Liquid-liquid equilibria of room-temperature ionic liquids and butan-1-ol

Article abstract of DOI:10.1021/je0340093

Room-temperature ionic liquids are salts that are liquid at room temperature. Their use as catalysts and catalytic support has been studied extensively. However, there are very few measurements on their solubility and phase equilibria in common organic solvents. In this work, the liquid-liquid phase equilibria of mixtures of room-temperature ionic liquids, 1-alkyl-3-methylimidazolium hexafluorophosphate, [R_nmim][PF₆] (1) where R_n = butyl, pentyl, hexyl, heptyl, and octyl, with butan-1-ol (2) over a composition range have been measured. The binodal coexistence curves of the mixtures were found to have an upper critical solution temperature (USCT) at x₂ ≈ 0.9. The UCST decreases with increase in the length of the alkyl chain of the ionic liquid, with the UCST of the butyl at 373 K and that of the octyl at 326 K. Both the UCST and the composition at the UCST as a function of the 1-alkyl group chain length can be reasonably well predicted from theory on the basis of unimolecular quantum chemical calculations.

Full text of DOI:10.1021/je0340093

486
J . Chem. Eng. Data 2003, 48, 486-491
Liqu id -Liqu id Equ ilibr ia of Room -Tem p er a tu r e Ion ic Liqu id s a n d
Bu ta n -1-ol†
C.-T. Wu , Ken n eth N. Ma r sh ,* Alexa n d er V. Deev, a n d J oh n A. Boxa ll
Department of Chemical & Process Engineering, University of Canterbury, Private Bag 4800,
Christchurch 8004, New Zealand
Room-temperature ionic liquids are salts that are liquid at room temperature. Their use as catalysts and
catalytic support has been studied extensively. However, there are very few measurements on their
solubility and phase equilibria in common organic solvents. In this work, the liquid-liquid phase equilibria
of mixtures of room-temperature ionic liquids, 1-alkyl-3-methylimidazolium hexafluorophosphate,
[Rnmim][PF6] (1) where Rn ) butyl, pentyl, hexyl, heptyl, and octyl, with butan-1-ol (2) over a composition
range have been measured. The binodal coexistence curves of the mixtures were found to have an upper
critical solution temperature (USCT) at x2 ≈ 0.9. The UCST decreases with increase in the length of the
alkyl chain of the ionic liquid, with the UCST of the butyl at 373 K and that of the octyl at 326 K. Both
the UCST and the composition at the UCST as a function of the 1-alkyl group chain length can be
reasonably well predicted from theory on the basis of unimolecular quantum chemical calculations.
In tr od u ction
Room-temperature ionic liquids, which are salts that are
liquids at ambient temperature, are normally composed of
relatively large organic cations and inorganic or organic
anions. Unlike molecular liquids, the ionic nature of these
F igu r e 1. Chemical structure of ionic liquids used in this work.
liquids results in a unique combination of properties such
tial for energy savings. In addition, they are potentially
as very low vapor pressure at room temperature and a
recoverable for reuse. Hence, the replacement of conven-
stable liquid range of over 300 K. Some ionic liquids are
tional organic solvents by ionic liquids in extraction pro-
readily hydrolyzed while some show unusual solubility
cesses is seen as a promising field of investigation. For the
behavior in water and organic solvents. For example, the
extraction of polar organic products of chemical reactions
ionic liquids based on aluminum chloride are generally very
that proceed in aqueous media, ionic liquids that have low
hydroscopic, and studies have to be made in the absence
solubility in water and high solubility in the organic liquid
of moisture. Those based on tetrafluoroborate are generally
would be preferred. An important criterion for any ionic
stable to moisture but have a relatively high solubility in
liquid used in extraction is that it be air and water stable,
water while ionic liquids based on, for example, hexafluo-
thus enabling extractions without special procedures. Our
rophosphate and bis(trifluormethylsulfyl)-imide are gener-
work concentrates on the 1-alkyl-3-alkylimidazolium hexa-
ally less soluble in water. Additionally, the change in chain
fluorophosphates that are liquids at room temperature,
length of the 1-alkyl group from 1 to 8 on 1-alkyl-3-
have low solubility in water, and do not hydrolyze at close
methylimadazolium hexafluorophosphate can turn the
to ambient conditions. The compounds studied were 1-alkyl-
liquid from being highly soluble in water to very im-
3-methylimidazolium hexafluorophosphates ([Rnmim][PF6],
miscible. Thus, by judicious variation in the length and
where Rn stands for an alkyl group with n carbon atoms)
branching of the alkyl chains of the anionic core and
having from (4 to 8) carbon atoms in the 1-alkyl chain. The
variation in the cationic precursor, it should be possible to
chemical structure is shown in Figure 1.
design a solvent for a specific application. Initially, the
At the present time, measurements on the solubility and
research of these “designer solvents” was focused on their
phase equilibria in common organic solvents are limited.
use as electrolytes,1-4 but later studies focused on their
To our knowledge, only a few studies on solubility have
application as new media for chemical reactions such as
been reported. Brennecke and co-workers have shown that
solvents for homogeneous catalysis5,6 for a variety of
ionic liquids are insoluble in supercritical CO2,15,16 sug-
organic reactions.7-10 Reviews on the use of ionic liquids
gesting that products of reactions carried out in ionic
as solvents for synthesis, with and without catalysis, have
liquids can be readily extracted with supercritical CO2.
been given by Welton11 and Wasserscheid.12
Some vapor-liquid and liquid-liquid equilibria17 and
In particular, ionic liquids have appeal as alternative
liquid-liquid equilibria18,19 measurements have been re-
solvents in liquid-liquid extraction.13,14 Their low vapor
ported on mixtures of imidazolium-based ionic liquids with
pressure allows the extracted product to be separated from
water. Some recent studies of liquid-liquid equilibria
the ionic liquid by low-pressure distillation with the poten-
between ionic liquids and alcohols have been reported.20,21
† This contribution will be part of a special print edition containing
papers presented at the Workshop on Ionic Liquids at the 17th IUPAC
Conference on Chemical Thermodynamics, Rostock, Germany, J uly 28
to August 2, 2002.
Exp er im en ta l Section
Ma ter ia ls. The ionic liquids were prepared by reaction
* Corresponding author. E-mail: ken.marsh@canterbury.ac.nz.
of 1-methylimidazole with 1-alkyl chlorides followed by
10.1021/je0340093 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/27/2003

J ournal of Chemical and Engineering Data, Vol. 48, No. 3, 2003 487
reaction with hexafluorophosphoric acid. 1-Methylimida-
zole was used as received from Aldrich (99+ mass %
redistilled). As the reagent was moisture sensitive, it was
transferred into the reaction vessel under continuous
nitrogen flushing. Hexafluorophosphoric acid was supplied
by Aldrich (60 mass % solution in water) and used as
received. The butan-1-ol was obtained from APS Finechem
with less than 0.6 mass % impurities. The butan-1-ol was
dried using activated type 5 Å molecular sieves, and the
water content was found to be less than 0.05 mass % as
determined by GLC (using a packed column, thermal
conductivity detector, and He gas). The reagents were kept
in sealed flasks in a desiccator to minimize contact with
moist air. 1-Chlorobutane, 1-chloropentane, 1-chlorohex-
ane, 1-chloroheptane, and 1-chlorooctane were obtained
from Aldrich (99 mass % grade) and used without further
purification.
F igu r e 2. Apparatus used for liquid-liquid equilibria measure-
ments.
P r epa r a tion of Ion ic Liqu id s. The ionic liquids were
prepared in-house by a metathesis method described by
Welton.11 Equimolar quantities of alkyl chlorides (1-chloro-
butane through 1-chlorooctane) were reacted with 1-me-
thylimidazole at 353 K, with stirring in a closed vessel
under an atmosphere of nitrogen for 72 h, to produce the
1-alkyl-3-methylimidazolium chlorides. The 1-alkyl-3-me-
thylimidazolium chlorides were then mixed with hexafluo-
rophosphoric acid in aqueous solution, and the ionic liquids
separated as a denser liquid phase. Residual chloride ion
was removed from the ionic liquids by washing with water
at least 10 times until no chloride precipitate formed with
silver nitrate. Initially, the ionic liquids were dried with
magnesium sulfate and then filtered with tetrahydrofuran
through neutral alumina. The residual volatile organic
solvents and water were removed by vacuuming at 10 Pa
and 353 K. The 1-alkyl-3-methylimidazolium hexafluoro-
phosphates appeared as light-yellow transparent liquids.
As this drying process has the possibility of introducing
additional salts into the ionic liquid, our later purifications
abandoned the drying stages using magnesium sulfate and
alumina in favor of pumping the washed sample with a
vacuum of 1 Pa at 340 K for over 48 h.
mixtures were obtained. The apparatus, shown in Figure
2, consists of a jacketed glass vessel containing a magnetic
stirrer connected to a temperature controlled circulating
bath (controlled to (0.01 K). The vessel was closed to
moisture and could be flushed with dry nitrogen. The
measurements were started with the addition of a known
mass of about 30 g of dry ionic liquid to the vessel. A known
mass of about 1 g of butan-1-ol was added to the ionic
liquid, the temperature was adjusted to about 1.5 K above
the expected cloud point, and the mixture was stirred
vigorously. The temperature was then reduced at the rate
of 10-2 K‚s-1 until the cloud point was observed. This step
was repeated several times to confirm the cloud point
temperature to within (0.02 K. A second known mass of
butan-1-ol was then added, and another cloud point tem-
perature was measured. Additions of butan-1-ol were
continued until x2 > x2(UCST), the mole fraction at the upper
critical solution temperature (UCST), giving up to 20 cloud
temperatures. The compounds were then interchanged, and
the ionic liquid was added to butan-1-ol until x2 < x2(UCST)
.
Agreement of the value of the UCST to within (0.1 K
approached from x2 ) 1 and x2 ) 0 indicated the reliability
of the results and that the results were not affected by
contamination with water (3), which would lower the UCST
by approximately 0.7 K for x3 ) 0.003.
High purity is essential for thermophysical property
measurements. The influence of chloride, water, and
organic solvents on the physical properties has been
reported by Seddon and co-workers.20 The purity of the
ionic liquids was investigated by various methods including
nuclear magnetic resonance (NMR), infrared spectroscopy
(IR), and mass spectra. H1 NMR (in CDCl4) spectra
confirmed the chemical structure of the ionic liquids, and
the results from mass spectra analysis show no substantial
impurities such as chloride compounds. However, the
sensitivity level of these instruments indicated that im-
purities with uncertainty better than mass fractions of
(1 to 2)% could not be determined. Water could be deter-
mined by IR spectroscopy, using a cell with spacers of 0.14
mm, as two peaks for the OH- absorbance in the (3500-
3700) cm-1 wavelength range. Further drying in a vacuum
at a pressure of less than 10 Pa allowed the removal of
water down to levels approaching the sensitivity of the
method, estimated at 0.01 mass % of water in ionic liquids.
A more sensitive method, using a differential scanning
calorimeter, was abandoned because small amounts of
residual water reacted with the ionic liquid to form HF gave
rise to a calorimeter response at about 410 K.
Temperature was measured with a calibrated platinum
resistance thermometer (DSIR RT200, New Zealand) with
the uncertainty of (0.01 K. Masses of liquids added were
determined with an uncertainty of (0.0003 g, and that
gave an uncertainty in the mole fraction of better than 1
part in 104.
Resu lts
The liquid-liquid equilibria for the mixtures [Rnmim]-
[PF6] (1) (n ) 4 to 8) + butan-1-ol (2) are given in Table 1
and shown as a function of x2 in Figure 3. The curves are
typical for a partially miscible two-component system with
an upper critical solution temperature (UCST). Measure-
ments were not made with ionic liquid Rn ) butyl above
373 K, where x2 was between 0.7 and 0.96, as that would
require a redesign of the apparatus to enable measure-
ments above 0.1 MPa. USCTs for the systems Rn ) pentyl,
hexyl, heptyl, and octyl are 366.23 K (x2 ) 0.88), 350.31 K
(x2 ) 0.90), 335.47 K (x2 ) 0.94), and 326.38 K (x2 ) 0.915),
respectively. The uncertainty in the UCST is estimated at
(0.1 K, and the uncertainty in the x2(UCST) is estimated at
(0.025. For butyl the UCST was determined to be (376 (
5) K (x2 ) 0.88 ( 0.05) by visual interpolation. Figure 3
shows that the coexisting curve moves to a higher temper-
Liqu id -Liqu id Equ ilibr ia Mea su r em en ts. Liquid-
liquid equilibria were studied for [Rnmim][PF6] (1) (n ) 4
to 8) + butan-1-ol (2). The so-called visual “cloud point
method” was used, and the binodal coexisting curves of the

488 J ournal of Chemical and Engineering Data, Vol. 48, No. 3, 2003
Ta ble 1. Liqu id -Liqu id Equ ilibr ia for [Rn m im ][P F 6] (1) + Bu ta n -1-ol (2)
Rn ) butyl
T/K
Rn ) pentyl
T/K
Rn ) hexyl
T/K
Rn ) heptyl
T/K
Rn ) octyl
T/K
x2
x2
x2
x2
x2
298.21
319.78
331.78
337.39
346.93
352.31
356.23
361.69
365.53
369.09
372.91
371.83
369.28
365.75
355.58
0.262
0.345
0.402
0.433
0.488
0.525
0.553
0.597
0.631
0.669
0.716
0.977
0.981
0.985
0.991
<275.15
280.09
299.53
308.34
313.51
318.00
324.53
332.34
337.02
343.40
347.88
354.28
357.90
360.13
362.20
363.72
365.28
365.78
366.15
366.23
366.18
365.99
365.11
362.98
357.87
329.90
0.137
0.209
0.297
0.337
0.361
0.391
0.433
0.482
0.514
0.558
0.593
0.650
0.690
0.717
0.747
0.774
0.804
0.823
0.859
0.875
0.900
0.922
0.944
0.962
0.978
0.995
<277.15
291.34
309.68
318.66
328.64
334.05
338.00
343.19
347.26
349.64
350.18
350.31
350.30
350.08
348.57
345.60
336.08
316.98
0.102
0.345
0.441
0.502
0.568
0.615
0.657
0.715
0.776
0.843
0.881
0.905
0.925
0.937
0.957
0.973
0.989
0.996
<276.15
282.17
295.09
301.43
307.83
314.18
319.88
325.37
328.18
331.76
334.10
334.79
335.08
335.32
335.47
335.05
333.56
330.10
314.89
0.217
0.362
0.446
0.493
0.544
0.598
0.648
0.703
0.737
0.788
0.838
0.887
0.909
0.918
0.936
0.952
0.969
0.981
0.995
<274.70
274.90
284.53
293.99
299.10
304.40
306.52
311.73
316.94
320.45
323.03
325.01
325.66
326.11
326.29
326.38
326.31
326.29
326.25
326.17
321.91
318.57
316.31
0.049
0.361
0.423
0.496
0.536
0.580
0.599
0.648
0.701
0.748
0.788
0.827
0.851
0.884
0.903
0.915
0.925
0.933
0.939
0.943
0.978
0.986
0.990
F igu r e 4. Relationship between the UCST and the number of
carbons in Rn: [, experiment; O, 1-butyl estimated from experi-
mental data; 4, COSMOtherm.
F igu r e 3. Phase diagrams for the systems [Rnmim][PF6] (1) +
butan-1-ol (2) at 1 bar: [, butyl; 9, pentyl; 2, hexyl; ×, heptyl; O,
octyl.
ature with a decrease of the alkyl chain length of the
cationic core. Hence, the higher the “organic content” of
the ionic liquid, the higher is its solubility in butan-1-ol.
The relationship between number of carbon atoms on the
Rn group and the UCST, shown in Figure 4, is linear within
experimental error. The relationship between x2(UCST) and
the number of carbons on Rn is also linear within experi-
mental error, as shown in Figure 5.
Com p a r ison w ith Th eor y
Traditional approaches for correlating or predicting the
properties of fluid mixtures include equation of state (EOS)
methods and schemes based primarily on dividing the
molecules into various groups (group contribution methods)
such as UNIFAC. EOS methods require an estimate of the
gas-liquid critical properties of the pure fluids while group
contribution schemes require the determination of residual
interaction terms between the various functional groups
on the ions as well as interaction terms between these
functional groups and the functional groups on the organic
solvent. To determine the parameters that would be
F igu r e 5. Relationship between x2 of the UCST and the number
of carbons in Rn for [Rnmim][PF6] (1) + butan-1-ol (2): [,
experiment; O, 1-butyl estimated from experiment data; 4, COS-
MOtherm.
suitable to predict vapor-liquid equilibria and liquid-
liquid equilibria would require an extensive experimental
program. At the present time the major requirement is a
predictive method that could screen the many possible ionic
liquids and their mixtures with organic liquids and water

J ournal of Chemical and Engineering Data, Vol. 48, No. 3, 2003 489
F igu r e 6. Comparison of experimental liquid-liquid phase diagrams for the systems [Rnmim][PF6] (1) + butan-1-ol (2) at 1 bar with
values calculated from COSMOtherm: 9, experimental; 0, COSMOtherm; s, eq 1 fit to COSMOtherm.
for properties that would be required for particular ap-
plications, prior to making extensive measurements.
COSMO-RS24 is a method for predicting the thermo-
dynamic properties of mixtures on the basis of unimolecu-
lar quantum chemical calculations of the individual mol-
ecules.23,24 The mixture properties are then calculated from
an entropy term based on the surface area and volume of
the molecules, and the enthalpy term is calculated from
the energies of interaction between the surfaces of the
molecules. The COSMO-RS calculation, as implemented in
COSMOtherm,25 first assumes the molecule is imbedded
in a conductor and gives the screening charge density σ on
each part of the molecular surface. It also calculates both
the surface area and volume of the molecule. The second
step is to describe all interactions between molecules as
contact interactions of the molecular surfaces, and these
interactions can then be related to the screening charge
densities σ and σ′ of the interacting surface pieces. For an
efficient statistical mechanical calculation, the molecular
surface is split into small areas aeff and contact with each
of these areas is considered to be independent. This step
is similar to the assumption of interacting surfaces in group
contribution methods and has been shown elsewhere to
give good results for interaction energies calculated from
molecular mechanics.24 This finite area approach allows
the reduction of the spatial screening charge distribution
to a one-dimensional histogram, called the σ profile. The
statistical thermodynamics of the mixture can then be
calculated by an equation somewhat similar to the UNI-
QUAC equation to give the chemical potential of each
component. From the chemical potentials, vapor-liquid
equilibria, liquid-liquid equilibria, and other properties of
the mixture can be derived.25 The calculations depend on
a small number of adjustable parameters, some of which
are predetermined from the known properties of the atoms.
The others are determined from selected properties of
mixtures, with none of the mixtures related to the mixtures
under study here.26 The parameters are not specific to
functional groups or molecule type. As the parameters are
used as a basis for the calculations only, the resulting
parametrization is completely general and can be used to
predict the properties of pure fluids and mixtures of many
classes of compounds including metals, salts, and polar and
nonpolar compounds.
The details of the COSMO calculations are outlined by
Diedenhofen et al.26 Within COSMOtherm25 a pseudobinary
approach was used to calculate the liquid-liquid equilib-
rium (LLE) of a mixture composed of an ionic liquid +
second component with the cation and anion of the ionic
liquid input as separate compounds with the same mole
fraction. The chemical potentials are calculated for the
ternary system with the potential of the ionic liquid as the
sum of the chemical potentials of the cation and anion. At
a particular temperature, a numerical gradient approach

490 J ournal of Chemical and Engineering Data, Vol. 48, No. 3, 2003
is used to find the two compositions having equal chemical
potentials of the three components (in the pseudobinary
system) in the two phases. If an LLE point is found, the
search steps to a new temperature using the last LLE
composition. If no LLE is found (due to no LLE or the
maximum number of steps being exceeded), the program
terminates. This latter problem occurs as the UCST is
approached.
Deter m in a tion of th e UCST fr om COSMOth er m
Resu lts. The COSMOtherm LLE numerical gradient pro-
gram was unable to complete calculations within about 4
K of the UCST, so a further method was required to
complete the LLE curve to find the UCST. The critical
points were obtained by fitting the COSMOtherm data with
the following equation.27
F igu r e 7. Comparison of liquid-liquid phase diagrams for the
1-butyl compound [bmim][PF6] (1) + butan-1-ol (2) at 1 bar with
those of alternative conformers of [bmim]: ×, experimental; O,
equilibrium mixture of conformers A + B + C; 0, conformers B +
C; 4, conformer A; ], conformer B; +, conformer C.
m
T/K ) Tc/K + k|y - yc|
(1)
where
conformer concentration for that mixture. These are the
results presented in Figure 6. However, it is of interest to
know the effect of the composition of the various conformers
on the predicted LLE. Using the expected equilibrium
concentrations of the three conformers as reference, the
lowest energy conformer, A, shifts the LLE so that a higher
UCST and a lower x2(UCST) are predicted. With the higher
energy conformers B or C or the mixture of conformers
(B + C), the LLE is shifted such that a lower UCST and a
higher x2(UCST) are predicted. The maximum difference in
the UCST for the various conformers or conformer mixtures
is about (5 K from the equilibrium conformer mixture
value, as described above, which is not significant. These
results are summarized in Figure 7.
Rx2
y )
(2)
(3)
1 + x2(R - 1)
Rx2c
yc )
1 + x2c(R - 1)
Equation 1 expresses the exponential dependence of
temperature T on the two-phase composition x2 near the
critical point. m, k, R, x2c (critical composition), and Tc
(critical temperature) are the coefficients to be fitted to the
COSMOtherm results. Excel’s Solver was used to minimize
the sum of the squared difference between the model and
the result calculated by COSMOtherm.
The difficulty in using the above model to best fit the
data was in choosing appropriate starting points for the
parameters. A fair estimate can be made for the critical
points; however, an estimate of the other parameters is
needed for Solver to suitably converge. m has a value of 2
in classical theory but a value >2 with experimentally
observed nonclassical behavior in the vicinity of a critical
point.27 The fit gave the value 2.7 ( 0.2. The parameter R
scales the composition variable between mole fraction and
volume fraction. All data were fit with R ) 0.3 ( 0.03. Only
values calculated with COSMOtherm within 20 K of the
UCST were used in the fit.
Con clu sion s
Experimental liquid-liquid equilibrium curves for bu-
tan-1-ol in ionic liquids [Rnmim][PF6] (n ) 4 to 8) have been
measured. The systems show UCST behavior, and the
mutual solubility increases with an increase in the length
of the alkyl chain of the cationic core. Quantum chemical
calculations based on the σ profiles of the cation, the anion,
and the alcohol give a good prediction of the observed LLE
equilibria.
Ack n ow led gm en t
The results of the COSMOtherm calculations for liquid-
liquid equilibria for the mixtures of [Rnmim][PF6] with
butan-1-ol are shown in Figure 6. The predicted composi-
tion dependence of the LLE is reasonable with x2(UCST) being
about 0.12 lower than the experimental values. The predic-
tion of the UCST is remarkably good, being within 3 K for
the pentyl through the octyl compounds. Even UNIFAC
cannot predict liquid-liquid equilibria to this accuracy
from parameters derived from VLE data. These calcula-
tions were made for a true three-component mixture where
the cation and anion of equal concentrations are treated
as separate species. A calculation needs to be performed
on a binary mixture where the cation and anion are treated
as an ion pair. This is not a simple calculation, as the
optimal energy configuration of the ion pair needs to be
determined.
The authors wish to thank A. Klamt, F. Eckert, and M.
Diedenhofen of COSMOlogic for advice and assistance in
the use of COSMOtherm.
Liter a tu r e Cited
(1) Fuller, J .; Carlin, R. T.; Osteryoung, R. A. The room-temperature
ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate: elec-
trochemical couples and physical properties. J . Electrochem. Soc.
1997, 144, 3881-3886.
(2) Bonhote, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundaram, K.;
Graetzel, M. Hydrophobic, highly conductive ambient-tempera-
ture molten salts. Inorg. Chem. 1996, 35, 1168-1178.
(3) Fannin, A. A.; Floreani, D. A.; King, L. A.; Landers, J . S.; Piersma,
B. J .; Stech, D. J .; Vaughn, R. L.; Wilkes, J . S.; Williams, J . L.
Properties of 1,3-dialkylimidazolium chloride-aluminum chloride
ionic liquids. 2. Phase transitions, densities, electrical conductivi-
ties, and viscosities. J . Phys. Chem. 1984, 88, 2614-2621.
(4) Liao, Q.; Hussey, L. Densities, viscosities, and conductivities of
mixtures of benzene with the lewis acidic aluminum chloride +
1-methyl-3-ethylimidazolium chloride molten salt. J . Chem. Eng.
Data 1996, 41, 1126-1130.
1-Bu tyl-3-m eth ylim id a zoliu m Con for m er s. There are
three significantly different energy states (with the energy
in the order A < B < C) for the various conformers that
can be formed as a result of torsional rotations on the butyl
chain of 1-butyl-3-methylimidazolium. One should calculate
the mixture properties with the expected equilibrium
(5) Suarez, P. A. Z.; Dullius, J . E. L.; Einoft, S.; de Souza, R. F.;
Dupont, J . The use of new ionic liquids in two-phase catalytic
hydrogenation reaction by rhodium complexes. Polyhedron 1996,
15, 1217-1219.

J ournal of Chemical and Engineering Data, Vol. 48, No. 3, 2003 491
(6) Suarez, P. A. Z.; Dullius, J . E. L.; Einoft, S.; de Souza, R. F.;
(18) Branco, L. C.; Rosa, J . N.; Ramos, J . J . M.; Afonso, C. A. M.
Preparation and characterization of new room-temperature ionic
liquids. Chem.-Eur. J . 2002, 8, 3671-3677.
(19) Wong, D. S. H.; Chen, J . P.; Chang, J . M.; Chou, C. H. Phase
equilibria of water and ionic liquids [emim][PF6] and [bmim][PF6].
Fluid Phase Equilib. 2002, 194-197, 1089-1095.
(20) Najdanovic-Visak, V.; Esperanca, J . M. S. S.; Rebelo, L. P. N.;
Nunes da Ponte, M.; Guedes, H. J . R.; Seddon, K. R.; Szydlowski,
J . Phase behaviour of room temperature ionic liquid solutions:
an unusually large cosolvent effect in (water + ethanol). Phys.
Chem. Chem. Phys. 2002, 4, 1701-1703.
(21) Swatloski, R. P.; Visser, A. E.; Reichert, W. M.; Broker, G. A.;
Farina, L. M.; Holbrey, J . D.; Rogers, R. D. On the solubilization
of water with ethanol in hydrophobic hexafluorophosphate ionic
liquids. Green Chem. 2002, 4, 81-87.
(22) Seddon, K. R.; Stark, A.; Torres, M.-J . Influence of chloride, water,
and organic solvents on the physical properties of ionic liquids.
Pure Appl. Chem. 2000, 72, 2275-2287.
(23) Eckert, F.; Klamt, A. COSMOtherm, Version C1.2, Release 01.02;
COSMOlogic GmbH & Co. KG: Leverkusen, Germany, 2002.
(24) Klamt, A.; Eckert, F. COSMO-RS: A novel and efficient method
for the a priori prediction of thermophysical data of liquids. Fluid
Phase Equilib. 2000, 172, 43-72.
Dupont, J . Two-phase catalytic hydrogenation of olefins by Ru-
(II) and Co(II) complexes dissolved in 1-n-butyl-3-methylimida-
zolium tetrafluoroborate ionic liquid. Inorg. Chim. Acta 1997, 255,
207-209.
(7) Silva, S. M.; Suarez, P. A. Z.; de Souza, R. F.; Dupont, J . Selective
linear dimerization of 1,3-butadiene by palladium compounds
immobilized into 1-n-butyl-3-methylimidazolium ionic liquids.
Polym. Bull. 1998, 40, 401-405.
(8) Mu¨ller, L. A.; Dupont, J .; De Souza, R. F. Two-phase catalytic
NBR hydrogenation by RuHCl(CO)(PCy3)2 immobilized in 1-bu-
tyl-3-methylimidazolium tetrafluoroborate molten salt. Macromol.
Rapid Commun. 1998, 19, 409-411.
(9) Chauvin, Y.; Mussmann, L.; Olivier, H. A novel class of versatile
solvents for two-phase catalysis: hydrogenation, isomerization,
and hydroformylation of alkenes catalyzed by rhodium complexes
in liquid 1,3-dialkylimidazolium salts. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2698-2700.
(10) Blanchard, L. A.; Hancu, D.; Beckman, E. J .; Brennecke, J . F.
Green processing using ionic liquids and CO2. Nature 1999, 399,
28-29.
(11) Welton, T. Room-temperature ionic liquids: Solvents for Synthesis
and Catalysis. Chem. Rev. 1999, 99, 2071-2083.
(12) Wasserscheid, P.; Keim, W. Ionic liquids-new “solutions” for
transition metal catalysis. Angew. Chem., Int. Ed. 2000, 39,
3772-3789.
(25) Eckert, F. COSMOtherm user’s manual version C1.2; COSMOlogic
GmbH & Co. KG: Leverkusen, Germany, 2000.
(13) Rogers, R. D.; Swatloski, R. P.; Visser, A. E. Liquid-liquid
extraction of organics in room-temperature ionic liquids: Cationic
effects. Book of Abstracts, 218th ACS National Meeting, New
Orleans, Aug 22-26, 1999; American Chemical Society: Wash-
ington, DC, 1999.
(26) Diedenhofen, M.; Eckert, F.; Klamt, A. Prediction of infinite
dilution activity coefficients of organic compounds in ionic liquids
using COSMO-RS. J . Chem. Eng. Data, submitted (J E025626e).
(27) Ott, J . B.; Holscher, I. F.; Schneider, G. M. (Liquid-Liquid) phase
equilibria in (methanol + heptane) and (methanol + octane) at
pressures from 0.1 to 150 MPa. J . Chem. Thermodyn. 1986, 18,
815-826.
(14) Dai, S.; J u, Y. H.; Barnes, C. E. Solvent extraction of strontium
nitrate by a crown ether using room-temperature ionic liquids.
J . Chem. Soc., Dalton Trans. 1999, 1201-1202.
(15) Blanchard, L. A.; Brennecke, J . F. Recovery of organic products
from ionic liquids using supercritical carbon dioxide. Ind. Eng.
Chem. Res. 2001, 40, 287-292.
Received for review J anuary 9, 2003. Accepted February 19, 2003.
The authors wish to thank the University of Canterbury for an
(16) Blanchard, L. A.; Gu, Z.; Brenneke, J . F. High-pressure phase
behavior of ionic liquid/CO2 systems. J . Phys. Chem. B 2001, 105,
2437-2444.
Internal Research Grant and the award of
a
Postdoctoral
Fellowship to A. Deev. This work forms part of the Green Products
and Processes Research Program.
(17) Anthony, J . L.; Maginn, E. J .; Brennecke, J . F. Solution thermo-
dynamics of imidazolium-based ionic liquids and water. J . Phys.
Chem. 2001, 105, 10942-10949.
J E0340093