Reaction of the Hydroxyl Radical with Phenol in Water Up to Supercritical Conditions

The rate constants for the reactions of phenol with the hydroxyl radical (OH^•) in water have been measured from room temperature to 380 °C using electron pulse radiolysis and transient absorption spectroscopy. The reaction scheme designed to fit the data shows the importance of an equilibrium, giving back reactants (OH^• radical and phenol) from the dihydroxycyclohexadienyl radical formed by their reaction, and the non-negligible contribution of the hydroxycyclohexadienyl radical absorption from H^• atom addition. The accuracy of the reaction scheme and the reaction rate constants determined from it have been determined by the analysis of two different experiments, one under pure N₂O atmosphere and the second under a mixture a N₂O and O₂. We report reaction rates for the H^• and OH^• radical addition to phenol, the formation of phenoxyl, the second-order recombination, the reaction of dihydroxycyclohexadienyl with O₂, and the decay of the peroxyl adduct. Nearly all of the reaction rates deviate strongly from Arrhenius behavior.