During the course of this work we have synthesized and evaluated a series of new enantiopure silyl triflmides as catalysts for asymmetric reactions. 3-Phenyl dialkylsilyl ketones, which were the key precursors to the target silyl triflmides were prepared by 1,4-addition of the corresponding silyl cuprate to enones, and resolved by chiral HPLC. Enantiopure trans silyl ketones were successfully reduced via the corresponding tosylhydrazones by the NaBH3CN/ZnCl2 system. However, due to an isomerization of the tosylhydrazone during the reaction, cis isomers (m = 0) were reduced via the corresponding dithioketals followed by desulfurization. The diastereoselective synthesis of enantiopure silyl triflimides from enantiomerically pure compounds has been also studied. The enantiopure trialkylsilyl triflimides were generated in situ by protodesilylation of the corresponding phenylsilanes with bis-(trifluoromethylsulfonyl)imide. The Diels-Alder reaction of methyl acrylate with cyclopentadiene was used as the model reaction for testing the new chiral catalysts : 1) Almost all silyl triflimides were efficient catalysts giving high yields and excellent diastereoselectivities in favour of the endo-isomer. 2) the best ee's (up to 56%) were obtained from catalysts carrying an aryl group directly attached to the cyclohexane ring (m = 0) which were much better than those obtained from catalysts carrying a benzyl-type group (m = 1). Interestingly catalysts of the same configuration carrying phenyl or naphthyl group gave cycloadducts of opposite configuration. 3) When m = 0, additional substituents at position-3 or 6 of the cyclohexyl ring had little influence on the ee. However, for m = 1, a methyl group at C2 increased the ee from 3% to 35%. 4) The replacement of the methyl groups connected to the silicon atom by bulkier ethyl groups decreased the ee (m = 0). 5) When m = 0, ee's for cycloaddition reactions of N,N-dimethyl acrylamide or acryloxazolidinone with cyclopentadiene were lower than those obtained with methyl acrylate.

Orientador: Carla Beatriz Grespan Bottoli / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T09:05:26Z (GMT). No. of bitstreams: 1 GutierrezPonce_MariadeJesusSanta_D.pdf: 3412773 bytes, checksum: 0fb510ed608f7a239752ee164a4215ad (MD5) Previous issue date: 2011 / Resumo: Monolitos à base de sílica têm sido usados como fases estacionárias em eletrocromatografia capilar e apresentam vantagens em relação aos materiais particulados tais como: melhor homogeneidade; controle do tamanho dos poros; alta estabilidade mecânica e térmica; minimização da formação de bolhas e diminuição de problemas com filtros. O presente trabalho teve como objetivo a síntese e caracterização de uma nova fase estacionária monolítica à base de sílica com grupos carboxílicos em sua estrutura, os quais ajudam a sustentar o fluxo eletrosmótico e conferem características de troca catiônica à fase. A fase estacionária monolítica foi sintetizada empregando o processo sol-gel. A síntese do agente sililante foi feita a partir de ácido 4-aminobenzóico e trietóxipropilisocianatossilano. A derivatização da fase estacionária monolítica foi feita adicionando-se ao monolito uma solução de 10% do silano em DMF e deixando reagir por 6 horas a 60 °C. A fase estacionária monolítica funcionalizada foi avaliada por microscopia eletrônica de varredura, espectroscopia no infravermelho e análise elementar. A fase estacionária também foi testada com um equipamento de eletroforese capilar construído no laboratório com detecção condutométrica sem contato (CD) e um equipamento de eletroforese capilar Agilent com detecção UV. Os resultados da microscopia eletrônica confirmaram a formação do monolito dentro do capilar e a espectroscopia no infravermelho, bem como a análise elementar permitiram caracterizar tanto o monolito como o silano empregado na funcionalização do monolito. Na avaliação com detector CD foram separados cátions e aminoácidos, evidenciando a característica de troca catiônica da fase. Na avaliação com detector UV foi confirmada a falta de seletividade da fase para compostos apolares, mas, foram separados alguns fármacos básicos com boa resolução e formato de pico o que indica a possibilidade de aplicação da nova fase em separações de compostos básicos / Abstract: Monoliths are used as stationary phases in capillary electrochromatography since they can effectively overcome the difficulties associated with packed capillary column technology. A remarkable advantage of monolithic columns is the elimination of the end frits required to retain particulate stationary phases. The aim of the present study was to synthesize and characterize a new silica-based monolithic stationary phase with carboxylic groups in its structure, which help to support the electroosmotic flow and confer characteristics of cation-exchange to the phase. The formation of the monolith inside the capillary was achieved using the sol-gel method. The silylant agent was made from 3-(triethoxysilyl)propylisocyanate and 4-aminobenzoic acid. The surface modification of the monolith with the silylant agent used a 10% solution in DMF, left to react for 6 h at 60 °C. The modified monolithic column was evaluated by scanning electron microscopy, infrared spectroscopy and elemental analysis. The column was tested using a homemade capillary electrophoresis system with a capacitively coupled contactless conductivity detector (CD) and with Agilent capillary electrophoresis equipment with UV detection. The results of scanning electron microscopy confirmed the formation of the monolith while infrared spectroscopy and elemental analysis characterized the synthesized silylant agent used in the modification of the monolithic column as well as the modified monolith. In evaluations with the CD cations and amino acids were separated, showing the characteristics of a cation-exchange phase. With UV detection the lack of phase selectivity for apolar compounds was confirmed, but some basic drugs were separated with good resolution and peak shape, which indicates the possibility of applying the new phase in separations of basic compounds / Doutorado / Quimica Analitica / Doutor em Ciências

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-02-16T13:10:45Z No. of bitstreams: 1 Romulo Augusto Lins de Campos.pdf: 5930168 bytes, checksum: 7553330ff526456aa81970434c7c3475 (MD5) / Made available in DSpace on 2017-02-16T13:10:45Z (GMT). No. of bitstreams: 1 Romulo Augusto Lins de Campos.pdf: 5930168 bytes, checksum: 7553330ff526456aa81970434c7c3475 (MD5) Previous issue date: 2011-03-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Potentiometric sensors are known for their high sensitivity and selectivity. Such sensors have versatility, low cost and robustness, which ensures their applicability in a wide variety of complex chemical samples. The ion-selective electrodes for polymeric membrane are the best known potentiometric sensors, has by these traits. However, modified carbon paste electrodes have gained prominence due a great advance in their studies. This paper proposes an electrode chemically modified carbon paste for potentiometric determination of copper (II), using a new ionophore lariat-crown ether synthesized from precursor aminopropyl triethoxysilane is a silylating agent known in the literature. Studies were conducted to evaluate the influence of pH on the potential, the best buffer as supporting electrolyte, and the experimental design of mixtures to obtain the best composition of EQMPC. The proposed electrode showed a sensitivity of 38.5 mV/decade of activity with a detection limit of 2.04 x 10-5 mol L-1, and as a supporting electrolyte buffer biftalate/HCl pH = 3.0 proving to be promising for application in the determination of Cu(II). The electrode showed no significant analytical sensitivity to Co(II), Ni(II) and Zn(II) being these their main interferences. / Sensores potenciométricos são conhecidos por sua alta sensibilidade e seletividade. Tais sensores apresentam versatilidade, baixo custo e robustez, o que garante a esses sensores aplicabilidade em uma grande variedade de amostras químicas complexas. Os eletrodos íon-seletivos de membrana polimérica são os sensores potenciométricos mais conhecidos, por possuirem essas características. Contudo, os eletrodos modificados de pasta de carbono têm ganhado forte destaque devido ao avanço em seus estudos. Neste trabalho é proposto um eletrodo quimicamente modificado de pasta de carbono para determinação potenciométrica de cobre (II), utilizando um novo ionóforo lariat-éter coroa sintetizado a partir de precursor aminopropil trietoxisilano que é um agente sililante conhecido na literatura. Foram realizados estudos para avaliar a influência do pH sobre o potencial, o melhor tampão como eletrólito de suporte, além do planejamento experimental de misturas para se obter a melhor composição do EQMPC. O eletrodo proposto apresentou uma sensibilidade de 38,5mV/década de atividade com limite de detecção de 2,04 x 10-5 mol L-1, tendo como eletrólito de suporte um solução-tampão biftalato/HCl pH = 3,0 demonstrando ser promissor para aplicação na determinação de íons Cu(II). O eletrodo não apresentou sensibilidade analítica significativa aos íons Co(II), Ni(II) e Zn(II) sendo esses seus principais interferentes.