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The Gaseous Enthalpy of Formation of the Ionic Liquid 1-Butyl-3-methylimidazolium Dicyanamide from Combustion Calorimetry, Vapor Pressure Measurements, and Ab Initio Calculations
journal contribution
posted on 2007-04-04, 00:00 authored by Vladimir N. Emel'yanenko, Sergey P. Verevkin, Andreas HeintzIonic 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.