Physicochemical properties of new imidazolium-based ionic liquids containing aromatic group

Article abstract of DOI:10.1021/acs.jced.5b00983

In this work, three novel imidazolium-based ionic liquids containing aromatic group in the cation combined with bis(trifluoromethylsulfonyl)imide anion were synthesized and characterized. Their thermophysical properties namely, density, viscosity, thermal decomposition, glass transition, and heat capacity were measured at various temperatures and atmospheric pressure. In addition, physicochemical properties such as molar volume (V_m) and crystal energy (U_POT) were also determined from the obtained density data. Novel group contribution parameters were obtained using Gardas and Coutinho model aiming at providing simple method to predict density and viscosity of ionic liquids.

Full text of DOI:10.1021/acs.jced.5b00983

Article
pubs.acs.org/jced
Physicochemical Properties of New Imidazolium-Based Ionic Liquids
Containing Aromatic Group
Massoud Kermanioryani,*,† M. Ibrahim A. Mutalib,† Yue Dong,‡ Kallidanthiyil Chellappan Lethesh,§
Ouahid Ben Omar Ben Ghanem,† Kiki Adi Kurnia,† Noor Fathanah Aminuddin,†
and Jean-Marc Leveque*,∥
†Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Perak, Malaysia
‡University of Oulu, Research Unit of Sustainable Chemistry, P.O.Box 3000, FIN-90014 Oulu, Finland
§Center for Biofuel and Biochemical Research, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Perak, Malaysia
∥Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Perak, Malaysia
S
* Supporting Information
ABSTRACT: In this work, three novel imidazolium-based
ionic liquids containing aromatic group in the cation combined
with bis(trifluoromethylsulfonyl)imide anion were synthesized
and characterized. Their thermophysical properties namely,
density, viscosity, thermal decomposition, glass transition, and
heat capacity were measured at various temperatures and
atmospheric pressure. In addition, physicochemical properties
such as molar volume (Vm) and crystal energy (UPOT) were
also determined from the obtained density data. Novel group
contribution parameters were obtained using Gardas and
Coutinho model aiming at providing simple method to predict
density and viscosity of ionic liquids.
n a m e l y , 1 - b u t y l - 3 H - b e n z o i m i d a z o l i u m b i s -
(trifluoromethylsulfonyl)imide, [BzBIm][NTf2]; 1-butyl-2-phe-
nyl-imidazolium bis(trifluoromethylsulfonyl)imide, [BPhIm]-
[NTf2 ]; and 1-benzyl-3-butyl-imidazolum bis-
(trifluoromethylsulfonyl)imide [BnBIm][NTf2]were studied
to investigate the impact of the location of aromatic groups at
different positions on the imidazolium ring. The structure of the
newly synthesized TSIL is given in Figure 1.
Notably, the density, viscosity, thermal decomposition, glass
transition, and heat capacity of the TSILs were measured at
different temperature and atmospheric pressure. Certain
significant physicochemical and thermal properties also were
determined from the experimental data. The thermal behavior of
the TSILs was studied using thermogravimetric (TGA) and
differential scanning calorimetric (DSC) analyses. Furthermore,
on the basis of the experimental data, novel group contribution
parameters for Gardas and Coutinho models18,19 are proposed
here for these newly synthesized cation aiming at predicting
densities and viscosities of ILs not previously investigated
experimentally.
1. INTRODUCTION
Room temperature ionic liquids (RTIL) are a new class of
organic salts based on bulky organic cations and organic or
inorganic anions with melting point below 100 °C.1 Interestingly,
their properties, such as density and viscosity, are tunable by
selecting proper cations and anions combinations.2 Nitrogen
atom containing heterocyclic compounds such as imidazole,
pyridine, pyrrolidine, and their derivatives remain as the most
common cations affording different types of ILs when linked to
various anions such as basic halides or more evolved organic/
inorganic moieties like [BF4]−, [PF6]−, [NTf2]−, [CH3COO]−,
prolinate [Pro], alaninate [Ala], and glycinate [Gly].3−5 These
families of compounds do display some unique and striking
properties making them of high interest in both academia and
industry such as high thermal stability, negligible vapor pressure
enabling possible recycling, relatively high ionic conductivity,
and good electrochemical stability. These properties make them
very promising in various applications such as catalysis,
capacitors, organic synthetic chemistry, batteries, solar cells,
separation, adsorption process, and so forth.6−12 Additionally,
over the past decade, there is a growing interest in a new class of
RTIL, which are called task-specific ILs (TSIL) specially
designed for specific applications. These latters do contain a
functional group that is incorporated either into the organic
cation or into the anion to achieve a special task in a given
chemical system.13−17 In this present work, several important
physicochemical properties of three newly synthesized TSILs
Received: November 20, 2015
Accepted: May 18, 2016
© XXXX American Chemical Society
A
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Figure 1. General route for the synthesis of studied ionic liquids. [BzBIm][NTf2], [BPhIm][NTf2], and [BnBIm][NTf2].
MeOD) δ = 0.84 (t, 3H), 1.51 (m, 2H), 1.75 (m, 2H), 4.04 (t,
2H), 7.2 (m, 5H), 7.96 (m, 2H).
2. EXPERIMENTAL SECTION
2.1. Materials. The following chemicals, namely, 1-bromo
butane (≥98%), 2-phenylimidazole (≥95%), benzimidazole
(≥99%), 1-butylimidazole (≥98%), and benzyl chloride
(≥99%) were purchased from Merck. Sodium bis-
(trifluoromethanesulfonyl)imide (≥97%) was supplied by
sigma Aldrich. Dichloromethane, acetonitrile (≥99.8%), and
diethyl acetate (≥99.99%) were purchased from Fisher Scientific
U.K. All reagents were used as received without any further
purification. The chemical information table is given in
Supporting Information (Table S1).
2.2.3. Synthesis of 1-Benzyl-3-butyl-imidazolum Bis-
(trifluoromethylsulfonyl)imide [BnBIm][NTf2]. The 1-benzyl-
3-butyl-imidazolum bis(trifluoromethylsulfonyl)imide was syn-
thesized using the general procedure as described for [BzBIm]-
[NTf2] from 1-butylimidazole (2.48 g, 0.02 mol), benzyl chloride
(2.52g, 0.02 mol), and sodium bis(trifluoromethylsulfonyl)imide
(6.06 g, 0.02 mol), respectively, and was obtained with a 98%
yield (9.7 g). 1H NMR (500 MHz, MeOD) δ= 0.98 (t, 3H), 1.38
(m, 2H), 1.90 (m, 2H), 4.25 (m, 2H), 5.46 (s, 2H), 7.44 (m, 5H),
7.66 (m, 2H).
2.2. Synthesis of Ionic Liquids. 2.2.1. Synthesis of 1-Butyl-
3H-BenzoImidazolium Bis(trifluoromethylsulfonyl)imide
[BzBIm][NTf2]. To a solution of benzimidazole (2.36 g, 0.02
mol) in acetonitrile (20 mL) in a three-neck round-bottom flask,
1-bromobutane (2.74 g, 0.02 mol) was added at room
temperature. The mixture was then heated under reflux in a
nitrogen atmosphere for 48 h. After the completion of the
reaction, acetonitrile was evaporated using a rotary evaporator
and the resulting slightly yellowish product was washed three
times with ethyl acetate (ca. 25 mL) to remove the unreacted
reagents. The solvent was then removed using a rotary
evaporator and the product obtained was further dried in a
vacuum oven (50 mbar) at 60 °C for 48 h. The IL was obtained as
a highly viscous and pale yellow liquid with 96% yield (4.89 g). In
the second step, to a solution of [BzBIm]Br (5.1 g, 0.02 mol) in
water, a solution of sodium bis(trifluoromethylsulfonyl)imide
(6.06 g, 0.02 mol) was added and the resulting solution was
stirred for 24 h at room temperature. The hydrophobic IL
formed was separated from water phase and washed several times
with deionized water until the washing water gave no precipitate
with AgNO3 solution. Traces of water were then removed by
drying under vacuum line (50 mbar) at 70 °C for 48 h. The IL
was obtained as a pale yellow liquid with a 97% yield (8.57 g). 1H
NMR (500 MHz, MeOD) δ = 1.03 (t, 3H), 1.46 (m, 2H), 2.01
(m, 2H), 4.52 (t, 2H), 7.91 (m, 4H), 9.33 (s, 1H).
2.3. Density and Viscosity Measurements. The measure-
ment of density and viscosity of TSILs was carried out using
Anton Paardensitometer (SVM 3000). The calibration of
instrument was carried with Millipore-grade water according to
the manual, for which the data was proven. Furthermore, the
equipment was also used to measure the density and viscosity of
other ILs published in literature20,21 and support the viability of
the equipment to determine the accurate properties of IL
samples.
2.4. Thermal Analysis and Heat Capacity. 2.4.1. Thermal
Decomposition. Thermal decomposition temperature of TSIL
was measured using PerkinElmer, Pyris V-3.81 thermal
gravimetric analyzer. The samples were placed in sealed
aluminum pans under nitrogen flow at a heating rate of 10 K/
min with temperature precision of 1 K.
2.4.2. Glass Transition. A differential scanning calorimeter
(Mettler Toledo, MODEL (DSC1/500) was used to measure
glass transition temperature. Small amounts of TSILs samples
were placed in sealed aluminum pans and cooled to 193.15 K and
then heated to 393.15 K with a heating rate of 10 K/Min. The
glass transition temperatures were determined with a temper-
ature accuracy of 1 K.
2.4.3. Heat Capacity Measurements. To ensure the high
accuracy of defining heat capacity of the TSILs, the sapphire
method22 was selected. Samples were set in sealed aluminum
pans and the temperature was increased from 303.15 K until
353.15 K with a heating rate of 5 K/min. Each rise of temperature
of 5 K was sustained for 15 min.
2.2.2. Synthesis of 1-Butyl-2-phenyl-imidazolium Bis-
(trifluoromethylsulfonyl)imide [BPhIm][NTf2]. The 1-butyl-2-
phenyl-imidazolium bis(trifluoromethylsulfonyl)imide was syn-
thesized using a similar two-step general procedure described as
for [BzBIm][NTf2] from 2-phenyl-imidazole (2.88 g, 0.02 mol),
1-bromobutane (2.74 g, 0.02 mol), and sodium bis-
(trifluooromethylsulfonyl)imide (6.06 g, 0.02 mol), respectively,
and was obtained with a 96% yield (9.23 g). 1H NMR (500 MHz,
3. RESULTS AND DISCUSSION
3.1. Characterization. The 1H NMR spectra were taken in
deuterated methanol (MeOD) and recorded on a Bruker
B
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Table 1. Chemical Name, Purification Method, Mole Fraction Purity, Analysis Method, and Water Content of ILs
chemical name
purification method
mole fraction purity analysis method water content (ppm)
1-butyl-3H-benzoimidazolium bis(trifluoromethanesulfonyl)imide
1-butyl-2-phenyl-imidazolium bis(trifluoromethylsulfonyl)imide
1-benzyl-3-butyl-imidazolum bis(trifluoromethylsulfonyl)imide
activated carbon + methanol
activated carbon + methanol
activated carbon + methanol
0.99
0.99
0.998
1H NMR
1H NMR
1H NMR
418
443
411
Advance 500 spectrometer. It is very important that the
examined TSILs are anhydrous as possible because the presence
of water can significantly influence the physicochemical
properties. Hence, all studied ILs were extensively dried in
vacuum oven at 343.15 K for 48 h followed by the determination
of water content by using a colulometric Karl Fischer titrator (DL
39, Mettler Toledo) using Hydranal coulomat AG reagent. The
average of three measurements of water content of each IL, mole
fraction purity, and analysis method are presented in Table 1.
3.2. Density. The densities of the studied ILs were
determined in the temperature range of 293.15−373.15 K and
the results are plotted in Figure 2. The ILs studied in this work
◆
Figure 3. Plot of Vm versus density of [NTf2]-based ionic liquids:
,
■
nonaromatic IL; , aromatic-containing IL. The line does not have any
specific physical meaning.
When looking at the three structures shown in Figure 1, it can
be assumed that when the degrees rotation freedom between the
imidazolium and aromatic rings increases, the rotation ability of
the aromatic ring increases and resulted in lower intermolecular
π−π interaction. Typically, the presence of the methylene group
of the benzyl group in [BnBIm][NTf2] leads to a 3D structure
where the free rotation of the phenyl group is authorized leading
to decreased intermolecular π−π interactions. On the other
hand, the flat 2D structure of the [BzBIm][NTf2] offers
enhanced intermolecular π−π forces and thus higher density
value.
■
■
Figure 2. Density as a function of temperature:  , [BzBIm][NTf2];
◆
◆
●
●
······ , [BPhIm][NTf2]; and · , [BnBIm][NTf2].
The density decreased with increasing temperature; a
common trend observed for the density−temperature depend-
ence of ILs. The experimental densities (ρ) were fitted using the
least-squares method based on the equation
allow us to investigate the cation structural impact, particularly
the presence of aromatic ring on the cation, toward their density.
The obtained data revealed that the density values follow the
order: [BzBIm][NTf2] ≥ [BPhIm][NTf2] > [BnBIm][NTf2].
Aiming at understanding the impact of aromatic ring on the
cation, the obtained density data in this work is compared with
nonaromatic IL from literature23 and is plotted as a function of
their molecular volume (Figure 3). According to the obtained
data, the density of studied ILs are lower than some commercial
[NTf2] ILs with short alkyl chain length (<4) and have higher
density than commercial [NTf2] ILs with longer alkyl spacer
length.24 For example, the density of [MMIm][NTf2] is 1.56 g/
cm3, which is higher than the studied ILs. On the other hand, the
density of [NTf2] ILs with six carbon atoms [HMIm][NTf2] is
1.37 g/cm3, which is lower than the ILs reported here.25,26 It is
clear that the density decreased with increasing molecular
volume of the ILs. However, it is interesting to note that even
though the density of aromatic group containing ILs studied in
this work also decrease with increasing the molecular volume,
[BzBIm][NTf2] and [BPhIm][NTf2] do not fall exactly on this
relationship (see the dot lines in the Figure 2). The higher
density of these two aromatic containing ILs might be due to the
position of aromatic group and its subsequent influence on the
π−π stacking interaction.
ρ/(g·cm)−3=A0 + A1T
(1)
where ρ denotes the density of the ILs, A0 and A1 are the
correlation coefficients, and T is the temperature in Kelvin. Plot
of ρ (g·cm−3) against T (K) is shown in Figure 2. The correlation
coefficients were calculated from the slope and intercept of the
plot, respectively, and their estimated values with the standard
deviations (SD) are presented in Table 2. According to the R2
values, which are close to 1 (0.99) for all three studied ILs, it was
concluded that the experimental densities were a good fit.
By using the experimental densities, the other thermophysical
properties, such as molar volume (Vm) and crystal energy
(UPOT), were determined.
3.2.1. Molar Volume. The molar volumes (Vm) of the ILs
were calculated according to eq 2 at standard temperature and
pressure
M
ρ
Vm/(cm3·mol−1) =
(2)
where M is the molar mass (g·mol−1) and ρ is the density (g·
cm−3). The values of Vm are tabulated in Table 2. According to
the Vm values, it is deduced that the molar volume (Vm) of
C
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Table 2. Fitting Parameter Values A0, A1, and R2 for Densities,
Standard Deviation SD, Molar Volume Vm, and Crystal
Energy UPOT of ILs at 298.15 K and 0.1 MPa
Table 3. Isobaric Thermal Expansion Coefficient α, of ILs as a
Function of Temperature
a
α·104/(K−1
)
parameter
[BzBIm][NTf2] [BPhIm][NTf2] [BnBIm][NTf2]
T/K
[BzBIm][NTf2]
[BPhIm][NTf2]
[BnBIm][NTf2]
A0
1.6942
−9
0.9997
2.13 × 10−03
309.242
397.02
1.6927
−9
0.9997
7.78 × 10−03
338.136
389.09
1.5463
−9
0.9998
1.62 × 10−02
381.698
377.21
293.15
303.15
313.15
323.15
333.15
343.15
353.15
363.15
373.15
6.29
6.33
6.37
6.41
6.45
6.50
6.54
6.58
6.63
6.30
6.34
6.38
6.42
6.46
6.50
6.55
6.59
6.63
7.02
7.07
7.12
7.17
7.22
7.27
7.33
7.38
7.44
A1 × 104
R2
SD
Vm (cm3·mol−1
)
U
POT (kJ·mol−1
)
∑(Zexp − Zcal
)
a
Standard deviation values were calculated using SD =
where SD, n, Zexp, and Zcal are the standard deviations, number of
experimental points, and experimental and calculated data values,
respectively.
n
studied ILs decreased in the order of [BnBIm][NTf2] >
[BPhIm][NTf2] > [BzBIm][NTf2]. By increasing the molar
mass of ILs (M), the molar volume (Vm) of ILs increase
accordingly.
3.2.2. Crystal Energy. The crystal energy (UPOT) is defined as
the energy needed to form salts from separated ions, molecules
or atoms which is calculated according to Glasser’s theory27 by
using the following equation:
1/3
⎛
⎜
⎞
⎟
ρ
Μ
−1
U
POT/(KJ·mol ) = 1981.2
+ 103.8
⎝
⎠
(3)
where ρ and M are density and molar mass of ILs, respectively,
and the UPOT values are listed in Table 2. Because of their lower
crystal energies compared to inorganic fused salts, ILs are liquids
at room temperature. For example, the UPOT values of
[BzBIm][NTf2], [BPhIm][NTf2], and [BnBIm][NTf2] are
397.02 kJ·mol−1, 389.09 kJ·mol−1, and 377.21 kJ·mol−1,
respectively, which are much lower than inorganic salts such as
NaI, NaCl, and CaCO3 with UPOT values 682 kJ·mol−1, 786 kJ·
mol−1, and 2804 kJ·mol−1, respectively.28 The calculated UPOT
values are in accordance with literature5 and follow the trend
[BzBIm][NTf2] > [BPhIm][NTf2] > [BnBIm][NTf2], clearly
showing that the lower the molecular weight is, the more
compact the ILs are, leading thus to a higher lattice energy.
3.2.3. Isobaric Thermal Expansion Coefficient. The
experimental density values were used to calculate the isobaric
thermal expansion coefficients (α) using the following equation:
■
●
Figure 4. Viscosity as a function of temperature: , [BzBIm][NTf2];
[BPhIm][NTf2]; , [BnBIm][NTf2].
,
◆
rotation freedom between the imidazolium and the different
types of aromatic rings greatly influence the nature of the
intermolecular π−π interactions thus impacting viscosity, that is,
the lesser the degrees of rotational freedom, the stronger the
intermolecular π−π interactions. This explains why the viscosity
of [BzBIm][NTf2] and [BPhIm][NTf2] are particularly much
higher than of commercial ILs ones bearing side alkyl chain. For
example the viscosity values of [BzBIm][NTf2], [BPhIm][NTf2]
and [BnBIm][NTf2] at 20 °C are 1150.40 mPa·s, 753.71 mPa·s
and 86.75 mPa·s, respectively, which are higher than the viscosity
values of [EMIm][NTf2] and [BMIm][NTf2] with 34 mPa·s and
52 mPa·s, respectively.25,30,31
⎛
⎜
⎞
⎟
⎠
⎛
⎜
⎞
⎟
δVm
Vm δT
1
δρ
δT
The experimental viscosities (η) for ILs were fitted by the
following equation:
α(K−1) =
= −
⎝
⎠
⎝
p
p
(4)
A3
T
log η(Pa·s) = A2 +
The values of the isobaric thermal expansion coefficient are
shown in Table 3. The α values of the studied ILs are in the order
[BnBIm][NTf2] > [BPhIm][NTf2] ≥ [BzBIm][NTf2]. It is
found that the temperature has no significant effect on the
coefficients of thermal expansion of the present ILs. The thermal
expansion coefficients of these ILs are higher than [BMIm]-
[NTf2], which has same alkyl chain length as that of the studied
ILs.29
3.3. Viscosity. The dynamic viscosity measurements of the
studied TSILs were carried out at different temperatures and the
results are plotted in Figure 4. The viscosities of the TSILs
decrease in the order of [BzBIm][NTf2] > [BPhIm][NTf2] >
[BnBIm][NTf2], which was expected according to the structures
of ILs. Indeed, the observed trend is similar to the one obtained
for density measurements and as mentioned before, the degrees
(5)
where η denotes the viscosity of the ILs, and A2 and A3 are the
correlation coefficients and T is temperature (K). By plotting the
logarithm viscosities of ILs over 1/T, the A2 and A3 are estimated
from intercept and slope of plot, respectively, and the values are
presented in Table 4.
3.4. Thermal Decomposition. Thermal gravimetric anal-
ysis (TGA) experiments were performed for the studied ILs to
compare their thermal stability with the commercially available
ones. Thermal decompositions (Td) were determined in terms of
onset temperature (Ts) and the results are present in Table 5 and
plotted in Figure 5. The Td values of the ILs were within the
range of 677−694 K and the thermal stability increased in the
order of [BzBIm][NTf2] > [BPhIm][NTf2] > [BnBIm][NTf2]
D
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Table 4. Fitting Parameter Values for Viscosities with
Correlation Coefficient R2
IL
A
B
T0
R2
[BzBIm][NTf2]
[BPhIm][NTf2]
[BnBIm][NTf2]
−1.20
−0.98
−1.01
455.58
390.78
377.86
186.26
191.84
165.17
1
1
0.99
Table 5. Decomposition Temperature in Terms of Onset
Temperature Ts and Glass Transition Temperature Tg of ILs
a
at 0.1 MPa
[BzBIm][NTf2]
[BPhIm][NTf2]
[BnBIm][NTf2]
Td/K
Tg/K
694.67
220.68
681.85
220.18
677.83
187.02
a
The standard uncertainties are u(Td) = 1 K, u(Tg) = 1 K, u(p) = 0.01
Figure 6. Experimental heat capacity Cp as a function of temperature of
ILs: , [BzBIm][NTf2]; , [BPhIm][NTf2]; , [BnBIm][NTf2].
MPa.
■
◆
●
imidazolium ring on several physicochemical properties of ILs
presented in this work.
3.7. Group Contribution. With the high number of possible
cation and anion to form ILs, a simple equation to predict the
physical properties of novel (or not yet synthesized) ILs is very
important.34 The density data measured in this work were also
used to broaden the group contribution parameter values in the
extension of the Ye and Shreeve group contribution method35
previously proposed by Gardas and Coutinho,19 intended to
enable the prediction of densities of ILs not experimentally
addressed. The contributions of the three novel cations were
estimated according to the following equation:
Mw
ρ =
NV(a + bT + cp)
Figure 5. Thermogravimetric profiles of ILs: red , [BzBIm][NTf2];
blue ······, [BPhIm][NTf2]; green − −, [BnBIm][NTf2].
(6)
where ρ is the density in kg·m−3, Mw is the IL molecular weight in
kg·mol−1, N is Avogadro constant, V is the IL volume in m3, T is
the temperature in K, and p is the pressure in MPa. The
coefficients a, b, and c were previously proposed using a large set
of experimental data and using the following values of 0.8005
0.002, (6.652 0.007) × 10−4 K−1, and (−5.919 0.024) × 10−4
MPa−1, respectively.19,36
with 694.67 K, 681.85 K, and 677.83 K, respectively. Previous
studies have reported8,32 that as the molecular weight of the IL
increases, the Td value decreases accordingly, which is in
accordance with our results. For example the Td values for
[EMIm][NTf2], [PMIm][NTf2], and [BMIm][NTf2] are
728.15 K, 725.15 K, and 712.15 K, respectively.
3.5. Glass Transition Temperature. The glass transition
temperature (Tg) is defined as the midpoint of a small heat
capacity change on heating from the amorphous glass state to a
hard and relatively frangible state and vice versa. The Tg values
for the studied ILs follow the trend [BzBIm][NTf2] >
[BPhIm][NTf2] > [BnBIm][NTf2].
3.6. Heat Capacity. The heat capacity (Cp) analyses for
studied ILs were performed in the temperature range of 303.15−
353.15 K and the results are plotted in Figure 6. The Cp values of
the studied ILs are relatively higher compared to analogs of
imidazolium ILs with same anion but with side alkyl chain. For
instance, the Cp of 1-ethyl-3-methyl-imidazolium bis-
(trifluoromethylsulfonyl)imide [EMIm][NTf2] and 1-butyl-3-
methyl-imidazolium bis(trifluoromethylsulfonyl)imide
[BMIm][NTf2] at 323.15 K are 532.2 and 543.9 J·mol−1·K,
respectively,33 whereas the Cp value of [BnBIm][NTf2],
[BPhIm][NTf2], and [BzBIm][NTf2] at 323.15 K are 706.15,
643.24, and 571.78 J·mol−1·K, respectively. It is known that the
larger the number of degrees of freedom available, the larger will
be the specific heat capacity of a substance. This goes again in the
direction of consolidating our hypothesis based on the high
impact exerted by the nature of the aromatic ring grafted on the
The new proposed ionic volumes are given in Table 6 along
with those previously reported for the CH2 and [NTf2].
Table 6. Group Contribution Parameters, V, aiη, and biη of the
Group Contribution Method for the Prediction of Density
and Viscosity According to the Gardas and Coutinho Model
ionic species
V/A3
Cations
aiη
biη/K
benzoimidazolium
2-phenylimidazolium
1-benzylimidazolium
202
−2.526
−2.223
−1.041
1174
269
1080
661
306
Anion19,36
248
[NTf2]
−1.119
94.2
40.92
Additional Group19,36
CH2
28
−0.07528
Table 7 compares the experimental density data with the
predicted density based on the group contribution method and
their density−temperature dependence. In general, with the
absolute average deviation of 0.06%, the predicted values are in
good agreement with the experimental data. The predicted
cation volume by the Gardas and Coutinho19,36 showing a strict
E
DOI: 10.1021/acs.jced.5b00983
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Article
Table 7. Comparison between Experimental and Predicted Density and Viscosity Using Gardas and Coutinho19,36 Group
Contribution Model
ρ/g·cm−3
η/mPa·s
T/K
experiment
predicted
AAD
experiment
predicted
AAD
[BzBIm][NTf2]
293.15
303.15
313.15
323.15
333.15
343.15
353.15
363.15
373.15
1.4228
1.4128
1.4033
1.3940
1.3848
1.3756
1.3665
1.3575
1.3488
1.4226
1.4132
1.4039
1.3947
1.3856
1.3766
1.3678
1.3591
1.3504
0.01
0.03
1150.4
497.14
244.69
133.61
79.3
1084.44
493.95
250.20
138.12
81.83
5.73
0.64
2.25
3.37
3.19
1.97
0.07
2.49
5.19
0.04
0.05
0.06
0.08
50.425
33.921
23.966
17.589
51.42
0.09
33.95
0.12
23.37
0.12
16.68
[BPhIm][NTf2]
0.08
293.15
303.15
313.15
323.15
333.15
343.15
353.15
363.15
373.15
1.4293
1.4195
1.4101
1.4009
1.3919
1.3830
1.3740
1.3652
1.3566
1.4281
1.4187
1.4093
1.4001
1.3910
1.3820
1.3731
1.3643
1.3557
753.71
339.74
173.94
98.778
60.902
40.104
27.866
20.237
15.215
704.60
338.45
179.50
103.15
63.31
6.52
0.38
3.20
4.43
3.96
2.37
0.03
2.76
5.57
0.06
0.06
0.06
0.07
0.07
41.05
0.07
27.87
0.06
19.68
0.07
14.37
[BnBIm][NTf2]
0.12
293.15
303.15
313.15
323.15
333.15
343.15
353.15
363.15
373.15
1.2971
1.2883
1.2796
1.2710
1.2624
1.2537
1.2453
1.2372
1.2292
1.2955
1.2869
1.2784
1.2700
1.2618
1.2536
1.2456
1.2376
1.2298
86.75
87.31
53.15
34.60
23.78
17.09
12.74
9.81
0.64
0.59
0.15
0.19
0.90
1.70
2.15
2.33
5.49
2.53
0.11
52.838
34.648
23.822
17.243
12.965
10.021
7.9322
5.9353
0.09
0.08
0.05
0.01
0.02
0.03
7.75
0.04
6.26
0.06
dependence of density with the ILs cation containing aromatic
ring−an increase in the ionic volume of the cation results in less
denser fluid, as observed experimentally.
The contribution of each aromatic-containing cation to the
viscosity of the related ILs was also estimated using group
contribution method proposed by Gardas and Coutinho19,36
according to the following equation:
[BPhIm][NTf2], and [BnBIm][NTf2] were studied. The
densities and viscosities of the ILs were found to follow the
trend of [BzBIm][NTf2] > [BPhIm][NTf2] > [BnBIm][NTf2].
As expected, the densities and viscosities values decrease with
increasing temperature. The measured thermal stability (Td) and
glass transition temperature (Tg) decrease in the order of
[BzBIm][NTf2] > [BPhIm][NTf2] > [BnBIm][NTf2] The heat
capacities of studied ILs decrease in order of [BnBIm][NTf2] >
[BPhIm][NTf2] > [BzBIm][NTf2] and the obtained values are
higher than imidazolium based ILs with short alkyl chain length.
The results indicate that the presence of the different types of
aromatic groups in ILs structures as functional groups exerts a
major influence in the physicochemical properties of ILs notably
through number of available degrees of freedom by strengthen-
ing/weakening intermolecular π−π interactions. The novel
group contribution parameter for the novel cation is presented,
aiming at providing simple method to predict the density and
viscosity of ILs.
k
A =
n a
∑
η
i
i,η
(7)
i=1
k
B =
n b
∑
η
i i,η
(8)
i=1
where ni is the number of groups of type i and k is the total
number of different groups in the molecule. The obtained
parameters aiη and biη are also provided in Table 7 and allow us to
predict the viscosity values of novel ILs with similar cations. The
predictive viscosity for the studied ILs is presented also in Table
7. The average relative deviation predicted by the Gardas and
Coutinho model was found to be 2.53%. The cation nature and
temperature−dependence viscosity is well predicted.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jced.5b00983.
1H NMR spectra for all synthesized ILs and experimental
density (ρ), viscosity (η), and heat capacity (Cp) as a
function of temperature, and 95% confidence intervals for
4. CONCLUSION
In this investigation, the physicochemical and thermal properties
of some new task specific ionic liquids, namely, [BzBIm][NTf2],
F
DOI: 10.1021/acs.jced.5b00983
J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data
Article
(19) Gardas, R. L.; Coutinho, J. A. Group contribution methods for the
prediction of thermophysical and transport properties of ionic liquids.
AIChE J. 2009, 55, 1274−1290.
density coefficients A0 and A1 and DSC thermograms of
ILs at various temperatures. (PDF)
(20) Ghanem, O. B.; Papaiconomou, N.; Abdul Mutalib, M. I.; Viboud,
AUTHOR INFORMATION
Corresponding Authors
*E-mail: masoud.kermani1984@gmail.com. Phone: +60-
195577289.
*E-mail: jm.leveque@petronas.com.my. Phone: +60-53687425.
́ ̂
S.; El-Harbawi, M.; Uemura, Y.; Gonfa, G.; Azmi Bustam, M.; Leveque,
■
J.-M. Thermophysical properties and acute toxicity towards green algae
and Vibrio fischeri of amino acid-based ionic liquids. J. Mol. Liq. 2015,
212, 352−359.
́ ̂
(21) Ben Ghanem, O.; Mutalib, M. A.; Leveque, J.-M.; Gonfa, G.; Kait,
C. F.; El-Harbawi, M. Studies on the Physicochemical Properties of
Ionic Liquids Based On 1-Octyl-3-methylimidazolium Amino Acids. J.
Chem. Eng. Data 2015, 60, 1756−1763.
Notes
The authors declare no competing financial interest.
́
́
(22) Gomez, E.; Calvar, N.; Domínguez, A.; Macedo, E. A. Thermal
Analysis and Heat Capacities of 1-Alkyl-3-methylimidazolium Ionic
Liquids with NTf2−, TFO−, and DCA−Anions. Ind. Eng. Chem. Res.
2013, 52, 2103−2110.
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DOI: 10.1021/acs.jced.5b00983
J. Chem. Eng. Data XXXX, XXX, XXX−XXX