Selective reduction ofpara-substituted diphenyldisulfides catalysed by a sulfided NiMo supported on alumina catalyst

Abstract

Abstract The reactivity of a series of para -substituted diphenyldisulfides (X-DPDS, X = OH, NH 2 , CH 3 , NO 2 , CH 3 ) have been determined in a G/L/S reactor in the presence of a sulfided nickel molybdenum sulfide catalyst. Except for the case of the para -nitro derivative, the reaction is highly selective towards S-S bond hydrogenolysis since thiols were the only products formed. Molecular mechanics calculations evidenced that all the X-DPDS adopted the same conformation. These results may account for a high accessibility of the S-S bond to a plane surface explaining the high selectivity observed. Among the substituted DPDS, the dinitro compound was found to be poorly reactive and under more severe experimental conditions, hydrogen attacks preferentially the N-O bond. Theoretical considerations may explain this behaviour. The presence of the other substituents i.e. Cl, NH 2 , CH 3 , OH, in a para position induces a diminution of the reaction rate whatever their nature. This behaviour is different from the one observed in homogeneous media using nucleophilic reagents to perform the same reaction. To interpret this discrepancy between the results of the heterogeneous reaction and those obtained in homogenous media, it is assumed that in the first case the reaction does not imply an important electron transfer from the catalytic site to the adsorbed molecules.