MECHANISTIC INVESTIGATION OF THE OXIDATION OF P-ANISIDINE IN UNBUFFERED DMF USING FAST-SCAN RATES AT ULTRAMICROELECTRODES

The primary radical cation intermediate of the one electron oxidation of p-anisidine into variamine blue dication has been characterized by cyclic voltammetry in the 10 kV s(-1) range at gold ultramicroelectrod es. Combined use of fast scan voltammetry with cyclic voltammetry in t he usual range of scan rates allowed us to establish that the rate det ermining step of the chemical sequence leading ultimately to the varia mine blue dication is a reaction between the electrogenerated radical cation and p-anisidine (DIM2 mechanism). The rate constant of this fas t reaction (5 X 10(7) M-1 s(-1)) has been measured, yet its exact natu re still remains unknown. This may correspond to the effective couplin g step, or to an irreversible proton exchange between the radical cati on and p-anisidine, this latter being the strongest base present in th e medium. In this latter case, the coupling step occurs after this rat e determining step and involves the radical thus formed with either p- anisidine or its cation radical. (C) 1997 Elsevier Science S.A.