The polarography of some substituted azobenzenes in acetonitrile. III The effect of strong proton donors

Abstract

The d.c. and a.c, polarographic behaviour, observed on the addition of strong proton donors such as sulphuric acid, hydrogen chloride, and hydrogen bromide to some 4-monosubstituted azobenzenes in acetonitrile is discussed. Diffusion controlled waves are observed at potentials up to 1.7 V more positive than the normal azobenzene reduction waves observed in the absence of proton donors. It is proposed that the reduction of azonium species, formed in labile equilibria by proton exchange between the acid and the azo compound, give rise to these waves. A general mechanism to account for the appearance of the prewaves is proposed. Unusual and complicated adsorption behaviour was observed in the 4-methoxyazobenzene-sulphuric acid system.