Mechanistic study of the synthesis of alquilfenilselenetos, the reaction type Zn-Barbier aqueous vehicle / Estudo mecanístico da síntese de alquilfenilselenetos, pela reação tipo Zn-Barbier em meio aquoso

AUTOR(ES)

José Ayron Lira dos Anjos

DATA DE PUBLICAÇÃO

2009

RESUMO

Alkyl phenyl selenides are versatile synthetic intermediates. In addition to the traditional methods, a method of synthesis was developed by Bieber by reacting diphenyl diselenide with organic halides using zinc dust in water / acetonitrile for a wide range of substrates. The lack of precedents in the understanding of this reaction limits the choice of the conditions that favor getting the best results; this prompted us to investigate the mechanism of the reaction. The study consists in analyzing the behavior of the reaction involving alkyl halides with different degree of steric hindrance and reactivity. In others experiments we use halides that indicate the involvement of radicals through of fast unimolecular rearrangements, and checking the sensitivity of this behavior for the modification of the conditions used, such as, the pH of the aqueous solution, the active surface and the way of addition from the zinc, the concentration of the disselenide, the quantity and nature of the organic solvent, the use of metal salts of transition or of inhibiting ones or of radicalar promoters, besides the application of alternative routes that promote specifically the reduction of the disselenide or of the alkyl halide. The analysis of the results indicates a competition between the mechanisms SN2 and SRN1. In reactions with primary and secondary halide the mechanism SN2 is favored and the mechanism of the type SRN1 appears only as a secondary way; in contrast in reactions that with tertiary halides the mechanism of the type SRN1 is the only possible and gives the product in high yield when we use alkyl halide in excess.

ASSUNTO(S)

relógio radicalar phenylselenide radical clock quimica reação de barbier fenilselenetos barbier reaction

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