Thermophysical properties of dual functionalized imidazolium-based ionic liquids

Article abstract of DOI:10.1021/je200710t

In this work, some new dual functionalized imidazolium-based ionic liquids 3-(3-butyl-1H-imidazol-3-ium-1-yl)propanenitrile chloride [C₂CNBim] Cl, 3-(3-allyl-1H-imidazol-3-ium-1-yl)propanenitrile chloride [C ₂CNAim]Cl, 3-[3-(2-hydrox

Full text of DOI:10.1021/je200710t

Article
pubs.acs.org/jced
Thermophysical Properties of Dual Functionalized Imidazolium-
Based Ionic Liquids
Nawshad Muhammad,*,† Zakaria Man,† Abobakr K. Ziyada,† M. Azmi Bustam,† M. I. Abdul Mutalib,
Cecilia D. Wilfred,‡ Sikander Rafiq,† and Isa Mohd Tan†
‡
†PETRONAS Ionic Liquid Center Chemical Engineering Department and Fundamental and Applied Sciences Department,
Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia
S
* Supporting Information
ABSTRACT: In this work, some new dual functionalized imidazolium-based ionic
liquids 3-(3-butyl-1H-imidazol-3-ium-1-yl)propanenitrile chloride [C2CNBim]Cl, 3-(3-
allyl-1H-imidazol-3-ium-1-yl)propanenitrile chloride [C2CNAim]Cl, 3-[3-(2-hydrox-
yethyl)-1H-imidazol-3-ium-1-yl]propanenitrile chloride [C2CNHEim]Cl, and 3-(3-
benzyl-1H-imidazol-3-ium-1-yl)propanenitrile chloride [C2CNBzim]Cl have been
synthesized and characterized by 1H NMR, FTIR, and elemental analysis. Their
thermophysical properties such as viscosity and density were measured for a
temperature range of (293.15 to 353.15) K at atmospheric pressure, and their
refractive indices were measured in the range of (293.15 to 333.15) K. The effect of
functionalized side chains on their thermophysical properties was studied. The thermal
expansion coefficient values were calculated using experimental density values. Thermal
behavior of these ionic liquids was investigated using a thermogravimetric analyzer
(TGA) and differential scanning calorimetry (DSC).
formulas are depicted in Figure 1. These ionic liquids are
synthesized with a fixed propyronitrile side chain in the first
position, and another functionalized side chain (butyl, ally,
ethoxyl, and benzyl) is incorporated in the third position of the
imidazolium-based cation with fixed chloride anion. These
synthesized ionic liquids, having these functionalized side
chains, were suggested to have useful applications in the field of
electrochemistry, biomass process, solubility of gases, etc. The
INTRODUCTION
■
Ionic liquids are organic salts with melting point less than 100
°C. Ionic liquids are considered to be relatively green solvents
due to their inherent characteristics such as negligible vapor
pressure, nonflammable, nonexplosive, electrochemically stable,
thermally stable, and highly conductive; in addition, they can be
easily recycled.1,2 Since ionic liquids mainly consist of an
organic cation, and either an inorganic or organic anion, there is
a great possibility to design and tune their properties for various
applications, like separation,3 tribology,4 biomass processing,5
etc. Currently, task-specific ionic liquids take great intention in
the field of ionic liquid research.6,7 It has been achieved by the
incorporation of different functional groups (such as sulfonic
acid, ether, alcohol, carboxylic, and nitrile, etc.)8−12 into the
alkyl side chains on the cationic part of ionic liquid, to impart
its additional specific properties. Among these, nitrile-based
ionic liquids are receiving more consideration due to their more
advantageous properties; they act as a suitable reaction media
and ligands for catalytic reactions,12as electrolyte in lithium
battery, as dye-sensitized solar cells,13 as solvent for extraction
of metals,6 and as a solvent for dissolution of cellulose;14 and
they are also observed to have better tribological properties.4
To date, the thermophysical properties of nitrile-based ionic
liquids have been studied with respect to the length of the alkyl
chain unit linking the imidazolium ring and the nitrile group
and also the effect of alkyl chain length in the third position
with a fixed propyronitrile side chain in the first position of the
imidazolium ring.4,15 In this work, some new ionic liquids, i.e.,
[C2CNBim]Cl, [C2CNAim]Cl, [C2CNHEim]Cl, and [C2CN
Bzim]Cl, are synthesized and characterized. Their structural
1
structures of the products are verified by H NMR, FTIR, and
elemental analysis. An attempt was made to measure some of
their thermophysical properties (such as density, viscosity, and
refractive index) at atmospheric pressure and different
temperatures. The values of the thermal expansion coefficient
were determined from the results of density values as a function
of temperature. Their thermal behaviors were studied using
TGA and DSC analysis.
EXPERIMENTAL SECTION
■
Materials. All the starting materials used were of analytical
grade. These include imidazole (Merck), acrylonitrile (Sigma),
methanol (Merck), 1-chlorobutane, allyl chloride (Sigma), 2-
chloroethanol, benzyl chloride (Merck), diethyl ether (Fisher),
and Millipore grade water.
Synthesis of RTILs. The ionic liquids [C2CNBim]Cl,
[C2CNAim]Cl, [C2CNHEim]Cl, and [C2CN Bzim]Cl were
synthesized by using the following procedure. In the first step,
Received: July 26, 2011
Accepted: January 4, 2012
Published: February 3, 2012
© 2012 American Chemical Society
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Journal of Chemical & Engineering Data
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Figure 1. General route for the synthesis and structure of the present ionic liquids.
imidazole (0.2 mol) and methanol were charged into a three-
necked flask and stirred until the imidazole completely
dissolved. Acrylonitrile (0.23 mol) was added dropwise, and
the system was heated at 55 °C for 16 h under nitrogen flow
with continuous stirring of 300 rpm. The methanol solvent and
unreacted acrylonitrile were removed by using vacuum rotary at
70 °C. In the second step, the resultant 1-propyronitrile
imidazole was again charged separately into a three-necked
flask, and the other reactants, i.e., 1-chlorobutane (0.4 mol),
allyl chloride (0.5 mol), chloroethanol (0.4 mol), and benzyl
chloride (0.5 mol), were added under cooling with continuous
stirring for synthesis of [C2CNBim]Cl, [C2CNAim]Cl,
[C2CNHEim]Cl, and [C2CN Bzim]Cl ionic liquids, respec-
tively. Then the mixture was heated at the desired temperature
for a known period of time, under a nitrogen atmosphere. The
resultant viscous product was washed three times with diethyl
ether, and the remaining solvent was removed by vacuum
rotary at 80 °C for 6 h, followed by a vacuum oven at 80 °C for
48 h.
Table 1. Mass Fraction of Water w and Estimated Purities of
Synthesized Ionic Liquids
[C2CNBim] [C2CNAim] [C2CNHEim]
[C2CN
Bzim] Cl
Cl
Cl
Cl
wH2O (106 w)
356
215
386
327
estimated
purities (%)
97.3
98.5
97.9
98.4
calibration of instruments. The instruments were also calibrated
with ionic liquids, namely, 1-hexyl-3-methylimidazolium bis-
(trifluoromethylsulfonyl)imide, [C6Mim]Tf2N, 1-butylpyridi-
nium bromide, [C4py]Br, and 1-propyronitrile-3-butylimidazo-
lium bromide, [C2CN Bim]Br, for which the data have been
established by our research group.15,16
Density and Viscosity Measurements. An Anton Paar
viscometer (model SVM3000) and Anton Paar densitometer
(DMA5000) were used for measurement of viscosity and
density, respectively, at a temperature range of (293.15 to
353.15) K. The temperature was controlled to within 0.01
1
°C. The uncertainty of measurements was
0.32 % and
Characterization. H NMR spectra were taken in CDCl3/
5·10−6 g·cm−3 for viscosity and density, respectively.15,17
Refractive Index Measurements. The refractive indices
of all samples were determined using an ATAGO program-
mable digital refractometer (RX-5000α), with a measuring
uncertainty of 4·10−5 at a temperature range of (293.15 to
333.15) K with control accuracy of 0.05 K. The apparatus
was calibrated before each series of measurements and was
checked using pure organic solvents with known refractive
indices.17
Thermal Decomposition. A Perkin-Elmer, Pyris V-3.81
thermal gravimetric analyzer was used to measure the onset
temperature and thermal decomposition temperature for the
synthesized ionic liquids. The samples were placed in an
aluminum pan under a nitrogen atmosphere at a heating rate of
10 °C·min−1 with temperature accuracy better than 3 K.
DMSO-d6 solvent and recorded on a Bruker Avance 300
spectrometer. FTIR spectra for the samples were taken by using
SHIMDZU 8400S in wavenumber range of 400−4000 cm−1,
and CHNS-932 (LECO instruments) was used for elemental
analysis.
All of the synthesized ionic liquids, before measuring their
properties, were purified under low pressure by keeping in a
vacuum oven for 4 h at 80 °C. A coulometric Karl Fischer
titrator, DL 39 (Mettler Toledo), was used to determine water
content of the above synthesized ILs, using Hydranal coulomat
AG reagent (Riedel-de Haen). The measurement for each IL
was made in triplicate, and the average values are reported in
Table 1.
Properties Measurement. Millipore grade water with
known viscosity, density, and refractive index was used for
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Differential Scanning Calorimetry. The thermal meas-
urements were performed using a Perkin-Elmer (model Pyris
1). The samples were kept in sealed Al pans and heated from
room temperature to 120 °C. Then the samples were cooled
(10 °C·min−1) to −40.75 °C and, then, heated (10 °C·min−1)
to 120 °C and again cooled to −40.75 °C. The onset and glass
transition temperatures were measured with temperature
uncertainty of 2 K.
RESULTS AND DISCUSSION
■
These ionic liquids can be synthesized using cheap materials,
and the yields of reactions were also high; however, it
consumed too much time for synthesis. The estimated purities
of the synthesized ionic liquids, namely, [C2CNBim]Cl,
[C2CNAim]Cl, [C2CNHEim]Cl, and [C2CN Bzim]Cl, are
97.3 %, 98.5 %, 97.9 %, and 98.4 %, respectively (Table 1). The
results acquired by NMR, elemental analysis, and FTIR for the
synthesized ionic liquids confirmed their structures.
1
[C2CNBim]Cl. H NMR (CDCl3): δ = 0.90 (3H, t), 1.38
(2H, m), 1.85, (2H, m), 3.20 (2H, t,), 4.25 (2H, t), 4.59 (2H,
t), 4.70 (1H, s), 7.75 (1H, s), 9.25 (1H, s).
Figure 2. FTIR spectrum of [C2CNBim]Cl, [C2CNAim]Cl,
[C2CNHEim]Cl, and[C2CN Bzim]Cl from upper to lower,
respectively.
Elemental Analysis (%). Calcd: C, 56.20; H, 7.54; N, 19.66.
Found: C, 56.05; H, 7.71; and N, 19.54.
1
[C2CNAim]Cl. H NMR (DMSO-d6): δ = 3.22 (2H, t),
Table 2. Experimental Dynamic Viscosities η for
[C2CNRim]Cl as a Function of Temperature
4.53 (2H, t), 4.89 (2H, d), 5.33 (2H, d), 6.05 (1H, m), 7.78
(1H, s), 7.87 (1H, s), 9.30 (1H, s).
η/(mPa·s)
Elemental Analysis (%). Calcd: C, 54.68; H, 6.11; N, 21.25.
Found: C, 54.49; H, 6.34; and N, 21.12.
[C2CNBim]
Cl
[C2CNAim]
Cl
[C2CNHEim]
Cl
[C2CN Bzim]
Cl
1
T/K
[C2CNHEim]Cl. H NMR (DMSO-d6): δ = 3.28 (2H, t),
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
4707
2637
1612
1020
668
451
314
224
164
123
94
-
-
-
3.73 (2H, t), 4.28 (2H, t), 5.33 (2H, d), 4.55 (2H, t), 5.43 (1H,
t), 7.85 (1H, s), 7.91 (1H, s), 9.40 (1H, s).
17544
10294
5761
3316
2046
1314
873
-
-
62813
33772
19046
11119
6721
4213
2708
1817
1245
873
-
Elemental Analysis (%). Calcd: C, 47.64; C, 5.99; N, 20.83.
Found: C, 47.39; H, 6.18; and N, 20.71.
-
1
-
[C2CN Bzim]Cl. H NMR (DMSO-d6): δ = 3.29 (2H, t),
-
4.55 (2H, t), 5.47 (2H, s), 7.44 (5H, m), 7.89 (1H, s), 7.93
(1H, s), 9.62 (1H, s).
Elemental Analysis (%), Calcd: C, 63.02, H, 5.69; N, 16.83.
Found: C, 62.95; H, 5.83; and N, 16.74.
95152
42665
20463
10434
5635
3190
1958
599
423
From FTIR analysis (Figure 2) it is observed that in all
spectra a characteristic peak appeared at 2248.84 cm−1, which is
assigned to the CN functional group and also for CN at
(1550 to 1570) cm−1. The C−H symmetric and asymmetric
stretching is observed between (2852 and 3134) cm−1, possibly
due to formation of hydrogen bonds with the anion.4,12 In the
spectrum of [C2CN Aim]Cl, the unsaturation of the allyl side
chain appeared at 1645.17 cm−1 ,and in the [C2CN HEim]Cl
spectrum, the alcoholic OH group stretching vibration is
observed at 3236.33 cm−1. While in the spectrum of [C2CN
Bzim]Cl, C−H out of plane bending (in benzene structure) is
observed at 713.16 cm−1.
Viscosity. Table 2 shows the effect of temperature and
functionalized side chain on viscosity of nitrile containing an
imidazole cation with fixed Cl anion ionic liquids. It is observed
that the viscosity increases in the order of [C2CNBim]Cl <
[C2CNAim]Cl < [C2CNHEim]Cl < [C2CN Bzim]Cl. These
differences in viscosities might be due to the different strength
of intermolecular forces (hydrogen bonding, π−π interaction,
van der Waals interactions, etc.) in each ionic liquid molecule
and the size of the functionalized side chain. Regarding the
structure moiety of each ionic liquid, the strength of
intermolecular forces (hydrogen bonding, π−π interaction,
van der Waals interactions, and size of functionalized side
chain) is found to increase in the order of [C2CNBim]Cl <
306
73
226
58
171
632
[C2CNAim]Cl < [C2CNHEim]Cl < [C2CN Bzim]Cl, while
temperature has an inverse effect on viscosity as shown in
Figure 3.
Density. Table 3 shows the densities of nitrile-containing
ILs with different functional side chains in the temperature
range from (293.15 to 353.15) K. The densities are found in
the same range of reported values for nitrile-containing ionic
liquids4 instead of [C2CN HEim]Cl, possibly having compact
structure due to more hydrogen bonding. It is observed that
density increases in the order [C2CN Bim]Cl < [C2CN Aim]Cl
< [C2CN Bzim]Cl < [C2CN HEim]Cl. No possible corelation
was observed among the densities of the above synthesized
ionic liquids, which might be due to different internal
arrangement of the cation and anion in each ionic liquid.
Similar to viscosity, temperature is observed to have an inverse
effect on density as shown in Figure 4. The densities of this
series of ILs were estimated using the Ye and Shreeve
method.18 The calculated density values are (1.1408, 1.1558,
1.2112, and 1.1990) g·cm−1, which show good agreement with
the experimental results.
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■
Figure 4. Densities as a function of temperature for ( ), [C2CN
●
▲
▼
Bim]Cl; ( ), [C2CN Aim]Cl; ( ), [C2CN HEim]Cl; and ( ),
[C2CN Bzim]Cl.
■
Figure 3. Viscosities as a function of temperature for ( ),
●
▲
[C2CNBim]Cl; ( ), [C2CNAim]Cl; ( ), [C2CNHEim]Cl; and
(
Table 4. Molar Volume Vm of the Present Ionic Liquids at
298.15 K and Atmospheric Pressure
▼
), [C2CN Bzim]Cl.
ionic liquids
Vm (cm3·mol−1
)
Table 3. Experimental Densities ρ for [C2CNRim]Cl as a
[C2CN Bim]Cl
[C2CN Aim]Cl
[C2CN HEim]Cl
[C2CN Bzim]Cl
189.23
168.82
160.67
205.97
Function of Temperature
ρ/(g·cm−3
)
[C2CNBim]
Cl
[C2CNAim]
Cl
[C2CNHEim]
Cl
[C2CN Bzim]
Cl
T/K
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
1.132547
1.129354
1.126147
1.122934
1.119665
1.116488
1.113338
1.110185
1.107027
1.103869
1.100717
1.097574
1.094436
1.173792
1.170785
1.167788
1.164804
1.161837
1.15888
1.257900
1.255047
1.252201
1.249381
1.246584
1.243807
1.241052
1.238316
1.23559
-
Table 5. Experimental Refractive Indices nD for [C2CNRim]
Cl as a Function of Temperature
1.202672
1.200284
1.197331
1.194370
1.191425
1.188500
1.185587
1.182688
1.179797
1.176881
1.174006
1.171158
nD
T/K
[C2CNBim]Cl
[C2CNAim]Cl
[C2CNHEim]Cl
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
1.5257
1.5243
1.5228
1.5213
1.5199
1.5184
1.5170
1.5156
1.5141
1.5473
1.5460
1.5447
1.5433
1.5420
1.5407
1.5394
1.5381
1.5368
1.5499
1.5484
1.5469
1.5455
1.5441
1.5427
1.5413
1.5398
1.5384
1.155932
1.152911
1.150012
1.147108
1.144221
1.141323
1.138419
1.232862
1.230134
1.227412
1.224567
Molar Volume. Molar volume is the volume (Vm) occupied
by one mole of a substance at a particular temperature and
pressure. Vm was calculated for the synthesized ionic liquids at
room temperature and atmospheric pressure using the
following equation
The experimental viscosity η, density ρ, and refractive index
nD were fitted by the least-squares method using the following
reported equations15−17
log η/(mPa·s) = A + (A /T)
(2)
0
1
V
= M/ρ
(1)
m
where M is the molecular weight in g·mol−1; ρ is the density in
g·cm−3; and Vm is molar volume in cm3·mol−1. The values of Vm
calculated for the ionic liquids are listed in Table 4. Table 4
shows that there is no specific correlation among the values of
molar volume, viscosities, and densities.
−1
ρ/(g·cm ) = A + A T
(3)
(4)
2
3
n
= A + A T
4 5
D
Refractive Index. Table 5 presents the refractive index of
the synthesized ionic liquids. It is observed that the refractive
index values are high in comparison to other reported nitrile-
containing ionic liquids.4 This could be due to extra electron
mobility around the functionalized side chain as compared to
the alkyl side chain on the cation part of the ionic liquid. The
refractive index is observed to be linearly decreasing with an
increase in temperature as shown in Figure 5.
where η, ρ, and nD denote the viscosity, density, and refractive
index of the synthesized ionic liquids, respectively. A0, A1, A2,
A3, A4, and A5 are correlation coefficients. T is temperature in
Kelvin. The correlation coefficients were estimated by a least-
squares fitting method using eqs 2, 3, and 4. The estimated
values of correlation coefficients are presented together with
standard deviation values (SD) in Tables 6, 7, and 8. The
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Table 9. Thermal Expansion Coefficient Values of Presented
Ionic Liquids As a Function of Temperature Using Equation
6
α·104/(K−1
)
[C2CNBim] [C2CNAim] [C2CNHEim] [C2CN Bzim]
T/K
Cl
Cl
Cl
Cl
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
5.60
5.62
5.64
5.65
5.67
5.68
5.70
5.72
5.73
5.75
5.77
5.78
5.80
5.02
5.03
5.04
5.06
5.07
5.08
5.10
5.11
5.12
5.14
5.15
5.16
5.18
4.39
4.40
4.41
4.42
4.43
4.44
4.45
4.46
4.47
4.48
4.49
4.50
4.51
4.80
4.81
4.82
4.83
4.85
4.86
4.87
4.88
4.89
4.90
4.92
4.93
4.94
■
Figure 5. Refractive index as a function of temperature: ( ), [C2CN
●
▲
Bim]Cl; ( ), [C2CN Aim]Cl; and ( ), [C2CN HEim]Cl.
Table 6. Fitting Parameter Values (Viscosities) of Equation
2 and the Standard Deviations (SDs) Using Equation 5
where A2 and A3 are the fitting parameters of eq 3 and αP, ρ,
and T are the thermal expansion coefficient, density, and
absolute temperature, respectively. The thermal expansion
coefficient (αP) is also known as volume expansivity. It can be
observed from Table 9 that the coefficients of thermal
expansion of the synthesized ionic liquids do not change
appreciably with respect to temperature and show its
independency on temperature. The sequence of the ionic
liquids with respect to thermal expansion coefficients is
[C2CNHEim]Cl < [C2CN Bzim]Cl < [C2CNAim]Cl <
[C2CNBim]Cl. The values of thermal expansion coefficient
tabulated in Table 9 are similar to those reported for
imidazolium, pyridinium, phosphonium, and ammonium-
based ILs, (4.8·10−4 to 6.5·10−4) K−1.19,20
ionic liquids
A0
A1
SD
R2
[C2CNBim]Cl
[C2CNAim]Cl
[C2CNHEim]Cl
[C2CN Bzim]Cl
−7.52
−8.78
−9.35
3253.30
3864.72
4271.52
6428.77
5.04·10−2
5.05·10−2
3.88·10−2
3.63·10−2
0.9969
0.9974
0.9985
0.9985
−14.95
Table 7. Fitting Parameter Values (Densities) of Equation 3
and the Standard Deviations (SDs) Using Equation 5
ionic liquids
A2
1.31
A3
SD
R2
[C2CNBim]Cl
[C2CNAim]Cl
[C2CNHeim]Cl
−6.35·10−4
6.61·10−5
8.01·10−5
8.50·10−5
1.28553·10−4
0.9999
0.9999
0.9999
0.9999
1.34
1.41
−5.89·10−4
−5.531·10−4
−5.79227·10−4
Thermal decomposition values of the synthesized ionic
liquids are reported in terms of onset temperature and thermal
decomposition temperature Td as shown in Table 10. It is clear
[C2CN Bzim]Cl 1.37568
Table 8. Fitting Parameter Values (Refractive Indices) of
Equation 4 and the Standard Deviations (SDs) Using
Equation 5
Table 10. Onset Ts and Decomposition Td Temperatures for
[C2CNRim]Cl
ionic liquids
A4
A5
SD
R2
[C2CNBim] [C2CNAim] [C2CNHEim] [C2CN Bzim]
[C2CNBim]Cl
[C2CNAim]Cl
[C2CNHEim]Cl
1.61
1.62
1.63
−2.89·10−4
−2.63·10−4
−2.86·10−4
2.43·10−5
3.22·10−5
4.62·10−5
0.9999
0.9998
0.9999
property
Cl
Cl
Cl
Cl
Ts/K
Td/K
473
514
491
526
494
560
504
529
standard deviation values were calculated by using the following
eq 515
that the thermal decomposition temperatures of [C2CNBim]-
Cl, [C2CNAim]Cl, and [C2CN Bzim]Cl are in the same range,
while [C2CNHEim]Cl has a higher Td than the rest, which
might be due to the presence of more hydrogen bonding,
thereby giving more thermal stability. The thermal decom-
position temperature values are in the same range as reported
for other nitrile-containing ionic liquids ([C2CNBim]Br, 524 K;
[C3CNMIm]Cl, 528 K).4,15 However, the thermal decom-
position temperature Td of the synthesized ionic liquids is less
compared with the corresponding ionic liquids without a CN
group (Td of [C4mim]Cl, [Amim]Cl are (528, 546) K,
respectively).21,22 It seems that the incorporation of the CN
group decreases the thermal stability of the corresponding ionic
liquids.
n
2
DAT
∑
(Z − Z )
cal
exp
i
SD =
n
(5)
DAT
where SDs, nDAT, Zexp, and Zcal are the standard deviations,
number of experimental points, and experimental and
calculated data values, respectively.
The calculated density for the synthesized ionic liquids was
used to calculate another thermophysical property, i.e., thermal
expansion coefficient (α) (Table 9), by using the following eq
615
The onset and glass transition temperatures were measured
as the inflection point of change in the DSC trace, and the
values are tabulated in Table 11. The onset temperature was
⎛
⎞
⎟
⎠
A
3
δρ
1
⎜
α = −
= −
P
⎝
ρ δT
A + A T
2 3
(6)
P
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Table 11. Onset Ts and Glass Temperatures Tg: Midpoint for
[C2CN Rim]Cl
[C2CNBim]
Cl
[C2CNAim]
Cl
[C2CNHEim]
Cl
[C2CN Bzim]
Cl
property
Ts/K
Tg/K
263.82
267.92
268.06
271.67
282.42
287.65
284.16
289.36
measured from cooling side, and Tg was measured as the
midpoint in the small change of DSC trace. All the synthesized
ionic liquids were room temperature. The ionic liquids in the
order of increasing Tg are [C2CNBim]Cl < [C2CNAim]Cl <
[C2CNHEim]Cl < [C2CN Bzim]Cl. Lower values of Tg are
reported for other nitrile-functionalized ionic liquids, which
might be due to different side chains attached to the imidazole
ring.4
CONCLUSIONS
■
Some new types of dual functionalized imidazolium-based ionic
liquids, namely, of [C2CNBim]Cl, [C2CNAim]Cl,
[C2CNHEim]Cl, and [C2CNBzim]Cl, have been synthesized,
and their thermophysical properties, viscosity, density, and
refractive indices, were measured. Different viscosities are
observed for each type of ionic liquid which is attributed to
different strengths of intermolecular interactions (hydrogen
bonding, pi−pi interaction, van der Waals interactions, etc.) in
each ionic liquid molecule. The viscosity increases in the order
of [C2CNBim]Cl < [C2CNAim]Cl < [C2CNHEim]Cl <
[C2CNBzim]Cl. The densities of three ionic liquids, namely,
[C2CNBim]Cl, [C2CNAim]Cl, and [C2CNBzim]Cl, are in the
range of reported values for nitrile-containing ionic liquids;
however, the density for [C2CNHEim]Cl is higher. They also
exhibit higher refractive index compared to other reported
nitrile-containing ionic liquids. In general, their thermophysical
properties of viscosity, density, and refractive index decrease as
temperature increases. The coefficient of thermal expansion is
considered to be independent of temperature in the range of
(293.15 to 353.15) K, as no appreciable change was observed
with an increase of temperature. The high thermal decom-
position temperature of [C2CNHEim]Cl is attributed to more
high hydrogen bonding. The Tg values observed for these ionic
liquids are higher compared to those reported for nitrile-based
ionic liquids.
ASSOCIATED CONTENT
* Supporting Information
Additional Figures 1 and 2. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*Tel.: 006053687702. Fax: 006053687598. E-mail:
nawshadchemist@yahoo.com.
■
Funding
This work has been supported by PETRONAS Ionic Liquid
Center, Department of Chemical Engineering, Universiti
Teknologi PETRONAS, Malaysia.
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