N-BROMOSUCCINIMIDE-CATALYSED TRANSESTERIFICATION AND RACEMIZATION OF SULPHINATES

Abstract

Both aliphatic and aromatic sulphinates undergo transesterification reaction in the presence of N-bromosuccinimide. Isopropanolysis of optically active alkyl arenesulphinates was found to give racemic isopropyl arenesulphinates. The rate of racemization of optically active isopropyl p-toluenesulphinate was found to be first order with respect to both N-bromosuccinimide and isopropyl alcohol, suggesting that the reaction is a bimolecular nucleophilic substitution at the sulphur atom. The para electrodonating substituents in the aromatic ring accelerate slightly the rate of racemization. At the same time the rate of racemization was found to be retarded by the increase of steric requirements of the substituent at the sulphinyl sulphur atom suggesting that the initial formation of bromoxonium salt is the rate-determining step. Completely nonstereospecific isopropanolysis of optically active alkyl p-toluenesulphinates suggests that a sulphurane is formed as an intermediate in the exchange step of the reaction.