The mechanism of the caffeic acid oxidation has been studied using cyclic voltammetry on a treated disk of gold in a mixture of water-acetone at volumetric fractions of acetone ranging between 0 and 80%. This firstly demonstrates that, at the interface electrode/solution, the caffeic acid is in equilibrium between adsorbed and dissolved form. The cyclic voltammograrn shows two reversible anodic peaks (I-a) and (I-a') (a post-peak) corresponding respectively to the oxidation of the dissolved and adsorbed caffeic acid. The relative importance of these two peaks depends on the caffeic acid concentration, the amount of electricity Q which characterizes the layer of Au oxides and the volumetric fraction of acetone. The proposed mechanism is based on the assumption of a bielectronic discharge of the caffeic acid molecule leading to the formation of three mesomere forms of a phenoxonium cation. The proportion of each one of these mesomere forms depends on its relative stability. Taking into account the proposed mechanism, the caffeic acid o-quinone (3,4-dioxocinnamic acid) could be the main product of the caffeic acid oxidation on Au/Au oxides. The preliminary results show that caffeic acid is quantitatively oxidized by electrolysis on lead dioxide leading to formic, oxalic and maleic acids formation whose degradation produces carbon dioxide; the degree of caffeic acid incineration can be determined from the total organic carbon (TOC) value. (C) 2003 Elsevier Ltd. All rights reserved.