Alkyl-imidazolium tetrafluoroborates: Vapor pressure, thermodynamics of vaporization, and enthalpies of formation

Abstract

The absolute vapor pressures for the series of [Cnmim][BF4] ionic liquids with (n=2, 4, 6, 8, and 10) were measured over the temperature range 404–457K by using the quartz-crystal microbalance. An absence of possible thermal decomposition was monitored by the ATR-IR spectroscopy. The molar enthalpies of vaporization of ionic liquids under study were derived from vapor pressure temperature dependences and adjusted to the reference temperature 298.15K. The liquid phase molar enthalpy of formation of [C2mim][BF4] was derived from the solution calorimetry and combined with its molar vaporization enthalpy to get the first experimental gas-phase molar enthalpy of formation of the [BF4]− containing ionic liquid. A computational approach based on the DLPNO-CCSD(T) method was used to calculate the theoretical gas-phase molar enthalpy of formation of [C2mim][BF4]. The theoretical and experimental results were found to be in agreement within the combined uncertainties, providing the mutual validation of experimental and computational procedures used in the current study.