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.
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