Perfluorobutylperoxyl radical as an oxidant in various solvents

Perfluorobutylperoxyl radicals were produced by pulse radiolysis of aerated solutions of perfluorobutyl iodide. The rate constants for reaction of this radical with several organic reductants, chlorpromazine, trolox, hydroquinone, and several other phenols, were determined in various solvents and were found to be in the range of 10⁵-10⁹ M^-1 s^-1. By comparison with other haloalkylperoxyl radicals, C₄F₉OO^• was found to be a much more powerful oxidant, whose reactions took place more rapidly and were less sensitive to solvent and substituent effects. The rate constants (k) for oxidation of a series of para-substituted phenols by C₄F₉OO^• gave a good linear correlation between log k and the electrophilic substituent constant σ⁺, with a slope of ρ⁺ = -2.3, indicating formation of a positively charge transition state. Parallel experiments with CCl₃OO^• were limited to the most reactive phenols and gave a higher slope, ρ⁺ = -3.3. The rates of reaction of C₄F₉OO^• with trolox and chlorpromazine were found to depend on solvent viscosity, but much less on solvent polarity and acid-base properties, probably because they were closer to the diffusion-controlled limit. The longer chain C₁₀F₂₁OO^• was somewhat less reactive than C₄F₉OO^• because of geometric factors.