Nucleophilic substitution at two-co-ordinate sulphur. Effect of the basicity of the nucleophile and structural effects on the sulphur substrate

Abstract

The rate of reaction of p-nitrobenzenesulphenyl chloride with substituted anilines has been measured in benzene at 20 °C with a stopped-flow spectrophotometer. The kinetic data, plotted in a Brønsted fashion against the pK_a of the conjugated acid of the nucleophile, yield good linear relationships characterized by β= 1·250 in absence of additives and by β= 1·256 in the presence of tetra-n-butylammonium perchlorate. The large effect of the basicity of the nucleophile is interpreted in terms of almost complete bond forming in the transition state and d-orbital participation is suggested. In contrast, the effect of para-substitution on the sulphur substrate is almost nil.