Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Two propionic acid ionic liquids (PrAILs) [Cnmim][Pro] (n = 2, 3) (1-alkyl-3-methylimidazolium propionate) were prepared by the neutralisation method and characterised by 1H NMR spectroscopy and differential scanning calorimetry (DSC). The values of vaporisation enthalpies, DvapHo m, for two PrAILs [Cnmim][Pro] (n = 2, 3) were determined using a simple, convenient, and highly reproducible thermogravimetric approach. The enthalpy of vaporisation, DvapHo m, for ionic liquids (ILs) is assumed to be composed of two parts: one part corresponds with the induced energy, DvapHo monP, and the other part corresponds with orientation energy from permanent dipole moment of ion pair in ILs, DvapHo molP. Using the values of DvapHo m, DvapHo monP and DvapHo molP, cohesive energy density, d2 (d is the solubility parameter), the contribution of inducted energy, d2n , and the contribution of orientation energy, d2 l, were obtained. If a liquid only has dn then it is a non-polar liquid, and if a liquid not only has dn also has dl then it is a polar liquid. Since the ion pairs in ILs have permanent dipole moment, ionic liquid has a certain polarity. Therefore, using dl as the polarity scaling of ILs is very convenient because the values of dl are very easy to calculate from the enthalpy of vaporisation and refractive index data.