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Mass spectrometric studies of 1‐ethyl‐3‐methylimidazolium and 1‐propyl‐2,3‐dimethylimidazolium bis(trifluoromethyl)‐sulfonylimides
Author(s) -
Chilingarov Norbert S.,
Medvedev Artem A.,
Deyko Grigoriy S.,
Kustov Leonid M.,
Chernikova Elena A.,
Glukhov Lev M.,
Markov Vitaliy Yu.,
Ioffe Il'ya N.,
Senyavin Vladimir M.,
Polyakova Marina V.,
Sidorov Lev N.
Publication year - 2015
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7214
Subject(s) - chemistry , vaporization , ionic liquid , mass spectrometry , vapor pressure , enthalpy , evaporation , analytical chemistry (journal) , enthalpy of vaporization , ionic bonding , desorption , ion , organic chemistry , chromatography , thermodynamics , adsorption , physics , catalysis
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, [C 2 MIM + ][Tf 2 N − ] and [C 3 MMIM + ][Tf 2 N − ], 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 [C 2 MIM + ][Tf 2 N − ] and [C 3 MMIM + ][Tf 2 N − ], respectively. The corresponding equations for their saturated vapor pressures are:ln pC 2 MIM +T f 2 N −/ Pa = – 14213 ± 325 / T / K + 26.57 ± 1.04 ,ln pC 3 MMIM +T f 2 N −/ 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 [C 3 MMIM + ][Tf 2 N − ] were accurately determined for the first time. MALDI is also capable of providing indirect information on hydrogen bonding. Copyright © 2015 John Wiley & Sons, Ltd.