No abstract

With the use of isothermogravimetrical analysis, the enthalpies of vaporization, Δ(g)lH(o)m(T(av)), at the average temperature, T(av) = 445.65 K, for the ionic liquids (ILs) 1-alkyl-3-methylimidazolium propionate [C(n)mim][Pro](n = 4, 5, 6) were determined. Using Verevkin's method, the difference of heat capacities between the vapor phase and the liquid phase, Δ(g)lC(p)(o)m, for [C(n)mim][Pro](n = 2, 3, 4, 5, 6), were calculated based on the statistical thermodynamics. Therefore, with the use of Δ(g)lC(p)(o)m, the values of Δ(g)lH(o)m(T(av)) were transformed into Δ(g)lH(o)m(298), 126.8, 130.3, and 136.5 for [C(n)mim][Pro](n = 4, 5, 6), respectively. In terms of the new scale of polarity for ILs, the order of the polarity of [C(n)mim][Pro](n = 2, 3, 4, 5, 6) was predicted, that is, the polarity decreases with increasing methylene. A new model of the relationship between the surface tension and the enthalpy of vaporization for aprotic ILs was put forward and used to predict the surface tension for [C(n)mim][Pro](n = 2, 3, 4, 5, 6) and others. The predicted surface tension for the ILs is in good agreement with the experimental one.

Three propionic acid ionic liquids (PrAILs), 1-alkyl-3-methylimidazolium propionate ([C n mim][Pro] (n = 4, 5, 6)), were prepared by the neutralization method and characterized by 1 H NMR spectroscopy. The values of the densities and surface tensions of aqueous [C 4 mim][Pro], [C 5 mim][Pro], and [C 6 mim][Pro] with various molalities were determined at 298 K, and the values of the parachor for these solutions were calculated. The values of the apparent molar volumes and partial molar volumes at infinite dilution for the ILs were estimated in terms of Pitzer's theory. With the use of Li's model of surface tension and the empirical equation of the parachor, the values of the surface tensions of these aqueous solutions for three PrAILs were estimated and the estimated values were in good agreement with experimental ones.