Density and Surface Tension of Amino Acid Ionic Liquid 1-Alkyl-3-methylimidazolium Glutamate

An amino acid ionic liquid (AAIL) [C(3)mim][Glu] (1-propyl-3-methylimidazolium glutamate) was prepared by the neutralization method and characterized by (1)H NMR spectroscopy and DSC trace. Since the AAIL has a strong hydrogen bonding ability, the water content (8.41 +/- 0.01).10(-3) mass fraction in the IL is difficult to remove by a common method, so trace water becomes the most problematic impurity. To eliminate the effect of the impurity water, the standard addition method (SAM) was applied to the measurement of densities and surface tensions for [C(3)mim][Glu] in the temperature range of (318.15 to 343.15 +/- 0.05) K and (318.15 to 338.15 +/- 0.05) K, respectively. Since per methylene (-CH(2)-) group in the alkyl chains of the imidazolium-based ionic liquids has almost the same chemical environment, using semiempirical methods we may predict physicochemical properties of 1-alkyl-3-methylimidazolium glutamate [C(n)mim][Glu] (n = 1, 2, 3, 4, 5, 6): the molecular volume, V(m) the standard molar entropy, S(0), the parachor, P, the surface tension, gamma, and the molar enthalpy of vaporization, Delta(g)(l)H(m)(0). In terms of the interstice model, the thermal expansion coefficient, a, was 3.28.10(-4) K(-1), which was in good agreement with experimental alpha for [C(3)mim][Glu], (4.35 +/- 0.03).10(-4) K(-1).