Estimation of Properties of Ionic Liquids 1-Alkyl-3-methylimidazolium Lactate Using a Semiempirical Method

The ionic liquids based on lactic acid (LAILs)-1-ethyl-3-methylimidazolium lactate ([C(2)rnim][Lact]) and 1-pentyl-3-methylimidazolium lactate ([C(5)mim][Lact])-have been prepared by the neutralization method and characterized by H-1 nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The values of their density, surface tension, and refractive index were measured at 298.15 +/- 0.05 K. Since the LAILs can form strong hydrogen bonds with water, small amounts of water are difficult to remove via common methods. In order to eliminate the effect of the impurity water, the standard addition method (SAM) was applied to these measurements. An improved semiempirical method to estimate the properties of the ILs has been put forward; that is, in terms of an extrathermodynamic assumption, the values of the individual ion volume, [C(2)mim](+) and [BF4](-), were successfully evaluated from the molecular volume of the IL [C(2)mim][BF4]. Then, using [C(2)mim](+) as the reference ion, the properties of [Lact](-) and [C(n)mim](+) (n = 3, 4, 5, 6) were calculated from the experimental data of this work. In order to further verify the reliability of this method, the values of the ionic properties for [Ala](-), [Pro](-), [Gly](-), [BF4](-), and [OAc](-) were calculated using the same methodology. In terms of the above ionic properties, properties of some ILs, such as molecular volume, parachor, molar refraction were estimated and the estimated values are highly correlated with the corresponding experimental values. At the same time, the parachor estimated by the method above were used to predict the surface tension of the ILs and the predicted values are highly correlated and extremely similar with the corresponding experimental ones. These facts demonstrate the reliability of the improved semiempirical method.