Markovnikoff fashion forming 9-[(4R, 8RS)-p-menthenyl] S-thiocarboxylates (71 and 61% yield, respectively). The montmorillonite K-10 clay-catalyzed reaction of (R)-limonene with S-thioacetic acid led to the S-thioester (65%) along with p-menthadienes and p-cymene. It was observed that K-10 clay promoted the isomerization of limonene to p-menthadienes and further disproportionation to p-cymene. (author)

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules

KAUST Repository

Guo, Lin; Rueping, Magnus

2018-01-01

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules.

Science.gov (United States)

Guo, Lin; Rueping, Magnus

2018-05-15

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules

KAUST Repository

Guo, Lin

2018-04-13

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel

Mechanistic aspects of the metal catalyzed alternating copolymerization of epoxides and carbon monoxide.

Science.gov (United States)

Allmendinger, Markus; Molnar, Ferenc; Zintl, Manuela; Luinstra, Gerrit A; Preishuber-Pflügl, Peter; Rieger, Bernhard

2005-09-05

The cobalt-catalyzed alternating copolymerization of epoxides and CO is a novel, direct approach to aliphatic polyesters, such as poly(hydroxybutyrate) (PHB). This reaction was found to be catalyzed by Ph3Si[Co(CO)4] (4) and pyridine affording in a first step the stable mono-insertion product Ph3Si-O-CH(CH3)-CH2-CO-Co(CO)4 (5). However, a profound mechanistic understanding, especially of the role of pyridine as the key component for the polymerization reaction was missing. ATR-IR online monitoring under catalytic conditions and DFT calculations were used to show that an acylpyridinium cation is formed by cleavage of the cobalt-acyl bond of 5 in the presence of pyridine. The Lewis acid thus generated activates the next incoming epoxide monomer for ring opening through [Co(CO)4]-. The catalytic cycle is completed by a subsequent CO insertion in the new cobalt-alkyl bond. The calculations are used to explore the energetic hypersurface of the polymerization reaction and are complemented by extended experimental investigations that also support the mechanistic hypotheses.

Flavin-catalyzed redox tailoring reactions in natural product biosynthesis.

Science.gov (United States)

Teufel, Robin

2017-10-15

Natural products are distinct and often highly complex organic molecules that constitute not only an important drug source, but have also pushed the field of organic chemistry by providing intricate targets for total synthesis. How the astonishing structural diversity of natural products is enzymatically generated in biosynthetic pathways remains a challenging research area, which requires detailed and sophisticated approaches to elucidate the underlying catalytic mechanisms. Commonly, the diversification of precursor molecules into distinct natural products relies on the action of pathway-specific tailoring enzymes that catalyze, e.g., acylations, glycosylations, or redox reactions. This review highlights a selection of tailoring enzymes that employ riboflavin (vitamin B2)-derived cofactors (FAD and FMN) to facilitate unusual redox catalysis and steer the formation of complex natural product pharmacophores. Remarkably, several such recently reported flavin-dependent tailoring enzymes expand the classical paradigms of flavin biochemistry leading, e.g., to the discovery of the flavin-N5-oxide - a novel flavin redox state and oxygenating species. Copyright © 2017 Elsevier Inc. All rights reserved.

Cu-catalyzed C(sp³)-H bond activation reaction for direct preparation of cycloallyl esters from cycloalkanes and aromatic aldehydes.

Science.gov (United States)

Zhao, Jincan; Fang, Hong; Han, Jianlin; Pan, Yi

2014-05-02

Cu-catalyzed dehydrogenation-olefination and esterification of C(sp(3))-H bonds of cycloalkanes with TBHP as an oxidant has been developed. The reaction involves four C-H bond activations and gives cycloallyl ester products directly from cycloalkanes and aromatic aldehydes.

Recovery of arabinan in acetic acid-catalyzed hydrothermal pretreatment on corn stover

DEFF Research Database (Denmark)

Xu, Jian; Hedegaard, Mette Christina; Thomsen, Anne Belinda

2009-01-01

Acetic acid-catalyzed hydrothermal pretreatment was done on corn stover under 195 °C, 15 min with the acetic acid ranging from 5 × 10−3 to 0.2 g g−1 corn stover. After pretreatment, the water-insoluble solids (WISs) and liquors were collected respectively. Arabinan recoveries from both WIS...... and liquors were investigated. The results indicate that there was no detectable arabinan left in the WIS when the acetic acid of 0.1 and 0.2 g g−1 corn stover were used in the pretreatment. The arabinan contents in the other WISs were not more than 10%. However, the arabinan found in the liquors...... was not covering the amount of arabinan released from the raw corn stover. For the arabinan recovery from liquor fractions, the highest of 43.57% was obtained by the pretreatment of acetic acid of 0.01 g g−1 of corn stover and the lowest was only 26.77% when the acetic acid of 0.2 g g−1 corn stover was used...

Oxidative decarboxylation of glycolic and phenylacetic acids with cerium(4) catalyzed by silver ions in the sulfuric acid media

International Nuclear Information System (INIS)

Venkatesvar Rao, G.; Nagardzhun Rao, Ch.; Sajprakash, P.K.

1981-01-01

Oxidative decarboxylation of glycolic and phenylacetic acids by cerium (4) in the presence of Ag + ions is studied. The Ce(4) order equals 1, glycolic acid order in the absence of a catalyst also equals 1 and is fractional (0.5) for a catalytic reaction. The phenylacetic acid order is fractional (0.75). The Ag + ion reaction order is fractional and constitutes 0.32 for glycolic and 0.36 for phenylacetic acids. The reaction mechanism is proposed [ru

Rhodium Catalyzed Decarbonylation

DEFF Research Database (Denmark)

Garcia Suárez, Eduardo José; Kahr, Klara; Riisager, Anders

2017-01-01

Rhodium catalyzed decarbonylation has developed significantly over the last 50 years and resulted in a wide range of reported catalyst systems and reaction protocols. Besides experimental data, literature also includes mechanistic studies incorporating Hammett methods, analysis of kinetic isotope...

Coulometric bioelectrocatalytic reactions based on NAD-dependent dehydrogenases in tricarboxylic acid cycle

Energy Technology Data Exchange (ETDEWEB)

Fukuda, Jun [Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Tsujimura, Seiya [Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)], E-mail: seiya@kais.kyoto-u.ac.jp; Kano, Kenji [Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)], E-mail: kkano@kais.kyoto-u.ac.jp

2008-12-30

This paper describes the characterization of mediated electro-enzymatic electrolysis systems based on NAD-dependent dehydrogenase reactions in the tricarboxylic acid (TCA) cycle. A micro-bulk electrolysis system with a carbon felt anode immersed in an electrolysis solution with a value of about 10 {mu}L was constructed for coulometric analysis of the substrate oxidation. Diaphorase (DI) was used to couple the NAD-dependent dehydrogenase reaction with the anode reaction of a suitable redox mediator. We focused on three types of NAD-dependant dehydrogenases reactions in this research: (1) isocitrate oxidation, in which the standard Gibbs energy change ({delta}G{sup o}') is negative; (2) {alpha}-ketoglutarate oxidation, which involves an electrochemically active coenzyme A (CoA); and (3) malate oxidation, which is thermodynamically unfavorable because of a large positive {delta}G{sup o}' value. The complete electrolysis of isocitrate was easily achieved, supporting the effective re-oxidation of NADH in the diaphorase-catalyzed electrochemical reaction. CoA was unfavorably oxidized at the electrodes in the presence of some mediators. The electrocatalytic oxidation of CoA was suppressed and the quantitative electrochemical oxidation of {alpha}-ketoglutarate was achieved by selecting a suitable mediator with negligibly slow electron transfer kinetics with CoA. The uphill malate oxidation was susceptible to product inhibition in the bioelectrochemical system, although NADH generated in the malate dehydrogenase reaction was immediately oxidized in the electrochemical system. The inhibition was successfully suppressed by linking citrate synthase to quench oxaloacetate and to make the total {delta}G{sup o}' value negative.

Coulometric bioelectrocatalytic reactions based on NAD-dependent dehydrogenases in tricarboxylic acid cycle

International Nuclear Information System (INIS)

Fukuda, Jun; Tsujimura, Seiya; Kano, Kenji

2008-01-01

This paper describes the characterization of mediated electro-enzymatic electrolysis systems based on NAD-dependent dehydrogenase reactions in the tricarboxylic acid (TCA) cycle. A micro-bulk electrolysis system with a carbon felt anode immersed in an electrolysis solution with a value of about 10 μL was constructed for coulometric analysis of the substrate oxidation. Diaphorase (DI) was used to couple the NAD-dependent dehydrogenase reaction with the anode reaction of a suitable redox mediator. We focused on three types of NAD-dependant dehydrogenases reactions in this research: (1) isocitrate oxidation, in which the standard Gibbs energy change (ΔG o ') is negative; (2) α-ketoglutarate oxidation, which involves an electrochemically active coenzyme A (CoA); and (3) malate oxidation, which is thermodynamically unfavorable because of a large positive ΔG o ' value. The complete electrolysis of isocitrate was easily achieved, supporting the effective re-oxidation of NADH in the diaphorase-catalyzed electrochemical reaction. CoA was unfavorably oxidized at the electrodes in the presence of some mediators. The electrocatalytic oxidation of CoA was suppressed and the quantitative electrochemical oxidation of α-ketoglutarate was achieved by selecting a suitable mediator with negligibly slow electron transfer kinetics with CoA. The uphill malate oxidation was susceptible to product inhibition in the bioelectrochemical system, although NADH generated in the malate dehydrogenase reaction was immediately oxidized in the electrochemical system. The inhibition was successfully suppressed by linking citrate synthase to quench oxaloacetate and to make the total ΔG o ' value negative

Vanadocene reactions with hydroxy acids

International Nuclear Information System (INIS)

Latyaeva, V.N.; Lineva, A.N.; Zimina, S.V.; Ehllert, O.G.; Arsen'eva, T.I.

1984-01-01

To prepare a series of vanadium cyclopentadienylcarboxylates soluble in water, the vanadocene reactions with lactic, γ-oxybutyric-, salicylic,- gallic-, orotic-, and acetylsalicylic acids have been studied. To determine the influence of cyclopentadienyl groups, bound with a vanadium atom, on the physiological activity of the complexes formed, vanadium halides are made to react with lactic acid. Only the vanadocene reaction with orotic acid was conducted in an aqueous medium, other interactions were realized in the diethyl ether, toluene, T, H, P medium. The interaction of vanadocene and vanadium halides with lactic-, salicylic-, acetylsalicylic- and gallic acids was found to lead to the formation of water-soluble vanadium complexes of Cp 2 , VOCOR or CpV (OCOR) 2 type. The data on the produced compounds yield, their IR spectra, decomposition temperatures, solubility, effective magnetic moments are presented

Degradation of sulfadimethoxine catalyzed by laccase with soybean meal extract as natural mediator: Mechanism and reaction pathway.

Science.gov (United States)

Liang, Shangtao; Luo, Qi; Huang, Qingguo

2017-08-01

Natural laccase-mediator systems have been well recognized as an eco-friendly and energy-saving approach in environmental remediation, whose further application is however limited by the high cost of natural mediators and relatively long treatment time span. This study evaluated the water extract of soybean meal, a low-cost compound system, in mediating the laccase catalyzed degradation of a model contaminant of emerging concern, sulfadimethoxine (SDM), and demonstrated it as a promising alternative mediator for soil and water remediation. Removal of 73.3% and 65.6% was achieved in 9 h using soybean meal extract (SBE) as the mediating system for laccase-catalyzed degradation of sulfadimethoxine at the concentration of 1 ppm and 10 ppm, respectively. Further degradation of sulfadimethoxine was observed with multiple SBE additions. Using SBE as mediator increased the 9-h removal of SDM at 1 ppm initial concentration by 52.9%, 49.4%, and 36.3% in comparison to the system mediated by 1-Hydroxybenzotriazole (HBT), p-Coumaric acid (COU) and 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), respectively. With the detection of stable coupling products formed with radical scavenger (5,5-Dimethyl-1-pyrroline N-oxide, DMPO), three phenolic compounds (vanillin, apocynin, and daidzein) in SBE were confirmed to serve as mediators for Trametes versicolor laccase. Reaction pathways were proposed based on the results of High Resolution Mass Spectrometry. SO 2 excursion happened during SDM transformation, leading to elimination of antimicrobial activity. Therefore, as a natural, phenol rich, and affordable compound system, the future application of SBE in wastewater and soil remediation is worth exploring. Copyright © 2017 Elsevier Ltd. All rights reserved.

Label-Free and Ultrasensitive Biomolecule Detection Based on Aggregation Induced Emission Fluorogen via Target-Triggered Hemin/G-Quadruplex-Catalyzed Oxidation Reaction.

Science.gov (United States)

Li, Haiyin; Chang, Jiafu; Gai, Panpan; Li, Feng

2018-02-07

Fluorescence biosensing strategy has drawn substantial attention due to their advantages of simplicity, convenience, sensitivity, and selectivity, but unsatisfactory structure stability, low fluorescence quantum yield, high cost of labeling, and strict reaction conditions associated with current fluorescence methods severely prohibit their potential application. To address these challenges, we herein propose an ultrasensitive label-free fluorescence biosensor by integrating hemin/G-quadruplex-catalyzed oxidation reaction with aggregation induced emission (AIE) fluorogen-based system. l-Cysteine/TPE-M, which is carefully and elaborately designed and developed, obviously contributes to strong fluorescence emission. In the presence of G-rich DNA along with K + and hemin, efficient destruction of l-cysteine occurs due to hemin/G-quadruplex-catalyzed oxidation reactions. As a result, highly sensitive fluorescence detection of G-rich DNA is readily realized, with a detection limit down to 33 pM. As a validation for the further development of the proposed strategy, we also successfully construct ultrasensitive platforms for microRNA by incorporating the l-cysteine/TPE-M system with target-triggered cyclic amplification reaction. Thus, this proposed strategy is anticipated to find use in basic biochemical research and clinical diagnosis.

The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

KAUST Repository

Ebner, Davidâ C.; Bagdanoff, Jeffreyâ T.; Ferreira, Ericâ M.; McFadden, Ryanâ M.; Caspi, Danielâ D.; Trend, Raissaâ M.; Stoltz, Brianâ M.

2009-01-01

The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

KAUST Repository

Ebner, Davidâ C.

2009-12-07

The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

The effects of reactants ratios, reaction temperatures and times on Maillard reaction products of the L-ascorbic acid/L-glutamic acid system

Directory of Open Access Journals (Sweden)

Yong-Yan ZHOU

2016-01-01

Full Text Available Abstract The transformation law of the Maillard reaction products with three different reactants ratios - equimolar reactants, excess L-glutamic acid and excess L-ascorbic acid reaction respectively, five different temperatures, and different time conditions for the L-ascorbic acid / L-glutamic acid system were investigated. Results showed that, the increase of the reaction time and temperature led to the increase of the browning products, uncoloured intermediate products, as well as aroma compounds. Compared with the equimolar reaction system, the excess L-ascorbic acid reaction system produced more browning products and uncoloured intermediate products, while the aroma compounds production remained the same. In the excess L-glutamic acid system, the uncoloured intermediate products increased slightly, the browning products remained the same, while the aroma compounds increased.

Synthesis of Bioactive 2-(Arylaminothiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation

Directory of Open Access Journals (Sweden)

Damien Hédou

2016-06-01

Full Text Available A library of thirty eight novel thiazolo[5,4-f]quinazolin-9(8H-one derivatives (series 8, 10, 14 and 17 was prepared via the Hügershoff reaction and a Cu catalyzed intramolecular C-S bond formation, helped by microwave-assisted technology when required. The efficient multistep synthesis of the key 6-amino-3-cyclopropylquinazolin-4(3H-one (3 has been reinvestigated and performed on a multigram scale from the starting 5-nitroanthranilic acid. The inhibitory potency of the final products was evaluated against five kinases involved in Alzheimer’s disease and showed that some molecules of the 17 series described in this paper are particularly promising for the development of novel multi-target inhibitors of kinases.

Transition Metal Catalyzed Reactions of Carbohydrates: a Nonoxidative Approach to Oxygenated Organics

Energy Technology Data Exchange (ETDEWEB)

Andrews, Mark

1997-01-08

There is a critical need for new environmentally friendly processes in the United States chemical industry as legislative and economic pressures push the industry to zero-waste and cradle-to-grave responsibility for the products they produce. Carbohydrates represent a plentiful, renewable resource, which for some processes might economically replace fossil feedstocks. While the conversion of biomass to fuels, is still not generally economical, the selective synthesis of a commodity or fine chemical, however, could compete effectively if appropriate catalytic conversion systems can be found. Oxygenated organics, found in a variety of products such as nylon and polyester, are particularly attractive targets. We believe that with concerted research efforts, homogeneous transition metal catalyzed reactions could play a significant role in bringing about this future green chemistry technology.

One-pot synthesis of 2H-pyrans by indium(III) chloride-catalyzed reactions. efficient synthesis of pyranocoumarins, pyranophenalenones, and pyranoquinolinones

International Nuclear Information System (INIS)

Lee, Yong Rok; Kim, Do Hoon; Shim, Jae Jin; Kim, Seog K.; Park, Jung Hag; Cha, Jin Soon; Lee, Chong Soon

2002-01-01

An efficient synthesis of 2H-pyrans is achieved by indium (III) chloride-catalyzed reactions of 1,3-dicarbonyl compounds with a variety of α.β-unsaturated aldehydes in moderates yields. This method has been applied to the synthesis of pyranocoumarins, pyranophenaleneones, and pyranoquinolinone alkaloids

One-pot synthesis of 2H-pyrans by indium(III) chloride-catalyzed reactions. efficient synthesis of pyranocoumarins, pyranophenalenones, and pyranoquinolinones

Energy Technology Data Exchange (ETDEWEB)

Lee, Yong Rok; Kim, Do Hoon; Shim, Jae Jin; Kim, Seog K.; Park, Jung Hag; Cha, Jin Soon; Lee, Chong Soon [Yeungnam Univ., Kyongsan (Korea, Republic of)

2002-08-01

An efficient synthesis of 2H-pyrans is achieved by indium (III) chloride-catalyzed reactions of 1,3-dicarbonyl compounds with a variety of {alpha}.{beta}-unsaturated aldehydes in moderates yields. This method has been applied to the synthesis of pyranocoumarins, pyranophenaleneones, and pyranoquinolinone alkaloids.

Rhodium-catalyzed chemo-, regio-, and enantioselective addition of 2-pyridones to terminal allenes.

Science.gov (United States)

Li, Changkun; Kähny, Matthias; Breit, Bernhard

2014-12-08

A rhodium-catalyzed chemo-, regio-, and enantioselective addition of 2-pyridones to terminal allenes to give branched N-allyl 2-pyridones is reported. Preliminary mechanistic studies support the hypothesis that the reaction was initiated from the more acidic 2-hydroxypyridine form, and the initial kinetic O-allylation product was finally converted into the thermodynamically more stable N-allyl 2-pyridones. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold-catalyzed direct alkynylation of tryptophan in peptides using TIPS-EBX

Directory of Open Access Journals (Sweden)

Gergely L. Tolnai

2016-04-01

Full Text Available The selective functionalization of peptides containing only natural amino acids is important for the modification of biomolecules. In particular, the installation of an alkyne as a useful handle for bioconjugation is highly attractive, but the use of a carbon linker is usually required. Herein, we report the gold-catalyzed direct alkynylation of tryptophan in peptides using the hypervalent iodine reagent TIPS-EBX (1-[(triisopropylsilylethynyl]-1,2-benziodoxol-3(1H-one. The reaction proceeded in 50–78% yield under mild conditions and could be applied to peptides containing other nucleophilic and aromatic amino acids, such as serine, phenylalanine or tyrosine.

KSF-supported heteropoly acids catalyzed one-pot synthesis of α ...

African Journals Online (AJOL)

In the presence of KSF-supported heteropoly acid as a heterogeneous, reusable and inexpensive catalyst, three-component reactions between aldehydes or ketones, amines, and trimethylsilyl cyanide preceded to afford α-aminonitriles in excellent yields, very short reaction times, and low loading of catalyst. This catalyst ...

Synthesis of bio-based methacrylic acid by decarboxylation of itaconic acid and citric acid catalyzed by solid transition-metal catalysts.

Science.gov (United States)

Le Nôtre, Jérôme; Witte-van Dijk, Susan C M; van Haveren, Jacco; Scott, Elinor L; Sanders, Johan P M

2014-09-01

Methacrylic acid, an important monomer for the plastics industry, was obtained in high selectivity (up to 84%) by the decarboxylation of itaconic acid using heterogeneous catalysts based on Pd, Pt and Ru. The reaction takes place in water at 200-250 °C without any external added pressure, conditions significantly milder than those described previously for the same conversion with better yield and selectivity. A comprehensive study of the reaction parameters has been performed, and the isolation of methacrylic acid was achieved in 50% yield. The decarboxylation procedure is also applicable to citric acid, a more widely available bio-based feedstock, and leads to the production of methacrylic acid in one pot in 41% selectivity. Aconitic acid, the intermediate compound in the pathway from citric acid to itaconic acid was also used successfully as a substrate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-catalyzed coupling reactions

CERN Document Server

Molnár, Árpád

2013-01-01

This handbook and ready reference brings together all significant issues of practical importance for interested readers in one single volume. While covering homogeneous and heterogeneous catalysis, the text is unique in focusing on such important aspects as using different reaction media, microwave techniques or catalyst recycling. It also provides a comprehensive treatment of modern-day coupling reactions and emphasizes those topics that show potential for future development, such as continuous flow systems, water as a reaction medium, and catalyst immobilization, among others. With i

Redox reactions of Pu(IV) and Pu(III) in the presence of acetohydroxamic acid in HNO(3) solutions.

Science.gov (United States)

Tkac, Peter; Precek, Martin; Paulenova, Alena

2009-12-21

The reduction of Pu(IV) in the presence of acetohydroxamic acid (HAHA) was monitored by vis-NIR spectroscopy. All experiments were performed under low HAHA/Pu(IV) ratios, where only the Pu(IV)-monoacetohydroxamate complex and Pu uncomplexed with HAHA were present in relevant concentrations. Time dependent concentrations of all absorbing species were resolved using molar extinction coefficients for Pu(IV), Pu(III), and the Pu(AHA)(3+) complex by deconvolution of spectra. From fitting of the experimental data by rate equations integrated by a numeric method three reactions were proposed to describe a mechanism responsible for the reduction and oxidation of plutonium in the presence of HAHA and HNO(3). Decomposition of Pu(AHA)(3+) follows a second order reaction mechanism with respect to its own concentration and leads to the formation of Pu(III). At low HAHA concentrations, a two-electron reduction of uncomplexed Pu(IV) with HAHA also occurs. Formed Pu(III) is unstable and slowly reoxidizes back to Pu(IV), which, at the point when all HAHA is decomposed, can be catalyzed by the presence of nitrous acid.

Lipase-catalyzed esterification of lactic acid with straight-chain alcohols

DEFF Research Database (Denmark)

Rønne, Torben Harald; Xu, Xuebing; Tan, Tianwei

2005-01-01

Enzymatic synthesis of esters of lactic acid and straight-chain alcohols with different chain lengths (C6–C18) were investigated in batch reactions with hexadecanol (C16) as the model alcohol. Cyclohexane was the best solvent for higher ester yields, and the best biocatalyst was the immobilized...... Candida antarctica lipase B (Novozym 435) as well as the textile-immobilized Candida sp. lipase. A method was established to obtain ester yields in the range of 71 to 82% for the different alcohols, and the most favorable conditions for the esterification reaction using Novozym 435 were an equimolar ratio...... of lactic acid to alcohol, each at a concentration of 120 mM each; a 50°C reaction temperature; 190 rpm shaking speed; and the addition of 100 mg molecular sieves (4 Å) for drying. The ester yield increased with increasing lipase load, and a yield of 79.2% could be obtained after 24 h of reaction at 20 wt...

Formation of organic acids from trace carbon in acidic oxidizing media

International Nuclear Information System (INIS)

Terrassier, C.

2003-01-01

Carbon 14 does not fully desorb as CO 2 during the hot concentrated nitric acid dissolution step of spent nuclear fuel reprocessing: a fraction is entrained in solution into the subsequent process steps as organic species. The work described in this dissertation was undertaken to identify the compounds arising from the dissolution in 3 N nitric acid of uranium carbides (selected as models of the chemical form of carbon 14 in spent fuel) and to understand their formation and dissolution mechanism. The compounds were present at traces in solution, and liquid-solid extraction on a specific stationary phase (porous graphite carbon) was selected to concentrate the monoaromatic poly-carboxylic acids including mellitic acid, which is mentioned in the literature but has not been formally identified. The retention of these species and of oxalic acid - also cited in the literature - was studied on this stationary phase as a function of the mobile phase pH, revealing an ion exchange retention mechanism similar to the one observed for benzyltrimethylammonium polystyrene resins. The desorption step was then optimized by varying the eluent pH and ionic strength. Mass spectrometry analysis of the extracts identified acetic acid, confirmed the presence of mellitic acid, and revealed compounds of high molecular weight (about 200 g/mol); the presence of oxalic acid was confirmed by combining gas chromatography and mass spectrometry. Investigating the dissolution of uranium and zirconium carbides in nitric acid provided considerable data on the reaction and suggested a reaction mechanism. The reaction is self-catalyzing via nitrous acid, and the reaction rate de pends on the acidity and nitrate ion concentration in solution. Two uranium carbide dissolution mechanisms are proposed: one involves uranium at oxidation state +IV in solution, coloring the dissolution solution dark green, and the other assumes that uranium monocarbide is converted to uranium oxide. The carboxylic acid

One-Pot Synthesis of N-(α-Peroxy)Indole/Carbazole via Chemoselective Three-Component Condensation Reaction in Open Atmosphere

KAUST Repository

Wang, Xinbo; Pan, Yupeng; Huang, Kuo-Wei; Lai, Zhiping

2015-01-01

A facile one-pot synthesis of N-(α-peroxy)indole and N-(α-peroxy)carbazole has been developed using metal-free, organo-acid-catalyzed three-component condensation reactions of indole/carbazole, aldehyde, and peroxide. Based on the reaction

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

Energy Technology Data Exchange (ETDEWEB)

Huang, Qinhua [Iowa State Univ., Ames, IA (United States)

2004-12-19

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I₂, ICl, PhSeCl, PhSCl and p-O₂NC₆H₄SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement

Metal-catalyzed asymmetric aldol reactions

Energy Technology Data Exchange (ETDEWEB)

Dias, Luiz C.; Lucca Junior, Emilio C. de; Ferreira, Marco A. B.; Polo, Ellen C., E-mail: ldias@iqm.unicamp.br [Universidade de Campinas (UNICAMP), SP (Brazil). Inst. de Quimica

2012-12-15

The aldol reaction is one of the most powerful and versatile methods for the construction of C-C bonds. Traditionally, this reaction was developed in a stoichiometric version; however, great efforts in the development of chiral catalysts for aldol reactions were performed in recent years. Thus, in this review article, the development of metal-mediated chiral catalysts in Mukaiyama-type aldol reaction, reductive aldol reaction and direct aldol reaction are discussed. Moreover, the application of these catalysts in the total synthesis of complex molecules is discussed. (author)

Bicyclic Guanidine Catalyzed Asymmetric Tandem Isomerization Intramolecular-Diels-Alder Reaction: The First Catalytic Enantioselective Total Synthesis of (+)-alpha-Yohimbine.

Science.gov (United States)

Feng, Wei; Jiang, Danfeng; Kee, Choon-Wee; Liu, Hongjun; Tan, Choon-Hong

2016-02-04

Hydroisoquinoline derivatives were prepared in moderate to good enantioselectivities via a bicyclic guanidine-catalyzed tandem isomerization intramolecular-Diels-Alder (IMDA) reaction of alkynes. With this synthetic method, the first enantioselective synthesis of (+)-alpha-yohimbine was completed in 9 steps from the IMDA products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Asymmetric Formal Aza-Diels-Alder Reaction of Trifluoromethyl Hemiaminals with Enones Catalyzed by Primary Amines.

Science.gov (United States)

Zhang, Sheng; Cha, Lide; Li, Lijun; Hu, Yanbin; Li, Yanan; Zha, Zhenggen; Wang, Zhiyong

2016-04-15

A primary amine-catalyzed asymmetric formal aza-Diels-Alder reaction of trifluoromethyl hemiaminals with enones was developed via a chiral gem-diamine intermediate. This novel protocol allowed facile access to structurally diverse trifluoromethyl-substituted piperidine scaffolds with high stereoselectivity. The utility of this method was further demonstrated through a concise approach to biologically active 4-hydroxypiperidine. More importantly, a stepwise mechanism involving an asymmetric induction process was proposed to rationalize the positive correlation between the chirality of the gem-diamine intermediate and the formal aza-Diels-Alder product.

Solvent-dependent reactions for the synthesis of β-keto-benzo-δ-sultone scaffolds via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences.

Science.gov (United States)

Ghandi, Mehdi; Bozcheloei, Abolfazl Hasani; Nazari, Seyed Hadi; Sadeghzadeh, Masoud

2011-12-16

We have developed a solvent-dependent method for the synthesis of novel benzo-δ-sultone scaffolds. A variety of benzylbenzo[e][1,2]oxathiin-4(3H)-one-2,2-dioxides were obtained in high yields in DMF using a one-pot, DBU-catalyzed condensation of 2-hydroxybenzaldehydes with a number of (E)-2-phenylethenesulfonyl chlorides. On the other hand, the initially prepared 2-formylphenyl-(E)-2-phenylethenesulfonate derivatives underwent DBU-catalyzed reactions to a series of 3-[methoxy(phenyl)methyl]benzo[e][1,2]oxathiine-2,2-dioxides in moderate to good yields in MeOH. These reactions presumably proceed via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences, respectively.

Visible-light photoredox catalyzed synthesis of pyrroloisoquinolines via organocatalytic oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade with Rose Bengal

Directory of Open Access Journals (Sweden)

Carlos Vila

2014-05-01

Full Text Available Pyrrolo[2,1-a]isoquinoline alkaloids have been prepared via a visible light photoredox catalyzed oxidation/[3 + 2] cycloaddition/oxidative aromatization cascade using Rose Bengal as an organo-photocatalyst. A variety of pyrroloisoquinolines have been obtained in good yields under mild and metal-free reaction conditions.

Biodiesel production by enzyme-catalyzed transesterification

Directory of Open Access Journals (Sweden)

Stamenković Olivera S.

2005-01-01

Full Text Available The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial application, the factors which influence the kinetics of chemically-catalysed transesterification are also considered. The advantages of lipase-catalyzed transesterification compared to the chemically-catalysed reaction, are pointed out. The cost of down-processing and ecological problems are significantly reduced by applying lipases. It was also emphasized that lipase-catalysed transesterification should be greatly improved in order to make it commercially applicable. The further optimization of lipase-catalyzed transesterification should include studies on the development of new reactor systems with immobilized biocatalysts and the addition of alcohol in several portions, and the use of extra cellular lipases tolerant to organic solvents, intracellular lipases (i.e. whole microbial cells and genetically-modified microorganisms ("intelligent" yeasts.

Cu-catalyzed aerobic oxidative cyclizations of 3-N-hydroxyamino-1,2-propadienes with alcohols, thiols, and amines to form α-O-, S-, and N-substituted 4-methylquinoline derivatives.

Science.gov (United States)

Sharma, Pankaj; Liu, Rai-Shung

2015-03-16

A one-pot, two-step synthesis of α-O-, S-, and N-substituted 4-methylquinoline derivatives through Cu-catalyzed aerobic oxidations of N-hydroxyaminoallenes with alcohols, thiols, and amines is described. This reaction sequence involves an initial oxidation of N-hydroxyaminoallenes with NuH (Nu = OH, OR, NHR, and SR) to form 3-substituted 2-en-1-ones, followed by Brønsted acid catalyzed intramolecular cyclizations of the resulting products. Our mechanistic analysis suggests that the reactions proceed through a radical-type mechanism rather than a typical nitrone-intermediate route. The utility of this new Cu-catalyzed reaction is shown by its applicability to the synthesis of several 2-amino-4-methylquinoline derivatives, which are known to be key precursors to several bioactive molecules. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

KAUST Repository

Wang, Tianli

2015-06-02

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

KAUST Repository

Wang, Tianli; Yu, Zhaoyuan; Hoon, Ding Long; Huang, Kuo-Wei; Lan, Yu; Lu, Yixin

2015-01-01

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

Lewis acid catalyzed transformations of Z-ligustilide

Energy Technology Data Exchange (ETDEWEB)

Rios, Maria Yolanda [Universidad Autonoma del Estado de Morelos, Cuernavaca, Morelos (Mexico); Delgado, Guillermo [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)

1999-08-01

Some Lewis acid mediated reactions of Z-ligustilide (1), a bioactive constituent of the medicinal species Ligusticum porteri, were investigated. These reactions provided varying mixtures of Z-butylidenephthalide (7), E-butylidenephthalide (8), n-butyphthalide (13), and novel linear dimeric phthalides (9-12) as the main products. The formation of the dimers occurred in low yields and with regio and situ-selectivity. Initial competitive O- and C- complexation of the Lewis acid with Z-ligustilide promoted the formation of the dimers occurred in low yields and with regio and situ- selectivity. Initial competitive O- and C- complexation of the Lewis acid with Z-ligustilide promoted the formation of carbocations at C(8), C(6) and C(7), which were stabilized by the addition of the C(6')-C(7') olefin of a second unit of the starting material, to provide cations at C(6') and C(7'). Subsequent isomerizations and elimination of the catalyst afforded the dimeric products 9-12. The yields and structure of the products are quite dependent on variations of the reaction conditions and the catalyst employed. [Spanish] Se investigaron algunas reacciones de Z-ligustilidas (1), un constituyente bioactivo de la planta medicinal Ligusticum porteri, catalizadas por acidos de Lewis. Estas reacciones produjeron mezclas variables de Z-butilidenftalida (7), E-butilidenftalida (8), n-butilftalida (13), y ftalidos dimetricos lineales novedosos (9-12) como productos principales. La formacion de los dimeros procedio en rendimientos bajos y con regio- y situ-selectividad. La O- y C- complejacion competitiva inicial del acido de Lewis con Z-lingustilida promueve la formacion de cationes en C(8), C(6) y C(7), los cuales son estabilizados por la adicion de la olefina C(6')-C(7') de una segunda unidad de la materia prima para generar los cationes en C(6')-C(7'). Isomerizaciones subsecuentes y la eliminacion del catalizador conducen a los productos dimericos 9

A new sol–gel synthesis of 45S5 bioactive glass using an organic acid as catalyst

Energy Technology Data Exchange (ETDEWEB)

Faure, J., E-mail: joel.faure@univ-reims.fr [Université de Reims Champagne-Ardenne, Laboratoire Ingénierie et Sciences des Matériaux, LISM EA 4695, 21 rue Clément ADER, 51685 REIMS Cedex 2 (France); Drevet, R., E-mail: richard.drevet@univ-reims.fr [Université de Reims Champagne-Ardenne, Laboratoire Ingénierie et Sciences des Matériaux, LISM EA 4695, 21 rue Clément ADER, 51685 REIMS Cedex 2 (France); Lemelle, A.; Ben Jaber, N.; Tara, A. [Université de Reims Champagne-Ardenne, Laboratoire Ingénierie et Sciences des Matériaux, LISM EA 4695, 21 rue Clément ADER, 51685 REIMS Cedex 2 (France); El Btaouri, H. [Université de Reims Champagne-Ardenne UMR CNRS MEDyC, EA 7369, Campus Moulin de la Housse, 51687 REIMS Cedex 2 (France); Benhayoune, H. [Université de Reims Champagne-Ardenne, Laboratoire Ingénierie et Sciences des Matériaux, LISM EA 4695, 21 rue Clément ADER, 51685 REIMS Cedex 2 (France)

2015-02-01

In this paper a new sol–gel approach was explored for the synthesis of the 45S5 bioactive glass. We demonstrate that citric acid can be used instead of the usual nitric acid to catalyze the sol–gel reactions. The substitution of nitric acid by citric acid allows to reduce strongly the concentration of the acid solution necessary to catalyze the hydrolysis of silicon and phosphorus alkoxides. Two sol–gel powders with chemical compositions very close to that of the 45S5 were obtained by using either a 2 M nitric acid solution or either a 5 mM citric acid solution. These powders were characterized and compared to the commercial Bioglass®. The surface properties of the two bioglass powders were assessed by scanning electron microscopy (SEM) and by Brunauer–Emmett–Teller method (BET). The Fourier transformed infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) revealed a partial crystallization associated to the formation of crystalline phases on the two sol–gel powders. The in vitro bioactivity was then studied at the key times during the first hours of immersion into acellular Simulated Body Fluid (SBF). After 4 h immersion into SBF we clearly demonstrate that the bioactivity level of the two sol–gel powders is similar and much higher than that of the commercial Bioglass®. This bioactivity improvement is associated to the increase of the porosity and the specific surface area of the powders synthesized by the sol–gel process. Moreover, the nitric acid is efficiently substituted by the citric acid to catalyze the sol–gel reactions without alteration of the bioactivity of the 45S5 bioactive glass. - Highlights: • Citric acid is employed as a catalyzer of the sol–gel process. • This catalyzer is used at a very low concentration for the hydrolysis reaction. • The chemical composition of the bioglass synthesized by the sol–gel process is optimized. • The properties of two sol–gel bioglasses are compared with those of the commercial

A new sol–gel synthesis of 45S5 bioactive glass using an organic acid as catalyst

International Nuclear Information System (INIS)

Faure, J.; Drevet, R.; Lemelle, A.; Ben Jaber, N.; Tara, A.; El Btaouri, H.; Benhayoune, H.

2015-01-01

In this paper a new sol–gel approach was explored for the synthesis of the 45S5 bioactive glass. We demonstrate that citric acid can be used instead of the usual nitric acid to catalyze the sol–gel reactions. The substitution of nitric acid by citric acid allows to reduce strongly the concentration of the acid solution necessary to catalyze the hydrolysis of silicon and phosphorus alkoxides. Two sol–gel powders with chemical compositions very close to that of the 45S5 were obtained by using either a 2 M nitric acid solution or either a 5 mM citric acid solution. These powders were characterized and compared to the commercial Bioglass®. The surface properties of the two bioglass powders were assessed by scanning electron microscopy (SEM) and by Brunauer–Emmett–Teller method (BET). The Fourier transformed infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) revealed a partial crystallization associated to the formation of crystalline phases on the two sol–gel powders. The in vitro bioactivity was then studied at the key times during the first hours of immersion into acellular Simulated Body Fluid (SBF). After 4 h immersion into SBF we clearly demonstrate that the bioactivity level of the two sol–gel powders is similar and much higher than that of the commercial Bioglass®. This bioactivity improvement is associated to the increase of the porosity and the specific surface area of the powders synthesized by the sol–gel process. Moreover, the nitric acid is efficiently substituted by the citric acid to catalyze the sol–gel reactions without alteration of the bioactivity of the 45S5 bioactive glass. - Highlights: • Citric acid is employed as a catalyzer of the sol–gel process. • This catalyzer is used at a very low concentration for the hydrolysis reaction. • The chemical composition of the bioglass synthesized by the sol–gel process is optimized. • The properties of two sol–gel bioglasses are compared with those of the commercial

Kinetics of aggregation growth with competition between catalyzed birth and catalyzed death

International Nuclear Information System (INIS)

Wang Haifeng; Gao Yan; Lin Zhenquan

2008-01-01

An aggregation growth model of three species A, B and C with the competition between catalyzed birth and catalyzed death is proposed. Irreversible aggregation occurs between any two aggregates of the like species with the constant rate kernels I n (n = 1,2,3). Meanwhile, a monomer birth of an A species aggregate of size k occurs under the catalysis of a B species aggregate of size j with the catalyzed birth rate kernel K(k,j) = Kkj v and a monomer death of an A species aggregate of size k occurs under the catalysis of a C species aggregate of size j with the catalyzed death rate kernel L(k,j)=Lkj v , where v is a parameter reflecting the dependence of the catalysis reaction rates of birth and death on the size of catalyst aggregate. The kinetic evolution behaviours of the three species are investigated by the rate equation approach based on the mean-field theory. The form of the aggregate size distribution of A species a k (t) is found to be dependent crucially on the competition between the catalyzed birth and death of A species, as well as the irreversible aggregation processes of the three species: (1) In the v k (t) satisfies the conventional scaling form; (2) In the v ≥ 0 case, the competition between the catalyzed birth and death dominates the process. When the catalyzed birth controls the process, a k (t) takes the conventional or generalized scaling form. While the catalyzed death controls the process, the scaling description of the aggregate size distribution breaks down completely

Production of Chemoenzymatic Catalyzed Monoepoxide Biolubricant: Optimization and Physicochemical Characteristics

Directory of Open Access Journals (Sweden)

Jumat Salimon

2012-01-01

Full Text Available Linoleic acid (LA is converted to per-carboxylic acid catalyzed by an immobilized lipase from Candida antarctica (Novozym 435. This per-carboxylic acid is only intermediate and epoxidized itself in good yields and almost without consecutive reactions. Monoepoxide linoleic acid 9(12-10(13-monoepoxy 12(9-octadecanoic acid (MEOA was optimized using D-optimal design. At optimum conditions, higher yield% (82.14 and medium oxirane oxygen content (OOC (4.91% of MEOA were predicted at 15 μL of H2O2, 120 mg of Novozym 435, and 7 h of reaction time. In order to develop better-quality biolubricants, pour point (PP, flash point (FP, viscosity index (VI, and oxidative stability (OT were determined for LA and MEOA. The results showed that MEOA exhibited good low-temperature behavior with PP of −41°C. FP of MEOA increased to 128°C comparing with 115°C of LA. In a similar fashion, VI for LA was 224 generally several hundred centistokes (cSt more viscous than MEOA 130.8. The ability of a substance to resist oxidative degradation is another important property for biolubricants. Therefore, LA and MEOA were screened to measure their OT which was observed at 189 and 168°C, respectively.

Reaction and catalyst engineering to exploit kinetically controlled whole-cell multistep biocatalysis for terminal FAME oxyfunctionalization.

Science.gov (United States)

Schrewe, Manfred; Julsing, Mattijs K; Lange, Kerstin; Czarnotta, Eik; Schmid, Andreas; Bühler, Bruno

2014-09-01

The oxyfunctionalization of unactivated C−H bonds can selectively and efficiently be catalyzed by oxygenase-containing whole-cell biocatalysts. Recombinant Escherichia coli W3110 containing the alkane monooxygenase AlkBGT and the outer membrane protein AlkL from Pseudomonas putida GPo1 have been shown to efficiently catalyze the terminal oxyfunctionalization of renewable fatty acid methyl esters yielding bifunctional products of interest for polymer synthesis. In this study, AlkBGTL-containing E. coli W3110 is shown to catalyze the multistep conversion of dodecanoic acid methyl ester (DAME) via terminal alcohol and aldehyde to the acid, exhibiting Michaelis-Menten-type kinetics for each reaction step. In two-liquid phase biotransformations, the product formation pattern was found to be controlled by DAME availability. Supplying DAME as bulk organic phase led to accumulation of the terminal alcohol as the predominant product. Limiting DAME availability via application of bis(2-ethylhexyl)phthalate (BEHP) as organic carrier solvent enabled almost exclusive acid accumulation. Furthermore, utilization of BEHP enhanced catalyst stability by reducing toxic effects of substrate and products. A further shift towards the overoxidized products was achieved by co-expression of the gene encoding the alcohol dehydrogenase AlkJ, which was shown to catalyze efficient and irreversible alcohol to aldehyde oxidation in vivo. With DAME as organic phase, the aldehyde accumulated as main product using resting cells containing AlkBGT, AlkL, as well as AlkJ. This study highlights the versatility of whole-cell biocatalysis for synthesis of industrially relevant bifunctional building blocks and demonstrates how integrated reaction and catalyst engineering can be implemented to control product formation patterns in biocatalytic multistep reactions. © 2014 Wiley Periodicals, Inc.

Lipase catalyzed epoxidation of fatty acid methyl esters derived from unsaturated vegetable oils in absence of carboxylic acid.

Science.gov (United States)

Sustaita-Rodríguez, Alejandro; Ramos-Sánchez, Víctor H; Camacho-Dávila, Alejandro A; Zaragoza-Galán, Gerardo; Espinoza-Hicks, José C; Chávez-Flores, David

2018-04-11

Nowadays the industrial chemistry reactions rely on green technologies. Enzymes as lipases are increasing its use in diverse chemical processes. Epoxidized fatty acid methyl esters obtained from transesterification of vegetable oils have recently found applications as polymer plasticizer, agrochemical, cosmetics, pharmaceuticals and food additives. In this research article, grapeseed, avocado and olive oils naturally containing high percents of mono and poly unsaturations were used as starting materials for the production of unsaturated fatty acid methyl esters. The effect of lauric acid as an active oxygen carrier was studied on epoxidation reactions where unsaturated fatty acid methyl esters were converted to epoxy fatty acid methyl esters using immobilized Candida antarctica Lipase type B as catalyst and hydrogen peroxide as oxygen donor at mild temperature and pressure conditions. After this study it was confirmed by 1 H NMR, 13 C NMR and GC-MS that the addition of lauric acid to the enzymatic reaction is unnecessary to transform the alkenes in to epoxides. It was found that quantitative conversions were possible in despite of a carboxylic acid absence.

Chemo- and regioselective homogeneous rhodium-catalyzed hydroamidomethylation of terminal alkenes to N-alkylamides.

Science.gov (United States)

Raoufmoghaddam, Saeed; Drent, Eite; Bouwman, Elisabeth

2013-09-01

A rhodium/xantphos homogeneous catalyst system has been developed for direct chemo- and regioselective mono-N-alkylation of primary amides with 1-alkenes and syngas through catalytic hydroamidomethylation with 1-pentene and acetamide as model substrates. For appropriate catalyst performance, it appears to be essential that catalytic amounts of a strong acid promoter, such as p-toluenesulfonic acid (HOTs), as well as larger amounts of a weakly acidic protic promoter, particularly hexafluoroisopropyl alcohol (HOR(F) ) are applied. Apart from the product N-1-hexylacetamide, the isomeric unsaturated intermediates, hexanol and higher mass byproducts, as well as the corresponding isomeric branched products, can be formed. Under optimized conditions, almost full alkene conversion can be achieved with more than 80% selectivity to the product N-1-hexylamide. Interestingly, in the presence of a relatively high concentration of HOR(F) , the same catalyst system shows a remarkably high selectivity for the formation of hexanol from 1-pentene with syngas, thus presenting a unique example of a selective rhodium-catalyzed hydroformylation-hydrogenation tandem reaction under mild conditions. Time-dependent product formation during hydroamidomethylation batch experiments provides evidence for aldehyde and unsaturated intermediates; this clearly indicates the three-step hydroformylation/condensation/hydrogenation reaction sequence that takes place in hydroamidomethylation. One likely role of the weakly acidic protic promoter, HOR(F) , in combination with the strong acid HOTs, is to establish a dual-functionality rhodium catalyst system comprised of a neutral rhodium(I) hydroformylation catalyst species and a cationic rhodium(III) complex capable of selectively reducing the imide and/or ene-amide intermediates that are in a dynamic, acid-catalyzed condensation equilibrium with the aldehyde and amide in a syngas environment. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Glutamic acid as anticancer agent: An overview

OpenAIRE

Dutta, Satyajit; Ray, Supratim; Nagarajan, K.

2013-01-01

The objective of the article is to highlight various roles of glutamic acid like endogenic anticancer agent, conjugates to anticancer agents, and derivatives of glutamic acid as possible anticancer agents. Besides these emphases are given especially for two endogenous derivatives of glutamic acid such as glutamine and glutamate. Glutamine is a derivative of glutamic acid and is formed in the body from glutamic acid and ammonia in an energy requiring reaction catalyzed by glutamine synthase. I...

Enantioselective rhodium enolate protonations. A new methodology for the synthesis of beta2-amino acids.

Science.gov (United States)

Sibi, Mukund P; Tatamidani, Hiroto; Patil, Kalyani

2005-06-23

[reaction: see text] Rhodium-catalyzed conjugate addition of an aryl boronic acid to alpha-methylamino acrylates followed by enantioselective protonation of the oxa-pi-allylrhodium intermediate provides access to aryl-substituted beta(2)-amino acids. The impact of the different variables of the reaction on the levels of enantioselectivity has been assessed.

Optimization of Two-Step Acid-Catalyzed Hydrolysis of Oil Palm Empty Fruit Bunch for High Sugar Concentration in Hydrolysate

Directory of Open Access Journals (Sweden)

Dongxu Zhang

2014-01-01

Full Text Available Getting high sugar concentrations in lignocellulosic biomass hydrolysate with reasonable yields of sugars is commercially attractive but very challenging. Two-step acid-catalyzed hydrolysis of oil palm empty fruit bunch (EFB was conducted to get high sugar concentrations in the hydrolysate. The biphasic kinetic model was used to guide the optimization of the first step dilute acid-catalyzed hydrolysis of EFB. A total sugar concentration of 83.0 g/L with a xylose concentration of 69.5 g/L and a xylose yield of 84.0% was experimentally achieved, which is in well agreement with the model predictions under optimal conditions (3% H2SO4 and 1.2% H3PO4, w/v, liquid to solid ratio 3 mL/g, 130°C, and 36 min. To further increase total sugar and xylose concentrations in hydrolysate, a second step hydrolysis was performed by adding fresh EFB to the hydrolysate at 130°C for 30 min, giving a total sugar concentration of 114.4 g/L with a xylose concentration of 93.5 g/L and a xylose yield of 56.5%. To the best of our knowledge, the total sugar and xylose concentrations are the highest among those ever reported for acid-catalyzed hydrolysis of lignocellulose.

Rh(III) -Catalyzed C-H Olefination of Benzoic Acids under Mild Conditions using Oxygen as the Sole Oxidant.

Science.gov (United States)

Jiang, Quandi; Zhu, Changlei; Zhao, Huaiqing; Su, Weiping

2016-02-04

Phthalide skeletons have been synthesized for the first time through a Rh(III) -catalyzed C-H olefination of benzoic acids under mild conditions using oxygen as the sole oxidant. Aromatic acids bearing a variety of functional groups could react with diverse alkenes to afford the desired cyclized lactones or uncyclized alkenylarenes in moderate-to-excellent yields. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lipase-catalyzed synthesis of palmitanilide: Kinetic model and antimicrobial activity study.

Science.gov (United States)

Liu, Kuan-Miao; Liu, Kuan-Ju

2016-01-01

Enzymatic syntheses of fatty acid anilides are important owing to their wide range of industrial applications in detergents, shampoo, cosmetics, and surfactant formulations. The amidation reaction of Mucor miehei lipase Lipozyme IM20 was investigated for direct amidation of triacylglycerol in organic solvents. The process parameters (reaction temperature, substrate molar ratio, enzyme amount) were optimized to achieve the highest yield of anilide. The maximum yield of palmitanilide (88.9%) was achieved after 24 h of reaction at 40 °C at an enzyme concentration of 1.4% (70 mg). Kinetics of lipase-catalyzed amidation of aniline with tripalmitin has been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The kinetic constants were estimated by using non-linear regression method using enzyme kinetic modules. The enzyme operational stability study showed that Lipozyme IM20 retained 38.1% of the initial activity for the synthesis of palmitanilide (even after repeated use for 48 h). Palmitanilide, a fatty acid amide, exhibited potent antimicrobial activity toward Bacillus cereus. Copyright © 2015 Elsevier Inc. All rights reserved.

Biodiesel forming reactions using heterogeneous catalysis

Science.gov (United States)

Liu, Yijun

Biodiesel synthesis from biomass provides a means for utilizing effectively renewable resources, a way to convert waste vegetable oils and animal fats to a useful product, a way to recycle carbon dioxide for a combustion fuel, and production of a fuel that is biodegradable, non-toxic, and has a lower emission profile than petroleum-diesel. Free fatty acid (FFA) esterification and triglyceride (TG) transesterification with low molecular weight alcohols constitute the synthetic routes to prepare biodiesel from lipid feedstocks. This project was aimed at developing a better understanding of important fundamental issues involved in heterogeneous catalyzed biodiesel forming reactions using mainly model compounds, representing part of on-going efforts to build up a rational base for assay, design, and performance optimization of solid acids/bases in biodiesel synthesis. As FFA esterification proceeds, water is continuously formed as a byproduct and affects reaction rates in a negative manner. Using sulfuric acid (as a catalyst) and acetic acid (as a model compound for FFA), the impact of increasing concentrations of water on acid catalysis was investigated. The order of the water effect on reaction rate was determined to be -0.83. Sulfuric acid lost up to 90% activity as the amount of water present increased. The nature of the negative effect of water on esterification was found to go beyond the scope of reverse hydrolysis and was associated with the diminished acid strength of sulfuric acid as a result of the preferential solvation by water molecules of its catalytic protons. The results indicate that as esterification progresses and byproduct water is produced, deactivation of a Bronsted acid catalyst like H2SO4 occurs. Using a solid composite acid (SAC-13) as an example of heterogeneous catalysts and sulfuric acid as a homogeneous reference, similar reaction inhibition by water was demonstrated for homogeneous and heterogeneous catalysis. This similarity together with

Acid-functionalized polyolefin materials and their use in acid-promoted chemical reactions

Science.gov (United States)

Oyola, Yatsandra; Tian, Chengcheng; Bauer, John Christopher; Dai, Sheng

2016-06-07

An acid-functionalized polyolefin material that can be used as an acid catalyst in a wide range of acid-promoted chemical reactions, wherein the acid-functionalized polyolefin material includes a polyolefin backbone on which acid groups are appended. Also described is a method for the preparation of the acid catalyst in which a precursor polyolefin is subjected to ionizing radiation (e.g., electron beam irradiation) of sufficient power and the irradiated precursor polyolefin reacted with at least one vinyl monomer having an acid group thereon. Further described is a method for conducting an acid-promoted chemical reaction, wherein an acid-reactive organic precursor is contacted in liquid form with a solid heterogeneous acid catalyst comprising a polyolefin backbone of at least 1 micron in one dimension and having carboxylic acid groups and either sulfonic acid or phosphoric acid groups appended thereto.

Synthesis of Phosphatidylcholine Containing Highly Unsaturated Fatty Acid by Phospholipase A2 and Effect on Retinoic Acid Induced Differentiation of HL-60 Cells

OpenAIRE

細川, 雅史; 大島, 宏哲; 甲野, 裕之; 高橋, 是太郎; 羽田野, 六男; 小田島, 粛夫

1993-01-01

Phosphatidylcholine containing highly unsaturated fatty acid (HUFA-PC) was prepared by porcine pancreatic phospholipase A2, which catalyzed esterification between lysophosphatidylcholine (LPC) and highly unsaturated fatty acid (HUFA), under a scaled-up reaction system. Fatty acid mixture prepared from sardine oil, purified eicosapentaenoic acid (EPA), and purified docosahexaenoic acid (DHA) were used as the substrates of HUFA. The yield of HUFA-PC was 17.0-19.9%. Synthesized phosphatidylcholi...

Fructose decomposition kinetics in organic acids-enriched high temperature liquid water

Energy Technology Data Exchange (ETDEWEB)

Li, Yinghua; Lu, Xiuyang; Yuan, Lei; Liu, Xin [Department of Chemical and Biochemical Engineering, Zhejiang University, Zheda Road 38, Hangzhou 310027, Zhejiang (China)

2009-09-15

Biomass continues to be an important candidate as a renewable resource for energy, chemicals, and feedstock. Decomposition of biomass in high temperature liquid water is a promising technique for producing industrially important chemicals such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid with high efficiency. Hexose, which is the hydrolysis product of cellulose, will be one of the most important starting chemicals in the coming society that is highly dependent on biomass. Taking fructose as a model compound, its decomposition kinetics in organic acids-enriched high temperature liquid water was studied in the temperature range from 180 C to 220 C under the pressure of 10 MPa to further improve reaction rate and selectivity of the decomposition reactions. The results showed that the reaction rate is greatly enhanced with the addition of organic acids, especially formic acid. The effects of temperature, residence time, organic acids and their concentrations on the conversion of fructose and yield of 5-HMF were investigated. The evaluated apparent activation energies of fructose decomposition are 126.8 {+-} 3.3 kJ mol{sup -1} without any catalyst, 112.0 {+-} 13.7 kJ mol{sup -1} catalyzed with formic acid, and 125.6 {+-} 3.8 kJ mol{sup -1} catalyzed with acetic acid, respectively, which shows no significant difference. (author)

Pentanidium-catalyzed enantioselective phase-transfer conjugate addition reactions

KAUST Repository

Ma, Ting

2011-03-09

A new chiral entity, pentanidium, has been shown to be an excellent chiral phase-transfer catalyst. The enantioselective Michael addition reactions of tert-butyl glycinate-benzophenone Schiff base with various α,β- unsaturated acceptors provide adducts with high enantioselectivities. A successful gram-scale experiment at a low catalyst loading of 0.05 mol % indicates the potential for practical applications of this methodology. Phosphoglycine ester analogues can also be utilized as the Michael donor, affording enantioenriched α-aminophosphonic acid derivatives and phosphonic analogues of (S)-proline. © 2011 American Chemical Society.

Natural separation of the acyl-CoA ligase reaction results in a non-adenylating enzyme.

Science.gov (United States)

Wang, Nan; Rudolf, Jeffrey D; Dong, Liao-Bin; Osipiuk, Jerzy; Hatzos-Skintges, Catherine; Endres, Michael; Chang, Chin-Yuan; Babnigg, Gyorgy; Joachimiak, Andrzej; Phillips, George N; Shen, Ben

2018-06-04

Acyl-coenzyme A (CoA) ligases catalyze the activation of carboxylic acids via a two-step reaction of adenylation followed by thioesterification. Here, we report the discovery of a non-adenylating acyl-CoA ligase PtmA2 and the functional separation of an acyl-CoA ligase reaction. Both PtmA1 and PtmA2, two acyl-CoA ligases from the biosynthetic pathway of platensimycin and platencin, are necessary for the two steps of CoA activation. Gene inactivation of ptmA1 and ptmA2 resulted in the accumulation of free acid and adenylate intermediates, respectively. Enzymatic and structural characterization of PtmA2 confirmed its ability to only catalyze thioesterification. Structural characterization of PtmA2 revealed it binds both free acid and adenylate substrates and undergoes the established mechanism of domain alternation. Finally, site-directed mutagenesis restored both the adenylation and complete CoA activation reactions. This study challenges the currently accepted paradigm of adenylating enzymes and inspires future investigations on functionally separated acyl-CoA ligases and their ramifications in biology.

catalyzed oxidation of formamidine derivative by hexacyanoferrate(III)

Indian Academy of Sciences (India)

Both uncatalyzed and catalyzed reactions showed first order kinetics with respect to [HCF], whereas ... The rate laws associated with the reaction mechanisms ... activation and thermodynamic parameters have been computed and discussed.

Ozonation of clofibric acid catalyzed by titanium dioxide.

Science.gov (United States)

Rosal, Roberto; Gonzalo, María S; Rodríguez, Antonio; García-Calvo, Eloy

2009-09-30

The removal of clofibric acid from aqueous solution has been investigated in catalytic and non-catalytic semicontinuous ozonation runs. Kinetic data were analyzed using second order expressions for the reaction between organics and ozone or hydroxyl radicals. Catalytic runs used a commercial titanium dioxide catalyst consisting of fumed colloidal particles. The kinetic constant of the non-catalytic ozonation of clofibric acid at pH 3 was 8.16 x 10(-3)+/-3.4 x 10(-4)L mmol(-1)s(-1). The extent of mineralization during non-catalytic runs ranged from 50% at pH 7 to 20% at pH 3 in a reaction that essentially took place during the first 10-20 min. The catalyst increased the total extent of mineralization, its effect being more important during the first part of the reaction. The pseudo-homogeneous catalytic rate constant was 2.17 x 10(-2) L mmol(-1)s(-1) at pH 3 and 6.80 x 10(-1)L mmol(-1)s(-1) at pH 5, with up to a threefold increase with respect to non-catalytic constants using catalyst load of 1g/L. A set of stopped-flow experiments were designed to elucidate the role of catalyst, whose effect was probably due to the adsorption of organics on catalytic sites rather than to the promotion of ozone decomposition.

Theoretical study on the reaction mechanisms of Michael chirality addition between propionaldehyde and nitroalkene catalyzed by an enantioselective catalyst.

Science.gov (United States)

Zhou, Xinming; Li, Ling; Sun, Xuejun; Wang, Yajun; Du, Dongmei; Fu, Hui

2018-06-01

The asymmetric Michael addition between propionaldehyde and nitroalkene catalyzed by 8-(ethoxycarbonyl)-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid has obtained relatively high yields and excellent enantioselectivities at room temperature. In this study, the molecular structures and optical activity of the most stable conformation I are optimized at B3LYP/6-311++ G(d,p) level. We find that levorotatory conformation I catalyzing the same Michael addition can produce laevo-product A and dextrorotatory conformation I' can obtain the dextral-product A'. These results have guiding significance for further studying on the new chemzymes and the mechanism of the obtained different chiral products. © 2018 Wiley Periodicals, Inc.

Kinetic Studies on the Oxidation of Some para and meta-Substituted Cinnamic Acids by Pyridinium Bromochromate in the Presence of Oxalic Acid (A Co-oxidation Study

Directory of Open Access Journals (Sweden)

G. Vanangamudi

2009-01-01

Full Text Available The kinetics of oxidation of cinnamic acids by pyridinium bromochromate (PBC in the presence of oxalic acid has been studied in acetic acid-water (60:40% medium. The reaction shows unit order dependence each with respect to oxidant as well as oxalic acid [OX], the order with respect to [H+] and [CA] are fractional. The reaction is acid catalyzed and a low dielectric constant favours the reaction. Increase the ionic strength has no effect on the reaction rate. In the case of substituted cinnamic acids the order with respect to substrate vary depending upon the nature of the substituent present in the ring. In general, the electron withdrawing substituents retard the rate while the electron releasing substituents enhance the rate of reaction. From the kinetic data obtained the activation parameters have been computed and a suitable mechanism has been proposed.

Structural Analysis of Substrate, Reaction Intermediate, and Product Binding in Haemophilus influenzae Biotin Carboxylase

Science.gov (United States)

Broussard, Tyler C.; Pakhomova, Svetlana; Neau, David B.; Bonnot, Ross; Waldrop, Grover L.

2015-01-01

Acetyl-CoA carboxylase catalyzes the first and regulated step in fatty acid synthesis. In most Gram-negative and Gram-positive bacteria, the enzyme is composed of three proteins: biotin carboxylase, a biotin carboxyl carrier protein (BCCP), and carboxyltransferase. The reaction mechanism involves two half-reactions with biotin carboxylase catalyzing the ATP-dependent carboxylation of biotin-BCCP in the first reaction. In the second reaction, carboxyltransferase catalyzes the transfer of the carboxyl group from biotin-BCCP to acetyl-CoA to form malonyl-CoA. In this report, high-resolution crystal structures of biotin carboxylase from Haemophilus influenzae were determined with bicarbonate, the ATP analogue AMPPCP; the carboxyphosphate intermediate analogues, phosphonoacetamide and phosphonoformate; the products ADP and phosphate; and the carboxybiotin analogue N1′-methoxycarbonyl biotin methyl ester. The structures have a common theme in that bicarbonate, phosphate, and the methyl ester of the carboxyl group of N1′-methoxycarbonyl biotin methyl ester all bound in the same pocket in the active site of biotin carboxylase and as such utilize the same set of amino acids for binding. This finding suggests a catalytic mechanism for biotin carboxylase in which the binding pocket that binds tetrahedral phosphate also accommodates and stabilizes a tetrahedral dianionic transition state resulting from direct transfer of CO2 from the carboxyphosphate intermediate to biotin. PMID:26020841

Supercritical CO2 as a reaction medium for synthesis of capsaicin analogues by lipase-catalyzed transacylation of capsaicin.

Science.gov (United States)

Kobata, Kenji; Kobayashi, Mamiko; Kinpara, Sachiyo; Watanabe, Tatsuo

2003-09-01

Capsaicin analogues having different acyl moiety were synthesized by lipase-catalyzed transacylation of capsaicin with a corresponding acyl donor in supercritical CO2 as a reaction medium. Transacylation with methyl tetradecanoate using Novozym 435 as a catalyst gave vanillyl tetradecanamide in a 54% yield at 80 degrees C and 19 MPa over 72 h. Vanillyl (Z)-9-octadecenamide, olvanil, was synthesized from triolein in a 21% yield over 7 d.

catalyzed oxidation of formamidine derivative by hexacyanoferrate(III

Indian Academy of Sciences (India)

triazol-3-yl) formamidine (ATF) by hexacyanoferrate(III) (HCF) was studied spectrophotometrically in aqueous alkalinemedium. Both uncatalyzed and catalyzed reactions showed first order kinetics with respect to [HCF],whereas the reaction ...

Kinetics and mechanism of oxidation of acetanilide by quinquevalent vanadium in acid medium

International Nuclear Information System (INIS)

Gupta, R.

1990-01-01

The kinetics of the oxidation of acetanilide with vanadium(V) in sulphuric acid medium at constant ionic strength has been studied. The reaction is first order with oxidant. The order of reaction in acetanilide varies from one to zero. The reaction follows an acid catalyzed independent path, exhibiting square dependence in H + . A Bunnett plot indicates that the water acts as a nucleophile. The thermodynamic parameters have been computed. A probable reaction mechanism and rate law consistent with these data are given. (Author)

MOLYBDENUM CATALYZED ACID PEROXIDE BLEACHING OF EUCALYPTUS KRAFT PULP

Directory of Open Access Journals (Sweden)

Marcos S. Rabelo

2008-08-01

Full Text Available Molybdenum catalyzed peroxide bleaching (PMo Stage consists of pulp treatment with hydrogen peroxide under acidic conditions in the presence of a molybdenum catalyst. Molybdenum is applied in catalytic doses (50-200 mg/kg pulp and may originate from various sources, including (NH46Mo7O24.4H2O, Na2MoO4.2H2O, siliconmolybdate, etc. This work is aimed at optimizing the PMo stage and evaluating its industrial application in the OAZDP sequence. Optimum PMo stage conditions for bleaching eucalyptus pulp were 90 ºC, pH 3.5, 2 h, 0.1 kg/adt Mo and 5 kg/adt H2O2. The PMo stage was more efficient to remove pulp hexenuronic acids than lignin. Its efficiency decreased with increasing pH in the range of 1.5-5.5, while it increased with increasing temperature and peroxide and molybdenum doses. The application of the PMo stage as replacement for the A-stage of the AZDP sequence significantly decreased chlorine dioxide demand. The PMo stage caused a decrease of 20-30% in the generation of organically bound chlorine. The quality parameters of the pulp produced during the PMo stage mill trial were comparable to those obtained with the reference A-stage.

First catalytic hetero-Diels-Alder reaction of imidazole-2-thiones and in silico biological evaluation of the cycloadducts

NARCIS (Netherlands)

Eleftheriadis, Nikolaos; Samatidou, Evanthia; Neochoritis, Constantinos G.

The Lewis acid-catalyzed Diels-Alder reactions of suitably substituted imidazole-2-thiones with dienes were studied. It was found that the electron density of the imidazole core influenced the reaction, since electron withdrawing groups led to the novel spiro-derivatives 2 whereas electron donating

Manganese Catalyzed C–H Halogenation

Energy Technology Data Exchange (ETDEWEB)

Liu, Wei; Groves, John T.

2015-06-16

The remarkable aliphatic C–H hydroxylations catalyzed by the heme-containing enzyme, cytochrome P450, have attracted sustained attention for more than four decades. The effectiveness of P450 enzymes as highly selective biocatalysts for a wide range of oxygenation reactions of complex substrates has driven chemists to develop synthetic metalloporphyrin model compounds that mimic P450 reactivity. Among various known metalloporphyrins, manganese derivatives have received considerable attention since they have been shown to be versatile and powerful mediators for alkane hydroxylation and olefin epoxidation. Mechanistic studies have shown that the key intermediates of the manganese porphyrin-catalyzed oxygenation reactions include oxo- and dioxomanganese(V) species that transfer an oxygen atom to the substrate through a hydrogen abstraction/oxygen recombination pathway known as the oxygen rebound mechanism. Application of manganese porphyrins has been largely restricted to catalysis of oxygenation reactions until recently, however, due to ultrafast oxygen transfer rates. In this Account, we discuss recently developed carbon–halogen bond formation, including fluorination reactions catalyzed by manganese porphyrins and related salen species. We found that biphasic sodium hypochlorite/manganese porphyrin systems can efficiently and selectively convert even unactivated aliphatic C–H bonds to C–Cl bonds. An understanding of this novel reactivity derived from results obtained for the oxidation of the mechanistically diagnostic substrate and radical clock, norcarane. Significantly, the oxygen rebound rate in Mn-mediated hydroxylation is highly correlated with the nature of the trans-axial ligands bound to the manganese center (L–Mn^V$=$O). Based on the ability of fluoride ion to decelerate the oxygen rebound step, we envisaged that a relatively long-lived substrate radical could be trapped by a Mn–F fluorine source, effecting carbon–fluorine bond

Graphene-Based Nanomaterials as Heterogeneous Acid Catalysts: A Comprehensive Perspective

Directory of Open Access Journals (Sweden)

Bhaskar Garg

2014-09-01

Full Text Available Acid catalysis is quite prevalent and probably one of the most routine operations in both industrial processes and research laboratories worldwide. Recently, “graphene”, a two dimensional single-layer carbon sheet with hexagonal packed lattice structure, imitative of nanomaterials, has shown great potential as alternative and eco-friendly solid carbocatalyst for a variety of acid-catalyzed reactions. Owing to their exceptional physical, chemical, and mechanical properties, graphene-based nanomaterials (G-NMs offer highly stable Brønsted acidic sites, high mass transfer, relatively large surface areas, water tolerant character, and convenient recoverability as well as recyclability, whilst retaining high activity in acid-catalyzed chemical reactions. This comprehensive review focuses on the chemistry of G-NMs, including their synthesis, characterization, properties, functionalization, and up-to-date applications in heterogeneous acid catalysis. In line with this, in certain instances readers may find herein some criticisms that should be taken as constructive and would be of value in understanding the scope and limitations of current approaches utilizing graphene and its derivatives for the same.

Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilylmethylaniline with cyclic α,β-unsaturated carbonyl compounds

Directory of Open Access Journals (Sweden)

Dominik Lenhart

2014-04-01

Full Text Available N-Methyl-N-((trimethylsilylmethylaniline was employed as reagent in visible-light-induced, iridium-catalyzed addition reactions to cyclic α,β-unsaturated carbonyl compounds. Typical reaction conditions included the use of one equivalent of the reaction substrate, 1.5 equivalents of the aniline and 2.5 mol % (in MeOH or 1.0 mol % (in CH2Cl2 [Ir(ppy2(dtbbpy]BF4 as the catalyst. Two major reaction products were obtained in combined yields of 30–67%. One product resulted from aminomethyl radical addition, the other product was a tricyclic compound, which is likely formed by attack of the intermediately formed α-carbonyl radical at the phenyl ring. For five-membered α,β-unsaturated lactone and lactam substrates, the latter products were the only products isolated. For the six-membered lactones and lactams and for cyclopentenone the simple addition products prevailed.

Studies on the reaction of nitric acid and sugar

International Nuclear Information System (INIS)

MacDougall, C.S.; Bayne, C.K.; Roberson, R.B.

1982-01-01

The design of vessels and off-gas systems for denitrating acidic radioactive process solutions by reacting nitric acid with sugar requires a fairly accurate determination of the rate of the controlling step. Therefore, the reaction of sugar with concentrated nitric acid was closely examined at temperatures of 100 and 110 0 C and in the presence of low levels of iron )0 to 0.2 M Fe(III)). Efficiencies of the sugar destruction by nitric acid ranged from 2.56 to 2.93 mol of acid consumed per mole of carbon added. Product off-gases were examined throughout the reaction. Release of CO was fairly constant throughout the reaction, but amounts of CO 2 increased as the nitric acid began to attack the terminal carboxylic acids produced from the consumption of sucrose. Voluminous quantities of NO 2 were released at the beginning of the reaction, but larger relative concentrations of NO were observed toward the end

Study of the electrocatalytic oxidation of Ethanol over platinum in medium acid

International Nuclear Information System (INIS)

Hoyos, Bibian; Gonzalez, Javier; Sanchez, Carlos

2002-01-01

Electro-catalytic oxidation of ethanol on platinum surfaces in sulfuric acid solutions at different temperatures and concentrations was studied by cyclic voltammetry. The results shown that there is ethanol adsorption at potentials below 0.4V (vs. RHE) with electrode coverage fraction for residues of 0.3 or less. There are also, two irreversible oxidation reactions. Former reaction seems be catalyzed by Pt(OH) species with electronic charge transfer control and the second reaction seems be catalyzed by Pt(OH) 4 with diffusion control while Pt(OH) 2 does not have catalytic activity. The activity and selectivity for total oxidation increases with ethanol concentration and temperature. Finally, a reaction mechanism, which explains the obtained data, is proposed

Iron-catalyzed intermolecular cycloaddition of diazo surrogates with hexahydro-1,3,5-triazines.

Science.gov (United States)

Liu, Pei; Zhu, Chenghao; Xu, Guangyang; Sun, Jiangtao

2017-09-26

We report here an unprecedented iron-catalyzed cycloaddition reaction of diazo surrogates with hexahydro-1,3,5-triazines, providing five-membered heterocycles in moderate to high yields under mild reaction conditions. This cycloaddition features C-N and C-C bond formation using a cheap iron catalyst. Importantly, different to our former report on a gold-catalyzed system, both donor/donor and donor/acceptor diazo substrates are tolerated in this iron-catalyzed protocol.

Cu-catalyzed esterification reaction via aerobic oxygenation and C-C bond cleavage: an approach to α-ketoesters.

Science.gov (United States)

Zhang, Chun; Feng, Peng; Jiao, Ning

2013-10-09

The Cu-catalyzed novel aerobic oxidative esterification reaction of 1,3-diones for the synthesis of α-ketoesters has been developed. This method combines C-C σ-bond cleavage, dioxygen activation and oxidative C-H bond functionalization, as well as provides a practical, neutral, and mild synthetic approach to α-ketoesters which are important units in many biologically active compounds and useful precursors in a variety of functional group transformations. A plausible radical process is proposed on the basis of mechanistic studies.

Metal-catalyzed living radical polymerization and radical polyaddition for precision polymer synthesis

Energy Technology Data Exchange (ETDEWEB)

Mizutani, M; Satoh, K [Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kamigaito, M, E-mail: kamigait@apchem.nagoya-u.ac.j

2009-08-01

The metal-catalyzed radical addition reaction can be evolved into two different polymerization mechanisms, i.e.; chain- and step-growth polymerizations, while both the polymerizations are based on the same metal-catalyzed radical formation reaction. The former is a widely employed metal-catalyzed living radical polymerization or atom transfer radical polymerization of common vinyl monomers, and the latter is a novel metal-catalyzed radical polyaddition of designed monomer with an unconjugated C=C double bond and a reactive C-Cl bond in one molecule. The simultaneous ruthenium-catalyzed living radical polymerization of methyl acrylate and radical polyaddition of 3-butenyl 2-chloropropionate was achieved with Ru(Cp*)Cl(PPh{sub 3}){sub 2} to afford the controlled polymers, in which the homopolymer segments with the controlled chain length were connected by the ester linkage.

Transesterification of oil mixtures catalyzed by microencapsulated cutinase in reversed micelles.

Science.gov (United States)

Badenes, Sara M; Lemos, Francisco; Cabral, Joaquim M S

2010-03-01

Recombinant cutinase from Fusarium solani pisi was used to catalyze the transesterification reaction between a mixture of triglycerides (oils) and methanol in reversed micelles of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane for the purposes of producing biodiesel. The use of a bi-phase lipase-catalyzed system brings advantages in terms of catalyst re-use and the control of water activity in the medium and around the enzyme micro-environment. Small-scale batch studies were performed to study the influence of the initial enzyme and alcohol concentrations, and the substrates molar ratio. Conversions in excess of 75 were obtained with reaction times under 24 h, which makes this enzymatic process highly competitive when compared to similar lipase catalyzed reactions for biodiesel production using methanol.

Reaction of acid esters of methylenebis(phosphonous acid) with carbonyl compounds

International Nuclear Information System (INIS)

Novikova, Z.S.; Odinets, I.L.; Lutsenko, I.F.

1987-01-01

The reaction of methylenebis(phosphonites) containing two hydrophosphoryl groupings with aliphatic and aromatic aldehydes and ketones in the presence of alkali metal fluorides leads to methylenebis(α-hydroxyalkylphosphinates). The reaction of methylenebis(phosphonites) containing one hydrophosphoryl groupings with carbonyl compounds in the presence of alkali metal fluorides proceeds with the formation of a new type of heterocyclic phosphorus compound, viz., 1,2λ 3 ,4λ 5 -oxadiphospholanes. The reaction of acid esters of methylenebis(phosphonous) acid with carbonyl compounds in the presence of alkali metal alkoxides or a tertiary amine is accompanied by phosphinate-phosphonate rearrangement of the intermediately formed α-hydroxylalkylphosphinates

A trifunctional mesoporous silica-based, highly active catalyst for one-pot, three-step cascade reactions.

Science.gov (United States)

Biradar, Ankush V; Patil, Vijayshinha S; Chandra, Prakash; Doke, Dhananjay S; Asefa, Tewodros

2015-05-18

We report the synthesis of a trifunctional catalyst containing amine, sulphonic acid and Pd nanoparticle catalytic groups anchored on the pore walls of SBA-15. The catalyst efficiently catalyzes one-pot three-step cascade reactions comprising deacetylation, Henry reaction and hydrogenation, giving up to ∼100% conversion and 92% selectivity to the final product.

Kinetic Behavior of Aggregation-Exchange Growth Process with Catalyzed-Birth

International Nuclear Information System (INIS)

Han Anjia; Chen Yu; Lin Zhenquan; Ke Jianhong

2007-01-01

We propose an aggregation model of a two-species system to mimic the growth of cities' population and assets, in which irreversible coagulation reactions and exchange reactions occur between any two aggregates of the same species, and the monomer-birth reactions of one species occur by the catalysis of the other species. In the case with population-catalyzed birth of assets, the rate kernel of an asset aggregate B k of size k grows to become an aggregate B k+1 through a monomer-birth catalyzed by a population aggregate A j of size j is J(k,j) = Jkj λ . And in mutually catalyzed birth model, the birth rate kernels of population and assets are H(k,j) = Hkj η and J(k,j) = Jkj λ , respectively. The kinetics of the system is investigated based on the mean-field theory. In the model of population-catalyzed birth of assets, the long-time asymptotic behavior of the assets aggregate size distribution obeys the conventional or modified scaling form. In mutually catalyzed birth system, the asymptotic behaviors of population and assets obey the conventional scaling form in the case of η = λ = 0, and they obey the modified scaling form in the case of η = 0,λ = 1. In the case of η = λ = 1, the total mass of population aggregates and that of asset aggregates both grow much faster than those in population-catalyzed birth of assets model, and they approaches to infinite values in finite time.

KSF-supported heteropoly acids catalyzed one-pot synthesis of α-aminonitriles

Directory of Open Access Journals (Sweden)

Ezzat Rafiee

2010-08-01

Full Text Available In the presence of KSF-supported heteropoly acid as a heterogeneous, reusable and inexpensive catalyst, three-component reactions between aldehydes or ketones, amines, and trimethylsilyl cyanide preceded to afford α-aminonitriles in excellent yields, very short reaction times, and low loading of catalyst. This catalyst was highly selective and other functional groups including carbon-carbon double bond, and heterocyclic moieties did not affect the reaction.

Roles of the redox-active disulfide and histidine residues forming a catalytic dyad in reactions catalyzed by 2-ketopropyl coenzyme M oxidoreductase/carboxylase.

Science.gov (United States)

Kofoed, Melissa A; Wampler, David A; Pandey, Arti S; Peters, John W; Ensign, Scott A

2011-09-01

NADPH:2-ketopropyl-coenzyme M oxidoreductase/carboxylase (2-KPCC), an atypical member of the disulfide oxidoreductase (DSOR) family of enzymes, catalyzes the reductive cleavage and carboxylation of 2-ketopropyl-coenzyme M [2-(2-ketopropylthio)ethanesulfonate; 2-KPC] to form acetoacetate and coenzyme M (CoM) in the bacterial pathway of propylene metabolism. Structural studies of 2-KPCC from Xanthobacter autotrophicus strain Py2 have revealed a distinctive active-site architecture that includes a putative catalytic triad consisting of two histidine residues that are hydrogen bonded to an ordered water molecule proposed to stabilize enolacetone formed from dithiol-mediated 2-KPC thioether bond cleavage. Site-directed mutants of 2-KPCC were constructed to test the tenets of the mechanism proposed from studies of the native enzyme. Mutagenesis of the interchange thiol of 2-KPCC (C82A) abolished all redox-dependent reactions of 2-KPCC (2-KPC carboxylation or protonation). The air-oxidized C82A mutant, as well as wild-type 2-KPCC, exhibited the characteristic charge transfer absorbance seen in site-directed variants of other DSOR enzymes but with a pK(a) value for C87 (8.8) four units higher (i.e., four orders of magnitude less acidic) than that for the flavin thiol of canonical DSOR enzymes. The same higher pK(a) value was observed in native 2-KPCC when the interchange thiol was alkylated by the CoM analog 2-bromoethanesulfonate. Mutagenesis of the flavin thiol (C87A) also resulted in an inactive enzyme for steady-state redox-dependent reactions, but this variant catalyzed a single-turnover reaction producing a 0.8:1 ratio of product to enzyme. Mutagenesis of the histidine proximal to the ordered water (H137A) led to nearly complete loss of redox-dependent 2-KPCC reactions, while mutagenesis of the distal histidine (H84A) reduced these activities by 58 to 76%. A redox-independent reaction of 2-KPCC (acetoacetate decarboxylation) was not decreased for any of the

Acid-catalyzed rearrangements of flavans to novelbenzofuran derivatives

Science.gov (United States)

Richard W. Hemingway; Weiling Peng; Anthony H. Conner; Petrus J. Steynberg; Jan P. Steynberg

1998-01-01

The objective of this work was to define reactions that occur when proanthocyanidins and their derivatives are reacted in the presence of acid catalysts. Pure compounds (either as the free phenols, the methyl ether, or the methyl ether-acetate derivatives) were isolated by a variety of chromatographic methods. Proof of their structure was based mainly on 2D-NMR, as...

Iridium‐Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

DEFF Research Database (Denmark)

Olsen, Esben Paul Krogh; Madsen, Robert

2012-01-01

A new iridium‐catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)2Cl]2 (coe=cyclooct......A new iridium‐catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)2Cl]2 (coe...... to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation...

Ionizing radiation induced attachment reactions of nucleic acids and their components

International Nuclear Information System (INIS)

Myers, L.S. Jr.

1975-01-01

An extensive bibliographic review is given of experimental and theoretical data on radiation-induced attachment reactions of nucleic acids and their components. Mechanisms of these reactions are reviewed. The reactions with water, formate, and alcohols, with amines and other small molecules, and with radiation sensitizers and nucleic acid-nucleic acid reactions are discussed. Studies of the reaction mechanisms show that many of the reactions occur by radical-molecule reactions, but radical-radical reactions also occur. Radiation modifiers become attached to nucleic acids in vitro and in vivo and there are indications that attachment may be necessary for the action of some sensitizers. (U.S.)

Preparation of acid-base bifunctional mesoporous KIT-6 (KIT: Korea Advanced Institute of Science and Technology) and its catalytic performance in Knoevenagel reaction

International Nuclear Information System (INIS)

Xu, Ling; Wang, Chunhua; Guan, Jingqi

2014-01-01

Acid-base bifunctional mesoporous catalysts Al-KIT-6-NH 2 containing different aluminum content have been synthesized through post synthetic grafting method. The materials were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM), transmission electron micrographs (TEM), Fourier-transform infrared spectroscopy (FTIR), IR spectra of pyridine adsorption, NH 3 -TPD and TG analysis. The characterization results indicated that the pore structure of KIT-6 was well kept after the addition of aluminum and grafting of aminopropyl groups. The acid amount of Al-KIT-6 increased with enhancing aluminum content. Catalytic results showed that weak acid and weak base favor the Knoevenagel reaction, while catalysts with strong acid and weak base exhibited worse catalytic behavior. - Graphical abstract: The postulated steps of mechanism for the acid-base catalyzed process are as follows: (1) the aldehyde gets activated by the surface acidic sites which allow the amine undergoes nucleophilic to attack the carbonyl carbon of benzaldehyde. (2) Water is released in the formation of imine intermediate. (3) The ethyl cyanoacetate reacts with the intermediate. (4) The benzylidene ethyl cyanoacetate is formed and the amine is regenerated. - Highlights: • KIT-6 and Al-KIT-6-NH 2 with different Si/Al ratios has been successfully prepared. • 79.4% Yield was obtained over 46-Al-KIT-6-NH 2 within 20 min in Knoevenagel reaction. • Low Al-content Al-KIT-6-NH 2 shows better catalytic stability than high Al-content catalysts. • There is acid-base synergistic effect in Knoevenagel reaction

Preparation of acid-base bifunctional mesoporous KIT-6 (KIT: Korea Advanced Institute of Science and Technology) and its catalytic performance in Knoevenagel reaction

Energy Technology Data Exchange (ETDEWEB)

Xu, Ling [College of Chemistry and Chemical Engineering, Inner Mongolia University for Nationalities, Tongliao 028000 (China); Wang, Chunhua [Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University, Changchun 130023 (China); Guan, Jingqi, E-mail: guanjq@jlu.edu.cn [Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University, Changchun 130023 (China)

2014-05-01

Acid-base bifunctional mesoporous catalysts Al-KIT-6-NH{sub 2} containing different aluminum content have been synthesized through post synthetic grafting method. The materials were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM), transmission electron micrographs (TEM), Fourier-transform infrared spectroscopy (FTIR), IR spectra of pyridine adsorption, NH{sub 3}-TPD and TG analysis. The characterization results indicated that the pore structure of KIT-6 was well kept after the addition of aluminum and grafting of aminopropyl groups. The acid amount of Al-KIT-6 increased with enhancing aluminum content. Catalytic results showed that weak acid and weak base favor the Knoevenagel reaction, while catalysts with strong acid and weak base exhibited worse catalytic behavior. - Graphical abstract: The postulated steps of mechanism for the acid-base catalyzed process are as follows: (1) the aldehyde gets activated by the surface acidic sites which allow the amine undergoes nucleophilic to attack the carbonyl carbon of benzaldehyde. (2) Water is released in the formation of imine intermediate. (3) The ethyl cyanoacetate reacts with the intermediate. (4) The benzylidene ethyl cyanoacetate is formed and the amine is regenerated. - Highlights: • KIT-6 and Al-KIT-6-NH{sub 2} with different Si/Al ratios has been successfully prepared. • 79.4% Yield was obtained over 46-Al-KIT-6-NH{sub 2} within 20 min in Knoevenagel reaction. • Low Al-content Al-KIT-6-NH{sub 2} shows better catalytic stability than high Al-content catalysts. • There is acid-base synergistic effect in Knoevenagel reaction.

Specific acid catalysis and Lewis acid catalysis of Diels–Alder reactions in aqueous media

NARCIS (Netherlands)

Mubofu, Egid B.; Engberts, Jan B.F.N.

2004-01-01

A comparative study of specific acid catalysis and Lewis acid catalysis of Diels–Alder reactions between dienophiles (1, 4 and 6) and cyclopentadiene (2) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas

Specific acid catalysis and Lewis acid catalysis of Diels-Alder reactions in aqueous media

NARCIS (Netherlands)

Mubofu, E.B.; Engberts, J.B.F.N.

A comparative study of specific acid catalysis and Lewis acid catalysis of Diells-Alder reactions between dienophiles (1, 4 and 6) and cyclopentadiene (2) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas

Boric Acid Catalyzed Convenient Synthesis of Benzimidazoles in Aqueous Media

Directory of Open Access Journals (Sweden)

Mohammad Reza Poor Heravi

2013-01-01

Full Text Available Synthesis of benzimidazoles has been developed by the o-phenylenediamine with aldehydes using boric acid an efficient catalyst under mild reaction conditions in aqueous media. The product is applicable to aryl and heteroaryl aldehydes. This reaction led to the formation of benzimidazoles new derivatives in good yields. The FT-IR, 19F-NMR, 1H-NMR, 13C-NMR spectra and elemental analysis confirm the structure of compounds.

Boric Acid Catalyzed Convenient Synthesis of Benzimidazoles in Aqueous Media

OpenAIRE

Poor Heravi, Mohammad Reza; Ashori, Marjan

2013-01-01

Synthesis of benzimidazoles has been developed by the o-phenylenediamine with aldehydes using boric acid an efficient catalyst under mild reaction conditions in aqueous media. The product is applicable to aryl and heteroaryl aldehydes. This reaction led to the formation of benzimidazoles new derivatives in good yields. The FT-IR, 19F-NMR, 1H-NMR, 13C-NMR spectra and elemental analysis confirm the structure of compounds.

Study on the Hydrolysis Kinetics of Xylan on Different Acid Catalysts

Energy Technology Data Exchange (ETDEWEB)

Na, Byeong-Il; Lee, Jae-Won [Chonnam National University, Gwangju (Korea, Republic of)

2014-04-15

In this study, we investigated kinetic model for the acid-catalyzed xylan hydrolysis at temperature 120-150 .deg. C. Also, we analyzed the kinetic parameters for xylose production and furfural decomposition. The hydrolysis of xylan and the degradation of xylose were promoted by high reaction temperature and acid concentration. The optimal hydrolysis condition for the highest reaction rate constants (k{sub 1}) was different depending on the acid catalysts. Among sulfuric, oxalic and maleic acid, the xylan reaction rate constants (k{sub 1}) to xylose had the highest value of 0.0241 min{sup -1} when 100 mM sulfuric acid was used at 120 .deg. C. However, sulfuric acid induced more xylose degradation compared to oxalic and maleic acid hydrolysis. The activation energy for xylan degradation was the highest when sulfuric acid was used.

General synthesis of C-glycosyl amino acids via proline-catalyzed direct electrophilic alpha-amination of C-glycosylalkyl aldehydes.

Science.gov (United States)

Nuzzi, Andrea; Massi, Alessandro; Dondoni, Alessandro

2008-10-16

Non-natural axially and equatorially linked C-glycosyl alpha-amino acids (glycines, alanines, and CH2-serine isosteres) with either S or R alpha-configuration were prepared by D- and L-proline-catalyzed (de >95%) alpha-amination of C-glycosylalkyl aldehydes using dibenzyl azodicarboxylate as the electrophilic reagent.

Copper-catalyzed oxidative desulfurization-oxygenation of thiocarbonyl compounds using molecular oxygen: an efficient method for the preparation of oxygen isotopically labeled carbonyl compounds.

Science.gov (United States)

Shibahara, Fumitoshi; Suenami, Aiko; Yoshida, Atsunori; Murai, Toshiaki

2007-06-21

A novel copper-catalyzed oxidative desulfurization reaction of thiocarbonyl compounds, using molecular oxygen as an oxidant and leading to formation of carbonyl compounds, has been developed, and the utility of the process is demonstrated by its application to the preparation of a carbonyl-18O labeled sialic acid derivative.

The browning kinetics of the non-enzymatic browning reaction in L-ascorbic acid/basic amino acid systems

Directory of Open Access Journals (Sweden)

Ai-Nong YU

Full Text Available Abstract Under the conditions of weak basis and the reaction temperature range of 110-150 °C, lysine, arginine and histidine were reacted with L-ascorbic acid at equal amount for 30-150 min, respectively and the formation of browning products was monitored with UV–vis spectrometry. The kinetic characteristics of their non-enzymatic browning reaction were investigated. The study results indicated that the non-enzymatic browning reaction of these three amino acids with L-ascorbic acid to form browning products was zero-order reaction. The apparent activation energies for the formation of browning products from L-ascorbic acid/lysine, L-ascorbic acid/arginine and L-ascorbic acid/histidine systems were 54.94, 50.08 and 35.31kJ/mol. The activation energy data indicated the degree of effects of reaction temperature on non-enzymatic browning reaction. Within the temperature range of 110-150 °C, the reaction rate of L-ascorbic acid/lysine system was the fastest one, followed by that of the L-ascorbic acid/arginine system. The reaction rate of L-ascorbic acid/histidine system was the slowest one. Based on the observed kinetic data, the formation mechanisms of browning products were proposed.

Ultrasound-assisted self-metathesis reactions of monounsaturated fatty acids

Directory of Open Access Journals (Sweden)

Elmkaddem Mohammed Kamal

2016-09-01

Full Text Available An efficient protocol for the self-metathesis of oleic acid, using ruthenium catalysts is described. The self-metathesis reaction under ultrasonic activation allows the conversion of monoenic fatty acids such as oleic acid, elaidic acid and erucic acid into diacids and olefins with very short reaction times in the presence of Grubbs ruthenium catalysts. These yields and selectivity towards the desired products are influenced by the nature of solvents. This study demonstrated that metathesis reaction carried out in DCM or 1-butanol showed promising results, since it produced a variety of products, like n-alkenes and diacids with good yields (45–75% and high selectivities (75–95%.

The crystal structure of tryptophan hydroxylase with bound amino acid substrate

DEFF Research Database (Denmark)

Windahl, Michael Skovbo; Petersen, Charlotte Rode; Christensen, Hans Erik Mølager

2008-01-01

Tryptophan hydroxylase (TPH) is a mononuclear non-heme iron enzyme, which catalyzes the reaction between tryptophan, O2, and tetrahydrobiopterin (BH4) to produce 5-hydroxytryptophan and 4a-hydroxytetrahydrobiopterin. This is the first and rate-limiting step in the biosynthesis of the neurotransmi......Tryptophan hydroxylase (TPH) is a mononuclear non-heme iron enzyme, which catalyzes the reaction between tryptophan, O2, and tetrahydrobiopterin (BH4) to produce 5-hydroxytryptophan and 4a-hydroxytetrahydrobiopterin. This is the first and rate-limiting step in the biosynthesis...... acid hydroxylase with bound natural amino acid substrate. The iron coordination can be described as distorted trigonal bipyramidal coordination with His273, His278, and Glu318 (partially bidentate) and one imidazole as ligands. The tryptophan stacks against Pro269 with a distance of 3.9 Å between...

Chiral Nickel(II) Complex Catalyzed Enantioselective Doyle-Kirmse Reaction of α-Diazo Pyrazoleamides.

Science.gov (United States)

Lin, Xiaobin; Tang, Yu; Yang, Wei; Tan, Fei; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming

2018-03-07

Although high enantioselectivity of [2,3]-sigmatropic rearrangement of sulfonium ylides (Doyle-Kirmse reaction) has proven surprisingly elusive using classic chiral Rh(II) and Cu(I) catalysts, in principle it is due to the difficulty in fine discrimination of the heterotopic lone pairs of sulfur and chirality inversion at sulfur of sulfonium ylides. Here, we show that the synergistic merger of new α-diazo pyrazoleamides and a chiral N, N'-dioxide-nickel(II) complex catalyst enables a highly enantioselective Doyle-Kirmse reaction. The pyrazoleamide substituent serves as both an activating and a directing group for the ready formation of a metal-carbene- and Lewis-acid-bonded ylide intermediate in the assistance of a dual-tasking nickel(II) complex. An alternative chiral Lewis-acid-bonded ylide pathway greatly improves the product enantiopurity even for the reaction of a symmetric diallylsulfane. The majority of transformations over a series of aryl- or vinyl-substituted α-diazo pyrazoleamindes and sulfides proceed rapidly (within 5-20 min in most cases) with excellent results (up to 99% yield and 96% ee), providing a breakthrough in enantioselective Doyle-Kirmse reaction.

An alkali catalyzed trans-esterification of rice bran, cottonseed and waste cooking oil

Directory of Open Access Journals (Sweden)

Akhtar Faheem H.

2014-01-01

Full Text Available In this research work, biodiesel production by trans-esterification of three raw materials including virgin and used edible oil and non edible oil has been presented. A two step method following acidic and alkali catalyst was used for non edible oil due to the unsuitability of using the straight alkaline-catalyzed trans-esterification of high FFA present in rice bran oil. The acid value after processing for rice bran, cottonseed and waste cooking oil was found to be 0.95, 0.12 and 0.87 respectively. The influence of three variables on percentage yield i.e., methanol to oil molar ratio, reaction temperature and reaction time were studied at this stage. Cottonseed oil, waste cooking oil and rice bran oil showed a maximum yield of 91.7%, 84.1% and 87.1% under optimum conditions. Fuel properties of the three biodiesel satisfied standard biodiesel fuel results.

Insights into the carboxyltransferase reaction of pyruvate carboxylase from the structures of bound product and intermediate analogues

Science.gov (United States)

Lietzan, Adam D.; St. Maurice, Martin

2014-01-01

Pyruvate carboxylase (PC) is a biotin-dependent enzyme that catalyzes the MgATP- and bicarbonate-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in central metabolism. The carboxyltransferase (CT) domain of PC catalyzes the transfer of a carboxyl group from carboxybiotin to the accepting substrate, pyruvate. It has been hypothesized that the reactive enolpyruvate intermediate is stabilized through a bidentate interaction with the metal ion in the CT domain active site. Whereas bidentate ligands are commonly observed in enzymes catalyzing reactions proceeding through an enolpyruvate intermediate, no bidentate interaction has yet been observed in the CT domain of PC. Here, we report three X-ray crystal structures of the Rhizobium etli PC CT domain with the bound inhibitors oxalate, 3-hydroxypyruvate, and 3-bromopyruvate. Oxalate, a stereoelectronic mimic of the enolpyruvate intermediate, does not interact directly with the metal ion. Instead, oxalate is buried in a pocket formed by several positively charged amino acid residues and the metal ion. Furthermore, both 3-hydroxypyruvate and 3-bromopyruvate, analogs of the reaction product oxaloacetate, bind in an identical manner to oxalate suggesting that the substrate maintains its orientation in the active site throughout catalysis. Together, these structures indicate that the substrates, products and intermediates in the PC-catalyzed reaction are not oriented in the active site as previously assumed. The absence of a bidentate interaction with the active site metal appears to be a unique mechanistic feature among the small group of biotin-dependent enzymes that act on α-keto acid substrates. PMID:24157795

Hantzsch Reaction Starting Directly from Alcohols through a Tandem Oxidation Process

Directory of Open Access Journals (Sweden)

Xiaobing Liu

2017-01-01

Full Text Available A Brønsted acidic ionic liquid, 3-(N,N-dimethyldodecylammonium propanesulfonic acid hydrogen sulphate ([DDPA][HSO4], has been successfully applied to catalyze sequential oxidation of aromatic alcohols with NaNO3 followed by their condensation with dicarbonyl compound and ammonium acetate. The corresponding pyridine analogues of Hantzsch 1,4-dihydropyridines could be obtained as a major product with high yields by the multicomponent reaction. The present work utilizing alcohols instead of aldehyde in Hantzsch reaction is a valid and green alternative to the classical synthesis of the corresponding pyridine analogues of Hantzsch 1,4-dihydropyridines.

Automated Quantum Mechanical Predictions of Enantioselectivity in a Rhodium-Catalyzed Asymmetric Hydrogenation.

Science.gov (United States)

Guan, Yanfei; Wheeler, Steven E

2017-07-24

A computational toolkit (AARON: An automated reaction optimizer for new catalysts) is described that automates the density functional theory (DFT) based screening of chiral ligands for transition-metal-catalyzed reactions with well-defined reaction mechanisms but multiple stereocontrolling transition states. This is demonstrated for the Rh-catalyzed asymmetric hydrogenation of (E)-β-aryl-N-acetyl enamides, for which a new C 2 -symmetric phosphorus ligand is designed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study on the reactive transient α-λ3-iodanyl-acetophenone complex in the iodine(III)/PhI(I) catalytic cycle of iodobenzene-catalyzed α-acetoxylation reaction of acetophenone by electrospray ionization tandem mass spectrometry.

Science.gov (United States)

Wang, Hao-Yang; Zhou, Juan; Guo, Yin-Long

2012-03-30

Hypervalent iodine compounds are important and widely used oxidants in organic chemistry. In 2005, Ochiai reported the PhI-catalyzed α-acetoxylation reaction of acetophenone by the oxidation of PhI with m-chloroperbenzoic acid (m-CPBA) in acetic acid. However, until now, the most critical reactive α-λ(3)-iodine alkyl acetophenone intermediate (3) had not been isolated or directly detected. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to intercept and characterize the transient reactive α-λ(3)-iodine alkyl acetophenone intermediate in the reaction solution. The trivalent iodine species was detected when PhI and m-CPBA in acetic acid were mixed, which indicated the facile oxidation of a catalytic amount of PhI(I) to the iodine(III) species by m-CPBA. Most importantly, 3·H(+) was observed at m/z 383 from the reaction solution and this ion gave the protonated α-acetoxylation product 4·H(+) at m/z 179 in MS/MS by an intramolecular reductive elimination of PhI. These ESI-MS/MS studies showed the existence of the reactive α-λ(3)-iodine alkyl acetophenone intermediate 3 in the catalytic cycle. Moreover, the gas-phase reactivity of 3·H(+) was consistent with the proposed solution-phase reactivity of the α-λ(3)-iodine alkyl acetophenone intermediate 3, thus confirming the reaction mechanism proposed by Ochiai. Copyright © 2012 John Wiley & Sons, Ltd.

Model Experiment of Thermal Runaway Reactions Using the Aluminum-Hydrochloric Acid Reaction

Science.gov (United States)

Kitabayashi, Suguru; Nakano, Masayoshi; Nishikawa, Kazuyuki; Koga, Nobuyoshi

2016-01-01

A laboratory exercise for the education of students about thermal runaway reactions based on the reaction between aluminum and hydrochloric acid as a model reaction is proposed. In the introductory part of the exercise, the induction period and subsequent thermal runaway behavior are evaluated via a simple observation of hydrogen gas evolution and…

Upgrading of bio-oil via acid-catalyzed reactions in alcohols : a mini review

NARCIS (Netherlands)

Hu, X.; Gunawan, R.; Mourant, D.; Mahmudul Hasan, M.D.; Wu, L.; Song, Y.; Lievens, C.; Li, C.Z.

2017-01-01

Bio-oil is a condensable liquid produced from the pyrolysis of biomass, which can be upgraded to biofuels. Bio-oil is corrosive as it contains significant amounts of carboxylic acids, creating difficulties in handling of bio-oil and applications of bio-oil. Acid-treatment of bio-oil in alcohols is

Switchable Diastereoselectivity in the Fluoride Promoted Vinylogous Mukaiyama-Michael Reaction of 2-Trimethylsilyloxyfuran Catalyzed by Crown Ethers

KAUST Repository

Della Sala, Giorgio

2017-05-31

The fluoride promoted vinylogous Mukaiyama-Michael reaction (VMMR) of 2-trimethylsilyloxyfuran with diverse α,β-unsaturated ketones is described. The TBAF catalyzed VMMR afforded high anti-diastereoselectivity irrespective of the solvents used. The KF/crown ethers catalytic systems proved to be highly efficient in terms of yields and resulted in a highly diastereoselective unprecedented solvent/catalyst switchable reaction. Anti-adducts were obtained as single diastereomers or with excellent diastereoselectivities when benzo-15-crown-5 in CH2Cl2 was employed. On the other hand, high syn-diastereoselectivities (from 76:24 to 96:4) were achieved by employing dicyclohexane-18-crown-6 in toluene. Based on DFT calculations, the catalysts/solvents-dependent switchable diastereoselectivities are proposed to be the result of loose or tight cation-dienolate ion pairs.

Lipase-catalyzed glycerolysis of fats and oils in ionic liquids: a further study on the reaction system

DEFF Research Database (Denmark)

Guo, Zheng; Xu, Xuebing

2006-01-01

Candida antarctica lipase B-catalyzed glycerolysis of sunflower oil in a tetraammonium-based ionic liquid (IL) was studied to elucidate its distinct characteristics and to evaluate the contributions of important parameters. Mass transfer limitations and occurring partial phase separation were found...... and enzyme loading study. Interestingly, increasing water activity resulted in a decreasing initial reaction rate and a prolonged induction period, which possibly resulted from an elevated solvation barrier and the phase separation at higher water content. Studies on thermodynamics of glycerolysis show......) equation, and the viscosity of the mixture is strongly agitation-dependent. A comparable diffusion time constant of the oil molecule in the IL to that of the reaction shows that the glycerolysis in the IL is controlled both diffusionally and kinetically, as experimentally verified by agitation effect...

Sequential Functionalization of Alkynes and Alkenes Catalyzed by Gold(I) and Palladium(II) N-Heterocyclic Carbene Complexes

KAUST Repository

Gó mez-Herrera, Alberto; Nahra, Fady; Brill, Marcel; Nolan, Steven P.; Cazin, Catherine S. J.

2016-01-01

The iodination of terminal alkynes for the synthesis of 1-iodoalkynes using N-iodosuccinimide in the presence of a AuI-NHC (NHC=N-heterocyclic carbene) catalyst is reported. A series of aromatic alkynes was transformed successfully into the corresponding 1-iodoalkynes in good to excellent yields under mild reaction conditions. The further use of these compounds as organic building blocks and the advantageous choice of metal-NHC complexes as catalysts for alkyne functionalization were further demonstrated by performing selective AuI-catalyzed hydrofluorination to yield (Z)-2-fluoro-1-iodoalkenes, followed by a Suzuki–Miyaura cross-coupling with aryl boronic acids catalyzed by a PdII-NHC complex to access trisubstituted (Z)-fluoroalkenes. All methodologies can be performed sequentially with only minor variations in the optimized individual reaction conditions, maintaining high efficiency and selectivity in all cases, which therefore, provides straightforward access to valuable fluorinated alkenes from commercially available terminal alkynes.

Sequential Functionalization of Alkynes and Alkenes Catalyzed by Gold(I) and Palladium(II) N-Heterocyclic Carbene Complexes

KAUST Repository

Gómez-Herrera, Alberto

2016-08-22

The iodination of terminal alkynes for the synthesis of 1-iodoalkynes using N-iodosuccinimide in the presence of a AuI-NHC (NHC=N-heterocyclic carbene) catalyst is reported. A series of aromatic alkynes was transformed successfully into the corresponding 1-iodoalkynes in good to excellent yields under mild reaction conditions. The further use of these compounds as organic building blocks and the advantageous choice of metal-NHC complexes as catalysts for alkyne functionalization were further demonstrated by performing selective AuI-catalyzed hydrofluorination to yield (Z)-2-fluoro-1-iodoalkenes, followed by a Suzuki–Miyaura cross-coupling with aryl boronic acids catalyzed by a PdII-NHC complex to access trisubstituted (Z)-fluoroalkenes. All methodologies can be performed sequentially with only minor variations in the optimized individual reaction conditions, maintaining high efficiency and selectivity in all cases, which therefore, provides straightforward access to valuable fluorinated alkenes from commercially available terminal alkynes.

Extraction of microalgal lipids and the influence of polar lipids on biodiesel production by lipase-catalyzed transesterification.

Science.gov (United States)

Navarro López, Elvira; Robles Medina, Alfonso; González Moreno, Pedro Antonio; Esteban Cerdán, Luis; Molina Grima, Emilio

2016-09-01

In order to obtain microalgal saponifiable lipids (SLs) fractions containing different polar lipid (glycolipids and phospholipids) contents, SLs were extracted from wet Nannochloropsis gaditana microalgal biomass using seven extraction systems, and the polar lipid contents of some fractions were reduced by low temperature acetone crystallization. We observed that the polar lipid content in the extracted lipids depended on the polarity of the first solvent used in the extraction system. Lipid fractions with polar lipid contents between 75.1% and 15.3% were obtained. Some of these fractions were transformed into fatty acid methyl esters (FAMEs, biodiesel) by methanolysis, catalyzed by the lipases Novozym 435 and Rhizopus oryzae in tert-butanol medium. We observed that the reaction velocity was higher the lower the polar lipid content, and that the final FAME conversions achieved after using the same lipase batch to catalyze consecutive reactions decreased in relation to an increase in the polar lipid content. Copyright © 2016 Elsevier Ltd. All rights reserved.

Catalytic effects of inorganic acids on the decomposition of ammonium nitrate.

Science.gov (United States)

Sun, Jinhua; Sun, Zhanhui; Wang, Qingsong; Ding, Hui; Wang, Tong; Jiang, Chuansheng

2005-12-09

In order to evaluate the catalytic effects of inorganic acids on the decomposition of ammonium nitrate (AN), the heat releases of decomposition or reaction of pure AN and its mixtures with inorganic acids were analyzed by a heat flux calorimeter C80. Through the experiments, the different reaction mechanisms of AN and its mixtures were analyzed. The chemical reaction kinetic parameters such as reaction order, activation energy and frequency factor were calculated with the C80 experimental results for different samples. Based on these parameters and the thermal runaway models (Semenov and Frank-Kamenestkii model), the self-accelerating decomposition temperatures (SADTs) of AN and its mixtures were calculated and compared. The results show that the mixtures of AN with acid are more unsteady than pure AN. The AN decomposition reaction is catalyzed by acid. The calculated SADTs of AN mixtures with acid are much lower than that of pure AN.

Redox-neutral rhodium-catalyzed C-H functionalization of arylamine N-oxides with diazo compounds: primary C(sp(3))-H/C(sp(2))-H activation and oxygen-atom transfer.

Science.gov (United States)

Zhou, Bing; Chen, Zhaoqiang; Yang, Yaxi; Ai, Wen; Tang, Huanyu; Wu, Yunxiang; Zhu, Weiliang; Li, Yuanchao

2015-10-05

An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct conversion of cellulose to glycolic acid with a phosphomolybdic acid catalyst in a water medium

KAUST Repository

Zhang, Jizhe

2012-08-03

Direct conversion of cellulose to fine chemicals has rarely been achieved. We describe here an eco-benign route for directly converting various cellulose-based biomasses to glycolic acid in a water medium and oxygen atmosphere in which heteromolybdic acids act as multifunctional catalysts to catalyze the hydrolysis of cellulose, the fragmentation of monosaccharides, and the selective oxidation of fragmentation products. With commercial α-cellulose powder as the substrate, the yield of glycolic acid reaches 49.3%. This catalytic system is also effective with raw cellulosic biomass, such as bagasse or hay, as the starting materials, giving rise to remarkable glycolic acid yields of ∼30%. Our heteropoly acid-based catalyst can be recovered in solid form after reaction by distilling out the products and solvent for reuse, and it exhibits consistently high performance in multiple reaction runs. © 2012 American Chemical Society.

Synthesis of 1,1-Diphenylethylene (DPE): The Marriage of a Grignard Reaction and a Column Chromatography Experiment

Science.gov (United States)

Alty, Lisa T.; France, Marcia B.; Alty, Isaac G.; Saber, Christine A.; Smith, Donna M.

2016-01-01

The synthesis of 1,1-diphenylethylene (DPE) via a Grignard reaction, followed by an acid-catalyzed dehydration reaction, yields a mixture of compounds. DPE is a high boiling liquid that cannot be purified using simple distillation. However, it is easily separated from the more polar starting material and intermediate alcohol using both thin layer…

Ligand-Controlled Synthesis of Azoles via Ir-Catalyzed Reactions of Sulfoxonium Ylides with 2-Amino Heterocycles.

Science.gov (United States)

Phelps, Alicia M; Chan, Vincent S; Napolitano, José G; Krabbe, Scott W; Schomaker, Jennifer M; Shekhar, Shashank

2016-05-20

An iridium-catalyzed method was developed for the synthesis of imidazo-fused pyrrolopyrazines. The presence or absence of a nitrogenated ligand controlled the outcome of the reaction, leading to simple β-keto amine products in the absence of added ligand and the cyclized 7- and 8-substituted-imidazo[1,2-a]pyrrolo[2,3-e]pyrazine products in the presence of ligand. This catalyst control was conserved across a variety of ylide and amine coupling partners. The substrate was shown to act as a ligand for the iridium catalyst in the absence of other ligands via NMR spectroscopy. Kinetic studies indicated that formation of the Ir-carbene was reversible and the slow step of the reaction. These mechanistic investigations suggest that the β-keto amine products form via an intramolecular carbene N-H insertion, and the imidazopyrrolopyrazines form via an intermolecular carbene N-H insertion.