Volumetric Properties of Aqueous Ionic-Liquid Solutions at Different Temperatures

Article abstract of DOI:10.1021/je501161t

Density measurements were carried out for aqueous solutions of the ionic liquids [BMIm]Cl, [BMIm]Br, [BMIm][BF₄], [HMIm]Br, [OMIm]Br, [MMIm][MSO₄], and [EMIm][ESO₄] at T = (288.15-318.15) K. The measured densities were use

Full text of DOI:10.1021/je501161t

Article
pubs.acs.org/jced
Volumetric Properties of Aqueous Ionic-Liquid Solutions at Different
Temperatures
Hemayat Shekaari,*,† Mohammed Taghi Zafarani-Moattar,† Amir Kazempour,‡
and Zakiyeh Ghasedi-Khajeh†
†Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, 51666-14766, Iran
‡Young Researchers and Elite Club, Tabriz Branch, Islamic Azad University, Tabriz, 1666976113, Iran
ABSTRACT: Density measurements were carried out for aqueous solutions
of the ionic liquids [BMIm]Cl, [BMIm]Br, [BMIm][BF4], [HMIm]Br,
[OMIm]Br, [MMIm][MSO4], and [EMIm][ESO4] at T = (288.15−318.15)
K. The measured densities were used to compute the standard partial molar
volumes (V0ϕ) of the ILs using Redlich−Mayer and Pitzer equations. The
results show that the V0ϕ values obtained from both equations are fully
compatible and that the difference is less than 0.5 cm3·mol−1 for all the ionic
liquids. The first derivative of V0ϕ with respect to temperature give the values of
partial molar expansivity (E0ϕ), and its second derivative with respect to
temperature provided Hepler’s constant ((∂2Vϕ0 /∂T2)P) an important
parameter to discuss the structure-making or -breaking tendency of the ILs
in aqueous solutions. The values of (∂2Vϕ0 /∂T2)P for all the ILs except for
[OMIm]Br were found to be negative, showing that these ILs behave as
structure breakers in aqueous media.
concentration range, IL and water domains coexist and form a
nanosegregated biphasic system. For solutions richer in water,
the IL networks start to break apart, generating IL clusters
dispersed in the continuous water phase.8,9 For most
imidazolium-based ILs, water interacts preferably with the
anionic moiety. This means that the anion breaks the structure
of water. However, imidazolium based cation was found to
enhance the water structure, which was opposite to the effect of
ILs.10,11
The interactions between water and ILs have recently been a
hot topic, and many works have been published to discuss these
interactions. The volumetric data of aqueous ILs solutions can
be of key role to understand more deeply the behavior of ILs in
water. Hence, in this work, densities of aqueous solutions of
some commonly used ILs were measured at different
temperatures and used to compute their volumetric properties.
The obtained results show the effect of cation and anion on the
volumetric behavior of ILs in water. The temperature
dependency of the volumetric parameters have been inves-
tigated.
INTRODUCTION
■
Ionic liquids (ILs) are a class of organic electrolytes which
composed of organic cations, such as alkyl-substituted
imidazolium, pyridinimum, or phosphonium based and organic
or inorganic anions ranging from simple ionic species (e.g., Cl−
and Br−) up to more bulky and hydrophobic moieties (e.g.,
−
BF4− and PF6 ). Ionic liquids have remarkable properties like a
large liquid range, nonflammability, negligible vapor pressure, a
wide electrochemical window, high thermal stability, and an
excellent ability to dissolve many organic and inorganic solutes.
These features allow them to be used in a variety of
applications, such as catalysis, organic synthesis, extraction,
electrochemical processes, and separation technology.1−4 They
are typically used not in their pure state but in the presence of
water or organic solvents in mixtures or as additives. Some ILs
are considerably soluble in water, and their aqueous solutions
therefore became the subject of a variety of potential
applications in different areas, such as extraction processes,
aqueous biphasic systems and organic and inorganic synthetic
reactions .5−7 The presence of water can dramatically affect the
physicochemical and diffusion properties of neat ILs. In most
cases, the miscibility of ILs in water is controlled by the
corresponding anion. From a microscopic perspective, the
structure of aqueous ionic liquid solutions is very complicated.
In very low concentrations of water, a general picture is
emerging that the water molecules tend to be isolated from
each other or exist as small independent clusters dispersed in
the continuous IL polar network. As the water concentration
increases, continuous water networks start to appear, which
dramatically change the properties of the mixture. At this
EXPERIMENTAL SECTION
■
Synthesis of the Ionic Liquids. 1-Alkyl-3-methylimidazo-
lium halide ([BMIm]Cl, [BMIm]Br, [HMIm]Br, and [OMIm]-
Br) was synthesized by direct alkylation of N-methylimidazole
with an excess amount of 1-haloalkane in a round-bottomed
Received: December 23, 2014
Accepted: May 4, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/je501161t
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Journal of Chemical & Engineering Data
Article
Table 1. Description of the Chemicals Used
molecular mass
purity
%
chemical
molecular formula
g·mol−1
source
Merck
purification method
none
analysis method
N-methylimidazole
diethylsulfate
C4H6N2
82.11
154.19
126.13
109.79
165.08
193.12
137.03
92.57
≥ 99
> 98
> 99
98
none
C4H10O4S
C2H6O4S
NaBF4
Merck
none
none
dimethylsulfate
sodium tetrafluoroborate
1-bromohexane
1-bromooctane
1-bromobutane
1-chlorobutane
ethyl acetate
Merck
none
none
Merck
none
none
C6H13Br
≥ 98
> 98
> 98
99
Merck
none
none
C8H17Br
Merck
none
none
C4H9Br
LOBA Chemie
Merck
none
none
C4H9Cl
none
none
C4H8O2
88.10
99.5
> 98
> 98
> 98
> 98
> 98
> 98
> 98
Merck
none
none
[BMIm]Cl
C8H15ClN2
C8H15BrN2
C10H19BrN2
C12H23BrN2
C8H15BF4N2
C6H12SO4N2
C8H16SO4N2
174.67
219.13
247.18
275.23
226.02
208.24
236.29
synthesis
synthesis
synthesis
synthesis
synthesis
synthesis
synthesis
(liquid + liquid) extraction
(liquid + liquid) extraction
(liquid + liquid) extraction
(liquid + liquid) extraction
(liquid + liquid) extraction
(liquid + liquid) extraction
(liquid + liquid) extraction
1H NMR
1H NMR
1H NMR
1H NMR
1H NMR
1H NMR
1H NMR
[BMIm]Br
[HMIm]Br
[OMIm]Br
[BMIm][BF4]
[MMIm][MSO4]
[EMIm][ESO4]
flask stirred vigorously by a magnetic stirrer under a nitrogen
atmosphere. The mixing of the chemicals was done first under
ice-cooling, but then the temperature was raised to room
temperature. The temperature was then gradually increased
over a period of several hours to a final reaction temperature of
about 50 °C and kept constant until the end of reaction. The
reaction mixture was stirred for 1 week. Finally, the crude
product was separated from reagents and then washed three
times with fresh ethyl acetate. The removal of residual volatile
compounds from the ionic liquid was done under high vacuum
at 60 °C using a rotary evaporator for at least 4 h under
reduced pressure. The obtained ionic liquid has a purity of
about 98 %, verified by 1H NMR spectroscopy. The ionic liquid
was used after vacuum desiccation for at least 48 h to remove
trace amounts of moisture. Water content in the ionic liquid
was less than 0.3 %, as found by the Karl Fischer method.
For synthesis of [BMIm][BF4], 1-chlorobutane was added
dropwise into a mixture of N-methylimidazole and sodium
tetrafluoroborate over 1 h. The mixture was stirred under
cooling for 3 h, and then the temperature was raised to 70 °C
and stirring continued for 4 h at this temperature. Upon
completion of the reaction, the mixture was filtrated to remove
the precipitated salt (NaCl). The purification of the IL was
done as above method. The purity of ionic liquid was more
than 98 %, and water content was found to be 0.2 %.
standard uncertainty in density measurements was estimated to
be 2.0·10−5 g·cm−3.
The solutions were prepared by completely dissolving the
ionic liquid in pure water. The weighings were done on a
analytical balance (AND, GR202, Japan) with precision of 1·
10−5 g. The standard uncertainty of molalities of the prepared
solutions is estimated to be 2.0·10−5 mol·kg−1.
RESULTS AND DISCUSSION
■
Densities of the studied aqueous ILs solutions at T = (288.15 to
318.15) K are given in Table 2, and their values of two ILs
([BMIm]Cl, [BMIm]Br) are plotted and compared as
examples with literature values in Figure 1. These values were
used to calculate apparent molar volumes (Vϕ) of the ILs by the
following equation:
1000(d − d0)
M
d
Vϕ =
−
mdd0
(1)
where M is the molar mass of the IL, m is the molality of the IL
in water, d is the density of the aqueous IL solutions, and d0 is
the density of water. The Vϕ values are also given in Table 2.
Apparent molar volumes can be represented using Redlich−
Mayer equation in dilute region12
Vϕ = Vϕ0 + AV m1/2 + BV m
(2)
The ILs [MMIm][MSO4] and [EMIm][ESO4] were
prepared by direct alkylation of N-methylimidazole with an
excess amount of dimethylsulfate and diethylsulfate, respec-
tively, in a round-bottomed flask under vigorous stirring by a
magnetic stirrer under a nitrogen atmosphere for 48 h. The
purification method was the same as above, and the obtained
ILs had purity greater than 98 % with water content of about
0.2 %. All the materials used to synthesize the ILs have been
collected in Table 1.
Density Measurement. Solution densities were measured
at atmospheric pressure and at T = (288.15 to 318.15) K using
a vibrating-tube densimeter (DSA 5000, Anton Paar, Austria)
with proportional temperature control that kept the samples at
working temperature with stability of 1.0·10−2 K. The
densimeter was calibrated using doubly distilled water. The
where AV is the Pitzer−Debye−Huckel limiting slope for
̈
volume which its values for aqueous 1:1 electrolyte solutions at
different temperatures are available in literature.12 BV is an
adjustable parameter related to the pair interactions and is
generally negative. The values of standard partial molar volume
(V0ϕ) of the ILs and BV values are included in Table 3. To
examine the reliability of Redlich−Mayer equation, the Vϕ0
values were also calculated using Pitzer model as follows
⎛ AV ⎞
0
⎜
⎝
⎟
⎠
Vϕ = Vϕ + v|z+z−|
ln(1 + bI1/2) + 2RTv+v−BV m
2b
+ 2RTv+2v−z+CVm2
(3)
in which v+ and v− are the number of cations and anions such
that v = v+ + v−, z+ and z− are respectively the number of
B
DOI: 10.1021/je501161t
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Journal of Chemical & Engineering Data
Article
a
Table 2. Densities (d) and Apparent Molar Volumes (Vϕ) of Aqueous IL Solutions at Different Temperatures
T = 288.15 K
T = 298.15 K
T = 308.15 K
T = 318.15 K
mIL
d
Vϕ
d
Vϕ
d
Vϕ
d
Vϕ
mol·kg−1
g·cm−3
cm3·mol−1
g·cm−3
cm3·mol−1
[BMIm]Cl
g·cm−3
cm3·mol−1
g·cm−3
cm3·mol−1
0.0000
0.0323
0.0586
0.0739
0.0899
0.1048
0.1254
0.1437
0.1687
0.1789
0.1910
0.2204
0.999096
0.999529
0.999875
1.000080
1.000289
1.000485
1.000760
1.001007
1.001330
1.001473
1.001631
1.002029
0.997040
0.997423
0.997736
0.997920
0.998113
0.998297
0.998550
0.998776
0.999091
0.999214
0.999373
0.999752
0.994020
0.994372
0.994658
0.994834
0.995007
0.995182
0.995409
0.995622
0.995913
0.996039
0.996185
0.996541
0.990192
0.990507
0.990768
0.990922
0.991091
0.991260
0.991473
0.991680
0.991942
0.992060
0.992216
0.992538
161.42
161.43
161.38
161.37
161.35
161.29
161.23
161.22
161.15
161.14
161.04
163.20
163.13
163.06
163.00
162.92
162.83
162.75
162.62
162.61
162.52
162.37
[BMIm]Br
169.66
169.71
169.67
169.73
169.73
169.64
169.68
169.69
169.66
[BMIm][BF4]
186.56
186.69
186.77
186.88
186.98
187.10
187.19
187.28
[HMIm]Br
201.93
201.96
201.97
201.91
201.84
201.88
201.76
201.69
201.66
[OMIm]Br
233.96
233.80
233.79
233.81
233.70
233.68
233.68
233.46
233.49
[MMIm][MSO4]
159.27
159.35
159.42
159.48
159.52
164.73
164.65
164.48
164.47
164.33
164.30
164.19
164.07
163.98
163.91
163.74
166.34
166.24
166.18
166.03
165.81
165.75
165.58
165.52
165.43
165.24
165.14
0.0317
0.0585
0.0730
0.0916
0.1140
0.1319
0.1508
0.1706
0.1910
1.000705
1.002052
1.002780
1.003699
1.004803
1.005688
1.006600
1.007559
1.008546
168.21
168.21
168.15
168.21
168.22
168.15
168.21
168.21
168.17
0.998612
0.999924
1.000633
1.001529
1.002606
1.003472
1.004364
1.005297
1.006259
0.995556
0.996840
0.997535
0.998413
0.999470
1.000321
1.001189
1.002117
1.003068
171.14
171.18
171.11
171.15
171.13
171.02
171.10
171.02
170.95
0.991699
0.992959
0.993641
0.994509
0.995544
0.996382
0.997243
0.998148
0.999080
172.55
172.58
172.51
172.48
172.49
172.36
172.38
172.35
172.29
0.0311
0.0527
0.0720
0.0904
0.1103
0.1326
0.1525
0.1788
1.000384
1.001260
1.002033
1.002760
1.003538
1.004402
1.005166
1.006161
184.51
184.70
184.83
184.95
185.07
185.16
185.23
185.34
0.998274
0.999116
0.999860
1.000559
1.001308
1.002134
1.002864
1.003820
0.995194
0.995999
0.996713
0.997385
0.998110
0.998921
0.999635
1.000575
188.96
189.01
189.02
189.08
189.08
189.05
189.06
189.04
0.991332
0.992114
0.992809
0.993467
0.994171
0.994948
0.995643
0.996555
190.66
190.70
190.69
190.69
190.71
190.77
190.76
190.75
0.0314
0.0515
0.0703
0.0881
0.1098
0.1310
0.1505
0.1711
0.1903
1.000584
1.001524
1.002398
1.003231
1.004226
1.005184
1.006080
1.007001
1.007870
199.69
199.72
199.71
199.57
199.58
199.64
199.52
199.54
199.46
0.998466
0.999368
1.000205
1.000998
1.001959
1.002880
1.003740
1.004639
1.005466
0.995404
0.996284
0.997097
0.997858
0.998787
0.999688
1.000504
1.001398
1.002201
203.83
203.74
203.76
203.80
203.76
203.72
203.74
203.52
203.48
0.991535
0.992389
0.993185
0.993932
0.994837
0.995704
0.996521
0.997358
0.998139
205.72
205.65
205.57
205.54
205.51
205.56
205.41
205.42
205.38
0.0323
0.0501
0.0722
0.0908
0.1112
0.1301
0.1485
0.1707
0.1910
1.000510
1.001285
1.002237
1.003035
1.003897
1.004694
1.005467
1.006392
1.007245
231.26
231.16
231.13
231.07
231.08
231.04
230.99
230.93
230.81
0.998383
0.999121
1.000023
1.000773
1.001602
1.002356
1.003082
1.003987
1.004772
0.995284
0.995975
0.996827
0.997539
0.998314
0.999033
0.999725
1.000545
1.001302
236.94
236.89
236.83
236.78
236.74
236.66
236.61
236.61
236.53
0.991366
0.992011
0.992796
0.993460
0.994171
0.994852
0.995483
0.996260
0.996981
240.56
240.44
240.50
240.41
240.45
240.25
240.29
240.19
240.02
0.0333
0.0520
0.0743
0.0945
0.1147
1.000778
1.001710
1.002810
1.003795
1.004769
157.38
157.54
157.68
157.81
157.93
0.998673
0.999578
1.000649
1.001610
1.002565
0.995619
0.996505
0.997553
0.998494
0.999435
160.73
160.78
160.84
160.89
160.86
0.991771
0.992648
0.993684
0.994617
0.995542
161.71
161.75
161.81
161.83
161.87
C
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Journal of Chemical & Engineering Data
Table 2. continued
Article
T = 288.15 K
T = 298.15 K
T = 308.15 K
T = 318.15 K
mIL
d
Vϕ
d
Vϕ
d
Vϕ
d
Vϕ
mol·kg−1
g·cm−3
cm3·mol−1
g·cm−3
cm3·mol−1
g·cm−3
cm3·mol−1
g·cm−3
cm3·mol−1
[MMIm][MSO4]
159.55
0.1309
0.1517
0.1791
1.005548
1.006536
1.007820
157.98
158.08
158.21
1.003325
1.004296
1.005557
1.000180
1.001137
1.002380
160.89
160.88
160.92
0.996280
0.997222
0.998460
161.88
161.90
161.87
159.58
159.66
[EMIm][ESO4]
191.47
0.0313
0.0499
0.0682
0.0901
0.1095
0.1322
1.000546
1.001396
1.002223
1.003210
1.004081
1.005089
189.88
189.93
190.01
190.00
189.97
189.96
0.998448
0.999270
1.000069
1.001037
1.001865
1.002863
0.995398
0.996212
0.996995
0.997930
0.998762
0.999712
192.98
192.89
193.03
193.07
192.99
193.05
0.991566
0.992377
0.993169
0.994105
0.994936
0.995897
193.59
193.54
193.53
193.57
193.52
193.50
191.61
191.73
191.60
191.74
191.56
a
Standard uncertainties of molality, density, and temperature are 2.0·10−5 mol·kg−1, 2.0·10−5 g·cm−3, and 1.0·10−2 K, respectively. All the
measurements were performed at the pressure 0.1 MPa.
electrolytes and α = 2.0 for all 1:1 electrolytes. b and α are
taken as temperature-independent.13 The results of fitting Vϕ
values to eq 4 are given in Table 3. Clearly, the difference
between the V0ϕ values obtained from the Redlich−Mayer
equation and those obtained from Pitzer equation for all the
ionic liquids is less than 0.5 cm3·mol−1.
Standard partial molar volume gives important information
about ion−water interaction. At infinite dilution, the ions are
far from each other; therefore, V0ϕ is unaffected by ion−ion
interaction. According to Table 3, the V0ϕ values show the order
[BMIm][BF4] > [BMIm]Br > [BMIm]Cl for their anion
dependency, and for a common anion, the V0ϕ values increase
with the elongation of alkyl chain of cation in the sequence
[OMIm]Br > [HMIm]Br > [BMIm]Br. The standard partial
molar volumes also increase when both cation and anion get
larger as the order [EMIm][ESO4] > [MMIm][MSO4].
The variation of standard partial molar volume with
temperature is shown as follows
Vϕ0 = a0 + a1T + a2T2
(5)
in which a0, a1, and a2 have been evaluated by the least-squares
fitting of apparent molar volume at different temperatures.
Differentiation of eq 5 with respect to temperature at constant
pressure gives the partial molar expansibilities (E0ϕ) using the
following relation
0
⎛
⎝
⎞
⎠
∂Vϕ
∂T
0
⎜
⎜
⎟
⎟
Eϕ =
= a1 + 2a2T
(6)
P
The obtained values of E0ϕ are listed in Table 3. Obviously, the
E0ϕ values at all temperatures are positive, which indicates that
the standard partial molar volumes increase with the increase of
temperature (see Figure 2). When the solution is heated, some
water molecules may be released from the hydration layers of
IL, which results in a rise in the solution volume a little more
rapidly than that observed with pure water, so E0ϕ would be
positive.
Figure 1. Comparison between the densities of aqueous solutions of
the two ILs (a) [BMIm]Cl and (b) [BMIm]Br with literature values.14
charges on the cations and anions, I is total ionic strength, R is
the gas constant, T is temperature, and BV is defined by the
following equation
⎛
⎜
⎞
⎟
The values of the isobaric thermal expansion coefficient of
ILs at infinite dilution (αIL) are determined using the following
equation
2
α I
BV = β 0 + β1
[1 − (1 + αI1/2) exp(−αI1/2)]
V
V
2
⎝
⎠
(4)
where β0V, βV1, and CV are pressure derivatives of Pitzer ion
interaction parameters for osmotic coefficient expressions. The
parameter b is given the value 1.2 kg1/2·mol−1/2 for all
Eϕ0
Vϕ0
αIL
=
(7)
D
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Article
Table 3. Coefficients of Redlich−Mayer and Pitzer Equations, Partial Molar Expansibilities (E0ϕ), Isobaric Thermal Expansion
Coefficients (αIL), and Hepler Constants of Aqueous IL Solutions at Different Temperatures
Redlich−Mayer
Pitzer
T
Vϕ0
cm3·mol−1
Eϕ0
BV
103·αIL
K−1
(∂2V0ϕ/∂T2)P
cm3·mol−1·K−2
−8.50·10−4
V0ϕ/
cm3·mol−1
1011·β0V
1011·β1V
1014·CV
K
cm3·mol−1·K−1
cm3·kg·mol−2
g·mol−1·Pa−1 g·mol−1·Pa−1 g2·mol−2·Pa−1
[BMIm]Cl
288.15
161.27 0.01
163.09 0.01
164.60 0.03
166.25 0.05
0.177
0.168
0.160
0.151
−4.68 0.11
−7.27 0.07
−8.27 0.19
−10.13 0.33
1.099
1.035
0.974
0.913
161.36 0.04
163.23 0.04
164.81 0.04
166.04 0.06
−0.0006
−0.0019
−0.0015
−0.0022
0.0014
0.0004
−0.0017
0.0030
298.15
308.15
0.0014
−0.0005
0.0035
318.15
−0.0025
[BMIm]Br
288.15
−4.00·10−4
−1.75·10−3
−2.35·10−3
4.80·10−3
167.95 0.03
169.42 0.02
170.92 0.03
172.31 0.03
0.152
0.148
0.144
0.140
−2.79 0.24
−3.05 0.20
−4.45 0.25
−5.35 0.22
0.904
0.872
0.841
0.811
168.00 0.02
169.24 0.02
170.62 0.04
171.85 0.03
−0.0004
−0.0003
−0.0003
−0.0009
0.0005
−0.0010
−0.0014
−0.0032
−0.0002
−0.0001
−0.0006
0.0023
298.15
308.15
318.15
[BMIm][BF4]
288.15
298.15
308.15
318.15
[HMIm]Br
288.15
298.15
308.15
318.15
[OMIm]Br
288.15
298.15
308.15
318.15
184.16 0.03
0.237
0.219
0.202
0.184
2.72 0.23
1.93 0.10
1.286
1.178
1.069
0.968
183.88 0.03
186.54 0.01
188.73 0.03
190.84 0.03
−0.0029
−0.0022
−0.0015
−0.0013
0.0037
−0.0001
0.0023
0.0035
0.0034
0.0030
0.0027
186.15 0.01
188.69 0.01
190.33 0.03
−2.88 0.13
−3.04 0.23
−0.0000
199.51 0.04
201.79 0.03
203.61 0.05
205.42 0.04
0.231
0.207
0.184
0.160
−4.15 0.30
−4.94 0.21
−5.09 0.41
−5.57 0.34
1.157
1.027
0.903
0.780
199.80 0.04
201.58 0.03
203.46 0.04
205.85 0.04
−0.0010
−0.0006
0.0004
0.0018
−0.0011
0.0015
0.0001
−0.0002
−0.0060
0.0010
−0.0013
0.0024
231.06 0.03
233.73 0.05
236.71 0.03
240.34 0.05
0.237
0.285
0.333
0.380
−5.05 0.23
−5.70 0.39
−5.84 0.22
−6.54 0.39
1.027
1.216
1.403
1.582
231.70 0.02
233.85 0.03
236.64 0.03
240.65 0.08
−0.0007
−0.0008
−0.0014
−0.0005
0.0051
0.0017
−0.0039
−0.0012
0.0026
−0.0011
0.0031
−0.0044
[MMIm][MSO4]
−5.05·10−3
−4.90·10−3
288.15
298.15
308.15
318.15
157.00 0.02
0.222
0.172
0.122
0.071
2.79 0.14
−0.54 0.07
−2.22 0.12
−2.48 0.09
1.414
1.079
0.754
0.437
157.32 0.01
159.30 0.01
160.71 0.01
161.79 0.03
0.0010
0.0000
0.0027
0.0024
0.0020
0.0033
−0.0031
−0.0014
−0.0016
−0.0037
158.95 0.01
160.44 0.01
161.38 0.01
−0.0002
0.0001
[EMIm][ESO4]
288.15
298.15
308.15
318.15
189.68 0.03
0.196
0.147
0.098
0.049
−2.44 0.36
−2.49 1.50
−2.79 0.72
−4.81 0.38
1.032
0.767
0.507
0.252
189.44 0.01
191.12 0.05
192.57 0.02
193.54 0.02
−0.0005
0.0007
−0.0020
−0.0003
−0.0005
0.0021
0.0021
−0.0064
0.0065
191.30 0.10
192.66 0.06
193.30 0.03
−0.0016
−0.0006
−0.0010
The coefficient of thermal expansion is a measure for the
response of a system’s volume to an increase in temperature.
The larger αIL value means that the volume of the system is
more sensitive versus a change of temperature. Table 3 reveals
that among the studied ILs, [OMIm]Br has the largest αIL
values at all temperatures except for 288.15 K.
Hepler’s constant is another useful thermodynamic param-
eter that provides qualitative information about the structure-
making or -breaking ability of a solute in solution.15 This
parameter is defined as follows
2
0
0
0
⎛
⎝
⎞
⎠
⎛
⎝
⎞
⎠
⎛
⎜
⎝
⎞
∂ Vϕ
∂T2
∂Eϕ
∂CP
⎜
⎜
⎟
⎟
⎜
⎜
⎟
⎟
⎟ = −T
= −T
∂P
∂T
⎠
(8)
T
P
P
where C0P is the heat capacity of solute at infinite dilution. If the
sign of (∂2Vϕ0 /∂T2)P is negative, then the solute is a structure
breaker; otherwise, it is a structure maker. Table 3 shows that
the (∂2V0ϕ/∂T2)P values of all the ILs with the exception of
[OMIm]Br are negative, indicating that the ILs act as a
structure breaker in water.
Figure 2. Influence of cation and anion on the standard partial molar
volumes of ILs in aqueous solutions.
E
DOI: 10.1021/je501161t
J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data
Article
Shekaari, H. Density and speed of sound of Lithium bromide with
organic solvents: Measurement and correlation. J. Chem. Thermodyn.
2007, 39, 1649−1660.
(13) Rowland, D.; May, P. M. A Pitzer-Based Characterization of
Aqueous Magnesium Chloride, Calcium Chloride and Potassium
Iodide Solution Densities to High Temperature and Pressure. Fluid
Phase Equilib. 2013, 338, 54−62.
(14) Lal, B.; Sahin, M.; Ayranci, E. Volumetric Studies to Examine
the Interactions of Imidazolium Based Ionic Liquids With Water by
Means of Density and Speed of Sound Measurements. J. Chem.
Thermodyn. 2012, 54, 142−147.
(15) Hepler, L. G. Thermal expansion and structure in water and 658
aqueous solutions. Can. J. Chem. 1969, 47, 4613−4617.
CONCLUSIONS
■
The influence of the cation and anion of ILs on their volumetric
properties was studied via density measurements of aqueous
solutions of the ILs [BMIm]Cl, [BMIm]Br, [BMIm][BF4],
[HMIm]Br, [OMIm]Br, [MMIm][MSO4], and [EMIm]-
[ESO4] at T = (288.15 to 318.15) K. The standard partial
molar volumes of the ILs with the cation [BMIm]+ show the
order BF4− > Br− > Cl−, and those of the ILs with the common
anion Br− have the order [OMIm]+ > [HMIm]+ > [BMIm]+.
The V0ϕ values also increase as both the cation and anion of IL
become larger in the sequence [EMIm][ESO4] > [MMIm]-
[MSO4]. The resulting positive values of partial molar
expansibilities (E0ϕ) for all the ILs indicate that the standard
partial molar volumes increase as temperature increases.
Furthermore, the sign of (∂2Vϕ0 /∂T2)P for all the ILs except
for [OMIm]Br is negative, showing that these ILs behave as
structure maker in aqueous media.
AUTHOR INFORMATION
Corresponding Author
*Tel.: +98 41 33393139. Fax: +98 41 33340191. E-mail:
hemayatt@yahoo.com, hemayatt@tabrizu.ac.ir.
■
Notes
The authors declare no competing financial interest.
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DOI: 10.1021/je501161t
J. Chem. Eng. Data XXXX, XXX, XXX−XXX