Thermodynamics and Activity Coefficients at Infinite Dilution for Organic Solutes in Trialkyl-Substituted Imidazolium-Based Ionic Liquid 1-Propyl-2,3-dimethylimidazolium Thiocyanate

Abstract

This work is a continuation of our studies on the determination of activity coefficients at infinite dilution (${\gamma }_{i}^{\infty }$) for organic solutes ($i$) in ionic liquids (ILs). New sets of experimental data for 32 organic solutes (alkanes, alkenes, aromatics, chlorinated alkanes, alcohols, and other polar organic solutes) in trialkyl-substituted imidazolium-based IL 1-propyl-2,3-dimethylimidazolium thiocyanate ([PMMIM][SCN]) in the temperature range of 313.15–363.15 K were measured by gas–liquid chromatography (GLC). The partial molar excess enthalpies at infinite dilution (${\overline{H} }_{i}^{\mathrm{E},\infty }$), entropies (${T}_{\mathrm{ref}}{\overline{S} }_{i}^{\mathrm{E},\infty }$), and Gibbs free energies (${\overline{G} }_{i}^{\mathrm{E},\infty }$) of organic solutes in [PMMIM][SCN] at a reference temperature ${T}_{\mathrm{ref}}$ = 298.15 K were obtained from the ${\gamma }_{i}^{\infty }$ values. The density of [PMMIM][SCN] as a function of temperature at pressure $p$ = 101.33 kPa was measured and gas–liquid partition coefficients (${K}_{\mathrm{L}}$) were calculated. Moreover, the Hildebrand’s solubility parameters of [PMMIM][SCN] were determined by the regular solution theory (RST) combined with Flory “combinatorial” equation. The selectivity (${S}_{ij}^{\infty }$) of [PMMIM][SCN] for n-hexane/benzene, cyclohexane/benzene, and the capacity (${k}_{j}^{\infty }$) at infinite dilution of benzene have been determined at T = 323.15 K and compared with literature data of [PDMIM][BF₄], [PMMIM][NTf₂], and of several ILs with thiocyanate anion.