Chemical and electrochemical oxidation of phenothiazine

The oxidation of phenothiazine in dilute solutions of sulphuric acid leads to the corresponding cation radical. Using a potentiometric technique, a pKa value of 5.72 ± 0.05 was determined for phenothiazine. The kinetics has been studied and participation of both protonated and unprotonated oxidant in the oxidation reaction has been confirmed. Using a voltammetric technique with a rotating disk electrode, the anodic oxidation of phenothiazine was shown to be a one-electron diffusion-controlled process. A quantum chemical explanation was found for the direction of phenothiazine protonation and the absence of a dimerization stage of oxidation.