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Issue 37, 2011
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The vapour of imidazolium-based ionic liquids: a mass spectrometry study

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Abstract

Eight common dialkylimidazolium-based ionic liquids have been successfully evaporated in ultra-high vacuum and their vapours analysed by line of sight mass spectrometry using electron ionisation. The ionic liquids investigated were 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]imide, [CnC1Im][Tf2N] (where n = 2, 4, 6, 8), 1-alkyl-3-methylimidazolium tetrafluoroborate, [CnC1Im][BF4] (where n = 4, 8), 1-butyl-3-methylimidazolium octylsulfate, [C4C1Im][C8OSO3] and 1-butyl-3-methylimidazolium tetrachloroferrate, [C4C1Im][FeCl4]. All ionic liquids studied here evaporated as neutral ion pairs; no evidence of decomposition products in the vapour phase were observed. Key fragment cations of the ionised vapour of the ionic liquids are identified. The appearance energies, Eapp, of the parent cation were measured and used to estimate the ionisation energies, Ei, for the vapour phase neutral ion pairs. Measured ionisation energies ranged from 10.5 eV to 13.0 eV. Using both the identity and Eapp values, the fragmentation pathways for a number of fragment cations are postulated. It will be shown that the enthalpy of vaporisation, ΔvapH, can successfully be measured using more than one fragment cation, although caution is required as many fragment cations can also be formed by ionisation of decomposition products.

Graphical abstract: The vapour of imidazolium-based ionic liquids: a mass spectrometry study

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Publication details

The article was received on 04 Jun 2011, accepted on 28 Jul 2011 and first published on 19 Aug 2011


Article type: Paper
DOI: 10.1039/C1CP21821B
Citation: Phys. Chem. Chem. Phys., 2011,13, 16841-16850
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    The vapour of imidazolium-based ionic liquids: a mass spectrometry study

    A. Deyko, K. R. J. Lovelock, P. Licence and R. G. Jones, Phys. Chem. Chem. Phys., 2011, 13, 16841
    DOI: 10.1039/C1CP21821B

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