Emel'yanenko Vladimir N, Verevkin Sergey P, Heintz Andreas
Department of Physical Chemistry, University of Rostock, Hermannstrasse 14, 18051 Rostock, Germany.
J Am Chem Soc. 2007 Apr 4;129(13):3930-7. doi: 10.1021/ja0679174. Epub 2007 Mar 13.
Ionic liquids are attracting growing interest as alternatives to conventional molecular solvents. Experimental values of vapor pressure, enthalpy of vaporization, and enthalpy of formation of ionic liquids are the key thermodynamic quantities, which are required for the validation and development of the molecular modeling and ab initio methods toward this new class of solvents. In this work, the molar enthalpy of formation of the liquid 1-butyl-3-methylimidazolium dicyanamide, 206.2 +/- 2.5 kJ.mol-1, was measured by means of combustion calorimetry. The molar enthalpy of vaporization of 1-butyl-3-methylimidazolium dicyanamide, 157.2 +/- 1.1 kJ.mol-1, was obtained from the temperature dependence of the vapor pressure measured using the transpiration method. The latter method has been checked with measurements of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, where data are available from the effusion technique. The first experimental determination of the gaseous enthalpy of formation of the ionic liquid 1-butyl-3-methylimidazolium dicyanamide, 363.4 +/- 2.7 kJ.mol-1, from thermochemical measurements (combustion and transpiration) is presented. Ab initio calculations of the enthalpy of formation in the gaseous phase have been performed for 1-butyl-3-methylimidazolium dicyanamide using the G3MP2 theory. Excellent agreement with experimental results has been observed. The method developed opens a new way to obtain thermodynamic properties of ionic liquids which have not been available so far.
离子液体作为传统分子溶剂的替代品正吸引着越来越多的关注。蒸气压、汽化焓和离子液体生成焓的实验值是关键的热力学量，对于针对这类新型溶剂的分子建模和从头算方法的验证与发展而言是必需的。在这项工作中，通过燃烧量热法测量了液态1-丁基-3-甲基咪唑二氰胺的摩尔生成焓，为206.2±2.5 kJ·mol⁻¹。1-丁基-3-甲基咪唑二氰胺的摩尔汽化焓为157.2±1.1 kJ·mol⁻¹，是通过使用蒸腾法测量的蒸气压对温度的依赖性获得的。后一种方法已通过对1-丁基-3-甲基咪唑双（三氟甲基磺酰）亚胺的测量进行了检验，该物质的相关数据可从隙透技术获得。本文首次通过热化学测量（燃烧和蒸腾）确定了离子液体1-丁基-3-甲基咪唑二氰胺的气态生成焓，为363.4±2.7 kJ·mol⁻¹。使用G3MP2理论对1-丁基-3-甲基咪唑二氰胺的气相生成焓进行了从头算计算。计算结果与实验结果吻合良好。所开发的方法为获取迄今为止尚无数据的离子液体的热力学性质开辟了一条新途径。
