Theoretical and experimental interpretations of phenol oxidation by the hydroxyl radical

Phenol oxidation by radical dotOH radicals produced by the Fenton reaction was studied and the oxidation process was monitored by the UVvisible, 13C NMR and LC techniques. The results show that benzoquinone is formed. In the NMR and LC experiments, since the peaks corresponding to isomers ortho and para- benzoquinones are unresolved, DFT was used to determine the branching ratios of the isomers formation that coincides with their ?G values (ortho > para > meta): 72% for ortho, 23% for para and 5.0% for meta. Furthermore, the energy profile of the radical dotOH attack at ortho is quite similar to that at the para position while the meta position attack is less favored by 2.0 kcal/mol.