Effect of anion species on infinite dilution activity coefficients of epoxides in imidazolium-based ionic liquids

The infinite dilution activity coefficients of 1,2-epoxypropane, 1,2-epoxybutane, 2-methyl-1,2-epoxypropane and 1,2-epoxyhexane in the ionic liquids with 1-butyl-3-methylimidazolium cation ([bmim]), [bmim][BF4] and [bmim][PF6] were measured by gas–liquid chromatograph (GC) from (325.2–363.4) K and atmospheric pressure. The ionic liquids were used as stationary phases in GC. The experimental data of the activity coefficients were determined from the extrapolations to zero of the gas flow rate on GC. The activity coefficients of the all epoxides in [bmim][PF6] are smaller than those in [bmim][BF4].The partial molar excess enthalpies and entropies at infinite dilution for the epoxides in the ionic liquids were obtained from the experimental data of the activity coefficients. The enthalpies for the epoxides in [bmim][PF6] are negative. The values of entropies in [bmim][PF6] are lower than those in [bmim][BF4]. It can be explained that the interactions of the epoxides with [bmim][PF6] are larger than those with [bmim][BF4].