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.