Solubilities of the gaseous and liquid solutes and their thermodynamics of solubilization in the novel room-temperature ionic liquids at infinite dilution by gas chromatography

The solubilities of C₂H₄ and CO₂ and the interactions of polar and nonpolar solutes with the novel ionic liquids (ILs) 1-butyronitrile-3-methylimidazolium bis(trifluoromethylsulfonyl) imidate (CpMIm[NTf₂]), 1-butyronitrile-2,3-dimethylimidazolium bis(trifiuoromethylsulfonyl) imidate (CpMMIm[NTf₂]), 1-butyronitrile-3-methylimidazolium dicyanamide (CpMIm[N(CN)₂]), 1-butyronitrile-2,3-dimethylimidazolium dicyanamide (CpMMIm-[N(CN) ₂]), 1-butyl-3-methylimidazolium palmitate (BMIm[n-C ₁₆H₃₃COO]), and 1-butyl-3-methylimidazolium stearate (BMIm[n-C₁₈H₃₅COO]) were studied by gas chromatography at infinite dilution at T = (303.15, 313.15, 323.15, and 333.15) K. Henry's law constant k_H of C₂H₄ and CO₂ gas, infinite dilution activity coefficient γ^∞, molar enthalpies of solution Δ_solH^∞, and partial molar excess enthalpies of solution ΔH^E∞ and of Gibbs energies ΔG^E∞ were determined for polar and nonpolar solutes in these novel ILs. Compared with the 1,3-dialkylimidazolium ILs, cyano functional group substitution on the alkyl chain results in a remarkable decrease of the interactions of hydrocarbons. BMIm[n-C₁₆H ₃₁OO] and BMIm[n-C₁₈H₃₅OO] demonstrate strong solubilization for both polar and nonpolar solutes. Straight lines of In V _g versus 1/T and In γ^∞ versus 1/T were obtained for the majority of solutes in the temperature range. BMIm[NTf ₂] and 1-octyl-3-methylimidazolium tetrafluoroborate (OMIm[BF ₄]) show much better solubility for thiophene and are better solvents for the separations of thiophene from hydrocarbons.