Kinetics of the nucleophilic addition of some aromatic thiols to aryl vinyl sulphones

Abstract

The rate of addition of aromatic thiols to aryl vinyl sulphones was measured in 1 : 1 (v/v) aqueous ethanol at 25°C. The reaction is kinetically of the second order, being of first order with respect to the sulphone and to the thiolate anion; the latter is the only active nucleophile. The nucleophilic behaviour of thiolate anions in this reaction is briefly compared with that in the nucleophilic substitution of benzyl bromides. Hammett's equation was used to study the effect of substituents in both aryl vinyl sulphones and aromatic thiols; substituents in the former were found to influence the reaction more than substituents in the latter. This indicates that the transition state closely resembles a carbanion intermediate.