Activity Coefficients at Infinite Dilution of Organic Compounds in 1

J. Phys. Chem. B 2008, 112, 3773-3785

3773

Activity Coefficients at Infinite Dilution of Organic Compounds in 1-(Meth)acryloyloxyalkyl-3-methylimidazolium Bromide Using Inverse Gas Chromatography Fabrice Mutelet,*,† Jean-Noe1 l Jaubert,† Marek Rogalski,‡ Julie Harmand,‡ Miche` le Sindt,‡ and Jean-Luc Mieloszynski‡ Laboratoire de Thermodynamique des Milieux Polyphase´ s, Nancy-UniVersite´ , 1 rue GrandVille, BP 20451 4001 Nancy, France, Laboratoire de Chimie et de Me´ thodologies pour l’EnVironnement, EA 4164, UniVersite´ Paul Verlaine, 1, bd Arago-57078 Metz, Cedex 3, France ReceiVed: NoVember 19, 2007; In Final Form: December 21, 2007

Activity coefficients at infinite dilution, γ∞, of organic compounds in two new room-temperature ionic liquids (n-methacryloyloxyhexyl-N-methylimidazolium bromide (C10H17O2MIM)(Br) at 313.15 and 323.15 K and n-acryloyloxypropyl-N-methylimidazolium bromide(C6H11O2MIM)(Br)) were determined using inverse gas chromatography. Phase loading studies of the net retention volume per gram of packing as a function of the percent phase loading were used to estimate the influence of concurrent retention mechanisms on the accuracy of activity coefficients at infinite dilution of solutes in both ionic liquids. It was found that most of the solutes were retained largely by partition with a small contribution from adsorption and that n-alkanes were retained predominantly by interfacial adsorption on ionic liquids studied in this work. The solvation characteristics of the two ionic liquids were evaluated using the Abraham solvation parameter model.

Introduction Ionic liquids (ILs) are low-melting organic salts built with an unsymmetrical organic cation and an anion that is mostly inorganic. Physical and chemical properties of ILs are influenced not only by the nature of the cation and the nature of cation substituents but also by the polarity and the size of the anion. Interactions between IL cations and anions are the consequence of energetic and geometric factors leading to a variety of strongly organized and oriented structures. These features confer to ILs numerous applications in organic synthesis, separation processes, and electrochemistry.1-9 This study is a continuation of our investigations on thermodynamic properties of imidazolium ionic liquids10-13 and more particularly on the influence of polar substituents on the cation. We previously studied two families of ILs: 1-propenyl3-alkyl-imidazolium bromides and 1-propyl boronic acid-3alkyl-imidazolium bromides. In this study, we deal with n-acryloyloxypropyl-N-methylimidazolium bromide and n-methacryloyloxyhexyl-N-methylimidazolium bromide. The aim of this work is to determine the influence of the acrylic moiety on the thermodynamic properties of the ionic liquid. For this purpose, we have measured activity coefficients at infinite dilution for a series of organic compounds dissolved in these ILs. All of these measurements were performed using the gas chromatography technique as described in our previous studies in which we measured activity coefficients at infinite dilution of organic compounds in various ionic liquids (1-butyl3-methylimidazolium hexafluorophosphate, 1-methyl-3-octylimidazolium chloride, 1-methyl-3- ethylimidazoliumbis(triflu* To whom the correspondence should be addressed. Phone: +33 3 83 17 51 31. Fax: +33 3 83 17 51 52. E-mail: [email protected]. † Nancy-Universite ´. ‡ Universite ´ Paul Verlaine.

oromethylsulfonyl)amide,10 1-butyl-3-methylimidazolium octyl sulfate, 1-ethyl-3-methylimidazolium tosylate,11 1-propyl boronic acid-3-alkylimidazolium bromide, and 1-propenyl-3alkylimidazolium bromide12). The retention in gas chromatography is a complex process involving partition between the gas and the liquid phases and the adsorption at solid-liquid and gas-liquid interfaces. The latter type of adsorption is observed with nonsoluble solutes in the stationary phase. Therefore, the comprehensive retention model would have to consider not only the contribution resulting from the gas-liquid partitioning but also the adsorption occurring at the interface between the bulk liquid and the solid support and at the interface between the gas phase and the bulk liquid.14-17 When supports of low surface area and high liquidphase loadings are used, the adsorption phenomena at the support-stationary phase interface may be neglected. A general equation encompassing partition and interfacial adsorption contributions to retention can be written as follows:18-20

VN ) VLKL + AGLKGL + ALSKGLS

(1)

where VN is the net retention volume per gram of packing, VL is the volume of the liquid phase per gram of packing, KL is the gas-liquid partition coefficient, AGL is the liquid surface area per gram of column packing, KGL is the adsorption coefficient at the gas-liquid interface, ALS is the liquid-solid interfacial surface area per gram of column packing, and KGLS is the coefficient for adsorption at the support surface. For practical purposes eq 1 can be rewritten as follows:

AGLKGL + ALSKGLS VN ) KL + VL VL

(2)

Equation 2 is valid when the solute is either at infinite dilution or at zero coverage with respect to all possible retention

10.1021/jp7109862 CCC: $40.75 © 2008 American Chemical Society Published on Web 03/05/2008

3774 J. Phys. Chem. B, Vol. 112, No. 12, 2008

Mutelet et al.

Figure 1. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-acryloyloxypropyl-N-methylimidazolium bromide for n-alkanes.

Figure 2. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-acryloyloxypropyl-N-methylimidazolium bromide for aromatics, alkenes and alkynes.

mechanisms or at constant concentration independent of VL. Performing a series of measurements with increasing loading of the liquid phase makes it possible to extrapolate the VN/VL ratio against against 1/VL toward 1/VL ) 0 and to obtain the value of the gas-liquid partition coefficient, KL, independent of adsorption contributions. This approach was successfully used to obtain gas-liquid partition coefficients of polar probes.6-17,21 Kersten and Poole16 studied the influence of concurrent retention mechanisms on the determination of stationary phase selectivity. Using eq 2, these authors estimated the values of partition coefficients of organic compounds. They found that the difference between the uncorrected and corrected retention indexes of some McReynolds solutes can rise up to 60%. Moreover,

they showed that the n-alkanes were retained predominantly by interfacial adsorption on butylammonium nitrate and propylammonium nitrate. This can be explained because of the immiscibility of n-alkanes with polar salts. Ionic liquids can easily adsorb onto solid surfaces and may form a strongly structured interface at the surface of the support. This interface may induce the adsorption of polar solutes. For this reason, it was decided to use the above-described experimental procedure that allows the separation of the adsorption contribution. To quantify intermolecular solute-IL interactions, we have used the linear solvation energy relationship (LSER) developed by Abraham et al.22-25 This method allows one to correlate

Activity Coefficients of Organic Compounds

J. Phys. Chem. B, Vol. 112, No. 12, 2008 3775

Figure 3. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-acryloyloxypropyl-N-methylimidazolium bromide for some polar probes.

Figure 4. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-acryloyloxypropyl-N-methylimidazolium bromide for some polar probes.

thermodynamic properties of phase transfer processes. The most recent representation of the LSER model is given by eq 3

log SP ) c + eE + sS + aA + bB + lL

(3)

where SP is a solute property related with the free energy change, such as the gas-liquid partition coefficient, specific retention volume or adjusted retention time at a given temperature. The capital letters represent the solutes properties, and the lower case letters, the complementary properties of the ionic liquids. The solute descriptors are the excess molar refraction E; dipolarity/polarizability S; hydrogen bond acidity basicity, A and B, respectively; and the gas-liquid partition coefficient

on n-hexadecane at 298 K, L. The coefficients c, e, s, a, b and l are not simply fitting coefficients, but they reflect complementary properties of the solvent phase. The system constants are identified as the opposing contributions of cavity formation and dispersion interactions, l; the contribution from interactions with lone pair electrons, e; the contribution from dipole-type interactions, s; the contribution from the hydrogen-bond basicity of the stationary phase (because a basic phase will interact with an acid solute), a; and b, the contribution from the hydrogen-bond acidity of the stationary phase. The system constants are determined by multiple linear regression analysis of experimental log SP (log KL in this work)


Mutelet et al.

Figure 5. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-methacryloyloxyhexyl-Nmethylimidazolium bromide for n-alkanes.

Figure 6. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-methacryloyloxyhexyl-Nmethylimidazolium bromide for aromatics, alkenes, and alkynes.

values for a group of solutes of sufficient number and variety to establish the statistical and chemical validity of the model. In this work, activity coefficients at infinite dilution of 31 polar and nonpolar compounds (alkanes, alkenes, alkynes, cycloalkanes, aromatics, alcohols) have been determined in two ionic liquids: n-methacryloyloxyhexyl-N-methylimidazolium bromide (C10H17O2MIM)(Br) at 313.15 and 323.15 K and

n-acryloyloxypropyl-N-methylimidazolium bromide (C6H11O2MIM)(Br). Experimental results were analyzed using LSER approach.

Experimental Procedures and Results Materials or Chemicals. The ionic liquids were prepared according to the following procedure: n-bromoalkyl (meth)-



acrylate was prepared via an esterification using a Dean-Starck apparatus. One equivalent of n-bromo-1-alcohol, 0.1 equiv of p-toluenesulfonic acid (PTSA), and a few parts per million of 4-ethoxyphenol were dissolved in cyclohexane and stirred at 80 °C for 1 h. A solution of 1.2 equiv of (meth)acrylic acid and cyclohexane was then added drop-by-drop to the latter mixture. Then the reaction mixture was maintained at 80 °C for 12 h. After cooling, the preparation was washed three times with NaOH 10%. The organic solution was dried on MgSO4, and evaporation under vacuum led to a pure n-bromoalkyl (meth)acrylate. The n-(meth)acryloyloxyalkyl-N-methylimidazolium bromide was obtained by the bromine atom substitution using Nmethylimidazole at 50 °C over 24 h and without any solvent. The reaction mixture was stirred in diethyl ether, filtered on Bu¨chner, and separated from the organic layer for n-acryloyloxypropyl-N-methylimidazolium bromide and n-methacryloyloxyhexyl-N-methylimidazolium bromide. After the removing of the solvent under reduced pressure, both ionic liquids were isolated with a yield higher than 95% and characterized with 1H NMR, 13C NMR, and IR spectra. Apparatus and Experimental Procedure. Inverse chromatography experiments were carried out using a Varian CP-3800 gas chromatograph equipped with a heated on-column injector and a flame ionization detector. The injector and detector temperatures were kept at 523 K during all experiments. The helium flow rate was adjusted to obtain adequate retention times. Methane was used to determine the column hold-up time. Exit gas flow rates were measured with an Alltech digital flow check mass flowmeter. The temperature of the oven was measured with a Pt 100 probe and controlled to within 0.1 K. A personal computer directly recorded detector signals, and corresponding chromatograms were obtained using Galaxie software. Column packing of 1 m length containing from 7 to 26% of stationary phases (RTIL) on Chromosorb W-AW (60-80 mesh) were prepared using the rotary evaporator technique. After evaporation of the dichloromethane under vacuum, the support was equilibrated at 323 K over 6 h. The mass of the packing material was calculated from the mass of the packed and empty column and was checked during experiments. The masses of the stationary phase were determined with a precision of 0.0003 g. A volume of the headspace vapor of samples of 1-5 µL were introduced to be in infinite dilution conditions. Each experiment was repeated at least twice to check the reproducibility. Retention times were generally reproducible to within 0.01-0.03 min. To check the stability of the experimental conditions, such as the possible eluation of the stationary phase by the helium stream, the measurements of retention times were repeated systematically every day for three selected solutes. No changes in the retention times were observed during 3 months of continuous operation. Theoretical Basis. The retention data determined with inverse chromatography experiments were used to calculate activity coefficients at infinite dilution of the solute in the ionic liquid. The standardized retention volume, VN, was calculated using the following usual relationship:26

VN ) JU0tR′

(

)

Tcol P0w × 1Tr P0

(4)

The adjusted retention time, tR′, was taken as a difference between the retention time of a solute and that of the methane. Tcol is the column temperature; U0 is the flow rate of the carrier gas measured at room temperature, Tr; P0w is the vapor pressure

of water at Tr; and P0 is the pressure at the column outlet. The factor J in eq 4 corrects for the influence of the pressure drop along the column and is given by eq 5,27

3 J) × 2

[( ) ] [( ) ] Pi 2 -1 P0 Pi 3 -1 P0

(5)

where Pi and P0 are respectively the inlet and outlet pressures. The activity coefficient at infinite dilution of a solute 1 in the stationary phase 2 (RTIL) was calculated using the following expression:26

ln γ∞1,2 ) ln

( ) n2RT

VNP10

- P01

B11 - V01 2B13 - V∞1 + JP0 (6) RT RT

n2 is the mole number of the stationary phase component inside the column, R is the ideal gas constant, T is the temperature of the oven, B11 is the second virial coefficient of the solute in the gaseous state at temperature T, B13 is the mutual virial coefficient between the solute 1 and the carrier gas helium 3, and P01 is the probe vapor pressure at temperature T. The values of P01 and B11 have been taken from the literature.28 The molar volume of the solute V01 was determined from experimental densities, and the partial molar volumes of the solutes at infinite dilution, V∞1 were assumed to be equal to V01. Values of B13 have been estimated using Tsonopolous’s method.29-31 Critical parameters and acentric factors used for the calculations were taken from the literature;28,32 however, in the case that gas-liquid adsorption takes place in the column, eq 6 when the last two terms are neglected can be rewritten as follows:

γ∞1,2 )

RTF2 P01M2KL

(7)

where F2 is the density of the solvent, M2 is the molecular weight of the stationary phase, and KL is the bulk solution partition coefficient. The best method of determining KL in the presence of interfering adsorption effects is to plot VN/VL against 1/VL. Then according to eq 2, KL is obtained from the intercept. Results and Discussion Influence of Concurrent Retention Mechanisms. The net retention volume, VN, was calculated for all the solutes at different solvent liquid loading, VL. To correct for gas-liquid adsorption, the graphs of VN/VL versus 1/VL were drawn for each solute, and the partition bulk coefficient, KL, was obtained from the intercept. A horizontal line is expected for a pure partitioning system, and a line with a slope and positive intercept on the VN/VL axis, for a mixed retention mechanism. The KL value is then used in eq 7 to calculate the activity coefficient at infinite dilution for bulk solvent loading, that is, assuming that no adsorption of the solute at the gas-liquid interface occurs. The activity coefficients at infinite dilution not corrected from interfacial adsorption are calculated using eqs 4-6. The errors in the γ∞ values may be obtained from the law of propagation of errors. The following measured parameters exhibit errors that must be taken into account in the error calculations with their corresponding standard deviations: the adjusted retention time, tR′, 0.01 min; the flow rate of the carrier gas, 0.1 cm3/min; mass


Mutelet et al.

Figure 7. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-methacryloyloxyhexyl-Nmethylimidazolium bromide for some polar probes.

Figure 8. A plot of the net retention volume per gram of packing as a function of percent phase loading of n-methacryloyloxyhexyl-Nmethylimidazolium bromide for some polar probes.

of the stationary phase, 2%; the inlet and outlet pressures, 0.002 bar; and the temperature of the oven, 0.2 K. The main source of error in the calculation of the net retention volume is the determination of the weight of the stationary phase. The estimated error in determining the net retention volume, VN, is ∼2%. Taking into account that thermodynamic parameters are also subject to an error, the resulting error in the γ∞ values is ∼3%; however, the peak shape of pyridine, 1-nitropropane, and triethylamine on both ionic liquids is asymmetric, resulting in inaccurate activity coefficients. In this case, the estimated error in the γ∞ values is ∼10%. In Figures 1-8, the net retention volume per gram of packing, VN/, as a function of the percent phase loading is plotted for nonpolar and polar solutes. In both ionic liquids, the polar solutes

are retained by partitioning with an actual contribution from adsorption whereas the n-alkanes are retained predominantly by adsorption. Indeed, n-alkanes are almost immiscible in ionic liquids. Figures 1 and 5 indicate that the retention of the n-alkanes with an ionic liquid stationary phase does not follow the pattern observed with polar solutes. Probably at low loading of the stationary, the support is not completely coated, and results do not follow the initial straight line. The relative percent contribution of gas-liquid partitioning and gas-liquid interfacial adsorption to retention on n-acryloyloxypropyl-N-methylimidazolium bromide (8.31%, w/w) at 313.15 K is represented in Figure 9. The average contribution of gas-liquid partitioning and gas-liquid interfacial adsorption of polar solutes to retention is 90% and 10%, respectively.



Figure 9. Relative percent contribution of gas-liquid partitioning and gas-liquid interfacial adsorption to retention on n-acryloyloxypropyl-Nmethylimidazolium bromide (8.30% w/w) at 313.15 K.

Figure 10. A plot of VN/VL against 1/VL for aromatics, alkenes, and alkynes on n-acryloyloxypropyl-N-methylimidazolium bromide.

The gas-liquid partition coefficients were calculated from Figures 10-15, and activity coefficients at infinite dilution were determined from values of the KL constants. Values for the gasliquid partition coefficients with their uncertainty and activity coefficients at infinite dilution uncorrected and corrected from interfacial adsorption are listed in Tables 1 and 2. The differences between the corrected and uncorrected activity coefficients at infinite dilution vary from ∼0.5 to 16%. The observed γ∞ values are lower in n-methacryloyloxyhexyl-Nmethylimidazolium bromide than in n-acryloyloxypropyl-Nmethylimidazolium bromide. The magnitude of the activity coefficient values obtained in this study is significantly higher than the corresponding values for other ionic liquids.9-12,38-41 As an example, the γ∞ value

for hexane in n-acryloyloxypropyl-N-methylimidazolium bromide is 171.0 (this work), but in 1-butyl-3-methylimidazolium octyl sulfate,38 it is 4.75; in 1-hexyl-3-methylimidazolium tetrafluoroborate,10 it is 22.1; in 1-ethyl-3-methylimidazolium trifluoroacetate,41 it is 77.8; and for 1-ethyl-3-methylimidazolium ethylsulphate,36 it is 112.7. The high values of the activity coefficients at infinite dilution of n-alkanes indicate their low solubility in both ionic liquids. This trend is in good agreement with the data obtained in the imidazolium10-13 and pyridinium33,34 ionic liquids. The γ∞ values for the n-alkanes increase with an increase in carbon number. The γ∞ values of n-alkanes are higher than the values obtained with cyclohexane, alkenes, alkynes, and aromatics. Introduction of a double or triple bond in the n-alkanes decreases the γ∞ values. Cyclization


Mutelet et al.

Figure 11. A plot of VN/VL against 1/VL for alcohols, ketones, 1.4 dioxane, and ether on n-acryloyloxypropyl-N-methylimidazolium bromide.

Figure 12. A plot of VN/VL against 1/VL for some test probes on n-acryloyloxypropyl-N-methylimidazolium bromide.

of the alkane skeleton reduces the value of γ∞ in comparison to that of the corresponding linear alkanes (e.g., hexane): the more polar the solute, the stronger interactions with ionic liquids. Aromatics with their π-delocalized electrons have smaller γ∞ values, presumably because of the interaction with the cation species. In the series of chloromethanes, it was observed that γ∞ values strongly increase from dichloromethane to tetrachloromethane. This behavior, already observed with different ionic liquids,11,13 indicates that polar compounds have better solubility in the RTILs when attractive interaction between polar molecules and the charged ions of the solvent is possible. The γ∞ values for the alcohols are relatively small (ranging between 0.33 and 1.40 with the n-acryloyloxypropyl-N-methylimidazolium bromide and between 0.15 and 0.65 with the n-methacryloyloxyhexyl-N-methylimidazolium bromide).

In the case of alcohols, the lone pair of electrons on the oxygen atom could interact with the ionic liquid cation, and the acidic proton is attracted by oxygen atoms in the cation. γ∞ values of n-alkanols increase with increasing chain length. γ∞ values of branched alkanol skeleton are smaller than γ∞ values of the corresponding linear alcohol. γ∞ values of ketones, pyridine, thiophene, acetonitrile, and acetone are higher in comparison with those of the alcohols. Letcher et al.42 published the experimental γ∞ of organic solutes in 1-butyl-3-methylimidazolium 2-(2-methoxyethoxy) ethyl sulfate, an ionic liquid with a similar polar group in the anion. γ∞ values obtained follow the same trend as those measured in this work. From these results and our previous works, some observations can be made. It is clear that increasing the alkyl chain length of imidazolium ionic liquids tends to increase the solubility of



Figure 13. A plot of VN/VL against 1/VL for aromatics, alkene,s and alkynes on n-methacryloyloxyhexyl-N-methylimidazolium bromide.

Figure 14. A plot of VN/VL against 1/VL for alcohols, ketones, 1.4 dioxane, and ether on n-methacryloyloxyhexyl-N-methylimidazolium bromide.

most organic compounds in ionic liquids. Introduction of a polar chain into ionic liquids also affects strongly the behavior of organic compounds in mixtures with the ionic liquids. The selectivity, S∞12, which indicates the suitability of a solvent for separating mixtures of components 1 and 2 by extractive distillation is given by35

S∞12 )

∞ γ1/RTIL ∞ γ2/RTIL

(8)

The selectivity values, S∞12, relative either to the IL studied in this work or to liquid solvents used in industry for the separation of benzene and n-hexane, are reported in Table 3. The selectivity of both ionic liquids studied in this work at 313.15 K is very large as compared to the value for classical solvents. The

selectivity increases with decreasing length of the alkyl chain. This trend was already observed with imidazolium compounds with bromide2 or bis-(trifluoromethylsulfonyl)imide36 as anion. It is obvious that the chemical nature of the cation and the anion play an important role in separation of mixtures of aromatic and aliphatic compounds. Table 3 shows that selectivity decreased when the (BF4)- was changed to (EtSO4)- or (Tf2N)-. The selective solubility of gaseous mixtures in ILs is also important information. In Table 3, we also give log KL2 - log KL1, the selective solubility of gases in solvents for the pair of solutes hexane and benzene. As observed by Abraham and Acree,43 the ILs show about the same selectivity as the polar organic solvents. LSER Characterization. Two ionic liquids studied in this work were analyzed using the above-described (eq 3) LSER approach. Coefficients c, e, s, a, b, and l of the ionic liquids


Mutelet et al.

Figure 15. A plot of VN/VL against 1/VL for some test probes on n-methacryloyloxyhexyl-N-methylimidazolium bromide.

TABLE 1: Experimental Activity Coefficients at Infinite Dilution of 30 Organic Compounds in the n-Acryloyloxypropyl-N-methylimidazolium Bromide at 313.15 and 323.15 K T/K 313.15

323.15

uncorrected values of γ∞ % phase loading solutes

8.30

uncorrected values of γ∞ corrected data

11.94

15.31

19.02

hexane 94.02 106.40 heptane 78.66 133.82 octane 107.31 169.32 nonane 117.09 193.61 cyclohexane 69.37 84.45 benzene 6.73 5.86 toluene 12.10 10.71 ethylbenzene 20.51 18.80 m-xylene 22.14 20.54 o-xylene 10.64 10.84 1-hexene 50.18 60.47 1-hexyne 16.15 16.12 1-heptyne 22.61 25.23 2-butanone 4.96 4.24 2-pentanone 7.45 6.54 1,4 dioxane 3.26 2.76 methanol 0.33 0.26 ethanol 0.52 0.63 1-propanol 1.00 0.99 2-propanol 1.28 1.27 2-methyl-1-propanol 1.40 1.45 diethyl ether 23.67 24.27 chloroform 0.50 0.46 dichloromethane 0.64 0.59 tetrachloromethane 4.42 3.76 acetonitrile 1.58 1.06 1-nitropropane 3.49 3.05 triethylamine 1.48 1.51 pyridine 1.49 1.57 thiophene 3.32 2.86

116.16 157.05 177.10 307.59 97.28 5.76 10.97 19.72 21.26 11.16 63.68 17.95 28.50 4.23 6.91 2.70 0.23 0.59

152.92 1.8 ( 0.2 227.10 5.3 ( 0.5 306.17 7.4 ( 0.6 355.12 13.0 ( 0.9 118.72 3.0 ( 0.3 5.84 75.5 ( 0.5 11.37 111.4 ( 1.4 20.82 151.2 ( 2.8 22.46 161.6 ( 3.8 11.46 282.2 ( 5.9 85.80 0.5 ( 0.4 17.98 12.1 ( 0.8 31.04 17.3 ( 0.9 4.32 111.1 ( 1.7 7.12 127.9 2.71 416.1 0.29 1026.4 ( 37.4 0.46 1252.0 ( 22.8 1642.2 ( 10.7 1.18 605.7 ( 12.1 1943.6 ( 15.1 28.91 2.3 ( 0.11 0.50 392.6 ( 8.7 0.60 123.3 ( 5.1 3.82 95.9 ( 2.1 0.99 610.7 ( 15.1 2.83 1278.8 ( 25.6 1.57 394.5 ( 6.1 1.98 434.3 ( 15.2 2.50 221.9 ( 12.2

1.26 26.83 0.48 0.58 3.96 0.96 2.92 1.84 1.83 2.83

KL

were obtained by multiple linear regression of the logarithm of the gas-liquid partition coefficients log KL of 29 solutes. LSER parameters of the probes are given in Table 4. The system constants for both ionic liquids studied in this work at 313.15

% phase loading γ∞

corrected data

11.94

15.31

19.02

KL

γ∞

171.00 46.40 83.30 174.11 74.26 127.39 211.51 101.19 162.94 245.68 110.40 185.27 153.24 65.53 84.61 6.18 6.64 5.63 12.94 11.69 10.45 31.00 19.60 18.85 27.76 21.13 19.68 13.41 10.32 15.48 474.61 47.49 56.67 26.89 15.50 16.58 70.96 21.57 25.57 4.33 4.98 4.15 8.07 7.32 7.04 2.73 3.38 2.85 0.31 0.62 0.34 0.51 0.80 0.50 1.63 1.26 0.98 1.35 1.52 1.23 2.96 1.63 1.44 48.63 22.56 22.43 0.60 0.79 0.51 0.69 0.92 0.65 4.16 4.47 3.87 0.82 1.80 1.07 2.89 3.59 3.11 1.63 1.71 1.15 4.34 1.72 1.90 2.47 3.44 2.87

109.52 147.95 166.81 289.48 91.77 5.73 10.63 18.85 20.30 10.81 60.18 17.19 27.10 4.29 6.81 2.86 0.53 0.87

144.08 213.81 288.14 334.17 111.92 5.80 11.01 19.89 21.43 11.09 80.97 17.22 29.49 4.38 7.01 2.87 0.58 0.75

1.50

1.42

25.54 0.77 0.86 4.04 1.22 3.06 2.05 2.03 2.97

27.50 0.78 0.88 3.91 1.25 2.98 1.79 2.18 2.66

2.1 ( 0.2 6.1 ( 0.4 8.3 ( 0.4 15.3 ( 0.5 4.1 ( 0.3 58.86 ( 0.6 78.97 ( 1.2 85.44 ( 2.2 107.10 ( 2.9 174.64 ( 4.8 16.90 ( 0.6 23.36 ( 0.7 24.07 ( 0.8 78.79 ( 1.4 88.21 ( 1.4 249.60 ( 5.4 591.37 ( 11.2 717.74 ( 15.2 574.47 ( 10.1 355.80 ( 5.2 545.03 ( 5.4 1.7 ( 0.1 236.44 ( 8.1 85.62 ( 1.1 70.29 ( 0.9 358.58 ( 7.8 732.71 ( 12.2 237.50 ( 5.1 259.81 ( 5.0 140.85 ( 2.4

163.29 168.15 202.54 222.84 141.32 5.51 12.09 28.57 26.24 19.73 10.72 10.03 27.05 4.08 8.30 2.98 0.36 0.56 1.68 1.39 2.92 45.2 0.72 0.76 4.01 0.96 3.14 1.87 4.70 2.68

8.30

K and other ionic and nonionic liquid stationary phases are summarized in Table 5. The system constants for nonionic or ionic liquids not studied in this work are taken from the literature.40,12,13



TABLE 2: Experimental Activity Coefficients at Infinite Dilution of 28 Organic Compounds in the n-Methacryloyloxyhexyl-N-methylimidazolium Bromide at 313.15 K T/K ) 313.15

T/K ) 313.15

uncorrected values of γ∞

uncorrected values of γ∞

% phase loading solutes

7.80

12.90

16.10

corrected data 19.80

KL

hexane 30.50 40.71 62.52 95.60 5.1 ( 0.3 heptane 45.62 60.64 95.60 128.40 10.3 ( 0.4 octane 62.12 83.08 135.20 177.64 22.6 ( 0.7 nonane 110.20 119.30 120.20 125.90 49.2 ( 1.1 cyclohexane 20.50 27.83 35.95 50.62 11.3 ( 0.4 benzene 2.62 2.55 2.45 2.47 158.1 ( 2.5 toluene 3.20 3.32 3.35 3.38 297.5 ( 4.5 ethylbenzene 5.12 5.26 5.30 5.33 495.8 ( 5.1 m-xylene 5.60 5.69 5.62 5.66 539.2 ( 5.6 o-xylene 3.10 3.17 3.22 3.26 818.1 ( 7.1 1-hexene 20.56 23.24 23.58 23.65 7.4 ( 0.2 1-hexyne 5.05 5.10 5.15 5.18 43.5 ( 1.2 1-heptyne 7.52 7.57 7.61 7.70 85.4 ( 1.4 2-butanone 2.12 2.06 2.08 2.09 159.9 ( 2.4

% phase loading

γ∞

solutes

123 143.5 198.7 133.2 62.1 2.44 3.33 5.24 5.63 3.25 25.60 5.01 7.70 2.09

2-pentanone 1,4 dioxane methanol ethanol 1-propanol 2-propanol diethyl ether chloroform dichloromethane tetrachloromethane acetonitrile 1-nitropropane pyridine thiophene

corrected data

7.80 12.90 16.10 19.80 2.85 2.10 0.15 0.33 0.46 0.65 6.12 0.22 0.30 1.60 0.95 1.85 1.17 1.52

2.79 1.99 0.15 0.35 0.48 0.68 6.38 0.18 0.31 1.56 0.76 1.77 1.19 1.50

2.75 1.95 0.14 0.35 0.47 0.67 6.58 0.22 0.58 1.50 0.78 1.75 1.25 1.48

2.77 1.94 0.16 0.34 0.48 0.65 6.77 0.25 0.60 1.48 0.76 1.72 1.28 1.45

KL

γ∞

253.1 ( 4.2 389.8 ( 6.1 1461.6 ( 12.1 1249.3 ( 11.9 2326.6 ( 19.1 826.7 ( 8.2 12.1 ( 0.5 915.6 ( 5.2 188.1 ( 0.4 174.6 ( 0.3 450.4 ( 0.7 1425.7 ( 15.1 1080.4 ( 12.1 250.1 ( 3.9

2.80 2.02 0.15 0.33 0.47 0.66 6.90 0.22 0.29 1.59 0.80 1.84 1.15 1.50

TABLE 3: Selectivity Values, S∞12, for the Solutes Hexane (1) and Benzene (2) in Solvents and Selectivity of Solvents toward Pairs of Gaseous Compounds in Terms of Log KL2 - Log KL1 solvent

S∞12

log KL2 - log KL1

ref

dichloroacetic acid acetonitrile dimethyl sulfoxide sulfolane n-acryloyloxypropyl-N-methylimidazolium bromide n-methacryloyloxyhexyl-N-methylimidazolium bromide 1-propenyl-3-methyl-imidazolium bromide 1-propenyl-3-octyl-imidazolium bromide 1-propenyl-3-decyl-imidazolium bromide 1-propenyl-3-dodecyl-imidazolium bromide 1-propyl boronic acid-3-octyl-imidazolium bromide 1-propyl boronic acid-3-decyl-imidazolium bromide 1-propyl boronic acid-3-dodecyl-imidazolium bromide 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide 1-ethyl-3-methylimidazolium ethylsulphate 1-butyl-3-methylimidazolium octylsulphate 1-ethyl-3-methylimidazolium tetrafluoroborate 1-butyl-3-methylimidazolium tetrafluoroborate 1-hexyl-3-methylimidazolium tetrafluoroborate 1-octyl-3-methylimidazolium tetrafluoroborate 1-hexyl-3-methylimidazolium hexafluorophosphate 1-hexadecyl-3-methylimidazolium tetrafluoroborate 1-octyl-3-methylimidazolium chloride

6.1 9.4 22.7 30.5 27.6 50.4 6.96 6.36 6.03 4.08 9.91 4.09 3.84 37.5 16.7 41.4 5.5 61.6 40.8 22.3 10.5 21.6 2.8 8.7

-0.970 -1.157 -1.540 -1.668 -1.626 -1.786 -1.037 -0.987 -0.965 -0.795 -1.180 -0.797 -0.769 -1.760 -1.407 -1.801 -0.925 -1.974 1.074 -1.532 -1.205 -1.519 -0.631 -1.123

35 35 35 35 this work this work 12 12 12 12 12 12 12 36 36 36 11 38 38 38 38 39 13 37

TABLE 4: LSER Descriptors of Solutes Used to Characterize Ionic Liquids solutes

E

S

A

B

L

solutes

E

S

A

B

L

hexane heptane octane nonane cyclohexane benzene toluene ethylbenzene m-xylene o-xylene 1-hexene 1-hexyne 1-heptyne 2-butanone 2-pentanone

0 0 0 0 0.305 0.610 0.601 0.613 0.623 0.663 0.078 0.166 0.160 0.166 0.143

0 0 0 0 0.10 0.52 0.52 0.51 0.52 0.56 0.08 0.23 0.23 0.70 0.68

0 0 0 0 0 0 0 0 0 0 0 0.12 0.12 0 0

0 0 0 0 0 0.14 0.14 0.15 0.16 0.16 0.07 0.1 0.1 0.51 0.51

2.668 3.173 3.677 4.182 2.964 2.768 3.325 3.778 3.839 3.939 2.572 2.510 3.000 2.287 2.755

1.4-dioxane methanol ethanol 1-propanol 2-propanol 2-methyl-1-propanol 1-butanol diethyl ether chloroform dichloromethane tetrachloromethane acetonitrile 1-nitropropane thiophene

0.329 0.278 0.246 0.236 0.212 0.217 0.224 0.041 0.425 0.387 0.458 0.237 0.242 0.687

0.75 0.44 0.42 0.42 0.36 0.39 0.42 0.25 0.49 0.57 0.38 0.9 0.95 0.57

0 0.43 0.37 0.37 0.33 0.37 0.37 0 0.15 0.10 0 0.07 0 0

0.64 0.47 0.48 0.48 0.56 0.48 0.48 0.45 0.02 0.05 0 0.32 0.31 0.15

2.892 0.970 1.485 2.031 1.764 2.413 2.601 2.015 2.48 2.019 2.833 1.739 2.894 2.819

LSER coefficients of both ionic liquids studied in this work are slightly different from those obtained with other ionic liquids of the imidazolium bromide type. The (c + lL) term gives information on the effect of the cohesion of the ionic liquids on solute transfer from the gas phase. In general, the ionic liquids

are cohesive solvents.40 The ionic liquid interacts weakly via nonbonding and π-electrons (e system constant is zero) and is not much different from other polar nonionic liquids. Dipolarity/ polarizability of ionic liquids is slightly higher than the most dipolar/polarizable nonionic stationary phases. The polarizability


Mutelet et al.

TABLE 5: LSER Descriptors of Ionic Liquids Determined at 313.15 Ka system constants e n-acryloyloxypropyl-N-methylimidazolium bromide n-methacryloyloxyhexyl-N-methylimidazolium bromide 1-propenyl-3-methylimidazolium bromide 1-propenyl-3-octylimidazolium bromide 1-propenyl-3-decylimidazolium bromide 1-propenyl-3-dodecylimidazolium bromide 1-butyl-3-methylimidazolium octyl sulfate 1-ethyl-3-methylimidazolium tosylate n-butylammonium thiocyanate di-n-propylammonium thiocyanate ethylammonium nitrate n-propylammonium nitrate 2-bis(2-hydroxyethyl)amino)ethanesulfonate 2-(cyclohexylamino)ethanesulfonate 2-hydroxy-4-morpholinepropanesulfonate 4-morpholinepropanesulfonate Squalane OV-17 Carbowax 20M 1,2,3-tris(2-cyanoethoxy) propane a

s

Ionic Liquids 0 2.88 (0.14) 0 2.46 (0.10) 0 2.16 (0.09) 0 1.72 (0.08) 0 1.73 (0.07) 0 1.44 (0.07) 0 1.47 (0.06) 0.54 2.40 (0.12) (0.12) 0.14 1.65 (0.09) (0.09) 0.30 1.73 (0.05) (0.06) 0.27 2.21 (0.16) (0.16) 0.25 2.02 (0.06) (0.06) 0.27 1.96 0.07 1.57 0 1.76 0 1.60

5.50 (0.19) 5.36 (0.18) 5.19 (0.18) 4.96 (0.16) 4.89 (0.17) 4.87 (0.16) 4.05 (0.14) 4.81 (0.19) 2.76 (0.16) 2.66 (0.10) 3.38 (0.28) 3.50 (0.10) 3.06 3.67 3.20 3.41

Nonionic Liquids 0.07 0 0 (0.03) 0.08 0.80 0.40 (0.05) (0.03) (0.07) 0.27 1.52 2.16 (0.07) (0.08) (0.13) 0.29 2.17 1.99

statistics

b

l

c

F

SE

n

-1.03 (0.119) -0.87 (0.11) -1.86

0.99

0.080

30

0.99

0.088

28

0.990

0.089

28

-1.60

0.989

0.088

28

-1.58

0.990

0.089

28

-1.51

0.991

0.088

28

-0.237 (0.09) -0.84 (0.12) -0.75 (0.10) -0.6 (0.06) -0.87 (0.20) -0.97 (0.07) -0.80 -0.83 -0.91 -0.94

0.990

0.082

29

0.17 (0.14) 1.32 (0.11) 0.68 (0.07) 1.03 (0.17) 0.9 (0.07) 0 0 0 0

0.48 (0.06) 0.57 (0.05) 0.53 (0.05) 0.57 (0.05) 0.66 (0.04) 0.72 (0.03) 0.68 (0.03) 0.48 (0.03) 0.45 (0.02) 0.47 (0.01) 0.21 (0.04) 0.36 (0.01) 0.32 0.51 0.49 0.44

0.99

0.080

29

0.995

0.058

23

0.998

0.032

23

0.994

0.089

17

0.998

0.037

23

0.996 0.996 0.994 0.990

0.048 0.060 0.053 0.097

27 18 18 34

0.73 (0.006) 0.64 (0.009) 0.53 (0.20) 0.36

-0.19 (0.02) -0.31 (0.04) -0.42 (0.10) -0.48

0.999

0.025

22

0.998

0.036

23

0.994

0.053

21

0.993

0.062

22

a 0 0 0 0 0 0 0

0 0 0 0

F: multiple correlation coefficient. SE: standard error in the estimation. n: number of solutes.

decreases slightly when the alkyl chain length is increased on the imidazolium ring. This observation is in good agreement with results of Giraud et al.44 Introducing a (meth)acryloyloxyalkyl chain in imidazolium bromide-based ionic liquids considerably increases its dipolarity/polarizability (s system constants). The hydrogen-bond basicity of the ionic liquid (a system constants) is considerably larger than values obtained for nonionic phases (0-2.1),40 and it is not hydrogen-bond acid (b ) 0). Ionic liquids have structural features that would facilitate hydrogen-bond acceptor basicity interactions (electron-rich oxygen, nitrogen, and fluorine atoms). Imidazolium bromidebased ionic liquids containing a (meth)acryloyloxyalkyl chain have the highest hydrogen-bond basicity, with an a constant of ∼5.4. This is great support for the idea that the interactions between the -OH group and ionic liquids are very strong. The selectivity value for (hexane (1)/ benzene (2)) agrees well with the LSER observation. Benzene is preferentially retained, as expected, because aromatics have a hydrogen-bond basicity parameter of about 0.14 and a dipolarity/polarizability of 0.52, whereas n-alkane has no hydrogen bond and no polarizability, the other LSER parameters being similar for the two organic compounds. Finally, the LSER treatment and the analysis of selectivity lead to the same conclusions about the interactions that are governing partitioning on the two ionic liquids. Recently, Sprunger et al.45 proposed to separate the anion and cation contributions in the LSER model. The authors have modified the LSER equation, eq 3, by rewriting each of the five solvent

coefficients (e, s, a, b, and l) as a summation of their respective cation and anion:

log SP ) c + (ecation + eanion)E + (scation + sanion)S + (acation + aanion)A + (bcation + banion)B + (lcation + lanion)L (9) Cation-specific and anion-specific equation coefficients of eight cations and four anions were established to estimate the logarithm of the gas-to-ILs partition coefficients. The major advantage of this method is that we can make predictions for more ILs by combining the set of ion coefficients. Nevertheless, the log K of the present ILs cannot be predicted using the general equation because cation and anion coefficients are missing. System constants determined at different phase loadings from log(VN/VL) and from the extrapolated values of the gas-liquid partition coefficients at T ) 313.15 K are summarized in Tables 6 and 7. We can see there is a statistical difference between the system constants calculated from the sorption coefficients, log(VN/VL), and from the gas-liquid partition coefficient, log KL. There is some dependence of the system constants on the phase loading. The LSER coefficients vary with phase loading. This result confirms that interfacial adsorption has an important influence on the determination of physicochemical properties of ionic liquids using inverse gas chromatography. Through this work, it is shown that measurement of thermodynamic properties of ILs should be conducted using the procedure proposed by



TABLE 6: System Constants for n-Acryloyloxypropyl-Nmethylimidazolium Bromide at T ) 313.15 K system constants loadings

e

8.30%

0

11.94% 15.31% 19.02% log KL

s

2.62 (0.12) 0 2.86 (0.14) 0 2.71 (0.14) 0 2.31 (0.15) 0

a

b

5.32 (0.18) 5.70 (0.16) 5.54 (0.15) 5.34 (0.18)

0

l

0.54 (0.04) 0 0.54 (0.06) 0 0.54 (0.07) 0 0.57 (0.07)

statistics c -0.98 (0.12) -1.09 (0.14) -1.00 (0.09) -0.90 (0.15)

F

SE

n

0.98 0.12 30 0.98 0.13 30 0.99 0.08 30 0.99 0.08 30

2.88 5.50 0 0.48 -1.03 0.99 0.08 30 (0.14) (0.19) (0.06) (0.129)

TABLE 7: System Constants for n-Methacryloyloxyhexyl-Nmethylimidazolium Bromide at T ) 313.15 K system constants

statistics

loadings

e

s

a

b

l

c

F

SE

n

7.80%

0

28

0.98

0.13

28

0

0.99

0.11

28

19.8%

0

-0.98 (0.10) -1.09 (0.15) -1.00 (0.10) -0.90 (0.14)

0.14

16.1%

0.50 (0.05) 0.53 (0.04) 0.55 (0.05) 0.57 (0.06)

0.98

0

5.50 (0.16) 5.40 (0.17) 5.20 (0.15) 5.30 (0.17)

0

12.90%

2.42 (0.13) 2.43 (0.14) 2.42 (0.15) 2.45 (0.12)

0.99

0.09

28

log KL

0

2.46 (0.10)

5.36 (0.18)

0.57 (0.05)

-0.87 0.99 (0.11)

0.08

28

0 0 0 0

Conder19 and Poole.40 Measurement of the activity coefficient using only one column should be avoided. Concluding Remarks Activity coefficients at infinite dilution of organic compounds in two new ionic liquids have been measured at 313.15 and 323.15 K. Through this work, we have shown that interfacial adsorption could play a significant role in the retention mechanism of organic compounds. When corrected, important increases of activity coefficients at infinite dilution of nonpolar compounds were observed. Results obtained in this work indicate that the introduction of polar substituents to the cation of imidazolium ionic liquids affects strongly the behavior of organic compounds in mixtures with the ionic liquids. In the separation of aliphatic hydrocarbons from aromatic hydrocarbons, the ionic liquid used shows a higher selectivity than that found by previous workers using classical organic solvents. References and Notes (1) Seddon, K. R. J. Chem. Technol. Biotechnol. 1997, 68, 351-356. (2) Sheldon, R. A. The role of catalysis in waste minimization. In Precision Process Technology, PerspectiVes for Pollution PreVention; Weijnem, M. P. C.; Drinkenburg, A. A. H.; Kluwer: Dodrecht, 1993. (3) Cull, S. G.; Holbery, J. D.; Vargas-Mora, V.; Seddon, K. R.; Lye, G. J. Biotechnol. Bioeng. 2000, 69, 227-233. (4) Wilkes, J. S. J. Mol. Catal. A: Chem. 2004, 214, 11-17. (5) Wasserschlid, P.; Keim, W. A. Chem. Int. Ed. 2000, 39, 37733789.

(6) Welton, T. Chem. ReV. 1999, 99, 2071-2083. (7) Brennecke, J. F.; Maginn, E. J. AIChE J. 2001, 47, 2384-2389. (8) Fredlake, C. P.; Crosthwaite, J. M.; Hert, D. G.; Aki, S. N. V. K.; Brennecke, J. F. J. Chem. Eng. Data 2004, 49, 954-964. (9) Henderson, W. A.; Passerini, S. Chem. Mater. 2004, 16, 28812885. (10) Mutelet, F.; Butet, V.; Jaubert, J.-N. Ind. Eng. Chem. Res. 2005, 44, 4120-4127. (11) Mutelet, F.; Jaubert, J-N. J. Chromatogr., A 2006, 1102, 256267. (12) Mutelet, F.; Jaubert, J.-N.; Rogalski, M.; Boukherissa, M.; Dicko, A. J. Chem. Eng. Data 2006, 51, 1274-1279. (13) Mutelet, F.; Jaubert, J.-N. J. Chem. Thermodyn. 2007, 39, 11441150. (14) Poole, C. F. The Essence of Chromatography; Elsevier: Amsterdam, 2003. (15) Poole, C. F.; Kollie, T. O.; Poole, S. K. Chromatographia 1992, 34, 281-302. (16) Kersten, B. R.; Poole, C. F. J. Chromatogr. 1987, 399, 1-31. (17) Poole, S. K.; Kollie, T. O.; Poole, C. F. J. Chromatogr., A 1994, 664, 229-251. (18) Liao, H. L.; Martire, D. E. Anal. Chem. 1972, 44, 498-502. (19) Conder, J. R.; Locke, D. C.; Purnell, J. H. J. Phys. Chem. 1969, 73, 700-708. (20) Nikolov, R. N. J. Chromatogr. 1982, 241, 237-256. (21) Pomaville, R. M.; Poole, C. F. J. Chromatogr. 1989, 468, 261278. (22) Abraham, M. H.; Grellier, P. L.; McGill, R. A. J. Chem. Soc. Perkin Trans II 1987, 797-803. (23) Abraham, M. H. Chem. Soc. ReV. 1993, 22, 73-83. (24) Abraham, M. H.; Whiting, G. S.; Doherty R. M. J. Chem. Soc. Perkin Trans II 1990, 1451-1460. (25) Abraham, M. H.; Whiting, G. S.; Doherty, R. M.; Shuely, W. J. J. Chromatogr. 1991, 587, 213-228. (26) Cruickshank, A. J. B.; Windsor, M. L.; Young, C. L. Proc. R. Soc. London 1966, A295, 259-270. (27) Grant, D. W. Gas-Liquid Chromatography; van Nostrand Reinhold: London, 1971. (28) Thermodynamics Research Center, Texas Engineering Experiment Station, The Texas A. and M. University System; College Station, TX, April 1987. (29) Tsonopoulos, C. AIChE J. 1974, 20, 263-272. (30) Tsonopoulos, C. AIChE J. 1975, 21, 827-829. (31) Tsonopoulos, C. AIChE J. 1978, 24, 1112-1115. (32) Reid, R. C.; Prausnitz, J. M.; Sherwood, T. K. The Properties of Gases and Liquids, 3rd ed.; Chemical Engineering Series; McGraw-Hill: New York, 1977. (33) Kato, R.; Gmehling, J. Fluid Phase Equilib. 2004, 226, 37-44. (34) Heintz, A.; Kulikov, D. V.; Verevkin, S. P. J. Chem. Thermodyn. 2002, 34, 1341-1347. (35) Tiegs, D.; Gmehling, J.; Medina, A.; Soares, M.; Bastos, J.; Alessi, P.; Kikic, I. DECHEMA Chemistry Data Series IX; Main: Frankfurt, 1986; Part 1, DECHEMA. (36) Krummen, M.; Wasserscheid, P.; Gmehling, J. J. Chem. Eng. Data 2002, 47, 1411-1417. (37) David, W.; Letcher, T. M.; Ramjugernath, D.; Raal, J. D. J. Chem. Thermodyn. 2003, 35, 1335-1341. (38) Foco, G. M.; Bottini, S. B.; Quezada, N.; de la Fuente, J. C.; Peters, C. J. J. Chem. Eng. Data 2006, 51, 1088-1091. (39) Letcher, T. M.; Soko, B.; Ramjugernath, D.; Deenadayalu, N.; Nevines, A.; Naicker, P. K. J. Chem. Eng. Data 2003, 48, 708-711. (40) Poole, C. F. J. Chromatogr., A 2004, 1037, 49-82. (41) Domanska, U.; Marciniak, A. J. Phys. Chem. B 2007, 111, 1198411988. (42) Letcher, T. M.; Domanska, U.; Marciniak, M.; Marciniak, A. J. Chem. Thermodyn. 2005, 37, 587-593. (43) Abraham, M. H.; Acree, W. E., Jr. Green Chem. 2006, 8, 906915. (44) Giraud, G.; Wynee, K. J. Chem. Phys. 2003, 119, 464-477. (45) Sprunger, L.; Clark, M.; Acree, W. E., Jr; Abraham, M. H. J. Chem. Inf. Modell. 2007, 47, 1123-1129.

Activity Coefficients at Infinite Dilution of Organic Compounds in 1

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