PULSE POLAROGRAPHY OF AZOBENZENE

Pulse polarography is applied to measure adsorption of azobenzene and hydrazobenzene in a wide acidity range between 5 M HClO4 and 0.5 M NaClO4 buffered to pH 7. The solvent is 20% v/v aqueous acetonitrile. In 5 M HClO4 the adsorption of azobenzene is weaker, while at pH 7 it is stronger than the adsorption of hydrazobenzene. In weakly acidic and neutral NaClO4 solutions, the surface protonization of azobenzene is a rate-determining step of the redox reaction. When the polarographic pulse is very short, the unprotonated azobenzene is reduced directly and at potentials which are more negative than the potentials at which the monoprotonated azobenzene is reduced if pulses are longer. The rate constants of benzidine rearrangement of adsorbed hydrazobenzene are measured in concentrated HClO4 solutions: k = 52 s(-1), 115 s(-1), and 224 s(-1), for 1, 3, and 5 M HClO4 respectively.