FORMATION AND REACTIVITY OF THE RADICAL-CATION OF BROMOBENZENE IN AQUEOUS-SOLUTION - A PULSE-RADIOLYSIS STUDY

A transient optical absorption band (lambda(max) = 325 nm) is formed u pon reaction of (OH)-O-. radical with bromobenzene in neutral aqueous solution and is assigned to the OH adduct. in strongly acidic solution (HClO4 > 3 mol dm(-3)), the OH adduct undergoes H+-catalyzed dehydrox ylation to form the bromobenzene radical cation. This radical cation a bsorbs at 550 nm and at 270-310 nm. Even at this high H+ concentration , only a fraction of the DH adduct is converted to the radical cation. SO4.- reacts with bromobenzene to form the hydroxycyclohexadienyl rad ical (lambda(max) = 325 nm) and the phenoxyl radical (lambda(max) = 40 0 nm). The bromobenzene radical cation is also observed in irradiated 1,2-dichloroethane solutions. C6H5Br.+ is a strong one-electron oxidan t and oxidizes Br-, SCN-, and organic sulfides with high rate constant s. C6H5Br.+ undergoes electron transfer reaction with Cl- to establish an equilibrium, from which a reduction potential value for C6H5Br.+/C 6H5Br was determined to be 2.31 +/- 0.15 V versus NHE.