Electrophilic cleavage of the sulphur–sulphur bond. Kinetics of the isotopic exchange between p-chlorophenylsulphenyl chloride and pp′-dichlorodiphenyl disulphide in the dark

Abstract

Kinetics of the isotopic exchange between p-chlorophenylsulphenyl chloride and the corresponding [³⁵S₂]disulphide in benzene in the dark are of the second order, first order with respect to each compound. Change to chlorobenzene as solvent results in a four-fold increase of the exchange rate. Moreover, addition of tetra-alkylammonium perchlorates in benzene dramatically accelerates the exchange which, however, remains of the first order with respect to the disulphide. Also, addition of tetra-n-butylammonium chloride does not depress the exchange rate in the presence of perchlorate salts. These results suggest a polar mechanism for the exchange in the dark which cannot involve a sulphenium ion in a kinetically important step. Rather, the sulphenyl chloride must be the electrophilic species involved in the sulphur–sulphur bond breaking.