infinite dilution activity coefficients of solutes dissolved in anhydrous...

Journal of Molecular Liquids 222 (2016) 295–312

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Journal of Molecular Liquids

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Infinite dilution activity coefficients of solutes dissolved in anhydrousalkyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imideionic liquids containing functionalized- andnonfunctionalized-alkyl chains

Fabrice Mutelet a, Dominique Alonso a, Sudhir Ravula b, Gary A. Baker b, Bihan Jiang c, William E. Acree Jr. c,⁎a Universite de Lorraine, Laboratoire de Reactions et Genie des Procedes (UPR CNRS 3349), 1 rue Grandville, BP 20451 54001 Nancy, Franceb Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, United Statesc Department of Chemistry, 1155 Union Circle #305070, University of North Texas, Denton, TX 76203-5017, United States

⁎ Corresponding author.E-mail address: [email protected] (W.E. Acree).

http://dx.doi.org/10.1016/j.molliq.2016.07.0120167-7322/© 2016 Elsevier B.V. All rights reserved.

a b s t r a c t
a r t i c l e i n f o
Article history:Received 19 May 2016Received in revised form 17 June 2016Accepted 2 July 2016Available online 5 July 2016

Infinite dilution activity coefficients and gas-to-liquid partition coefficients have been determined for atleast 42 different organic solutes of varying polarity and hydrogen-bonding character dissolved in anhy-drous ionic liquids comprising propyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide,hexyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, 2-hydroxyethyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, cyanomethyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide, and N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminiumdi[bis(trifluoromethylsulfonyl)imide]. The measured gas-to-liquid partition coefficient data were converted towater-to-liquid partition coefficients using standard thermodynamic relationships. Abraham model predictivecorrelations were developed from both sets of partition coefficients. The derived correlations describe theobserved partitioning behavior to within 0.14 (or fewer) log units.

© 2016 Elsevier B.V. All rights reserved.

Keywords:Ionic liquid solventsActivity coefficients at infinite dilutionPartition coefficientsPredictive methodsChemical separations

1. Introduction

Ionic liquids (ILs) have emerged as a new solvent class possessingproperties that can be fine-tuned andmodulated by judicious alterationof the cation-anion combination or introduction of task-specific polarand/or hydrogen-bonding functional groups onto the pendant chainsattached to the cation. Task-specific ionic liquids have been designedfor distinct purposes, such as sorbents for greenhouse gas and acidicgas capture in natural gas and post-combustion treatments, stationaryphase materials for gas-liquid chromatographic separations, extractionsolvents/additives for the selective removal of metal ions from aqueoussolution [1–3], components of aqueous two-phase systems for theenantiomeric separation of racemic amino acids [4], and more recently,for the dissolution and fractionation of cellulose, hemicellulose, and lig-nin in biomass processing [5–8]. Amine-functionalized ILs have beenshown to exhibit increased carbon dioxide sorption efficiency [9–11],whereas hydroxyl-functionalized ILs provide an efficient means forsorbing ammonia gas [12]. Nitrile-terminated alkyl chains are reported[13] to afford improved CO2/N2 and CO2/CH4 solubility selectivity when

compared to their non-functionalized alkyl-chain counterparts. ILscontaining acetate, formate, and chloride anions have been found tobe especially effective in dissolving cellulose [14]. The fore-mentionedexamples represent just a few of the many disparate applicationsinvolving ILs in practical industrial and manufacturing processes. Ex-panded utilization of ILs in chemical synthesis and chemical separationprocesses requires both the experimental determination of chemicaland physical properties of additional ILs, as well as the developmentof predictive methods that allow for the estimation of IL properties inthe absence of direct measured values.

Our contribution towards facilitating the use of IL solvents hasfocused on physical property measurements [15,16] and on determin-ing the solubilizing ability of ILs as reflected by the infinite dilutionactivity coefficients of organic solutes dissolved in anhydrous ILs. Interms of activity coefficient measurements, we have previously studieda series of ILs containing the 1,3-dialkylimidazolium cation [17–28],the tetraalkylammonium cation [22,29], the tetraalkylphosphoniumcation [30,31], the 1,1-dialkylpyrrolidinium cation [32–35], the 1,4-dialkylpyridinium cation [26], the 1,1-dialkylpiperidinium cation [34,35], the 1-alkylquinuclidinium cation [36], and several dicationic [27]and tricationic [37] ILs. The specific ILs studied are listed in Table 1according to cation type. The results of our experimental activity

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Table 1List of ionic liquids studied.

Ionic liquid Ref.

1,3-Dialkylimidazolium cation1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [20]1-Ethyl-3-methylimidazolium dicyanamide [22]1,3-Dimethoxyimidazolium bis(trifluoromethylsulfonyl)imide [21]1-(Methylethylether)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [21]1-Ethanol-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [21]1-Hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [24]1-Butyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide [24]1,3-Didecyl-2-methylimidazolium bis(trifluoromethylsulfonyl)imide [24]1-Ethyl-3-methylimidazolium methanesulfonate [24]1-(3-Cyanopropyl)-3-methylimidazolium dicyanamide [21]1-Ethyl-3-methylimidazolium tetracyanoborate [28]1-Ethyl-3-methylimidazolium methylphosphonate [25]1,3-Dimethylimidazolium methylphosphonate [25]1-Ethanol-3-methylimidazolium tetrafluoroborate [17]1-Ethanol-3-methylimidazolium hexafluorophosphate [17]1,3-Dimethylimidazolium dimethylphosphate [17]1-Ethyl-3-methylimidazolium diethylphosphate [17]1-Butyl-3-methylimidazolium tetrafluoroborate [23]1-Hexadecyl-3-methylimidazolium tetrafluoroborate [19]1-Butyl-3-methylimidazolium hexafluorophosphate [20]1-Butyl-3-methylimidazolium octyl sulfate [18]1-Methyl-2-propoxymethylimidazolium bis(trifluoromethylsulfonyl)imide [27]1-Methyl-3-propoxymethylimidazoilum tetrafluoroborate [27]1-Methyl-3-propoxymethylimidazolium dicyanamide [27]2-Methyl-1-octyl-3-propoxymethylimidazolium bis(trifluoromethylsulfonyl)imide [27]2-Methyl-1-octyl-3-propoxymethylimidazolium dicyanamide [27]1-Benzyl-3-propoxymethylimidazolium bis(trifluoromethylsuflonyl)imide [27]1-Benzyl-3-propoxymethylimidazolium tetrafluoroborate [27]1-Benzyl-3-propoxymethylimidazoium dicyanamide [27]1-Ethyl-3-methylimidazolium tosylate [18]1-Butyl-3-methylimidazolium tricyanomethanide [26]

Tetraalkylammonium cationTrimethyl(hexyl)ammonium bis(trifluoromethylsulfonyl)amide [22]Decyl(trimethyl)ammonium bis(trifluoromethylsulfonyl)imide [29]Methyl(tributyl)ammonium bis(trifluoromethylsulfonyl)imide [29]Octyl(trimethyl)ammonium bis(trifluoromethylsulfonyl)imide [29]Tetraoctylammonium bis(trifluoromethylsulfonyl)imide [29]

Tetraalkylphosphonium cationTrihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide [30]Trihexyl(tetradecyl)phosphonium L-lactate [31]Trihexyl(tetradecyl)phosphonium (1S)-(+)-10-camphorsulfonate [31]

1,1-Dialkylpyrrolidinium cation1-Butyl-1-methylpyrrolidinium thiocyanate [34]1-Butyl-1-methylpyrrolidinium tetracyanoborate [35]1-Propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [32]1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [32]1-Pentyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [32]1-Hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [33]1-Octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [33]1-Decyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [33]

1,4-Dialkylpyridinium cation1-Butyl-4-methylpyridinium tricyanomethanide [26]

1,1-Dialkylpiperidinium cation1-Propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide [34]1-Butyl-1-methylpiperdidinium bis(trifluoromethylsulfonyl)imide [35]

1-Alkylquinuclidinium cation1-Hexylquinuclidinium bis(trifluoromethylsulfonyl)imide [36]1-Octylquinuclidinium bis(trifluoromethylsulfonyl)imide [36]

Miscellaneous dicationic3,3′-[1,7-(2,6-Dioxaheptane)]bis(1-methylimidazolium) dicyanamide [27]3,3′-[1,7-(2,6-Dioxaheptane)]bis(2-methyl-1-octylimidazolium)tetrafluoroborate [27]3,3′-[1,7-(2,6-Dioxaheptane)]bis(2-methy-1-octylimidazolium)dicyanamide [27]3,3′-[1,7-(2,6-Dioxaheptane)]bis(1-benzylimidazolium)dicyanamide [27]1,1′-[1,7-(2,6-Dioxaheptane)]bis(4-dimethylaminopyridinium)bis(trifluoromethylsulfonyl)imide [27]3,3′-[1,7-(2,6-Dioxaheptane)]bis(2-methy-1-octylimidazolium)bis(trifluoromethylsulfonyl)imide [27]

Miscellaneous tricationic3,3′,3″-[1,2,3-Propanetriyltris(oxymethylene)]tris[1-methylimidazolium]bis(trifluoromethylsulfonyl)imide [37]3,3′,3″-[1,2,3-Propanetriyltris(oxymethylene)]tris[1-(phenylmethyl)imidazolium]bis(trifluoromethylsulfonyl)imide [37]1,1′,1′-[1,2,3-Propanetriyltris(oxymethylene)]tris[4-(dimethylamino)pyridinium]bis(trifluoromethylsulfonyl)imide [37]

296 F. Mutelet et al. / Journal of Molecular Liquids 222 (2016) 295–312

Table 1 (continued)

Ionic liquid Ref.

3,3′,3″-[1,2,3-Propanetriyltris(oxymethylene)]tris[1-methylimidazolium]dicyanamide [37]3,3′,3″-[1,2,3-Propanetriyltris(oxymethylene)]tris[2-methyl-1-octyl-imidazolium]bis(trifluoromethylsulfonyl)imide [37]3,3′,3″-[1,2,3-Propanetriyltris(oxymethylene)]tris[2-methyl-1-octylimidazolium]tetrafluoroborate [37]

297F. Mutelet et al. / Journal of Molecular Liquids 222 (2016) 295–312

coefficient measurements have led to the development of IL-specificAbrahammodel correlations for the various IL studied, as well as the cal-culation of ionic-specific equation coefficients for the Abraham model[38–41] and the determination of group fragment values [42,43] forpredicting both gas-to-liquid partition coefficients and infinite dilutionactivity coefficients for solutes dissolved in ILs. The ion-specific equationcoefficients and fragment group values thatwe have obtained during thecourse of our studies can be used to make predictions for many ILs thathave not yet been synthesized nor studied.

As a continuation of our past experimental efforts, we havemeasuredthe infinite dilution activity coefficients and gas-to-liquid partitioncoefficients of 42 to 47 organic solutes dissolved in anhydrouspropyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide ([PM2iPAm]+ [Tf2N]−), hexyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide ([HM2iPAm]+ [Tf2N]−), 2-hydroxyethyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide([EtOHM2iPAm]+[Tf2N]−), cyanomethyl(dimethyl)isopropylammoniumbis(trifluoromethyl-sulfonyl)imide ([CNMeM2iPAm]+[Tf2N]−),and N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminiumdi[bis(trifluoromethylsulfonyl)imide] ([C1,9(M2iPAm)2]2+[Tf2N]−2).The chemical structures of these five ionic liquids are given in Fig. 1.The measured experimental partition coefficient data will be used toderive Abraham model correlations for each of the five individualionic liquids, as well as ionic-specific equation coefficients for the fivedifferent tetraalkylammonium cations. As an informational note, thetetraalkylammonium ILs that we have studied thus far have containedonly non-functionalized linear alkyl chains. This represents that firsttime that we have studied tetraalkylammonium cations containingeither branched alkyl chains or functionalized alkyl chains. The experi-mental partition coefficient data determined during this study will beavailable to us when we decide to update our existing functionalgroup values for the fragment group version of the Abraham model.Our fragment group method does not have a numerical value for thetertiary carbon atom group, –C(H)b.

Fig. 1. Molecular structures of cations in the IL solvents propyl(dimethyl)isopropylamisopropylammonium bis(trifluoromethylsulfonyl)imide ([HM2iPAm]+[Tf2N]−), 2-hydroxyethyl(dcyanomethyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide ([CNMeMdi[bis(trifluoromethylsulfonyl)imide] ([C1,9(M2iPAm)2]2+[Tf2N]−2).

2. Experimental methods

2.1. Preparation of alkyl(dimethyl)isopropyl ammoniumbis(trifluoromethylsulfonyl)imide ionic liquids

2.1.1. Propyl(dimethyl)isopropylammonium bromide, ([PM2iPAm]+[Br]−)In a 500 mL round-bottomed flask, 78.32 g of N,N-

dimethylisopropylamine (≥99%, 0.898mol) and 150mL of ethyl acetate(EtOAc)were taken and the solutionflask chilled in an ice bath for 30min.Chilled 1-bromopropane (118.17 g; 99%, 0.944mol)was added slowly viaa dropping funnel to the reactionmixture over a period of 45min. This re-actionmixturewas stirred in an ice bath for 30min and thenat roomtem-perature for twodays. The obtainedwhite solidwas filtered,washedwithEtOAc (3 × 150mL) and dried under vacuum overnight at 60 °C to obtainthe desired product ([PM2iPAm]+[Br]−) as a pristinely white solid (ca.20% yield) suitable for spec-grade applications. 1H NMR (300 MHz,D2O): δ 3.80–3.63 (m, 1H), 3.33–3.27 (m, 2H), 2.98 (s, 6H), 1.88–1.71(m, 2H), 1.38 (dd, J= 1.8, 6.6 Hz, 3H), 0.98 (m, 6H).

2.1.2. Propyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide ([PM2iPAm]+[Tf2N]

−)A solution of 35.9 g (0.171 mol) of [PM2iPAm]+[Br]− was dissolved

in 30 mL of 18.2 MΩ cm NANOpure water and added dropwise to asolution prepared by dissolving 51.6 g (0.180 mol) of lithiumbis(trifluoromethylsulfonyl)imide [LiTf2N] in 30 mL of NANOpurewater. The cloudymixturewas stirred for a few hours and then allowedto settle down. The aqueous phase was decanted and the lower phasethen washed multiple times (6 × 30 mL) with NANOpure water untilno residual halidewas detected in the aqueous phase using concentratedsilver nitrate. The resultant liquid was dried under high vacuum at 60 °Cfor two days, resulting a viscous colorless IL with a yield of 53.5 g (76%).1H NMR (300 MHz, CDCl3): δ 3.80–3.62 (m, 1H), 3.26–3.12 (m, 2H), 3.0(s, 3H), 2.93 (s, 3H), 1.88–1.67 (m, 2H), 1.42 (d, J = 6.6 Hz, 3H), 1.47–1.30 (d, J= 6.6 Hz, 3H), 1.1–0.92 (m, 3H).

monium bis(trifluoromethylsulfonyl)imide ([PM2iPAm]+[Tf2N]−), hexyl(dimethyl)imethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide ([EtOHM2iPAm]+[Tf2N]−),2iPAm]+[Tf2N]−), and N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminium

Table 2GC operating conditions for activity coefficient measurements.

Injector temperature 250 °CCarrier gas HeliumFlow rate 10 mL min−1

Column oven Isothermal (323 K–363 K)Detector type TCDDetector temperature 250 °C

Table 3Densities (ρ) for the alkyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide ILs as a function of temperatureat P = 101.33 kPa.a

T/K ρ/(kg m−3)

([CNMeM2iPAm]+[Tf2N]−)293.15 1493.4303.15 1479.2313.15 1472.2323.15 1468.0333.15 1465.1343.15 1463.1

([PM2iPAm]+[Tf2N]−)293.15 1397.0303.15 1381.6313.15 1373.8323.15 1369.2333.15 1366.1343.15 1363.9

([HM2iPAm]+[Tf2N]−)293.15 1318.0303.15 1299.5313.15 1290.3323.15 1284.3333.15 1281.0343.15 1278.4

([EtOHM2iPAm]+[Tf2N]−)323.15 1450.9333.15 1449.4343.15 1448.3

([C1,9(M2iPAm)2]2+[Tf2N]−2)323.15 1382.2333.15 1379.9343.15 1378.3

a Standard uncertainties are u(ρ)= 0.0001 g·cm−3, u(T)= 0.1 K,u(P) = ±0.1 kPa.


2.1.3. Hexyl(dimethyl)isopropylammonium bromide, ([HM2iPAm]+[Br]−)The halide precursor ([HM2iPAm]+[Br]−) was synthesized following

the same procedure used for [PM2iPAm]+[Br]−. The slow reaction of18.0 g of N,N-dimethylisopropylamine (≥99%, 0.206 mol) and 36.33 gof 1-bromohexane (99%, 0.217 mol) in 150 mL of EtOAc yielded 56% ofthe desired product ([HM2iPAm]+[Br]−) after two days. 1H NMR(300 MHz, D2O): δ 3.80–3.63 (m, 1H), 3.37–3.20 (m, 2H), 2.98 (s, 6H),1.84–1.68 (m, 2H), 1.46–1.23 (m, 12H), 0.97–0.80 (m, 3H).

2.1.4. Hexyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide, ([HM2iPAm]+[Tf2N]

−)Ion exchange was performed as for the [PM2iPAm]+[Br]− salt de-

scribed above. The colorless viscous [HM2iPAm]+[Tf2N]− IL was obtain-ed with a yield of 89%. 1H NMR (300 MHz, DMSO-d6): δ 3.73–3.54 (m,1H), 3.27–3.08 (m, 2H), 2.92 (s, 6H), 1.74–1.53 (m, 2H), 1.40–1.12 (m,12H), 0.94–0.75 (m, 3H).

2.1.5. 2-Hydroxyethyl(dimethyl)isopropylammonium bromide,([EtOHM2iPAm]+[Br]−)

[EtOHM2iPAm]+[Br]− was synthesized according to previouslyreported procedures [16]. 1H NMR (300 MHz, D2O): δ 4.12–4.03(m, 2H), 3.89–3.73 (m, 1H), 3.49 (t, J = 5.4 Hz, 2H), 3.08 (s, 6H), 1.42(d, J = 6.6 Hz, 6H).

2.1.6. 2-Hydroxyethyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide, ([EtOHM2iPAm]+[Tf2N]

−)Ion exchange was performed as for the [PM2iPAm]+[Br]− salt

described earlier. A colorless viscous [EtOHM2iPAm]+[Tf2N]− IL wasobtained with a yield of 50%. 1H NMR (300 MHz, DMSO-d6): δ 5.26(t, J = 4.8 Hz, 1H), 3.89–3.67 (m, 3H), 3.35 (t, J = 5.4 Hz, 2H), 2.98(s, 6H), 1.29 (d, J = 6.6 Hz, 6H).

2.1.7. Cyanomethyl(dimethyl)isopropylammonium bromide,([CNMeM2iPAm]+[Br]−)

The halide precursor [CNMeM2iPAm]+[Br]− was synthesized usinga procedure similar to that for [PM2iPAm]+[Br]−. The reaction of30.0 g of N,N-dimethylisopropylamine (≥99%, 0.344 mol) with 27.39 gof chloroacetonitrile (99%, 0.361 mol) in 150 mL of EtOAc afforded89% of the desired product ([HM2iPAm]+[Br]−). 1H NMR (300 MHz,DMSO-d6): δ = 5.07 (s, 2H), 3.98–3.82 (m, 1H), 3.17 (s, 6H), 1.36(d, J = 6.3 Hz, 6H).

2.1.8. Cyanomethyl(dimethyl)isopropylammoniumbis(trifluoromethylsulfonyl)imide, ([CNMeM2iPAm]+[Tf2N]

−)Ion exchange was performed as for the [PM2iPAm]+[Br]− salt

described already. A colorless viscous [CNMeM2iPAm]+[Tf2N]− IL wasobtained with a yield of 63%. 1H NMR (300 MHz, DMSO-d6): δ = 4.81(s, 2H), 3.82–3.76 (m, 1H), 3.12 (s, 6H), 1.35 (d, J = 6.6 Hz, 6H).

2.1.9. N,N,N′,N′-Tetramethyl-N,N′-diisopropyl-1,9-nonanediaminiumdibromide, ([C1,9(M2iPAm)2]

2+[Br]−2)In a typical synthesis, 9.18 g of N,N-dimethylisopropylamine (≥99%,

0.105 mol), 10 g of 1,9-dibromononane (≥99%, 0.034 mol), and 25 mLof EtOAc were combined in a 60 mL pressure tube (Ace Glass, Inc.)equipped with a FETFE® O-ring and sealed. The reaction mixture wasallowed to react at 90 °C overnight. The obtained white solid wasfiltered, washed with EtOAc (3 × 120 mL) and dried under vacuum forovernight at 60 °C to obtain 70% of the desired dicationic product([C1,9(M2iPAm)2]2+[Br]−2). 1H NMR (300 MHz, D2O): δ 3.85–3.67(m, 2H), 3.40–3.24 (m, 4H), 3.02 (s, 12H), 1.91–1.72 (m, 4H), 1.54–1.32 (m, 22H).

2.1.10. N,N,N′,N′-Tetramethyl-N,N′-diisopropyl-1,9-nonanediaminiumdi[bis(trifluoromethylsulfonyl)imide], ([C1,9(M2iPAm)2]2+[Tf2N]

−2)

In a typical preparation, 9.40 g (0.021 mol) of [C1,9(M2iPAm)2]2+

[Br]−2 was dissolved in 20 mL of NANOpure water and then added to

11.78 g (0.041 mol) of lithium bis(trifluoromethylsulfonyl)imide[LiTf2N] predissolvedwithin 15mLof NANOpurewater, giving a slightlyyellow solid precipitate. To this mixture was added 100 mL of EtOAc,followed by stirring for a few hours. The aqueous phase was removedusing a separatory funnel. The organic layer was washed multipletimes (6 × 30 mL) with NANOpure water until no residual halide wasdetectable in the aqueous phase (AgNO3 test). The solventwas removedin vacuo and the resultant yellowish glassy material dried under highvacuum at 60 °C for two days, yielding 6.0 g (51%) of product. 1H NMR(300 MHz, DMSO-d6): δ 3.73–3.56 (m, 2H), 3.26–3.13 (m, 4H), 2.91(s, 12H), 1.73–1.57 (m, 4H), 1.44–1.15 (m, 22H).

2.2. Chromatographic instrumentation and experimental procedures

The experimental procedures used for the determination of activitycoefficients were described in previous works [17-24]. A Bruker 450gas chromatograph equipped with a heated on-column injector anda thermal conductivity detector (TCD) detector was used for themeasurements. The GC operating conditions are given in Table 2. Thedead time of the packed column was determined using air. Heliumcarrier gas flow rate was measured using an Alltech Digital Flow

Table 4Activity coefficients at infinite dilution (γ1,2

∞ ) for organic solutes in [PM2iPAm]+[Tf2N]−.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Hexane 17.043 15.493 14.083 13.197 12.1383-Methylpentane 15.145 13.698 12.583 11.822 10.897Heptane 24.982 22.888 20.908 19.106 17.7012,2,4-Trimethylpentane 24.767 22.597 20.868 19.492 18.088Octane 36.510 33.299 30.300 28.068 25.884Nonane 57.877 52.125 46.837 42.662 38.929Decane 75.442 67.816 61.587 56.897 52.075Undecane 109.57 97.310 86.637 78.857 71.195Dodecane 150.64 133.28 119.68 108.12 97.853Tridecane 219.93 188.17 167.71 151.62 134.62Tetradecane 300.89 263.12 230.10 203.48 181.23Methylcyclopentane 10.731 10.063 9.449 9.025 8.536Cyclohexane 10.811 10.000 9.169 8.585 7.992Methylcyclohexane 14.813 13.766 12.690 11.705 10.956Benzene 1.092 1.104 1.110 1.119 1.126Toluene 1.515 1.535 1.557 1.576 1.595Ethylbenzene 2.316 2.334 2.352 2.368 2.384m-Xylene 2.168 2.191 2.214 2.234 2.254p-Xylene 2.171 2.179 2.184 2.192 2.198o-Xylene 1.976 2.001 2.032 2.061 2.0851-Hexene 9.069 8.617 8.174 7.776 7.4361-Hexyne 3.384 3.338 3.297 3.244 3.2091-Heptyne 4.870 4.814 4.722 4.665 4.6032-Butanone 0.593 0.549 0.508 0.482 0.4502-Pentanone 0.918 0.932 0.942 0.960 0.9713-Pentanone 0.849 0.872 0.892 0.922 0.9411,4-Dioxane 0.743 0.750 0.756 0.760 0.766Methanol 1.362 1.258 1.161 1.099 1.025Ethanol 1.767 1.631 1.493 1.396 1.2981-Propanol 2.196 1.999 1.834 1.682 1.5562-Propanol 2.021 1.862 1.717 1.597 1.4892-Methyl-1-propanol 2.586 2.350 2.151 2.017 1.8611-Butanol 2.865 2.573 2.318 2.174 1.980Diethyl ether 2.733 2.728 2.718 2.712 2.705Diisopropyl ether 6.981 6.728 6.554 6.360 6.188Chloroform 0.930 0.960 0.990 1.028 1.055Dichloromethane 0.719 0.755 0.776 0.813 0.839Tetrachloromethane 2.888 2.888 2.888 2.889 2.889Acetonitrile 0.515 0.515 0.515 0.516 0.515Nitromethane 0.593 0.583 0.574 0.566 0.5581-Nitropropane 0.787 0.790 0.795 0.798 0.801Triethylamine 9.253 9.015 8.638 8.373 8.130Pyridine 0.639 0.645 0.654 0.660 0.667Thiophene 0.973 0.982 0.990 0.998 1.005Tetrahydrofuran 0.799 0.810 0.655 0.857 0.773Ethyl acetate 0.996 1.003 1.005 1.010 1.014

a Standard uncertainties u are u(γ1,2∞ ) = 3%, u(T) = 0.1 K.

Table 5Logarithm of the partition coefficient (log K) for organic solutes in [PM2iPAm]+[Tf2N]−.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Hexane 0.852 0.757 0.671 0.582 0.5083-Methylpentane 0.820 0.732 0.647 0.560 0.489Heptane 1.142 1.022 0.915 0.817 0.7232,2,4-Trimethylpentane 1.131 1.019 0.912 0.810 0.720Octane 1.427 1.287 1.162 1.041 0.933Nonane 1.711 1.551 1.407 1.269 1.143Decane 1.997 1.818 1.652 1.493 1.352Undecane 2.275 2.076 1.896 1.723 1.569Dodecane 2.557 2.342 2.140 1.953 1.781Tridecane 2.835 2.608 2.386 2.177 1.995Tetradecane 3.121 2.863 2.629 2.411 2.209Methylcyclopentane 1.094 0.985 0.885 0.787 0.700Cyclohexane 1.222 1.114 1.020 0.926 0.843Methylcyclohexane 1.380 1.258 1.152 1.054 0.960Benzene 2.219 2.069 1.931 1.802 1.681Toluene 2.541 2.371 2.214 2.069 1.935Ethylbenzene 2.770 2.587 2.415 2.255 2.106

(continued on next page)


Table 5 (continued)

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

m-Xylene 2.861 2.669 2.493 2.331 2.184p-Xylene 2.843 2.655 2.479 2.312 2.156o-Xylene 2.989 2.795 2.615 2.450 2.2981-Hexene 1.047 0.937 0.836 0.744 0.6561-Hexyne 1.608 1.468 1.337 1.215 1.0991-Heptyne 1.895 1.739 1.596 1.459 1.3302-Butanone 2.442 2.283 2.134 1.987 1.8632-Pentanone 2.678 2.505 2.345 2.189 2.0463-Pentanone 2.671 2.496 2.336 2.181 2.0411,4-Dioxane 2.748 2.573 2.411 2.260 2.117Methanol 1.937 1.802 1.680 1.557 1.450Ethanol 2.099 1.945 1.809 1.675 1.5551-Propanol 2.388 2.220 2.061 1.913 1.7732-Propanol 2.137 1.973 1.824 1.685 1.5572-Methyl-1-propanol 2.536 2.354 2.187 2.026 1.8871-Butanol 2.700 2.513 2.344 2.174 2.032Diethyl ether 1.148 1.029 0.919 0.816 0.720Diisopropyl ether 1.239 1.117 1.000 0.893 0.794Chloroform 2.007 1.859 1.720 1.588 1.468Dichloromethane 1.706 1.580 1.467 1.351 1.246Tetrachloromethane 1.736 1.596 1.466 1.345 1.233Acetonitrile 2.574 2.426 2.288 2.158 2.037Nitromethane 2.848 2.688 2.539 2.399 2.2701-Nitropropane 3.213 3.021 2.844 2.681 2.529Triethylamine 1.432 1.291 1.165 1.043 0.927Pyridine 3.028 2.850 2.682 2.527 2.382Thiophene 2.334 2.181 2.038 1.905 1.782Tetrahydrofuran 2.146 2.001 1.964 1.728 1.660Ethyl acetate 2.237 2.081 1.937 1.803 1.679

a Standard uncertainties u are u(K) = 3%, u(T) = 0.1 K.


Check Mass Flowmeter. The temperature of the oven was measuredwith a Pt 100 probe and controlled within 0.1 K. Data were collectedand treated with Galaxie software (Varian).

The preparation of columns was described in detail in our previouspublications [20–24]. Packed columns of 1-m length containing between30 and 40% IL stationary phase coated onto a 60–80 mesh Chromosorb


∞ ) for organic solutes in [HM2iPAm]+[Tf2N]−.a

Solutes

T/K

323.15 K 333.15 K

Hexane 8.164 7.8433-Methylpentane 7.288 6.948Heptane 11.178 10.4652,2,4-Trimethylpentane 10.900 10.318Octane 15.124 14.142Nonane 22.511 20.908Decane 27.855 25.705Undecane 37.685 34.606Dodecane 48.892 45.043Tridecane 67.463 62.064Tetradecane 87.988 79.489Methylcyclopentane 5.489 5.246Cyclohexane 5.468 5.157Methylcyclohexane 7.032 6.685Cycloheptane 7.085 6.682Benzene 0.815 0.828Toluene 1.071 1.093Ethylbenzene 1.535 1.562m-Xylene 1.475 1.496p-Xylene 1.478 1.500o-Xylene 1.352 1.4001-Hexene 4.921 4.7621-Hexyne 2.190 2.1771-Heptyne 2.921 2.9102-Butanone 0.457 0.4252-Pentanone 0.649 0.6643-Pentanone 0.602 0.6211,4-Dioxane 0.629 0.636Methanol 1.316 1.213

WHP support material were prepared by a rotary evaporation method.Briefly, the desired ILwas dissolved in ethanol in the presence of a precisemass of Chromosorb WHP. Ethanol was then removed from the mixtureusing rotary evaporation. The support was equilibrated at 343 K undervacuum during 6 h. Then, the conditioning of the packed columns wasperformed at 373 K over 12 h using a gas flow rate of 20 cm3 min−1.

343.15 K 353.15 K 363.15 K

7.379 7.057 6.8416.552 6.437 6.0479.889 9.450 8.9199.902 9.432 8.942

13.246 12.713 12.02719.302 18.183 16.92323.656 22.458 21.12331.691 29.549 27.63241.302 38.515 36.01455.343 51.362 47.10871.605 67.129 61.8794.955 4.814 4.5764.916 4.704 4.5306.306 6.071 5.8076.294 6.040 5.7630.831 0.854 0.8651.109 1.152 1.1811.578 1.624 1.6421.519 1.578 1.6231.513 1.542 1.5401.404 1.465 1.5094.599 4.501 4.4632.153 2.144 2.1182.899 2.889 2.8790.395 0.377 0.3610.676 0.694 0.7020.642 0.669 0.6890.643 0.658 0.6641.128 1.064 1.001

Table 6 (continued)

Solutes

T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Ethanol 1.507 1.422 1.342 1.274 1.1931-Propanol 1.815 1.651 1.514 1.406 1.2882-Propanol 1.701 1.549 1.442 1.348 1.2722-Methyl-1-propanol 1.998 1.820 1.667 1.582 1.4781-Butanol 2.143 1.934 1.780 1.679 1.575Chloroform 0.727 0.750 0.771 0.803 0.820Dichloromethane 0.585 0.609 0.629 0.655 0.673Tetrachloromethane 1.964 1.963 1.961 1.960 1.958Acetonitrile 0.503 0.502 0.500 0.498 0.496Nitromethane 0.588 0.576 0.565 0.559 0.5481-Nitropropane 0.670 0.670 0.670 0.670 0.670Triethylamine 4.908 4.821 4.745 4.674 4.613Pyridine 0.518 0.521 0.530 0.546 0.556Thiophene 0.759 0.765 0.777 0.805 0.822Acetone 0.405 0.410 0.416 0.423 0.430Tetrahydrofuran 0.586 0.594 0.606 0.630 0.641Ethyl acetate 0.739 0.747 0.763 0.789 0.804Water 4.144 3.560 3.244 2.871 2.614


Table 7Logarithm of the partition coefficient (log K) for organic solutes in [HM2iPAm]+[Tf2N]−.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Hexane 1.129 1.010 0.910 0.811 0.7153-Methylpentane 1.096 0.985 0.888 0.782 0.703Heptane 1.449 1.320 1.197 1.081 0.9792,2,4-Trimethylpentane 1.445 1.317 1.194 1.083 0.984Octane 1.768 1.617 1.479 1.342 1.223Nonane 2.078 1.905 1.749 1.597 1.462Decane 2.387 2.197 2.025 1.854 1.701Undecane 2.696 2.483 2.290 2.107 1.938Dodecane 3.003 2.770 2.559 2.359 2.173Tridecane 3.306 3.048 2.825 2.605 2.408Tetradecane 3.601 3.341 3.094 2.850 2.634Methylcyclopentane 1.343 1.226 1.123 1.017 0.929Cyclohexane 1.476 1.359 1.248 1.144 1.047Methylcyclohexane 1.661 1.530 1.413 1.297 1.193Cycloheptane 1.943 1.801 1.672 1.546 1.432Benzene 2.304 2.151 2.014 1.876 1.753Toluene 2.649 2.476 2.318 2.162 2.023Ethylbenzene 2.906 2.718 2.546 2.377 2.226m-Xylene 2.986 2.793 2.614 2.440 2.284p-Xylene 2.967 2.775 2.596 2.423 2.268o-Xylene 3.111 2.907 2.733 2.555 2.3971-Hexene 1.271 1.152 1.044 0.939 0.8361-Hexyne 1.754 1.611 1.479 1.353 1.2371-Heptyne 2.075 1.915 1.767 1.623 1.4922-Butanone 2.513 2.351 2.200 2.052 1.9172-Pentanone 2.786 2.610 2.446 2.288 2.1443-Pentanone 2.778 2.601 2.436 2.278 2.1351,4-Dioxane 2.777 2.602 2.438 2.280 2.137Methanol 1.909 1.776 1.650 1.528 1.418Ethanol 2.126 1.963 1.812 1.672 1.5491-Propanol 2.429 2.261 2.102 1.949 1.8132-Propanol 2.170 2.011 1.858 1.716 1.5822-Methyl-1-propanol 2.606 2.423 2.256 2.089 1.9451-Butanol 2.784 2.594 2.416 2.244 2.090Chloroform 2.071 1.923 1.787 1.652 1.535Dichloromethane 1.753 1.630 1.516 1.403 1.300Tetrachloromethane 1.861 1.725 1.595 1.471 1.359Acetonitrile 2.542 2.398 2.263 2.130 2.011Nitromethane 2.810 2.651 2.503 2.358 2.2271-Nitropropane 3.240 3.060 2.887 2.712 2.564Triethylamine 1.665 1.516 1.366 1.237 1.131Pyridine 3.077 2.900 2.730 2.566 2.419Thiophene 2.400 2.246 2.101 1.956 1.827Acetone 2.252 2.116 1.983 1.854 1.736Tetrahydrofuran 2.238 2.119 1.955 1.819 1.699Ethyl acetate 2.325 2.166 2.014 1.868 1.737Water 2.064 1.935 1.795 1.679 1.562




∞ ) for organic solutes in [EtOHM2iPAm]+[Tf2N]−.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

2,2,4-Trimethylpentane 51.122 44.932 40.828 36.752 33.216Octane 78.739 70.570 60.579 54.725 47.529Decane 185.89 162.42 142.96 125.58 110.61Undecane 281.77 243.51 212.46 188.27 162.64Dodecane 404.47 351.67 307.44 273.54 236.67Tridecane 605.69 520.01 447.14 396.82 343.27Tetradecane 845.65 737.27 643.37 563.26 486.82Methylcyclopentane 19.139 16.993 15.856Cyclohexane 18.982 16.826 15.661 13.987 12.828Methylcyclohexane 27.909 24.944 22.632 20.425Cycloheptane 27.280 24.428 22.103 20.224 18.224Benzene 1.548 1.547 1.546 1.545 1.544Toluene 2.271 2.273 2.275 2.278 2.280Ethylbenzene 3.636 3.614 3.599 3.584 3.572m-Xylene 3.456 3.452 3.447 3.442 3.438p-Xylene 3.297 3.290 3.284 3.278 3.274o-Xylene 3.159 3.158 3.159 3.158 3.1571-Hexene 16.014 14.451 13.609 12.579 11.6601-Hexyne 5.389 5.168 5.030 4.833 4.5961-Heptyne 8.238 7.992 7.732 7.532 7.1592-Butanone 0.462 0.438 0.414 0.400 0.3862-Pentanone 0.776 0.802 0.826 0.856 0.8643-Pentanone 0.746 0.777 0.811 0.852 0.8751,4-Dioxane 0.506 0.525 0.546 0.573 0.584Methanol 0.793 0.764 0.739 0.727 0.699Ethanol 0.994 0.956 0.925 0.908 0.8741-Propanol 1.334 1.274 1.218 1.175 1.0992-Propanol 1.119 1.081 1.057 1.036 0.9992-Methyl-1-propanol 1.755 1.650 1.580 1.536 1.4751-Butanol 1.880 1.732 1.653 1.599 1.528Diethyl ether 2.298 2.328 2.363 2.385 2.400Diisopropyl ether 5.740 5.854 5.975 6.050 6.130Chloroform 1.370 1.384 1.415 1.448 1.461Dichloromethane 0.922 0.953 0.982 1.013 1.021Tetrachloromethane 4.645 4.513 4.413 4.319 4.217Acetonitrile 0.412 0.414 0.419 0.425 0.427Nitromethane 0.556 0.550 0.546 0.542 0.540Triethylamine 1.355 1.475 1.570 1.659 1.812Thiophene 1.300 1.311 1.323 1.334 1.339Acetone 0.333 0.344 0.355 0.371 0.375Tetrahydrofuran 0.569 0.594 0.618 0.651 0.661Ethyl acetate 0.862 0.878 0.900 0.935 0.954Water 1.463 1.359 1.294 1.233 1.179



2.3. Density measurements

Densities of ILs were measured using an Anton Paar DMA 60 digitalvibrating-tube densimeter, with a DMA 512P measuring cell in the

temperature range from 293.15 to 343.15 K at atmospheric pressure.The detailed procedure was given in our previous work [32]. Allexperimental data are given in Table 3.

3. Results and discussion

3.1. Activity coefficients and selectivity at infinite dilution

Activity coefficients at infinite dilution for model solutes in [Tf2N]− based ILs studied in this work were calculated using the theoretical basisdescribed in our previous researches [29–32]. The uncertainties in infinite dilution activity coefficients (γ1,2

∞ ) and gas-to-IL partition coefficients(K) were b3% [29–32]. All experimental data measured in this work are presented in Tables 4–13.

The solubility of n-alkanes is related to the alkyl chain length; that is, an increase of the chain length leads to an increase of solubility. Nevertheless,the solubility of n-alkanes in typical ILs remains low. Functionalized ILs containing cyano or hydroxyl groups have the tendency to increase repulsiveforces between alkanes and IL. Experimental data show that activity coefficients of alkanes increase according to γ[CNMeM2iPAm]Nγ[EtOHMeiPAm]N

γ[PM2iPAm]Nγ[HM2iPAm]. In most cases, (γ1,2∞ ) values decrease with an increase of temperature. Some exceptions can be found. Indeed, the solubility of

aromatics, 1,4-dioxane, pentanone, and chloroform slightly decrease with increasing temperature. Not surprisingly, the best solubility for alcoholicsolutes is obtained with the alcohol-bearing IL [EtOHM2iPAm]+[Tf2N]−. Similar results were observed with 1-(4-sulfobutyl)-3-methylimidazoliumbased ILs [44]. Ab initio calculations have shown that the anionwill then associate with the hydroxyl group of the cation aswell as with the alcohols.This leads to a decrease in the disruption of the cation/anion interaction and a better solubility for the alcohol in functionalized ILs than in non-functionalized dialkylimidazolium based ILs. Numerous [Tf2N]− based ILs were characterized by gas chromatography and large data sets of activitycoefficients at infinite dilution can be found in the literature. We have found that most selected organic compounds studied in this work have better

Table 9Logarithm of the partition coefficient (log K) for organic solutes in [EtOHM2iPAm]+[Tf2N]−.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

2,2,4-Trimethylpentane 0.815 0.718 0.619 0.531 0.454Octane 1.092 0.959 0.859 0.749 0.667Decane 1.603 1.437 1.284 1.147 1.023Undecane 1.862 1.676 1.504 1.343 1.208Dodecane 2.126 1.918 1.728 1.548 1.396Tridecane 2.393 2.165 1.958 1.757 1.586Tetradecane 2.670 2.414 2.180 1.967 1.778Methylcyclopentane 0.841 0.756 0.658Cyclohexane 0.976 0.886 0.785 0.712 0.635Methylcyclohexane 1.102 0.998 0.898 0.811Cycloheptane 1.399 1.279 1.167 1.061 0.972Benzene 2.066 1.922 1.786 1.658 1.542Toluene 2.363 2.200 2.047 1.901 1.771Ethylbenzene 2.572 2.395 2.227 2.069 1.928m-Xylene 2.662 2.478 2.305 2.140 1.928p-Xylene 2.659 2.477 2.304 2.140 1.981o-Xylene 2.787 2.606 2.431 2.263 2.1151-Hexene 0.798 0.710 0.613 0.533 0.4591-Hexyne 1.403 1.276 1.151 1.040 0.9411-Heptyne 1.665 1.517 1.380 1.249 1.1362-Butanone 2.547 2.379 2.220 2.065 1.9282-Pentanone 2.749 2.568 2.399 2.237 2.0943-Pentanone 2.725 2.544 2.375 2.213 2.0711,4-Dioxane 2.913 2.726 2.550 2.380 2.233Methanol 2.170 2.017 1.874 1.734 1.614Ethanol 2.347 2.175 2.015 1.860 1.7241-Propanol 2.603 2.414 2.237 2.067 1.9222-Propanol 2.392 2.207 2.033 1.871 1.7282-Methyl-1-propanol 2.702 2.505 2.319 2.143 1.9861-Butanol 2.881 2.683 2.488 2.305 2.143Diethyl ether 1.221 1.091 0.983 0.870 0.770Diisopropyl ether 1.322 1.151 1.038 0.913 0.803Chloroform 1.837 1.697 1.563 1.437 1.325Dichloromethane 1.596 1.476 1.363 1.254 1.159Tetrachloromethane 1.528 1.400 1.280 1.169 1.067Acetonitrile 2.669 2.519 2.375 2.240 2.117Nitromethane 2.874 2.711 2.558 2.410 2.278Triethylamine 2.265 2.075 1.966 1.792 1.577Thiophene 2.207 2.056 1.919 1.777 1.655Acetone 2.378 2.228 2.087 1.950 1.835Tetrahydrofuran 2.291 2.139 1.987 1.845 1.726Ethyl acetate 2.298 2.137 1.983 1.834 1.703Water 2.556 2.394 2.234 2.087 1.921



solubility in ILs based on the 1-alkylquinuclidinium cation than tetraalkylammonium or dialkylpyrrolidinium analogs. Solute interactions with thedicationic [C1,9(M2iPAm)2]2+[Tf2N]− were also found to be quite similar to those observed with its monocat tetraalkylammonium analogs.

The performance of the ILs as extractant media for separation problems can be evaluated through the calculation of selectivity (S12∞ ) and infinitedilution capacity (k2∞) values using the following expressions:

S∞1;2 ¼γ∞1=IL

γ∞2=IL

ð1Þ

k∞2 ¼ 1γ∞2=IL

ð2Þ

where γ1/IL∞ and γ2/IL

∞ correspond to the infinite dilution activity coefficients of solutes 1 and 2, respectively, within the IL of interest. The performanceof selected [Tf2N]− based ILswas evaluated for hexane/benzene, hexane/pyridine, hexane/thiophene, and heptane/thiophene separations at 323.15Kand compared to N-methyl-2-pyrrolidone (NMP) and sulfolane. Results for different separation problems are compiled in Table 14, along with thereferences [32,33,36,45–51] from which the data used to calculate the selectivities and capacity factors were drawn. In the case of the hexane/benzene separation problem, numerous ILs present larger capacities than sulfolane or NMP. Five ILs with better performance than sulfolane canbe identified: N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminium di[bis(trifluoromethylsulfonyl)imide], 1-ethyl-3-methylimidazolumbis(trifluoromethylsulfonyl)imide, 1-methyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide, 4-methyl-N-butylpyridiniumbis(trifluoromethylsulfonyl)imide, and 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide. The IL 1-propyl-1-methylpyrrolidiniumbis(trifluoromethylsulfonyl)imide presents a hexane/benzene selectivity comparable to sulfolane but with a better capacity. In addition, the ILs


∞ ) for organic solutes in [CNMeM2iPAm]+[Tf2N]−.a

Solutes T/K

313.15 K 323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Octane 159.91 139.66 118.05 102.16 92.020 82.715Nonane 288.03 244.01 210.46 176.76 149.45 134.69Decane 393.98 341.68 293.82 252.44 220.38 198.58Undecane 565.01 503.47 457.04 388.45 334.78 296.57Dodecane 884.70 744.83 657.33 561.42 495.15 443.28Tridecane 1285.6 1097.7 969.46 834.34 734.01 631.22Tetradecane 1643.4 1524.3 1350.3 1174.3 1036.6 893.87Methylcyclopentane 37.396 31.737 27.607 25.430 23.074 20.497Cyclohexane 36.934 31.360 27.489 24.400 21.648 19.243Methylcyclohexane 57.070 48.968 42.844 37.470 33.622 29.799Benzene 2.291 2.253 2.217 2.196 2.165 2.139Toluene 3.363 3.357 3.350 3.343 3.337 3.331Ethylbenzene 5.681 5.605 5.541 5.479 5.471 5.417m-Xylene 5.133 5.080 5.028 4.997 4.958 4.914p-Xylene 5.073 5.032 4.961 4.918 4.881 4.836o-Xylene 4.523 4.513 4.504 4.495 4.486 4.4821-Hexene 29.129 24.792 24.346 21.151 20.1091-Hexyne 9.607 9.048 8.483 8.022 7.8791-Heptyne 15.279 14.525 13.784 13.089 12.434 11.6922-Butanone 0.652 0.628 0.585 0.547 0.521 0.5022-Pentanone 1.100 1.112 1.131 1.148 1.170 1.1803-Pentanone 0.964 1.000 1.029 1.062 1.105 1.131Methanol 1.426 1.319 1.225 1.150 1.093 1.039Ethanol 2.097 1.916 1.757 1.633 1.530 1.4201-Propanol 2.971 2.720 2.458 2.263 2.088 1.9382-Propanol 2.703 2.441 2.226 2.067 1.924 1.8722-Methyl-1-propanol 4.118 3.661 3.291 3.035 2.846 2.6961-Butanol 4.575 3.931 3.484 3.194 2.986 2.804Diethyl ether 5.337 5.004 4.827 4.781 4.574Diisopropyl ether 18.874 16.873 16.938 15.538 14.838 14.133Chloroform 2.211 2.211 2.210 2.210 2.208 2.208Dichloromethane 1.224 1.273 1.294 1.332 1.362Tetrachloromethane 8.577 8.106 7.655 7.352 7.146 6.763Acetonitrile 0.474 0.473 0.475 0.481 0.488 0.497Nitromethane 0.591 0.591 0.591 0.591 0.591 0.5911-Nitropropane 1.040 1.040 1.040 1.040 1.040 1.040Triethylamine 21.770 21.555 21.434 21.332 21.115 20.905Pyridine 0.746 0.771 0.791 0.796 0.825 0.848Thiophene 1.883 1.882 1.883 1.878 1.884 1.883Acetone 0.437 0.453 0.464 0.461 0.474 0.478Ethyl acetate 1.119 1.138 1.152 1.167 1.215 1.220Water 2.858 2.453 2.281 2.103 1.954 1.709



propyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,and 1-butyl-3-methylpyrrolidinum bis(trifluoromethylsulfonyl)imide have slightly lower selectivity values (S12∞ ) than sulfolane; however,their capacity values (k2∞) are larger.

3.2. Development of Abraham model correlations for solute partition coefficients

Selectivities and capacity factors can be calculated for any pair of organic compounds for which infinite dilution activity coefficients have beenexperimentally determined. Activity coefficient measurements can be very time consuming. This is particularly the case in studies involving manyorganic solutes dissolved in a series of IL solvents or select organic solutes dissolved in many different IL solvents of varying polarity andhydrogen-bonding character as would be needed to solve practical chemical separation problems. Predictive methods based on linear free energyrelationships (LFERs) or quantitative structure-property relationships (QSPRs) can reduce the number of experimental measurements required tomake informed decisions. The Abraham solvation parameter is among themore versatile of the LFERs that have been developed for predicting soluteproperties in both traditional organic solvents and ILs. Themethod is capable of predicting the logarithm of thewater-to-ionic liquid and gas-to-ionicliquid partition coefficients, log P and log K, respectively [28–36]:

logP ¼ cp;il þ ep;il � Eþ sp;il � Sþ ap;il � A þ bp;il � Bþ vp;il � V ð3Þ

logK ¼ ck;il þ ek;il � Eþ sk;il � Sþ ak;il � A þ bkil � Bþ lk;il � L ð4Þ

as well as the solubility of organic nonelectrolyte solutes dissolved in anhydrous ILs:

log CS;organic=CS;water� � ¼ cp;il þ ep;il � Eþ sp;il � Sþ ap;il � A þ bp;il � Bþ vp;il � V ð5Þ

log CS;organic=CS;gas� � ¼ ck;il þ ek;il � Eþ sk;il � Sþ ak;il � A þ bkil � Bþ lk;il � L ð6Þ

Table 11Logarithm of the partition coefficient (log K) for organic solutes in [CNMeM2iPAm]+[Tf2N]−.a

Solutes T/K

313.15 K 323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Octane 0.985 0.848 0.741 0.637 0.528 0.431Nonane 1.238 1.089 0.948 0.833 0.728 0.607Decane 1.526 1.344 1.185 1.042 0.908 0.774Undecane 1.836 1.616 1.408 1.248 1.098 0.953Dodecane 2.082 1.866 1.652 1.472 1.295 1.129Tridecane 2.390 2.140 1.900 1.692 1.496 1.327Tetradecane 2.729 2.420 2.156 1.924 1.707 1.520Methylcyclopentane 0.703 0.627 0.550 0.459 0.382 0.323Cyclohexane 0.847 0.763 0.678 0.598 0.527 0.464Methylcyclohexane 0.963 0.864 0.768 0.685 0.599 0.528Benzene 2.059 1.908 1.769 1.638 1.518 1.406Toluene 2.376 2.198 2.035 1.885 1.746 1.619Ethylbenzene 2.577 2.389 2.214 2.051 1.895 1.753m-Xylene 2.693 2.494 2.312 2.142 1.988 1.849p-Xylene 2.676 2.481 2.301 2.130 1.968 1.817o-Xylene 2.838 2.633 2.445 2.273 2.115 1.9691-Hexene 0.688 0.614 0.489 0.427 0.3341-Hexyne 1.313 1.184 1.066 0.954 0.8331-Heptyne 1.574 1.424 1.285 1.156 1.036 0.9292-Butanone 2.592 2.420 2.258 2.104 1.956 1.8192-Pentanone 2.780 2.598 2.424 2.262 2.107 1.9653-Pentanone 2.796 2.603 2.427 2.263 2.105 1.965Methanol 2.102 1.954 1.817 1.687 1.563 1.447Ethanol 2.231 2.067 1.916 1.773 1.639 1.5191-Propanol 2.483 2.299 2.134 1.973 1.823 1.6812-Propanol 2.231 2.058 1.899 1.747 1.607 1.4602-Methyl-1-propanol 2.582 2.388 2.211 2.041 1.880 1.7291-Butanol 2.756 2.566 2.384 2.208 2.039 1.884Diethyl ether 0.990 0.889 0.785 0.677 0.593Diisopropyl ether 0.961 0.859 0.719 0.628 0.528 0.438Chloroform 1.780 1.634 1.500 1.375 1.259 1.150Dichloromethane 1.590 1.461 1.348 1.236 1.130Tetrachloromethane 1.418 1.291 1.176 1.064 0.955 0.867Acetonitrile 2.773 2.614 2.464 2.321 2.185 2.056Nitromethane 3.033 2.853 2.685 2.529 2.384 2.2481-Nitropropane 3.301 3.095 2.905 2.731 2.569 2.419Triethylamine 1.226 1.068 0.918 0.776 0.644 0.520Pyridine 3.153 2.950 2.764 2.599 2.433 2.281Thiophene 2.213 2.051 1.901 1.763 1.632 1.512Acetone 2.412 2.250 2.103 1.979 1.849 1.735Ethyl acetate 2.357 2.183 2.024 1.876 1.726 1.601Water 2.480 2.337 2.174 2.029 1.892 1.792



where (CS,organic/CS,water) and (CS,organic/CS,gas) denote the solute's molar solubility ratios, with the subscripts indicating the phase to which the solutemolar concentrations pertain. Partition coefficients predicted through Eqs. (3) and (4) can be converted to infinite dilution activity coefficients,γsolute

∞ ,using standard thermodynamic relationships (see Eq. (7)):

logK ¼ logP þ logKW ¼ logRT

γsolute∞Psolute

o Vsolvent

� �ð7Þ

and a prior knowledge of the solute's gas-to-water partition coefficient, Kw. In Eq. (7), R is the universal constant law constant, Vsolvent is the molarvolume of the IL solvent, Psoluteo is the vapor pressure of the solute at the system temperature, and T is the system temperature.

The Abraham model describes the various solute–solvent interactions that are believed to be present in solution in terms of products of soluteproperties (called solute descriptors) and solvent properties (called equation or process coefficients). The solute properties are denoted by thecapitalized alphabetical letters on the right-hand side of Eqs. (3) to (6), while the solvent properties are denoted by the lowercase alphabeticalcharacters. Solute descriptors are available for N5000 different organic and inorganic compounds, and are defined as follows: the solute excessmolar refractivity in units of (cm3 mol−1)/10 (E), the solute dipolarity/polarizability (S), the overall or summation hydrogen-bond acidity andbasicity (A and B, respectively), the McGowan volume in units of (cm3 mol−1)/100 (V), and the logarithm of the gas-to-hexadecane partitioncoefficient at 298 K (L). Solvent/process coefficients describe the complimentary solvent property and, when combined with the appropriate solutedescriptor, the product describes a particular type of molecular interaction. For example, the lowercase characters ail and bil refer to the hydrogen-bond basicity and hydrogen-bond acidity of the dissolving solventmedium. The products ail·A and bil·B describe the hydrogen-bonding interactionsthat occur between the acidic sites on the solute molecule and the basic site(s) of the solvent (ail·A), and that occur between the basic sites on thesolute molecule and acidic sites on the solvent molecule (bil·B), respectively. To date, Abraham model correlations have been reported for N60different ILs. The derived correlations allow one to predict log K and log P values for solutes dissolved in anhydrous ILs at 298.15 K.

The numerical log K (at 298.15 K) values used in the present study were calculated from the standard thermodynamic log K versus 1 / T linearrelationship based on the measured values at 323.15 K and 333.15 K, as these were the two lowest temperatures studied for each IL. The linearextrapolation should be valid as the measurements were performed at temperatures not too far removed from the desired temperature of


∞ ) for organic solutes in [C1,9(M2iPAm)2]2+[Tf2N]−2.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Hexane 21.057 18.349 16.977 15.188 14.3583-Methylpentane 18.687 16.535 14.701 13.244 12.594Heptane 29.935 27.426 24.502 22.092 19.9812,2,4-Trimethylpentane 32.329 28.820 25.988 22.943 20.717Octane 44.094 40.003 35.502 32.489 29.981Nonane 69.918 62.400 56.512 51.539 45.396Decane 92.629 83.176 74.602 69.364 60.814Undecane 134.68 119.48 107.20 98.641 85.762Dodecane 187.64 167.05 150.21 137.84 122.06Tridecane 275.78 239.35 214.31 193.99 168.76Tetradecane 382.97 334.68 297.41 269.75 236.30Methylcyclopentane 12.655 11.221 10.360 9.748 9.150Cyclohexane 12.360 11.018 10.090 9.333 8.666Methylcyclohexane 17.027 15.384 14.139 13.088 11.978Cycloheptane 16.319 14.811 13.673 12.682 11.644Benzene 1.089 1.112 1.133 1.160 1.184Toluene 1.548 1.567 1.608 1.667 1.692Ethylbenzene 2.411 2.433 2.480 2.520 2.545m-Xylene 2.215 2.273 2.319 2.406 2.460p-Xylene 2.254 2.271 2.290 2.308 2.328o-Xylene 1.918 2.041 2.101 2.201 2.2421-Hexene 10.549 9.848 9.179 8.871 8.1641-Hexyne 3.837 3.755 3.705 3.665 3.6151-Heptyne 5.526 5.460 5.402 5.356 5.3072-Butanone 0.656 0.604 0.568 0.541 0.5112-Pentanone 1.020 1.036 1.058 1.082 1.1073-Pentanone 0.947 0.971 1.006 1.046 1.0751,4-Dioxane 0.775 0.790 0.802 0.822 0.823Methanol 1.440 1.331 1.247 1.188 1.092Ethanol 1.919 1.750 1.618 1.539 1.3971-Propanol 2.386 2.175 2.002 1.858 1.6932-Propanol 2.267 2.074 1.919 1.794 1.6822-Methyl-1-propanol 2.876 2.594 2.398 2.247 2.0931-Butanol 3.101 2.778 2.554 2.398 2.212Diethyl ether 3.199 3.103 3.016 2.951 2.876Diisopropyl ether 7.935 7.805 7.637 7.518 7.363Chloroform 0.989 1.016 1.035 1.093 1.127Tetrachloromethane 3.173 3.134 3.113 3.080 3.064Acetonitrile 0.567 0.566 0.565 0.565 0.564Nitromethane 0.643 0.628 0.624 0.624 0.6161-Nitropropane 0.883 0.883 0.882 0.883 0.883Triethylamine 7.389 7.672 8.089 8.357 8.665Pyridine 0.632 0.638 0.648 0.676 0.685Thiophene 0.972 0.990 1.000 1.011 1.028Acetone 0.530 0.530 0.530 0.530 0.530Tetrahydrofuran 0.734 0.736 0.740 0.904 0.750Ethyl acetate 1.129 1.138 1.143 1.187 1.223Water 3.637 3.195 2.899 2.711 2.286



298.15 K (within ca. 35 K in the worst case). The calculated log K and log P values for [PM2iPAm]+[Tf2N]− are given in Table 15, along with the nu-merical solute descriptor values of the organic compounds studied in the present communication. Partition coefficient data for [HM2iPAm]+[Tf2N]−,[EtOHM2iPAm]+[Tf2N]−, [CNMeM2iPAm]+[Tf2N]−, and [C1,9(M2iPAm)2]2+[Tf2N]−2 are displayed in Tables S1 to S4 of the Supporting Information.Each partition coefficient determination contained experimental data for aminimumof 40 different organic solutes of varying polarity and hydrogenbonding character.

Analysis of the experimental log P and log K values in Table 14 in accordance with Eqs. (3) and (4) of the Abrahammodel gave the following twoIL-specific correlations:

log P 298 Kð Þ ¼ −0:378 0:118ð Þ þ 0:115 0:114ð Þ Eþ 0:723 0:117ð Þ S− 1:061 0:178ð Þ A− 4:594 0:109ð Þ Bþ 3:388 0:094ð Þ V ðSD ¼ 0:113;N ¼ 44;R2 ¼ 0:996; and F ¼ 1889Þð8Þ

and

log K 298 Kð Þ ¼ −0:702 0:071ð Þ þ 2:532 0:064ð Þ Sþ 2:578 0:139ð Þ A þ 0:331 0:083ð Þ Bþ 0:682 0:017ð Þ L ðSD ¼ 0:096;N ¼ 46;R2 ¼ 0:985; and F ¼ 654:2Þð9Þ

where the standard error in each calculated equation coefficient is given in parenthesis immediately after the respective coefficient. The statisticalinformation associated with each correlation includes the standard deviation (SD), the number of experimental data points used in the regression

Table 13Logarithm of the partition coefficient (log K) for organic solutes in [C1,9(M2iPAm)2]2+[Tf2N]−2.a

Solutes T/K

323.15 K 333.15 K 343.15 K 353.15 K 363.15 K

Hexane 0.718 0.641 0.548 0.478 0.3933-Methylpentane 0.687 0.608 0.537 0.468 0.384Heptane 1.021 0.901 0.803 0.712 0.6282,2,4-Trimethylpentane 0.973 0.871 0.775 0.697 0.619Octane 1.303 1.165 1.051 0.935 0.826Nonane 1.586 1.431 1.283 1.145 1.034Decane 1.866 1.687 1.526 1.365 1.242Undecane 2.143 1.945 1.761 1.583 1.446Dodecane 2.419 2.201 1.999 1.805 1.643Tridecane 2.694 2.461 2.237 2.028 1.854Tetradecane 2.974 2.716 2.475 2.246 2.052Methylcyclopentane 0.980 0.896 0.803 0.711 0.628Cyclohexane 1.122 1.029 0.936 0.847 0.765Methylcyclohexane 1.277 1.168 1.062 0.963 0.879Cycloheptane 1.581 1.456 1.335 1.223 1.126Benzene 2.171 2.023 1.880 1.743 1.625Toluene 2.489 2.320 2.157 2.002 1.867Ethylbenzene 2.710 2.526 2.350 2.181 2.035m-Xylene 2.791 2.611 2.430 2.257 2.104p-Xylene 2.784 2.595 2.414 2.239 2.088o-Xylene 2.938 2.744 2.558 2.379 2.2241-Hexene 0.939 0.836 0.744 0.644 0.5741-Hexyne 1.511 1.374 1.244 1.120 1.0171-Heptyne 1.798 1.642 1.495 1.356 1.2392-Butanone 2.355 2.230 2.042 1.894 1.7652-Pentanone 2.590 2.417 2.252 2.095 1.9583-Pentanone 2.581 2.407 2.241 2.084 1.9471,4-Dioxane 2.687 2.397 2.343 2.183 2.044Methanol 1.870 1.736 1.607 1.481 1.380Ethanol 2.021 1.872 1.731 1.590 1.4801-Propanol 2.310 2.141 1.981 1.828 1.6942-Propanol 2.045 1.884 1.733 1.592 1.4612-Methyl-1-propanol 2.447 2.269 2.098 1.937 1.7941-Butanol 2.623 2.437 2.259 2.089 1.942Diethyl ether 1.038 0.944 0.832 0.744 0.638Diisopropyl ether 1.086 1.010 0.891 0.778 0.663Chloroform 1.938 1.791 1.658 1.519 1.397Tetrachloromethane 1.653 1.521 1.395 1.271 1.165Acetonitrile 2.489 2.360 2.208 2.076 1.955Nitromethane 2.771 2.613 2.460 2.314 2.1841-Nitropropane 3.120 2.941 2.762 2.594 2.444Triethylamine 1.386 1.319 1.152 0.973 0.857Pyridine 2.991 2.812 2.643 2.474 2.328Thiophene 2.293 2.145 1.845 1.857 1.729Acetone 2.138 2.003 1.875 1.748 1.640Tetrahydrofuran 2.140 2.000 1.869 1.662 1.631Ethyl acetate 2.141 1.983 1.839 1.690 1.642Water 2.121 1.982 1.844 1.704 1.620



analysis (N), the squared correlation coefficient (R2) and the Fisher F-statistic (F). The regression analyses used in deriving Eqs. (8) and (9) wereperformed using IBM SPSS Statistics 22 commercial software.

The Abrahammodel correlations given by Eqs. (8) and (9) are statistically very good with standard deviations of b0.12 log units. Fig. 2 comparesthe observed log K values against the back-calculated values based on Eq. (9). The experimental data covers a range of approximately 2.78 log units,from logK=1.066 for 2-methylpentane to log K=3.842 for tetradecane. A comparison of the back-calculated versusmeasured log P data is depictedin Fig. 3. As expected, the standard deviation for the log P correlation is slightly larger than that of the log K correlations because the log P valuescontain the additional experimental uncertainty in the gas-to-water partition coefficients used in the log K to log P conversion. There are insufficientexperimental data to permit a training set and test set assessment of thepredictive ability of Eqs. (8) and (9) by randomly splitting the entire databasein half.

The log P and log K data sets for [HM2iPAm]+[Tf2N]−, [EtOHM2iPAm]+[Tf2N]−, [CNMeM2iPAm]+[Tf2N]−, and [C1,9(M2iPAm)2]2+[Tf2N]−2 wereanalyzed in similar fashion. Numerical values of the equation coefficients and the associated statistical information are compiled in Table 16. Eachderived correlation provides a very good mathematical description of the observed partition coefficient data, as evidenced by the low standarddeviations and near unity values for the squared correlation coefficients. Based on our past experience, we would expect each derived expressionto provide reasonably accurate predictions for additional organic compounds dissolved in the given IL, provided that the solute descriptor valuesof the additional compounds fall within the range of values used in deriving each respective log K and log P correlation. The predicted log K andlog P values can be converted first to activity coefficients and then to selectivity values for use in solving chemical separation problems. The derivedexpressions are specific to the given IL solvent, however, and cannot be used to predict activity coefficients for solutes in other IL solvents per se.

Table 14Selectivity S12

∞ and capacity k2∞ values at infinite dilution for different separation problems at T = 323.15 K using [Tf2N]− based ILs.

ILs S12∞ /k12∞

Anion Cation Hexane/benzene Hexane/pyridine Hexane/thiophene Heptane/thiophene Reference

[Tf2N]− Propyl(dimethyl)isopropylammonium 15.60/0.92 26.67/1.56 17.51/1.02 22.87/1.02 This workHexyl(dimethyl)isopropylammonium 10.02/1.23 20.69/1.88 3.49/0.43 4.78/0.43 This workN,N,N′,N′-Tetramethyl-N,N′-diisopropyl-1,9-nonanediaminium 19.33/0.92 33.32/1.58 21.66/1.03 30.80/1.03 This work1-Hexylquinuclidinium 10.17/1.51 13.76/2.05 11.25/1.67 14.92/1.67 [36]1-Octylquinuclidinium 7.58/1.81 9.69/2.31 8.08/1.93 10.21/1.93 [36]1-Propyl-1-methylpyrrolidinium 16.69/1.01 26.2/1.59 19.23/1.16 27.95/1.16 [32]1-Butyl-1-methylpyrrolidinium 15.2/1.10 23.64/1.69 17/1.22 24.01/1.22 [32]1-Pentyl-1-methylpyrrolidinium 14.3/1.22 22.13/1.89 15.8/1.35 20.39/1.35 [32]1-Hexyl-1-methylpyrrolidinium 10.2/1.32 14.88/1.92 11.1/1.43 [33]1-Propyl-1-methylpiperidinium 20.5/1.06 23.14/1.19 30.19/1.19 [45]1-Methyl-3-methylimidazolium 24.85/0.73 [46]1-Ethyl-3-methylimidazolium 20/0.83 [46]1-Butyl-3-methylimidazolium 14.06/1.11 18.29/1.43 22.14/1.43 [46,47]4-Methyl-N-butylpyridinium 18.2/1.37 20.70/1.56 27.01/1.56 [48]N-Octylisoquinolinium 6.71/1.62 7.48/1.81 8.91/1.81 [49]N-Methyl-2-pyrrolidone (NMP) 10.38/0.95 [50]Sulfolane 16.86/0.43 34.61/0.88 [51]

Table 15Logarithm of gas-to-IL partition coefficients, log K, and logarithm of water-to-IL partition coefficients, log P, for solutes dissolved in anhydrous [PM2iPAm]+[(Tf)2N]− at 298.15 K.

Solute E S A B L V Log K log P

Hexane 0.000 0.000 0.000 0.000 2.668 0.9540 1.118 2.9383-Methylpentane 0.000 0.000 0.000 0.000 2.581 0.9540 1.066 2.906Heptane 0.000 0.000 0.000 0.000 3.173 1.0949 1.479 3.4392,2,4-Trimethylpentane 0.000 0.000 0.000 0.000 3.106 1.2358 1.446 3.566Octane 0.000 0.000 0.000 0.000 3.677 1.2358 1.819 3.929Nonane 0.000 0.000 0.000 0.000 4.182 1.3767 2.156 4.306Decane 0.000 0.000 0.000 0.000 4.686 1.5176 2.497 4.817Undecane 0.000 0.000 0.000 0.000 5.191 1.6590 2.828 5.208Dodecane 0.000 0.000 0.000 0.000 5.696 1.7994 3.158 5.688Tridecane 0.000 0.000 0.000 0.000 6.200 1.9400 3.468Tetradecane 0.000 0.000 0.000 0.000 6.705 2.0810 3.842Methylcyclopentane 0.225 0.100 0.000 0.000 2.907 0.8454 1.399 2.569Cyclohexane 0.310 0.100 0.000 0.000 2.964 0.8454 1.526 2.426Methylcyclohexane 0.244 0.060 0.000 0.000 3.319 0.9863 1.719 2.969Benzene 0.610 0.520 0.000 0.140 2.786 0.7164 2.640 2.010Toluene 0.601 0.520 0.000 0.140 3.325 0.8573 3.015 2.365Ethylbenzene 0.613 0.510 0.000 0.150 3.778 0.9982 3.283 2.703m-Xylene 0.623 0.520 0.000 0.160 3.839 0.9982 3.396 2.786p-Xylene 0.613 0.520 0.000 0.160 3.839 0.9982 3.369 2.779o-Xylene 0.663 0.560 0.000 0.160 3.939 0.9982 3.532 2.8721-Hexene 0.080 0.080 0.000 0.070 2.572 0.9110 1.357 2.5171-Hexyne 0.166 0.220 0.100 0.120 2.510 0.8680 1.997 2.2071-Heptyne 0.160 0.230 0.090 0.100 3.000 1.0089 2.331 2.7712-Butanone 0.166 0.700 0.000 0.510 2.287 0.6879 2.886 0.1562-Pentanone 0.143 0.680 0.000 0.510 2.755 0.8288 3.159 0.5793-Pentanone 0.154 0.660 0.000 0.510 2.811 0.8288 3.158 0.658Tetrahydrofuran 0.289 0.520 0.000 0.480 2.636 0.6220 2.551 0.0011,4-Dioxane 0.329 0.750 0.000 0.640 2.892 0.6810 3.236 −0.474Methanol 0.278 0.440 0.430 0.470 0.970 0.3082 2.312 −1.428Ethanol 0.246 0.420 0.370 0.480 1.485 0.4491 2.528 −1.1451-Propanol 0.236 0.420 0.370 0.480 2.031 0.5900 2.858 −0.7022-Propanol 0.212 0.360 0.330 0.560 1.764 0.5900 2.595 −0.8852-Methyl-1-propanol 0.217 0.390 0.370 0.480 2.413 0.7309 3.045 −0.2551-Butanol 0.224 0.420 0.370 0.480 2.601 0.7309 3.223 −0.237Diethyl ether 0.041 0.250 0.000 0.450 2.015 0.7309 1.481 0.311Diisopropyl ether −0.063 0.170 0.000 0.570 2.501 1.0127 1.582 0.532Chloroform 0.425 0.490 0.150 0.020 2.480 0.6167 2.421 1.631Dichloromethane 0.390 0.570 0.100 0.050 2.019 0.4943 2.059 1.099Carbon tetrachloride 0.458 0.380 0.000 0.000 2.823 0.7390 2.128 2.318Acetonitrile 0.237 0.900 0.070 0.320 1.739 0.4042 2.987 0.137Nitromethane 0.313 0.950 0.060 0.310 1.892 0.4237 3.294 0.3441-Nitropropane 0.242 0.950 0.000 0.310 2.894 0.7055 3.747 1.297Triethylamine 0.101 0.150 0.000 0.790 3.040 1.0538 1.828 −0.532Pyridine 0.631 0.840 0.000 0.520 3.022 0.6753 3.527 0.087Thiophene 0.687 0.570 0.000 0.150 2.819 0.6411 2.764 1.724Ethyl acetate 0.106 0.620 0.000 0.450 2.314 0.7470 2.675 0.515


Fig. 2. Comparison between the observed log K data and calculated log K values based on Eq. (9) for the 46 organic solutes dissolved in [PM2iPAm]+[Tf2N]− at 298.15 K.


The ion-specific equation coefficient version of the Abraham model [38–41]:

log P ¼ cp;cation þ cp;anion þ ep;cation þ ep;anion� �

Eþ sp;cation þ sp;anion� �

Sþ ap;cation þ ap;anion� �

A þ bp;cation þ bp;anion� �

Bþ vp;cation þ vp;anion� �

V ð10Þ

log K ¼ ck;cation þ ck;anion þ ek;cation þ ek;anion� �

Eþ sk;cation þ sk;anion� �

Sþ ak;cation þ ak;anion� �

A þ bk;cation þ bk;anion� �

Bþ lk;cation þ lk;anion� �

L ð11Þ

and fragment-group version of the Abrahammodel [42]:

log P ¼Xgroup

ni cp;i þXgroup

ep;i ni EþXgroup

sp;i ni SþXgroup

ap;i niAþXgroup

bp;i ni BþXgroup

vp;i niVþ cp;anion þ ep;anionEþ sp;anion Sþ ap;anionAþ bp;anionBþ vp;anionV� �

ð12Þ

log K ¼Xgroup

ni ck;i þXgroup

ek;i ni EþXgroup

sk;i ni SþXgroup

ak;i niAþXgroup

bk;i ni BþXgroup

lk;i ni L þ ck;anion þ ek;anionEþ sk;anion Sþ ak;anionAþ bk;anion Bþ lk;anion L� �

ð13Þ

have been developed for predicting partition coefficients of solutes into those IL solvents whenever one does not have an IL-specific correlationequation. In Eqs. (12) and (13), ni denotes the number of times that the given fragment group appears in the cation and the summations extendover all fragment groups contained in the IL under consideration. Thus far, ion-specific equation coefficients have been derived for 43 different cationsand 17 different anions (Eqs. (10) and (11)), with numerical group values for 12 cation fragments (CH3–, –CH2–, –O–, –O–Ncyclic, –OH, CH2cyclic,CHcyclic, Ccyclic, Ncyclic, NNb+, NPb+, and NS–+) and 9 individual anions (Tf2N−, PF6−, BF4−, EtSO4

−, OcSO4−, SCN−, CF3SO3

−, AcF3−, and (CN)2N−)(Eqs. (12) and (13)). The 43 different cation-specific and 17 different anion-specific equation coefficients can be combined to permit the estimation

Fig. 3. Comparison between the observed log P data and calculated log P values based on Eq. (8) for the 44 organic solutes dissolved in [PM2iPAm]+[Tf2N]− at 298.15 K.

Table 16Equation coefficients for Log P and Log K Abraham model correlations for [PM2iPAm]+[Tf2N]−, [HM2iPAm]+[Tf2N]−, [EtOHM2iPAm]+[Tf2N]−, [CNMeM2iPAm]+[Tf2N]−, and[C1,9(M2iPAm)2]2+[Tf2N]−2 at 298.15 K.

Ionic liquid/property c e s a b v l N SD R2 F

([PM2iPAm]+[(Tf)2N]−)Log P −0.378 0.115 0.723 −1.061 −4.594 3.388 44 0.113 0.996 1889

(0.118) (0.114) (0.117) (0.178) (0.109) (0.094)Log K −0.702 2.532 2.578 0.331 0.682 46 0.096 0.985 654.2

(0.071) (0.064) (0.139) (0.083) (0.017)

([HM2iPAm]+[(Tf)2N]−)Log P −0.340 0.582 −1.194 −4.631 3.640 45 0.125 0.996 2527

(0.129) (0.115) (0.183) (0.118) (0.104)Log K −0.531 −0.124 2.232 2.297 0.344 0.736 47 0.099 0.980 407.8

(0.077) (0.092) (0.091) (0.137) (0.100) (0.018)

([EtOHM2iPAm]+[Tf2N]−)Log P −0.669 0.236 0.617 −0.850 −3.356 3.270 41 0.122 0.994 1188

(0.143) (0.129) (0.138) (0.178) (0.123) (0.109)Log K −0.934 0.200 2.361 2.695 1.532 0.641 43 0.086 0.986 538.2

(0.075) (0.088) (0.086) (0.115) (0.086) (0.017)

([CNMeM2iPAm]+[Tf2N]−)Log P −1.001 1.512 −0.459 −4.191 3.529 40 0.134 0.994 1341

(0.151) (0.126) (0.198) (0.120) (0.117)Log K −1.344 −0.140 3.283 3.118 0.819 0.735 42 0.126 0.978 316.6

(0.114) (0.122) (0.116) (0.174) (0.129) (0.025)

([C1,9(M2iPAm)2]2+[Tf2N]−2)Log P −0.606 0.225 0.798 −1.034 −4.438 3.429 45 0.131 0.995 1511

(0.137) (0.127) (0.142) (0.190) (0.156) (0.110)Log K −0.894 0.175 2.533 2.544 0.492 0.690 47 0.086 0.988 684.7

(0.064) (0.082) (0.086) (0.116) (0.103) (0.015)


of log P and log K values for solutes in a total of 731 different ILs. The number of ion-specific equation coefficients and fragment group values isexpected to increase as additional experimental data become available for functionalized IL solvents.

The experimental partition coefficient data thatwe havemeasured for solutes dissolved in anhydrous [PM2iPAm]+[Tf2N]−, [HM2iPAm]+[Tf2N]−,[EtOHM2iPAm]+[Tf2N]−, [CNMeM2iPAm]+[Tf2N]−, and [C1,9(M2iPAm)2]2+[Tf2N]−2 can be used to calculate ion-specific equation coefficients for anadditional five cations. At the time that Eqs. (10) and (11) were proposed, provisions were made for calculating equation coefficients for additionalcations and anions fromnewlymeasured experimental datawithout having to perform a regression analysis on the entire logK (or log P) dataset. Theproposed methodology allows one to retain the numerical values of the ion-specific equation coefficients that have already been calculated. Forexample, ion-specific equation coefficients of a new cation could be obtained as the difference in the calculated IL-specific equation coefficientminus the respective anion-specific equation coefficient (e.g., ck,cation = ck,il − ck,anion, ek,cation = ek,il − ek,anion, sk,cation = sk,il − sk,anion, ak,cation =ak,il − ak,anion, bk,cation = bk,il − bk,anion, lk,cation = lk,il − lk,anion), provided of course that the anion-specific equation coefficients are known. Thefive ILs studied in the current communication all contain the [Tf2N]− anion, and the equation coefficients for this particular anion are all equal tozero. The IL-specific equation coefficients in the Abrahammodel always represent the sum of a cation-specific plus an anion-specific contribution.It is impossible to compute numerical values for individual ions unless one sets a reference point. This is analogous to calculating chemical potentialsfor single ions or calculating ionic limitingmolar conductances for individual ions. In each case, onemust define a reference state fromwhich all sin-gle-ion values are calculated. Thus, with the defined [Tf2N]−-anion reference point, the coefficients in Eqs. (10) and (11) represent the ion-specificvalues for the [PM2iPAm]+ cation. This is also the casewith the equation coefficients for the other four ILswe investigate here. Hence, the coefficientsprovided in Table 15 pertain to both the specific IL as well as the respective cation that comprises the IL solvent.

4. Conclusion

Infinite dilution activity coefficients and gas-to-liquid partition coefficients are reported for 42 or more different organic solutes of varyingpolarity and hydrogen-bonding character dissolved in anhydrous propyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide,hexyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, 2-hydroxyethyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, cyanomethyl(dimethyl)isopropylammonium bis(trifluoromethylsulfonyl)imide, and N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminium di[bis(trifluoromethylsulfonyl)imide] as determined by inverse gas chromatography in the temperature range from323.15 K to 363.15 K. The measured gas-to-anhydrous IL partition coefficient data were converted to water-to-anhydrous IL partition coeffi-cient data using standard thermodynamic relationships and published gas-to-water partition coefficient data. Both sets of partition coefficientdata were analyzed in terms of the Abraham general solvation model and a modified version of the Abraham model containing ion-specificequation coefficients. Equation coefficients were calculated for the five additional cations: namely, propyl(dimethyl)isopropylammonium,hexyl(dimethyl)isopropylammonium, 2-hydroxyethyl(dimethyl)isopropylammonium, cyanomethyl(dimethyl)isopropylammonium, and N,N,N′,N′-tetramethyl-N,N′-diisopropyl-1,9-nonanediaminium. The five newly calculated cation-specific equation coefficients that are reported in the pres-ent communication can be combined with our previously published values for 17 IL anions [41,52] to enable one to predict log K, log P, and infinitedilution activity coefficients of solutes dissolved in an additional 85 ILs, bringing the total number of ILs for which such predictions can be made to816. Based on our past experience, Abraham model correlations obtained by combining cation-specific and anion-specific equation coefficientsshould be able to predict the partitioning behavior of solutes dissolved in additional anhydrous ILs to within 0.14 log units, provided that the solutedescriptors fall within the range of values used in deriving the respective ion-specific equation coefficients.


Acknowledgement

Bihan Jiang thanks the University of North Texas's Texas Academy ofMath and Science (TAMS) program for a summer research award.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.molliq.2016.07.012.

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