Reduction of dicarbonyl compounds on the DME: Part IV. Electrochemical behaviour of phenylglyoxal: Second wave

Abstract

Polarographic (dc and DP), chronoamperometric and kinetic studies of the second reduction wave of phenylglyoxal have been carried out in the 0–12 pH range. At potentials corresponding to the limiting current, this process is governed by diffusion, although the i L − t recordings indicate the existence of an adsorption process. DP polarography indicates that in the 4–6 pH range two processes at very similar reduction potentials take place on the electrode surface, the electroactive species being the protonated and unprotonated forms of hydrated phenylglyoxal. Above pH 9, a new process takes place at potentials close to the supporting electrolyte discharge, due to the reduction product of phenylglyoxal. The Tafel slopes and reaction orders with respect to phenylglyoxal and H + ion have been obtained at potentials corresponding to the foot of the wave. The values of these parameters and their variations with the ethanol content and phenylglyoxal concentration agree with those expected from the application of the “combined isotherm” given by Gileadi. Reaction mechanisms are thus proposed in this zone of potentials.