Reactions of organo sulfur compounds with superoxide ion oxidations of 1,3-diphenylthiourea and 2-mercaptobenzimidazole

Abstract

The reactions of 1,3-disubstituted thiourea with potassium superoxide ($KO_2$) were carried out in various solvents such as dimethyl sulfoxide, tetrahydrofuran, and acetonitrile in order to study on the peroxy intermediates such as peroxy tetrahedral anion, peroxy-sulfenate, -sulfinate, and -sulfonate which have been postulated to be unstable intermediates. The treatment of 1,3-diphenylthiourea with $KO_2$ in DMSO gave 1,3-diphenylurea. The reaction appears to be initiated by a nucleophilic attack of thiocarbonyl carbon by superoxide ion ($O_2^{\bar{\cdot}}$) to form a peroxy tetrahedral anion intermediate in DMSO. These peroxy anion should react with DMSO of the trapping reagent for the peroxy oxygen to give 1,3-diphenylurea and dimethyl sulfone. While, the reaction of 1,3-diphenylthiourea with $KO_2$ in THF or acetonitrile appears initiated by redox system (reductant as 1,3-diphenylthiourea, oxidant as as ($O_2^{\bar{\cdot}}$) to form thiyl radidal. The radical combination of thiyl radicals and $O_2^{\bar{\cdot}}$. may produce peroxysulfenate intermediate. The reaction of peroxysulfenate with the oxygen trapping reagent such as DMSO, acetonitrile, or chalcone let to dimethyl sulfone, acetamide, or chalcone epoxide. The treatment of 2-mercaptobenzimidazole with excess $KO_2$ in DMSO, THF, or acetonitrile gave the corresponding sulfonic acid quantitatively. The mechanisms of the reactions of sulfur compounds with $O_2^{\bar{\cdot}}$ in the various solvents and of the reactions of these trapping agents with peroxy intermediates are discussed.