THEORETICAL-STUDY OF THE OXIDATION MECHANISM OF AROMATIC-AMINES

The overall mechanism of the chemical step involved in the electrochemical oxidation of tertiary aromatic amines has been investigated by means of the quantum-chemical AM1 method. By using the parent compound aniline as a model it is found that, in good accord with previous electrochemical data, dimerization of two radical cations takes place before deprotonation, the dimerization step involving a higher energy barrier. An analysis of the radical cations of different aromatic amines shows that the unpaired electron is mainly located at the carbon in the para position with respect to the respect to the amino group. This resonant effect is reduced when more than one aromatic ring is attached to the nitrogen so that triphenylamine is much less reactive than N,N-dimethylaniline. Finally, the observed lack of reactivity of para-substituted carbons is attributed to the inability of leaving groups to form stable cations.