Predicting properties of ionic liquid homologue of N-alkylpyridinium acetate

As a green material, ionic liquids were widely concerned and applied, but thermodynamic study of ionic liquids were not comprehensive and in-depth. The bridge between the properties of ILs needs to be built. As a continuation, N-alkylpyridinium acetate ILs [CnPy][OAc] (n = 5, 6) were prepared by the neutralization method and characterized by (Rantwijk and Sheldon, 2007) HNMR spectroscopy, TG, DSC and elemental analysis. The density, surface tension, refractive index and conductivity for [CnPy][OAc] (n = 5, 6) were measured by the standard addition method (SAM) in the temperature range of 293.15 to 343.15 K every 5 K. The molecular volume Vm, the standard molar entropy S0, and the lattice energy UPOT were calculated. The parachor P was obtained and used to predict physicochemical properties. The molar vaporization enthalpies ∆lgHmθ were calculated according to the Kabo's and Rebelo's empirical equation. In addition, the molar surface Gibbs energy was calculated based on the experimental density and surface tension, and the traditional Eötvös equation was improved, whose parameters have clear physical meaning. The surface tension could be estimated by combining the mole surface Gibbs free energy and Lorentz-Lorenz relationship. The polarity of [CnPy][OAc] (n = 5, 6) were also predicted based on the ∆lgHmθ(298 K). The molar conductivity and diffusion coefficient were calculated. In addition, the prediction of physicochemical properties for homologues [CnPy][OAc] (n = 2, 3, 4) were carried out based on the semi-empirical method. The relationship between the properties of ILs is described and calculated, and the reasonable calculation and prediction provide strong evidence and model for the follow-up study on the properties of ILs. Further more, the accuracy of the prediction results is enough to serve as the reference data for the selection and application of ILs.