The study of the vapor pressure and the enthalpy of vaporization of ionic liquids

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A reliable knowledge of the vapor pressure of RTILs is of considerable interest for many reasons. Such data would be import for testing theoretical calculations of vapor pressures and heats of vaporization based on MD technique or other techniques. Several attempts have been made in the literature to estimate vapor pressures of RTILs in a more or less semiempirical way. We have developed a concept, which offers a direct way to measure the vapor pressure of RTILs using an extended version of the ¿transpiration technique¿, which has successfully been applied for determining vapor pressures of substances of very low valatility in our laboratory. In addition high precision measurements of the heats of combustion of different RTILs will be carried out using a ¿rotating bomb¿ calorimeter available in our group. This leads immediately to the heats of formation of RTILs in the liquid state. Heats of formation in the gaseous state will be obtained by high level quantum mechanical calculations, which have reached today a quality ensuring the required accuracy of a few percent for heats of formation in the gaseous state. The difference of the heats of formation in the gaseous and the liquid state is the heat of vaporization. Values obtained by this method will be compared with experimental values derived from the temperature dependence of the measured vapor pressure providing a sensitive but indispensable consistency test of both ways to obtain heats of vaporization. Theoretical calculations described will be performed in cooperation with the group of Theoretical Chemistry in Rostock (Prof. Ludwig) where the highest possible computer capacities guarantee the required reliably.