Effect of Side Chain Functional Group on Interactions in Ionic Liquid Systems: Insights from Infinite Dilution Thermodynamic Data

Measurements of infinite dilution
activity coefficients of 48 molecular
solutes (including alkanes, alkenes, alkynes, aromatics, ethers, alcohols,
water, ketones, pyridine, thiophene, acetonitrile, and 1-nitropropane)
in two ionic liquids (ILs), namely, 1-(2-hydroxyethyl)-3-methylimidazolium
dicyanamide and 1-(2-chloroethyl)-3-methylimidazolium dicyanamide,
are reported in the temperature range from T = 308.15
to 358.15 K. Comparative analysis of an effect of OH/Cl substitution
of terminal carbon in side chains of imidazolium cations is presented
and discussed in terms of different types of intermolecular forces
acting between ILs and solutes. The new data also are confronted to
those published previously for a “plain” counterpart
of the studied ILs, namely, 1-ethyl-3-methylimidazolium dicyanamide.
Infinite dilution capacity and selectivity of the studied ILs are
presented to evaluate them as separating agents in extraction of aromatics
from alkanes and sulfur compounds from alkanes. Three modeling approaches,
namely, linear solvation energy relationship (LSER), regular solution
theory, and conductor-like screening model for real solvents (COSMO-RS),
are tested for their capabilities of capturing the substitution effects
detected experimentally.