Estimation and Prediction of the Physicochemical Properties of Imidazolium-Based Ionic Liquids

Abstract

The physicochemical properties of ionic liquids (ILs) at 298.15 K could be estimated and predicted in terms of empirical and semi-empirical equations as well as by interstice model theory. In this paper, the molecular volume, density, standard molar entropy, lattice energy, surface tension, parachor, molar enthalpy of vaporization, interstice volume, interstice fraction, and thermal expansion coefficient are discussed. These properties were first estimated by experimentally determining the density and surface tension for 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim][EtSO4]), 1-butyl-3-methylimidazolium octylsulfate ([C4mim][OcSO4]), and 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([C2mim][NTf2]). The molecular volume and parachor of the three homologues of the imidazolium-based ILs [C(subscript n)mim][EtSO4], [C(subscript n)mim][OcSO4], and [C(subscript n)mim][NTf2] (n=1-6) were predicted and their densities and surface tensions were obtained. Other properties were also calculated using the obtained density and surface tension values. The predicted density was compared to the experimental values for [C4mim] [NTf2] and [C2mim] [OcSO4], which shows that the deviation between experimental and predicted data are within experimental error. Finally, we compared the values for the molar enthalpy of vaporization estimated by Kabo's empirical equation with those predicted by Verevkin's simple rule for [C2mim] [EtSO4], [C4mim][OcSO4], [C2mim] [NTf2], [C4mim][NTf2], N-butyltrimethylammonium bis (trifluoromethylsulfonyl)imide [N4111][NTf2], N-methyltrioctylammonium bis (trifluoromethylsulfonyl)imide ([N8881][NTf2]), and N-octyl-3-methylpyridinium tetrafluoroborate ([m3opy][BF4]) and found that the values obtained by these two equations were in good agreement with each other. Therefore, we suggest that the molar enthalpy of vaporization of ILs can be predicted by Verevkin's simple rule when experimental data for density and surface tension are not available.