The electro-oxidation of toluene on glassy carbon electrodes in 30% CH3CN in H2O, using 1.0 M H2SO4 as supporting electrolyte, was studied by electrochemical and spectroelectrochemical techniques. The results suggest that the electro-oxidation is controlled by the charge transfer reaction, followed by a chemical process. Some of the reaction products are electrochemically active and are weakly adsorbed on the glassy carbon surface. Depending on the applied potential, in situ Uv/visible and Fourier transform infrared (FTIR) studies showed the formation of toluene-oxygenated species and carbon dioxide as principal products. The produced carbon dioxide was quantified using a method based on an ex situ FTIR technique. (c) 2006 The Electrochemical Society.