The use of microelectrodes for studying the process involved in 1-naphthylamine oxidation in dimethyl sulphoxide

The electrochemical oxidation of 1-naphthylamine at platinum electrodes has been investigated in dimethyl sulphoxide. Such a process occurs through a pathway involving a very fast chemical reaction interposed between two one-electron charge transfers. The kinetic constant of this chemical step is inaccessible to voltammetric measurements performed at conventional electrodes. Conversely, microelectrodes are suitable for this purpose when used at both high and low scan rates, thus allowing one to establish that the interposed chemical reaction occurs through a two-step pathway involving an acid-base dissociation equilibrium of the cation radical formed in the primary electrode step followed by a faster radical dimerization. By following this approach, a mean value of 3.3 × 103 s-1 is found for the relevant pseudo-first-order rate constant. The competition of this rate-determining step with a second-order dissociation reaction involving a proton transfer from the cation radical to the basic starting species has also been considered and discussed. © 1989.