Pulse radiolysis of aryl bromides in aqueous solutions: some properties of aryl and arylperoxyl radicals

Abstract

Aryl radicals were generated pulse-radiolytically in aqueous solutions by reacting the solvated electron with phenyl bromide and substituted phenyl bromides. The aryl radicals react rapidly (k 2.5 × 109 dm3 mol–1 s–1) with O2 giving rise to arylperoxyl radicals which display characteristic absorptions in the visible spectrum (490–600 nm, depending on the substituent). Aryl radicals react with alcohols by H-abstraction. Making use of the strong absorptions of the arylperoxyl radicals in the visible spectrum, rate constants of the reaction of the aryl radicals with various alcohols have been determined by competition kinetics [e.g. 4-methoxyphenyl: 1.1 × 107(2-PrOH), 5.8 × 106(EtOH), 1.1 × 106(MeOH), 5.2 × 105 dm3 mol–1 s–1(ButOH)]. The temperature dependence of the reaction of the 4-CN-phenyl radical was studied and reaction parameters of its reaction with O2(A= 4 × 1011 s–1; Ea= 12 kJ mol–1), propan-2-ol (A= 1.5 × 109 s–1; Ea= 13 kJ mol–1) and tert-butanol (A= 6 × 109 s–1; Ea= 25 kJ mol–1) determined.