Interactions of Volatile Organic Compounds with the Ionic Liquid 1-Butyl-1-methylpyrrolidinium Dicyanamide

Interactions of volatile organic compounds with the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium dicyanamide [BMPYR][DCA] were explored through systematic gas–liquid chromatography retention measurements. Infinite dilution activity coefficients γ₁^∞ and gas–liquid partition coefficients K_L of 30 selected hydrocarbons, alcohols, ketones, ethers, esters, haloalkanes, and nitrogen- or sulfur-containing compounds in [BMPYR][DCA] were determined at five temperatures in the range from (318.15 to 353.15) K. Partial molar excess enthalpies and entropies at infinite dilution were derived from the temperature dependence of the γ₁^∞ values. The linear free energy relationship (LFER) solvation model was used to correlate successfully the K_L values. The LFER correlation parameters and excess thermodynamic functions were analyzed to disclose molecular interactions operating between the IL and the individual solutes. Among other ILs, [BMPYR][DCA] was identified to be a fairly cohesive solvent medium, which is capable of interacting specifically through all modes (lone electron pairs, dipolarity/polarizibility, and hydrogen bonding) with solutes of complementary capabilities. The hydrogen-bond basicity of [BMPYR][DCA] is somewhat lower than that of [EMIM][NO₃] and [EMIM][MeSO₃], but in contrast to these latter ILs studied by us previously [BMPYR][DCA] appears to possess also some proton-donating capability. The selectivities of [BMPYR][DCA] for the separation of aromatic hydrocarbons and thiophene from saturated hydrocarbons were found to be only (30 to 70) % of those exhibited by the most selective ILs, as [EMIM][SCN], [EMIM][MeSO₃], or [EMIM][NO₃]. On the other hand, the use of [BMPYR][DCA] as an entrainer in extractive distillations of some other mixtures which are difficult to separate (e.g., acetone + methanol) appears to be very promising.