PULSE-RADIOLYSIS OF ARYL BROMIDES IN AQUEOUS-SOLUTIONS - SOME PROPERTIES OF ARYL AND ARYLPEROXYL RADICALS

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 greater than or e qual to 2.5 x 10(9) dm(3) mol(-1) s(-1)) with O-2 giving rise to arylp eroxyl radicals which display: characteristic absorptions in;the visib le spectrum (490-600 nm, depending on the substituent). Aryl radicals react with alcohols by H-abstraction. Making use of the strong absorpt ions of the arylperoxyl radicals in the visible spectrum rate constant s of the reaction of the aryl radicals with various alcohols have been determined by competition kinetics [e.g. 4-methoxyphenyl: 1.1 x 10(7) (2-PrOH), 5.8 x 10(6) (EtOH), 1.1 x 10(6) (MeOH), 5.2 x 10(5) dm(3) m ol(-1) s(-1) (Bu(t)OH)]. The temperature dependence of the reaction of the 4-CN-phenyl radical was studied and reaction parameters of its re action with O-2 (A = 4 x 10(11) s(-1); E(a) = 12 kJ mol(-1)), propan-2 -ol (A = 1.5 x 10(9) s(-1); E(a) = 13 kJ mol(-1)) and tert-butanol (A = 6 x 10(9) s(-1); E(a) = 25 kJ mol(-1)) determined. While most of the arylperoxyl radicals decay by second-order processes by reacting with one another and other peroxyl radicals present (k greater than or equ al to 3 x 10(9) dm(3) mol(-1) s(-1)) HO- and H2N-substituted arylperox yl radicals also decay by first-order processes. It has been noted tha t the reaction of 4-nitrobromobenzene with the solvated electron does not lead to the formation of an aryl radical by halide elimination.