Electrochemical Oxidation of Ferulic Acid in Aqueous Solutions at Gold Oxide and Lead Dioxide Electrodes

A kinetic study of the electrochemical oxidation of ferulic acid (3-methoxy-4-hydroxycinnamic acid) by direct electron transfer at treated gold disk was combined with results of electrolyses in order to produce total degradation into CO₂ and H₂O at Ta/PbO₂ anode. The oxidation of ferulic acid at gold electrode was studied by cyclic voltammetry. At low concentration, ferulic acid shows one irreversible anodic peak. The peak current shows adsorption characteristics. For ferulic acid concentrations higher than 0.02 mmol dm⁻³, the voltammogram shows two anodic peaks. The effect of experimental conditions on the ratio of these two peaks was examined. The proposed mechanism is based on the hypothesis of two-electron oxidation of ferulic acid molecule involving a three intermediate cation mesomers. Hydrolysis of these mesomers leads to the formation of caffeic acid, methoxyhydroquinone and 3,4-dihydroxy-5-methoxycinnamic acid. Then ferulic acid was quantitatively oxidised by electrolysis on lead dioxide to produce, via intermediate aromatic compounds, maleic acid, oxalic acid and formic acid whose oxidation leads to carbon dioxide.