Solvent effect on the electrochemical reduction of S-phenyl benzenethiosulfonate

Abstract

The electrochemical reduction of S-phenyl benzenethiosulfonate (1) was investigated by cyclic voltammetry at different scan rates (0.1–60 V/s) using glassy carbon electrodes in three different solvents; acetonitrile, dimethyl sulfoxide, and dimethyl formamide. The initial electron transfer (ET) to the investigated compound follows a concerted process with the formation of a radical/ion pair before complete dissociation (“sticky” dissociative ET mechanism). Application of classical and “sticky” dissociative electron transfer theories, as well as theoretical calculations supported the proposed ET mechanism. The theoretical calculations showed that the LUMO of S-phenyl benzenethiosulfonate and SOMO of its reduced form are homed on the S-SO2 chemical bond with a low contribution on the rest of the molecule. This indicates that the incoming electron is directly injected to the chemical bond causing its cleavage. The controlled potential electrolysis of the investigated compound, monitored by high performance liquid chromatography and cyclic voltammetry, indicated the consumption of one electron per molecule, and final formation of diphenyl disulfide and phenyl sulfinate. All experimental and theoretical findings were used to propose the full reduction mechanism. Also, a solvent effect was observed on certain parameters including reduction peak potentials, transfer coefficient values, the strength of the interaction between the ion/radical fragments, and the chemical reaction processes following the first ET. This solvent effect was rationalized by comparison of the solvent’s properties.