Voltammetric investigation of the anodic dimerization of p-halogenoanilines in DMF - Reactivity of their electrogenerated cation radicals

The electrodimerization mechanisms of p-chloro- and p-bromoaniline were stu died in unbuffered DMF medium. By combined application of conventional and fast voltammetry (100 kV s(-1) range), the primary radical cation intermedi ates, formed by the one electron oxidation of each p-halogenoaniline were c haracterized. The overall reaction path involves a dimerization via a N-C b ond formation and de-halogenation at the para position. A detailed mechanis tic investigation demonstrates that this proceeds through a fast reversible deprotonation of the primary radical cation followed by the subsequent N-C bond formation between the resulting radical and its parent radical cation which is the rate-determining step of the sequence (e-p-RRC-p kinetic sequ ence). The effect of a relatively strong, but weakly nucleophilic base, 2,6 -lutidine, has been also investigated and confirmed the involvement of the fast deprotonation pre-equilibria. The fast voltammetric experiments were s imulated and the apparent rate constants for the overall deprotonation/dime rization sequence obtained on the basis of peak potential shift analysis we re thus confirmed. (C) 1999 Elsevier Science S.A. All rights reserved.