Thermochemical investigations of solute transfer into ionic liquid solvents: updated Abraham model equation coefficients for solute activity coefficient and partition coefficient predictions Timothy W. Stephens a , Vicky Chou a , Amanda N. Quay a , Connie Shen a , Nishu Dabadge a , Amy Tian a , Matthew Loera a , Bria Willis a , Anastasia Wilson a , William E. Acree, Jr. a *, Pamela Twu b , Jared L. Anderson b and Michael H. Abraham c a Department of Chemistry, University of North Texas, 1155 Union Circle Drive #305070, Denton, TX 76203, USA; b Department of Chemistry, University of Toledo, 2801 Bancroft Street MS 602, Toledo, OH 43606, USA; c Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK (Received 11 November 2013; final version received 31 December 2013) Experimental data have been compiled from the published chemical and engineering literature pertaining to the infinite dilution activity coefficients, gas solubilities and chromatographic retention factors for solutes dissolved in ionic liquid (IL) solvents. Chromatographic retention factors for 45 solutes on a 1-butyl-1-methylpyrrolidinium tricyanomethanide IL gas–liquid chromatographic stationary phase are included in the compilation. The published experimental data were converted to gas-to-IL and water- to-IL partition coefficients and correlated with the ion-specific equation coefficient version of the Abraham general solvation model. Ion-specific equation coefficients were calculated for 40 different cations and 16 different anions. The calculated ion- specific equation coefficients describe the experimental gas-to-IL and water-to-IL partition coefficient data to within 0.123 and 0.149 log units, respectively. Keywords: ionic liquids; partition coefficients; activity coefficients; gas solubilities; predictive methods 1. Introduction Task-specific ionic liquids (ILs) can be designed by judicious selection of the cation– anion pair combination or by functionalisation of the cation/anion alkyl chain(s). IL solvents have been designed that exhibit good selectivity in alkane/alkene and alkane/ aromatic hydrocarbon separations [1], in removing sulphur and nitrogen compounds from petroleum products [2–7], in capturing carbon dioxide and sulphur dioxide from post- combustion gases [8–12] and in microfluidic ‘on-drop’ separations and chemical sensing [13]. Predictive methods [14–19] have been developed to assist researchers in selecting a suitable cation–anion pair combination needed to achieve the desired chemical separation. In the case of functionalised ILs group contribution methods [20,21] are available for ILs containing 1,3-dialkylimidazolium, N-alkylpyridinium, N,N-dialkylpyrrolidinium, tetra- alkylammonium and tetraphosphonium cations with cyano (–CN), oxy (–O–) and hydro- xyl (–OH) substituents. *Corresponding author. Email: acree@unt.edu Physics and Chemistry of Liquids, 2014 Vol. 52, No. 4, 488–518, http://dx.doi.org/10.1080/00319104.2014.880114 © 2014 Taylor & Francis