Volumetric properties of 1-butyl-3-methylimidazolium tetrafluoroborate- glucose-water systems

Article abstract of DOI:10.1021/je201161p

Densities for 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF ₄)-glucose-water solutions were determined at 298.15 K. The measured densities were used to calculate the apparent molar volumes of glucose (V _Φ,S) and [Bmim]BF

Full text of DOI:10.1021/je201161p

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Article
pubs.acs.org/jced
Volumetric Properties of 1-Butyl-3-methylimidazolium
Tetrafluoroborate−Glucose−Water Systems
Hui X. Jin† and Han Y. Chen*,‡
†Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China
‡Department of Environment Engineering, Henan University of Urban Construction, Pingdingshan, 467044, China
ABSTRACT: Densities for 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4)−
glucose−water solutions were determined at 298.15 K. The measured densities were used to
calculate the apparent molar volumes of glucose (VΦ,S) and [Bmim]BF4 (VΦ,IL) in the
∞
studied solutions. Infinite dilution apparent molar volumes, VΦ,S and VΦ,IL∞, have been
evaluated, together with the standard transfer volumes of the sucrose (ΔtVS∞) from water to
aqueous solutions of [Bmim]BF4 and those of [Bmim]BF4 (ΔtVIL∞) from water to aqueous
∞
∞
glucose solution. It was shown that the ΔtVS and ΔtVIL values are positive and increase
∞
with increasing molalities of [Bmim]BF4 and glucose, respectively, and the values of VΦ,S
have the order of glucose < sucrose. The volumetric interaction parameters for
[Bmim]BF4−glucose pairs in water were also obtained and interpreted by the structural
interactions model.
Chemical Reagents Company. They are of analytical grade and
used as received. Doubly distilled water was used in all
experiments.
INTRODUCTION
■
In recent years, aqueous biphasic systems (ABS) have been
highly regarded due to their applications as a powerful
technique for purification, extraction and enrichment. Recently,
Wu and co-workers have demonstrated that the addition of
saccharides to an aqueous solution of a hydrophilic ionic liquid
(IL) produces aqueous two-phase systems (ABS),1−3 which
have great potential use for purification, extraction, and
enrichment. Chen et al. have investigated the effect of
temperature and IL structure on this type of ABS systems.4,5
These chemical separation processes require reliable and
systematic data of thermodynamic properties, such as densities.
Actually, there exist very few reliable data of liquid densities for
IL−sugar−water systems,6−9 beside of some systematic work
done on IL-containing mixtures.10−17 In our previous works, we
investigated the volumetric properties of [Amim]Cl−sucrose−
water mixtures and made a comparison with the system of
[Bmim]BF4−sucrose−water.18
As a continuation, densities of 1-butyl-3-methylimidazolium
tetrafluoroborate ([Bmim]BF4)−glucose−water systems have
been measured at 298.15 K. The standard partial molar
volumes of glucose and the corresponding transfer volumes
were calculated. These parameters have been interpreted in
terms of the various structural interactions, solute−solvent
interactions, and the hydration model of glucose molecules in
aqueous IL solutions. These results were compared with that of
the 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]-
BF4)−sucrose−water system,6 and their similarities and
differences were explained.
Synthesis of [Bmim]BF4. [Bmim]BF4 was prepared based
on the reported procedures.19 Equal molar amounts of
chlorobutane and 1-methylimidazole were added to a round-
bottomed flask fitted with a reflux condenser for 72 h at 70 °C.
The unreacted starting material was extracted with ethyl
acetate. Any remaining ethyl acetate was removed by rotating
evaporation at 70 °C, and the product [Bmim]Cl was obtained.
Then, equal molar amounts of [Bmim]Cl and NaBF4 were
mixed in a round-bottomed flask for 48 h at 25 °C, using
acetone as the solvent. The product [Bmim]BF4 was obtained
after filtration and rotating evaporation and dried under
vacuum at 373.15 K for 24 h. The purity of the [Bmim]BF4
was verified in terms of NMR analysis (> 99 %), and the Cl−1
content is smaller than 130 ppm. The water content of
[Bmim]BF4 (0.18 %) was determined by Karl Fischer titration
(ZSD-2 KF with an uncertainty of 0.05 %, Cany Precision
Instruments Co., Ltd.).
Measurement of Density. All aqueous solutions to be
studied were freshly prepared by weight with correction for air
buoyancy. The solutions were prepared in glass vials by weight
using a MS204 analytical balance with an uncertainty of
2·10−4 g. The solutions were based on molality with respect to
1 kg of pure water. The uncertainty for molalities of the
solutions is less than 2.0·10−4 mol·kg−1. Before measuring the
densities of [Bmim]BF4 + glucose + water mixtures, a Westphal
balance (PZ-D-5) was corrected with pure water at 298.15 K.
EXPERIMENTAL SECTION
■
Materials. The D-glucose (≥ 99.5 %), chlorobutane (≥ 99
%), 1-methylimidazole (≥ 99 %), ethyl acetate (99 %), acetone
(99 %), and NaBF4 (≥ 99 %) were all purchased from Shanghai
Received: October 30, 2011
Accepted: February 29, 2012
Published: March 12, 2012
© 2012 American Chemical Society
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dx.doi.org/10.1021/je201161p | J. Chem. Eng. Data 2012, 57, 1134−1138

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Table 1. Densities and Apparent Molar Volumes of Glucose and [Bmim]BF4 in Glucose−Water, [Bmim]BF4−Water, and
Glucose−[Bmim]BF4−Water Systems at 298.15 K
mIL
d
VΦ,S
VΦ,IL
mE
d
VΦ,S
VΦ,IL
mol·kg−1
g·cm−3
cm3·mol−1
cm3·mol−1
mol·kg−1
g·cm−3
cm3·mol−1
cm3·mol−1
mS = 0.0200 mol·kg−1
mS = 0.1500 mol·kg−1
0
0.99850
1.00038
1.00221
1.00397
1.007405
1.01543
1.02273
1.02935
110.112
110.258
110.428
110.621
110.810
110.947
111.223
111.306
0
1.00737
1.00912
1.01082
1.01245
1.01562
1.02317
1.03005
1.03628
110.668
110.842
111.037
111.256
111.758
111.931
112.062
112.248
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
188.136
188.294
188.598
188.799
189.050
189.227
189.432
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
188.597
188.784
189.118
189.295
189.398
189.476
189.646
mS = 0.0600 mol·kg−1
mS = 0.2000 mol·kg−1
0
1.00126
1.00310
1.00489
1.00661
1.00997
1.01785
1.02502
1.03152
110.476
110.632
110.812
111.014
111.309
111.402
111.533
111.649
0
1.01069
1.01239
1.01405
1.01562
1.01869
1.02607
1.03281
1.03890
110.818
111.000
111.154
111.434
111.954
112.096
112.132
112.291
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
188.265
188.432
188.746
188.944
189.127
189.282
189.479
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
188.808
188.903
189.352
189.528
189.548
189.653
189.703
mS = 0.1000 mol·kg−1
mS = 0.2500 mol·kg−1
0
1.00399
1.00579
1.00754
1.00922
1.01251
1.02024
1.02727
1.03365
110.608
110.772
110.960
111.170
111.444
111.607
111.846
111.996
0
1.01394
1.01559
1.01721
1.01873
1.02175
1.02887
1.03541
1.04141
111.046
111.238
111.371
111.650
112.147
112.506
112.553
112.718
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
188.406
188.582
188.904
189.078
189.216
189.362
189.547
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
189.040
189.044
189.537
189.676
189.746
189.775
189.826
[Bmim]BF4−Water6
0
0.997100
0.999000
1.000850
1.002630
0.2500
0.5000
0.7500
1.0000
1.006100
1.014200
1.021570
1.028250
188.743
189.016
189.197
189.408
0.0500
0.1000
0.1500
188.077
188.239
188.530
The uncertainty in density was estimated to be
2.0·10−6
presence of glucose. The VΦ,IL values for [Bmim]BF4 in
aqueous solutions of glucose and VΦ,S values for glucose in
aqueous [Bmim]BF4 solutions have been plotted in Figures 1
and 2, where VΦ,IL (VΦ,S) values increase with a rise in the
molality of glucose ([Bmim]BF4). It can be explained that the
g·cm−3.
RESULTS AND DISCUSSION
■
Apparent Molar Volume. The densities of [Bmim]BF4 +
glucose + water mixtures are summarized in Table 1. The
apparent molar volumes of glucose, VΦ,S, and [Bmim]BF4,
VΦ,IL, respectively, were calculated from20
M
d
(1000 + m M )(d − d )
IL IL IL
S
V
=
−
Φ,S
m dd
(1)
S
IL
M
d
(1000 + m M )(d − d )
S S S
IL
V
=
−
Φ,IL
m dd
(2)
IL
S
where MIL and MS are the molar masses of [Bmim]BF4 and
glucose, mIL and mS are the molalities of [Bmim]BF4 and
glucose, and d, dS, and dIL are the densities of the [Bmim]BF4 +
glucose + water, glucose + water, and [Bmim]BF4 + water
solutions, respectively. The calculated VΦ,S and VΦ,IL values are
also included in Table 1. The average uncertainty of VΦ values
is about 0.035 cm3·mol−1. The values of VΦ,IL for [Bmim]BF4
are in line with the results by Malham et al.21
Figure 1. Apparent molar volume, VΦ,IL, of [Bmim]BF4 plotted against
the molality of the glucose.
To analyze the structure of these ternary solutions through
examining the volumetric behavior of [Bmim]BF4 in the
1135
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molalities of [Bmim]BF4 and glucose are represented in Figure
3, respectively.
∞
∞
∞
Δ V = V (glucose−water) − V (water)
(5)
(6)
t IL
IL
IL
∞
∞
∞
Δ V = V ([Bmim]BF −water) − V (water)
t S
S
4
S
∞
∞
As shown in Figure 3, the values of ΔtVS and ΔtVIL for
both system studied are positive and increase with increasing
molalities of [Bmim]BF4 and glucose, respectively. This can be
interpreted in terms of the structural interaction model
proposed by Desnoyers et al.25 and the group additivity
model.26 According to these models, the interactions between
glucose and [Bmim]BF4 can be classified into four types of
interactions: (i) hydrophobic−cation interactions between the
hydrophobic parts of glucose and [Bmim]+; (ii) hydrophilic−
cation interactions between the hydrophilic −OH, −CO, and
−O− groups of glucose and [Bmim]+; (iii) hydrophobic−anion
interactions between the hydrophobic parts of glucose and
Figure 2. Apparent molar volume, VΦ,S, of glucose plotted against the
molality of the [Bmim]BF4.
−
BF4 ; and (iv) hydrophilic−hydrophobic interactions between
hydrophilic −OH, −CO, and −O− groups of glucose and
structure-breaking effect of [Bmim]BF4 decreases due to its
interaction with the glucose molecules and thus more water
molecules are released to the bulk water in the presence of
glucose and then contribute to the positive volume changes
observed.22
−
BF4 .
According to the structural interaction model,22 the
interactions of types (i), (iii), and (iv) are repulsive because
these two groups are incompatible in their structural influence
or their tendencies to orient water and consequently contribute
a negative volume. Only interactions of type (ii) contribute a
positive volume owing to the overlap of the hydration cosphere
of the ion ([Bmim]+) and a hydrophilic −OH, −CO, and
−O− group, which leads to a decrease in the structure-breaking
tendency of the ion and a reduction in the electrostriction of
the water caused by these ions. Thus, there are competing
interactions that result in both negative and positive values to
Furthermore, it has been found that both plots of VΦ,S
1/2
against mS and VΦ,IL against mIL
are completely linear.
Therefore, infinite-dilution apparent molar volumes, VΦ,S∞ and
VΦ,IL∞, which are equal to the standard partial molar volume
values (VS∞ and VIL∞), are obtained from least-squares weighed
fits of the experimental data by the following equations:23,24
∞
*
V
= V
− S m
Φ,S
Φ,S
S
S
(3)
∞
ΔtVIL for the systems studied. These values can be
∞
1/2
IL
*
V
= V
− S m
IL
rationalized by considering these interactions and various
other characteristics of the [Bmim]BF4 and glucose. The
Φ,IL
Φ,IL
(4)
∞
where SS*and SIL* are the experimental slopes. The infinite
dilution apparent molar volumes for the systems studied are
given in Tables 2 and 3. The VΦ∞ ([Bmim]BF4) in pure water
is 187.78, which is consistent with the results by Malham et al.
(188 cm3·mol−1).21
positive ΔtVIL observed indicated that the interaction of type
(ii), that is, hydrophilic−cationic interactions, predominate
over those of the other types. Furthermore, the increase in their
values with an increase in the concentration of glucose points
toward a strengthening of the hydrophilic−ionic interactions
over the concentration range studied.
∞
More interestingly, it was shown that VΦ,S of glucose in
The standard partial molar volume, VΦ,S∞, of glucose can also
be expressed as22,27
aqueous [Bmim]BF4 solutions were lower than that of sucrose
in aqueous [Bmim]BF4 solutions.6 This is ascribed to the fact
that glucose contains less OH groups on its molecule (glucose
(4.56) <sucrose (6.2)). The less the OH groups on saccharide
molecules fit into the water structure, the more they break the
∞
V
= V + V
v,w void
− V
shrinkage
Φ,S
(7)
water structure.2 That is why the VΦ,S is in the order of
where Vv,w is the van der Waals volume, Vvoid is the associated
void or empty volume, and Vshrinkage is the shrinkage in volume
caused by interactions of hydrogen bonding groups with water
molecules. If Vv,w and Vvoid are assumed to have the same
magnitudes in water and aqueous [Bmim]BF4 solutions,
∞
glucose < sucrose.
Volume of Transfer. Standard transfer volumes for
[Bmim]BF4, ΔtVIL∞, from water to glucose−water solutions
and those for glucose, ΔtVS∞, from water to [Bmim]BF4−water
∞
∞
solutions were calculated as follows by using values of VΦ,S
positive values of ΔtVS might arise from Vshrinkage in aqueous
and VΦ,IL∞, respectively. Plots of ΔtVS∞ and ΔtVIL∞ against the
[Bmim]BF4 solutions. Since ions of [Bmim]BF4 can be
Table 2. Infinite-Dilution Apparent Molar Volumes (VΦ,S∞/cm3·mol−1) of Glucose in Aqueous [Bmim]BF4 Solutions and
Slopes (SS*/cm3·kg·mol−2) of Equation 3 at 298.15 K
mIL/mol·kg−1
quantities
0
0.0500
0.1000
0.1500
0.2500
0.5000
0.7500
1.0000
a
∞
VΦ,S
110.16 ( 0.02)
3.52 ( 0.04)
110.31 ( 0.04) 110.50 ( 0.02) 110.68 ( 0.02) 110.86 ( 0.03) 110.93 ( 0.03) 111.20 ( 0.02) 111.30 ( 0.01)
a
SS*
3.71 ( 0.03)
3.54 ( 0.01)
3.96 ( 0.01)
5.47 ( 0.02)
6.26 ( 0.02)
5.31 ( 0.01)
5.65 ( 0.01)
a
Uncertainty.
1136
dx.doi.org/10.1021/je201161p | J. Chem. Eng. Data 2012, 57, 1134−1138

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Table 3. Infinite-Dilution Apparent Molar Volumes (VΦ,IL∞/cm3·mol−1) of [Bmim]BF4 in Aqueous Glucose Solutions and
Slopes (SIL*/cm3·kg·mol−2) of Equation 4 at 298.15 K
mS/mol·kg−1
quantities
0
0.0200
0.0600
0.1000
0.1500
0.2000
0.2500
a
∞
VΦ,IL
187.78 ( 0.01)
1.67 ( 0.01)
187.87 ( 0.01)
1.61 ( 0.01)
188.05 ( 0.02)
1.47 ( 0.03)
188.24 ( 0.04)
1.35 ( 0.05)
188.51 ( 0.01)
1.20 ( 0.02)
188.78 ( 0.02)
1.00 ( 0.01)
188.95 ( 0.03)
0.99 ( 0.04)
SIL*
a
Uncertainty.
their mean values are taken as the final values and are given in
Table 4 together with their standard deviations.
The results show that both νIS values are positive. This can
be interpreted on the basis of the structural interactions model
proposed Desnoyers et al.25 and the hydration model by
Conway.29 The positive νIS values are mainly due to the
hydrophilic−ionic interactions, since the dehydration of ions
and −OH, −CO, and −O− group contribute a positive value
to the volume.
In addition, we found that the νIS of the [Bmim]BF4−
glucose−water system (3.30) is larger than that of the
[Bmim]BF4−sucrose−water system (2.20),6 which indicates
that the interaction between [Bmim]BF4 and glucose is more
significant than [Bmim]BF4−sucrose. More importantly, it was
shown that νISS is positive, which means glucose and
[Bmim]BF4 have not only pairwise, but triplet interaction.
This was not found in the [Bmim]BF4−sucrose−water system.6
0
Figure 3. Variation of the standard transfer volumes, ΔtVS , of glucose
■
from water to aqueous [Bmim]BF4 solutions ( ) with the molality of
CONCLUSIONS
[Bmim]BF4; variation of the standard transfer volumes, ΔtVIL0, of
■
In this work, we investigated the volumetric properties of
□
[Bmim]BF4 from water to aqueous glucose solutions ( ) with the
[Bmim]BF4−glucose−water mixtures. It was found that values
molality of glucose.
∞
∞
of ΔtVS and ΔtVIL are positive and increase with increasing
∞
hydrated, the presence of [Bmim]BF4 in water will decrease the
hydration effects of hydroxyl groups of glucose molecules, thus
causing the decrease in Vshrinkage. This is a reason why ΔtVS
molalities of [Bmim]BF4 and glucose, respectively, and VΦ,S
have the order of glucose < sucrose. It could be concluded that
the interaction of cation−O (O represents OH, CO, and
−O− groups of glucose) is predominant. Furthermore, we
found that the volumetric interaction parameters νIS and νISS
are positive, suggesting that the interactions between the
glucose and the [Bmim]BF4 are mainly pair and triplet
interaction, which is different from the [Bmim]BF4−sucrose−
water system.
∞
rises with increasing molalities of [Bmim]BF4.
Volumetric Interaction Parameters. Volumetric inter-
action parameters can be obtained by separately fitting
experimental data by the following equations20,28
2
2
Δ V
t Φ,S
= 2υν m + 3υ ν
m
+ 3υν m m + ...
ISS IL
IS IL
IIS IL
S
(8)
AUTHOR INFORMATION
■
2
2
Δ V
t Φ,IL
= 2υν m + 3υ ν m m + 3υν m + ...
IS S
IIS IL
S
ISS S
Corresponding Author
*E-mail: chypds@126.com.
(9)
where ΔtVΦ,S and ΔtVΦ,IL are, respectively, the transfer volumes
of glucose at molality mS from water to a solution of electrolyte
at molality mIL and of [Bmim]BF4 at molality mIL from water to
a solution of glucose at mS. Here, υ is the number of ions into
which the electrolyte dissociates, and νIS, νIIS, and νISS are pair
and triplet interaction parameters. The interaction parameters
were obtained by least-squares regression from these two
equations, respectively. Since the values from eqs 8 and 9 are in
good agreement with each other within experimental error,
Funding
This work was financially supported by the Ningbo Region
Sustainable Development Science and Technology Promotion
Motion Project (Project No. 2007C10074) and the National
Spark Project Foundation of China (Project No.
2007EA701002).
Notes
The authors declare no competing financial interest.
Table 4. Volumetric Interaction Parameters for the [Bmim]BF4−Glucose−Water System at 298.15 K
2υ vIS
3υ vISS
3υ2 vIIS
σ
IL
cm3·mol−2·kg
3.300 0.015
cm3· mol−3·kg2
2.115 0.012
cm3·mol−3·kg2
−2.165 0.018
cm3·mol−1
0.03
a
[Bmim]BF4
a
Uncertainty.
1137
dx.doi.org/10.1021/je201161p | J. Chem. Eng. Data 2012, 57, 1134−1138