DIRECT EVIDENCE FOR H-CATALYZED DEHYDRATION OF FLUOROHYDROXYCYCLOHEXADIENYL RADICAL - A PULSE-RADIOLYSIS STUDY()

The OH-adduct of fluorobenzene (lambda(max) = 310 nm) formed on reacti on of (OH)-O-. radicals in a neutral aqueous solution reacts with H+ t o form solute radical cations (lambda(max) = 385, 395, <270 nm) when [ HClO4] > 1.5 mol dm(-3). When the concentration of HClO4 is between 1. 5 and 4.0 mol dm(-3), the H+-catalysed dehydration of the OH-adduct is observed with a bimolecular rate constant of 1.4 x 10(5) dm(3) mol(-1 ) s(-1). The formation of solute radical cations of halogenated benzen e depends on the electron affinity of the halogen. The lambda(max) val ues of solute radical cations of halogenated benzene vary linearly wit h the size of the halogen. On the other hand, SO4.- is able to undergo a direct electron-transfer reaction with fluorobenzene (k = 1.4 x 10( 9) dm(3) mol(-1) s(-1)); the OH-adduct is then formed on hydrolysis of solute radical cations. The radical cation of fluorobenzene is a stro ng one-electron oxidant with a reduction potential value of >2.0 V. In acidic aqueous solution ([HClO4] > 6.0 mol dm(-3)) of 3-chlorofluorob enzene, (OH)-O-. radicals react to form radical cations; and their for mation is influenced by chlorine but not by fluorine.