The reactions of trifluoromethyl radicals with pyrene, phenanthrene, crotonic acid, and 2-propanol (2-PrOH) in the ionic liquid methyltributylammonium bis(trifluoromethylsulfonyl)imide (R 4 NNTf 2 ) are studied by pulse radiolysis. Radiolysis of R 4 NNTf 2 leads to formation of solvated electrons and organic radicals, including • CF 3 . The solvated electrons do not react rapidly with the solvent and are reacted with CF 3 Br to produce additional • CF 3 radicals. The rate constants for addition of • CF 3 radicals to pyrene and phenanthrene are determined to be (1.1 ± 0.1) × 10 7 L mol -1 s -1 and (2.6 ± 0.4) × 10 6 L mol -1 s -1, respectively. By competition kinetics, the rate constant for reaction of • CF 3 radicals with crotonic acid is determined to be (2.7 ± 0.4) × 10 6 L mol -1 s -1, and the reaction is predominantly addition to the double bond. Competition kinetics with 2-PrOH in the absence of CF 3 Br gives a rate constant of (4 ± 1) × 10 4 L mol -1 s -1 for H-abstraction from 2-PrOH, but in the presence of CF 3 Br, the rate constant cannot be determined because a chain reaction develops through the reduction of CF 3 Br by the (CH 3 ) 2 ĊOH radical. The rate constants for reactions of • CF 3 radicals in acetonitrile solutions are slightly higher, by a factor of 2.3 for pyrene and phenanthrene and a factor of 1.3 for crotonic acid. The rate constant for pyrene in aqueous acetonitrile (30% water) solutions is 4 times higher than that in the ionic liquid. Rate constants for H-abstraction and addition reactions of • CF 3 radicals in the ionic liquid are of the same order of magnitude as in water and acetonitrile, whereas electron-transfer reactions were reported to be one or more orders of magnitude slower in ionic liquids than in water or alcohols.
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Grodkowski et al. (2002) studied this question.