Mechanistic investigation of xanthene oxidation by heterogeneous and homogeneous electron transfers

Anodic oxidation of xanthene is investigated in acetonitrile at a platinum electrode by means of cyclic voltammetric and exhaustive potentiostatic electrolysis techniques. On the voltammetric scale time, the process involves two electrons and leads to xanthydrol. The corresponding mechanism is an ECE (electron–deprotonation–electron) type electrode reaction, the rate-determining step being the deprotonation of the cation radical obtained after the first electron transfer. On the other hand the analysis of the oxidation by homogeneous redox catalysis is carried out, using three organic catalysts. This allows the determination of the rate constants of the homogeneous electron transfers between xanthene and catalysts, the xanthene cation radical deprotonation rate constant and the standard potential of the xanthene cation radical/xanthene couple.