Direct evidence for H+-catalysed dehydration of fluorohydroxycyclohexadienyl radical: a pulse radiolysis study

Mohan, Hari ; Mittal, Jai P. (1995) Direct evidence for H+-catalysed dehydration of fluorohydroxycyclohexadienyl radical: a pulse radiolysis study Journal of the Chemical Society, Faraday Transactions, 91 (14). pp. 2121-2126. ISSN 0956-5000

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Official URL: http://pubs.rsc.org/en/Content/ArticleLanding/1995...

Related URL: http://dx.doi.org/10.1039/FT9959102121

Abstract

The OH-adduct of fluorobenzene (λ max= 310 nm) formed on reaction of OH radicals in a neutral aqueous solution reacts with H+ to form solute radical cations (λ 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 × 105 dm3 mol-1 s-1. The formation of solute radical cations of halogenated benzene depends on the electron affinity of the halogen. The λ max values of solute radical cations of halogenated benzene vary linearly with the size of the halogen. On the other hand, SO4¯ is able to undergo a direct electron-transfer reaction with fluorobenzene (k= 1.4 × 109 dm3 mol-1 s-1); the OH-adduct is then formed on hydrolysis of solute radical cations. The radical cation of fluorobenzene is a strong one-electron oxidant with a reduction potential value of >2.0 V. In acidic aqueous solution ([HClO4] >6.0 mol dm-3) of 3-chlorofluorobenzene, OH radicals react to form radical cations; and their formation is influenced by chlorine but not by fluorine.

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