Reaction Kinetics in the Ionic Liquid Methyltributylammonium Bis(trifluoromethylsulfonyl)imide. Pulse Radiolysis Study of (CF3)-C-Center Dot Radical Reactions
J Grodkowski, Pedatsur Neta
The reactions of trifluoromethyl radicals with pyrene, phenanthrene, crotonic acid, and 2-propanol in the ionic liquid methyltributylammonium bis(trifluoromethylsulfonyl)imide (R4NNTf2) are studied by pulse radiolysis. Radiolysis of R4NNTf2 leads to formation of solvated electrons and organic radicals, including CF3. The solvated electrons do not react rapidly with the solvent and are reacted with CF3Br to produce additional CF3 radicals. The rate constants for addition of CF3 radicals to pyrene and phenanthrene are determined to be (1.1 0.1) 107 L mol-1 s-1 and (2.6 0.4) 106 L mol-1 s-1, respectively. By competition kinetics, the rate constant for reaction of CF3 radicals with crotonic acid is determined to be (2.7 0.4) 106 L mol-1 s-1. Competition kinetics with 2-PrOH in the absence of CF3Br gives a rate constant of (4 1) 104 L mol-1 s-1 but in the presence of CF3Br the rate constant cannot be determined because a chain reaction develops through the reduction of CF3Br by the (CH3)2 OH radical. The rate constants for reactions of CF3 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 as high as that in the ionic liquid. Thus, rate constants for H-abstraction and addition reactions in ionic liquids are of the same order of magnitude as in water and organic solvents whereas electron transfer reactions are one or more orders of magnitude slower in ionic liquids than in water or alcohols.
and Neta, P.
Reaction Kinetics in the Ionic Liquid Methyltributylammonium Bis(trifluoromethylsulfonyl)imide. Pulse Radiolysis Study of (CF<sub>3</sub>)-C-Center Dot Radical Reactions, Journal of Physical Chemistry A
(Accessed June 2, 2023)