Electrochemical behaviour of some 3-methylthio-1,2-dithiolium cations in dimethylformamide solution

Substituted 3-methylthio-1,2-dithiolium cations were prepared by alkylation of the corresponding 1,2-dithiole-3-thiones. These compounds were easily reduced in DMF at a mercury electrode, following two one-electron waves. Electrolysis, carried out at a mercury pool electrode and followed by an alkylation or an acylation, provided the corresponding alkyl (or acyl) dithioesters and by-products. At a platinum or glassy carbon electrode the reduction was an irreversible process, which was dependent upon the cathode nature. Whatever the electrode, the reduction was a combination of two reactions, a two-electron reduction and a one-electron one involving a dimerization. The electrochemical behaviour of 3-methylthio-1,2-dithiolium cations exhibited many analogies with the cathodic behaviour of the corresponding 1,2-dithiole-3-thiones. Moreover, identical intermediates were implicated in the reduction of 3-methylthio-1,2-dithiolium cations and in the reductive alkylation of 1,2-dithiole-3-thiones.