Reaction Kinetics in the Ionic Liquid Methyltributylammonium Bis(trifluoro- methylsulfonyl)imide. Pulse Radiolysis Study of 4-Mercaptobenzoic Acid

Published

October 1, 2002

Author(s)

J Grodkowski, Pedatsur Neta

Abstract

Hydrogen-abstraction reactions of various radicals with 4-mercaptobenzoic acid (MB) to produce the 4-carboxyphenylthiyl radical have been studied by pulse radiolysis in aqueous solutions and in the ionic liquid methyltributylammonium bis(trifluoromethylsulfonyl)imide (R₄NNTf₂). The rate constants in aqueous solutions are in the range of (1 to 3) x 108 L mol^-1 s^-1 for several alkyl radicals, are higher for reducing radicals (6.4 x 10⁸ L mol^-1 s^-1 for CH₃IHOH and 1.4 x 10⁹ L mol^-1 s^-1 for (CH₃)₂IOH) and lower for oxidizing radicals (less than or equal to 10⁷ L mol^-1 s^-1 for CH₂COCH₃). Since the bond dissociation energy for the S-H bond is much lower than that for the C-H bonds involved in these reactions, it appears that hydrogen abstraction from mercaptobenzoic acid is controlled by the electron density at the radical site rather than by the bond dissociation energy. The rate constants in alcohols are slightly lower than those in water. The rate constants in the ionic liquid are in the range of (10⁷ to 10⁸) L mol^-1 s^-1 and are essentially controlled by the diffusion rate; variations within this range appear to be due mainly to changes in viscosity. Only the CF₃ radical reacts slightly more slowly (3.6 x 10⁶ L mol^-1 s^-1).

Citation

Journal of Physical Chemistry A

Volume

106

Issue

No. 39

Pub Type

Journals

Keywords

Free radicals, Ionic Liquids, Pulse radiolysis, Reaction kinetics, Thiols

Citation

Grodkowski, J. and Neta, P. (2002), Reaction Kinetics in the Ionic Liquid Methyltributylammonium Bis(trifluoro- methylsulfonyl)imide. Pulse Radiolysis Study of 4-Mercaptobenzoic Acid, Journal of Physical Chemistry A (Accessed June 3, 2023)