Kinetics of the Synthesis of 1‐Alkyl‐3‐methylimidazolium Ionic Liquids in Dilute and Concentrated Solutions

Abstract

The kinetics of the reactions of 1‐methylimidazole with iodoethane, 1‐iodobutane, 1‐bromobutane, 1‐bromohexane, 1‐bromooctane resulting in the formation of corresponding 1‐alkyl‐3‐methylimidazolium halide ionic liquids in acetonitrile and cyclopentanone solutions has been studied in a wide range of concentrations and degrees of conversion. The studied reactions were found to follow the SN2 rate law in the dilute solutions. The significant deviations from the simple SN2 rate law observed at higher concentrations of the reactants were assigned to the concentration dependence of activity coefficients for the reactants and the transition states. The experimental data were processed with the conductor‐like screening model–segment activity coefficient (COSMO‐SAC) model and the Scatchard–Hildebrand equation. The latter was found to provide somewhat better description of the experimental results; however, the former has a wider predictive ability. The Arrhenius activation energies and the activation enthalpies were calculated for the investigated systems. The rate constants at infinite dilution were obtained for a large number of 1‐haloalkane + 1‐methylimidazole + solvent systems with the use of the COSMO‐SAC model. It was demonstrated that the rate constants of the studied reactions in various non‐hydrogen‐bonding solvents can be estimated from a correlation with the Hildebrand solubility parameter.