Reactions of Phosphate Radicals with Monosubstituted Benzenes. A Mechanistic Investigation

The kinetics and reaction mechanism of phosphate radicals with substituted benzenes, PhX (X=OH, Me, H, Cl, MeO, and CHO), were studied by flash photolysis and continuous irradiation of aqueous solutions containing potassium peroxodiphosphate (K₄[(PO₃)₂O₂]). The rate constants for the reactions of phosphate radicals with the aromatic contaminants PhX were measured and the reaction intermediates and products detected. A correlation between the logarithm of the rate constant for every substrate with H₂PO₄^., HPO₄^.?, and PO₄^.2? and the logarithm of the dissociation constant K_a for H₃PO₄, , and was found. A general mechanism is proposed (Scheme 1), which accounts for the experimental results.