Activity Coefficients at Infinite Dilution for Organic Compounds Dissolved in 1‑Alkyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquids Having Six‑, Eight‑, and Ten-Carbon Alkyl Chains William E. Acree, Jr.,* ,† Gary A. Baker, ‡ Anne-Laure Revelli, § Jean-Charles Moise, § and Fabrice Mutelet § † Department of Chemistry, University of North Texas, 1155 Union Circle #305070, Denton, Texas 76203-5017, United States ‡ Department of Chemistry, University of MissouriColumbia, Columbia, Missouri 65211, United States § Laboratoire de Ré actions et Ge ́ nie des Proce ́ de ́ s (UPR CNRS 3349), Universite ́ de Lorraine, 1 rue Grandville, BP 20451 54001 Nancy, France ABSTRACT: Activity coefficients at infinite dilution (γ 1,2 ∞ ) for 40 diverse probe solutes, including various (cyclo)alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, thiophene, ethers, nitroalkanes, and ketones, were measured by inverse gas chromatography at temperatures from 323 to 343 K in three homologous 1-alkyl-1- methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs), bearing hexyl, octyl, and decyl side chains. The retention data were further converted to gas- to-IL and water-to-IL partition coefficients using the corresponding gas-to-water partition coefficients. Both sets of partition coefficients were analyzed using the modified Abraham solvation parameter model, with the derived equations tightly correlating the experimental gas-to-IL and water-to-IL partition coefficient data to within average standard deviations of 0.088 and 0.111 log units, respectively. ■ INTRODUCTION Ionic liquids (ILs) have been increasingly utilized as solvent media in industrial manufacturing and chemical separation processes because of their low volatility and good thermal stability at high temperatures, recyclability, and thermal nonflammability. Representative applications include the use of ILs as potential green solvents in liquid-liquid extractions involving the removal of aromatic nitrogen and aromatic sulfur compounds from petroleum crude products and fuel oils, 1-6 as entrainers and azeotrope breakers in extractive distillations, 7 and as membrane coatings and absorbents for ethylene/ acetylene, 8,9 propyne/propylene, 10 propylene/propane, 11,12 1- hexene/hexane, 13 and CO 2 /CH 4 14,15 separations. Judicious selection of the cation-anion pair, combined with the introduction of functional groups to the IL, enables one to fine-tune the chemical selectivity and efficiency of the separation process. For example, ether- and hydroxyl-function- alized ILs are reported 16 to show especially high capacity for solubilizing carbon dioxide and sulfur dioxide. The present study continues our methodical investigation of the solubilizing ability of IL solvents using the solvation parameter model developed by Abraham and co-workers. 17,18 The basic model is described by two linear free energy relationships (LFERs). The first relationship involves solute transfer between two condensed phases: = + · + · + · + · + · P E S A V log c e s a bB v p p p p p p (1) and the second relationship governs solute transfer from the gas phase to a condensed phase = + · + · + · + · + · K E S A L log c e s a b B l L k k k k k k (2) where P and K L refer to the solute’s condensed phase-to- condensed phase partition coefficient (often the water-to- organic solvent partition coefficient) and the gas-to-condensed phase partition coefficient, respectively. The uppercase letters in eqs 1 and 2 represent the solute properties, whereas the lowercase letters represent the complementary properties of the ILs. The solute descriptors are the excess molar refraction (E), the combined dipolarity/polarizability (S), the hydrogen-bond acidity (A) and basicity (B), the logarithm of the solute’s gas- to-n-hexadecane partition coefficient at 298 K (L), and the solute’s McGowan volume in units of (cm 3 mol -1 )/100 (V). Solute descriptors have been reported for about 5000 solutes based on experimental partition coefficient and chromato- graphic retention factor data or calculated by the group contribution method. 17-24 The advantage of characterizing ILs with the Abraham model is that once the equation coefficients are calculated, one can estimate log P and log K L values of additional solutes provided that the solute coefficients are known. To date, we have Received: June 25, 2012 Accepted: October 17, 2012 Published: October 31, 2012 Article pubs.acs.org/jced © 2012 American Chemical Society 3510 dx.doi.org/10.1021/je300692s | J. Chem. Eng. Data 2012, 57, 3510-3518