Aromatic hydroxylation reactions by electrogenerated HO radicals: A kinetic study

The oxidation of benzoic acid (BA) and of 4-hydroxybenzoic acid (4-HBA) by galvanostatic electrolysis with simultaneous oxygen evolution, using BDD or Pt as anode materials is studied. Results concerning the oxidation kinetics as well as the identification and quantification of hydroxylated products are reported. First order kinetics are used to describe the consumption rates of both compounds despite of the anode material and of the applied current density. A simple kinetic model that accounts for the anode surface coverage by HO radicals is proposed. Based on this model it is possible to correlate the apparent rate constant of the organic consumption with kinetic parameter related to the organics reactivity and to the degree of the adsorption of HO radicals to the anode surface.