Investigacao electroquimica de grupos protectores

The anodic oxidation of 2-(4-nitrophenylthio)ethyl esters in acetonitrile containing NaC1O_4.H_4O or Bu_4NBF_4, using vitreous carbon and platinum electrodes, was investigated. The oxidation reaction occurs in two steps, the corresponding sulphoxide being formed at the first followed by, at more positive potentials, the oxidation to sulphone. The model compound studied was the derivative of the acetic acid and the investigation was extended to a derivative of alanine with the amine function protected by the benzyloxycarbonyl group, Z, and, the carboxyl function with the referred group. The results of cyclic voltammetry, potential step method and controlled potential bulk electrolysis indicate the conversion of the esters to the corresponding sulphoxides, occurs in good yields. The oxidation into sulphone, however, is more complex reaction which occurs in moderate yields. For the alanine derivative, protected with the Z group, it was observed that both protecting groups are electroactive in the same potential region of the conversion into sulphone being perturbed by the presence of the Z group. These results suggest the need to find other protecting groups of the amine function which are inactive at this potential region. The method of homogeneous redox catalysis was applied to the alanine derivative in order to determine the half life of the anion radical formed during the first oxidation step and also, the standard reduction potential for the couple molecule/anion radical. In this thesis, electrochemical studies of thiols protected with the benzyl group in DMF solutions containing Bu_4NBF_4 at vitreous carbon electrodes, are also presented. The reduction of these compounds occurs at very negative potentials, with formation of toluene and free thiol in good yields. Cyclic voltammetry and controlled potential bulk electrolysis were used to establish the reduction mechanism. The same methods were used to study the reduction of an aminoacid protected with the benzyl group and similar behaviour was observed. It is also shown that the introduction of the nitro group in the benzene ring gives rise to a reduction process at a less negative potential which..Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga