Polarography of azobenzene and its p-sulphonic acids

Abstract

The behaviour at the dropping mercury electrode of trans-azobenzene and its p-sulphonic acids has been studied by several techniques including d.c., a.c., single sweep, and Kalousek polarography. Current-potential curves recorded at the streaming mercury electrode provided information on the reversibility of the electrode processes, while current-time and electrocapillary curves aided in elucidating the effects of adsorption. The results show that the rate of the electrode reaction of the azo-hydrazo couple is dependent on pH, the minimum rate occurring near pH 9 for azobenzene-4-sulphonic acid in aqueous media. At very low and high pH values, the couple approaches full reversibility at the dropping mercury electrode. This pH effect is apparently due to strong adsorption of both the azo and hydrazo derivatives near the potential of the electrocapillary maximum. Ammonium ions associate with azobenzene-4-sulphonate, and improve the reversibility in intermediate pH regions.