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Thermal stability of dialkylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids: ex situ bulk heating to complement in situ mass spectrometry

Clarke, C. J., Puttick, S., Sanderson, T. J., Taylor, A. W., Bourne, R., Lovelock, K. R. J. and Licence, P. (2018) Thermal stability of dialkylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids: ex situ bulk heating to complement in situ mass spectrometry. Physical Chemistry Chemical Physics, 20. pp. 16786-16800. ISSN 1463-9076

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To link to this item DOI: 10.1039/C8CP01090K

Abstract/Summary

Thermal decomposition (TD) products of the ionic liquids (ILs) [CnC1Im][BF4] and [CnC1Im][PF6] ([CnC1Im]+ = 1-alkyl-3-methylimidazolium, [BF4]- = tetrafluoroborate, and [PF6]- = hexafluorophosphate) were prepared, ex situ, by bulk heating experiments in a bespoke setup. The respective products, CnC1(C3N2H2)BF3 and CnC1(C3N2H2)PF5 (1-alkyl-3-methylimidazolium-2-trifluoroborate and 1-alkyl-3-methylimidazolium-2-pentafluorophosphate), were then vaporized and analyzed by direct insertion mass spectrometry (DIMS) in order to identify their characteristic MS signals. During IL DIMS experiments we were subsequently able, in situ, to identify and monitor signals due to both IL vaporization and IL thermal decomposition. These decomposition products have not been observed in situ during previous analytical vaporization studies of similar ILs. The ex situ preparation of TD products is therefore perfectly complimentary to in situ thermal stability measurements. Experimental parameters such as sample surface area to volume ratios and heating rates are consequently very important for ILs that show competitive vaporization and thermal decomposition. We have explained these experimental factors in terms of Langmuir evaporation and Knudsen effusion-like conditions, allowing us to draw together observations from previous studies to make sense of the literature on IL thermal stability. Hence, the design of experimental setups are crucial and previously overlooked experimental factors.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
ID Code:77586
Publisher:Royal Society of Chemistry

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