Electrochemical study of 2,3-dihydroxybenzoic acid and its interaction with Cu(II) and H2O2 in aqueous solutions: implications for wood decay

The electrochemical behavior of 2,3-dihydroxybenzoic acid (2,3-DHBA) and the electron-transfer characteristics between Cu(II) and 2,3-DHBA were studied in aqueous solutions using cyclic voltammetry (CV). The overall electrochemical oxidation process of 2,3-DHBA by Cu(II) may be classified as a chemical reaction involving one-electron oxidation of 2,3-DHBA to its semiquinone radical in solution, followed by an electron-transfer reaction involving the oxidation of the semiquinone radical to a quinone at the electrode surface. In the presence of H2O2, oxidation of 2,3-DHBA by Cu(II) is enhanced due to the regeneration of Cu(II) by H2O2 oxidizing Cu(I). The redox cycling between Cu(I)/Cu(II) and H2O2 also produces hydroxyl radicals (OH). Even though the presence of OH may not be detected at the surface of a glassy carbon electrode, production of electroactive dissolved oxygen (O2) suggests the presence of OH. The production of O2 is dependent on Cu(II):H2O2 concentration ratio. At the electrode surface and when the initial Cu(II):H2O2 is less than 1, O2 is produced, suggesting that H2O2 may act as a scavenger for OH; at initial Cu(II):H2O2 > 1, the production of O2 is not favored, and OH will be involved in the oxidation of Cu(I) and the organic ligand. The reaction mechanisms proposed in this study indicate that OH production by chelator-mediated Fenton reactions is favorable under conditions found in the wood cell wall.