Estimation of physicochemical properties of 1-alkyl-3-methylimidazolium glutamate

Abstract

Amino acid ionic liquids (AAILs) [C5mim][Glu] (1-pentyl-3-methylimidazolium glutamate) and [C6mim][Glu] (1-hexyl-3-methylimidazolium glutamate) were prepared by the neutralization method and characterized by 1H NMR spectroscopy and DSC. The values of their density, surface tension were measured over the temperature range (308.15 to 343.15±0.05)K, and the refractive index was measured within the temperature range (293.15 to 328.15±0.05)K. Since the AAILs can form strong hydrogen bonds with water, a small amount of water is difficult to remove from the AAILs by common methods. In order to eliminate the effect of water as an impurity existed in AAIL sample, the standard addition method (SAM) was applied to these measurements. In terms of a semi-empirical method, the following physico-chemical properties were predicted: molecular volume, Vm, standard molar entropy, S0, parachor, P, surface tension, γ, thermal expansion coefficients, α, molar refraction, RM, and refractive index, nD, of the homologue of [Cnmim][Glu] (n=2,3,4).