• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 133
  • 21
  • 20
  • 9
  • 9
  • 9
  • 9
  • 9
  • 9
  • 4
  • 4
  • 1
  • 1
  • Tagged with
  • 227
  • 227
  • 44
  • 21
  • 21
  • 20
  • 20
  • 19
  • 16
  • 16
  • 16
  • 16
  • 15
  • 14
  • 13
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Chemical vapor deposition of ruthenium-based layers by a single-source approach

Jeschke, Janine, Möckel, Stefan, Korb, Marcus, Rüffer, Tobias, Assim, Khaybar, Melzer, Marcel, Herwig, Gordon, Georgi, Colin, Schulz, Stefan E., Lang, Heinrich 06 March 2017 (has links) (PDF)
A series of ruthenium complexes of the general type Ru(CO)2(P(n-Bu)3)2(O2CR)2 (4a, R = Me; 4b, R = Et; 4c, R = i-Pr; 4d, R = t-Bu; 4e, R = CH2OCH3; 4f, R = CF3; 4g, R = CF2CF3) was synthesized by a single-step reaction of Ru3(CO)12 with P(n-Bu)3 and the respective carboxylic acid. The molecular structures of 4b, 4c and 4e–g in the solid state are discussed. All ruthenium complexes are stable against air and moisture and possess low melting points. The physical properties including the vapor pressure can be adjusted by modification of the carboxylate ligands. The chemical vapor deposition of ruthenium precursors 4a–f was carried out in a vertical cold-wall CVD reactor at substrate temperatures between 350 and 400 °C in a nitrogen atmosphere. These experiments show that all precursors are well suited for the deposition of phosphorus-doped ruthenium layers without addition of any reactive gas or an additional phosphorus source. In the films, phosphorus contents between 11 and 16 mol% were determined by XPS analysis. The obtained layers possess thicknesses between 25 and 65 nm and are highly conformal and dense as proven by SEM and AFM studies. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
192

Biorredução de compostos carbonílicos alfa,beta-insaturados visando à síntese de substâncias opticamente ativas / Bioreduction of alfa,beta-unsaturated carbonyl compounds toward the synthesis of optically active substances

Silva, Rafaela Marcucci 27 April 2015 (has links)
Nos últimos anos, a preparação de substâncias enantiomericamente puras tornou-se uma preocupação constante e um desafio para a indústria. Tal fato é consequência da relação tênue entre a estrutura espacial das substâncias e os diferentes sabores, odores, processos farmacocinéticos e farmacodinâmicos e toxicidade que elas desempenham no organismo. Nesse contexto, a síntese assimétrica de compostos carbonílicos ?-alquil substituídos opticamente ativos tem recebido grande atenção já que estes são importantes blocos de construção na síntese de fármacos quirais e produtos naturais. Assim, o presente trabalho buscou o desenvolvimento de metodologias que permitissem a preparação desses compostos enantiomericamente puros através do controle na formação de centros estereogênicos usando a biocatálise. Para isso, foram preparadas diversas olefinas ativadas por grupos retiradores de elétrons (carbonila) utilizando dois procedimentos, a saber, reações de condensação aldólica e esterificação. Esses compostos carbonílicos ?,?-insaturados foram obtidos com bons rendimentos (48-94%) e foram submetidos à reduções biocatalíticas mediadas por células íntegras de micro-organismos. Inicialmente, utilizou-se a olefina (E)-4-fenil-3-metil-3-buten-2-ona (51a) como substrato modelo para a otimização das condições experimentais e determinação daquela que fornecesse o produto biorreduzido com a melhor conversão e pureza enantiomérica. Nesses testes, avaliaram-se diversos parâmetros reacionais, tais como, composição do meio reacional (aquoso, bifásico e tamponante), presença de aditivos (glicose e catalisador de transferência de fase), diferentes micro-organismos e efeito do uso de resina adsorvente Amberlite XAD-7. Dessa forma, a biorredução em meio aquoso, sem aditivos, mediada pela levedura LSC-II e com a utilização da resina Amberlite XAD-7 foi a condição reacional que apresentou o melhor excesso enantiomérico (81%) e foi a selecionada para um estudo metodológico que avaliou os efeitos estérico e eletrônico dos substituintes. Observou-se que a posição do substituinte no ?-aril, o alongamento do ?-substituinte e a adição de um grupamento éster apresentaram um importante papel na estereosseletividade da reação. Por fim, avaliou-se a aplicação da metodologia na síntese enantiosseletiva da muguesia, uma fragrância floral. Os resultados obtidos revelaram o grande potencial da metodologia na biorredução quimiosseletiva de compostos carbonílicos ?,?-insaturados e preparação de substâncias opticamente ativas. / In recent years, the preparation of enantiomerically pure compounds has become a concern and a challenge to the industry. This fact is a consequence of the tenuous relationship between the spatial structure of substances and the different flavors, odors, pharmacokinetic and pharmacodynamic processes and toxicity that they play in the body. In this context, the asymmetric synthesis of ?-alkyl substituted optically active carbonyl compounds has received great attention because they are important building blocks in the synthesis of chiral drugs and natural products. Thus, this study aimed to develop methodologies that allow the preparation of this enantiomerically pure compounds by controlling the formation of stereogenic centers using biocatalysis. To this end, various activated olefins substituted with electron withdrawing groups (carbonyl) were synthesized using two procedures, aldol condensation and esterification reactions. These ?,?-unsaturated carbonyl compounds were obtained in good yields (48-94%) and subjected to the biocatalytic reduction mediated by whole cells of microorganisms. Initially, we used the olefin (E)-3-methyl-4-phenyl-3-buten-2-one (51a) as a model substrate for the optimization of the experimental conditions and determine wich one provide the product with better conversion and enantiomeric purity. In these tests, we evaluated various reaction parameters such as the composition of the reaction medium (aqueous, biphasic and buffer), the presence of additives (glucose and phase transfer catalyst), different microorganisms and adsorbing effect of using Amberlite XAD-7. Thus, the biorreduction in aqueous medium, without additives, mediated by LSC-II yeast and with the application of Amberlite XAD-7 was the reaction condition that presented the best enantiomeric excess (81%) and was selected for a methodological study that evaluated the steric and electronic effects of the substituents. It was observed that the substituent in the ?-position of the aryl group, the size increase of the ?-substituent and the presence of an ester group had an important role in the stereoselectivity of the reaction. Finally, application of the methodology on muguesia enantioselective synthesis, a floral fragrance, was evaluated. The results obtained showed the high potential of the methodology in chemoselective bioreduction of ?,?-unsaturated carbonyl compounds and preparation of optically active substances.
193

Avaliação ambiental de compostos orgânicos voláteis (VOC) provenientes da queima da cana-de-açúcar / Environmental assessment of volatile organic compounds (VOC) from sugar cane burnin

Lopes, Marcelo Luiz Araujo 09 June 2010 (has links)
A queima de biomassa é uma atividade amplamente difundida em muitos países tropicais em desenvolvimento. Esta atividade tem implicações em escala regional e global devido à emissão de quantidades significativas de gases traço para a atmosfera, tais como: CO, hidrocarbonetos não metanicos (HCNM) e material particulado (MP). Os resíduos da cana-de-açúcar representam 11% da produção mundial de resíduos agrícolas, cuja queima libera quantidades expressivas de gases e partículas que influenciam a química da atmosfera. No Brasil, nos últimos anos houve um aumento do uso de etanol como combustível e um aumento nas plantações de cana-de-açúcar no Estado de São Paulo. Apesar da proibição das queimadas, episódios de queima são ainda muito freqüentes, uma vez que 50 % dos canaviais paulistas são queimados na etapa de pré-colheita. O presente estudo teve como objetivo avaliar as emissões de VOCs provenientes da queima da palha de cana-de-açúcar. Para estimar o impacto ambiental causado por esse processo de combustão em regiões urbanas próximas as queimadas foram feitos estudos em laboratório e campo. A contribuição biogênica dos compostos carbonílicos na região do canavial foi avaliada e os resultados mostraram que as folhas de cana-de-açucar, na maioria dos experimentos, não atuaram como fonte de emissão. Os experimentos de laboratório permitiram determinar os produtos de combustão incompleta na pluma. Medidas de emissão de CO, CO2, e VOC foram caracterizadas pela razão de emissão (ER) e fator de emissão (EF). Razões de mistura, em ppbv, de formaldeído (175 - 309), acetaldeído (2 - 71), acetona (1 - 36), acroleína (0,3 - 3), propionaldeído (0,2 - 10), crotonaldeído (3 -10), butiraldeído (1 - 3), benzaldeído (0,5 - 6), valeraldeído - total (2 - 60) e hexaldeído (4 - 136) foram identificados e quantificados; e outros VOCs, tais como, aromáticos, haletos de alquila, compostos contendo nitrogênio, furanos foram apenas identificados. No laboratório também foi avaliado a eficiência da combustão da palha de cana-deaçúcar (ΔCO/CO2 = 4,0±0,4%) e foi observado que a fase flaming foi predominante neste processo. A contribuição dos compostos carbonílicos na atmosfera de regiões urbanas próximas às queimadas foi avaliada através da comparação entre as medidas feitas antes e durante a queima. Os resultados estatísticos mostraram que as medidas nos dois períodos são diferentes sugerindo que a origem dos compostos é diferente. Fontes de emissão direta e principalmente reações fotoquímicas foram responsáveis pela presença de formaldeído e acetaldeído nas amostras coletadas antes da queima (medidas diurnas), enquanto que apenas fontes de emissão direta foram responsáveis pela presença desses compostos nas amostras coletadas durante a queima (medidas noturnas). Trajetórias de massas de ar que chegaram à área urbana e os focos de queima registrados nos dias de coleta mostraram que a região urbana estudada foi afetada pelas queimadas. / Biomass burning is an activity widely practiced in many tropical developing countries. This activity has implications at regional and global scales due to the emissions of significant quantities of trace gases to the atmosphere such as CO, non-methane hydrocarbons (NMHC) and particulate matter (PM). The sugar cane residues represent 11% of worldwide production of agricultural residues whose burning releases significant amounts of gases and particles that influence the atmospheric chemistry. In the last years, in Brazil, there has been an increase of the use of the ethanol as fuel and an increase of the sugar cane plantations in the State of São Paulo. Although the sugar cane burning prohibition, burning episodes are still very frequent, as 50% of the sugar cane plantations of São Paulo are burned in the the pre-harvest stage. The aim of this study was to evaluate VOC emissions of sugar cane burning. In order to estimate the environmental impact caused by the combustion process in urban regions near fires laboratory and field studies were conducted. The contribution of biogenic carbonyl compounds in the area of sugar cane was evaluated and results showed that the cane sugar leaves, in the most of the experiments, do not act as emission source. Laboratory experiments were carried out to determine incomplete combustion products in plume. Measurements of CO, CO2, and VOC were characterized by the emission ratio (ER) and emission factor (EF). Mixture ratio, in ppbv, of formaldehyde (175 - 309), acetaldehyde (2 - 71), acetone (1 - 36), acrolein (0,3 - 3), propionaldehyde (0,2 - 10), crotonaldehyde (3 -10), butyraldehyde (1 - 3), benzaldehyde (0,5 - 6), valeraldehyde-total (2 - 60) and hexaldehyde (4 - 136) were identified and quantified; and other VOCs, such as aromatic hydrocarbons, alkyl halides, nitrogen containing compounds and furans were only identified. The efficiency of the sugar cane combustion was evaluated (ΔCO/CO2 = 4.0±0.4%) in the laboratory and the predominant burning phase was the flaming phase. By comparing statistically filed measurements done before and during fire in the atmosphere of urban areas near fires, it was possible to distinguish two different groups of the measurements suggesting that the origin of the compounds is different. Direct emission sources and mainly photochemical reactions were responsible by the presence of formaldehyde and acetaldehyde in samples collected before fire (daytime measurements), whereas only direct emission sources were responsible by the presence of these compounds in samples collected during the fire (night measurements). Trajectories of air masses that reached the urban area and spots of burning recorded in the sampling days showed that the region studied was affected by fires.
194

Application of Pd Catalyzed Alkylation: Synthesis of Bicyclic Furans, Isoxazolines and New Cyclopentane Amino acid Analogs

Khan, Pasha Moeenuddin 17 November 2008 (has links)
Palladium is probably the most useful metal in organic syntheses. It has shown great utility in various reactions such as C-C, C-N, C-O bond formation under mild conditions. The presence of abundant amount of palladium-chemistry related literature in the form of books, reviews emphasizes the growing importance of these reagents. Nowadays organopalladium chemistry is being used in various fields such as new methodology development, natural product synthesis, synthesis of polymers. Regio- and stereoselectivity is another facet of Pd catalyzed methodologies which has been extensively utilized in the last decade to obtain enantiopure compounds. The main emphasis of this work is to utilize Pd catalyzed allylic alkylation to synthesize new heterocycles including furans, isoxazolines and new cyclopentane amino-acid analogs in an enantioselective manner. The stereochemical outcome of these reactions is influenced by desymmetrization catalyzed by hydrolytic enzymes namely lipases. Chapter 1 reviews the recent advances in the field of palladium catalyzed synthesis of bicyclic furan analogs and provides a mechanistic explanation for these processes. Chapter 2 describes synthesis of new optically pure isoxazoline-2-oxide and furan analogs using Pd(0) catalyzed intramolecular cyclizations. Starting from a meso-diol, optically pure compounds were prepared without utilizing chiral ligands at any stage of the synthesis. The stereochemical outcome of the product (>99 % ee) was influenced by desymmetrization catalyzed by Pseudomonas cepacia lipase and the stereoselective nature of the palladium catalyzed transformations. Chapter 3 describes Pd(0) catalyzed allylic alkylation of allylic esters using various 1°, 2° nitroalkanes. This reaction resulted in the formation of nitro substituted aldehydes and ketones via an isomerization-alkylation step. The effect of various solvents, catalyst-ligand systems and bases was also studied. The presence of versatile nitro group in these compounds which can be easily converted to a ketone, reduced to amine or transformed into carboxyl group, imines, hydroxylamines, makes them an attractive starting material for various other synthetic compounds. Chapter 4 describes the chemoenzymatic synthesis of L-carbafuranomycin and related cyclopentane amino acids analogs. The synthesis utilizes the hydrolytic enzymes to induce enantioselectivity in the whole process. Out of all the peptidomimetics and related compounds, unnatural amino acids such as bicyclic and carbocyclic amino acids are of valuable interest as they have provided new building blocks for large number of potential drug candidates. The work presented here provides a more general and efficient route to these class of unnatural amino acids.
195

Manganese(iii) Acetate Mediated Regeneration Of Carbonyl Compounds From Oximes

Altinel, Ertan 01 June 2006 (has links) (PDF)
A facile method for the direct conversion of oximes into carbonyl compounds by treatment with manganese triacetate is described. Manganese triacetate can be used for an effective and mild oxidizing agent for the regeneration of carbonyl compounds in good yield. Many functional groups are tolerated under reaction conditions.
196

Ligações de hidrogênio intramoleculares: um estudo teórico de compostos di-carbonílicos / Intramolecular hydrogen bonds in di-carbonyl compounds: a theoretical study

Bezerra, Aline Fonseca 14 October 2009 (has links)
Made available in DSpace on 2015-05-14T13:21:35Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1225184 bytes, checksum: aea7240aacf52c5036cf6d487576423c (MD5) Previous issue date: 2009-10-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The intramolecular hydrogen bond occurs when the same molecules has both proton donor and proton acceptor groups in satisfactory configuration space for the formation of this interaction. It is important to note the changes in the structural, electronic and vibrational properties that occur due to the formation of this interaction. In the hydrogen bonding formation is an important phenomenon called charge transfer , where part of the electronic density of the proton acceptor species, Y, is transferred o the proton donor specie, HX. With respect to the vibrational spectrum are observed changes in the way of straightening of donor and acceptor proton species. Di-carbonyl compounds (C3H2O2R2) with their substituent groups (R=CH3, CN, H, NH2, OH and SH) were studied focusing on the energetic, structural, vibrational and electron density analysis. Initially the energy and structural analysis were carried out starting from the molecules optimized geometry. We also evaluated of the strength s hydrogen bonding and the length s intramolecular bond. The QTAIM study was performed to obtain the electron density s values and the electron density s Laplacian values and verify the existence of the bond critical point in the intramolecular hydrogen bond. From the harmonic vibrational spectra was possible to identify changes in the vibrational modes, related the intramolecular interaction s formation. / A ligação de hidrogênio intramolecular ocorre quando uma mesma molécula apresenta, simultaneamente, um grupo doador e outro receptor de próton, em configuração espacial favorável à formação dessa interação. É importante salientar as mudanças nas propriedades estruturais, eletrônicas e vibracionais que ocorrem devido à formação dessa interação. Na formação da ligação de hidrogênio ocorre um fenômeno importante denominado de transferência de carga , onde parte da densidade eletrônica da espécie receptora de próton, Y, é transferida para a espécie doadora de próton, HX. Com respeito aos espectros vibracionais, são observadas modificações nos modos de estiramento das espécies doadora e receptora de próton. Compostos di-carbonílicos (C3H2O2R2) com suas substituições (R=CH3, CN, H, NH2, OH e SH) foram estudados enfocando as análises energética, estrutural, vibracional e de densidade eletrônica. Inicialmente foram realizadas as análises energéticas e estruturais a partir da geometria otimizada das moléculas. Foram avaliados a força da ligação de hidrogênio e do comprimento da ligação intramolecular. O estudo usando a QTAIM foi realizado para adquirir os valores de densidade eletrônica e do Laplaciano da densidade eletrônica e verificar a existência do ponto crítico de ligação na ligação de hidrogênio intramolecular. A partir dos espectros vibracionais harmônicos foi possível identificar as variações no infravermelho, referentes à formação da interação intramolecular.
197

Avaliação ambiental de compostos orgânicos voláteis (VOC) provenientes da queima da cana-de-açúcar / Environmental assessment of volatile organic compounds (VOC) from sugar cane burnin

Marcelo Luiz Araujo Lopes 09 June 2010 (has links)
A queima de biomassa é uma atividade amplamente difundida em muitos países tropicais em desenvolvimento. Esta atividade tem implicações em escala regional e global devido à emissão de quantidades significativas de gases traço para a atmosfera, tais como: CO, hidrocarbonetos não metanicos (HCNM) e material particulado (MP). Os resíduos da cana-de-açúcar representam 11% da produção mundial de resíduos agrícolas, cuja queima libera quantidades expressivas de gases e partículas que influenciam a química da atmosfera. No Brasil, nos últimos anos houve um aumento do uso de etanol como combustível e um aumento nas plantações de cana-de-açúcar no Estado de São Paulo. Apesar da proibição das queimadas, episódios de queima são ainda muito freqüentes, uma vez que 50 % dos canaviais paulistas são queimados na etapa de pré-colheita. O presente estudo teve como objetivo avaliar as emissões de VOCs provenientes da queima da palha de cana-de-açúcar. Para estimar o impacto ambiental causado por esse processo de combustão em regiões urbanas próximas as queimadas foram feitos estudos em laboratório e campo. A contribuição biogênica dos compostos carbonílicos na região do canavial foi avaliada e os resultados mostraram que as folhas de cana-de-açucar, na maioria dos experimentos, não atuaram como fonte de emissão. Os experimentos de laboratório permitiram determinar os produtos de combustão incompleta na pluma. Medidas de emissão de CO, CO2, e VOC foram caracterizadas pela razão de emissão (ER) e fator de emissão (EF). Razões de mistura, em ppbv, de formaldeído (175 - 309), acetaldeído (2 - 71), acetona (1 - 36), acroleína (0,3 - 3), propionaldeído (0,2 - 10), crotonaldeído (3 -10), butiraldeído (1 - 3), benzaldeído (0,5 - 6), valeraldeído - total (2 - 60) e hexaldeído (4 - 136) foram identificados e quantificados; e outros VOCs, tais como, aromáticos, haletos de alquila, compostos contendo nitrogênio, furanos foram apenas identificados. No laboratório também foi avaliado a eficiência da combustão da palha de cana-deaçúcar (ΔCO/CO2 = 4,0±0,4%) e foi observado que a fase flaming foi predominante neste processo. A contribuição dos compostos carbonílicos na atmosfera de regiões urbanas próximas às queimadas foi avaliada através da comparação entre as medidas feitas antes e durante a queima. Os resultados estatísticos mostraram que as medidas nos dois períodos são diferentes sugerindo que a origem dos compostos é diferente. Fontes de emissão direta e principalmente reações fotoquímicas foram responsáveis pela presença de formaldeído e acetaldeído nas amostras coletadas antes da queima (medidas diurnas), enquanto que apenas fontes de emissão direta foram responsáveis pela presença desses compostos nas amostras coletadas durante a queima (medidas noturnas). Trajetórias de massas de ar que chegaram à área urbana e os focos de queima registrados nos dias de coleta mostraram que a região urbana estudada foi afetada pelas queimadas. / Biomass burning is an activity widely practiced in many tropical developing countries. This activity has implications at regional and global scales due to the emissions of significant quantities of trace gases to the atmosphere such as CO, non-methane hydrocarbons (NMHC) and particulate matter (PM). The sugar cane residues represent 11% of worldwide production of agricultural residues whose burning releases significant amounts of gases and particles that influence the atmospheric chemistry. In the last years, in Brazil, there has been an increase of the use of the ethanol as fuel and an increase of the sugar cane plantations in the State of São Paulo. Although the sugar cane burning prohibition, burning episodes are still very frequent, as 50% of the sugar cane plantations of São Paulo are burned in the the pre-harvest stage. The aim of this study was to evaluate VOC emissions of sugar cane burning. In order to estimate the environmental impact caused by the combustion process in urban regions near fires laboratory and field studies were conducted. The contribution of biogenic carbonyl compounds in the area of sugar cane was evaluated and results showed that the cane sugar leaves, in the most of the experiments, do not act as emission source. Laboratory experiments were carried out to determine incomplete combustion products in plume. Measurements of CO, CO2, and VOC were characterized by the emission ratio (ER) and emission factor (EF). Mixture ratio, in ppbv, of formaldehyde (175 - 309), acetaldehyde (2 - 71), acetone (1 - 36), acrolein (0,3 - 3), propionaldehyde (0,2 - 10), crotonaldehyde (3 -10), butyraldehyde (1 - 3), benzaldehyde (0,5 - 6), valeraldehyde-total (2 - 60) and hexaldehyde (4 - 136) were identified and quantified; and other VOCs, such as aromatic hydrocarbons, alkyl halides, nitrogen containing compounds and furans were only identified. The efficiency of the sugar cane combustion was evaluated (ΔCO/CO2 = 4.0±0.4%) in the laboratory and the predominant burning phase was the flaming phase. By comparing statistically filed measurements done before and during fire in the atmosphere of urban areas near fires, it was possible to distinguish two different groups of the measurements suggesting that the origin of the compounds is different. Direct emission sources and mainly photochemical reactions were responsible by the presence of formaldehyde and acetaldehyde in samples collected before fire (daytime measurements), whereas only direct emission sources were responsible by the presence of these compounds in samples collected during the fire (night measurements). Trajectories of air masses that reached the urban area and spots of burning recorded in the sampling days showed that the region studied was affected by fires.
198

Palladium catalysed asymmetric hydroxy- and alkoxycarbonylation of alkenes

Durrani, Jamie T. January 2015 (has links)
Palladium catalysed asymmetric hydroxy- and alkoxycarbonylation reactions of alkenes have the potential to deliver valuable chiral carboxylic acid and ester building blocks from cheap feedstocks: alkenes, carbon monoxide and water (alcohols in the case of alkoxycarbonylation). Despite the attractive nature of these reactions, extensive research has so far been unable to produce effective catalysts which are capable of controlling both regio- and enantioselectivity. Building on exciting recent results involving the use of highly enantioselective palladium catalysts derived from Phanephos-type ligands, this research focuses on paracyclophane-diphosphines and their use in asymmetric hydroxy- and alkoxycarbonylation reactions. An investigation into reaction conditions analysed several factors, including solvents, CO-pressure, acidic additives and halide sources, to provide optimal activity and selectivities. Two novel electron-poor paracyclophane-diphosphines and their mono- and di-palladium complexes were synthesised and shown to provide exceptional levels of regioselectivity while maintaining high levels of asymmetric induction. These are the first such examples of hydroxy- or alkoxycarbonylation catalysts to facilitate simultaneous control over both regio- and enantioselectivity. The most effective catalyst was used to promote the reactions of a selection of aryl alkenes and was shown to be tolerant of several different functional groups. A selection of non-symmetric paracyclophane-diphosphine ligands and their palladium complexes were also synthesised and assessed for their performance in hydroxy- and alkoxycarbonylation. We also report the use of Phanephos-type ligands to promote the highly enantioselective hydroxycarbonylation of N-(p-toluenesulfonyl)-3-pyrroline to deliver a chiral proline derivative in high ee.
199

Kinetics Studies of Substituted Tungsten Carbonyl Complexes

Wang, I-Hsiung, 1950- 08 1900 (has links)
Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond.
200

Avaliação da qualidade do ar de cabines de veículos automotores recém-manufaturados / Evaluation of new vehicles cabin indoor air quality

Valvassori Filho, Auzebio 23 September 2008 (has links)
Cabines de veículos automotores recém-manufaturados podem ser consideradas críticas quando se avalia a qualidade do ar interno, pois concentrações de compostos orgânicos voláteis encontram-se em níveis mais altos que os ambientes externos. Determinadas substâncias presentes no ar da cabine podem ser prejudiciais ao ser humano em função da sua toxicidade, pricipalmente nos grandes centros urbanos. A avaliação do ar da cabine automotiva se faz necessária. Nesse estudo, foi feita uma avaliação da qualidade do ar interno da cabine de 7 veículos populares recém-manufaturados contendo materiais de acabamento interno iguais. Um total de 46 compostos orgânicos voláteis foi identificado, sendo que 14 deles são compostos carbonílicos e 32 são hidrocarbonetos alifáticos e aromáticos, compostos halogenados e um nitrogenado. Os compostos carbonílicos foram identificados e quantificados por cromatografia a líquido e os outros VOCs apenas identificados por GC-MS. No ar interno da cabine dos veículos estudados, as concentrações médias encontradas para os compostos carbonílicos (µg/m3) em ordem decrescente foram: formaldeído (165,3); acetona (67,5); acetaldeído (56,8); isovaleraldeído (40,8); propionaldeído (21,1); butiraldeído (17,9); crotonaldeído (14,9); hexaldeído (14,9) valeraldeído (9,8); 2.5- dimetilbenzaldeído (9,3); otolualdeído (8,4); p/m tolualdeído (6,8); acroleína (4,2) e benzaldeído (3,8). Com relação aos outros VOCS foram identificados o metilbutano, que apresentou a maior porcentagem de abundância relativa, 8,5%, seguido de outros hidrocarbonetos com abundância relativa entre 5 e 2% , como, 2,7,10-trimetildodecano, 2,2,6-trimetildecano, ciclopentano, 2,3,4-trimetildecano, n-pentano, 3,6-dimetilundecano, 4-metildodecano, 4,6- dimetildodecano, 3,6-dimetildecano e 1,2-dimetilbenzeno. Dois derivados de hidrocarbonetos halogenados também foram encontrados, sendo que o triclorofluormetano foi o majoritário com 5,7%, e um composto nitrogenado, a acetonitrila com 5,4%. Os compostos derivados do benzeno identificados foram: 1,2-dimetilbenzeno, etilbenzeno, metilbenzeno, 1-etil-3- metilbenzeno, 1-etil-3-metilbenzeno e 1,3,5-trimetilbenzeno que perfazem 6,6 % de abundância relativa. O mais abundante entre os aromáticos foi o 1,2-dimetilbenzeno (2,5%). Os resultados experimentais revelaram também a liberação de VOCs pelos materiais de acabamento interno dos veículos automotores recém-manufaturados. / New motor vehicles cabins may be critical when considering the internal air quality, because concentrations of volatile organic compounds are at levels higher than the outdoors. Certain substances present in the cabin air can be harmful to humans according to their toxicity, mainly in the big cities. Assessment of the cabin air becomes necessary. In this study, cabin air quality was assessed and 7 popular new vehicles containing same interior trim materials were evaluated. A total of 46 volatile organic compounds were identified, with 14 of them were carbonylic compounds and 32 are aliphatic and aromatic hydrocarbons, halogenated compounds and a nitrogenated compound. The carbonylic compounds were identified and quantified by the liquid chromatography and other VOCs only identified by GC-MS. Cabin air vehicles studied showed the following average concentrations found for carbonylic compounds ( µg/m3) in a descending order: formaldehyde (165.3), acetone (67.5); acetaldehyde (56.8); Isovaleraldehyde ( 40.8); propionaldehyde (21.1); butyraldehyde (17.9); crotonaldeído (14.9); hexaldeído (14.9) Valeraldehyde (9.8); dimetilbenzaldeído-2.5 (9.3); the - tolualdeído (8.4), p / m - tolualdeído (6.8); acrolein (4.2) and benzaldehyde (3.8). Concerning the other VOCs the following compounds were identified: methylbutane, which had the highest percentage of relative abundance, 8.5%, followed by other hydrocarbons with relative abundance between 5 and 2%, 2,7,10-trimetildodecano, 2.2 ,6- Trimetildecano, ciclopentano, 2,3,4-trimetildecano, n-pentane, 3.6-dimetilundecano, 4- metildodecano, dimetildodecano-4.6, 3.6 and 1.2-dimetildecano-dimetilbenzeno. Two halogenated hydrocarbons were also found, and triclorofluormetano had the biggest relative abundance percentage 5.7%, and a nitrogen compound, the acetonitrile with 5.4%. The benzene compounds identified were: 1.2-dimetilbenzeno, ethylbenzene, methylbenzene, 1- ethyl-3-methyl, ethyl-1-and 3-methyl 1,3,5-trimethylbenzene which comprise 6.6% of relative abundance. 1.2-dimetilbenzeno was the most abundant aromatic compound with relative abundance 2.5%. Results also showed that VOCs were released by studied vehicles interior trim materials.

Page generated in 0.0815 seconds