The rates of the two consecutive reactions, OH radical addition and H2O/OH- elimination, were studied by pulse radiolysis in highly acidic (pH = 1.3-1.9) and alkaline (pH ≃ 11) solutions, respectively, for phenol and for the three cresol isomers. The rate coefficient of the addition as measured by the build-up of phenoxyl radical absorbance and by a competitive method is the same (1.4 ± 0.1) x 1010 mol-1 dm3 s-1 both in acidic and alkaline solution. The rate coefficient of the H2O elimination in acidic solution is (1.6 ± 0.2) x 106 s-1, whereas the coefficient of the OH- elimination in alkaline solutions is 6-8 times higher. The kinetics of the phenoxyl radical formation was described by the two-exponential equation of the consecutive reactions: the first exponential is related to the pseudo- first-order addition, while the second to the elimination reaction. No considerable structure dependence was found in the rate coefficients, indicating that the methyl substitutent in these highly acidic or alkaline solutions influences neither the addition nor the elimination rate.
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