The reaction of sulphides with iodobenzene dichloride in aqueous pyridine. Synthesis of sulphoxides free from sulphone and 18O-labelled sulphoxides

Abstract

Sulphides react with the stoicheiometric quantity of iodobenzene dichloride in aqueous pyridine between –40 and 20° to give high yields of the corresponding sulphoxides. The reaction applies to aliphatic, aromatic, and heterocyclic sulphides. The influence of electronic and steric effects is small. In vinylic sulphides containing electron-withdrawing groups β to the sulphur atom, oxidation is followed by heterolytic cleavage of the S–C(ethylenic) bond. An excess of reagent may lead to the formation of sulphones or chlorosulphoxides. Both reactions are much slower than mono-oxidation, so that, under the conditions indicated, oxidation of sulphides with one molar proportion of reagent leads exclusively to sulphoxides. Use of ¹⁸O-enriched water readily gives ¹⁸O-labelled sulphoxides.