WorldWideScience

Sample records for carbanions

  1. Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Mader, Mary M.; Vitale, Maxime

    2003-01-01

    Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjecte...

  2. Synthesis of tetrahydrokhusitone. Annulation of the cyclohexane ring by free radical and carbanionic sequence of reactions

    Directory of Open Access Journals (Sweden)

    ZIVORAD CEKOVIC

    2003-05-01

    Full Text Available The synthesis of norcadinane sesquiterpene tetrahydrokhusitone 1 has been achieved by a new method for annulation of cyclohexane ring involving a sequence of free radical d-alkylation of the non-activated carbon atom and intramolecular carbanionic alkylation. (–-Menthol was used as the starting compound.

  3. Formation of Benzyl Carbanion in Collision-Induced Dissociation of Deprotonated Phenylalanine Homologues.

    Science.gov (United States)

    Sekimoto, Kanako; Matsuda, Natsuki; Takayama, Mitsuo

    2014-01-01

    The fragmentation behavior of deprotonated L-phenylalanine (Phe) and its homologues including L-homophenylalanine (HPA) and L-phenylglycine (PG) was investigated using collision-induced dissociation mass spectrometry coupled with a negative ion atmospheric pressure corona discharge ionization (APCDI) technique. The deprotonated molecules [M-H](-) fragmented to lose unique neutral species, e.g., the loss of NH3, CO2, toluene and iminoglycine for [Phe-H](-); styrene and ethenamine/CO2 for [HPA-H](-); and CO2 for [PG-H](-). All of the fragmentations observed are attributable to the formation of intermediates and/or product ions which include benzyl carbanions having resonance-stabilized structures. The carbanions are formed via proton rearrangement through a transition state or via a simple dissociation reaction. These results suggest that the principal factor governing the fragmentation behavior of deprotonated Phe homologues is the stability of the intermediate and/or product ion structures.

  4. Stereoselective nucleophilic fluoromethylation of aryl ketones: dynamic kinetic resolution of chiral α-fluoro carbanions.

    Science.gov (United States)

    Shen, Xiao; Miao, Wenjun; Ni, Chuanfa; Hu, Jinbo

    2014-01-13

    Although many methods are available for the synthesis of optically enriched monofluoromethyl secondary alcohols, synthesizing optically enriched monofluoromethyl tertiary alcohols remains a challenge. An efficient and easy-to-handle nucleophilic fluoromethylation protocol was developed. The current monofluoromethylation showed much higher facial selectivity than the corresponding difluoromethylation and proceeded via a different type of transition state. Excellent stereoselective control at the fluorinated carbon chiral center was found, an effect believed to be facilitated by the dynamic kinetic resolution of the chiral α-fluoro carbanions.

  5. Mercury Methylation by HgcA: Theory Supports Carbanion Transfer to Hg(II)

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Jing [University of Tennessee (UT); Riccardi, Demian M [ORNL; Beste, Ariana [ORNL; Smith, Jeremy C [ORNL; Parks, Jerry M [ORNL

    2014-01-01

    Many proteins use corrinoid cofactors to facilitate methyl transfer reactions. Recently, a corrinoid protein, HgcA, has been shown to be required for the production of the neurotoxin methylmercury by anaerobic bacteria. A strictly conserved Cys residue in HgcA was predicted to be a lower-axial ligand to Co(III), which has never been observed in a corrinoid protein. Here, we use density functional theory to study homolytic and heterolytic Co-C bond dissociation and methyl transfer to Hg(II) substrates with model methylcobalamin complexes containing a lower-axial Cys or His ligand to cobalt, the latter of which is commonly found in other corrinoid proteins. We find that Cys thiolate coordination to Co facilitates both methyl radical and methyl carbanion transfer to Hg(II) substrates, but carbanion transfer is more favorable overall in the condensed phase. Thus, our findings are consistent with HgcA representing a new class of corrinoid protein capable of transferring methyl groups to electrophilic substrates.

  6. NMR Crystallography of a Carbanionic Intermediate in Tryptophan Synthase: Chemical Structure, Tautomerization, and Reaction Specificity

    Science.gov (United States)

    2016-01-01

    Carbanionic intermediates play a central role in the catalytic transformations of amino acids performed by pyridoxal-5′-phosphate (PLP)-dependent enzymes. Here, we make use of NMR crystallography—the synergistic combination of solid-state nuclear magnetic resonance, X-ray crystallography, and computational chemistry—to interrogate a carbanionic/quinonoid intermediate analogue in the β-subunit active site of the PLP-requiring enzyme tryptophan synthase. The solid-state NMR chemical shifts of the PLP pyridine ring nitrogen and additional sites, coupled with first-principles computational models, allow a detailed model of protonation states for ionizable groups on the cofactor, substrates, and nearby catalytic residues to be established. Most significantly, we find that a deprotonated pyridine nitrogen on PLP precludes formation of a true quinonoid species and that there is an equilibrium between the phenolic and protonated Schiff base tautomeric forms of this intermediate. Natural bond orbital analysis indicates that the latter builds up negative charge at the substrate Cα and positive charge at C4′ of the cofactor, consistent with its role as the catalytic tautomer. These findings support the hypothesis that the specificity for β-elimination/replacement versus transamination is dictated in part by the protonation states of ionizable groups on PLP and the reacting substrates and underscore the essential role that NMR crystallography can play in characterizing both chemical structure and dynamics within functioning enzyme active sites. PMID:27779384

  7. Spectra of carbanions formed from allyl cyanide during isomerization in zeolite NaY-FAU with strong basic sites

    Science.gov (United States)

    Hannus, István; Förster, Horst; Tasi, Gyula; Kiricsi, Imre; Molnár, Árpád

    1995-03-01

    Double bond isomerization of allyl cyanide to crotononitrile over a basic zeolite catalyst was monitored by IR and UV-VIS spectroscopy in order to get information on the surface intermediates involved. Due to the spectral changes the occurence of a carbanionic intermediate seems to be highly probable characterized by an absorption at 400 nm.

  8. Chiral fluorinated α-sulfonyl carbanions: enantioselective synthesis and electrophilic capture, racemization dynamics, and structure.

    Science.gov (United States)

    Hellmann, Gunther; Hack, Achim; Thiemermann, Eric; Luche, Olaf; Raabe, Gerhard; Gais, Hans-Joachim

    2013-03-18

    Enantiomerically pure triflones R(1) CH(R(2) )SO2 CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3 Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3 SSCF3 . The deprotonation of RCH(Me)SO2 CF3 (R=CH2 Ph, iHex) with nBuLi with the formation of salts [RC(Me)SO2 CF3 ]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2 CF3 group of (S)-MeOCH2 C(Me)(CH2 Ph)SO2 CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2 C(Me)(CH2 Ph)Et of 96 % ee. Racemization of salts [R(1) C(R(2) )SO2 CF3 ]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα S bond rotation as the rate-determining step. Lithium α-(S)-trifluoromethyl- and α-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH2 C(Me)SO2 tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105 °C of 2.4 h, that of [PhCH2 C(Me)SO2 CF3 ]Li at -78 °C is 30 d. DNMR spectroscopy of amides (PhCH2 )2 NSO2 CF3 and (PhCH2 )N(Ph)SO2 CF3 gave NS rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2 C(Ph)SO2 R]M (M=Li, K, NBu4 ; R=CF3 , tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2 C(Ph)SO2 CF3 ]Li⋅L}2 (L=2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2 C(Ph)SO2 CF3 ]NBu4 have

  9. Nucleophilic Benzoylation Using a Mandelic Acid Dioxolanone as a Synthetic Equivalent of the Benzoyl Carbanion. Oxidative Decarboxylation of α-Hydroxyacids

    Directory of Open Access Journals (Sweden)

    José R. Pedro

    2004-04-01

    Full Text Available The synthesis of alkyl aryl ketones using a mandelic acid dioxolanone as a synthetic equivalent (Umpolung of the benzoyl carbanion is reported. The methodology involves alkylation of the mandelic acid dioxolanone, hydrolysis of the dioxolanone moiety in the alkylated products and oxidative decarboxylation of the resulting α-hydroxyacids. The last step is carried out in a catalytic aerobic way using a Co (III complex in the presence of pivalaldehyde under very mild conditions.

  10. Relative reactivities of halogen-substituted substrates (R-Br, R-Cl) toward the halophilic attack by a carbanion

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Relative reactivities of bromine-substituted substrates (R-Br) or chlorine-substituted substrates (R-Cl) toward bromophilic or chlorophilic attack by a carbanion have been evaluated by the intermolecular competition kinetics. Relative reactivity orders are CF3CFBr2 >CF3CBr3≥CBr4>CHBr3>CF3CFBrCF2Br>CF2Br2>BrCF2CF2Br>BrCH2CO2Et≥BrCF2CFHBr>CH2Br2 > BrCH2CH2Br, and Cl3CNO2>Cl3CCN>Cl3CCOPh >cyclo-C5Cl6>Cl3CCOCl>CCl3CF2Cl>CCl3CF3≥CCl4>CCl3CCl3≥CCl3(CF2)2Cl>Cl3CCOCCl3>CCl3(CF2)6Cl>Cl3CCO2Et>Cl3CF >Cl3CPh>Cl3CCH2O2CCH3.

  11. Syntheses of 2-substituted indoles and fused indoles by photostimulated reactions of o-iodoanilines with carbanions by the SRN1 mechanism.

    Science.gov (United States)

    Barolo, Silvia M; Lukach, Andrés E; Rossi, Roberto A

    2003-04-04

    2-Substituted indoles (5a,b and 7) and fused indoles (9a-c, 11a,b, and 12) have been obtained by the S(RN)1 mechanism from photostimulated reactions of o-iodoaniline (1) and 1-halo-2-naphthalen-2-ylamines (3a,b) with enolate ions of acyclic (acetophenone (6), 2- (4a) and 4-acetylpyridine (4b)) and cyclic ketones (1- (8a) and 2-indanone (10a), 1- (8b) and 2-tetralone (10b) and 1-benzosuberone (8c)) in DMSO and liquid ammonia as solvents. The carbanions derived from 4a,b, 8a, and 10b are novel nucleophiles that form new C-C bonds by the S(RN)1 mechanism.

  12. Lithium choreography: intramolecular arylations of carbamate-stabilised carbanions and their mechanisms probed by in situ IR spectroscopy and DFT calculations.

    Science.gov (United States)

    Fournier, Anne M; Nichols, Christopher J; Vincent, Mark A; Hillier, Ian H; Clayden, Jonathan

    2012-12-14

    Deprotonation of O-allyl, O-propargyl or O-benzyl carbamates in the presence of a lithium counterion leads to carbamate-stabilised organolithium compounds that may be quenched with electrophiles. We now report that when the allylic, propargylic or benzylic carbamate bears an N-aryl substituent, an aryl migration takes place, leading to stereochemical inversion and C-arylation of the carbamate α to oxygen. The aryl migration is an intramolecular S(N) Ar reaction, despite the lack of anion-stabilising aryl substituents. Our in situ IR studies reveal a number of intermediates along the rearrangement pathway, including a "pre-lithiation complex," the deprotonated carbamate, the rearranged anion, and the final arylated carbamate. No evidence was obtained for a dearomatised intermediate during the aryl migration. DFT calculations predict that during the reaction the solvated Li cation moves from the carbanion centre, thus freeing its lone pair for nucleophilic attack on the remote phenyl ring. This charge separation leads to several alternative conformations. The one having Li(+) bound to the carbamate oxygen gives rise to the lowest-energy transition structure, and also leads to inversion of the configuration. In agreement with the IR studies, the DFT calculations fail to locate a dearomatised intermediate.

  13. How reliable are gas-phase proton affinity values of small carbanions? A comparison of experimental data with values calculated using Gaussian-3 and CBS compound methods

    Science.gov (United States)

    Danikiewicz, Witold

    2009-08-01

    Gas-phase proton affinities (PA) of a series of 25 small, aliphatic carbanions were computed using different Gaussian-3 methods: G3, G3(B3LYP), G3(MP2) and G3(MP2, B3LYP) and Complete Basis Set Extrapolation methods: CBS-4M, CBS-Q, CBS-QB3, and CBS-APNO. The results were compared with critically selected experimental data. The analysis of the results shows that for the majority of the studied molecules all compound methods (Gaussian-3 and CBS), except for CBS-4M, give comparable results, which differ no more than +/-2 kcal mol-1 from the experimental data. Taking into account the calculation time, G3(MP2) and G3(MP2, B3LYP) methods offer the best compromise between accuracy and computational cost. As an additional proof, the results obtained by these two methods were compared with the values obtained using CCSD(T) ab initio method with large basis set. It was found also that some of the published experimental data are erroneous and should be corrected. The results described in this work show that for the majority of the studied compounds PA values calculated using compound methods can be used with the same or even higher confidence as the experimental ones because even the largest differences between Gaussian-3 and CBS methods listed above are still comparable with the accuracy of the typical PA measurements.

  14. Synthesis of 4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide ring systems on sugar templates via carbanion-mediated sulfonamide intramolecular cyclization reactions (CSIC protocols) of glyco-alpha-sulfonamidonitriles.

    Science.gov (United States)

    Domínguez, Laura; van Nhien, Albert Nguyen; Tomassi, Cyrille; Len, Christophe; Postel, Denis; Marco-Contelles, José

    2004-02-01

    The carbanion-mediated sulfonate intramolecular cyclizations (CSIC protocols) of glyco-alpha-sulfonamidonitriles derived from readily available monosaccharides have been extensively investigated using potassium carbonate, cesium carbonate, n-BuLi, and LDA as bases. As a result, a series of enantiomerically pure spiro(4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide) derivatives have been prepared efficiently and isolated in good yield. The synthesis of these new bicyclic systems is key to accessing a novel range of aza analogues of TSAO nucleosides (ATSAOs).

  15. Electron transfer in acetohydroxy acid synthase as a side reaction of catalysis. Implications for the reactivity and partitioning of the carbanion/enamine form of (alpha-hydroxyethyl)thiamin diphosphate in a "nonredox" flavoenzyme.

    Science.gov (United States)

    Tittmann, Kai; Schröder, Kathrin; Golbik, Ralph; McCourt, Jennifer; Kaplun, Alexander; Duggleby, Ronald G; Barak, Ze'ev; Chipman, David M; Hübner, Gerhard

    2004-07-13

    Acetohydroxy acid synthases (AHAS) are thiamin diphosphate- (ThDP-) and FAD-dependent enzymes that catalyze the first common step of branched-chain amino acid biosynthesis in plants, bacteria, and fungi. Although the flavin cofactor is not chemically involved in the physiological reaction of AHAS, it has been shown to be essential for the structural integrity and activity of the enzyme. Here, we report that the enzyme-bound FAD in AHAS is reduced in the course of catalysis in a side reaction. The reduction of the enzyme-bound flavin during turnover of different substrates under aerobic and anaerobic conditions was characterized by stopped-flow kinetics using the intrinsic FAD absorbance. Reduction of enzyme-bound FAD proceeds with a net rate constant of k' = 0.2 s(-1) in the presence of oxygen and approximately 1 s(-1) under anaerobic conditions. No transient flavin radicals are detectable during the reduction process while time-resolved absorbance spectra are recorded. Reconstitution of the binary enzyme-FAD complex with the chemically synthesized intermediate 2-(hydroxyethyl)-ThDP also results in a reduction of the flavin. These data provide evidence for the first time that the key catalytic intermediate 2-(hydroxyethyl)-ThDP in the carbanionic/enamine form is not only subject to covalent addition of 2-keto acids and an oxygenase side reaction but also transfers electrons to the adjacent FAD in an intramolecular redox reaction yielding 2-acetyl-ThDP and reduced FAD. The detection of the electron transfer supports the idea of a common ancestor of acetohydroxy acid synthase and pyruvate oxidase, a homologous ThDP- and FAD-dependent enzyme that, in contrast to AHASs, catalyzes a reaction that relies on intercofactor electron transfer.

  16. Synthesis of Ethers via Reaction of Carbanions and Monoperoxyacetals

    Science.gov (United States)

    2015-01-01

    Although transfer of electrophilic alkoxyl (“RO+”) from organic peroxides to organometallics offers a complement to traditional methods for etherification, application has been limited by constraints associated with peroxide reactivity and stability. We now demonstrate that readily prepared tetrahydropyranyl monoperoxyacetals react with sp3 and sp2 organolithium and organomagnesium reagents to furnish moderate to high yields of ethers. The method is successfully applied to the synthesis of alkyl, alkenyl, aryl, heteroaryl, and cyclopropyl ethers, mixed O,O-acetals, and S,S,O-orthoesters. In contrast to reactions of dialkyl and alkyl/silyl peroxides, the displacements of monoperoxyacetals provide no evidence for alkoxy radical intermediates. At the same time, the high yields observed for transfer of primary, secondary, or tertiary alkoxides, the latter involving attack on neopentyl oxygen, are inconsistent with an SN2 mechanism. Theoretical studies suggest a mechanism involving Lewis acid promoted insertion of organometallics into the O–O bond. PMID:26560686

  17. Relative reactivities of halogen-substituted substrates (R-Br, R-Cl) toward the halophilic attack by a carbanion

    Institute of Scientific and Technical Information of China (English)

    FU; Weimin

    2001-01-01

    Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm-1, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm-1 and two baseline methods, the most suitable ratios Aprobe band/Areference band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to be A1560/A2880, A1560/A2920 and A1655/A3430(A1560/A2880 is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm-1 bands. The determination range of the D.D. (1%-100%) covered almost the whole range. The standard curves with A1560/A2880 and A1655/A3430 were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-propionyl chitosan, N-butyryl chitosan and N-hexanoyl chitosan.

  18. Facile Formation and Dissociation Behaviour of C–C Bond Resulted from the Nucleophilic Attack of Carbanions on a Carbonyl Carbon in [Pt(hfac)2

    OpenAIRE

    2000-01-01

    [Pt(hfac)2] (hfac:hexafluoroacetylacetonate) reacts with MeNH2 in CH2Cl2/MeOH to give an –NHMe adduct complex on one of the carbonyl carbons, (MeNH3)[Pt(hfac)(hfac–NHMe)] 1 which is a tetrahedral intermediate of a Schiff base complex,[Pt(CF3COCHC(NMe)CF3)2] 2. Complex 1 activates H2O,MeOH, MeNO2 or acetone in solution to form the correspondingconjugate base adducts. The C–C bond in–CH2NO2 adduct 6, easily cleaves and generates nitromethane in solution.

  19. Crystal structure of an ethylene sorption complex of fully vacuum-dehydrated fully Ag+-exchanged zeolite X (FAU). Silver atoms have reduced ethylene to give CH2 2- carbanions at framework oxide vacancies.

    Science.gov (United States)

    Lee, Young Mi; Choi, Seo Jung; Kim, Yang; Seff, Karl

    2005-11-03

    The crystal structure of an ethylene sorption complex of fully vacuum-dehydrated fully Ag(+)-exchanged zeolite X (FAU), a = 24.865(2) A, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd at 21 degrees C. It is very different from the ethylene complex of Ag(92)-X that had been dehydrated at 400 degrees C in flowing oxygen, as were the two dehydrated structures. The crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M AgNO(3) for 3 days, followed by dehydration at 400 degrees C and 2 x 10(-6) Torr for 2 days, followed by exposure to 300 Torr of zeolitically dry ethylene gas for 2 h at 21 degrees C. The structure was determined in this atmosphere and was refined using all data to the final error indices (based upon the 534 reflections for which F(o) > 4sigma(F(o))) R(1) = 0.062 and wR(2) = 0.135. In this structure, per unit cell, 14 Ag(+) ions were found at the octahedral site I (Ag-O = 2.611(9) A), and 32 partially reduced Ag(+) ions fill two different site I' positions deep in the sodalite cavities (Ag-O = 2.601(13) and 2.618(12) A). The sodalite cavities host two different cationic silver clusters. In about 47% of sodalite units, eight silver atoms form interpenetrating tetrahedra, Ag(8)(n+) (n = 4 is suggested), with T(d)() symmetry. The other 53% of the sodalite units host cyclo-Ag(4)(m+) (m = 2 is suggested) cations with near S(4) symmetry. These clusters are very similar to those in vacuum-dehydrated Ag(92)-X. Thirty-two Ag(+) ions fill the single 6-rings, 15 at site II' (Ag-O = 2.492(10) A), and 17 at site II (Ag-O = 2.460(9) A). The latter 17 lie in supercages where each forms a lateral pi-complex with an ethylene molecule. In turn, each C(2)H(4) molecule forms two cis electrostatic hydrogen bonds to framework oxygens. The remaining 14 Ag+ ions occupy three different II' sites. Vacuum dehydration had caused substantial decomposition: per unit cell, 30 of the 92 Ag(+) ions were reduced and 15 of the 384 framework oxide ions were oxidized to O2(g), leaving lattice vacancies. The sorption of C(2)H(4) at 21 degrees C reoxidized about 7 of the 30 Ag(0) atoms to Ag(+) and reduced 1.75 ethylene molecules to give CH(2)(2-) groups which refilled 3.5 of these 15 lattice vacancies. The remaining vacancies may have been filled with H(2)C=C(2-) ions. The unit cell formula, which originally contained 384 oxygen atoms, may be |Ag(92)(C2H4)17|[Si(100)Al(92)O(369)(CH2)3.5] or |Ag(92)H(23)(C2H4)17|[Si(100)Al(92)O(369)(CH2)3.5(C2H2)11.5].

  20. Polystyrene-supported Benzyl Selenide: An Efficient Reagent for Highly Stereocontrolled Synthesis of Substituted Olefins

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Polystyrene-supported benzyl selenide has been prepared. This novel reagent was treated with LDA to produce a selenium stabilized carbanion, which reacted with alkyl halide, followed by selenoxide syn-elimination, to give substituted olefins stereospecificly.

  1. Base initiated halogen-exchange reactions between perhaloalkanes

    Institute of Scientific and Technical Information of China (English)

    傅伟敏; 李兴亚; 蒋锡夔

    1997-01-01

    Halophilic attacks on C-X bonds (X=Br,Cl) by a base can easily initiate mtermolecular bromme-chlonne exchange reactions either among bromine-or chlorine-containing perhaloalkane molecules of different compounds of among molecules of the same compound It provides a new and convenient method to synthesize perhaloal-kanes Apparently,it pertains to an amomc mechanism,i e.the reaction is initiated by halophilic attack on C-X bonds by the base,and an intermediate carbanion is formed.Distributions of the products depend on the equilibria involving all carbanion intermediates and perhaloalkane product molecules.

  2. Substituent Effects on the Photodeprotection Reactions of Selected Ketoprofen Derivatives in Phosphate Buffered Aqueous Solutions

    Science.gov (United States)

    Liu, Mingyue; Li, Ming-De; Huang, Jinqing; Li, Tianlu; Liu, Han; Li, Xuechen; Phillips, David Lee

    2016-02-01

    Photodeprotection is an important reaction that has been attracting broad interest for use in a variety of applications. Recent advances in ultrafast and vibrational time-resolved spectroscopies can facilitate obtaining data to help unravel the reaction mechanisms involving in the photochemical reactions of interest. The kinetics and reaction mechanisms for the photodeprotection reactions of ketoprofen derivatives containing three different substituents (ibuprofen, Br and I) were investigated by femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy methods in phosphate buffered solutions (PBS). Fs-TA allows us to detect the decay kinetics of the triplet species as the key precursor for formation of a carbanion species for three different substituents attached to ketoprofen. To characterize the structural and electronic properties of the corresponding carbanion and triplet intermediates, TR3 spectroscopic experiments were conducted. The transient spectroscopy work reveals that the different substituents affect the photodecarboxylation reaction to produce carbon dioxide which in turn influences the generation of the carbanion species which determines the rate of the photorelease of the functional groups attached on the ketoprofen parent molecule. The fingerprint TR3 spectroscopy results suggest that ketoprofen derivatives may be deactivated to produce a triplet carbanion when increasing the atom mass of the halogen atoms.

  3. Polystyrene-supported Selenides and Selenoxide:Versatile Routes to Synthesize Allylic Alcohols

    Institute of Scientific and Technical Information of China (English)

    Wei Ming XU; You Chu ZHANG; Xian HUANG

    2003-01-01

    Several polystyrene-supported selenides and selenoxide have been prepared firstly. These novel reagents were treated with LDA to produce selenium stabilized carbanions, which reacted with aldehydes and alkyl halides, followed by selenoxide syn-elimination and [2,3] sigmatropic rearrangement respectively to give Z-allylic alcohols stereoselectively.

  4. Reaction of Grignard Reagents with Diethyl Perfluoroacyl( 1-Cyanoethyl ) phosphonates. Synthesis of Perfluoroalkylated α, β-Unsaturated Nitriles with Predominant Z-Selectivity

    Institute of Scientific and Technical Information of China (English)

    SHEN,Yan-Chang(沈延昌); JIANG,Guo-Fang(江国防)

    2002-01-01

    Diethyl (1-cyanoethyl)phosphonate 1 was reacted with n-butyllithium in tetrahydrofuran ( THF ) at - 78 ℃ and the resulting carbanion 2 reacted with perfluoroalkanoic acid anhydride to afford perfluoroacylated phosphonate 3. Without isolation 3was attacked by Grognard reagents giving perfluoroalkylated α,β-unsaturated nitries in 46%-88% yields with high Zstereoselectivity(Z:E=89-62:11-38).

  5. SN2' versus SN2 reactivity: control of regioselectivity in conversions of Baylis-Hillman adducts.

    Science.gov (United States)

    Baidya, Mahiuddin; Remennikov, Grygoriy Y; Mayer, Peter; Mayr, Herbert

    2010-01-25

    TiCl(4)-induced Baylis-Hillman reactions of alpha,beta-unsaturated carbonyl compounds with aldehydes yield the (Z)-2-(chloromethyl)vinyl carbonyl compounds 5, which react with 1,4-diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6. Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (S(N)2' reactions). When more than one equivalent of the carbanions is used, a second S(N)2' reaction converts 8 into their thermodynamically more stable allyl isomers 9. The second-order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile-specific parameters N and s for the stabilized carbanions, the correlation log k (20 degrees C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (-19 reactions to proceed via an addition-elimination mechanism with a rate-determining addition step.

  6. Benzothiazines in organic synthesis. An approach to floresolide B

    Science.gov (United States)

    Chen, Yugang; Harmata, Michael

    2011-01-01

    The intramolecular conjugate addition of a sulfoximine carbanion to an α,β-unsaturated ester results in the formation of a benzothiaine bearing a benzylic stereocenter with extremely high fidelity. We have used this methodology to complete a formal total synthesis of the antitumor agent (+)-floresolide B. PMID:21818165

  7. Synthesis of New Quinoxalines Containing an Oxirane Ring by the TDAE Strategy and in Vitro Evaluation in Neuroblastoma Cell Lines

    Directory of Open Access Journals (Sweden)

    Marc Montana

    2014-09-01

    Full Text Available Neuroblastoma is an aggressive pediatric malignancy with significant chemotherapeutic resistance. In order to obtain new compounds active on neuroblastoma cell lines, we investigated the reactivity of carbanion formed via TDAE in quinoxaline series. The new synthesized compounds were tested for their anti-proliferative activity on two neuroblastoma cell lines, and seven oxirane derivatives obtained interesting activities.

  8. Polystyrene-supported Selenomethyl-sulfonates:Efficient Reagents for Stereocontrolled Synthesis of Substituted Vinyl Sulfones

    Institute of Scientific and Technical Information of China (English)

    Wei Ming XU; Lu Ling WU; Xian HUANG

    2004-01-01

    Polystyrene-supported selenomethyl-sulfonates have been prepared. These novel reagents were treated with LDA to produce selenium stabilized carbanions, which reacted with alkyl halide and epoxides, followed by selenoxide syn-elimination, to give E-vinyl sulfones and γ-hydroxy-substituted-E-vinyl sulfones respectively.

  9. Theoretical study on the distribution of atomic charges in the Schiff bases of 3-hydroxypyridine-4-aldehyde and alanine. The effect of the protonation state of the pyridine and imine nitrogen atoms

    Energy Technology Data Exchange (ETDEWEB)

    Casasnovas, Rodrigo; Salva, Antoni; Frau, Juan; Donoso, Josefa [Institut Universitari d' Investigacio en Ciencies de la Salut (IUNICS), Departament de Quimica, Universitat de les Illes Balears, Cra. Valldemossa km 7.5, E-07122 Palma de Mallorca (Spain); Munoz, Francisco [Institut Universitari d' Investigacio en Ciencies de la Salut (IUNICS), Departament de Quimica, Universitat de les Illes Balears, Cra. Valldemossa km 7.5, E-07122 Palma de Mallorca (Spain)], E-mail: dqufmi0@uib.es

    2009-01-27

    The protonation state of the pyridine and imine nitrogen atoms on the 'electron-sink' effect was studied by DFT(B3LYP/6-31+G*) calculations in the Schiff bases formed between 3-hydroxypyridine-4-aldehyde and alanine and their C{alpha}-carbanionic counterparts. Results indicate that the protonation of pyridine nitrogen promotes the enolimine-ketoenamine tautomerism. The importance of pyridine nitrogen on the 'electron-sink' effect in the carbanionic molecules clearly depends on the protonation state of the imine nitrogen: in the enolimine tautomers, where the imine nitrogen is deprotonated, a 70% of the electron charge is delocalized on the pyridine ring, whereas in the ketoenamine type structures, where the imine nitrogen is fully protonated, just a 20% of this charge is delocalized in this molecular moiety. The results are discussed in relation to the chemistry of some PLP-dependent enzymes and the structure of their active sites.

  10. Carbenic vs. ionic mechanistic pathway in reaction of cyclohexanone with bromoform.

    Science.gov (United States)

    Vitnik, Vesna D; Vitnik, Zeljko J; Juranić, Ivan O

    2012-10-01

    The extensive computation study was done to elucidate the mechanism of formation dibromoepoxide from cyclohexanone and bromoform. In this reaction, the formation of dihaloepoxide 2 is postulated as a key step that determines the distribution and stereochemistry of products. Two mechanistic paths of reaction were investigated: the addition of dibromocarbene to carbonyl group of ketone, and the addition of tribromomethyl carbanion to the same (C=O) group. The mechanisms for the addition reactions of dibromocarbenes and tribromomethyl carbanions with cyclohexanone have been investigated using ab initio HF/6-311++G** and MP2/6-311+G* level of theory. Solvent effects on these reactions have been explored by calculations which included a continuum polarizable conductor model (CPCM) for the solvent (H₂O). The calculations showed that both mechanisms are possible and are exothermic, but have markedly different activation energies.

  11. New Processes for Annulation

    Institute of Scientific and Technical Information of China (English)

    Liu Hsing-Jang

    2004-01-01

    Making use of the high propensity of 2-cyano-2-cycloalkenones to undergo conjugate addition with various carbanions and the high reactivity of the ensuing α -cyano ketone system, a number of new annulation processes have been developed recently in our laboratories. As shown in Eq. 1 (n=1) with a specific example, one such process involves the addition of 3-butenylmagnesium bromide, followed by a palladium (Ⅱ) acetate mediated oxidative cyclization, to facilitate methylenecyclopentane ring formation. This annulation process could be readily extended to effect methylenecyclohexane ring formation (Eq. 1, n=2), using 4-pentenylmagnesinm bromide as the initial reagent, and to install the carbomethoxy-substituted methylenecyclopentane and methylenecyclohexane rings, using the carbanions derived from methyl 4-pentenoate and methyl 5-hexenoate, respectively (Eq. 2). In another annulation process, the addition of the enolate of methyl 5-chloropentanoate is involved initially, and the ring formation is readily effected by an intramolecular alkylation process. A specific example is given in Eq. 3.

  12. Coenzyme metabolism in rat liver transketolase

    Energy Technology Data Exchange (ETDEWEB)

    Gorbach, Z.V.; Kubyshin, V.L.; Maglysh, S.S.; Zabrodskaya, S.V.

    1987-01-10

    On the basis of the results of kinetic investigations, two binding sites for hydroxythiamine diphosphate were determined in apotransketolase, with sharply differing values of K/sub i/: (7-22) x 10/sup -9/ and (13.0-19.7) x 10/sup -8/ M. A study was made of the turnover rate of thiamine diphosphate in holotransketolase in rat liver tissue by a radioisotope method, using (/sup 14/C) thiamine as the labeled precursor. The half-substitution time and rate constant of degradation of the coenzyme in transketolase are close in absolute values to the analogous indices for the protein portion of the enzyme and constitute 153 h and 0.108 day/sup -1/, respectively. Rat liver transketolase exists in vivo in the form of a substituted ..cap alpha..-carbanion. Replacement of thiamine diphosphate by hydroxythiamine diphosphate in the holoenzyme has no effect on the formation of the intermediate ..cap alpha..-carbanion form of the enzyme.

  13. United States Air Force Graduate Student Summer Support Program 1986. Program Technical Report. Volume 2

    Science.gov (United States)

    1986-12-01

    Park Hypersonic Flow Over a Compression Ramp 66 Characterization of Alkoxide Derived April G. Parker Zirconia Toughened Fused Silica 67 On the...methyl sulfinyl carbanion with DMAc/LiCl resulted in the formation of an insoluble precipitate whose identity was not investigated. The use of 18- crown -6...of the role of the interface and thermostability of the matrix and the reinforcement. Zirconia has been used for increasing the toughness, resistance

  14. Lithiation of a silyl ether: formation of an ortho-Fries hydroxyketone.

    Science.gov (United States)

    Lo, Hong-Jay; Lin, Chin-Yin; Tseng, Mei-Chun; Chein, Rong-Jie

    2014-08-18

    A hydroxy-directed alkylation of an N,N-diethylarylamide using CIPE-assisted α-silyl carbanions (CIPE = complex-induced proximity effect) has been developed using a simple reagent combination of LDA (lithium diisopropylamide) and chlorosilane. A study of the mechanism, and the application of the procedure to an anionic Snieckus-Fries rearrangement for a highly efficient synthesis of the potent phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, are reported.

  15. Heterocycles from α-aminonitriles.

    Science.gov (United States)

    Otto, Nicola; Opatz, Till

    2014-10-06

    Owing to their various modes of reactivity, α-aminonitriles represent versatile building blocks for the construction of a wide range of nitrogen heterocycles. The present Concept article focuses on synthetic methodologies using their bifunctional nature which is the basis of their reactivity as α-amino carbanions and as iminium ions. Reactions exclusively taking place on either the amine or on the nitrile moiety will not be considered.

  16. A modular approach to marine macrolide construction. 4. Assembly of C36-C51 and C29-C44 building blocks and evaluation of key coupling reactions targeting spongistatin 1 (altohyrtin A).

    Science.gov (United States)

    Ciblat, Stephane; Kim, Jungchul; Stewart, Catherine A; Wang, Jizhou; Forgione, Pat; Clyne, Dean; Paquette, Leo A

    2007-02-15

    Routes have been developed for the stereocontrolled elaboration of two highly functionalized sectors of spongistatin 1. The approach to ring F takes advantage of B-alkyl Suzuki-Miyaura coupling to install the C44-C45 bond. The E-ring pyran moiety was generated by acylation of an alpha-sulfonyl carbanion, the stereogenic centers of which were incorporated by sequential asymmetric aldol reactions. [structure: see text].

  17. Crystal Structure of 2-Ethylimidazole-1-sulfonyl Azide: A New Azidation Reagent

    Directory of Open Access Journals (Sweden)

    Herwig Schottenberger

    2012-03-01

    Full Text Available Crystalline 2-ethylimidazole-1-sulfonyl azide was designed as a convenient reagent with improved thermal stability for electrophilic azidation of carbanions. The compound crystallized in the monoclinic space group P21/c. The molecules are arranged into chains by short C–H...O contacts along a two-fold screw axis. The quaternary 1-azidosulfonyl-2-ethyl-3-methylimidazolium tetrafluoroborate crystallized in Fdd2 with two independent ion pairs which engage in C–H...F interactions.

  18. The Co-III-C bond in (1-thia-4,7-diazacyclodecyl-kappa N-3(4),N-7,C-10)(1,4,7-triazacyclononane-kappa N-3(1),N-4,N-7)-cobalt(III) dithionate hydrate

    DEFF Research Database (Denmark)

    Harris, Pernille; Kofod, P.; Song, Y.S.

    2003-01-01

    In the title compound, [Co(C6H15N3)(C7H15N2S)]S2O6.H2O, the Co-C bond distance is 1.9930 (13) Angstrom, which is shorter than for related compounds with the linear 1,6-diamino-3-thiahexan-4-ide anion in place of the macrocyclic 1-thia-4,7-diazacyclodecan-8-ide anion. The coordinated carbanion pro...

  19. Synthesis and quantitative structure–activity relationship study of substituted imidazophosphor ester based tetrazolo[1,5-b]pyridazines as antinociceptive/anti-inflammatory agents

    Directory of Open Access Journals (Sweden)

    Wafaa M. Abdou

    2013-08-01

    Full Text Available A high-yielding general synthesis of imidazophosphor ester based tetrazolo[1,5-b]pyridazines is described. A conjugated reaction between 3,6-diazidopyridazine and different types of phosphonyl carbanion reagents followed by intramolecular cyclization afforded the target products, by using sodium ethanolate solution as a reaction medium. Among the products, five compounds, at a dose of 50 mg per kilogram body weight, showed a notable antinociceptive and anti-inflammatory activity without toxic side-effects.

  20. Mg2+-Imidazole-Catalyzed Self-Condensation of Malonyl Thioesters: Getting Tuned for Biomimetic Polyketide Synthesis?

    Directory of Open Access Journals (Sweden)

    Stefan Matile

    2001-10-01

    Full Text Available We report that a subtle balance of carbanion reactivity, leaving group activation, and pKa of the catalyst is required for efficient self-condensation of thiomalonates to thioacetoacetates in up to 71% yield under “biomimetic” conditions originally proposed by Kobuke and Yoshida (Tetrahedron Lett. 1978, 19, 367.

  1. Photochemical reaction of 2-(3-benzoylphenyl)propionic acid (ketoprofen) with basic amino acids and dipeptides.

    Science.gov (United States)

    Suzuki, Tadashi; Shinoda, Mio; Osanai, Yohei; Isozaki, Tasuku

    2013-08-22

    Photoreaction of 2-(3-benzoylphenyl)propionic acid (ketoprofen, KP) with basic amino acids (histidine, lysine, and arginine) and dipeptides (carnosine and anserine) including a histidine moiety in phosphate buffer solution (pH 7.4) has been investigated with transient absorption spectroscopy. With UV irradiation KP(-) gave rise to a carbanion through a decarboxylation reaction, and the carbanion easily abstracted a proton from the surrounding molecule to yield a 3-ethylbenzophenone ketyl biradical (EBPH). The dipeptides as well as the basic amino acids were found to accelerate the proton transfer reaction whereas alanine and glycine had no effect on the reaction, revealing that these amino acids having a protonated side chain act as a proton donor. The formation quantum yield of EBPH was estimated to be fairly large by means of an actinometrical method with benzophenone, and the bimolecular reaction rate constant for the proton transfer between the carbanion and the protonated basic amino acids or the protonated dipeptides was successfully determined. It has become apparent that the bimolecular reaction rate constant for the proton transfer depended on the acid dissociation constant for the side chain of the amino acids for the first time. This reaction mechanism was interpreted by difference of the heat of reaction for each basic amino acid based on the thermodynamical consideration. These results strongly suggest that the side chain of the basic amino acid residue in protein should play an important role for photochemistry of KP in vivo.

  2. The Reactivity of 2,4,6-Tirphenylpyridinium Ylids

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Triphenylpyridinium ylid 2, generated by the decarboxylation of betaine 1, were noted to react with acetyl chloride, chloroform or acetone to form addition-elimination product and proton extraction - carbanion addition products, respectively. The reaction with chloroform was determined as pseudo first order from kinetic experiments. The values of kobsd and t1/2 for decarboxylation at 20, 40 and 50°C were calculated to be 4.6 x 10-4, 8.8 x 10-3, 2.8 x 10-2 min-1 and 1.5 x 103, 78, 24 minutes, respectively.

  3. A Strained Disilane-Promoted Carboxylation of Organic Halides with CO2 under Transition-Metal-Free Conditions.

    Science.gov (United States)

    Mita, Tsuyoshi; Suga, Kenta; Sato, Kaori; Sato, Yoshihiro

    2015-11-01

    By using a strained four-membered ring disilane (3,4-benzo-1,1,2,2-tetraethyldisilacyclobutene) and CsF, a wide range of aryl, alkenyl, alkynyl, benzyl, allyl, and alkyl halides was successfully carboxylated under an ambient CO2 atmosphere (CO2 balloon) at room temperature within 2 h. In this carboxylation, a highly reactive silyl anion, which is generated from the disilane and CsF, is a key to facilitating the formation of a carbanion equivalent. The resulting anionic species can be trapped with CO2 to produce carboxylic acids with high efficiency.

  4. Aqueous thermal degradation of gallic acid

    Science.gov (United States)

    Snow Boles, Jennifer; Crerar, David A.; Grissom, Grady; Key, Tonalee C.

    1988-02-01

    Aqueous thermal degradation experiments show gallic acid, a naturally occurring aromatic carboxylic compound, decomposes rapidly at temperatures between 105° and 150°C, with an activation energy of 22.9 or 27.8 kcal/ mole, depending on pH of the starting solution. Pyrogallol is the primary product identified, indicating degradation via decarboxylation and a carbanion transition state. Relatively rapid degradation of vanillic, phthalic, ellagic and tannic acids has also been observed, suggesting that these and perhaps other aromatic acids could be short-lived in deep formation waters.

  5. The Co-III-C bond in (1-thia-4,7-diazacyclodecyl-kappa N-3(4),N-7,C-10)(1,4,7-triazacyclononane-kappa N-3(1),N-4,N-7)-cobalt(III) dithionate hydrate

    DEFF Research Database (Denmark)

    Harris, P.; Kofod, Pauli; Song, Y.

    2003-01-01

    In the title compound, [Co(C6H15N3)(C7H15N2S)]S2O6·H2O, the Co-C bond distance is 1.9930 (13) Å, which is shorter than for related compounds with the linear 1,6-di­amino-3-thia­hexan-4-ide anion in place of the macrocyclic 1-thia-4,7-diazacyclo­decan-8-ide anion. The coordinated carbanion produce...

  6. Structural basis for substrate activation and regulation by cystathionine beta-synthase (CBS) domains in cystathionine [beta]-synthase

    Energy Technology Data Exchange (ETDEWEB)

    Koutmos, Markos; Kabil, Omer; Smith, Janet L.; Banerjee, Ruma (Michigan-Med)

    2011-08-17

    The catalytic potential for H{sub 2}S biogenesis and homocysteine clearance converge at the active site of cystathionine {beta}-synthase (CBS), a pyridoxal phosphate-dependent enzyme. CBS catalyzes {beta}-replacement reactions of either serine or cysteine by homocysteine to give cystathionine and water or H{sub 2}S, respectively. In this study, high-resolution structures of the full-length enzyme from Drosophila in which a carbanion (1.70 {angstrom}) and an aminoacrylate intermediate (1.55 {angstrom}) have been captured are reported. Electrostatic stabilization of the zwitterionic carbanion intermediate is afforded by the close positioning of an active site lysine residue that is initially used for Schiff base formation in the internal aldimine and later as a general base. Additional stabilizing interactions between active site residues and the catalytic intermediates are observed. Furthermore, the structure of the regulatory 'energy-sensing' CBS domains, named after this protein, suggests a mechanism for allosteric activation by S-adenosylmethionine.

  7. TDDFT Study on Different Sensing Mechanisms of Similar Cyanide Sensors Based on Michael Addition Reaction

    Institute of Scientific and Technical Information of China (English)

    Guang-yue Li; Ping Song; Guo-zhong He

    2011-01-01

    The solvents and substituents of two similar fluorescent sensors for cyanide, 7-diethylamino-3-formylcoumarin (sensor a) and 7-diethylamino-3-(2-nitrovinyl)coumarin (sensor b), are proposed to account for their distinct sensing mechanisms and experimental phenomena.The time-dependent density functional theory has been applied to investigate the ground states and the first singlet excited electronic states of the sensor as well as their possible Michael reaction products with cyanide, with a view to monitoring their geometries and photophysical properties. The theoretical study indicates that the protic water solvent could lead to final Michael addition product of sensor a in the ground state, while the aprotic acetonitrile solvent could lead to carbanion as the final product of sensor b. Furthermore,the Michael reaction product of sensor a has been proved to have a torsion structure in its first singlet excited state. Correspondingly, sensor b also has a torsion structure around the nitrovinyl moiety in its first singlet excited state, while not in its carbanion structure. This could explain the observed strong fluorescence for sensor a and the quenching fluorescencefor the sensor b upon the addition of the cyanide anions in the relevant sensing mechanisms.

  8. Correlation between the structure and infra-red absorption characteristics of mono-deuterated compounds: contribution to the study of organo-magnesium compounds; Correlations entre structure et absorption infrarouge de composes monodeuteries; contribution a l'etude des composes organomagnesiens

    Energy Technology Data Exchange (ETDEWEB)

    Paillous, A. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1965-10-01

    The high sensitivity of the {nu} (C-D) vibration to the variations brought about by the substitution of the carbon attached to the deuterium is shown in the case of organic or organo-metallic mono-deuterated molecules. In particular, syntheses of various mono-deuterated organo-magnesium compounds have been carried out; results are given concerning an infra-red spectrometric examination of these compounds in the range 2100 - 2250 cm{sup -1}. The results show the existence of only one type of deuterated carbon, which suggests that the same carbanion is involved in various ionic associations for the different magnesium-containing compounds. (authors) [French] La grande sensibilite de la vibration {nu} (C-D) aux variations apportees dans la substitution du carbone porteur du deuterium est mise en evidence pour des molecules organiques au organometalliques monodeuteriees. On a notamment realise la synthese de divers composes organomagnesiens monodeuteries; les observations auxquelles ils ont donne lieu en spectrometrie infrarouge, dons la zone 2100 - 2250 cm{sup -1}, sont rapportees; les resultats ne mettent en evidence qu'un seul type de carbone deuterie ce qui suggere I'intervention d'un meme carbanion dans des associations ioniques diverses pour les differents reactifs magnesiens. (auteur)

  9. Progress in the experimental observation of thiamin diphosphate-bound intermediates on enzymes and mechanistic information derived from these observations.

    Science.gov (United States)

    Jordan, Frank; Nemeria, Natalia S

    2014-12-01

    Thiamin diphosphate (ThDP), the vitamin B1 coenzyme is an excellent representative of coenzymes, which carry out electrophilic catalysis by forming a covalent complex with their substrates. The function of ThDP is to greatly increase the acidity of two carbon acids by stabilizing their conjugate bases, the ylide/carbene/C2-carbanion of the thiazolium ring and the C2α-carbanion/enamine, once the substrate binds to ThDP. In recent years, several ThDP-bound intermediates on such pathways have been characterized by both solution and solid-state methods. Prominent among these advances are X-ray crystallographic results identifying both oxidative and non-oxidative intermediates, rapid chemical quench followed by NMR detection of several intermediates which are stable under acidic conditions, solid-state NMR and circular dichroism detection of the states of ionization and tautomerization of the 4'-aminopyrimidine moiety of ThDP in some of the intermediates. These methods also enabled in some cases determination of the rate-limiting step in the complex series of steps. This review is an update of a review with the same title published by the authors in 2005 in this Journal. Much progress has been made in the intervening decade in the identification of the intermediates and their application to gain additional mechanistic insight.

  10. Chloro({2-[mesityl(quinolin-8-yl-κNboryl]-3,5-dimethyl-phenyl}methyl-κCpalladium(II as a Catalyst for Heck Reactions

    Directory of Open Access Journals (Sweden)

    Sem Raj Tamang

    2015-07-01

    Full Text Available We recently reported an air and moisture stable 16-electron borapalladacycle formed upon combination of 8-quinolyldimesitylborane with bis(benzonitriledichloropalladium(II. The complex features a tucked mesityl group formed upon metalation of an ortho-methyl group on a mesityl; however it is unusually stable due to contribution of the boron pz orbital in delocalizing the carbanion that gives rise to an η4-boratabutadiene fragment coordinated to Pd(II, as evidenced from crystallographic data. This complex was observed to be a highly active catalyst for the Heck reaction. Data of the catalyst activity are presented alongside data found in the literature, and initial comparison reveals that the borapalladacycle is quite active. The observed catalysis suggests the borapalladacycle readily undergoes reductive elimination; however the Pd(0 complex has not yet been isolated. Nevertheless, the ambiphilic ligand 8-quinolyldimesitylborane may be able to support palladium in different redox states.

  11. IR spectroscopy of gaseous fluorocarbon ions: The perfluoroethyl anion

    Energy Technology Data Exchange (ETDEWEB)

    Crestoni, Maria Elisa; Chiavarino, Barbara [Dipartimento di Chimica e Tecnologie del Farmaco, Universita di Roma ' La Sapienza' , P. le A. Moro 5, I-00185 Roma (Italy); Lemaire, Joel; Maitre, Philippe [Universite Paris Sud, Laboratoire de Chimie Physique - UMR8000 CNRS, Faculte des Sciences - Batiment 350, 91405 Orsay Cedex (France); Fornarini, Simonetta, E-mail: simonetta.fornarini@uniroma1.it [Dipartimento di Chimica e Tecnologie del Farmaco, Universita di Roma ' La Sapienza' , P. le A. Moro 5, I-00185 Roma (Italy)

    2012-04-04

    Highlights: Black-Right-Pointing-Pointer C{sub 2}F{sub 5}{sup -} ions are formed by dissociative electron capture in perfluoropropane. Black-Right-Pointing-Pointer Both their reactivity towards neutrals and IRMPD spectroscopy are investigated. Black-Right-Pointing-Pointer The sampled C{sub 2}F{sub 5}{sup -} ions are best described as covalently bound pentafluoroethyl anions. - Abstract: The first IR spectrum of a perfluorinated carbanion has been obtained in the gas phase by IRMPD spectroscopy. Quantum chemical calculations at the MP2/cc-pVTZ level were performed yielding the optimized geometries and IR spectra for a covalently bound C{sub 2}F{sub 5}{sup -} species and for conceivable loosely bound F{sup -}(C{sub 2}F{sub 4}) complexes. Both the computational results and the IR characterization point to a covalent structure for the assayed species in agreement with the reactivity pattern displayed with selected neutrals.

  12. Thermodynamic and kinetic studies of the equilibration reaction between the sulfur and carbon bonded forms of a cobalt(III) complex with the ligands 1,4,7-triazycyclononane and 1,4-diaza-7-thiacyclodecane

    DEFF Research Database (Denmark)

    Song, Y.S.; Becker, J.; Kofod, Pauli

    1996-01-01

    -sulfur complex to form the alkyl complex gave 100% loss of deuterium. It is concluded that the labile methylene proton is bound to the carbon atom which in the alkyl complex is bound to cobalt(III). From the kinetic data it is estd. that the carbanion reacts with water 270 times faster than it is captured......The new cyclic thioether 1,4-diaza-7-thiacyclodecane, dathicd, has been synthesized and used for the prepn. of the sulfur- and carbon-bonded cobalt(III) complexes: [Co(tacn)(S-dathicd)]Cl3.5H2O and [Co(tacn)(C-dathicd)](ClO4)2 (tacn, 1,4,7-triazacyclononane; C-dathicd, 1,4-diamino-7-thiacyclodecan...

  13. A New Approach to the Asymmetric Reaction of the Chiron 5-L-Menthyloxy-2(5H)-furanones with Horner-Emmons Reagent

    Institute of Scientific and Technical Information of China (English)

    李学强; 王凤荣; 何兰; 陈庆华

    2003-01-01

    The asymmetric reaction of the chiron 2(5H )-furanones (4a-4c) with the Horner-Emmons reagents (5a-5b) has been investigated. The newly chirai organophosphorus derivatives 6 and 7 were obtained using the phosphoryl-stabilized carbanion as a building block in DMSO under mild conditions. Through the asymmetric introduction, the Horner-Emmons reagent could be transformed to a chiral building block to afford the novel functionalized phosphorus derivatives. The structures of the synthesized compounds 6 and 7 were identified on the basis of their elementary and spectroscopic data, such as IR,1H NMR, 13C NMR, MS and X-ray crystallography. These resuits provided a valuable approach to the synthesis of potentially interesting chirai organophosphorus derivatives and probing their biological activities.

  14. A New Asymmetric α-Amido-hydroxyalkylation Mediated by SmI2

    Institute of Scientific and Technical Information of China (English)

    ZHENG Xiao; FENG Chen-Guo; HUNG Pei-Qiang

    2004-01-01

    Polyhydroxylated indolizidine alkaloids, such as castanospermine (Ⅰ) and swainsonine (H)are of longstanding interest due to their powerful glycosidase inhibitory activity. Asymmetric hydroxyatkylation via α-amido carbanions to form C-C bands would provide a convenient approach to these compounds.In continuation of our efforts in developing asyrmmetric o-amido-hydroxyalkylation method,1 we report a new SmI2 mediated flexible asymmetric α-amido-hydroxyalkylation method. Starting from the known (S)-3-hydroxy-2-pyrrolidinone 1,2 sulfide 2 and 3 were prepared. SmI2-mediated reductive metallation of these sulfides followed by reaction with ketones or aldehydes under Barbier conditions provided C2 hydroxyalkylated products 4 in yields ranged from 30% to 83%. High C2/C3 trans diastereoselectivity and mediocre diastereoselectivity at newly formed carbinolic center have been observed. The present method will open an avenue for the asymmetric synthesis of polyhydroxylated indolizidine alkaloids.

  15. How thiamine diphosphate is activated in enzymes.

    Science.gov (United States)

    Kern, D; Kern, G; Neef, H; Tittmann, K; Killenberg-Jabs, M; Wikner, C; Schneider, G; Hübner, G

    1997-01-03

    The controversial question of how thiamine diphosphate, the biologically active form of vitamin B1, is activated in different enzymes has been addressed. Activation of the coenzyme was studied by measuring thermodynamics and kinetics of deprotonation at the carbon in the 2-position (C2) of thiamine diphosphate in the enzymes pyruvate decarboxylase and transketolase by use of nuclear magnetic resonance spectroscopy, proton/deuterium exchange, coenzyme analogs, and site-specific mutant enzymes. Interaction of a glutamate with the nitrogen in the 1'-position in the pyrimidine ring activated the 4'-amino group to act as an efficient proton acceptor for the C2 proton. The protein component accelerated the deprotonation of the C2 atom by several orders of magnitude, beyond the rate of the overall enzyme reaction. Therefore, the earlier proposed concerted mechanism or stabilization of a C2 carbanion can be excluded.

  16. A Serendipitous Synthesis of Bis-Heterocyclic Spiro 3(2H)-Furanones.

    Science.gov (United States)

    Picado, Alfredo; Li, ShengJian; Dieter, R Karl

    2016-02-19

    (Z) Enol triflates 6, 11b-d, (E) enol triflate 11e, and phenol triflate 11a, derived from β-keto esters or 2-carboalkoxy phenols, respectively, react with N-Boc 2-lithiopyrrolidine (5a), N-Boc N-methylaminomethyllithium (5b), or 2-lithio-1,3-dithiane (14) to afford 3(2H)-furanones in modest to good yields (38-81%). Product and carbanion reagent studies suggest that the 3(2H)-furanone is formed in a cascade of reactions involving nucleophilic acyl substitution, enolate formation, trifluoromethyl transfer, iminium or sulfenium ion formation, and subsequent ring closure to form the 3(2H)-furanone. The use of 2-lithio-1,3-dithiane affords a cyclic α-keto-S,S,O-orthoester in which the functionality can be selectively manipulated for synthetic applications.

  17. Nucleophilic reactivities of the anions of nucleobases and their subunits.

    Science.gov (United States)

    Breugst, Martin; Corral Bautista, Francisco; Mayr, Herbert

    2012-01-02

    The kinetics of the reactions of different heterocyclic anions derived from imidazoles, purines, pyrimidines, and related compounds with benzhydrylium ions and structurally related quinone methides have been studied in DMSO and water. The second-order rate constants (log k(2)) correlated linearly with the electrophilicity parameters E of the electrophiles according to the correlation log k(2) = s(N)(N+E) (H. Mayr, M. Patz, Angew. Chem. 1994, 106, 990-1010; Angew. Chem. Int. Ed. Engl. 1994, 33, 938-957) allowing us to determine the nucleophilicity parameters N and s(N) for these anions. In DMSO, the reactivities of these heterocyclic anions vary by more than six orders of magnitude and are comparable to carbanions, amide and imide anions, or amines. The azole anions are generally four to five orders of magnitude more reactive than their conjugate acids.

  18. Mechanism of formation of oil by the hot aqueous alkaline digestion of cellulose

    Energy Technology Data Exchange (ETDEWEB)

    Molten, P.M.; Miller, R.K.; Donovan, J.M.; Demmitt, T.F.

    1977-01-01

    The overall mechanism of cellulose converson in hot aqueous alkali appears to be one of degradation through glucose to low molecular weight saccharinic acids, dihydroxybutyric acid, glycolic acid, and carbonyl products such as acetone, acetaldehyde, formaldehyde, and similar compounds. Although the products identified in the present report were fairly complex furans, carbocyclic ketones, unsaturated hydrocarbons, and aromatic compounds, nevertheless, in most cases, they could have been formed from simple carbonyl compounds through a series of condensations involving carbanion intermediates. It is conceivable that residual alkali in the oil during acetone extraction could have given rise to diacetone alcohol as an artifact. This is refuted by examination of an aqueous residue which was extracted with diethyl ether and which was never exposed to any acetone: Compounds derived from diacetone alcohol (such as mesityl oxide or 4-methyl-3-penten-2-one) were also identified in the diethyl ether extract of the aqueous phase. Other compounds were identified in the oil acetone extract which could not have been derived from acetone or diacetone alcohol, but which could have been formed from other carbonyl compounds by the same mechanism. Hence, diacetone alcohol is a genuine product of cellulose conversion although apparently not an intermediate in further synthesis of other products. The further reaction of the postulated cyclic intermediates, and the route to formation of unsaturated hydrocarbons of high molecular weight is intended to be the next subject of investigation in the current work. The fundamental difference in the mechanism of cellulose conversion to oil by pyrolysis and by aqueous alkaline digestion predicted by theory is therefore confirmed. Pyrolysis products may be explained generally by carbonium ion and free radical reactions (in fact, cellulose decomposition is acid-catalyzed), while in aqueous alkali, nucleophilic carbanion reactions are favored.

  19. Catalysis of acetoin formation by brewers' yeast pyruvate decarboxylase isozymes.

    Science.gov (United States)

    Stivers, J T; Washabaugh, M W

    1993-12-14

    Catalysis of C(alpha)-proton transfer from 2-(1-hydroxyethyl)thiamin diphosphate (HETDP) by pyruvate decarboxylase isozymes (PDC; EC 4.1.1.1) from Saccharomyces carlsbergensis was investigated by determining the steady-state kinetics of the reaction of [1-L]acetaldehyde (L = H, D, or T) to form acetoin and the primary kinetic isotope effects on the reaction. The PDC isozyme mixture and alpha 4 isozyme (alpha 4-PDC) have different steady-state kinetic parameters and isotope effects for acetoin formation in the presence and absence of the nonsubstrate allosteric effector pyruvamide: pyruvamide activation occurs by stabilization of the acetaldehyde/PDC ternary complex. The magnitudes of primary L(V/K)-type (L = D or T) isotope effects on C(alpha)-proton transfer from alpha 4-PDC-bound HETDP provide no evidence for significant breakdown of the Swain-Schaad relationship that would indicate partitioning of the putative C(alpha)-carbanion/enamine intermediate between HETDP and products. The substrate concentration dependence of the deuterium primary kinetic isotope effects provides evidence for an intrinsic isotope effect of 4.1 for C(alpha)-proton transfer from alpha 4-PDC-bound HETDP. A 1.10 +/- 0.02-fold 14C isotope discrimination against [1,2-14C]acetaldehyde in acetoin formation is inconsistent with a stepwise mechanism, in which the addition step occurs after rate-limiting formation of the C(alpha)-carbanion/enamine as a discrete enzyme-bound intermediate, and provides evidence for a concerted reaction mechanism with an important component of carbon-carbon bond formation in the transition state.

  20. Structure of a Class I Tagatose-1,6-bisphosphate Aldolase - Investigation into an Apparent Loss of Stereospecificity

    Energy Technology Data Exchange (ETDEWEB)

    LowKam, C.; Liotard, B; Sygusch, J

    2010-01-01

    Tagatose-1,6-bisphosphate aldolase from Streptococcus pyogenes is a class I aldolase that exhibits a remarkable lack of chiral discrimination with respect to the configuration of hydroxyl groups at both C3 and C4 positions. The enzyme catalyzes the reversible cleavage of four diastereoisomers (fructose 1,6-bisphosphate (FBP), psicose 1,6-bisphosphate, sorbose 1,6-bisphosphate, and tagatose 1,6-bisphosphate) to dihydroxyacetone phosphate (DHAP) and d-glyceraldehyde 3-phosphate with high catalytic efficiency. To investigate its enzymatic mechanism, high resolution crystal structures were determined of both native enzyme and native enzyme in complex with dihydroxyacetone-P. The electron density map revealed a ({alpha}/{beta}){sub 8} fold in each dimeric subunit. Flash-cooled crystals of native enzyme soaked with dihydroxyacetone phosphate trapped a covalent intermediate with carbanionic character at Lys{sup 205}, different from the enamine mesomer bound in stereospecific class I FBP aldolase. Structural analysis indicates extensive active site conservation with respect to class I FBP aldolases, including conserved conformational responses to DHAP binding and conserved stereospecific proton transfer at the DHAP C3 carbon mediated by a proximal water molecule. Exchange reactions with tritiated water and tritium-labeled DHAP at C3 hydrogen were carried out in both solution and crystalline state to assess stereochemical control at C3. The kinetic studies show labeling at both pro-R and pro-S C3 positions of DHAP yet detritiation only at the C3 pro-S-labeled position. Detritiation of the C3 pro-R label was not detected and is consistent with preferential cis-trans isomerism about the C2-C3 bond in the carbanion as the mechanism responsible for C3 epimerization in tagatose-1,6-bisphosphate aldolase.

  1. Mechanistic and stereochemical studies of glycine oxidase from Bacillus subtilis strain R5.

    Science.gov (United States)

    Jamil, Farrukh; Gardner, Qurra-Tul-Ann Afza; Bashir, Qamar; Rashid, Naeem; Akhtar, Muhammad

    2010-08-31

    Glycine oxidase gene from a strain of Bacillus subtilis was cloned and expressed in Escherichia coli. The purified enzyme was found, by mass spectrometry, to have a protein M(r) of 40763 (value of 40761.6 predicted from DNA sequence) and a FAD prosthetic group M(r) of 785.1 (theoretical value of 785.5). Glycine oxidase optimally catalyzes the conversion of glycine and oxygen into glyoxylate, hydrogen peroxide, and ammonia. Using samples of [2-RS-(3)H(2),2-(14)C]-, [2-R-(3)H,2-(14)C]-, and [2-S-(3)H,2-(14)C]glycine, we found that in the overall process H(Si) is removed. Incubation of the enzyme with [2-RS-(3)H(2),2-(14)C]glycine under anaerobic conditions, when only the reducing half of the reaction can occur, led to the recovery of 98.5% of the original glycine, which had the same (3)H:(14)C ratio as the starting substrate. The primary isotope effect was studied using [2-(2)H(2)]glycine, and we found that the specificity constants, k(cat)/K(M), for the protio and deuterio substrates were 1.46 x 10(3) and 1.05 x 10(2) M(-1) s(-1), respectively. Two alternative mechanisms for FAD-containing oxidases that involve either the intermediacy of a FADH(2)-imino acid complex or an amino acid covalently linked to FAD, formed via a carbanion, have been considered. The current knowledge of the mechanisms is reviewed, and we argue that a mechanism involving the FADH(2)-imino acid complex can be dissected to satisfactorily explain some of puzzling observations for which the carbanion mechanism was originally conceived. Furthermore, our results, together with observations in the literature, suggest that the interaction of glycine with the enzyme occurs within a tight ternary complex, which is protected from the protons of the medium.

  2. Mechanistic and computational studies of the reductive half-reaction of tyrosine to phenylalanine active site variants of D-arginine dehydrogenase.

    Science.gov (United States)

    Gannavaram, Swathi; Sirin, Sarah; Sherman, Woody; Gadda, Giovanni

    2014-10-21

    The flavin-mediated enzymatic oxidation of a CN bond in amino acids can occur through hydride transfer, carbanion, or polar nucleophilic mechanisms. Previous results with D-arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) using multiple deuterium kinetic isotope effects (KIEs) and computational studies established preferred binding of the substrate protonated on the α-amino group, with cleavages of the NH and CH bonds occurring in asynchronous fashion, consistent with the three possible mechanisms. The hydroxyl groups of Y53 and Y249 are ≤4 Å from the imino and carboxylate groups of the reaction product iminoarginine, suggesting participation in binding and catalysis. In this study, we have investigated the reductive half-reactions of the Y53F and Y249F variants of PaDADH using substrate and solvent deuterium KIEs, solvent viscosity and pH effects, and quantum mechanical/molecular mechanical computational approaches to gain insights into the catalytic roles of the tyrosines and evaluate whether their mutations affect the transition state for substrate oxidation. Both Y53F and Y249F enzymes oxidized D-arginine with steady-state kinetic parameters similar to those of the wild-type enzyme. Rate constants for flavin reduction (k(red)) with D-leucine, a slow substrate amenable to rapid kinetics, were 3-fold smaller than the wild-type value with similar pKa values for an unprotonated group of ∼10.0. Similar pKa values were observed for (app)Kd in the variant and wild-type enzymes. However, cleavage of the substrate NH and CH bonds in the enzyme variants occurred in synchronous fashion, as suggested by multiple deuterium KIEs on k(red). These data can be reconciled with a hydride transfer mechanism, but not with carbanion and polar nucleophilic mechanisms.

  3. Diversification of ortho-Fused Cycloocta-2,5-dien-1-one Cores and Eight- to Six-Ring Conversion by σ Bond C-C Cleavage.

    Science.gov (United States)

    Eccleshare, Lee; Lozada-Rodríguez, Leticia; Cooper, Phillippa; Burroughs, Laurence; Ritchie, John; Lewis, William; Woodward, Simon

    2016-08-22

    Sequential treatment of 2-C6 H4 Br(CHO) with LiC≡CR(1) (R(1) =SiMe3 , tBu), nBuLi, CuBr⋅SMe2 and HC≡CCHClR(2) [R(2) =Ph, 4-CF3 Ph, 3-CNPh, 4-(MeO2 C)Ph] at -50 °C leads to formation of an intermediate carbanion (Z)-1,2-C6 H4 {CA (=O)C≡CB R(1) }{CH=CH(CH(-) )R(2) } (4). Low temperatures (-50 °C) favour attack at CB leading to kinetic formation of 6,8-bicycles containing non-classical C-carbanion enolates (5). Higher temperatures (-10 °C to ambient) and electron-deficient R(2) favour retro σ-bond C-C cleavage regenerating 4, which subsequently closes on CA providing 6,6-bicyclic alkoxides (6). Computational modelling (CBS-QB3) indicated that both pathways are viable and of similar energies. Reaction of 6 with H(+) gave 1,2-dihydronaphthalen-1-ols, or under dehydrating conditions, 2-aryl-1-alkynylnaphthlenes. Enolates 5 react in situ with: H2 O, D2 O, I2 , allylbromide, S2 Me2 , CO2 and lead to the expected C-E derivatives (E=H, D, I, allyl, SMe, CO2 H) in 49-64 % yield directly from intermediate 5. The parents (E=H; R(1) =SiMe3 , tBu; R(2) =Ph) are versatile starting materials for NaBH4 and Grignard C=O additions, desilylation (when R(1) =SiMe) and oxime formation. The latter allows formation of 6,9-bicyclics via Beckmann rearrangement. The 6,8-ring iodides are suitable Suzuki precursors for Pd-catalysed C-C coupling (81-87 %), whereas the carboxylic acids readily form amides under T3P® conditions (71-95 %).

  4. Mechanism of the Orotidine 5’-Monophosphate Decarboxylase-Catalyzed Reaction: Importance of Residues in the Orotate Binding Site†

    Science.gov (United States)

    Iiams, Vanessa; Desai, Bijoy J.; Fedorov, Alexander A.; Fedorov, Elena V.; Almo, Steven C.; Gerlt, John A.

    2011-01-01

    The reaction catalyzed by orotidine 5’-monophosphate decarboxylase (OMPDC) is accompanied by exceptional values for the rate enhancement [kcat/knon = 7.1 × 1016] and catalytic proficiency [(kcat/KM)/knon = 4.8 × 1022 M−1]. Although a stabilized vinyl carbanion/carbene intermediate is located on the reaction coordinate, the structural strategies by which the reduction in the activation energy barrier is realized remain incompletely understood. This laboratory recently reported that “substrate destabilization” by Asp 70 in the OMPDC from Methanothermobacter thermoautotrophicus (MtOMPDC) lowers the activation energy barrier by ~5 kcal/mol (contributing ~2.7 × 103 to the rate enhancement) [K. K. Chan, B. M. Wood, A. A. Fedorov, E. V. Fedorov, H. J. Imker, T. L. Amyes, J. P. Richard, S. C. Almo, and J. A. Gerlt (2009) Biochemistry 48, 5518–31]. We now report that substitutions of hydrophobic residues in a pocket proximal to the carboxylate group of the substrate (Ile 96, Leu 123, and Val 155) with neutral hydrophilic residues decrease the value of kcat by as much as 400-fold but have minimal effect on the value of kex for exchange of H6 of the FUMP product analog with solvent deuterium; we hypothesize that this pocket destabilizes the substrate by preventing hydration of the substrate carboxylate group. We also report that substitutions for Ser 127 that is proximal to O4 of the orotate ring decrease the value of kcat/KM, with the S127P substitution that eliminates hydrogen-bonding interactions with O4 producing a 2.5 × 106-fold reduction in the value of kcat/KM; this effect is consistent with delocalization of the negative charge of the carbanionic intermediate on O4 to produce an anionic carbene intermediate and thereby provide a structural strategy for stabilization of the intermediate. These observations provide additional information on the identities of the active site residues that contribute to the rate enhancement and, therefore, insights into the

  5. Microwave-Assisted Decarboxylation of Sodium Oleate and Renewable Hydrocarbon Fuel Production

    Institute of Scientific and Technical Information of China (English)

    Wang Yunpu; Liu Yuhuan; Ruan Rongsheng; Wen Pingwei; Wan Yiqin; Zhang Jinsheng

    2013-01-01

    The carboxyl terminal of sodium oleate has a stronger polarity than that of oleic acid;this terminal is more likely to be dipole polarized and ionically conductive in a microwave ifeld. Sodium oleate was used as the model compound to study the decarboxylation of oleic acid leading to hydrocarbon formation via microwave-assisted pyrolysis technology. The pyrolysis gas, liquid, and solid products were precisely analyzed to deduce the mechanism for decarboxylation of sodium oleate. Microwave energy was able to selectively heat the carboxyl terminal of sodium oleate. During decarboxylation, the double bond in the long hydrocarbon chain formed a p-πconjugated system with the carbanion intermediate. The resulting p-πconjugated system was more stable and beneifcial to the pyrolysis reaction (decarboxylation, terminal allylation, isomeriza-tion, and aromatization). The physical properties of pyrolysis liquid were generally similar to those of diesel fuel, thereby demonstrating the possible use of microwaves for controlling the decarboxylation of sodium oleate in order to manufacture renewable hydrocarbon fuels.

  6. Enhanced ethylene and ethane production with free-radical cracking catalysts.

    Science.gov (United States)

    Kolts, J H; Delzer, G A

    1986-05-09

    A series of free-radical catalysts have been discovered that increase the yield of highly valuable olefins from the cracking of low molecular weight paraffins. For example, catalytic cracking of n-butane, isobutane, and propane over manganese or iron supported on magnesium oxide (MgO) gave product distributions different from those given by thermal (free-radical) cracking or cracking over traditional acid catalysts. With n-butane and propane feeds, the products from catalytic cracking included large amounts of ethylene and ethane; with isobutane feed, propylene was the major product. Physical characterization of the MgO-supported catalyst showed the manganese to be in a 2+ oxidation state in the reduced catalyst and a 4+ oxidation state in the fully oxidized catalyst. Manganese was also shown to be uniformly distributed in the support material with very little enrichment at the surface. Matrix isolation of the gasphase radicals from n-butane feed showed that ethyl and methyl radicals were produced over the active catalysts. In the thermal process, only methyl radicals were produced. The mechanism of the catalytic reaction appears to be selective formation of primary carbanions at the catalyst surface followed by electron transfer and release of primary hydrocarbon radicals to the gas phase.

  7. C{sub 2}{sup +} selectivity enhancement in oxidative coupling of methane over microwave-irradiated catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Roussy, G.; Marchal, E.; Thiebaut, J.M.; Kiennemann, A.; Maire, G. [L.S.T.M. Universite Henri Poincare Nancy, Vandoeuvre-les-Nancy (France)

    1997-02-01

    The oxidative coupling of methane over Li/MgO and BaBiO{sub 3-x} catalysts irradiated by microwaves and classically heated is reported. Enhanced selectivities in C{sub 2}{sup +} products are observed at lower temperatures under microwave conditions, especially with the Li/MgO catalyst. The complex permittivity measurements of BaBiO{sub 3-x} show that the regeneration of the active oxygen species on the surface is lower under microwave irradiation than classical heating. X-ray diffraction analyses of the catalyst before and after catalytic reaction, when it is classically heated and when it is heated by microwave irradiation, corroborate these results. Therefore, the CH{sub 3}{sup -} carbanions are less oxidated at the catalyst surface under microwave irradiation. On the other hand, the quenching of the output gas probably decreases the oxidation of CH{sub 3}{sup 0} radicals in the gas phase when the Li/MgO catalyst is irradiated by microwaves. The quenching of the output gas is a unique consequence of microwave irradiation which heats the catalyst without heating the wall of the reactor. 26 refs., 9 figs.

  8. Investigation of the gas-phase hydrogen/deuterium exchange behavior of aromatic dicarboxylic acids in a quadrupole ion trap

    Science.gov (United States)

    Chipuk, Joseph E.; Brodbelt, Jennifer S.

    2007-11-01

    Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid and 2,6-naphthalic acid) with D2O were performed in a quadrupole ion trap mass spectrometer. Experimental results showed significant differences in the rate and extent of exchange when the relative position of the carboxylic acid groups varied. Spontaneous and near complete exchange of one aromatic hydrogen atom occurred when the carboxylic acid groups were in the meta-position, whereas no additional exchange was observed for either the ortho- or para-isomers or for the structurally similar naphthalic acid. Computational investigations support the participation of several possible exchange mechanisms with the contribution of each relying heavily on the relative orientation of the acid moieties. A relay mechanism that bridges the deprotonation site and the labile hydrogen site appears to be responsible for the H/D exchange of not only the labile hydrogen atom of isophthalic acid, but also for the formation of a stable carbanion and corresponding subsequent exchange of one aromatic hydrogen atom. The impact of hydrogen bonding on the relay mechanism is demonstrated by the reaction of phthalic acid as the extent and rate of reaction are greatly retarded by the favorable interaction of the two carboxylic acid groups. Finally, a flip-flop mechanism is likely responsible for the exchange of both terephthalic acid and 2,6-naphthalic acid where the reactive sites are too remote for exchange via relay.

  9. Insights into the Thiamine Diphosphate Enzyme Activation Mechanism: Computational Model for Transketolase Using a Quantum Mechanical/Molecular Mechanical Method.

    Science.gov (United States)

    Nauton, Lionel; Hélaine, Virgil; Théry, Vincent; Hecquet, Laurence

    2016-04-12

    We propose the first computational model for transketolase (TK), a thiamine diphosphate (ThDP)-dependent enzyme, using a quantum mechanical/molecular mechanical method on the basis of crystallographic TK structures from yeast and Escherichia coli, together with experimental kinetic data reported in the literature with wild-type and mutant TK. This model allowed us to define a new route for ThDP activation in the enzyme environment. We evidenced a strong interaction between ThDP and Glu418B of the TK active site, itself stabilized by Glu162A. The crucial point highlighted here is that deprotonation of ThDP C2 is not performed by ThDP N4' as reported in the literature, but by His481B, involving a HOH688A molecule bridge. Thus, ThDP N4' is converted from an amino form to an iminium form, ensuring the stabilization of the C2 carbanion or carbene. Finally, ThDP activation proceeds via an intermolecular process and not by an intramolecular one as reported in the literature. More generally, this proposed ThDP activation mechanism can be applied to some other ThDP-dependent enzymes and used to define the entire TK mechanism with donor and acceptor substrates more accurately.

  10. Computational exploration of the reaction mechanism of the Cu(+)-catalysed synthesis of indoles from N-aryl enaminones.

    Science.gov (United States)

    Bernardo, Carlos E P; Silva, Pedro J

    2016-02-01

    We have studied the role of Cu(+)-phenantroline as a catalyst in the cyclization of N-aryl-enaminones using density-functional theory computations. The catalyst was found to bind the substrate upon deprotonation of its eneaminone, and to dramatically increase the acidity of the carbon adjacent to the ketone functionality. The deprotonation of this carbon atom yields a carbanion which attacks the aryl moiety, thereby closing the heterocycle in the rate-determining step. This C-C bond forming reaction was found to proceed much more rapidly when preceded by re-protonation of the substrate N-atom (which had lost H(+) in the initial step). Hydride transfer to the catalyst then completes the indole synthesis, in a very fast step. The influence of Li(+) and K(+) on the regio-selectivity of the cyclization of bromo-substituted analogues could not, however, be reproduced by our model. Alternative pathways involving either single-electron transfer from the catalyst to the substrate or ring cyclization without previous carbon α-deprotonation were found to be kinetically or thermodynamically inaccessible.

  11. Atomic resolution structures of discrete stages on the reaction coordinate of the [Fe4S4] enzyme IspG (GcpE)

    KAUST Repository

    Quitterer, Felix

    2015-04-11

    IspG is the penultimate enzyme in non-mevalonate biosynthesis of the universal terpene building blocks isopentenyl diphosphate and dimethylallyl diphosphate. Its mechanism of action has been the subject of numerous studies but remained unresolved due to difficulties in identifying distinct reaction intermediates. Using a moderate reducing agent as well as an epoxide substrate analogue, we were now able to trap and crystallographically characterize various stages in the IspG catalyzed conversion of 2-C-methyl-D-erythritol-2,4-cyclo-diphosphate (MEcPP) to (E)-1-hydroxy-2-methylbut-2-enyl-4-diphosphate (HMBPP). In addition, the enzyme’s structure was determined in complex with several inhibitors. These results, combined with recent electron paramagnetic resonance data, allowed us to deduce a detailed and complete IspG catalytic mechanism which describes all stages from initial ring opening to formation of HMBPP via discrete radical and carbanion intermediates. The data presented in this article provide a guide for the design of selective drugs against many pro- and eukaryotic pathogens to which the non-mevalonate pathway is essential for survival and virulence.

  12. Electrochemical Studies of Betti Base and Its Copper(II Complex by Cyclic and Elimination Voltammetry

    Directory of Open Access Journals (Sweden)

    Shardul Bhatt

    2013-01-01

    Full Text Available The electrochemical behavior of Betti base 1-(α-amino benzyl-2-naphthol (BB and its copper(II complex by cyclic and elimination voltammetry (EVLS is reported in the present study. The cyclic voltammetric studies carried out at a glassy carbon working electrode, Ag/Ag+ reference electrode (0.01 M AgNO3 in acetonitrile in DCM at 100 mV/sec, 200 mV/sec, and 400 mV/sec scan rates indicated a preceding chemical oxidation of the adsorbed BB species to form an iminium ion followed by formation of a carbanion via two-step quasireversible reduction. The suggested reaction mechanism has been supported by the elimination voltammetry. The CV and EVLS studies revealed Cu(IIBB complex to undergo a chemical or a surface reaction before electron transfer from the electrode at −0.49 V to form Cu(IBB species. The oxidation of Cu(IBB species has been observed to be CV silent.

  13. Crystal and Molecular Structure Studies of Ethyl 4-(4-Hydroxyphenyl-6-(6-methoxy-2-naphthyl-2-oxocyclohex-3-ene-1-carboxylate and Ethyl 4-(3-Bromophenyl-6-(6-methoxy-2-naphthyl-2-oxocyclohex-3-ene-1-carboxylate

    Directory of Open Access Journals (Sweden)

    Badiadka Narayana

    2012-08-01

    Full Text Available The crystal and molecular structures of the title compounds, ethyl 4-(4-hydroxyphenyl-6-(6-methoxy-2-naphthyl-2-oxocyclohex-3-ene-1-carboxylate (I and ethyl 4-(3-bromophenyl-6-(6-methoxy-2-naphthyl-2-oxocyclohex-3-ene-1-carboxylate (II, are reported and confirmed by single crystal X-ray diffraction data. Compound (I, C26H24O5, crystallizes from a methanol solution in the monoclinic C2/c space group with eight molecules in the unit cell. The unit cell parameters are: a = 25.4114(5 Å, b = 8.47440(10 Å, c = 20.6921(4 Å, β = 108.328(2° and V = 4229.92(13 Å3. Disorder is observed throughout the entire molecule with an occupancy ratio 0.690(2:0.310(2. Compound (II, C26H23O4Br, crystallizes from an ethyl acetate solution in the monoclinic P21/c spacegroup with four molecules in the unit cell. The unit cell parameters are a = 17.8991(9 Å, b = 11.4369(6 Å, c = 10.8507(5 Å, β = 92.428(4° and V = 2219.25(19 Å3. Disorder is observed in the cyclohexenone ring and the carboxylate group with an occupancy ratio 0.830(6:0.170(6. Weak O–H...O (I or C–H...O (II intermolecular interactions are observed which influence crystal packing stability. These chalcone derivative types of molecules are important in their ability to act as activated unsaturated systems in conjugated addition reactions of carbanions in the presence of basic catalysts which exhibit a multitude of biological activities.

  14. Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

    Directory of Open Access Journals (Sweden)

    Shinichi Yamabe

    2014-01-01

    Full Text Available Wolff–Kishner reduction reactions were investigated by DFT calculations for the first time. B3LYP/6-311+G(d,p SCRF=(PCM, solvent = 1,2-ethanediol optimizations were carried out. To investigate the role of the base catalyst, the base-free reaction was examined by the use of acetone, hydrazine (H2N–NH2 and (H2O8. A ready reaction channel of acetone → acetone hydrazine (Me2C=N–NH2 was obtained. The channel involves two likely proton-transfer routes. However, it was found that the base-free reaction was unlikely at the N2 extrusion step from the isopropyl diimine intermediate (Me2C(H–N=N–H. Two base-catalyzed reactions were investigated by models of the ketone, H2N–NH2 and OH−(H2O7. Here, ketones are acetone and acetophenone. While routes of the ketone → hydrazone → diimine are similar, those from the diimines are different. From the isopropyl diimine, the N2 extrusion and the C–H bond formation takes place concomitantly. The concomitance leads to the propane product concertedly. From the (1-phenylethyl substituted diimine, a carbanion intermediate is formed. The para carbon of the phenyl ring of the anion is subject to the protonation, which leads to a 3-ethylidene-1,4-cyclohexadiene intermediate. Its [1,5]-hydrogen migration gives the ethylbenzene product. For both ketone substrates, the diimines undergoing E2 reactions were found to be key intermediates.

  15. Advances in flowing afterglow and selected-ion flow tube techniques

    Science.gov (United States)

    Squires, Robert R.

    1992-09-01

    New developments in flowing afterglow and selected-ion flow tube (SIFT) techniques are briefly reviewed. Particular emphasis is given to the new chemical and physical information that can be obtained with use of the tandem flowing afterglow-triple quadrupole apparatus developed in the author's laboratory. Several outstanding recent achievements in the design and utilization of flowing afterglow and SIFT instruments in other laboratories are briefly highlighted that illustrate the power and flexibility of flow-tube-based methods. These include isotope tracer experiments with the tandem flowing afterglow-SIFT instrument in Boulder, studies of large molecular cluster ions with the variable temperature facility at Penn State, and gas-phase metal ion reactions with the laser ablation/fast flow reactor in Madison. Recent applications of the flowing afterglow-triple quadrupole instrument in our laboratory have made use of collision-induced dissociation (CID) as a tool for synthesizing novel ions and for obtaining new thermo-chemical information from threshold energy measurements. Collision-induced decar☐ylation of organic car☐ylate ions provides access to a variety of unusual and highly basic carbanions that cannot be generated with conventional ion sources. The formation and properties of saturated alkyl ions and studies of gas-phase reactions of the methyl anion are briefly described. We have developed a new method for carrying out "preparative CID" in a flowing afterglow with use of a mini-drift tube; some recent applications of this new ion source are presented. Measurement of CID thresholds for simple cleavage reactions of thermalized ions can provide accurate measures of bond strengths, gas-phase acidities and basicities, and heats of formation for ions and reactive neutral species. Applications of this approach in the thermochemical characterization of carbenes, benzynes and biradicals are described. Future prospects for the continued development of flow

  16. Primary deuterium isotope effects for the 3-methylaspartase-catalyzed deamination of (2S)-aspartic acid, (2S,3S)-3-ethylaspartic acid, and (2S,3S)-3-ethylaspartic acid

    Energy Technology Data Exchange (ETDEWEB)

    Botting, N.P.; Cohen, M.A.; Akhtar, M.; Gani, D.

    1988-04-19

    3-Methylaspartate ammonia-lyase catalyzes the deamination of (2S)-aspartic acid 137 times more slowly than the deamination of (2S,3S)-3-methylaspartic acid but catalyzes the amination of fumaric acid 1.8 times faster than the amination of mesaconic acid. In order to understand the mechanistic basis for these observations, the deamination reaction was examined kinetically with (2S)-aspartic acid, (2S,3S)-3-methylaspartic acid, (2S,3S)-3-ethylaspartic acid, and the corresponding C-3-deuteriated isotopomers. Comparison of the double-reciprocal plots of the initial reaction velocities for each of the three pairs of substrates revealed that the magnitude of the primary isotope effect on both V/sub max/ and VK varied with the substituent at C-3 of the substrate. These results, which are inconsistent with earlier reports that there is no primary isotope effect for 3-methylaspartic acid, suggest that for both 3-methylaspartic acid and 3-ethylaspartic acid elimination occurs via a predominantly concerted mechanism whereas for aspartic acid in El/sub cb/ mechanism prevails. It is expected that the change in mechanism arises as a result of the loss of the hydrophobic interaction between the C-3-alkyl substituent of the substrate and the complementary active site pocket of the enzyme, which leads to poor orbital alignment of the nascent negative charge with the C-N bond in the carbanion derived from aspartic acid. Substrate C-3 hydrogen exchange experiments suggest that the intermediate carbanionconjugate acid is not accessible to solvent during catalysis.

  17. Mechanism of Hg-C Protonolysis in the Organomercurial Lyase MerB

    Energy Technology Data Exchange (ETDEWEB)

    Parks, Jerry M [ORNL; Guo, Hong [ORNL; Liang, Liyuan [ORNL; Miller, Susan M [ORNL; Summers, Anne O [ORNL; Smith, Jeremy C [ORNL

    2009-01-01

    Demethylation is a key reaction in global mercury cycling. The bacterial organomercurial lyase, MerB, catalyzes the demethylation of a wide range of organomercurials via Hg-C protonolysis. Two strictly conserved cysteine residues in the active site are required for catalysis, but the source of the catalytic proton and the detailed reaction mechanism have not been determined. Here, the two major proposed reaction mechanisms of MerB are investigated and compared using hybrid density functional theory calculations. A model of the active site was constructed from an X-ray crystal structure of the Hg(II)-bound MerB product complex. Stationary point structures and energies characterized for the Hg-C protonolysis of methylmercury rule out the direct protonation mechanism in which a cysteine residue delivers the catalytic proton directly to the organic leaving group. Instead, the calculations support a two-step mechanism in which Cys96 or Cys159 first donates a proton to Asp99, enabling coordination of two thiolates with R-Hg(II). At the rate-limiting transition state, Asp99 protonates the nascent carbanion in a trigonal planar, bis thiol-ligated R-Hg(II) species to cleave the Hg-C bond and release the hydrocarbon product. Reactions with two other substrates, vinylmercury and cis-2-butenyl-2-mercury, were also modeled, and the computed activation barriers for all three organomercurial substrates reproduce the trend in the experimentally observed enzymatic reaction rates. Analysis of atomic charges in the rate-limiting transition state structure using Natural Population Analysis shows that MerB lowers the activation free energy in the Hg-C protonolysis reaction by redistributing electron density into the leaving group and away from the catalytic proton.

  18. The properties and the use of substituted benzofuroxans in pharmaceutical and medicinal chemistry: a comprehensive review.

    Science.gov (United States)

    Jovené, Cyril; Chugunova, Elena A; Goumont, Régis

    2013-06-01

    Since the synthesis of 4,6-dinitrobenzofuroxan in 1899 by Drost, benzofuroxans have attracted particular attention. This peculiar series of compounds exhibit a broad spectrum of biological activity including antibacterial, antifungal, antileukemic, acaricide and immunodepressive properties. These works embrace a period of more than 50 years since the pioneering paper of Gosh and Whitehouse and papers in this major field of the heterocyclic chemistry are still published in 2013. The review has been built in two independent parts. The first one is directly dedicated to the structure of substituted benzofuroxans and will show many medicinal applications of these compounds such as nitric oxide-releasing abilities, induction of oxidative stress, potent anti-cancer agents, anti-chagas agent, target for antiamoebic agent, Ca2+ channel blockers or cytotoxic, mutagenic and genotoxic agent… The second part of this review will be in close connection with the use of benzofuroxans as synthetic precursors in the preparation of new biological compounds such as quinoxaline dioxide, benzimidazole and phenazine derivatives. The interaction of substituted benzofuroxans with electron rich heterocycles or carbanions is the key step in the synthesis of these new biological active compounds. These derivatives can be used as cytotoxic drugs, antimycobacterial agent and display anti-malarial, antileishmanial and antituberculosis activity. The nature of the substituent linked to the carbocyclic ring of benzofuroxan is of primary importance to understand the medicinal properties of this family of compounds. For example, when benzofuroxans are substituted by electron-releasing substituents, the chemical reactivity is transferred from the carbocyclic ring to the furoxan ring.

  19. Reaction monitoring using hyperpolarized NMR with scaling of heteronuclear couplings by optimal tracking

    Science.gov (United States)

    Zhang, Guannan; Schilling, Franz; Glaser, Steffen J.; Hilty, Christian

    2016-11-01

    Off-resonance decoupling using the method of Scaling of Heteronuclear Couplings by Optimal Tracking (SHOT) enables determination of heteronuclear correlations of chemical shifts in single scan NMR spectra. Through modulation of J-coupling evolution by shaped radio frequency pulses, off resonance decoupling using SHOT pulses causes a user-defined dependence of the observed J-splitting, such as the splitting of 13C peaks, on the chemical shift offset of coupled nuclei, such as 1H. Because a decoupling experiment requires only a single scan, this method is suitable for characterizing on-going chemical reactions using hyperpolarization by dissolution dynamic nuclear polarization (D-DNP). We demonstrate the calculation of [13C, 1H] chemical shift correlations of the carbanionic active sites from hyperpolarized styrene polymerized using sodium naphthalene as an initiator. While off resonance decoupling by SHOT pulses does not enhance the resolution in the same way as a 2D NMR spectrum would, the ability to obtain the correlations in single scans makes this method ideal for determination of chemical shifts in on-going reactions on the second time scale. In addition, we present a novel SHOT pulse that allows to scale J-splittings 50% larger than the respective J-coupling constant. This feature can be used to enhance the resolution of the indirectly detected chemical shift and reduce peak overlap, as demonstrated in a model reaction between p-anisaldehyde and isobutylamine. For both pulses, the accuracy is evaluated under changing signal-to-noise ratios (SNR) of the peaks from reactants and reaction products, with an overall standard deviation of chemical shift differences compared to reference spectra of 0.02 ppm when measured on a 400 MHz NMR spectrometer. Notably, the appearance of decoupling side-bands, which scale with peak intensity, appears to be of secondary importance.

  20. Stereoselective synthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-ulose via autoxidation reaction

    Institute of Scientific and Technical Information of China (English)

    LIU Hong-Min; ZHANG Fuyi; TAO Jing-Chao

    2004-01-01

    can be rationalized by autoxidationof 1 followed by 1,4-Michael addition of various carbanions as the main steps.

  1. Conformational Changes in Orotidine 5’-Monophosphate Decarboxylase: A Structure-Based Explanation for How the 5’-Phosphate Group Activates the Enzyme†

    Science.gov (United States)

    Desai, Bijoy J.; Wood, McKay; Fedorov, Alexander A.; Fedorov, Elena V.; Goryanova, Bogdana; Amyes, Tina L.; Richard, John P.; Almo, Steven C.; Gerlt, John A.

    2012-01-01

    The binding of a ligand to orotidine 5’-monophosphate decarboxylase (OMPDC) is accompanied by a conformational change from an open, inactive conformation (Eo) to a closed, active conformation (Ec). As the substrate traverses the reaction coordinate to form the stabilized vinyl carbanion/carbene intermediate, interactions are enforced that destabilize the carboxylate group of the substrate as well as stabilize the intermediate (in the Ec•S‡ complex). Focusing on the OMPDC from Methanothermobacter thermautotrophicus, the “remote” 5’-phosphate group of the substrate activates the enzyme 2.4 × 108-fold; the activation is equivalently described by an intrinsic binding energy (IBE) of 11.4 kcal/mol. We studied residues in the activation that 1) directly contact the 5’-phosphate group; 2) participate in a hydrophobic cluster near the base of the active site loop that sequesters the bound substrate from solvent; and 3) form hydrogen-bonding interactions across the interface between the “mobile” and “fixed” half-barrel domains of the (β/α8-barrel structure. Our data support a model in which the IBE provided by the 5’-phosphate group is used to enable interactions both near the N-terminus of the active site loop and across the domain interface that stabilize both the Ec•S and Ec•S‡ complexes relative to the Eo•S complex. The conclusion that the IBE of the 5’-phosphate group provides stabilization of both the Ec•S and Ec•S‡ complexes, not just the Ec•S‡ complex, is central to understanding the structural origins of enzymatic catalysis as well as the requirements for the de novo design of enzymes that catalyze novel reactions. PMID:23030629

  2. Breakdown kinetics of C-hydroxymethyl beta-dicarbonyl derivatives of carbon acids: implications in the bioconversion rate of C-phosphoryloxymethyl prodrugs of carbon acids.

    Science.gov (United States)

    Dhareshwar, Sundeep S; Stella, Valentino J

    2009-05-01

    The kinetics of conversion of C-hydroxymethyl derivatives of pharmaceutically relevant beta-dicarbonyl carbon acids of two series, pyrazolidin-3,5-diones and inden-1,3-diones, and a model carbon acid back to the respective carbon acids were studied as a function of pH at 25 degrees C and an ionic strength of 0.15 M. This is a somewhat surprising reaction since it involves the facile breakdown of a carbon-carbon bond. The slopes of the pH-rate profiles for the dehydroxymethylation were approximately unity, which along with the lack of buffer catalysis, indicates a specific-base mechanism involving spontaneous breakdown of the oxymethyl anion. This breakdown generates the conjugate base of the respective carbon acids. Thus within a series, there exists a correlation between the second-order rate constant for dehydroxymethylation and the pK(a) of the corresponding carbon acid with a shorter conversion/dehydroxymethylation half-life (at all given pH values) with decreasing pK(a) of the parent carbon acid. The increasing acidity of the carbon acid affords an increase in the leaving group ability of the carbanion, and therefore facilitation of the rate-determining unimolecular carbon-carbon bond cleavage. Since the hydroxymethyl derivative is an intermediate in the bioconversion of C-phosphoryloxymethyl prodrugs of carbon acids, also under study, the relationship allows one to reasonably predict how facile the dehydroxymethylation would be for any new beta-dicarbonyl carbon acid.

  3. Inorganic base-catalyzed formation of antivirally active N-substituted benzamides from α-amido sulfones and N-nucleophile

    Directory of Open Access Journals (Sweden)

    Wang Zhenchao

    2011-05-01

    Full Text Available Abstract Background Heteronucleophiles as well as carbanionic reagents can be used to react with α-amido sulfones, thus giving the opportunity to prepare a large array of amino derivatives. Since, novel 1,3,4-oxadiazole-2-thiol derivatives can serve as potent nucleophiles, we employed 5-subsititued phenyl-1,3,4-oxadiazole-2-thiols as the nucleophilic source of nitrogen in the reaction with α-amido sulfones. Results A series of N-substituted benzamides bearing 1,3,4-oxadiazol unit were prepared for the first time by the reaction of in situ generated protected imine from α-amido sulfones with 5-subsititued phenyl-1,3,4-oxadiazole-2-thiols as the source of nitrogen nucleophile. Some of the synthesized products displayed favourable antiviral activity against cucumber mosaic virus (CMV in preliminary antiviral activity tests. The title compounds 5c, 5o and 5r revealed curative activity of 42.2%, 48.7% and 40.5%, respectively against CMV (inhibitory rate compared to the commercial standard Ningnanmycin (53.4% at 500 μg/mL. Conclusion A practical synthetic route to N-benzoyl-α-amido sulfones by the reaction of 5-subsititued phenyl-1,3,4-oxadiazole-2-thiols as the source of nitrogen nucleophiles with in situ generated protected imine from N-benzoyl-α-amido sulfones is presented. The reaction catalyzed by an inorganic base has considerable significance to exploit the potential of α-amido sulfones in organic synthesis.

  4. Study of the lithiated phenylacetonitrile monoanions and dianions formed according to the lithiated base used (LHMDS, LDA, or n-BuLi). 2. Alkylation and deuteriation mechanism study by vibrational and NMR spectroscopy and quantum chemistry calculations.

    Science.gov (United States)

    Strzalko, Tekla; Wartski, Lya; Corset, Jacques; Castellà-Ventura, Martine; Froment, Françoise

    2012-08-01

    Mechanisms of alkylation by PhCH(2)Cl or CH(3)I in THF and of deuteriation by DCl (4 N in D(2)O) in THF or THF-toluene of lithiated phenylacetonitrile monoanions and dianions obtained with LHMDS, LDA, or n-BuLi are studied by vibrational and NMR spectroscopy and quantum chemistry calculations. Dialkylation of the three dilithio dianions generated with n-BuLi (2.0-2.7 equiv, THF-hexane) depends on their structure: N-lithio (PhCCNLi)(-)Li(+) and (C,N)-dilithio PhCLiCNLi dianions afford PhCR(2)CN (R = PhCH(2), CH(3)) from the intermediate N-lithio monoalkylated monoanion PhCRCNLi 10; C-lithio dianion (PhCLiCN)(-)Li(+) leads to a carbenoid species, the C-lithio monoalkylated nitrile PhCLiRCN 11, which either eliminates carbene Ph-C-R and different LiCN species or isomerizes to PhCRCNLi in the presence of LiX (X = Cl, I). Dialkylation or dideuteriation of monoanions (monomers, dimers, and heterodimers [PhCHCNLi·LiR'], R' = (SiMe(3))(2)N, (i-Pr)(2)N) obtained with LHMDS or LDA (2.4 equiv, THF) proceeds via a sequential mechanism involving monometalation-monoalkylation (or monodeuteriation) reactions. Some carbene and (LiCNLi)(+) are also observed, and explained by another mechanism implying the C-lithio monoalkylated monoanion PhCLiRCN 9 in the presence of LiX. These results show the ambiphilic behavior of PhCLiRCN as a carbenoid (11) or a carbanion (9) and the importance of LiX formed in situ in the first alkylation step.

  5. Gas chromatographic determination and mechanism of formation of D-amino acids occurring in fermented and roasted cocoa beans, cocoa powder, chocolate and cocoa shell.

    Science.gov (United States)

    Pätzold, R; Brückner, H

    2006-07-01

    Fermented cocoa beans of various countries of origin (Ivory Coast, Ghana, Sulawesi), cocoa beans roasted under defined conditions (100-150 degrees C; 30-120 min), low and high fat cocoa powder, various brands of chocolate, and cocoa shells were analyzed for their contents of free L-and D-amino acids. Amino acids were isolated from defatted products using a cation exchanger and converted into volatile N(O)-pentafluoropropionyl amino acid 2-propyl esters which were analyzed by enantioselective gas chromatography mass spectrometry on a Chirasil-L-Val capillary column. Besides common protein L-amino acids low amounts of D-amino acids were detected in fermented cocoa beans. Quantities of D-amino acids increased on heating. On roasting cocoa beans of the Forastero type from the Ivory Coast at 150 degrees C for 2 h, relative quantities of D-amino acids approached 17.0% D-Ala, 11.7% D-Ile, 11.1% D-Asx (Asp + Asn), 7.9% D-Tyr, 5.8% D-Ser, 4.8% D-Leu, 4.3% D-Phe, 37.0% D-Pro, and 1.2% D-Val. In cocoa powder and chocolate relative quantities amounted to 14.5% D-Ala, 10.6% D-Tyr, 9.8% D-Phe, 8.1% L-Asx, and 7.2% D-Ile. Lower quantities of other D-amino acids were also detected. In order to corroborate our hypothesis that D-amino acids are generated from Amadori compounds (fructose amino acids) formed in the course of the Maillard reaction, fructose-L-phenylalanine and fructose-D-phenylalanine were synthesized and heated at 200 degrees C for 5-60 min. Already after 5 min release of 11.7% D-Phe and 11.8% L-Phe in the free form could be analyzed. Based on the data a racemization mechanism is presented founded on the intermediate and reversible formation of an amino acid carbanion in the Amadori compounds.

  6. Hyperbranched Polycarbosilanes via Nucleophilic Substitution Reactions

    Science.gov (United States)

    Interrante, L.; Shen, Q.

    Nucleophilic substitution reactions involving organomagnesium (Grignard) [1] and organolithium reagents have been used extensively for many years to form Si—C bonds (see Reaction Scheme 12.1). However, their use for the construction of hyperbranched polymers whose backbone contains, as a major structural component, silicon—carbon bonds, i.e., polycarbosilanes [2] is relatively more recent. (12.1) begin{array}{l} {{R}}_3 {{SiX + MR'}} to {{R}}_3 {{SiR' + MX}} \\ left({{{R,R' = alkyl}} {{or aryl;}} {{M = Mg(X),}} {{Li,}} {{Na}};{{X = halogen, OR''}}} right) \\ This chapter focuses on the application of such nucleophilic substitution reactions toward the synthesis of hyperbranched polycarbosilanes, with particular emphasis on those preparations that have resulted in relatively well characterized products. These syntheses are organized by the type of ABn monomer unit used (see Section 1.2), where A and B refer to the (C)X and (Si)Xn, respectively, functional ends of the monomer unit and where the nature of the coupling reaction leads to entirely or primarily Si—C bond formation. In most cases, these are “one-pot” reactions that employ monomers that bear halogen or alkoxy groups on the C and Si ends of the unit. Indeed, hyperbranched polycarbosilanes have been described, in general, as “obtained in one synthetic step via a random, one-pot polymerization of multifunctional monomers of AB n type” [2]. Treatment of the ABn monomer with either elemental Mg or an organolithium reagent, ideally (but not always) forms a complexed carbanion (the nucleophile) by reaction with the C-X end of the monomer unit, resulting in an intermediate of the type, (XxM)CSiXn, where M = Mg or Li, X = halogen or alkoxy, and x = 1 (Mg) or 0 (Li). Self-coupling of this reagent via reactions of the type shown in Reaction Scheme 12.1 leads to oligomeric and polymeric products that are connected primarily through Si—C bonds and yield an inorganic MXx by-product.

  7. Catalytic Hydration of Alkenes and Alkynes

    Energy Technology Data Exchange (ETDEWEB)

    Atwood, Jim, D.

    2003-03-18

    The fifteen years of DOE support have encompassed two different projects, electron-transfer reactions of metal carbonyl anions and water-soluble organometallic complexes. Each of these is related to homogeneous catalysis and will be described in separate sections. Electron Transfer--Twenty-one manuscripts resulted from our studies of electron-transfer reactions of metal carbonyl anions and acknowledge DOE support. Construction of an infrared stopped-flow system allowed us to measure rates of reactions for the extremely air-sensitive metal carbonyl anions. As for carbanions, both one-electron and two-electron processes occur for metal carbonyl anions. The most unexpected feature was examples of a very rapid two-electron process, followed by a much slower one-electron back transfer. The two-electron processes were accompanied by transfer of a ligand between two metals, M-X + M{prime}{sup -} {yields} M{sup -} + M{prime}-X with X groups of CO{sup 2}, H{sup +}, CH{sub 3}{sup +} and Br{sup +}. These transfers, which can be considered nucleophilic displacements, occurred when M{prime}{sup -} was more nucleophilic than M{sup -}. The 21 published manuscripts explore one- and two-electron processes for many such organometallic complexes. Water-Soluble Organometallic Complexes--The potential of water-soluble organometallic complexes in ''green chemistry'' intrigued us. Sixteen manuscripts acknowledging DOE support have appeared thus far in this field. Our research centered on sulfonated phosphine ligands, PPh{sub 2}(m-C{sub 6}H{sub 4}SO{sub 3}Na) and P(m-C{sub 6}H{sub 4}SO{sub 3}Na){sub 3}, to solubilize organometallic complexes in water. These analogues of PPH{sub 3} allowed us to synthesize complexes of Ir, Rh, Ru, Ni, Pd, Pt and Ag that are water-soluble and contain such common organometallic ligands as CO, H and CH{sub 3} in addition to halides and the phosphine ligands. These metal complexes show the ability to activate H{sub 2}, CO, C{sub 2}H{sub 4

  8. Cationic methyl complexes of the rare-earth metals: an experimental and computational study on synthesis, structure, and reactivity.

    Science.gov (United States)

    Kramer, Mathias U; Robert, Dominique; Arndt, Stefan; Zeimentz, Peter M; Spaniol, Thomas P; Yahia, Ahmed; Maron, Laurent; Eisenstein, Odile; Okuda, Jun

    2008-10-20

    Synthesis, structure, and reactivity of two families of rare-earth metal complexes containing discrete methyl cations [LnMe(2-x)(thf)n]((1+x)+) (x = 0, 1; thf = tetrahydrofuran) have been studied. As a synthetic equivalent for the elusive trimethyl complex [LnMe3], lithium methylates of the approximate composition [Li3LnMe6(thf)n] were prepared by treating rare-earth metal trichlorides [LnCl3(thf)n] with 6 equiv of methyllithium in diethyl ether. Heteronuclear complexes of the formula [Li3Ln2Me9L(n)] (Ln = Sc, Y, Tb; L = Et2O, thf) were isolated by crystallization from diethyl ether. Single crystal X-ray diffraction studies revealed a heterometallic aggregate of composition [Li3Ln2Me9(thf)n(Et2O)m] with a [LiLn2Me9](2-) core (Ln = Sc, Y, Tb). When tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = Y, Lu) was reacted with less than 1 equiv of [NR3H][BPh4], the dimethyl cations [LnMe2(thf)n][BPh4] were obtained. The coordination number as well as cis/trans isomer preference was studied by crystallographic and computational methods. Dicationic methyl complexes of the rare-earth metals of the formula [LnMe(thf)n][BAr4]2 (Ln = Sc, Y, La-Nd, Sm, Gd-Lu; Ar = Ph, C6H4F-4) were synthesized, by protonolysis of either the ate complex [Li3LnMe6(thf)n] (Ln = Sc, Y, Gd-Lu) or the tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = La-Nd, Sm, Dy, Gd) with ammonium borates [NR3H][BAr4] in thf. The number of coordinated thf ligands varied from n = 5 (Ln = Sc, Tm) to n = 6 (Ln = La, Y, Sm, Dy, Ho). The configuration of representative examples was determined by X-ray diffraction studies and confirmed by density-functional theory calculations. The highly polarized bonding between the methyl group and the rare-earth metal center results in the reactivity pattern dominated by the carbanionic character and the pronounced Lewis acidity: The dicationic methyl complex [YMe(thf)6](2+) inserted benzophenone as an electrophile to give the alkoxy complex [Y(OCMePh2)(thf)5](2+). Nucleophilic addition of

  9. Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups

    Science.gov (United States)

    Meng, Fanke; Li, Xiben; Torker, Sebastian; Shi, Ying; Shen, Xiao; Hoveyda, Amir H.

    2016-09-01

    Conjugate (or 1,4-) additions of carbanionic species to α,β-unsaturated carbonyl compounds are vital to research in organic and medicinal chemistry, and there are several chiral catalysts that facilitate the catalytic enantioselective additions of nucleophiles to enoates. Nonetheless, catalytic enantioselective 1,6-conjugate additions are uncommon, and ones that incorporate readily functionalizable moieties, such as propargyl or allyl groups, into acyclic α,β,γ,δ-doubly unsaturated acceptors are unknown. Chemical transformations that could generate a new bond at the C6 position of a dienoate are particularly desirable because the resulting products could then be subjected to further modifications. However, such reactions, especially when dienoates contain two equally substituted olefins, are scarce and are confined to reactions promoted by a phosphine-copper catalyst (with an alkyl Grignard reagent, dialkylzinc or trialkylaluminium compounds), a diene-iridium catalyst (with arylboroxines), or a bisphosphine-cobalt catalyst (with monosilyl-acetylenes). 1,6-Conjugate additions are otherwise limited to substrates where there is full substitution at the C4 position. It is unclear why certain catalysts favour bond formation at C6, and—although there are a small number of catalytic enantioselective conjugate allyl additions—related 1,6-additions and processes involving a propargyl unit are non-existent. Here we show that an easily accessible organocopper catalyst can promote 1,6-conjugate additions of propargyl and 2-boryl-substituted allyl groups to acyclic dienoates with high selectivity. A commercially available allenyl-boron compound or a monosubstituted allene may be used. Products can be obtained in up to 83 per cent yield, >98:2 diastereomeric ratio (for allyl additions) and 99:1 enantiomeric ratio. We elucidate the mechanistic details, including the origins of high site selectivity (1,6- versus 1,4-) and enantioselectivity as a function of the catalyst

  10. Effect of the nature of the substituent in N-alkylimidazole ligands on the outcome of deprotonation: ring opening versus the formation of N-heterocyclic carbene complexes.

    Science.gov (United States)

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía; Díaz, Jesús; López, Ramón

    2010-07-26

    Complexes [Re(CO)(3)(N-RIm)(3)]OTf (N-RIm=N-alkylimidazole, OTf=trifluoromethanesulfonate; 1a-d) have been straightforwardly synthesised from [Re(OTf)(CO)(5)] and the appropriate N-alkylimidazole. The reaction of compounds 1a-d with the strong base KN(SiMe(3))(2) led to deprotonation of a central C-H group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1a contains three N-MeIm ligands, and its product 2a features a C-bound imidazol-2-yl ligand. When 2a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3a or 4a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2a with [AuCl(PPh(3))] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1b-d, with at least one N-arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2-H group of an imidazole ligand attacks a central C-H group of a neighbouring N-RIm ligand, thus affording the product of C-C coupling and ring-opening of the imidazole moiety that has been attacked (2c, d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3c, d or 4c, d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N-RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product.

  11. Amine oxidation mediated by lysine-specific demethylase 1: quantum mechanics/molecular mechanics insights into mechanism and role of lysine 661.

    Science.gov (United States)

    Karasulu, Bora; Patil, Mahendra; Thiel, Walter

    2013-09-11

    We report classical molecular dynamics (MD) simulations and combined quantum mechanics/molecular mechanics (QM/MM) calculations to elucidate the catalytic mechanism of the rate-determining amine oxidation step in the lysine-specific demethylase 1 (LSD1)-catalyzed demethylation of the histone tail lysine (H3K4), with flavin adenine dinucleotide (FAD) acting as cofactor. The oxidation of substrate lysine (sLys) involves the cleavage of an α-CH bond accompanied by the transfer of a hydride ion equivalent to FAD, leading to an imine intermediate. This hydride transfer pathway is shown to be clearly favored for sLys oxidation over other proposed mechanisms, including the radical (or single-electron transfer) route as well as carbanion and polar-nucleophilic mechanisms. MD simulations on six NVT ensembles (covering different protonation states of sLys and K661 as well as the K661M mutant) identify two possible orientations of the reacting sLys and FAD subunits (called "downward" and "upward"). Calculations at the QM(B3LYP-D/6-31G*)/CHARMM22 level provide molecular-level insights into the mechanism, helping to understand how LSD1 achieves the activation of the rather inert methyl-CH bond in a metal-free environment. Factors such as proper alignment of sLys (downward orientation), transition-state stabilization (due to the protein environment and favorable orbital interactions), and product stabilization via adduct formation are found to be crucial for facilitating the oxidative α-CH bond cleavage. The current study also sheds light on the role of important active-site residues (Y761, K661, and W695) and of the conserved water-bridge motif. The steric influence of Y761 helps to position the reaction partners properly, K661 is predicted to get deprotonated prior to substrate binding and to act as an active-site base that accepts a proton from sLys to enable the subsequent amine oxidation, and the water bridge that is stabilized by K661 and W695 mediates this proton

  12. 不同碱金属乌桕油皂微波极化脱羧成烃类燃料的工艺%Microwave polarizing decarboxylation of different saponificated Chinese tallow seed oil for the preparation of renewable hydrocarbon fuel

    Institute of Scientific and Technical Information of China (English)

    王允圃; 刘玉环; 阮榕生; 温平威; 马雯; 万益琴

    2014-01-01

    不饱和脂肪酸盐微波极化条件下更容易脱羧成烃,本研究分别以氢氧化锂、氢氧化钠、氢氧化钾皂化乌桕油,以不同碱金属乌桕油皂化物和乌桕油为研究对象,在恒定的微波功率下裂解脱羧成烃,通过GC-MS等分析裂解产物,微波能选择性地加热乌桕油皂羧基端,不饱和键在微波极化过程中与碳负离子中间体形成P-π共轭体系,使裂解反应(脱羧、端烯化、异构化和芳构化等)顺利进行。皂化物极性越大,升温速率越快,液体烃类产率越高,脱羧效果越明显,裂解液体的密度为0.825~0.865 g/cm3,黏度为2.10~2.55 mm2/s,与柴油的性质非常相似,从而证明微波极化乌桕油皂脱羧制烃类燃料的可行性。%It is easier for the decarboxylation reaction of unsaturated fatty acid salt. The Chinese tallow seed oil was saponified by lithium hydroxide,sodium hydroxide,potassium hydroxide. Different saponificated Chinese tallow seed oils were used as model compounds to study the decarboxylation leading to hydrocarbon formation via microwave-assisted pyrolysis technology,the pyrolysis products were analyzed by GC-MS and FT-IR. Microwave energy was able to selectively heat the carboxyl terminal of saponificated Chinese tallow seed oil. During decarboxylation,the double bond in the long hydrocarbon chain formed a P-πconjugated system with the carbanion intermediate. The resulting P-πconjugated system was more stable and beneficial to the pyrolysis reaction (decarboxylation,terminal allylation,isomerization,and aromatization). The saponificated oil has a stronger polarity,the heating rate is higher,liquid hydrocarbon yield is bigger. The viscosity(2.10-2.55 mm2/s) and density(0.825-0.865 g/cm3) of the pyrolysis liquid obtained from this experiment were similar to those of diesel. It was proved feasible to derive renewable hydrocarbon fuel from saponificated Chinese tallow seed oil by microwave

  13. Detection of DNA and globin adducts of polynuclear aromatic hydrocarbon diol epoxides by gas chromatography-mass spectrometry and -3H-CH3I postlabeling of released tetraols.

    Science.gov (United States)

    Melikian, A A; Sun, P; Coleman, S; Amin, S; Hecht, S S

    1996-03-01

    Gas chromatography-negative ion chemical ionization mass spectrometry--selected ion monitoring (GC-NICI-MS-SIM) was employed to detect tetramethyl ether derivatives of tetraols formed upon hydrolysis of DNA and globin adducts derived from diol epoxides of benzo[a]-pyrene (BP) and other polynuclear aromatic hydrocarbons (PAH). The tetramethyl ether derivatives could also be detected by [3H]CH3I postlabeling. The methodology involves the following steps: (1) isolation of DNA or globin; (2) mild acid hydrolysis under vacuum; (3) isolation of the resulting tetraols and derivatization to the corresponding tetramethyl ethers using methyl sulfinyl carbanion and unlabeled or 3H-labeled CH3I; (4) analysis by GC-NICI-MS-SIM or HPLC with radioflow detection. The optimum conditions for hydrolysis of adducts and derivatization of the resulting tetraols as well as the feasibility of this approach for detecting PAH adducts in mice and humans were explored. Using the set of four BP-tetraols that can be formed upon hydrolysis of adducts formed from r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) or r-7,t-8-dihydroxy-c-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (syn-BPDE) as models, the stability of the tetraols under the hydrolysis conditions was investigated. Adducts derived from anti-BPDE yield predominantly the stable r-7,t-8,9-c-10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (trans-anti-BP-tetraol), while adducts derived from syn-BPDE released cis-syn-BP-tetraol as a major hydrolysis product. Hydrolysis under vacuum significantly increased the recovery of tetraols. Conditions for derivatization of the BP-tetraols as well as tetraols derived from several other PAH anti-diol epoxides were investigated. Tetramethyl ethers proved to be superior derivatives that were stable, easy to prepare in high yields, and detectable with high sensitivity by GC-NICI-MS-SIM (1-50 fmol per injection). Alternatively, these derivatives could be detected by HPLC with

  14. Progress in the catalysts for cracking of waste plastics%废塑料裂解催化剂研究进展

    Institute of Scientific and Technical Information of China (English)

    伍艳辉; 吴高胜; 刘春燕; 朱志荣

    2014-01-01

    废塑料造成的环境污染日趋严重,处理回收废塑料已成为全球关注的问题。催化裂解作为一种新的塑料回收方法,具有高效、环保、无二次污染和产物油品质高等特点。综述了国内外废塑料裂解制油催化剂如分子筛、氧化物、黏土和过渡金属负载型双功能催化剂的研究进展。分子筛类、黏土类和无定形氧化铝-二氧化硅催化剂属酸性催化剂,其裂解废塑料机理为碳正离子机理;碱金属氧化物催化剂裂解废塑料机理为碳负离子机理;过渡金属负载型催化剂具有双功能,其中,金属活性位起加氢-脱氢作用,载体酸性位起异构化作用;而粉煤灰催化剂可同时实现废塑料与粉煤灰两种废弃物的综合回收利用。今后应注意在催化机理指导下,进一步提高催化剂性能,并研究对复杂废塑料混合物的催化裂解效果。%Because environmental pollution caused by waste plastics is getting worse,treatment and recov-ery of waste plastics has become a global concern. As a novel recovery method of plastics,catalytic crack-ing of waste plastics possessed the advantages of high efficiency,environment-friendliness and getting high quality fuel oil without secondary pollution. The progress in various catalysts for catalytic cracking of waste plastics such as molecular sieves,oxides,clay and transition metal supported bi-functional catalysts was reviewed in this paper. The catalytic degradation mechanisms of acidic catalysts such as molecular sieves, clay and amorphous Al2 O3-SiO2 followed carbocation mechanism,whereas alkali metal oxides catalysts for degrading waste plastic followed carbanion mechanism. Transition metal supported catalysts possessed the dual function,in which metal catalytic active sites played a role in hydrogenation-dehydrogenation,while acidic sites of the supports performed an isomerization function. Fly ash catalysts could recycle waste plas-tics and

  15. Synthesis of main group, rare-earth, and d{sup 0} metal complexes containing beta-hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Ka King [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe2)3 and KC(SiHMe2})3TMEDA are synthesized by deprotonation of the hydrocarbon HC(SiHMe2)3 with potassium benzyl. KC(SiHMe2)3TMEDA crystallizes as a dimer with two types of three-center-two-electron KH- Si interactions. Homoleptic Ln(III) tris(silylalkyl) complexes containing β-SiH groups M{C(SiHMe2)3}3 (Ln = Y, Lu, La) are synthesized from salt elimination of the corresponding lanthanide halide and 3 equiv. of KC(SiHMe2)3. The related reactions with Sc yield bis(silylalkyl) ate-complexes containing either LiCl or KCl. The divalent calcium and ytterbium compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2 or TMEDA) are prepared from MI2 and 2 equiv of KC(SiHMe2)3. The compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2 or TMEDA) and La{C(SiHMe2)3}3 react with 1 equiv of B(C6F5)3 to give 1,3- disilacyclobutane {Me2Si-C(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L, and La{C(SiHMe2)3}2HB(C6F5)3, respectively. The corresponding reactions of Ln{C(SiHMe2)3}3 (Ln = Y, Lu) give the β-SiH abstraction product [{(Me2HSi)3C}2LnC(SiHMe2)2SiMe2][HB(C6F5)3] (Ln = Y, Lu), but the silene remains associated with the Y or Lu center. The abstraction reactions of M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2or TMEDA) and Ln{C(SiHMe2)3}3 (Ln = Y, Lu, La) and 2 equiv of B(C6

  16. Synthesis of main group, rare-earth, and d{sup 0} metal complexes containing beta-hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Ka King [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe2)3 and KC(SiHMe2})3TMEDA are synthesized by deprotonation of the hydrocarbon HC(SiHMe2)3 with potassium benzyl. KC(SiHMe2)3TMEDA crystallizes as a dimer with two types of three-center-two-electron KH- Si interactions. Homoleptic Ln(III) tris(silylalkyl) complexes containing β-SiH groups M{C(SiHMe2)3}3 (Ln = Y, Lu, La) are synthesized from salt elimination of the corresponding lanthanide halide and 3 equiv. of KC(SiHMe2)3. The related reactions with Sc yield bis(silylalkyl) ate-complexes containing either LiCl or KCl. The divalent calcium and ytterbium compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2 or TMEDA) are prepared from MI2 and 2 equiv of KC(SiHMe2)3. The compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2 or TMEDA) and La{C(SiHMe2)3}3 react with 1 equiv of B(C6F5)3 to give 1,3- disilacyclobutane {Me2Si-C(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L, and La{C(SiHMe2)3}2HB(C6F5)3, respectively. The corresponding reactions of Ln{C(SiHMe2)3}3 (Ln = Y, Lu) give the β-SiH abstraction product [{(Me2HSi)3C}2LnC(SiHMe2)2SiMe2][HB(C6F5)3] (Ln = Y, Lu), but the silene remains associated with the Y or Lu center. The abstraction reactions of M{C(SiHMe2)3}2L (M = Ca, Yb; L = THF2or TMEDA) and Ln{C(SiHMe2)3}3 (Ln = Y, Lu, La) and 2 equiv of B(C6

  17. Reduction by metals dissolved in liquid ammonia of keto steroids. Equilibration of the alcohols; Reduction par les metaux dissous dans l'ammoniac liquide de cetones en serie steroide. Equilibration des alcools

    Energy Technology Data Exchange (ETDEWEB)

    Giroud, A.M. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1970-07-01

    'une cetone par les metaux en dissolution fait intervenir deux electrons: on peut considerer comme intermediaire un radical-anion, puis un dianion ou un carbanion. Le radical-anion pouvant aussi se dimeriser pour donner des pinacols. Pour interpreter les resultats des reductions, il nous fallait connaitre les stabilites relatives des alcools ce qui nous a conduit a faire des equilibrations. Dans un premier chapitre, nous etudions les methodes de preparation de l'androstanone-ll et des androstanols-ll{alpha} et ll{beta}. Nous verifions ensuite qu'il n'est pas possible selon nos methodes de conclure sur la stabilite relative des deux alcools par equilibrations experimentales. Nous decrivons enfin les methodes de reduction de la cetone par les metaux alcalins et alcalino-terreux dissous dans l'ammoniac liquide, suivant deux procedes: soit en presence de donneur de protons, soit avec addition posterieure de donneur de protons. Ces reductions conduisent a un melange des deux alcools ou l'isomere {alpha} equatorial stable predomine. Dans un deuxieme chapitre, nous etudions l'action de l'acide selenique et de l'eau oxygenee sur la cholestanone-3, reaction qui nous a permis d'etudier la preparation et la stereochimie des derives du A-nor cholestane. Nous decrivons ensuite la preparation des A-nor cholestanols 2{alpha} et 2{beta} et des acetates correspondants. L'equilibration par des methodes chimiques de ces alcools montre que l'alcool 2 {alpha} est plus stable que l'alcool 2{beta}, ce qui est confirme par le calcul. Enfin, la reduction de la A-nor cholestanone-2 par les metaux en dissolution conduit toujours de facon preponderante a l'epimere 2 {beta} le moins stable avec en outre formation de pinacols. Nous consacrons enfin le troisieme chapitre a l'etude des reductions de l'androstanone-17 et des stabilites relatives des deux alcools 17{alpha} et 17{beta}. Quel que soit le mode operatoire utilise, nous