离子液体1-丙基-3-甲基咪唑醋酸盐[C3mim][OAc]蒸气压和蒸发焓的测定及极性预测

The measurement of vapor pressure, enthalpy of vaporization and the prediction of the polarity for 1-propyl-3-methylimidazolium acetate [C3mim][OAc] ionic liquid

用中和法制备了离子液体1-丙基-3-甲基咪唑醋酸盐[C3mim][OAc]，并用核磁共振氢谱（1H NMR）和差示扫描量热仪（DSC）对其进行了表征. 在418.15-438.15 K温度范围内，用恒温热重法测定了离子液体[C3mim][OAc]的蒸气压和蒸发焓. 根据Verevkin方法，在统计热力学的基础上计算了离子液体[C3mim][OAc]的气态和液态热容差ΔvapCpm = -88.8 J K-1 mol-1，进而将实验测得平均温度的蒸发焓ΔvapH（Tav）转换成参考温度298.15 K时的蒸发焓，即ΔvapH（298.15 K）= 116.8 kJ mol-1，并讨论了该离子液体的蒸发焓、蒸发熵和蒸发吉布斯自由能随温度的变化规律. 在Hildebrand理论基础上，本文提出了预测离子液体极性的新方法，即将溶解度参数δ看作极性贡献部分δμ和非极性贡献δn的加和，δ可由实验得到的蒸发焓计算，δn可用Lawson-Ingham方程计算，进而得到的δμ可看作离子液体极性的量度. 根据δμ大小预测的离子液体极性次序与实验结果一致.

Ionic liquid （IL） 1-propyl-3-methylimidazolium acetate [C3mim][OAc] was prepared by the neutralization method and characterized by 1H NMR spectroscopy and differential scanning calorimetry （DSC）. The vapor pressures （p）, and enthalpy of vaporization （ΔvapH）, for the IL were determined using isothermogravimetrical analysis in the temperature range of 418.15-438.15 K. Using Verevkin＇s method, the difference of heat capacity between vapor phase and liquid phase of the IL, ΔvapCpm, was calculated based on the statistical thermodynamics. In terms of the value of ΔvapCpm, the values of ΔvapH（Tav）, experimentally obtained at an average temperature, can be transformed into one of ΔvapH（298.15 K） at reference temperature （298.15 K）. Based on Hildebrand＇s theory, a new method to predict the polarity of IL was put forward： it is considered that the solubility parameter （δ）, of IL is the sum of the contribution part of nonpolarity （δn）, and the contribution part of polarity （δμ）. The value of δ can be calculated from ΔvapH for IL and the value of δn can be calculated from Lawson-Ingham Equation so that the value of δμ was obtained which can be taken for a measure of polarity of IL. The order of polarity for ILs predicted by δμis in good agreement with the experiment and the experience.