Studies on properties of ionic liquids 1-alkyl-3-methylimidazolium lactate at temperatures from (288.15 to 333.15) K

Abstract

Two chiral ionic liquids based on lactic acid (LAILs), 1-ethyl-3-methylimidazolium lactate ([C2mim][Lact]) and 1-pentyl-3-methylimidazolium lactate ([C5mim][Lact]), have been prepared by the neutralization method and characterized by 1H NMR and DSC. Their density, surface tension and refractive index were measured at T {(288.15 to 333.15)±0.05}K. Since the LAILs can form strong hydrogen bonds with water, small amounts of water are difficult to remove by conventional methods. In order to eliminate the effect of the impurity as water, the standard addition method (SAM) was applied to these measurements. The molar volume of [Cnmim][Lact] (n=2,5), the thermal expansion coefficient, α, the surface excess entropy, Sa, the surface excess energy Ea, parachor, P, and molar refraction, Rm, were obtained. According to the methods of both Kabo and Rebelo, the molar enthalpy of evapouration of the LAILs was estimated using experimental values for the surface tension and molar volume. At the same time, the surface tension of the LAILs may be estimated using the data of the parachor and refractive index. The estimated values of the surface tension correlate quite well with the corresponding experimental values.