Reaction Kinetics in Ionic Liquids: Pulse Radiolysis Studies of 1-Butyl-3-methylimidazolium Salts

Abstract

Radiolysis of liquid 1-butyl-3-methylimidazolium (BMI+) salts leads to formation of several species with similar absorption spectra. To identify and characterize these species, experiments were carried out with BMI+ in solution under various conditions. BMI+ is reduced by eaq- very rapidly (k = 1.9 × 1010 L mol-1 s-1) but not by (CH3)2ĊO- radicals (k ≤ 1 × 105 L mol-1 s-1). The reduced species exhibits an absorption peak at 323 nm (e = 5.9 × 103 L mol-1 cm-1). It decays via radical−radical reactions but does not react with O2 or with methyl viologen. BMI+ reacts rapidly also with OH radicals (k = 3.7 × 109 L mol-1 s-1) to produce a mixture of isomeric OH-adducts. The spectrum of these adducts is similar to that of the reduced species, it exhibits a peak at 322 nm (e = 2.5 × 103 L mol-1 cm-1) but with a pronounced shoulder at 380 to 420 nm. The adducts react with O2 and with OH-. In the latter reaction they lose H+ to form a hydroxylated analogue of the electron adduct. Irradiation of liquid BMI+ salts pro...