Electrosynthesis of 4,4′-dinitroazobenzene from para-nitroaniline in acetonitrile/water media

4,4′-Dinitroazobenzene was electrosynthesized from p-nitroaniline at graphite, (Ir-Ru)O₂, NiCo₂C₄, PbO₂, PdO_y and PtO_x-coated titanium electrodes in acetonitrile/water media. The influences of CH₃CN volume content, OH^- concentration, and anolyte temperature on the current efficiency (C.E.) of 4,4′-dinitrooazobenzene formation were also investigated. The formation of 4,4′-dinitroazobenzene was found to be mainly depressed by the adsorption of a thick organic layer (mainly consisted of 4,4′-dinitroazobenzene) on the electrode surface, rendering an increase in electrode potentials during bulk electrolysis, which enhances the evolving rate of oxygen. The low activation energy for the chemical combination step of the 4,4′-dinitroazobenzene formation implied that the intermediate species oxidized from p-nitroaniline possessed radical properties.