Pulse Radiolysis Study of the Reactions of Hydrogen Atoms in the Ionic Liquid Methyltributylammonium Bis[(trifluoromethyl)sulfonyl]imide

Abstract

Reactions of hydrogen atoms with pyrene, phenanthrene, benzophenone, 2-propanol, and crotonic acid in the ionic liquid methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide (R4NNTf2) were studied by pulse radiolysis. Radiolysis of the ionic liquid leads to formation of dry electrons and solvated electrons, which are scavenged by H3O+ to produce H• atoms. Hydrogen atoms react very rapidly with pyrene (3.8 × 109 L mol-1 s-1) and phenanthrene (2.9 × 109 L mol-1 s-1) to form H-adduct radicals with sharp absorption peaks at 405 and 395 nm, respectively. They also react with benzophenone to form ring adducts, but the reaction is much slower. By competition kinetics with pyrene, the rate constants for reactions of H• atoms with 2-PrOH and with crotonic acid were estimated to be ≈6 × 107 and 4.6 × 109 L mol-1 s-1, respectively. All the rate constants, except for benzophenone, are similar to the values measured or estimated for the same reactions in aqueous solutions. The reactions with the aromatic hydrocarbons must be diffusion-controlled but are faster than diffusion-controlled reactions for solvated electrons in the same ionic liquid.