A comparative study of the electro-oxidation of some phenolic compounds by electrogenerated O-3 and by direct electrolysis at PbO2 anodes

The oxidation of phenolic compounds (1-4 chlorophenol and 1-4 nitrophenol was studied using different electrochemical systems involving ozone formation at PbO2 anodes: i) direct electrolysis at constant current; ii) ex-situ use of O-3 and iii) combined use of anodically generated O-3, and H2O2 produced at a graphite cathode (cathodic oxidation). We show that the last method gives better results. It seems to be possible to rule out a significant role of O-3 in the electrooxidation of phenol at the anode. Rather, the organic compounds react competitively with adsorbed oxygen intermediates (OH. and O) leading to an inhibition of O-3 formation.