Vaporisation thermodynamics of ionic liquids: What to do if the experiment fails

The vaporisation of three high-purity ionic liquids based on 3,5-dimethyl-1-octyl-pyridinium cation with the anions bis(trifluoromethanesulfonyl)imide, thiocyanate and dicyanamide was investigated using the quartz crystal microbalance. Since the samples exhibited different thermal stability under experimental conditions, decomposition was avoided only for the ionic liquid with bis(trifluoromethanesulfonyl)imide anion and its enthalpy of vaporisation was derived from the vapour pressure-temperature dependence. To validate these experimental results and to assess the vaporisation enthalpies of ionic liquids with thiocyanate and dicyanamide anions, which we failed to measure, a modification of the group additivity approach was applied and the results were validated using the structure-property correlations and the COSMO-RS thermodynamic model. • Thermodynamics of vaporisation of three pyridinium based ILs studied by FSC. • Thermal decomposition for two ILs observed during measurements. • Modified group-additivity method suggested to obtain vaporisation enthalpies. • Structure-property correlations used to validate experimental and empirical results.