Mechanism for the reactions of sulfides and sulfoxides with hypochlorites: racemization and oxygen exchange of oxysulfonium salts and sulfoxides

Abstract

Density functional theory computations have been performed on the oxidations of sulfides and sulfoxides with hypochlorite ion (OCl−), hypochlorous acid, and alkyl hypochlorites to study the mechanism of the reactions. The OCl− anion transforms sulfides to sulfoxides and sulfoxides to sulfones in oxygen transfers. The oxygen atom of QOCl hypochlorites (Q = H, Me, t‐Bu) attacks at the sulfur atom of the substrates, and oxysulfonium cation intermediates are formed; the departure of the leaving Cl− is catalyzed by soft Lewis acids. The structures of the early transition states are determined by highest occupied molecular orbital–lowest unoccupied molecular orbital interactions. The sulfur compounds are the electron acceptors in the reaction with OCl−, but they are the electron donors in the reactions with QOCl. The attack of Cl− at the oxygen atom of oxysulfonium cation intermediates leads to the sulfide and QOCl precursors and can result in racemization, oxygen exchange, and reduction of oxysulfonium salts in reversible reactions. The attack of Cl− at the sulfur atom of oxysulfonium salts produces λ4‐sulfane intermediates. Oxysulfonium cations can be transformed into sulfoxide products with the attack of Cl− or water at the α‐carbon atom of the O‐alkyl group. The attack of water at the sulfur atom of oxysulfonium cation leads to hydrolysis or oxygen exchange reactions. Racemization and oxygen exchange of sulfoxides proceeds in similar reactions, through the formation of hydroxysulfonium cation intermediates in acidic media in the presence of Cl−. Chlorosulfonium cations are of very high energy; their intermediacy can be ruled out in the reactions of sulfides with hypochlorites. Copyright © 2012 John Wiley & Sons, Ltd.