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Issue 38, 2009
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Measuring and predicting ΔvapH298 values of ionic liquids

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We report the enthalpies of vaporisation (measured using temperature programmed desorption by mass spectrometry) of twelve ionic liquids (ILs), covering four imidazolium, [CmCnIm]+, five pyrrolidinium, [CnCmPyrr]+, two pyridinium, [CnPy]+, and a dication, [C3(C1Im)2]2+ based IL. These cations were paired with a range of anions: [BF4], [FeCl4], [N(CN)2], [PF3(C2F5)3] ([FAP]), [(CF3SO2)2N] ([Tf2N]) and [SCN]. Using these results, plus those for a further eight imidazolium based ILs published earlier (which include the anions [CF3SO3] ([TfO]), [PF6] and [EtSO4]), we show that the enthalpies of vaporisation can be decomposed into three components. The first component is the Coulombic interaction between the ions, ΔUCou,R, which is a function of the IL molar volume, Vm, and a parameter Rr which quantifies the relative change in anion–cation distance on evaporation from the liquid phase to the ion pair in the gas phase. The second and third components are the van der Waals contributions from the anion, ΔHvdw,A, and the cation, ΔHvdw,C. We derive a universal value for Rr, and individual values of ΔHvdw,A and ΔHvdw,C for each of the anions and cations considered in this study. Given the molar volume, it is possible to estimate the enthalpies of vaporisation of ILs composed of any combination of the ions considered here; values for fourteen ILs which have not yet been studied experimentally are given.

Graphical abstract: Measuring and predicting ΔvapH298 values of ionic liquids

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The article was received on 24 Apr 2009, accepted on 17 Jun 2009 and first published on 27 Jul 2009

Article type: Paper
DOI: 10.1039/B908209C
Citation: Phys. Chem. Chem. Phys., 2009,11, 8544-8555
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    Measuring and predicting ΔvapH298 values of ionic liquids

    A. Deyko, K. R. J. Lovelock, J. Corfield, A. W. Taylor, P. N. Gooden, I. J. Villar-Garcia, P. Licence, R. G. Jones, V. G. Krasovskiy, E. A. Chernikova and L. M. Kustov, Phys. Chem. Chem. Phys., 2009, 11, 8544
    DOI: 10.1039/B908209C

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