Electrochemistry of Caffeic Acid Aqueous Solutions with pH 2.0 to 8.5

The electrochemical behavior of caffeic acid (H(3)CAF) in aqueous solutions with pH 2.0 to 8.5 was studied by cyclic voltammetry, controlled potential electrolysis and UV-vis spectroscopy. The electro-oxidation of H(3)CAF involves a reversible transfer of two electrons and two protons in solutions of pH up to 5.5, in agreement with the one step-two electron mechanism. In solutions of pH higher than 5.5, the process of electro-oxidation of H(3)CAF follows an ECi mechanism. The main oxidation product is the corresponding omicron-quinone (omicron-HCAF), which is decomposed quickly at pH higher than 7.4 obeying a first order kinetics. In the pH range investigated, the formal potential (E-0') varies linearly with pH, generating a straight line with an angular coefficient of -60.83 mV/pH. In parallel, the anodic peak current (i(pa)) decreases in a nonlinear mode. The processes are controlled by diffusion over the whole pH range studied.