THE APPLICATION OF RAPID SCAN CYCLIC VOLTAMMETRY AND DIGITAL-SIMULATION TO THE STUDY OF THE MECHANISM OF DIPHENYLAMINE OXIDATION, RADICAL CATION DIMERIZATION, AND POLYMERIZATION IN ACETONITRILE

Cyclic voltammetry, performed with ultramicrodisk electrodes, was used to investigate the mechanism of the initial step of the electropolymerization of diphenylamine in acetonitrile. The Ph2NH.+ radical cations were electrochemically detected at scan rates above 100 V/s. Initially, the electrogenerated Ph2NH.+ radical cations undergo a second-order radical cation-radical cation coupling reaction to form diphenylbenzidine. Digital simulations of the voltammograms suggest the reaction occurs by an initial dimerization of the radical cations, followed by proton loss and additional electron transfer reactions (an EC2EE-type of mechanism). A rate constant of 2.0 (+/- 0.5) X 10(5) M-1 s-1 for the radical cation coupling reaction was determined. Deprotonation associated with the coupling depends upon the water content. A new criterion for distinguishing among different mechanisms of following chemical reactions by cyclic voltammetry, based on changes in peak shape, is proposed.