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 NaC lO4 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 n eutral NaClO4 solutions, the surface protonization of azobenzene is a rate-determining step of the redox reaction. When the polarographic pu lse is very short, the unprotonated azobenzene is reduced directly and at potentials which are more negative than the potentials at which th e monoprotonated azobenzene is reduced if pulses are longer. The rate constants of benzidine rearrangement of adsorbed hydrazobenzene are me asured in concentrated HClO4 solutions: k = 52 s(-1), 115 s(-1), and 2 24 s(-1), for 1, 3, and 5 M HClO4 respectively.