On-line electrochemical–mass spectrometry study of the mechanism of oxidation of N,N-dimethyl-p-phenylenediamine in aqueous electrolytes

The mechanism of electrochemical oxidation of N,N-dimethyl-p-phenylenediamine (DPD) in aqueous electrolyte solutions in the pH range 1.4–9.7 was studied using on-line electrochemical–mass spectrometry. A radial flow electrochemical cell was used to generate the product stream which was analyzed by a mass spectrometer equipped with an electrospray interface (ESI-MS). It was shown that DPD oxidation in the pH 1.4–9.7 range brings about formation of the Wurster red cation radical, quinonediimine, quinonemonoimine and dimer and trimer products of coupling reactions of DPD with quinonediimine and quinonemonoimine. Coupling reactions were found to be strongly pH dependent. The kinetics of the coupling reaction between DPD and quinonemonoimine were studied at pH 3.6.