Kinetics and mechanism of the oxidation of dimethyl, dipropyl and diphenyl sulfides by benzimidazolium dichromate

Department of Chemistry, JNV University, Jodhpur-342 005, Rajasthan, India

E-mail : seemakothari23@gmail.com

Department of Chemistry, MLS University, Udaipur-313 001, Rajasthan, India

Manuscript received online 03 November 2014, revised 25 December 2014, accepted 31 December 2014

The oxidation of dimethyl-, dipropyl- and diphenyl sulfides by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide, to the corresponding sulfoxides, is first order with respect to BIDC. Michaelis-Menten type kinetics were observed with respect to sulfide. The reaction is catalysed by hydrogen ions and the order is less than one. It appears that the BIDC-H⁺ is the active electrophile. An intermediate of composition Sulfide-BIDC-H⁺ has envisaged. An analysis of the solvent effect by Swain’s equation indicated that though both the anion- and cation-solvating powers of the solvent contribute to the observed solvent effect, the role of cation-solvation is major. A mechanism involving the rate-determining oxygen atom transfer within complex, formed by a nucleophilic attack of sulfide-sulfur on BIDCH⁺ in a rapid pre-equilibrium, is suggested to give product via a cyclic transition state.