KINETICS OF THE P-AMINODIPHENYLAMINE RADICAL IN ORGANIC SOLUTION - ANELECTROCHEMICAL AND ELECTRON-SPIN-RESONANCE STUDY

In studying the reaction mechanism of anodic aniline oxidation the dim er p-aminodiphenylamine (ADPA) was found to be the main intermediate p roduct in acidic solution. It is oxidized in both the free amine and t he protonated form. The cyclic voltammograms have been simulated by ta king into account an electrochemical reaction of both the protonated a nd the nonprotonated forms. Thus, it was also found that the ADPA conc entration is determined by the protonation equilibrium. The oxidation product N-phenylquinone diimine (PQDI) undergoes a symproportionation reaction with ADPA forming the ADPA(.+) cation radical. The equilibriu m constant for this reaction of PQDI in dimethyl sulfoxide was determi ned and found to be independent of the concentration of the protons in solution. The ADPA(.+) cation radical decay can be described by a rat e equation based on a second-order reaction for the radical dimerizati on and a pre-equilibrium for the radical formation by symproportionati on. The reaction mechanisms of the anodic oxidation of p-aminodiphenyl amine and its chemical follow-up reactions are given.