Study of benzyl- or cyclohexyl-functionalized ionic liquids using inverse gas chromatography Fabrice Mutelet a , Hamid Djebouri b , Gary A. Baker c , Sudhir Ravula c , Bihan Jiang d , Xin Tong d , Delani Woods d , William E. Acree Jr. d, ⁎ a Universite de Lorraine, Laboratoire de Reactions et Genie des Procedes (UPR CNRS 3349), 1 rue Grandville, BP 20451, 54001 Nancy, France b Université des Sciences et de la Technologie Houari Boumediene, BP 32, El Alia, 16111 Bab Ezzouar, Alger, Algeria c Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA d Department of Chemistry, 1155 Union Circle #305070, University of North Texas, Denton, TX 76203-5017, USA abstract article info Article history: Received 7 June 2017 Received in revised form 10 July 2017 Accepted 11 July 2017 Available online 16 July 2017 Inverse gas-liquid chromatography has been used to measure infinite dilution activity coefficients and gas-to-ionic liq- uid partition coefficients for a chemically diverse set of organic solutes dissolved in 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-benzyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-cyclohe xylmethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and N-cyclohexylmethylpyridinium bis (trifluoromethylsulfonyl)imide ionic liquids in the temperature range from 323.15 K to 373.15 K. The measured experimental data were extrapolated to 298.15 K and the resulting values correlated mathematically with the Abraham solvation parameter model. The derived Abraham model correlations rigorously describe the experimental partition coefficient data to within 0.14 (or fewer) log units. © 2017 Elsevier B.V. All rights reserved. Keywords and phrases: Ionic liquids Activity coefficients Gas-to-ionic liquid partition coefficients Inverse gas chromatography 1. Introduction Considerable attention has been afforded in recent years to design- ing chemical separations that utilize ionic liquids (ILs) as designer, mo- lecularly-tunable solvent media. For example, IL-based aqueous biphasic systems have been used to purify active pharmaceutical ingre- dients and biomolecules [1,2]. Recently, Pereira et al. [2] examined the selectivity of aqueous biphasic systems containing polyethylene glycol and select imidazolium-based ILs concerning their ability to separate the three alkaloids caffeine, xanthine, and nicotine. These authors ob- served that caffeine was preferentially partitioned into the polymer- rich phase. Xanthine and nicotine, on the other hand, were found to pre- fer the IL-rich phase. Lee et al. [3] reviewed recent advances in protein extractions that were achieved using IL-based aqueous two-phase sys- tems. The tunable nature of ILs, made possible through cation-anion pair combination combined with the introduction of polar functional groups onto the alkyl chains of the cation (or anion), facilitates the chemical separation selectivities required in the bioseparation field. ILs have also been employed as stationary phases in gas-liquid chro- matographic separations of volatile organic compounds in cider apple juices [4] and wines [5], as well as the separation of nonpolar analytes in kerosene [6], the resolution of alkyl-substituted polycyclic aromatic sulfur heterocycle isomers [7,8], and the separation of thia-arenes and aza-arenes from polycyclic aromatic hydrocarbons in snowpack sam- ples collected from the Athabasca oil sands area of Alberta, Canada [9]. Several excellent review articles have further documented the applica- bility of IL solvents in gas-liquid chromatography [10–13] and liquid- liquid micro-extractions [14–17]. Our contributions in the area of chemical separations using IL sol- vents have focused primarily on measurements of infinite dilution ac- tivity coefficients, γ i ∞ , and gas-to-liquid partition coefficients for representative organic solutes dissolved in ILs [18–31], as well as the de- velopment of Abraham model correlations that describe the observed partitioning behavior. To date, we have performed experimental γ i ∞ measurements in more than 40 different ILs of varying polarity and hy- drogen-bonding character based on inverse gas-liquid chromatographic methods using an IL stationary phase. For each different IL studied, we have developed Abraham model IL-specific correlations of the type log P ¼ c p;il þ e p;il Á E þ s p;il Á S þ a p;il Á A þ b p;il Á B þ v p;il Á V ð1Þ log K ¼ c k;il þ e k;il Á E þ s k;il Á S þ a k;il Á A þ b k;il Á B þ l k;il Á L ð2Þ where log K and log P represent the logarithm of the gas-to-IL and water-to-IL partition coefficients, respectively. The various terms on the right-hand side of Eqs. (1) and (2) represent different types of sol- ute–IL molecular interactions. Each type of interaction corresponds to the product of a solute property times the complementary IL property. Journal of Molecular Liquids 242 (2017) 550–559 ⁎ Corresponding author. E-mail address: acree@unt.edu (W.E. Acree). http://dx.doi.org/10.1016/j.molliq.2017.07.036 0167-7322/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq