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Mass Spectrometric Studies of 1-ethyl-3-methylimidazolium and 1-propyl-2,3-dimethylimidazolium Bis(trifluoromethyl)-Sulfonylimides

Mass Spectrometric Studies of 1-ethyl-3-methylimidazolium and 1-propyl-2,3-dimethylimidazolium Bis(trifluoromethyl)-Sulfonylimides

Norbert S Chilingarov, Artem A Medvedev, Grigoriy S Deyko, Leonid M Kustov, Elena A Chernikova, Lev M Glukhov, Vitaliy Yu Markov, Il'ya N Ioffe, Vladimir M Senyavin, Marina V Polyakova, Lev N Sidorov

Rapid Commun Mass Spectrom. 2015 Jul 15;29(13):1227-32.

PMID: 26395606

Abstract:

Rationale:
Ionic liquids ([Cat(+)][An(-)]) were believed to decompose before reaching vaporization temperatures, but recently some of them have been shown to vaporize congruently. Low-temperature vaporization of ionic substances is an intriguing phenomenon, so the vapor-phase composition and reactions of ionic liquids deserve more extensive study.
Methods:
Evaporation of two ionic liquids, [C2MIM(+)][Tf2 N(-)] and [C3MMIM(+)][Tf2N(-)], was studied by means of Knudsen effusion mass spectrometry. These liquids were also characterized using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, UV/Vis, IR, NMR spectroscopy, and elemental analysis.
Results:
The vaporization enthalpies of (118 ± 3) and (124 ± 2) kJ·mol(-1) were determined for [C2MIM(+)][Tf2N(-)] and [C3MMIM(+)][Tf2N(-)], respectively. The corresponding equations for their saturated vapor pressures are: ln(p{[C2MIM(+)][Tf2N(-)]}/Pa) = -(14213 ± 325)/(T/K) + (26.57 ± 1.04), ln(p{[C2MMIM(+)][Tf2N(-)]}/Pa) = -(14868 ± 221)/(T/K) + (27.19 ± 0.60). The MALDI studies (positive and negative ion modes) enabled detection of monomeric [Cat(+)] and [An(-)] ions, the cluster ions {[Cat(+)]2 [An(-)]}(+) and {[Cat(+)][An(-)]2}(-), and some complex anions {2[An(-)] + Na(+)}(-), {2[An(-)] + K(+)}(-), {2[An(-)] + Cu(+)}(-) and {3[An(-)] + Ca(2+)}(-).
Conclusions:
Knudsen effusion mass spectrometry proved to be a valuable method to study the thermodynamics of ionic liquids. The saturated vapor pressure and vaporization enthalpy of [C3MMIM(+)][Tf2N(-)] were accurately determined for the first time. MALDI is also capable of providing indirect information on hydrogen bonding.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP880084639	1-Ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate		880084-63-9	Price

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