Electrochemical reduction of azo sulfonates and sulfones. A cyclic voltammetry and EPR study

Abstract

Two reduction peaks can be seen in cyclic voltammograms of azo compounds such as X–C₆H₄–N₂–Y, where X is o-, m-, p-OCH₃, m-, p-CH₃, p-Cl, p-NO₂, di-o-CO₂CH₃, di-o-CO₂H and Y is –SO₃Na, –SO₂Ph, –BF₄, –CCH₃(CN)₂, C(CH₃)₂CN, investigated in acetonitrile. Their degree of reversibility depends on the substituents X and Y. Sulfonates and Sulfones form anion radicals in the first reduction wave, as detected by electron paramagnetic resonance (EPR) spectroscopy, with unpaired spin density centred on the azo nitrogens and distributed also over the phenyl ring. The reduction products of azo compounds decompose with elimination of N₂ and the radicals thus formed terminate either by abstracting hydrogen from the solvent and the supporting electrolyte, or by forming cage products.