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Anderson, J. L., Dixon, J. K., Maginn, E. J., Brennecke, J. F. Measurement of SO2 Solubility in Ionic Liquids. Journal of Physical Chemistry B, 110:15059-15062, 2006. view abstract // link Measurements of the solubility of sulfur dioxide (SO2) in the ionic liquids 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) and 1-n-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([hmpy][Tf2N]) at temperatures from 25 to 60 °C and pressures up to 4 bar indicate that large amounts (up to 85 mol %) of SO2 dissolve in ionic liquids by simple physical absorption.

Jennifer L. Anthony, Jessica L. Anderson, Edward J. Maginn, and Joan F. Brennecke. Anion Effects on Gas Solubility in Ionic Liquids. Journal of Physical Chemistry B, 109:6366-6374, 2005. view abstract // link This work presents the results of solubility measurements for a series of gases in 1-n-butyl-3-methyl imidazolium tetrafluoroborate and 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide. The gases considered include benzene, carbon dioxide, nitrous oxide, ethylene, ethane, oxygen, and carbon monoxide. Carbon dioxide and oxygen solubilities are also reported in methyl-tributylammonium bis(trifluoromethylsulfonyl) imide, butyl-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide, and tri-isobutyl-methyl phosphonium ptoluenesulfonate. We report the associated Henry's constants and enthalpies and entropies of absorption. In general, benzene, followed by carbon dioxide and nitrous oxide, have the highest solubilities and strongest
interactions with the ionic liquids, followed by ethylene and ethane. Oxygen had very low solubilities and weak interactions. Carbon monoxide had a solubility below the detection limit of our apparatus. Ionic liquids with the bis(trifluoromethylsulfonyl) imide anion had the largest affinity for CO2, regardless of whether the cation was imidazolium, pyrrolidinium, or tetraalkylammonium. These results suggest that the nature of the anion has the most significant influence on the gas solubilities.

Daniel G. Hert, Jessica L. Anderson, Sudhir N. V. K. Aki and Joan F. Brennecke. Enhancement of oxygen and methane solubility in 1-hexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl) imide using carbon dioxide. Chemical Communications, :2603–2605, 2005. view abstract // link The presence of CO2 increases the solubility of O2 and CH4 in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide at 25 oC and pressures to 13 bar.

Jacob M. Crosthwaite, Mark J. Muldoon, JaNeille K. Dixon, Jessica L. Anderson, Joan F. Brennecke. Phase transition and decomposition temperatures, heat capacities and viscosities of pyridinium ionic liquids. Journal of Chemical Thermodynamics, 37:559–568, 2005. view abstract // link Ionic liquids are organic salts with low melting points. Many of these compounds are liquid at room temperature in their pure state. Since they have negligible vapor pressure and would not contribute to air pollution, they are being intensively investigated for a variety of applications, including as solvents for reactions and separations, as non-volatile electrolytes, and as heat transfer fluids. We present melting temperatures, glass transition temperatures, decomposition temperatures, heat capacities, and viscosities for a large series of pyridinium-based ionic liquids. For comparison, we include data for several imidazolium and quaternary ammonium salts. Many of the compounds do not crystallize, but form glasses at temperatures between 188 K and 223 K. The thermal stability is largely determined by the coordinating ability of the anion, with ionic liquids made with the least coordinating anions, like bis(trifluoromethylsulfonyl) imide, having the best thermal stability. In particular, dimethylaminopyridinium bis(trifluoromethylsulfonyl)imide salts have some of the best thermal stabilities of any ionic liquid compounds investigated to date. Heat capacities increase approximately linearly with increasing molar mass, which corresponds with increasing numbers of translational, vibrational, and rotational modes. Viscosities generally increase with increasing number and length of alkyl substituents on the cation, with the pyridinium salts typically being slightly more viscous than the equivalent imidazolium compounds.

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