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Physics and Chemistry of LiquidsAn International Journal

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Abraham model ion-specific equation coefficientsfor the 1-butyl-2,3-dimethyimidazolium and 4-cyano-1-butylpyridinium cations calculated frommeasured gas-to-liquid partition coefficient data

Amber Lu, Bihan Jiang, Sarah Cheeran, William E. Acree Jr. & Michael H.Abraham

To cite this article: Amber Lu, Bihan Jiang, Sarah Cheeran, William E. Acree Jr. & MichaelH. Abraham (2016): Abraham model ion-specific equation coefficients for the 1-butyl-2,3-dimethyimidazolium and 4-cyano-1-butylpyridinium cations calculated frommeasured gas-to-liquid partition coefficient data, Physics and Chemistry of Liquids, DOI:10.1080/00319104.2016.1191634

To link to this article: http://dx.doi.org/10.1080/00319104.2016.1191634

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Abraham model ion-specific equation coefficients for the1-butyl-2,3-dimethyimidazolium and 4-cyano-1-butylpyridiniumcations calculated from measured gas-to-liquid partitioncoefficient dataAmber Lua, Bihan Jianga, Sarah Cheerana, William E. Acree Jr.a and Michael H. Abrahamb

aDepartment of Chemistry, University of North Texas, Denton, TX, USA; bDepartment of Chemistry, UniversityCollege London, London, UK

ABSTRACTPartition coefficient and gas solubility data have been assembled fromthe published chemical and engineering literature for solutes dissolvedin anhydrous 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and 4-cyano-1-butylpyrridinium bis(trifluoromethylsulfonyl)imide. More than 60 experi-mental data points were gathered for each IL solvent. The compiledexperimental data were used to derive Abraham model correlations fordescribing the solute transfer properties into the three anhydrous ILsolvents from both the gas phase and water. The derived mathematicalcorrelations described the observed solute transfer properties, expressedas the logarithm of the water-to-IL partition coefficient and logarithm ofthe gas-to-IL solvent partition coefficient, to within standard deviationsof 0.125 log units (or less). Abraham model ion-specific equation coeffi-cients are also calculated for the 1-butyl-2,3-dimethylimidazolium and 4-cyano-1-butylpyridinium cations.

ARTICLE HISTORYReceived 24 March 2016Accepted 16 May 2016

KEYWORDSIonic liquid solvents;partition coefficients;predictive methods; cation-specific contributions; anion-specific contributions

1. Introduction

Chemical sustainability and environmental safety are important considerations in the solventselection process. Organic solvents are omnipresent in most chemical synthetic procedures and inchemical separation processes, such as liquid–liquid extraction and high-performance liquidchromatography. Organic solvents represent a major manufacturing expense, and is one of themajor contributors to industrial manufacturing waste streams. Growing environmental awareness,combined with more stringent governmental regulations regarding both worker safety andchemical waste disposal, has prompted the manufacturing sector to search for safer and envir-onmentally benign chemical replacements for the more toxic and more harmful organic solvents.Of the suggested chemical replacements, ionic liquids (ILs) have shown considerable promise asan organic solvent media for synthesising many different classes of organic compounds, as asorbent for greenhouse gas and acidic gas capture in natural gas and post-combustion treatments,as a dissolving media for lignocellulosic biomass, and as a stationary phase liquid or surface-bonded stationary phase for gas–liquid chromatography and high-performance liquid chromato-graphy, respectively. Favourable physicochemical properties, such as high thermal and chemicalstabilities, negligible vapour pressures, low melting point temperatures, wide liquid temperatureranges, and immiscibility with many organic solvents facilitate the use of ILs in many practical

CONTACT William E. Acree, Jr. acree@unt.edu© 2016 Informa UK Limited, trading as Taylor & Francis Group

PHYSICS AND CHEMISTRY OF LIQUIDS, 2016http://dx.doi.org/10.1080/00319104.2016.1191634

industrial applications. The physicochemical properties and solubilising character of ILs can becontrolled by the judicious selection of cation–anion pair, and by the addition of polar and/orhydrogen-bonding groups onto the alkyl chain of the cation. Considerable attention has beengiven in recent years towards developing mathematical expressions for estimating the physicalproperties and solubilising characteristics of IL solvents based on both group contributionmethods and quantitative structure–property relationships. To date group contribution methodshave been developed for predicting infinite dilution activity coefficients and gas–liquid partitioncoefficients of solutes dissolved in ILs,[1–3] for predicting enthalpies of solvation of organicsolutes dissolved in ILs,[4] and for estimating viscosities,[5,6] thermal conductivities [7,8] isobaricheat capacities,[9–11] refractive indices,[12] static dielectric constants,[13] surface tensions,[14]densities,[15] and Daphnia magna water flea toxicities [16] of ILs at both 298 K and as a functionof temperature.

Our contributions in the area of solvent selection has been to develop solution models thatenable prediction of the solubility of crystalline non-electrolyte solutes in binary [17–21] andternary [22–28] solvent mixtures based on the Nearly Ideal Binary Solvent Model and Abrahammodel correlations that enable estimation of the logarithm of gas-to-organic solvent partitioncoefficients (log K) and logarithm of water-to-organic solvent partition coefficients (log P) in bothtraditional and anhydrous IL organic solvents. Abraham model correlations have been reportedfor well over 100 total different tradition organic solvents [29–46] and IL organic solvents,[47–61]as well as for binary aqueous-ethanol [62] mixtures. Our focus in the present study is IL solvents.For neat, anhydrous IL solvents, we have reported IL-specific Abraham model correlations[47–61]:

logP ¼ cp;il þ ep;il � Eþ sp;il � Sþ ap;il � Aþ bp;il � Bþ vp;il � V (1)

log K ¼ ck;il þ ek;il � Eþ sk;il � Sþ ak;il � Aþ bk;il � B þ lk;il � L (2)

and Abraham model correlations containing ion-specific equation coefficients [63–66]:

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

(3)

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

(4)

Abraham model correlations containing fragment-group values [1,2]:

log P ¼Xgroup

ni cp;i þXgroup

ep;i ni EþXgroup

sp;i ni SþXgroup

ap;i ni AþXgroup

bp;i ni B þXgroup

vp;i ni Vþ

ðcp;anion þ ep;anion Eþ sp;anion Sþ ap;anion Aþ bp;anion Bþ vp;anion VÞ(5)

logK ¼Xgroup

ni ck;i þXgroup

ek;i ni EþXgroup

sk;i ni SþXgroup

ak;i ni AþXgroup

bk;i ni B þXgroup

lk;i ni L þ

ðck;anion þ ek;anion Eþ sk;anion Sþ ak;anion Aþ bk;anion Bþ lk;anion LÞ(6)

have also been published for predicting the logarithms of solute partition coefficients intoanhydrous IL solvents from both water (log P) and gas phase (log K). In Equations (5) and (6),

2 A. LU ET AL.

ni denotes the number of times that the given fragment group appears in the cation, and thesummations extend over all fragment groups.

Predictive applications using Equations (1)–(6) require knowledge of the solute descriptors(upper-case letters) and equation coefficients/fragment group values (lower-case letters) for thesolutes and ILs of interest. Solute descriptors are available for more than 5000 different organicand inorganic compounds, and are defined as follows: the solute excess molar refractivity in unitsof (cm3 mol−1)/10 (E), the solute dipolarity/polarizability (S), the overall or summation hydrogen-bond acidity and basicity (A and B, respectively), the McGowan volume in units of (cm3 mol−1)/100 (V), and the logarithm of the gas-to-hexadecane partition coefficient at 298 K (L). To date, wehave reported IL-specific equation coefficients for more than 60 different ILs (Equations (1) and(2)), ion-specific equation coefficients for 43 different cations and 17 different anions (Equations(3) and (4)), and numerical group values for 12 cation fragments (CH3-, –CH2-, –O-, -O─Ncyclic,-OH, CH2cyclic, CHcyclic, Ccyclic, Ncyclic, >N<

+, >P<+, and >S–+) and 9 individual anions (Tf2N−,

PF6−, BF4

−, EtSO4−, OcSO4

−, SCN−, CF3SO3−, AcF3

−, and (CN)2N−) (Equations (5) and (6)). The

43 different cation-specific and 16 different anion-specific equation coefficients can be combinedto permit the estimation of log P and log K values for solutes in a total of 731 different ILs (i.e.43 × 17). The number of ion-specific equation coefficients and fragment group values is expectedto increase as additional experimental data become available for functionalised IL solvents.

At the time Equations (3) and (4) were published, we proposed a computational methodologyfor adding new ion-specific equation coefficients to our existing database. The methodologyenables new ion-specific coefficients to be added without having to perform a regression analysison the entire log K (or log P) data. The methodology allows one to retain the numerical values ofthe ion-specific equation coefficients that have already been calculated. For example, ion-specificequation coefficients of a new cation could be obtained as the difference in the calculated IL-specific equation coefficient minus the respective anion-specific equation coefficient, for example,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 equationcoefficients are known. Our goal is to develop a similar computational methodology that allowsone to calculate values for new fragment groups from known cation-specific equation coefficientsand from known fragment group values, for example, ck;cation ¼

Pgroup

ni ck;i; ek;cation ¼Pgroup

ek;i ni ; sk;cation ¼ Pgroup

sk;i ni; and so on: The advantage of such a computational method is

that the equation coefficients for the anions would be the same in both the ion-specific Abrahammodel and fragment-group Abraham model, thus allowing one to add new anions in thefragment-group model with minimal effort. Implementation and assessment of the new metho-dology, however, does require us to add additional cation-specific equation coefficients to ourexisting values as some functional groups are poorly represented in the ILs that we have studiedthus far. In the present study, we develop IL-specific Abraham model log K and log P correlationsfor three additional anhydrous IL solvents, namely 1-butyl-3-methylimidazolium dicyanamide([BMIm]+[N(CN)2]

−), 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide([BM2Im]+[(Tf)2N]

−), and 4-cyano-1-butylpyrridinium bis(trifluoromethylsulfonyl)imide ([4-CNBPy]+[(Tf)2N]

−) from recently published log K data taken from the chemical literature [67–69] Cation-specific equation coefficients are also calculated for both [BM2Im]+ and [4-CNBPy]+.As an information note, Xiang and co-workers [69] did report IL-specific Abraham model log Kcorrelations for ([BM2Im]+[(Tf)2N]

−) at 313.15 K, 323.15 K, and 333.15 K. We have extended thelog K correlations for ([BM2Im]+[(Tf)2N]

−) to include 298.15 K. Xiang and co-workers did notreport an Abraham model correlation for log P, nor did the authors consider the ion-specificequation coefficient version of the Abraham general solvation model.

PHYSICS AND CHEMISTRY OF LIQUIDS 3

2. Gas-to-IL and water-to-IL partition coefficient data sets

The published partition coefficient data for the solutes dissolved in ([BMIm]+[N(CN)2]−),

([BM2Im]+[(Tf)2N]−) and ([4-CNBPy]+[(Tf)2N]

−) were performed at several temperatures slightlyhigher than 298.15 K. The numerical log K (at 298.15 K) used in the present study were calculatedfrom the standard thermodynamic log K versus 1/T linear relationship based on the measuredvalues at either 318.15 K and 328.15 K for ([BMIm]+[N(CN)2]

−), or 313.15 K and 323.15 K for([BM2Im]+[(Tf)2N]

−), or 308.15 K and 318.15 K for ([4-CNBPy]+[(Tf)2N]−). These were the two

lowest temperatures that were studied for each IL solvent. The linear extrapolation should be validas the measurements were performed at temperatures not too far removed from the desiredtemperature of 298.15 K (about 30 K in the worst case).

Our search of the published literature for additional log K values did find gas solubility data forcarbon dioxide,[70] nitrogen gas,[70] nitrous oxide,[71] ethane,[72] ethylene,[72] and vinylacetate [73] dissolved in ([BMIm]+[N(CN)2]

−). The published gas solubility data was reportedin terms of Henry’s law constants, KHenry. Experimental Henry’s law constants can be converted togas-to-IL partition coefficients through Equation (7):

logK ¼ log

�RT

KHenry Vsolvent

�; (7)

where R is the universal constant law constant, Vsolvent is the molar volume of the IL solvent, andT is the system temperature. We were unable to find any solubility data for the inorganic gases orsmall gaseous organic solutes dissolved in ([BM2Im]+[(Tf)2N]

−) and ([4-CNBPy]+[(Tf)2N]−).

The Abraham general solvation parameter model also contains provisions for describing solutetransfer from water into anhydrous IL solvents. Here, the solute transfer represents a hypotheticpartitioning process in which the IL solvent is not in direct contact with the aqueous phase. Westill denote the transfer process as log P, and calculate the numerical via Equation (8)

logP ¼ logK � logKw (8)

The conversion of log K data to log P requires a prior knowledge of the solute’s gas-phasepartition coefficient into water, Kw, which is available for most of the solutes being studied. Log Pvalues calculated in this fashion are still useful because the predicted log P values can be used toestimate the solute’s infinite dilution activity coefficient in the IL, γsolute

∞,

log P þ logKW ¼ log

�RT

γsolute1Psoluteo Vsolvent

�; (9)

where Psoluteo is the vapour pressure of the organic solute at the system temperature (T). Infinite dilution

activity coefficients assist practicing analytical chemists and process chemical engineers in selecting the‘best’ IL solvent for achieving the desired chemical separation. The solutes’ gas-phase partition coeffi-cients into water (KW) needed for these calculations were taken from the published literature.[47,48,74]

The calculated log K and log P values at 298.15 K are assembled in Tables 1–3 for solutes dissolvedin ([BMIm]+[N(CN)2]

−), ([BM2Im]+[(Tf)2N]−) and ([4-CNBPy]+[(Tf)2N]

−), respectively. The collec-tion ofmore than 60 chemically diverse organic solutes include alkanes, alkenes, alkynes, aromatic andheterocyclic compounds, primary and secondary alcohols, dialkyl ethers and cyclic ethers, alkanones,alkyl alkanoates, and nitroalkanes. Also, collected in Tables 1–3 are the numerical solute descriptorsfor the organic compounds studied in the present investigation. Numerical values of the solutedescriptors in our database are of experimental origin and were based on observed solubility dataand Henry’s law constants,[75–78] on measured gas–liquid and high-performance liquid chromato-graphic retention times and retention factors,[79,80] and on experimental practical partition coeffi-cient measurements for the equilibrium solute distribution between water and an immiscible (orpartially miscible) organic solvent.[81–83] The numerical solute descriptors define a set of chemical

4 A. LU ET AL.

Table1.

Measuredlogarithm

ofgas-to-IL

partition

coefficients,logK,andlogarithm

ofwater-to-ILpartition

coefficients,logP,forsolutesdissolvedin

anhydrou

s([B

MIm]+[N(CN) 2]−)at

298.15

K.

Solute

ES

AB

LV

LogK

LogP

Carbon

dioxide

0.000

0.280

0.050

0.100

0.058

0.2809

0.167

0.245

Nitrog

en0.000

0.000

0.000

0.000

−0.978

0.2222

−1.540

0.260

Nitrou

soxide

0.068

0.350

0.000

0.100

0.164

0.2810

0.168

0.398

Ethane

0.000

0.000

0.000

0.000

0.492

0.3900

−0.339

1.001

Pentane

0.000

0.000

0.000

0.000

2.162

0.8131

0.622

2.322

Hexane

0.000

0.000

0.000

0.000

2.668

0.9540

0.968

2.788

3-Methylpentane

0.000

0.000

0.000

0.000

2.581

0.9540

0.938

2.778

2,2-Dimethylbutane

0.000

0.000

0.000

0.000

2.352

0.9540

0.717

2.557

Heptane

0.000

0.000

0.000

0.000

3.173

1.0949

1.317

3.277

Octane

0.000

0.000

0.000

0.000

3.677

1.2358

1.627

3.737

2,2,4-Trimethylpentane

0.000

0.000

0.000

0.000

3.106

1.2358

1.190

3.310

Non

ane

0.000

0.000

0.000

0.000

4.182

1.3767

1.945

4.095

Decane

0.000

0.000

0.000

0.000

4.686

1.5176

2.245

4.565

Cyclop

entane

0.263

0.100

0.000

0.000

2.477

0.7045

1.210

2.090

Cycloh

exane

0.305

0.100

0.000

0.000

2.964

0.8454

1.551

2.451

Methylcyclohexane

0.244

0.060

0.000

0.000

3.319

0.9863

1.660

2.910

Cycloh

eptane

0.350

0.100

0.000

0.000

3.704

0.9863

2.081

2.661

Cyclooctane

0.413

0.100

0.000

0.000

4.329

1.1272

2.542

3.312

Ethene

0.107

0.100

0.000

0.070

0.289

0.3470

−0.120

0.820

1-Pentene

0.093

0.080

0.000

0.070

2.047

0.7701

0.952

2.182

1-Hexene

0.078

0.080

0.000

0.070

2.572

0.9110

1.285

2.445

Cycloh

exene

0.395

0.280

0.000

0.090

2.952

0.8204

1.968

2.238

1-Heptene

0.092

0.080

0.000

0.070

3.063

1.0519

1.620

2.840

1-Octene

0.094

0.080

0.000

0.070

3.568

1.1928

1.940

3.350

1-Decene

0.093

0.080

0.000

0.070

4.554

1.4746

2.541

4.181

1-Pentyne

0.172

0.230

0.120

0.120

2.010

0.7271

1.838

1.848

1-Hexyne

0.166

0.220

0.100

0.120

2.510

0.8680

2.178

2.388

1-Heptyne

0.160

0.230

0.120

0.100

3.000

1.0089

2.478

2.918

1-Octyne

0.155

0.220

0.090

0.100

3.521

1.1498

2.790

3.310

Benzene

0.610

0.520

0.000

0.140

2.786

0.7164

2.773

2.143

Toluene

0.601

0.520

0.000

0.140

3.325

0.8573

3.100

2.450

Ethylbenzene

0.613

0.510

0.000

0.150

3.778

0.9982

3.335

2.755

o-Xylene

0.663

0.560

0.000

0.160

3.939

0.9982

3.603

2.943

m-Xylene

0.623

0.520

0.000

0.160

3.839

0.9982

3.418

2.808

p-Xylene

0.613

0.520

0.000

0.160

3.839

0.9982

3.420

2.830

Prop

ylbenzene

0.604

0.500

0.000

0.150

4.230

1.1390

3.591

3.201

Isop

ropylbenzene

0.602

0.490

0.000

0.160

4.084

1.1390

3.475

3.035

Styrene

0.849

0.650

0.000

0.160

3.908

0.9550

3.905

2.955

α-Methylstyrene

0.851

0.640

0.000

0.190

4.290

1.0960

4.095

3.135

Methano

l0.278

0.440

0.430

0.470

0.970

0.3082

3.297

−0.443

(Con

tinued)

PHYSICS AND CHEMISTRY OF LIQUIDS 5

Table1.

(Con

tinued).

Solute

ES

AB

LV

LogK

LogP

Ethano

l0.246

0.420

0.370

0.480

1.485

0.4491

3.403

−0.267

1-Prop

anol

0.236

0.420

0.370

0.480

2.031

0.5900

3.741

0.181

2-Prop

anol

0.212

0.360

0.330

0.560

1.764

0.5900

3.375

−0.105

1-Bu

tano

l0.224

0.420

0.370

0.480

2.601

0.7309

4.101

0.641

2-Bu

tano

l0.217

0.360

0.330

0.560

2.338

0.7309

3.677

0.287

tert-Butanol

0.180

0.300

0.310

0.600

1.963

0.7309

3.316

0.036

Thioph

ene

0.687

0.570

0.000

0.150

2.819

0.6411

3.076

2.036

Tetrahydrofuran

0.289

0.520

0.000

0.480

2.636

0.6223

2.627

0.077

1,4-Dioxane

0.329

0.750

0.000

0.640

2.892

0.6810

3.432

−0.278

Methyltert-bu

tyle

ther

0.024

0.220

0.000

0.550

2.372

0.8718

1.773

0.153

Ethyltert-bu

tyle

ther

−0.020

0.180

0.000

0.590

2.699

1.0127

1.635

0.365

Methyltert-am

ylether

0.050

0.210

0.000

0.600

2.916

1.0127

2.099

0.629

Diethylether

0.041

0.250

0.000

0.450

2.015

0.7309

1.451

0.281

Dipropyle

ther

0.008

0.250

0.000

0.450

2.954

1.0127

1.872

0.982

Diisop

ropyle

ther

−0.063

0.170

0.000

0.570

2.501

1.0127

1.508

0.458

Dibutylether

0.000

0.250

0.000

0.450

3.924

1.2945

2.479

1.789

Aceton

e0.179

0.700

0.040

0.490

1.696

0.5470

2.670

−0.120

2-Pentanon

e0.143

0.680

0.000

0.510

2.755

0.8288

3.170

0.590

3-Pentanon

e0.154

0.660

0.000

0.510

2.811

0.8288

3.150

0.650

Methylacetate

0.142

0.640

0.000

0.450

1.911

0.6057

2.500

0.200

Ethylacetate

0.106

0.620

0.000

0.450

2.314

0.7466

2.636

0.476

Methylp

ropano

ate

0.128

0.600

0.000

0.450

2.431

0.7470

2.711

0.561

Methylb

utanoate

0.106

0.600

0.000

0.450

2.943

0.8880

2.966

0.886

Butanal

0.187

0.650

0.000

0.450

2.270

0.6879

2.761

0.431

Aceton

itrile

0.237

0.900

0.070

0.320

1.739

0.4042

3.177

0.327

Pyrid

ine

0.631

0.840

0.000

0.520

3.022

0.6750

3.779

0.339

1-Nitrop

ropane

0.242

0.950

0.000

0.310

2.894

0.7055

3.904

1.454

Vinylfluoride

0.417

6 A. LU ET AL.

Table2.

Measuredlogarithm

ofgas-to-IL

partition

coefficients,logK,andlogarithm

ofwater-to-ILpartition

coefficients,logP,forsolutesdissolvedin

anhydrou

s([B

M2Im]+[(T

f) 2N]−)at

298.15

K.

Solute

ES

AB

LV

LogK

LogP

Heptane

0.000

0.000

0.000

0.000

3.173

1.0949

1.597

3.557

Octane

0.000

0.000

0.000

0.000

3.677

1.2358

1.994

4.104

Non

ane

0.000

0.000

0.000

0.000

4.182

1.3767

2.345

4.495

Decane

0.000

0.000

0.000

0.000

4.686

1.5176

2.654

4.974

Methylcyclopentane

0.225

0.100

0.000

0.000

2.907

0.8454

1.594

2.764

Cycloh

exane

0.305

0.100

0.000

0.000

2.964

0.8454

1.734

2.634

Methylcyclohexane

0.244

0.060

0.000

0.000

3.319

0.9863

1.922

3.172

Cycloh

eptane

0.350

0.100

0.000

0.000

3.704

0.9863

2.241

2.821

Cyclooctane

0.413

0.100

0.000

0.000

4.329

1.1272

2.686

3.456

1-Hexene

0.078

0.080

0.000

0.070

2.572

0.9110

1.517

2.677

Cyclop

entene

0.335

0.220

0.000

0.080

2.273

0.6605

1.592

2.002

Cycloh

exene

0.395

0.280

0.000

0.090

2.952

0.8204

2.034

2.304

1-Heptene

0.092

0.080

0.000

0.070

3.063

1.0519

1.857

3.077

1-Octene

0.094

0.080

0.000

0.070

3.568

1.1928

2.218

3.628

1-Non

ene

0.090

0.080

0.000

0.070

4.073

1.3337

2.536

4.046

1-Decene

0.093

0.080

0.000

0.070

4.554

1.4746

2.868

4.508

1-Hexyne

0.166

0.220

0.100

0.120

2.510

0.8680

2.185

2.395

1-Heptyne

0.160

0.230

0.120

0.100

3.000

1.0089

2.503

2.943

1-Octyne

0.155

0.220

0.090

0.100

3.521

1.1498

2.835

3.355

1-Non

yne

0.150

0.220

0.090

0.100

4.019

1.2907

3.164

3.944

Benzene

0.610

0.520

0.000

0.140

2.786

0.7164

2.828

2.198

Toluene

0.601

0.520

0.000

0.140

3.325

0.8573

3.192

2.542

Ethylbenzene

0.613

0.510

0.000

0.150

3.778

0.9982

3.444

2.864

o-Xylene

0.663

0.560

0.000

0.160

3.939

0.9982

3.693

3.033

m-Xylene

0.623

0.520

0.000

0.160

3.839

0.9982

3.527

2.917

p-Xylene

0.613

0.520

0.000

0.160

3.839

0.9982

3.529

2.939

Methano

l0.278

0.440

0.430

0.470

0.970

0.3082

2.457

−1.283

Ethano

l0.246

0.420

0.370

0.480

1.485

0.4491

2.633

−1.037

1-Prop

anol

0.236

0.420

0.370

0.480

2.031

0.5900

2.946

−0.614

2-Prop

anol

0.212

0.360

0.330

0.560

1.764

0.5900

2.720

−0.760

1-Bu

tano

l0.224

0.420

0.370

0.480

2.601

0.7309

3.322

−0.138

2-Bu

tano

l0.217

0.360

0.330

0.560

2.338

0.7309

2.991

−0.399

2-Methyl-1-propano

l0.217

0.390

0.370

0.480

2.413

0.7309

3.121

−0.179

tert-Butanol

0.180

0.300

0.310

0.600

1.963

0.7309

2.715

−0.565

Thioph

ene

0.687

0.570

0.000

0.150

2.819

0.6411

2.924

1.884

Tetrahydrofuran

0.289

0.520

0.000

0.480

2.636

0.6223

2.667

0.117

1,4-Dioxane

0.329

0.750

0.000

0.640

2.892

0.6810

3.369

−0.341

Methyltert-bu

tyle

ther

0.024

0.220

0.000

0.550

2.372

0.8718

1.955

0.335

Ethyltert-bu

tyle

ther

−0.020

0.180

0.000

0.590

2.699

1.0127

1.938

0.668

Methyltert-am

ylether

0.050

0.210

0.000

0.600

2.916

1.0127

2.334

0.864

(Con

tinued)

PHYSICS AND CHEMISTRY OF LIQUIDS 7

Table2.

(Con

tinued).

Solute

ES

AB

LV

LogK

LogP

Diethylether

0.041

0.250

0.000

0.450

2.015

0.7309

1.604

0.434

Diisop

ropyle

ther

−0.063

0.170

0.000

0.570

2.501

1.0127

1.814

0.764

Aceton

e0.179

0.700

0.040

0.490

1.696

0.5470

2.746

−0.044

2-Pentanon

e0.143

0.680

0.000

0.510

2.755

0.8288

3.314

0.734

3-Pentanon

e0.154

0.660

0.000

0.510

2.811

0.8288

3.297

0.787

Ethylformate

0.146

0.660

0.000

0.380

1.845

0.6057

2.496

0.536

Methylacetate

0.142

0.640

0.000

0.450

1.911

0.6057

2.563

0.263

Ethylacetate

0.106

0.620

0.000

0.450

2.314

0.7466

2.814

0.654

Vinylacetate

0.223

0.640

0.000

0.430

2.152

0.7040

2.665

0.955

Prop

anal

0.196

0.650

0.000

0.450

1.815

0.5470

2.469

−0.051

Butanal

0.187

0.650

0.000

0.450

2.270

0.6879

2.811

0.481

Isob

utanal

0.144

0.620

0.000

0.450

2.120

0.6879

2.620

0.520

Aceton

itrile

0.237

0.900

0.070

0.320

1.739

0.4042

3.120

0.270

Nitrom

ethane

0.313

0.950

0.060

0.310

1.892

0.4237

3.400

0.450

Nitroethane

0.270

0.950

0.020

0.330

2.414

0.5646

3.632

0.912

1-Nitrop

ropane

0.242

0.950

0.000

0.310

2.894

0.7055

3.854

1.404

2-Nitrop

ropane

0.216

0.920

0.000

0.330

2.550

0.7055

3.649

1.349

Dichlorom

ethane

0.390

0.570

0.100

0.050

2.019

0.4943

2.238

1.278

Trichlorom

ethane

0.430

0.490

0.150

0.020

2.480

0.6167

2.555

1.765

Tetrachlorom

ethane

0.460

0.380

0.000

0.000

2.823

0.7391

2.264

2.454

8 A. LU ET AL.

Table3.

Measuredlogarithm

ofgas-to-IL

partition

coefficients,logK,andlogarithm

ofwater-to-ILpartition

coefficients,logP,forsolutesdissolvedinanhydrou

s([4

-CNBPy]+[(T

f) 2N]−)at298.15

K.

Solute

ES

AB

LV

LogK

LogP

Pentane

0.000

0.000

0.000

0.000

2.162

0.8131

0.622

2.322

Hexane

0.000

0.000

0.000

0.000

2.668

0.9540

1.064

2.884

3-Methylpentane

0.000

0.000

0.000

0.000

2.581

0.9540

0.999

2.839

2,2-Dimethylbutane

0.000

0.000

0.000

0.000

2.352

0.9540

0.704

2.544

Heptane

0.000

0.000

0.000

0.000

3.173

1.0949

1.440

3.400

Octane

0.000

0.000

0.000

0.000

3.677

1.2358

1.792

3.902

2,2,4-Trimethylpentane

0.000

0.000

0.000

0.000

3.106

1.2358

1.395

3.515

Non

ane

0.000

0.000

0.000

0.000

4.182

1.3767

2.146

4.296

Decane

0.000

0.000

0.000

0.000

4.686

1.5176

2.526

4.846

Cyclop

entane

0.263

0.100

0.000

0.000

2.477

0.7045

1.152

2.032

Cycloh

exane

0.305

0.100

0.000

0.000

2.964

0.8454

1.516

2.416

Methylcyclohexane

0.244

0.060

0.000

0.000

3.319

0.9863

1.726

2.976

Cycloh

eptane

0.350

0.100

0.000

0.000

3.704

0.9863

2.065

2.645

Cyclooctane

0.413

0.100

0.000

0.000

4.329

1.1272

2.594

3.364

1-Pentene

0.093

0.080

0.000

0.070

2.047

0.7701

0.918

2.148

1-Hexene

0.078

0.080

0.000

0.070

2.572

0.9110

1.384

2.544

Cycloh

exene

0.395

0.280

0.000

0.090

2.952

0.8204

1.960

2.230

1-Heptene

0.092

0.080

0.000

0.070

3.063

1.0519

1.701

2.921

1-Octene

0.094

0.080

0.000

0.070

3.568

1.1928

2.032

3.442

1-Decene

0.093

0.080

0.000

0.070

4.554

1.4746

2.739

4.379

1-Pentyne

0.172

0.230

0.120

0.120

2.010

0.7271

1.644

1.654

1-Hexyne

0.166

0.220

0.100

0.120

2.510

0.8680

2.000

2.210

1-Heptyne

0.160

0.230

0.120

0.100

3.000

1.0089

2.342

2.782

1-Octyne

0.155

0.220

0.090

0.100

3.521

1.1498

2.670

3.190

Benzene

0.610

0.520

0.000

0.140

2.786

0.7164

2.811

2.181

Toluene

0.601

0.520

0.000

0.140

3.325

0.8573

3.199

2.549

Ethylbenzene

0.613

0.510

0.000

0.150

3.778

0.9982

3.430

2.850

o-Xylene

0.663

0.560

0.000

0.160

3.939

0.9982

3.741

3.081

m-Xylene

0.623

0.520

0.000

0.160

3.839

0.9982

3.563

2.958

p-Xylene

0.613

0.520

0.000

0.160

3.839

0.9982

3.543

2.953

Prop

ylbenzene

0.604

0.500

0.000

0.150

4.230

1.1390

3.686

3.296

Isop

ropylbenzene

0.602

0.490

0.000

0.160

4.084

1.1390

3.534

3.094

Styrene

0.849

0.650

0.000

0.160

3.908

0.9550

3.922

2.972

α-Methylstyrene

0.851

0.640

0.000

0.190

4.290

1.0960

4.109

3.149

Methano

l0.278

0.440

0.430

0.470

0.970

0.3082

2.551

−1.189

Ethano

l0.246

0.420

0.370

0.480

1.485

0.4491

2.723

−0.947

1-Prop

anol

0.236

0.420

0.370

0.480

2.031

0.5900

3.064

−0.496

2-Prop

anol

0.212

0.360

0.330

0.560

1.764

0.5900

2.767

−0.713

1-Bu

tano

l0.224

0.420

0.370

0.480

2.601

0.7309

3.419

−0.041

2-Bu

tano

l0.217

0.360

0.330

0.560

2.338

0.7309

3.080

−0.310

(Con

tinued)

PHYSICS AND CHEMISTRY OF LIQUIDS 9

Table3.

(Con

tinued).

Solute

ES

AB

LV

LogK

LogP

2-Methyl-1-propano

l0.217

0.390

0.370

0.480

2.413

0.7309

3.219

−0.081

tert-Butanol

0.180

0.300

0.310

0.600

1.963

0.7309

2.775

−0.505

1-Pentanol

0.219

0.420

0.370

0.480

3.106

0.8718

3.774

0.424

Thioph

ene

0.687

0.570

0.000

0.150

2.819

0.6411

2.955

1.915

Tetrahydrofuran

0.289

0.520

0.000

0.480

2.636

0.6223

2.820

0.270

1,4-Dioxane

0.329

0.750

0.000

0.640

2.892

0.6810

3.634

−0.076

Methyltert-bu

tyle

ther

0.024

0.220

0.000

0.550

2.372

0.8718

1.941

0.321

Ethyltert-bu

tyle

ther

−0.020

0.180

0.000

0.590

2.699

1.0127

1.739

0.469

Methyltert-am

ylether

0.050

0.210

0.000

0.600

2.916

1.0127

2.296

0.826

Diethylether

0.041

0.250

0.000

0.450

2.015

0.7309

1.586

0.416

Dipropyle

ther

0.008

0.250

0.000

0.450

2.954

1.0127

2.048

1.158

Diisop

ropyle

ther

−0.063

0.170

0.000

0.570

2.501

1.0127

1.636

0.586

Dibutylether

0.000

0.250

0.000

0.450

3.924

1.2945

2.688

1.998

Aceton

e0.179

0.700

0.040

0.490

1.696

0.5470

2.894

0.104

2-Pentanon

e0.143

0.680

0.000

0.510

2.755

0.8288

3.426

0.846

3-Pentanon

e0.154

0.660

0.000

0.510

2.811

0.8288

3.410

0.910

Methylacetate

0.142

0.640

0.000

0.450

1.911

0.6057

2.714

0.414

Ethylacetate

0.106

0.620

0.000

0.450

2.314

0.7466

2.929

0.769

Methylp

ropano

ate

0.128

0.600

0.000

0.450

2.431

0.7470

2.991

0.841

Methylb

utanoate

0.106

0.600

0.000

0.450

2.943

0.8880

3.249

1.169

Butanal

0.187

0.650

0.000

0.450

2.270

0.6879

2.927

0.597

Aceton

itrile

0.237

0.900

0.070

0.320

1.739

0.4042

3.231

0.381

Pyrid

ine

0.631

0.840

0.000

0.520

3.022

0.6750

3.831

0.391

1-Nitrop

ropane

0.242

0.950

0.000

0.310

2.894

0.7055

3.935

1.485

10 A. LU ET AL.

compounds having a fairly wide range of polarities and hydrogen-bonding capabilities as documentedby the values that fall within the range of: E = −0.063–0.851; S = 0.000–0.950; A = 0.000–0.430;B = 0.000–0.640; V = 0.2222–1.5176; and L = −0.978–4.686. The above range of solute descriptorspertain to ([BMIm]+[N(CN)2]

−). Slightly smaller ranges are observed in the case of both([BM2Im]+[(Tf)2N]

−) and ([4-CNBPy]+[(Tf)2N]−). The smaller ranges for the latter two IL solvents,

particularly in the V and L solute descriptor ranges, results from the absence of inorganic and smallerorganic gases in the data sets. The inorganic gases and smaller organic gases have smaller V and Ldescriptor values. Inorganic gases, such as nitrogen gas, nitrous oxide, and carbon dioxide have anegative value for their L solute descriptor.

3. Results and discussion

Solute descriptors are available for 67 of the 68 organic and inorganic compounds in the([BMIm]+[N(CN)2]

−) database. Analysis of the experimental log P and log K values in Table 1 inaccordance with Equations (1) and (2) of the Abraham model gave the following two IL-specificcorrelations:

log P ¼ � 0:272 0:065ð Þ þ 0:448 0:098ð Þ Eþ 0:722 0:113ð Þ Sþ 1:103 0:165ð Þ A� 4:437 0:113ð Þ Bþ 3:131 0:063ð Þ V

SD ¼ 0:118; N ¼ 67;R2 ¼ 0:992; and F ¼ 1609� � (10)

and

log K ¼ �0:773 0:034ð Þ þ 0:435 0:074ð Þ Eþ 2:553 0:075ð Þ Sþ 4:844 0:113ð Þ Aþ 0:505 0:078ð Þ Bþ 0:658 0:011ð Þ L

SD ¼ 0:082; N ¼ 67;R2 ¼ 0:995; and F ¼ 2561:7� �

;

(11)

where the standard error in each calculated equation coefficients is given in parenthesis imme-diately after the respective coefficient. The statistical information associated with each correlationincludes the standard deviation (SD), the number of experimental data points used in theregression analysis (N), the squared correlation coefficient (R2), and the Fisher F-statistic (F).The regression analyses used in deriving Equations (10) and (11) were performed using the IBMSPSS Statistics 22 commercial software.

The Abraham model correlations given by Equations (10) and (11) are statistically very good withSDs of less than 0.12 log units. Figure 1 compares the observed logK values against the back-calculatedvalues based on Equation (11). The experimental data covers a range of approximately 5.64 log units,from log K = −1.540 for nitrogen gas to log K = 4.101 for 1-butanol. A comparison of the back-calculated versus measured log P data is depicted in Figure 2. As expected, the SD for the log Pcorrelation is slightly larger than that of the log K correlations because the log P values contain theadditional experimental uncertainty in the gas-to-water partition coefficients used in the log K to log Pconversion. There is insufficient experimental data to permit a training set and test set assessment ofthe predictive ability of each derived equation by randomly splitting the entire database in half.

There is solubility data for xylitol dissolved in ([BMIm]+[N(CN)2]−) that can be used to assess

the predictive ability of our derived correlations. Xylitol was not included in the regressionanalysis, as we wanted to illustrate the predictive nature of Equations (10) and (11) with acompound not included in the regression analysis. The solute descriptors of xylitol are known(E = 1.040; S = 1.770; A = 0.540; B = 1.430; V = 1.1066; L = 6.087; logarithm of the aqueous molarsolubility = log 0.62; log Kw = 12.13), and when substituted into Equations (10) and (11) givepredicted values of log P = −0.812 and log K = 11.544. The predicted values are in reasonablygood agreement with the experimental values of log P = −0.631 and log K = 11.499, which werecalculated from the measured solubility of data of Carneiro and co-workers.[84] We note that

PHYSICS AND CHEMISTRY OF LIQUIDS 11

Paduszynski et al. [85] also measured the solubility of xylitol in ([BMIm]+[N(CN)2]−), and our

predicted values are in good agreement with this second set of solubility data, log P = −0.812(predicted) versus log P = −0.666 [85] and log K = 11.544 (predicted) versus log K = 11.464.[85]

The derived Abraham model correlations for ([BMIm]+[N(CN)2]−) provide us with the opportu-

nity to assess the predictive applicability of the ion-specific equation coefficient form of the Abrahammodel on a data set that was not used in determining the numerical values of the cation-specific andanion-specific equation coefficients. We recently updated our existing ion-specific equation coeffi-cients for both [BMIm]+ cation and [N(CN)2]

− anion based on 485 experimental log K and 509experimental log P values for solutes dissolved in ILs containing the [BMIm]+ cation, and based on150 experimental K and 136 experimental log P values for solutes dissolved in ILs containing the [N(CN)2]

− anion.[66] The majority of the experimental partition coefficient data given in Table 1 wasmeasured after our updated ion-specific equation coefficients were published. The only ([BMIm]+[N(CN)2]

−) values from Table 1 used in determining the [BMIm]+-specific and [N(CN)2]−-specific

equation coefficients were the partition coefficient data for nitrogen gas, carbon dioxide, and nitrous

Figure 1. Comparison between the observed log K data and calculated log K values based on Equation (11) for the 67inorganic and organic solutes dissolved in ([BMIm]+[N(CN)2]

−) at 298.15 K.

Figure 2. Comparison between the observed log P data and calculated log P values based on Equation (10) for the 67 inorganicand organic solutes dissolved in ([BMIm]+[N(CN)2]

−) at 298.15 K.

12 A. LU ET AL.

oxide. The calculated [BMIm]+-specific and [N(CN)2]−-specific equation coefficients are combined in

accordance with Equations (3) and (4) to yield the following predictive log P and log K correlations:

log P ¼ � 0:305 0:094ð Þ þ 0:492 0:126ð Þ Eþ 0:742 0:139ð Þ Sþ 0:835 0:180ð Þ A� 4:593 0:148ð Þ Bþ 3:147 0:085ð Þ V (12)

and

logK ¼ � 0:793 0:056ð Þ þ 0:378 0:108ð Þ Eþ 2:610 0:108ð Þ Sþ 4:551 0:142ð Þ Aþ 0:405 0:120ð Þ Bþ 0:657 0:017ð Þ L (13)

Comparison of Equations (10)–(13) shows that the equation coefficients obtained from theindividual ion-specific equation coefficients are identical to the equation coefficients of the IL-specific Abraham model correlations to within the combined standard errors in the respectiveequation coefficients. Equations (12) and (13) predict the experimental partition coefficient datagiven in Table 1 to within a standard error of SE = 0.16 log units and SE = 0.11 log units,respectively. These calculations represent outright predictions, rather than back calculations, inthat the experimental values were not used in determining the equation coefficients. The calcula-tions are in accord with our earlier observations, in that the IL-specific Abraham model correla-tions generally provide a slightly better mathematical description of the experimental data for thegiven IL than do Abraham model correlations constructed with ion-specific equation coefficients.

Data sets for both ([BM2Im]+[(Tf)2N]−) and ([4-CNBPy]+[(Tf)2N]

−) contain experimental parti-tion coefficient data for a minimum of 60 different liquid organic compounds of varying polarityand hydrogen-bonding character. Preliminary analysis of the experimental partition coefficient datacompiled in Table 2 revealed that the ek,il·E term in the log K equation for ([BM2Im]+[(Tf)2N]

−)contributed very little to the overall partition coefficient calculation. The numerical value of thecoefficient was small (ek,il = 0.031). Moreover, the standard error (standard error = 0.081) in thecalculated ek,il coefficient was more than 2.5 times greater than the coefficient itself. The ek,il·E termwas deleted from the log K correlation for ([BM2Im]+[(Tf)2N]

−), and the data in Tables 2 and 3 wereanalysed to yield the following Abraham model correlations for ([BM2Im]+[(Tf)2N]

−):

log P ¼ � 0:347 0:128ð Þ þ 0:111 0:116ð Þ Eþ 0:718 0:105ð Þ S� 1:195 0:166ð Þ A� 4:418 0:114ð Þ Bþ 3:502 0:102ð Þ V

SD ¼ 0:121; N ¼ 60;R2 ¼ 0:994; and F ¼ 1896� � (14)

log K ¼ � 0:641 0:078ð Þ þ 2:429 0:052ð Þ Sþ 2:663 0:110ð Þ Aþ 0:521 0:072ð Þ Bþ 0:721 0:020ð Þ LSD ¼ 0:085; N ¼ 60;R2 ¼ 0:981; and F ¼ 692� �

(15)

and for ([4-CNBPy]+[(Tf)2N]−):

log P ¼ � 0:316 0:105ð Þ þ 0:132 0:105ð Þ Eþ 1:015 0:124ð Þ S� 1:040ð0:164Þ A� 4:399 0:122ð Þ Bþ 3:272 0:093ð Þ V

SD ¼ 0:123;N ¼ 64;R2 ¼ 0:992; and F ¼ 1641� � (16)

log K ¼ � 0:768 0:065ð Þ þ 0:086 0:085ð Þ Eþ 2:810 0:086ð Þ Sþ 2:685 0:119ð Þ Aþ 0:553 0:090ð Þ Bþ 0:691 0:020ð Þ L

SD ¼ 0:091;N ¼ 64;R2 ¼ 0:990; and F ¼ 1127� � (17)

PHYSICS AND CHEMISTRY OF LIQUIDS 13

No loss in descriptive ability was observed from removal of the ek,il·E term from Equation (14).An identical SD of 0.085 was calculated for the correlation with and without the ek,il·E term. Asbefore, the IBM SPSS Statistics 22 software was used in performing the four regression analyses.The low SDs and near-unity squared correlations associated with each of the derived correlationsindicate that the four IL-specific mathematical equations provide a reasonably accurate mathe-matical description of the observed partition coefficient data. Comparisons of the observed log Kand log P data versus calculated values based on Equations (14)–(17) are depicted in Figures 3–6.

The derived Abraham model correlations for ([BM2Im]+[(Tf)2N]−) and ([4-CNBPy]+[(Tf)

2N]−) can be used to calculate ion-specific equation coefficients for both the [BM2Im]+ and [4-

CNBPy]+ cations with minimal effort. At the time we proposed the ion-specific version of theAbraham model, we had to establish a reference point in order to calculate equation coefficientsfor the individual ions. In IL solvents the ions appear as cation–anion pairs, and it is not possibleto calculate single-ion coefficients in the absence of a reference point. This is analogous to trying

Figure 3. Comparison between the observed log K data and calculated log K values based on Equation (15) for the 60 organicsolutes dissolved in ([BM2Im]+[(Tf)2N]

−) at 298.15 K.

Figure 4. Comparison between the observed log P data and calculated log P values based on Equation (14) for the 60 organicsolutes dissolved in ([BM2Im]+[(Tf)2N]

−) at 298.15 K.

14 A. LU ET AL.

to calculate the chemical potentials of single ions or ionic-limiting molar conductances ofindividual ions for a dissolved ionic salt. In the latter case, one often utilises the tetrabutylammo-nium tetraphenylborate reference electrolyte, [86] which assumes that ionic-limiting molar con-ductance of tetrabutylammonium cation is equal to the ionic-limiting molar conductance of thetetraphenylborate anion. The rationale for setting the ionic limiting molar conductances of thesetwo specific ions equal to each other was that both ions were large and were of approximatelyequal size. Neither ion was expected to undergo much (if any) specific interactions with thesurrounding solvent molecules.

The reference point for calculating ion-specific Abraham model equation coefficients for ILsolvents was set more from the standpoint of mathematical convenience. At the time the ion-specific equation version of the Abraham model was first proposed, the majority of the ILs in theregression database contained the bis(trifluoromethylsulfonyl)imide anion, [(Tf)2N]

−. Setting allof the [(Tf)2N]

− equation coefficients equal to zero greatly simplified the calculations. Other

Figure 5. Comparison between the observed log K data and calculated log K values based on Equation (17) for the 64 organicsolutes dissolved in ([4-CNBPy]+[(Tf)2N]

−) at 298.15 K.

Figure 6. Comparison between the observed log P data and calculated log P values based on Equation (16) for the 64 organicsolutes dissolved in ([4-CNBPy]+[(Tf)2N]

−) at 298.15 K.

PHYSICS AND CHEMISTRY OF LIQUIDS 15

reference points could have been set; however, the end result would still be the same. The sum ofthe respective cation-specific plus anion-specific equation coefficients would be independent ofthe reference point. Thus, the calculated coefficients in Equations (14) and (15) represent thecation-specific Abraham model equation coefficients for [BM2Im]+, while the calculated coeffi-cients in Equations (16) and (17) correspond to the cation-specific equation coefficients for [4-CNBPy]+. The newly calculated cation-specific equation coefficients can be combined with ourexisting 17 anion-specific equation coefficients [61,66] to enable one to predict log K and log Pvalues for solutes dissolved in an additional 34 IL solvents.

4. Conclusions

The ionic-liquid-specific Abraham model correlations that have been developed in the presentstudy for anhydrous 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-2,3-dimethylimidazo-lium bis(trifluoromethylsulfonyl)imide, and 4-cyano-1-butylpyrridinium bis(trifluoromethylsulfo-nyl)imide provide very good mathematical descriptions of solute transfer into these three ILsolvents from both the gas phase and from water. The derived mathematical correlations describethe observed solute transfer properties, log P and log K, to within SDs of 0.125 log units (or less).The applicability of the ion-specific equation coefficient form of the Abraham model is success-fully illustrated for 1-butyl-3-methylimidazolium dicyanamide. Previously calculated ion-specificequation coefficients for [BMIm]+ cation and [N(CN)2]

− anion are combined to give predictiveAbraham model correlations, Equations (12) and (13), that estimate the measured log P and log Kvalues to within 0.16 and 0.11 log units, respectively. The measured log P and log K values foranhydrous ([BMIm]+[N(CN)2]

−) were not used in deriving the ion-specific equation coefficients,so the calculations represent outright predictions. Ion-specific equation coefficients are calculatedfor two additional cations, [BM2Im]+ and [4-CNBPy]+, allowing one to estimate the partitioningbehaviour of solutes dissolved in 34 more anhydrous IL solvents.

Disclosure statement

No potential conflict of interest was reported by the authors.

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