Sample records for hydrogenation
from WorldWideScience.org

Sample records 1 - 15 shown.



1

Hidrogenação de compostos orgânicos utilizando método eletroquímico para geração de hidrogênio in situ: hidrogenação eletrocatalítica/ Hydrogenation of organic compounds by an electrochemical method for in situ hydrogen generation: electrocatalytic hydrogenation

Navarro, Daniela Maria do Amaral Ferraz; Navarro, Marcelo
2004-04-01

Resumo em inglês Electrocatalytic hydrogenation (HEC) may be compared to catalytic hydrogenation (HC). The difference between these methods is the hydrogen source: HC needs a hydrogen gas supply; HEC needs a source of protons (solvent) to be reduced at a cathode surface. HEC has presented interesting advances in the last decades due to investigation of the influence of the supporting electrolyte, co-solvent, surfactant, presence of inert gas and the composition of the electrode on the rea (mais) ction. Several classes of organic compounds have been hydrogenated through HEC: olefins, ketones, aldehydes, aromatics, polyaromatics and nitro-compounds. This paper shows some details about the HEC which may be regarded as a promising technique for the hydrogenation of organic compounds both in industrial processes and in laboratories.

Scientific Electronic Library Online (Portuguese)

2

Hidrogenação eletrocatalítica de substratos orgânicos utilizando eletrodos modificados poliméricos contendo partículas de Ni/Pd e Ni/Pt/ Electrocatalytic hydrogenation of organic substrates on polymer modified electrodes embedding Ni/Pd and Ni/Pt particles

Purgato, Fabiana L. S.; Romero, José R.; Abrantes, Luisa M.
2009-01-01

Resumo em inglês Novel modified electrodes bearing dispersed Pd and Pt particles have been prepared from poly (allyl ether of the p-benzenesulfonic acid) films with incorporated nickel particles making use of galvanic displacement reactions. The SEM analysis of the new modified electrodes revealed efficient deposition of Pd but weak up-take of Pt. Electrocatalytic hydrogenation of several classes of organic substrates were carried out using the MEs Ni, Ni/Pd and Ni/Pt. The Ni/Pd ME showed (mais) to be the best of them for the hydrogenation of double, triple and carbonyl bonds. The complete hydrogenation of the aromatic rings for the well-adsorbed substrates acetophenone and benzophenone is noteworthy.

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3

Hidrogenação eletrocatalítica de substratos orgânicos: estudo da eficiência dos metais nobres níquel, paládio e platina usando eletrodos modificados/ Electrocatalytic hydrogenation of organic substrates: study of the efficiency of the nickel, paladium and platinum noble metals using modified electrodes

Pontólio, José Olavo S.; Purgato, Fabiana L. S.; Romero, José R.
2004-08-01

Resumo em inglês Nickel, palladium and platinum micro-crystals were dispersed in films covering a vitreous carbon plate electrode by ion exchange followed by electroreduction of their ions. These modified electrodes were used in the electrocatalytic hydrogenation of several substrates of different classes and their efficiency is reported. A comparison among them was performed based on the structural characteristics of the metals. A modified electrode containing platinum showed to be more efficient than a palladium modified electrode and the one of nickel was the less efficient.

Scientific Electronic Library Online (Portuguese)

4

Métodos para a hidrogenação de ligações olefínicas em polímeros/ Hydrogenation methods of polydienes

Holleben, Maria Luiza Ambros von; Calcagno, Carmen Iara Walter; Mauler, Raquel Santos
1999-04-01

Resumo em inglês The broad variety of hydrogenation methods of polydienes is presented. Homogeneous and heterogeneous catalysis are reviewed emphasizing also hydrogen transfer from donor compounds.

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5

Modificações estruturais induzidas por hidrogenação catódica em aço austenítico soldado e nitretado a plasma/ Structural modification induced by cathodic hydrogenation on plasma nitrided austenitic steel welds

Nascimento, Fabiana Cristina; Ferreira, Elton L. D.; Foerster, Carlos Eugênio; Alves Júnior, Clodomiro; Kuromoto, Neide Kazue; Paredes, Ramon Siguifredo Cortes; Lepienski, Carlos Maurício
2010-03-01

Resumo em português Nesse trabalho, apresentamos a caracterização estrutural de regiões soldadas em aço austenítico AISI-304, que foram submetidas a processo de nitretação a plasma (20%N2 + 80%H2). Posteriormente as amostras foram hidrogenadas catodicamente. As temperaturas de nitretação foram de 400, 500 e 550°C. As regiões da solda e fora da solda hidrogenadas após a nitretação foram comparadas por DRX, microscopia ótica e microscopia eletrônica de varredura (MEV). As fases (mais) austenita-γ, martensita-α', martensita-ε, ferrita-α e os nitretos CrN, γ'-Fe4N e e-Fe2+xN foram identificados. As microestruturas de ambas as regiões e da zona termicamente ativada (ZTA) foram similares. Para 400°C, a estequiometria das fases formadas foi diferente das observadas em 500°C e 550°C. Os efeitos provocados pela hidrogenação foram mais acentuados em 550°C, com o arrancamento da camada nitretada. Resumo em inglês Structural characterization of weld and outside weld regions of AISI-304 nitrided (20%N + 80%H) and cathodically hydrogenated is presented. Nitriding temperatures were 400, 500 e 550°C. The weld and outside weld regions were compared by XRD, optical microscopy and SEM. The phases γ-austenite, α'-martensite, ε-martensita and α-ferrite and the nitrides: CrN, γ'-Fe4N e e-Fe2+xN were identified. Microstructures of both regions and the thermal active (mais) zone were similar. For 400°C the stoichiometry of the formed phases was different from that formed at 500°C and 550°C. Hydrogen effects were more intense for 550°C, due to chipping occurrence.

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6

Bastões de grafite reciclados de baterias comuns e seu uso como eletrodo modificado em hidrogenação eletrocatalítica de alguns substratos orgânicos/ Graphite sticks recycled from common batteries and their use as a modified electrode in electrocatalytic hydrogenation of some organic substrates

Lofrano, Renata C. Z.; Padovan, Nei A.; Romero, José R.
2002-12-01

Resumo em inglês This paper presents some results on the employ of recycled graphite electrode obtained from used common 1.5 V batteries in the preparation of modified electrode and the electrocatalytical hydrogenation of benzaldehyde and of n-valeraldehyde. This inexpensive and easy to obtain electrode was prepared by coating it with a 1:1 mixed film of poly-(allylfenil ether): poly-[allyl p-(2-ethylammonium) benzene ether] and introduction of dispersed platinum particles by ion exchange (mais) and reduction of PtCl4-2. Electroreduction of H+ from aqueous H2SO4 using the proposed electrode hydrogenated the substrates in a way comparable with that of vitreous carbon electrode.

Scientific Electronic Library Online (Portuguese)

7

Ácidos graxos trans: doenças cardiovasculares e saúde materno-infantil/ Trans fatty acids: cardiovascular diseases and mother-child health

CHIARA, Vera Lucia; SILVA, Rosilaine; JORGE, Renata; BRASIL, Ana Paula
2002-09-01

Resumo em português Este estudo revê a literatura sobre o tema nas últimas décadas, destacando seu efeito no metabolismo humano quanto às doenças coronarianas e à saúde materno-infantil. Recentemente, os ácidos graxos trans foram incluídos entre os fatores dietéticos de risco para doenças cardiovasculares. Discute-se ainda sua relação com o processo de crescimento e desenvolvimento da criança desde a fase fetal e período gestacional. Os trans originam-se dos ácidos graxos ins (mais) aturados no processo de hidrogenação e bio-hidrogenação, apresentando ação diferenciada destes. Diversas pesquisas ressaltam seu efeito hipercolesterolêmico e o bloqueio e inibição da biossíntese de ácidos graxos essenciais. Estas ações têm repercussões na saúde materno-infantil e elevam o risco de doenças cardiovasculares. Recomenda-se a redução do consumo de alimentos que contenham gordura hidrogenada, adotando os limites de 2% a 5% de gorduras trans/energia totais, já empregados em outros países. Resumo em inglês This article reviews the literature produced on the theme during the last decades, focusing on its effect on human metabolism, concerning coronary diseases and mother-child health. Trans fatty acids have been recently included among dietary risk factors for cardiovascular diseases. Their relation with the child's growing and developing processes, since fetal phase and gestational period, has also been discussed. Trans fatty acids originate from unsaturated fatty acids, in (mais) hydrogenation and biohydrogenation processes, and their action is different from the latter. Many works emphasize their hypercholesterolemic effect and influence on blocking and inhibiting biosynthesis of essential fatty acids. These actions reflect on mother-child health and increase the risk of cardiovascular diseases. The author recommends the consumption of food containing hydrogenated fat within the limits of 2-5% of trans fatty acids for total calories, as in other countries.

Scientific Electronic Library Online (Portuguese)

8

Formação de toxinas durante o processamento de alimentos e as possíveis conseqüências para o organismo humano/ Toxin formation during food processing and possible consequences to the human body

Marques, Anne y Castro; Valente, Tessa Bitencourt; Rosa, Cláudia Severo da
2009-04-01

Resumo em português A produção de alimentos envolve inúmeras reações químicas, durante as quais podem ser geradas substâncias tóxicas ao organismo humano. A produção destas substâncias pode ocorrer de diferentes maneiras, variando em quantidade e em grau de toxicidade. Este trabalho objetivou estudar a produção de toxinas no processamento de alimentos, assim como as conseqüências da ingestão dessas substâncias para o ser humano. O estudo foi realizado a partir de extensa pes (mais) quisa bibliográfica. As principais reações na formação de compostos tóxicos apresentadas no decorrer do estudo são: degradação de lipídios, hidrogenação, pirólise e defumação. Entre as substâncias formadas, destacam-se: peróxidos, ácidos graxos trans, aminas heterocíclicas e hidrocarbonetos aromáticos policíclicos. O profissional nutricionista necessita conhecer como ocorre a formação de toxinas durante os variados processamentos que envolvem alimentos, assim como os riscos para a saúde de quem consome essas substâncias. Também é preciso propor técnicas de processamento adequadas, visando ao bem-estar do consumidor e à manutenção das propriedades nutricionais do alimento. Resumo em inglês Food production involves innumerable chemical reactions that may generate substances that are toxic to the human body. These substances can be produced in different ways, in varying amounts and degree of toxicity. The objective of this study was to investigate the production of toxins during food processing, as well as theconsequences of their ingestion. This study was based on extensive literature research. The main reactions leading to toxic compounds are: lipid degrada (mais) tion, hydrogenation, pyrolysis and smoking. Some of the formed substances are: peroxides, trans fatty acids, heterocyclic amines and polycyclic aromatic hydrocarbons. Dietitians need to know how toxins form during the various foods processing methods, as well as their health risks for consumers. It is also necessary to propose processing techniques that ensure the consumer's wellbeing and retain the nutritional properties of the food.

Scientific Electronic Library Online (Portuguese)

9

Conteúdo de gordura sólida da gordura abdominal de frango, de suas estearinas e de suas misturas binárias com toucinho/ Solid fat content of abdominal chicken fat, its stearins and its binary mixtures with bacon

Chiu, Ming Chih; Gioielli, Luiz Antonio
2002-08-01

Resumo em português O conteúdo de gordura sólida é um parâmetro utilizado para definir as aplicações mais indicadas de uma gordura, ou de misturas de gorduras, em um determinado produto. Este parâmetro é normalmente determinado por ressonância magnética nuclear e se relaciona com a consistência da gordura. O fracionamento a seco de óleos e gorduras consiste na separação dos triacilgliceróis de acordo com seu ponto de fusão através da cristalização. Além da mistura, o frac (mais) ionamento é o método mais econômico no processamento de lipídios, pois se trata de um processo puramente físico, comparado às modificações químicas tais como a hidrogenação e a interesterificação, que alteram os triacilgliceróis. As interações que ocorrem entre os triacilgliceróis nas misturas promovem alterações nas propriedades físicas das gorduras. O objetivo do trabalho foi analisar as interações que ocorrem em misturas binárias de duas gorduras animais (gordura abdominal de frango e toucinho) quanto a sua propriedade de conteúdo de gordura sólida a diferentes temperaturas. Foi aplicado um modelo de regressão múltipla do tipo quadrático. Os resultados demonstraram que ocorreram os efeitos eutético e de formação de compostos entre as misturas. Resumo em inglês Solid fat content is a parameter used to define the most appropriate applications of a fat or fat blends in a specific product. This parameter is normally measured by the nuclear magnetic resonance method, and it is related to the consistency of fat. Dry fractionation of oils and fats is the separation of high melting from low melting triacylglycerols by crystallization from the melt. Apart from blending, this is the most economical process in oil and fat processing. It i (mais) s a purely physical process compared to other chemical modification processes, such as hydrogenation and interesterification, which modify the triacylglycerols. The interactions that occur among the triacylglycerols in the mixtures change the physical properties of the fat. The objective of the paper was to analyze the interactions that occur in binary mixtures of two animal fats (abdominal chicken fat and bacon fat), regarding their solid fat content at different temperatures. A mathematical model of multiple regression of the quadratic type was applied. The results showed that an eutectic effect and compound formation can be observed.

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10

Síntese, caracterização e estudo das propriedades catalíticas e magnéticas de nanopartículas de Ni dispersas em matriz mesoporosa de SiO2/ Synthesis, characterization and study of magnetic and catalytic properties of dispersed Ni nanoparticles on mesoporous SiO2 matrix

Carreño, Neftalí L. V.; Leite, Edson R.; Santos, Luís P. S.; Lisboa-Filho, Paulo N.; Longo, Elson; Araújo, Geórgia C. L.; Barison, Andersson; Ferreira, Antônio G.; Valentini, Antoninho; Probst, Luiz Fernando D.
2002-11-01

Resumo em inglês Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Scientific Electronic Library Online (Portuguese)

11

Estudo de alguns compostos organolantanídeos: [LnCp2Cl.PPh3]/ Study of some organolanthanide compounds: [LnCp2Cl.PPh3]

Gatti, Paula M.; Luz, Marcelo A. da; Oliveira, Wanda de
2000-04-01

Resumo em inglês In this work we present the synthesis and characterization of some organolanthanide compounds [LnCp2Cl.PPh3], Ln = La, Nd, Eu, Yb and Lu. The catalytic activity of these compounds has been verified in cyclohexene hydrogenation. Cyclohexane was identified by¹H NMR analysis in the reaction products.

Scientific Electronic Library Online (Portuguese)

12

Estabilidade relativa de alcenos: análise dos critérios encontrados nos livros textos de graduação e uma proposta de explicação operacional para alcenos dissubstituídos/ Analysis of criteria for relative stability of alkenes found in undergraduate textbooks and an operational model for disubstituted alkenes

Cunha, Silvio
2003-12-01

Resumo em inglês Despite of being used as thermodynamic criterion to rank alkene stability in a number of undergraduate textbooks, the heat of hydrogenation does not describe adequately the relative stability of disubstituted alkenes. In this work, both the heat of formation and the heat of combustion were used as thermodynamic criteria to rank correctly the stability of alkenes according to the degree of alkyl substitution and also in the disubstituted series (geminal > trans > cis). An (mais) operational model based on molecular orbital and valence bond representations of hyperconjugation is proposed to show how this effect can explain the order of stability of this class of compounds.

Scientific Electronic Library Online (Portuguese)

13

Derivados citotóxicos de vitanolidos isolados das folhas de Acnistus arborescens/ Cytotoxic derivatives of withanolides isolated from the leaves of Acnistus arborescens

Minguzzi, Sandro; Barata, Lauro E. S.; Cordell, Geoffrey A.
2011-01-01

Resumo em inglês In view of anticancer activity of 7 β-acetoxywithanolide D (2) and 7β-16α-diacetoxywithonide D (3), isolated from the leaves of Acnistus arborescens (Solanaceae), five withanolide derivatives were obtained and their structures were determined by NMR, MS and IV data analysis. The in vitro anticancer activity of these derivatives was evaluated in a panel of cancer cell lines: human breast (BC-1), human lung (Lu1), human colon (Col2) and human oral epidermoid (mais) carcinoma (KB). Compounds 2a (acetylation of 2), 3b (oxidation of 3) and 2c (hydrogenation of 2) exhibited the highest anticancer activity against human lung cancer cells, with ED50 values of 0.19, 0.25 and 0.63 μg/mL, respectively.

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14

Caracterização de amostras petroquímicas e derivados utilizando cromatografia gasosa bidimensional abrangente (GCxGC)/ Characterization of petrochemical samples and their derivatives by comprehensive two-dimensional gas chromatography

von Mühlen, Carin; Zini, Claudia Alcaraz; Caramão, Elina Bastos; Marriott, Philip J.
2006-07-01

Resumo em inglês The goal of this article is to discuss the application of comprehensive two-dimensional gas chromatography (GCxGC) to petrochemical samples. The use of GCxGC for petroleum and petroleum derivatives characterization, through group type analysis, or BTEX (benzene, toluene, ethylbenzene, xylenes), total aromatic hydrocarbons, polyaromatic hydrocarbons, sulfur-containing, oxygen-containing, and nitrogen-containing compounds is presented. The capability of GCxGC to provide add (mais) itional specific chemical information regarding petroleum processing steps, such as dehydrogenation of linear alkanes, the Fischer-Tropsch process, hydrogenation and oligomerization is also described. In addition, GCxGC analyses of petrochemical biomarkers and environmental pollutants derived from petrochemicals are reported.

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15

Atualizando a química orgânica experimental da licenciatura/ Updating undergraduate experimental organic chemistry

Navarro, Marcelo; Sena, Vera L. M. de; Srivastava, Rajendra M.; Navarro, Daniela M. do Amaral Ferraz
2005-12-01

Resumo em inglês The present contribution describes three different modern experiments for possible adoption in undergraduate organic chemistry laboratories. These are: 1. electrocatalytic hydrogenation of benzaldehyde to benzyl alcohol; 2. identification of three volatile components, obtained from pineapple fruit, by mass spectrometry and 3. microwave mediated fast synthesis of N-(p-chlorophenyl)phthalamic acid from phthalic anhydride and p-chloroaniline under solvent-free conditions. Th (mais) e experiments can be executed in a short period of time, putting the undergraduate student in contact with a variety of topics in organic chemistry and several techniques of analysis, showing multidisciplinarity in organic chemistry.

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