Effect of temperature and anion on densities, viscosities, and refractive indices of 1-Octyl-3-propanenitrile Imidazolium-based ionic liquids

Article abstract of DOI:10.1021/je400824z

A series of 1-octyl-3-propanenitrile imidazolium based room temperature ionic liquids incorporated with different sulfonate-based anions were synthesized and characterized using ¹H NMR, Fourier transform infrared spectroscopy (FTIR), and elemental analysis. The density and viscosity were measured at T = (293.15 to 353.15) K, the refractive index was measured at T = (298.15 to 383.15) K, and the thermal expansion coefficient was estimated from the density values. The effects of the anions on these physical properties and on the lattice energy were discussed.

Full text of DOI:10.1021/je400824z

Article
pubs.acs.org/jced
Effect of Temperature and Anion on Densities, Viscosities, and
Refractive Indices of 1‑Octyl-3-propanenitrile Imidazolium-Based
Ionic Liquids
Abobakr K. Ziyada*,† and Cecilia D. Wilfred‡
‡
†Chemical Engineering Department and Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS,
Tronoh 31750, Perak, Malaysia
S
* Supporting Information
ABSTRACT: A series of 1-octyl-3-propanenitrile imidazolium based room
temperature ionic liquids incorporated with different sulfonate-based anions
1
were synthesized and characterized using H NMR, Fourier transform infrared
spectroscopy (FTIR), and elemental analysis. The density and viscosity were
measured at T = (293.15 to 353.15) K, the refractive index was measured at T =
(298.15 to 383.15) K, and the thermal expansion coefficient was estimated from
the density values. The effects of the anions on these physical properties and on
the lattice energy were discussed.
adjusting the cationic, anionic, or both components is
important for extending the knowledge and applications of
relevant types of RTILs.
Recent advances in functionalized ILs further enhanced their
applications. Imidazolium-based functionalized ILs has proven
to be more adaptable and attractive compared to other
functionalized ILs due to the capability to tune and control
their properties to a greater extent which results in an increased
number of applications.5
Many researchers studied the thermophysical properties of
the nitrile functionalized ILs and reported the effect of the alkyl
chain linking the nitrile group and the imidazolium ring.6
Imidazolium-based nitrile functionalized ILs with a long length
of the alkyl chain attached to the N-3 of the imidazolium ring
and incorporating sulfonate-based anions have been synthe-
sized recently by our group.7 Moreover, accurate and reliable
basic experimental data of thermophysical properties are
essential for a better understanding of the new ILs. This is
essential for choosing an appropriate liquid for each of their
envisaged applications and required for the improvement of the
property prediction methods.8
The present study involves the synthesis of new series of 1-
octyl-3-propanenitrile imidazolium based RTILs [CNC2Oim]
incorporating different sulfonate-based anions such as dode-
cylsulfate (DDS), dioctysulfosuccinate (DOSS), benzenesulfo-
nate (BS), sulfobenzoic acid (SBA), and trifluoromethanesul-
fonate (TFMS).3,7,9 The synthesized RTILs in the present work
INTRODUCTION
■
Room temperature ionic liquids (RTILs) are liquid organic
salts at room temperature, which are generally composed of
bulky asymmetric organic cations (e.g., pyridinium, imidazo-
lium, phosphonium, ammonium) and inorganic or organic
anions (e.g., Cl−, BF4 ,PF6 , CF3SO3 , NTf2 ) with different
molecular sizes.1 These compounds received increasing interest
and intensive investigation due to the distinctive combination
of properties that resulted from their ionic nature. Moreover,
the structures of these compounds can be designed to achieve
the desired properties tailored for a specific application by the
careful selection of the ions or by incorporating new
functionalities such as hydroxyl, carboxylic, amine, and fluorous
groups.2,3 The physiochemical properties of ILs depend on the
structures of the cation and anion; hence the alkyl chain length
and functionality have a remarkable influence on these
properties. RTILs exhibit many distinctive properties such as
negligible vapor pressure, high thermal stability, nonflamm-
ability, a wide electrochemical window, high electrical
conductivity, and high solvation capacity.2 The distinctive
properties of RTILs resulted in a superfluity of an increasing
number of applications.3 The bulk of research involves using
RTILs as solvents and/or catalysts in many reactions; they
enhance the synthetic processes, decrease the environmental
load, increase reaction efficiency, and provide higher yields,
selectivity, and rate enhancements. Moreover, there has also
been an increasing interest in using the RTILs for gas
separations.4 Further development of RTILs to other important
processes often require synthesis of new ionic liquids with
favorable properties. Further, the structure−property correla-
tions are still not well understood. Hence, controlling and
−
−
−
−
Received: September 10, 2013
Accepted: March 13, 2014
Published: April 21, 2014
© 2014 American Chemical Society
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were characterized using Fourier transformation infrared
spectroscopy−attenuated total reflectance (FTIR-ATR), ele-
mental analysis (CHNS), and 13C and 1H NMR spectra.
Moreover, an effort was made to measure the essential
thermophysical properties at atmospheric pressure. The molar
refraction, thermal expansion coefficient, lattice energy, and
standard molar entropy were estimated from the experimental
values.
zolium benzenesulfonate [CNC2Oim] BS, 1-octyl-3-propane-
nitrile imidazolium sulfobenzoic acid [CNC2Oim] SBA, and 1-
octyl-3-propanenitrile imidazolium trifluoromethylsulfonate
[CNC2Oim] TFMS, respectively, and a similar procedure for
the synthesis of [CNC2Oim] DDS was adopted.
Characterization. Fourier transform infrared (FTIR)
spectra, 1H and 13C NMR spectra, and elemental analysis
were used to confirm the structures of the synthesized RTILs.
FTIR spectra were recorded in a Shimadzu FTIR-8400S in the
mid region (4000 cm−1 to 400 cm−1) using the attenuated total
EXPERIMENTAL SECTION
■
1
reflectance ((MIRacle ATR) measurement mode. H and 13C
Materials. In the present study the ionic liquids were
synthesized using chemicals of analytical grade. The CAS
(Chemical Abstracts Service) number, source, and grades of the
chemicals used are as follows: imidazole (288-32-4, Aldrich 99
%), acrylonitrile (107-13-1, Aldrich 99 %), methanol,
anhydrous (67-56-1, Sigma-Aldrich 99.8 %), 1-bromooctane
(111-81-1, Aldrich 99 %), ethylacetate, anhydrous (141-78-6,
Sigma-Aldrich 99.8 %), sodium dodecylsulfate (205-788-1,
Sigma-Aldrich 99 %), sodium dioctylsulfosuccinate (209-406-4,
Aldrich 98 %), sodium benzenesulfonate (515-42-4, Aldrich 97
%), sodium 3-sulfobenzoic acid (17625-03-5, Aldrich 97 %),
sodium triflouromethanesulfonate (2926-30-9, Aldrich 98 %),
and diethyl ether (60-29-7, Sigma-Aldrich 99 %). All chemicals
used in the present study were used without further
purification.
NMR spectra were determined using A Burcher Avance 300
spectrometer, and deuterated water (D2O) was used as a
solvent. Elemental analysis was carried out using elemental
analyzer (CHNS-932, LECO instruments).3
A coulometric Karl Fischer titrator DL 39 (Mettler Toledo)
was used for the water content measurements of the present
RTILs using CombiCoulomat fritless Karl Fischer reagent
(Merck).3,10 The average value for a triplicate measurement was
reported. The bromide content measurements were conducted
using ion chromatography (Metrohm model 761 Compact IC)
with (5.0 × 4.0) mm guard column (Metrosep A Supp 4/5)
and (150 × 4.0) mm analytical column (Metrosep A Supp 5-
150).10 The samples were diluted in acetonitrile, and the results
were analyzed using Metrodata IC Net 2.3 software.
Density and Viscosity Measurements. Values of density
and viscosity of the present RTILs were measured using a
Stabinger viscometer (Anton−Paar model SVM3000) at
atmospheric pressure and over the temperature range (293.15
to 353.15) K.3 The temperature was controlled precisely to
Synthesis of RTILs. The synthesis of the presently studied
ionic liquids (Figure S1) involves three steps: incorporation of
the nitrile group to imidazole followed by the formation of the
desired cation (by the reaction of imidazole bearing nitrile
group with 1-bromooctane) and finally anion exchange to form
the final desired product. A nitrile functionalized IL was
synthesized by direct quaternization reaction of the imidazole
bearing nitrile group with 1-bromobutane as reported recently
by our group.3
The reaction involved in the synthesis of 1-octyl-3-propane-
nitrile imidazolium bromide [CNC2Oim] Br and 1-octyl-3-
propanenitrile imidazolium incorporating sulfonate-based
anions [CNC2Oim] X is shown in Figure S1. A sample of
0.5 mol of imidazole, methanol, and acrylonitrile were mixed
and heated at 55 °C for 10 h in a nitrogen atmosphere. The
product was distilled and reacted with an excess of 1-
bromooctane. The product was purified according to the
standard procedure.3
For the synthesis of [CNC2Oim] DOSS, [CNC2Oim] Br
(0.03 mol) and sodium dioctylsulfosuccinate (0.03 mol) were
dissolved and mixed in acetone. The mixture was stirred at
room temperature for 48 h; then, the solid precipitate and the
solvent was removed. The product was cooled to room
temperature and washed with diethyl ether and ethyl acetate.
The solvent was removed at 80 °C under vacuum, and then the
product was dried in a vacuum oven for 48 h.
within
0.01 °C. The reproducibility of the density and
viscosity measurements are
5·10−4 g·cm−3 and 0.35 %,
respectively. The instrument was calibrated using standard
calibration fluid followed by ionic liquids with a known density
and viscosity.3,10
Refractive Index Measurements. The refractive index
values of the present RTILs were determined using an ATAGO
programmable digital refractometer (RX-5000 alpha) with a
measuring accuracy of 4·10−5 in a temperature range (298.15
to 333.15) K at atmospheric pressure.10 The temperature of the
apparatus was controlled to within
0.05 °C. Pure organic
solvents with known refractive indices were used to calibrate
and check the instrument before each series of measure-
ments.3,10 The samples were dried and kept in desiccators prior
to the measurement; then the samples were directly placed into
the measuring cell. Three experiments were performed for each
IL in the whole temperature range studied in the present work
to confirm the reproducibility of the results.
RESULTS AND DISCUSSION
■
1
The H and 13C NMR spectral data, elemental analysis, water
1-Octyl-3-propanenitrile imidazolium dodecylsulfate
[CNC2Oim] DDS was synthesized by mixing [CNC2Oim] Br
(0.04 mol) and sodium dodecyl sulfate (0.04 mol) in 40 mL of
hot dionized water (60 °C). The mixture was stirred for 48 h,
and the product was dried under vacuum at 80 °C; then 50 mL
of dichloromethane was added to the product, and the mixture
was filtrated. The product was then washed with deionized
water, and the remaining solvent was removed at 80 °C under
vacuum and then dried in a vacuum oven for 48 h.
content, and bromide contents (as mass fraction) are shown in
the Supporting Information. The main feature in the FTIR
spectra of the present RTILs was the characteristic absorption
of a CN group in the ranges (2245 to 2255) cm−1 and (1562 to
1664) cm−1. Moreover the characteristic absorption of a SO3
group ranging from (1190 to 1218) cm−1 and (1122 to 1163)
cm−1 was observed. The FTIR exhibits C−H bond and weaker
C−H bonds stretches at (2920 to 3150) cm−1 and (2855 to
2880) cm−1, respectively, which are possibly resulting from the
hydrogen bonds with the anions.11 Furthermore, [CNC2Oim]
DOSS exhibits CO and C−O−C stretches at (1730 and
1159) cm−1, respectively, [CNC2Oim] SBA exhibits CO and
Sodium benzenesulfonate (0.04 mol), sodium sulfobenzoic
acid (0.04 mol), and sodium trifluoromethanesulfonate (0.04
mol) were used to synthesize 1-octyl-3-propanenitrile imida-
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a
Table 1. Density Values (ρ) for the Ionic Liquids Investigated as a Function of Temperature at Pressure p = 0.1 MPa
ρ/(g·cm−3
)
T/K
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
[CNC2Oim] TFMS
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
1.0579
1.0543
1.0508
1.0473
1.0439
1.0404
1.0370
1.0336
1.0302
1.0267
1.0233
1.0199
1.0165
1.0849
1.0817
1.0785
1.0751
1.0724
1.0686
1.0655
1.0623
1.0592
1.0561
1.0532
1.0500
1.0469
1.1859
1.1828
1.1794
1.1757
1.1721
1.1690
1.1656
1.1619
1.1583
1.1549
1.1512
1.1481
1.1444
1.2087
1.2052
1.2019
1.1987
1.1956
1.1923
1.1888
1.1854
1.1828
1.1795
1.1764
1.1721
1.1691
1.2331
1.2294
1.2256
1.2220
1.2184
1.2147
1.2112
1.2076
1.2040
1.2005
1.1960
1.1932
1.1897
a
Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, and u(ρ) = 5·10−4 g·cm−3.
a
Table 2. Viscosity Values (η) for the Ionic Liquids Investigated as a Function of Temperature at Pressure p = 0.1 MPa
η/(mPa·s)
T/K
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
[CNC2Oim] TFMS
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
23617.2
14420.2
9263.4
5820.8
3685.0
2404.8
1524.7
1065.6
701.7
12692.5
8291.9
4880.1
3110.7
2097.8
1311.2
883.5
6784.2
4135.2
2798.9
1816.5
1181.9
753.4
503.4
341.9
235.7
165.0
107.9
74.5
21645.1
12998.5
8322.7
5094.2
3195.1
2071.3
1390.8
974.8
16785.3
10623.7
6374.8
4059.2
2672.6
1783.3
1226.1
866.3
565.9
378.0
694.8
455.3
253.8
604.1
461.4
298.6
172.5
417.8
329.6
188.2
120.1
284.6
230.0
121.4
88.9
52.8
a
Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, and the relative standard uncertainty for viscosity ur(η) = 3.5·10−3.
C−O−H stretch at (1562 and 1161) cm−1, respectively, and
[CNC2Oim] TFMS exhibits CF3 stretches at (1226 and 1159)
cm−1.
decreases linearly with increasing temperature as expected. As is
general for the ILs, linear performance is common as a result of
the great difference between their critical temperatures and
their working temperature range.13
The density values for the studied RTILs are presented in
Table 1. [CNC2Oim] TFMS has the utmost value, and
[CNC2Oim] DOSS has the lowest value of density among the
studied RTILs. The density values for the five [CNC2Oim]-
based RTILs studied decreased in the following order:
[CNC2Oim]TFMS, [CNC2Oim]SBA, [CNC2Oim]BS,
[CNC2Oim]DDS, and [CNC2Oim]DOSS, which is similar to
the size of the anions order. Compared with the density of the
[CNC2Oim]Br IL, the present RTILs incorporating DOSS and
DDS anions show lower density values, while SBA, BS, and
TFMS anions show higher values of density. Moreover, the
density values of the investigated RTILs are lower compared
with the other nitrile-functionalized ILs reported by Zhao et
al.;11 the densities of [CNC2Mim]BF4, [CNC3Mim]BF4, and
[CNC4Mim]Cl were (2.15, 1.87, and 1.61) g·cm−3, respec-
tively. The effect of each anion on the density values was
studied taking into account that the present RTILs are
incorporating the same cations and all of the anions are
incorporating the SO3 group. The differences in density are
resulted from the contributions of the anions. The density
values decrease as the anion size increase, and this trend is
consistent with the literature.12 Figure S2 shows that density
The viscosity values of [CNC2Oim]DOSS, [CNC2Oim]-
DDS, [CNC2Oim]SBA, [CNC2Oim]BS, and [CNC2Oim]-
TFMS ILs at atmospheric pressure and at temperature T=
(293.15 to 353.15) K are shown in Table 2 and Figure S3. The
RTILs investigated show higher viscosities compared with
other nitrile functionalized ILs; for [CNC3Mim]BF4 and
[CNC4Mim]Cl the viscosities are (352 and 5222) mPa·s,
respectively.11,14 Furthermore, these RTILs show lower
viscosity compared to the same RTILs incorporating the
bromide anion; for [CNC2Oim] Br the viscosity at 308.15 is
19620.3 mPa·s.3 The high viscosity of the RTILs incorporating
the DOSS and DDS anions may be owing to the large volume
of the anions which results in low ion mobility.15 The viscosity
values of the investigated RTILs decrease following the anion
order: DOSS, DDS, SBA, BS, and TFMS. These results show
that a higher anion size results in higher viscosity which is in
consistence with the literature.12 As shown in Figure S3, the
viscosity values decrease as temperature increases, and a linear
correlation was obtained by plotting the viscosity values
logarithm versus the reciprocal of the absolute temperature
(1/T).
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Table 3. Refractive Index Values (nD) for the Ionic Liquids Investigated as a Function of Temperature at Pressure p = 0.1 MPa
nD
T/K
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
[CNC2Oim] TFMS
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
1.47692
1.47518
1.47393
1.47253
1.47099
1.46946
1.46798
1.46636
1.47928
1.47758
1.47597
1.47454
1.47274
1.47098
1.46963
1.46785
1.51801
1.51692
1.51572
1.51450
1.51321
1.51191
1.51058
1.50912
1.52174
1.52084
1.51973
1.51856
1.51740
1.51619
1.51499
1.51373
1.52679
1.52584
1.52470
1.52356
1.52248
1.52119
1.51991
1.51873
a
Standard uncertainties u are u(T) = 0.05 K, u(p) = 0.01 MPa, and u(nD) = 5·10−4.
The refractive index values for the investigated RTILs are
Table 6. Coefficients of Equation 3 for the Viscosity of the
RTILs Listed in Table 2 and Standard Deviations (SD)
Calculated Using Equation 4
presented in Table 3. Among the studied anions, TFMS shows
the highest value for the refractive index, while DOSS shows
the lowest value. The refractive index value of the SBA anion is
in good agreement with that reported for [CNC2Oim] Br,
1.51473;3 while DOSS and DDS anions show lower values.
Generally the refractive indices for the investigated RTILs are
in the range from (1.45965 to 1.52174). These values are in
comparison to other nitrile functionalized ILs (1.4188 to
1.5454).3,11 The values of the refractive index decrease linearly
with increasing temperature as is shown in Figure S4.
ionic liquid
A4
A5
SD
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
3750.75
3759.78
3897.85
3768.40
3635.15
−8.16300
−8.29300
−8.89036
−8.73200
−8.55184
1.26·10−2
1.45·10−2
2.86·10−2
1.23·10−2
1.45·10−2
[CNC2Oim] TFMS
ndat
i
∑
(Zexp + Zcal)2
The dependence of density (ρ), refractive index (nD), and
viscosity (η) for the present RTILs on temperature can be
represented by the following empirical equations:3,10
SD =
ndat
(4)
where, ndat is the number of experimental points and Zexp and
Zcal. are the experimental and calculated values, respectively.
The values of density as a function of temperature were used
to estimate the thermal expansion coefficients using the
following equation.10
ρ = A0 + A1T
(1)
nD = A2 + A3T
(2)
log η = A4 + (A5/T)
(3)
αP/(K−1) = −(1/ρ)·(∂ρ/∂T)P = −(A1)/(A0 + A1T)
where T is the absolute temperature; A0, A1, A2, A3, A4, and A5
are fitting parameters. The method of least-squares was used to
estimate the fitting parameters, and the results are presented in
Tables 4, 5, and 6 together with the standard deviations (SD).
(5)
where α is the coefficient of thermal expansion in K−1, ρ is the
density, and A0 and A1 are the fitting parameters of eq 1. The
thermal expansion coefficients of this series of ILs (Table 7) do
not noticeably change with temperature for the range T =
(293.15 to 353.15) K studied in the present work. The present
ILs show weak temperature dependency for the coefficients of
thermal expansion, αP = (5.93·10−4 to 6.79·10−4) K−1, which
are markedly smaller than those for molecular organic liquids
and adequately agree with those reported for ammonium,
imidazolium-, phosphonium-, and pyridinium-based ILs (αP =
(5.0·10−4 to 6.5·10−4) K−1).16
The refractive index values are informative about the
behavior of the molecules in solution and the forces between
these molecules using its relation with the electronic polar-
izability of the molecule. This informative relation was takes the
equation form known as the Lorenz−Lorentz equation.13 This
equation takes the form:
Table 4. Coefficients of Equation 1 for the Density of the
RTILs Listed in Table 1 and Standard Deviations (SD)
Calculated Using Equation 4
ionic liquid
A0
A1
SD
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
1.25950
1.27076
1.38990
1.40032
1.44563
−0.00069
−0.00063
−0.00065
−0.00065
−0.00073
0.54·10−3
1.47·10−3
1.34·10−3
1.34·10−3
1.47·10−3
[CNC2Oim] TFMS
Table 5. Coefficients of Equation 2 for the Refractive Index
of the RTILs Listed in Table 3 and Standard Deviations
(SD) Calculated Using Equation 4
ionic liquid
A2
A3
SD
2
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
1.56551
1.57618
1.59390
1.59087
1.59631
−0.00030
−0.00033
−0.00025
−0.00023
−0.00023
0.675·10−3
1.560·10−3
1.247·10−3
0.387·10−3
0.818·10−3
⎛
= Vm⎜
⎝
⎞
⎟
⎠
N αe
3ε0
nD − 1
A
RM
=
n2 + 2
(6)
D
where RM is the molar refraction in cm3·mol−1, NA is the
Avogadro’s number in mol−1, αe is mean molecular polar-
izability (electronic polarizability), ε0 is the permittivity of free
space, Vm is the molar volume in cm3·mol−1, and nD is the
refractive index. The molar refraction and molar volume for the
studied RTILs are presented in Table S1.
[CNC2Oim] TFMS
The standard deviations were calculated by applying the
following expression:3
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Table 7. Coefficients of Thermal Expansion (αP) for the Ionic Liquids Investigated as a Function of Temperature
104 αP/K−1
T/K
[CNC2Oim] DOSS
[CNC2Oim] DDS
[CNC2Oim] SBA
[CNC2Oim] BS
[CNC2Oim] TFMS
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
6.53
6.55
6.57
6.59
6.61
6.63
6.66
6.68
6.70
6.72
6.75
6.77
6.79
5.80
5.82
5.83
5.85
5.87
5.89
5.90
5.92
5.94
5.96
5.97
5.99
6.01
5.81
5.83
5.84
5.86
5.88
5.90
5.91
5.93
5.95
5.97
5.98
6.00
6.02
5.37
5.39
5.40
5.42
5.43
5.45
5.46
5.48
5.49
5.51
5.52
5.54
5.55
5.93
5.94
5.96
5.98
6.00
6.02
6.03
6.05
6.07
6.09
6.11
6.13
6.15
The molar refractions are often dealt as a quantity of the
hard-core molecular volumes13 and consequently were used to
calculate the molar free volume (unoccupied part of the molar
volume of a substance)17 of the present RTILs. The molar free
volumes for the present RTILs are decreasing following the
order [CNC2Oim] DOSS, [CNC2Oim] DDS, [CNC2Oim]
SBA, [CNC2Oim] BS, and [CNC2Oim] TFMS. The refractive
indices of the present RTILs decrease as the molar free volume
increases; this behavior is in good agreement with that reported
in the literature for other imidazolium-based RTILs.18
[CNC2Oim] DOSS shows very high molar refraction, while
the other ILs in this study show comparable values when
compared with the values (47.93 to 121.73) cm3·mol−1
reported for the ILs [Cnmim]X (where n = 2 to 14, X =
NTf2, PF6, BF4, OAc, MeSO4).13
Thermodynamics is essential and principal to the science of
matter. None of the experimental, simulation, or theoretical
studies can afford dependable data for hypothesized materials
or conserve pace with the rate of synthesis of new materials.
Correlation methods can fill this gap. Glasser and Jenkins19
depict a range of advanced relationship methods that rely on
volume to estimate thermodynamic quantities.
The lattice energy of IL is dependent on the interaction
energy between ions. Moreover, the underlying reason for
forming the IL at room temperature is the low crystal energy.21a
Glasser theory22 was used to estimate the lattice energies of the
synthesized RTILs using the following equation:
UPOT = 1981.2(ρ/M)1/3 + 103.8
(8)
where UPOT is the lattice energy in kJ·mol−1. The results
presented in Table S2 show that lattice energies of the
inorganic fused salts are much elevated than that of the present
synthesized RTILs; among the alkali chlorides the minimal
lattice energy (UPOT) is 602.5 kJ·mol−.21a The results indicate
that the lattice energies for the nitrile-functionalized ILs are
lower than that of the other ILs (for [CnMim] glycine and
[CnMim] alanine (where n = 2 to 6), the lattice energies are
ranging from (429 to 469) kJ·mol−1 and (421 to 456) kJ·mol−1,
respectively.21a Also, these values are lower than that reported
by Guan; for [CnMim] Gly and [CnMim] Glu the lattice
energies are in the range (410 to 450) kJ·mol−1.23 The results
of the lattice energy for the present RTILs show that the lattice
energy was found to decrease as the anion volume increased.
Based on the thermodynamic correlations for a linear
entropy−volume relationship, Glasser and Jenkins20 plotted
some absolute entropies values against molecular volumes, for
organic liquids, and find very satisfactory linear regressions. The
relationships have small intercepts that agrees to the zero-
volume entropy influences of the entities concerned. Glasser
and Jenkins20 used the following equation to estimate the
standard molar entropy for ionic liquids:
CONCLUSIONS
■
In the present work we have synthesized and characterized five
RTILs containing [CNC2Oim] cation incorporating five
different anions (DOSS, DDS, SBA, BS, TFMS). The
thermophysical properties of the present RTILs such as
densities, viscosities, and refractive indices were measured in
atmospheric pressure at different temperatures to explore the
effect of anion nature and temperature on those properties. The
density and refractive index increase with the decrease of the
anion volume, while the viscosities show the opposite trend.
The presently RTILs showed lower densities, higher viscosities,
and comparable refractive indices compare with other nitrile
functionalized ILs. The density values of the present RTILs
were correlated linearly and used to calculate the thermal
expansion coefficient. The temperature dependence of the
thermal expansion coefficient was studied, and these ionic
liquids show a weak temperature dependency. The exper-
imental results showed that the type of possible interactions
between cation and anion and the nature of the producing ions
determine the ionic liquid properties.
S0 = 1246.5(Vm) + 29.5
(6)
Vm = 1021·M/(N ρ)
(7)
A
where S0 is the standard entropy at 298.15 K in J·K−1·mol−1, Vm
is the molecular volume in nm3, M is the molecular weight in g·
mol−1, NA is the Avogadro’s number in mol−1, and ρ is the
density in g·cm−3. The standard entropies for the nitrile-
functionalized ILs were estimated using eq 6, and the results are
showed in Table S2. The present RTILs show high values
compared to other ILs; for [CnMim] alanine and [CnMim]
glycine; where n = 2 to 6, the standard entropy ranges from
(396.9 to 535.8) J·K−1·mol−1 and from (360.2 to 498.8) J·K−1·
mol−1, respectively.21
1389
dx.doi.org/10.1021/je400824z | J. Chem. Eng. Data 2014, 59, 1385−1390

Journal of Chemical & Engineering Data
Article
(9) Ziyada, A. K.; Bustam, M. A.; Murugesan, T.; Wilfred, C. D.
Effect of sulfonate-based anions on the physicochemical properties of
1-alkyl-3-propanenitrile imidazolium ionic liquids. New J. Chem. 2011,
35, 1111−1116.
(10) Yunus, N. M.; Mutalib, M. I. A.; Man, Z.; Bustam, M. A.;
Murugesan, T. Thermophysical properties of 1-alkylpyridinum bis-
(trifluoromethylsulfonyl)imide ionic liquids. J. Chem. Thermodyn.
2010, 42, 491−495.
(11) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Synthesis and
Characterization of Ionic Liquids Incorporating the Nitrile Function-
ality. Inorg. Chem. 2004, 43, 2197−2205.
(12) Torrecilla, J. S.; Palomar, J.; Garcí, J. N.; Rodríguez, F. Effect of
Cationic and Anionic Chain Lengths on Volumetric, Transport, and
Surface Properties of 1-Alkyl-3-methylimidazolium Alkylsulfate Ionic
Liquids at (298.15 and 313.15) K. J. Chem. Eng. Data 2009, 54, 1297−
1301.
(13) Tariq, M.; Forte, P. A. S.; Costa, M. F.; Canongia, J. N.; Rebelo,
L. P. N. Densities and refractive indices of imidazolium- and
phosphonium-based ionic liquids: Effect of temperature, alkyl chain
length, and anion. J. Chem. Thermodyn. 2009, 41, 790−798.
(14) Zhang, Q.; Li, Z.; Zhang, J.; Zhang, S.; Zhu, L.; Yang, J.; Zhang,
X.; Deng, Y. Physicochemical Properties of Nitrile-Functionalized
Ionic Liquids. J. Phys. Chem. B 2007, 111, 2864−2872.
(15) Yao, M.; Fan, M.; Liang, Y.; Zhou, F.; Xia, Y. Imidazolium
hexafluorophosphate ionic liquids as high temperature lubricants for
steel−steel contacts. Wear 2010, 268, 67−71.
ASSOCIATED CONTENT
■
S
* Supporting Information
Table S1, molar volume (Vmolar) and molar refraction (Rm)
values of [CNC2Oim] based ILs at temperatures (298.15 to
333.15) K; Table S2, estimated values of molecular volume
(Vm), standard molar entropy (S0), and crystal energy (UPOT
)
for the ionic liquids investigated; Figure S1, synthesis route for
the present RTILs; Figure S2, plot of density against
temperature; Figure S3, plot of viscosity against temperature;
Figure S4, plot of refractive index against temperature. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E mail: abubakrkhz@yahoo.com; abubakrkhz@uofg.edu.sd.
Present Address
A.K.Z.: Applied Chemistry and Chemical Technology Depart-
ment, University of Gezira, Wad Medani-Sudan.
Notes
The authors declare no competing financial interest.
(16) (a) Kilaru, P.; Baker, G. A.; Scovazzo, P. Density and surface
tension measurements of imidazolium-, quaternary phosphonium-, and
ammonium-based room-temperature ionic liquids: data and correla-
tions. J. Chem. Eng. Data 2007, 52 (6), 2306−2314. (b) Gu, Z.;
Brennecke, J. F. Volume expansivities and isothermal compressibilities
of Imidazolium and Pyridinium-based ionic liquids. J. Chem. Eng. Data
2002, 47, 339−345.
ACKNOWLEDGMENTS
■
The author would like to thank Universiti Teknologi
PETRONAS and PETRONAS Ionic Liquids Centre for the
facilities provided in this work and PETRONAS sponsorship
for A.K.Z.
(17) Soriano, A. N.; Doma, B. T., Jr.; Li, M. H. Measurements of the
density and refractive index for 1-n-butyl-3-methylimidazolium-based
ionic liquids. J. Chem. Thermodyn. 2009, 41 (3), 301−307.
REFERENCES
■
(1) Lopes, J. N. C.; Cordeiro, T. C.; Esperancua, J. M. S. S.; Guedes,
̈
H. J. R.; Huq, S.; Rebelo, L. P. N.; Seddon, K. R. Deviations from
Ideality in Mixtures of Two Ionic Liquids Containing a Common Ion.
J. Phys. Chem. B 2005, 109, 3519−3525.
(2) Newington, I.; Perez-Arlandis, J. M.; Welton, T. Ionic liquids as
Designer Solvents for Nucleophilic Aromatic Substitutions. Org. Lett.
2007, 25, 5247−5250.
(3) Ziyada, A. K.; Wilfred, C. D.; Bustam, M. A.; Man, Z.;
Murugesan, T. Thermophysical Properties of 1-Propyronitrile-3-
alkylimidazolium Bromide Ionic Liquids at Temperatures from
(293.15 to 353.15) K. J. Chem. Eng. Data 2010, 55, 3886−3890.
(4) Karadas, F.; Atilhan, M.; Aparicio, S. Review on the Use of Ionic
Liquids (ILs) as Alternative Fluids for CO2 Capture and Natural Gas
Sweetening. Energy Fuels 2010, 24, 5817−5828.
(5) Schrekker, H. S.; Stracke, M. P.; Schrekker, C. M. L.; Dupont, J.
Ether-functionalized imidazolium hexafluorophosphate ionic liquids
for improved water miscibilities. Ind. Eng. Chem. Res. 2007, 46 (22),
7389−7392.
(6) (a) Carlisle, T. K.; Bara, J. E.; Gabriel, C. J.; Noble, R. D.; Gin, D.
L. Interpretation of CO2 solubility and selectivity in nitrile-function-
alized room-temperature ionic liquids using a group contribution
approach. Ind. Eng. Chem. Res. 2008, 47 (18), 7005−7012. (b) Zhang,
J.; Zhang, Q.; Qiao, B.; Deng, Y. Solubilities of the gaseous and liquid
solutes and their thermodynamics of solubilization in the novel room-
temperature ionic liquids at infinite dilution by gas chromatography. J.
Chem. Eng. Data 2007, 52 (6), 2277−2283.
(7) Ziyada, A. K.; Bustama, M. A.; Wilfred, C. D.; Murugesan, T.
Densities, viscosities and refractive Indices of 1-Hexyl-3-propanenitrile
imidazolium Ionic Liquids Incorporated with Sulfonate −based
Anions. J. Chem. Eng. Data 2011, 56, 2343−2348.
́
(18) (a) Brocos, P.; Pineiro, A.; Bravo, R.; Amigo, A. Refractive
̃
indices, molar volumes and molar refractions of binary liquid mixtures:
concepts and correlations. Phys. Chem. Chem. Phys. 2003, 5 (3), 550−
557. (b) Hasse, B.; Lehmann, J.; Assenbaum, D.; Wasserscheid, P.;
Leipertz, A.; Froba, A. P. Viscosity, Interfacial Tension, Density, and
̈
Refractive Index of Ionic Liquids [EMIM][MeSO3], [EMIM]-
[MeOHPO2], [EMIM][OcSO4] and [BBIM][NTf2] in Dependence
on Temperature at Atmospheric Pressure. J. Chem. Eng. Data 2009, 54
(9), 2576−2583.
(19) Glasser, L.; Jenkins, H. D. B. Volume-based thermodynamics: a
prescription for its application and usage in approximation and
prediction of thermodynamic data. J. Chem. Eng. Data 2010, 56 (4),
874−880.
(20) Glasser, L.; Jenkins, H. D. B. Standard absolute entropies, S◦298,
from volume or density Part II. Organic liquids and solids.
Thermochim. Acta 2004, 414, 125−130.
(21) (a) Fang, D. W.; Guan, W.; Tong, J.; Wang, Z. W.; Yang, J. Z.
Study on Physicochemical Properties of Ionic Liquids Based on
Alanine [Cnmim]Ala (n = 2,3,4,5,6). J. Phys. Chem. B 2008, 112,
7499−7505. (b) Yang, J.-Z.; Zhang, Q.-G.; Wang, B.; Tong, J. Study
on the Properties of Amino Acid Ionic Liquid EMIGly. J. Phys. Chem.
B 2006, 110, 22521−22524.
(22) Glasser, L. Lattice and phase transition thermodynamics of ionic
liquids. Thermochim. Acta 2004, 421, 87−93.
(23) Guan, W.; Tong, J.; Chen, S. P.; Liu, Q. S.; Gao, S. L. Density
and Surface Tension of Amino Acid Ionic Liquid 1-Alkyl-3-
methylimidazolium Glutamate. J. Chem. Eng. Data 2010, 639−646.
(8) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.;
Broker, G. A.; Rogers, R. D. Characterization and comparison of
hydrophilic and hydrophobic room temperature ionic liquids
incorporating the imidazolium cation. Green Chem. 2001, 3 (4),
156−164.
1390
dx.doi.org/10.1021/je400824z | J. Chem. Eng. Data 2014, 59, 1385−1390