Predicting properties of amino acid ionic liquid homologue of 1-alkyl-3-methylimidazolium glycine.

Amino acid ionic liquids (AAILs) [C(5)mim][Gly] (1-pentyl-3-methylimidazolium glycine) and [C(6)mim][Gly] (1-hexyl-3-methylimidazolium glycine) were prepared by the neutralization method and characterized by (1)H NMR spectroscopy and differential scanning calorimetry (DSC). The values of their density, surface tension, and refractive index were measured in the temperature range of 293.15-343.15 (±0.05) K. Since the AAILs can strongly form hydrogen bonds with water, the small amounts of water are difficult to remove from the AAILs by common methods. In order to eliminate the effect of the impurity water, the standard addition method (SAM) was applied to these measurements. In terms of semiempirical method, physicochemical properties molecular volume V(m), standard molar entropy S(0), parachor P, surface tension γ, thermal expansion coefficients α, molar refraction R(m), and refractive index n(D) of the homologue of [C(n)mim][Gly] (n = 2-6) were predicted. In comparison with the values of [C(2)mim][Gly] in literature, the predicted results were in good agreement within an order of magnitude.