Autoxidation of gentisic acid in aqueous media

The oxidation behaviour of gentisic acid, from which a humic acid model was synthesized, was studied. Electrochemical investigation coupled with Electron Spin Resonance analysis revealed the complexity of the mechanism. Coupled chemical reactions appeared after the two electron oxidation, leading to trihydroxybenzoic acids, and to dimeric compounds. The presence of methylenic groups, particularly important to mimic the flexibility and aggregative properties of natural humic substance, was confirmed. Assuming a free radical mechanism for the chemical evolution of humic substances, metal ions could help the reaction process, leading to efficient spin-trapping matters to be considered in water treatments.