Study on physicochemical properties of ionic liquids based on alanine [Cnmim][Ala] (n=2,3,4,5,6)

According to Fukumoto's method, a new series of ionic liquids (ILs) based on alanine, [C(n)mim][Ala] (n = 2,3,4,5,6), which comprise 1-alkyl-3-methylimidazolium cation ([C(n)mim](+)) and alanine anions ([Ala](-)), were prepared and characterized. In terms of standard addition method, the density and surface tension of amino acid ILs [C(n)mim][Ala] (1-alkyl-3-methylimidazolium alpha-aminopropionic acid salt) were measured in the temperature range 293.15-343.15 +/- 0.05 K. The volume and surface properties of the ILs [C(n)mim][Ala] were discussed. A new method of determining parachor of ionic compound was proposed and was applied to estimate the physicochemical properties of amino acid ionic liquids (AAILs): molecular volume, surface tension, molar enthalpy of vaporization, and thermal expansion coefficient. In comparison with Deetlefs's method of using neutral parachor contribution, the method proposed in this work makes smaller error in estimating properties of AAILs.