The electrochemical reduction of O-nitrotoluene to O-tolidine—II. Voltammetry and reaction mechanism

O-tolidine obtained by reduction of o-nitrotoluene is used in the production of dyestuffs. Various steps in this reduction have been investigated by means of controlled-potential electrolysis and measuring voltammograms at rotating disc electrodes. Results of the first types of experiments are already published and those of the latter type are presented in the recent paper. Voltammograms are measured for the reduction of nitrotoluene, azoxytoluene and azotoluene with various electrode materials in alkaline ethanol—water solution and in alkaline aqueous solutions containing McKee salt and for the reduction of azoxytoluene and azotoluene in acidic ethanol—water solutions as well as in acidic aqueous solution containing McKee salt and acid. The reduction wave of nitrotoluene does not correspond to a single product reaction, whereas those of azoxytoluene and azotoluene correspond to a single-product process, respectively. It has been found likely that dimerization of the intermediate nitrosotoluene radical anion occurs on formation of azoxytoluene. This conclusion strongly deviates from the Haber scheme mostly proposed for the reduction mechanism of aromatic nitro-compounds and supports that of Fry.