Formation and redox properties of radical ions of iodopentafluorobenzene in aqueous solution: a pulse radiolysis study

Abstract

The transient optical absorption bands λ_max = 290 and 400 nm) formed on reaction of ^•OH radicals in neutral aqueous solution of iodopentafluorobenzene are assigned to the phenoxyl radical. The radical decays by second-order kinetics with 2k/εl = 4.2 × 10⁶ s^-1 and results in the formation of F^- and I^- [G(F^-) = 5.3, G(I^-) = 0.2]. The rate constant for the reaction of ^•OH radical with iodopentafluorobenzene is 1.1 × 10⁹ dm³ mol^-l s^-1. In acidic solution ([HClO₄] < 1 mol dm^-3, the nature of the transient optical absorption spectrum remained the same whereas when [HClO₄] > 1 mol dm^-3, the transient optical absorption bands formed at 310 and 660 nm are assigned to the solute radical cation. Cl₂^•- radical anion is unable to undergo electron transfer reaction with C₆F₅I whereas SO₄^•- radical anion is able to react with a bimolecular rate constant of 3.3 × 10⁸ dm³ mol^-1 s^-1, and transient bands observed at 290 and 390 nm are assigned to the phenoxyl radical. The solute radical cation is a powerful one-electron oxidant and is able to oxidize a number of organic compounds with high rate constant values. The hydrated electron reacts with C₆F₅I by a nondissociative electron capture process, and the resulting radical anion undergoes fast protonation to form the cyclohexadienyl radical (λ_max) = 290 mm). The bimolecular rate constant for the reaction of e_aq ^- with C₆F₅I was 8 × 10⁹ dm³ mol^-1 s^-1. Similar transient species is also observed on reaction of CO₂^•- radical anion with C₆F₅I. The spectrum of the radical anion is not observed even at pH 14.