Measurement and estimation of the vaporization enthalpy for amino acid ionic liquids [Cnmim][Thr](n = 2, 4)

•The enthalpy of vaporization for the ionic liquids were determined by using the isothermogravimetrical analysis.•The difference of heat capacities between the gaseous phase and the liquid phase for ILs were calculated based on the statistical thermodynamics.•Using a new scale of polarity to predict the order of the polarity of ILs.•A new model about the enthalpy of vaporization for aprotic ILs was proposed and used to predict the vaporization enthalpy for ILs.

The molar enthalpy of vaporization, ΔglHom(Tav), at the average temperature, Tav = 438.15 K, for the ionic liquids (ILs), 1-alkyl-3-methylimidazolium threonine salt [Cnmim][Thr](n = 2, 4) were determined by using the isothermogravimetrical analysis. With the use of Verevkin's method, the difference of heat capacities between the gaseous phase and the liquid phase, ΔglCpom, for [Cnmim][Thr](n = 2, 4) were calculated based on the statistical thermodynamics. Therefore, with the use of ΔglCpom, the values of ΔglHom(Tav) were transformed into ΔglHom(298). According to the new scale of polarity for ILs, the order of the polarity of [Cnmim][Thr](n = 2, 4) was predicted, that is, the polarity reduces with the increasing of methylene. In addition, a new model about the enthalpy of vaporization for aprotic ILs was proposed and used to predict the vaporization enthalpy for [Cnmim][Thr](n = 3, 5, 6), but these predicted values also need to be verified in our future experiments.

Graphical abstractThe isothermal TGA mass loss curves are all rigorously linear with correlation coefficients exceeding 0.999. The high linearity associated with the isothermal TGA curves reveals zero-order mass loss kinetics, providing strong evidence that the observed decrease in mass over time at constant temperature results from vaporization of the IL.Download high-res image (115KB)Download full-size image