Estimation of the polarity and prediction of the molar surface Gibbs energy for amino acid ionic liquids — [C4Dmim][Gly] and [C4Dmim][Ala]

Abstract 1-Butyl-2,3-dimethylimidazolium glycine ([C4Dmim][Gly]) and 1-butyl-2,3-dimethylimidazolium alanine ([C4Dmim][Ala]) were synthesized by neutralization method and characterized by 1H NMR and 13C NMR spectrum. The experimental values of the density, surface tension and refractive index of two amino acid ionic liquids were measured by standard addition method. Firstly, the polarity coefficients of [C4Dmim][Gly] and [C4Dmim][Ala] were calculated by polarity coefficient (P), and the polarity trend of other ionic liquids (ILs) was predicted. For the same anion, the polarity values of the same series of ILs decrease with increasing carbon chain length, and the anion species also affect the polarity of ILs. Secondly, according to the relationship between the slope of the new Eotvos empirical equation and the molar surface entropy (s), the polarity values of other ILs were also estimated and the conclusion obtained was basically consistent with polarity coefficient. Furthermore, the predicted molar surface Gibbs energy values of samples were obtained by the new Eotvos empirical equation, and the predicted values were highly consistent with the corresponding experimental values.