Behaviour of triphenyl phosphine oxide at the dropping mercury electrode in methanol

Abstract

Summary Triphenyl phosphine oxide (TPO) which is known as a strong inhibitor in aqueous solutions is adsorbed at the DME from methanol in the potential range −0.5 to −1.3 V (Ag/AgCl) although its adsorption activity decreases markedly as compared with that from water. A desorption peak at negative potentials is observed from methanolic solution which is rounded as compared to both desorption peaks of TPO from water which are sharp. The desorption potential of TPO becomes more negative in the presence of the depolarizer and the inhibiting action of TPO in methanol seems to be the same as in the case of aqueous-alcoholic solutions, although large concentrations of the surfactant are needed in methanol. The effect of concentration and nature of the supporting electrolyte as well as the addition of water in methanol on (i) the desorption potential of TPO in presence and in the absence of depolarizer and (ii) the half-wave potential of azobenzene with and without inhibitor have been studied and the results are explained on the variation of the potential 2 between the plane of the closest approach and the bulk of the solution as well as on the specific adsorbability of cations.