Effect of sulfonate-based anions on the physicochemical properties of 1-alkyl-3-propanenitrile imidazolium ionic liquids

Article abstract of DOI:10.1039/c0nj00950d

In this paper, the physicochemical properties of a new series of ionic liquids (ILs) based on nitrile-functionalised imidazolium cations ([C ₂CN C_nim]⁺) with sulfonate-based anions were studied. The ILs were prepared by re

Full text of DOI:10.1039/c0nj00950d

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PAPER
Effect of sulfonate-based anions on the physicochemical properties
of 1-alkyl-3-propanenitrile imidazolium ionic liquids
Abobakr Khidir Ziyada,a Mohamad Azmi Bustam,a Thanapalan Murugesana and
Cecilia Devi Wilfred*b
Received (in Victoria, Australia) 1st December 2010, Accepted 24th February 2011
DOI: 10.1039/c0nj00950d
In this paper, the physicochemical properties of a new series of ionic liquids (ILs) based on
nitrile-functionalised imidazolium cations ([C2CN Cnim]+) with sulfonate-based anions were
studied. The ILs were prepared by reacting imidazole with acrylonitrile, followed by butyl-
and decyl bromide. The anions of the resulting bromide salts exchanged by metathesis to
dioctylsulfosuccinate (DOSS), dodecylsulfate (DDS), benzenesulfonate (BS) and
trifluoromethanesulfonate (TFMS). The densities of these ILs are lower compared to
the those of other reported nitrile-functionalised ILs, while on the other hand, the viscosities
of the ILs are higher due to the effects of the large anions and the long alkyl chain of the cations.
Nitrile-functionalised ILs are a relatively new class of ILs
Introduction
with special properties and potential applications in many
The term ionic liquids (ILs) is the common name given to
areas. These include reaction media, ligands for catalytic
organic salts that have melting points below 100 1C and
reactions, electrolytes for lithium batteries, dye-sensitised solar
cells,10–12 and also in the fields of organic synthesis, extraction
and dissolution.13 In fact, it appears that an advantage of
organic cations and inorganic or organic anions, they vary in
negligible vapor pressure.1 ILs are exclusively composed of
size and can be either hydrophilic or hydrophobic.2,3 The
nitrile-functionalised ILs over the conventional ILs is that they
unique combination of their inherent physical and chemical
provide more opportunities to fine-tune physical and chemical
properties, namely low melting points, high thermal stability,
properties by modifying the hydrogen bonding network
architecture of the IL.14
liquidity over a wide temperature range, negligible vapor
pressures, low flammability, highly solvating capacity for both polar
To facilitate the molecular design of nitrile-functionalised
and non-polar compounds, high electrical conductivity,3,4 and
ILs, a fundamental understanding of the effects of alkyl chain
easy recycling, mean these compounds attract a considerable
length, type of functional group and anion choice on the IL’s
amount of attention in many fields.5 Their unique properties
properties is essential. Although nitrile-functionalised ILs with
as a designer solvent receive increasing and continuing attention
short and long alkyl chain lengths have been synthesised, the
in many important areas of research and commercial applications,
effect of anions with different functional groups and alkyl
such as absorption media for gas separations, solvents for
chain lengths in these ILs with cationic species incorporating
different alkyl chains still needs to be explored.14,15 The cation
reactions, heat transfer fluids, separating agents in extractive
distillation, biomass processing, as the working fluid in a
and anion structures can certainly influence the physical and
variety of electrochemical applications (batteries, capacitors,
chemical properties such as viscosity, density, refractive index
solar cells, etc.),6 as lubricants7 and in biocatalysts with great
and thermal stability, as well as interaction with dissolved
molecules.12
advantages.8
The combination of cations and anions, the type of
Many researchers have synthesised the imidazolium-based
functional groups and the alkyl chain length has a prominent
nitrile-functionalised ILs with different lengths of the alkyl
influence on the chemical and physical properties of ILs. The
chain unit linking the imidazolium ring and the nitrile
group.12,15 Imidazolium-based nitrile-functionalised ILs with
term task-specific or functionalised ILs was introduced in
order to illustrate ILs with functional groups that provide
particular properties.9
long alkyl chains attached to the N-3 of the imidazolium ring
have recently been synthesised by our group.14 This present
study involves the synthesis of a new series of 1-alkyl-3-
a Chemical Engineering Department, Universiti Teknologi
PETRONAS, Tronoh-31750, Perak, Malaysia
propanenitrile imidazolium ionic liquids incorporating different
sulfonate-based anions, such as dioctylsulfosuccinate (DOSS),
b Fundamental and Applied Sciences Department, Universiti Teknologi
PETRONAS, Tronoh-31750, Perak, Malaysia.
E-mail: cecili@petronas.com.my
dodecylsulfate (DDS), benzenesulfonate (BS), and trifluoro-
methanesulfonate (TFMS). They are synthesised by reacting
c
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imidazole with acrylonitrile and then reacting the product with
1-bromoalkane. After the reaction was completed, a metathesis
reaction was carried out using (DOSS), (DDS), (BS) and
(TFMS) anions. The structure of the products was verified
with 1H and 13C-NMR, FTIR and elemental analysis. Despite
their importance and interest in their commercial applications,
a detailed study on the physicochemical properties of these
ionic liquids has not been performed. In the present work, the
important properties, namely density, viscosity, refractive
index and thermal stability for the ILs were measured.
Results and discussion
The following scheme shows the route taken for this synthesis
(Scheme 1).
The 1H NMR spectra showed that the C-2 peak of the
imidazolium ring of these ionic liquids lies between 7.77–9.95
ppm. Sulfonate-based anions that have strong electron with-
drawing groups, such as trifluoromethyl and carbonyl, cause
the C-2 of the imidazolium cation to resonate downfield
compared to benzene sulfonate and dodecylsulfonate.
The main feature in the FTIR spectra was the weak
absorption of the CN group in the range 2245–2265 cmÀ1
(Fig. 1). The larger the sulfonate-based anions, the weaker thÀe
CN peak. Characteristic absorption peaks for the –SO3
group in the regions 1190–1249 cmÀ1 and 1029–1163 cmÀ1
were observed.
Fig. 1 FTIR-ATR spectra of the ionic liquids [C2CN Cnim]X.
The effects of impurities (especially water and halide) on the
physical properties of ILs are well known. The presence of
water may have a rather dramatic effect on density, viscosity,
refractive index and thermal stability. The water content and
bromide contents (as a mass fraction) of the synthesised ILs
were determined and are in the ranges 170–235 ppm (water)
and 70–103 ppm (bromide).
Table 1 shows the density, viscosity and refractive indices of
the synthesised ILs at 298.15 K. The measured densities are
low when compared to those of analogous nitrile-functiona-
lised ILs with different anions, as reported by Zhao et al.15 The
densities of [C2CN Mim]BF4, [C3CN Mim]BF4 and [C4CN
Mim]Cl are 2.15, 1.87 and 1.61 g cmÀ3, respectively. The
densities of the synthesised ILs are lower compared to those
of the pyrrolidinium-based nitrile-functionalised ILs, for
1-cyanoalkyl-1-methylpyrrolidinium bistriflimide ([C1CnCNPyr]-
[NTf2], n = 1, 2, 3, 5), the densities are in the range
1.157–1.435 g cmÀ3 16
.
The viscosities of these nitrile-functionalised ILs with
sulfonate anions are much higher than [C3CN Mim]BF4 where
the reported viscosity is 352 mPa s.15 The viscosities of the
Table
1
Densitya, r; viscositya, Z; refractive indexa, nD; start
temperature, Ts and decomposition temperature Td for the synthesised
RTILs
Ionic liquids
r/g cmÀ3 Z/mPa s nD
Ts/1C Td/1C
[C2CN Bim]DOSS 1.1105
[C2CN Bim DDS
[C2CN Bim]BS
[C2CN Bim]TFMS 1.3324
[C2CN Dim]DOSS 1.0358
12 006
7875
2352
719
31 028
26 863
1.4805 291
307
297
312
328
261
246
1.1119
1.2368
1.4880 279
1.5329 298
1.5324 314
1.4761 245
1.4745 235
[C2CN Dim]DDS
1.0666
a
Measured at 298.15 K.
Scheme 1 Synthesis route of the ionic liquids [C2CN Cnim]X.
c
1112 New J. Chem., 2011, 35, 1111–1116
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Table 2 Molecular volume Vm, standard entropy S0 and lattice
energy UPOT of the [C2CN Cnim]X ILs at 298.15 K
The molecular volume (Vm) is the sum of the anion volume
and cation volume. Vm was calculated for the ILs at 298.15 K
and atmospheric pressure using the following equation:19,20
Ionic liquids
Vm (cm3)
S0 (J KÀ1 molÀ1
)
UPOT/kJ molÀ1
[C2CN Bim]DOSS 8.98 Â 10À22 1149.41
347
373
410
421
332
355
Vm = M/(NAr)
(1)
[C2CN Bim]DDS 6.64 Â 10À22 857.26
[C2CN Bim]BS
4.52 Â 10À22 592.55
where M is the molecular weight in g molÀ1, NA is Avogadro’s
number in molÀ1, r is the density in g cmÀ3 and Vm is
molecular volume in cm3. The values of Vm are listed in
Table 2.
[C2CN Bim]TFMS 4.08 Â 10À22 538.00
[C2CN Dim]DOSS 1.10 Â 10À21 1398.36
[C2CN Dim]DDS 8.23 Â 10À22 1055.74
The standard entropy for these ionic liquids was estimated
as suggested by Glasser and Jenkins:21
synthesised ILs are higher compared to the other nitrile-
functionalised ILs (for [C1CnCNPyr][NTf2] (n = 1, 2, 3, 5);
the viscosities are in the range 345–540 cP, as reported by
Nockeman and coworkers.16 The differences in these two
properties can be explained by anion size and cation chain
length. The lower densities when compared to the other nitrile-
functionalised ILs are due to the presence of larger anions and
more and longer alkyl chains in the cations (butyl and decyl).
This causes a bigger free volume that decreases the density.
Also, the presence of more –CH2– functions reduces the overall
density; this is also the same for large phosphonium ILs. The
increased volumes of the anions here (trifluoromethanesulfonate
excepted) lead to higher viscosities through reductions in ion
mobility.17 In addition, the high viscosity can also be ascribed
to increased electrostatic interactions between the cation and
anion. The [C2CN Dim]DOSS IL showed the lowest density
and the highest viscosity since it possesses the largest anions,
while [C2CN Bim]TFMS showed the highest density values
and the lowest viscosity.
S0 = 1246.5 (Vm) + 29.5
(2)
where S0 is the standard entropy at 298.15 K in J KÀ1 molÀ1
and Vm is the molecular volume in nm3. The standard
entropies estimated are listed in Table 2. The results show higher
values compared with the other ILs, for [CnMim]alaninate and
[CnMim]glycinate; where n = 2–6, the standard entropy ranges
from 396.9–535.8 J KÀ1 molÀ1 and from 360.2–498.8 J KÀ1 molÀ1
respectively.20,22
The lattice energy of an IL is the surface excess energy,
which is reliant on the interaction energy between ions. The
low lattice energy is the underlying reason for forming the IL
at room temperature. Lattice energies of ionic liquids were
estimated according to Glasser theory23 using the following
equation:
UPOT + 1981.2(r/M)1/3 + 103.8
(3)
The refractive index is related to the excess molar refraction,
which is used in the least squares energy relationships (LSERs) as
a predictor of solute distribution.18 The refractive index values
of the synthesised ILs are in the range (1.47334–1.53939), and
the values are in good agreement with those reported for other
imidazolium-based nitrile-functionalised ILs; for [C3CN Mim]-
NTf2, [C3CN Mim]BF4, [C2CN Bim]Br and [C2CN Oim]Br
these are 1.4398, 1.4349, 1.54540 and 1.51473,12,14 respectively. The
refractive indices of these nitrile-functionalised ILs with sulfonate
anions are much higher compared to [C1CnCNPyr][Tf2N], where
the reported refractive indices are in the range 1.4305–1.4365.16
The refractive index values are found to increase after the
incorporation of a nitrile group, which may be due to the high
electron mobility around the nitrile group.12
where UPOT is the lattice energy in kJ molÀ1. The results
presented in Table 2 show that lattice energies of ILs are much
less than that of inorganic fused salts; the minimal lattice
energy (UPOT) among alkali chlorides is 602.5 kJ molÀ1 20
.
The results indicate that the lattice energies for the nitrile-
functionalised ILs are lower compared with that of the other ILs
(for [CnMim]alaninate and [CnMim]glycinate (where n = 2–6),
ranging from 421–456 and 429–469 kJ molÀ1, respectively.22
The values of the glass transition temperatures (Tg), melting
temperatures (Tm) and cold crystallisation temperatures (Tc)
were investigated. The glass transition temperature is the
midpoint of a small heat capacity change on heating from
the amorphous glass state to a liquid state. The melting point
is the onset of an endothermic peak on heating. The cold
crystallisation temperature is the onset of an exothermic peak
on heating from a subcooled liquid state to a crystalline solid
state.24 The Tg of [C2CN Bim]DOSS, [C2CN Dim]DOSS,
[C2CN Bim]DDS and [C2CN Dim]DDS ILs are À56.92,
À55.59, À60.63 and À51.50 1C, respectively. [C2CN Bim]DDS
and [C2CN Dim]DDS showed a Tm of 9.00 and À22.95 1C,
respectively, whilst the Tc was 6.24 and À25.65 1C, respectively
When these two ILs were subjected to heating and cooling of
up to 100 1C, there was nothing else happening, as observed
from the DSC results. A significant change in the phase change
behaviour occurred when the alkyl chain length was increased
for the dodecylsulfate anions. This led to weaker Coulombic
interactions in the crystal lattice, poor packing of the ions, and
a decrease in the melting temperatures. In addition, these ILs
did not show any liquid-crystalline phase, compared to many
The start temperatures for weight loss (Ts) and decomposition
temperatures (Td) of the ILs, measured by TGA, are presented
in Table 1. The Td of ILs in this study are higher compared to
the other common ionic liquids.14 Also, the decomposition
temperatures of the synthesised ILs are high compared with
that reported for [C3CN Mim]Cl of 254.9 1C,14 as a result of
replacing the basic, reactive chloride with more stable anions.
The thermal stability of the trifluoromethanesulfonate-
containing IL is the highest due to the extremely stable anion.
The thermal stability is also affected by the size of the alkyl
chain of the cation on the nitrile group, the decomposition
temperature decreases as the alkyl chain increases. The thermal
stability of the ILs with DOSS, DDS, BS and TFMS anions
were high in comparison with the corresponding ILs with the
bromide anion (Td of [C2CN Bim]Br and [C2CN Dim]Br are
251 1C and 238 1C, respectively).14
c
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1-alkyl-3-methylimidazolium salts that also have twelve
carbons atoms in an alkyl chain.25–27
analytical column (Metrosep
A
Supp 5-150) and a
(5.0 Â 4.0) mm guard column (Metrosep A Supp 4/5).28 The
samples were diluted by dissolving 0.5 cmÀ3 of each IL in
10 cmÀ3 of acetonitrile then the volume was made up to 50 cmÀ3
with deionised water. The analysis of the results was made
using Metrodata IC Net 2.3 software.
Conclusion
In the current work, novel ILs containing imidazolium-based
cations incorporating a nitrile functionality [C2CNCnim] and
sulfonate-based anions (DOSS, DDS, BS and TFMS) were
synthesised. The ILs show a lower density and a higher
viscosity and higher thermal stability compared with other
nitrile-functionalised ILs. Moreover, these ILs have a low
lattice energy and a high standard entropy compared with
the other ILs.
1-Alkyl-3-propanenitrile imidazolium bromide [C2CN Cnim]Br.
A 250 mL, round-bottomed flask equipped with a heating oil
bath, a nitrogen inlet adapter, magnetic stirrer and reflux
condenser was flushed with dry nitrogen. The flask was
charged with imidazole (0.5 mol, 34.04 g) in methanol and
mixed with acrylonitrile (0.6 mol, 39.5 mL). The solution was
heated under reflux and nitrogen atmosphere at 50–55 1C for
10 h and then cooled to room temperature. The volatile
materials were removed from the mixture under reduced
pressure at 70 1C. Nitrile-functionalised IL was synthesised
by the direct quaternisation reaction of the imidazole-bearing
nitrile group with 1-bromobutane.14 (0.5 mol, 53.9 mL) of
1-bromobutane was added and the mixture was stirred and
maintained at 70 1C under a nitrogen atmosphere for 48 h. The
resulting compound was cooled to room temperature and
washed with ethyl acetate three times and the remaining
solvent was removed at 80 1C under reduced pressure. It was
then dried in a vacuum oven for 72 h14 to give 1-butyl-3-
propanenitrile imidazolium bromide [C2CN Dim]Br.
Experimental methods
Materials
The CAS number, source and grades of the chemicals that
were used for synthesis are: imidazole (288-32-4, Aldrich 99%),
acrylonitrile (107-13-1, Aldrich 99%), methanol, anhydrous
(67-56-1, Sigma-Aldrich 99.8%), 1-bromobutane (109-65-9,
Merck 98%), 1-bromodecane (112-29-8, Aldrich 98%), ethyl
acetate, anhydrous (141-78-6, Sigma-Aldrich 99.8%), sodium
dioctylsulfosuccinate (577-11-7, Aldrich 98%), sodium dodecyl
sulfate (151-21-3, Sigma-Aldrich 99%), sodium benzenesulfonate
(515-42-4, Aldrich 97%), sodium trifluoromethanesulfonate
(2926-30-9, Aldrich 98%), diethylether (Sigma-Aldrich 99%)
and acetone (Sigma-Aldrich 99.9%). All the chemicals were
used without further purification.
A similar procedure was used to synthesise 1-decyl-3-
propanenitrile imidazolium bromide [C2CN Dim]Br where
(0.5 mol, 103.8 mL) of 1-bromodecane was used.
[C2CN Bim]Br; 1H NMR (CDCl3): d = 0.98 (t, 3H,
CH2–CH3), 1.38 (m, 2H, CH2–CH2–CH3), 1.90 (m, 2H,
N–CH2–CH2–CH2–), 3.21 (t, 2H, N–CH2–CH2–CN), 4.29
(t, 2H, N–CH2–CH2–CN), 4.60 (t, 2H, N–CH2–(CH2)2–CH3),
4.75 (s, 1H, N–CH–CH), 7.79 (s, 1H, N–CH–CH), 9.24 (s, 1H,
N–CH–N) ppm. 13C NMR (75 MHz; CDCl3) = 136.80,
121.54, 120.58, 117.28, 48.22, 42.96, 30.02, 19.08, 17.99.
11.43 ppm. FTIR-ATR nmax/cmÀ1: 2246 and 1562 (CN),
2923 and 2854 (C–H).
FTIR, NMR and elemental analysis
The ionic liquids in the current study were characterised using
Fourier transform infrared (FTIR) spectroscopy. The spectra
were recorded in a Shimadzu FTIR-8400S Fourier Transform
Infrared Spectrometer (FTIR) in the mid region (4000–400 cmÀ1
)
using the Attenuated Total Reflectance ((MIRacle ATR)
measurement mode. A CHNS-932 (LECO instruments) elemental
analyzer was used to determine the individual percentage of
elements in these ILs. A Bruker Avance 300 spectro-
photometer was used to determine the 1H and 13C NMR
spectra of the present ILs using deuterated water (D2O) and
CDCl3 as solvents.14,28
Elemental analysis: found C, 46.62; H, 6.01; N, 16.97%.
C10H16N3Br requires C, 46.52; H, 6.26; N, 16.28%.
[C2CN Dim]Br; dH (300 MHz; CDCl3): = 0.47 (15 H, t,
CH3CH2), 0.93 (12 H, br m, CH2), 1.54 (2 H, t, CH2CH2N),
3.05 (2 H, t, CH2CH2CN), 3.92 (2 H, t, CNCH2), 4.54
(2 H, t, NCH2), 7.27(1 H, s, CHN), 7.88(1 H, s, CHN), 9.82
(1 H, s, NCHN) ppm. 13C NMR (75 MHz; CDCl3) = 137.02,
122.95, 121.13, 116.87, 49.61, 45./9, 31.23, 29.68, 28.21, 23.12,
22.65, 18.97, 13.42 ppm. FTIR-ATR nmax/cmÀ1: 2244 and
1562 (CN), 2921 and 2852 (C–H).
A coulometric Karl Fischer titrator, DL 39 (Mettler Toledo)
with CombiCoulomat fritless Karl Fischer reagent
(Merck)14,28 was used to determine the water content of the
synthesised ILs. The measurement for each IL was made in
triplicate and the average values are reported. The instruments
used for the measurements of the physical properties in the
present study were calibrated using Millipore quality water
with known density, viscosity and refractive index. The data
established by our research group14,29,30 for the ILs 1-butyl-3-
propanenitrile imidazolium bromide; [C2CN Bim]Br, bis-(2-
hydroxyethyl)ammonium acetate; BHEAA and 1-hexyl-3-methyl-
imidazolium bis(trifluoromethylsulfonyl)imide; [C6Mim]NTf2
were used for the validation of the accuracy and reproducibility
of the instruments.
Elemental analysis: found C, 56.22; H, 8.04; N, 12.59%.
C16H28N3Br requires C, 56.13; H, 8.26; N, 12.28%.
1-Alkyl-3-propanenitrile imidazolium dioctylsulfosuccinate
[C2CN Cnim]DOSS. [C2CN Bim]Br (0.03 mol) and sodium
dioctylsulfosuccinate (0.03 mol) in acetone was mixed together
in a 250 mL round-bottomed flask. The mixture was stirred at
room temperature for 48 h. The solid precipitate formed was
separated and the solvent removed in vacuo. The resulting pale
yellow viscous compound was cooled to room temperature
and washed with ethyl acetate and diethyl ether. It was then
Bromide measurements were conducted by ion chromato-
graphy (Metrohm Model 761 Compact IC) with a (150 Â 4.0) mm
c
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dried in a vacuum oven for 48 h to give 1-butyl-3-propanenitrile
imidazolium dioctylsulfosuccinate [C2CN Dim]DOSS. A similar
procedure was repeated to synthesise 1-decyl-3-propanenitrile
imidazolium dioctylsulfosuccinate [C2CN Dim]DOSS by
replacing [C2CN Bim]Br with [C2CN Dim]Br.
Elemental analysis: found C, 59.35, H, 9.61; N, 9.49; S,
7.15%. C22H42N3O4S requires C, 59.43; H, 9.52; N, 9.49;
S, 7.15%.
[C2CN Dim]DDS; dH (300 MHz; D2O): = 0.88 (6 H, t,
CH3CH2), 1.29 (20 H, br m, CH2), 1.36 (12 H, br m, CH2),
1.90 (2 H, t, CH2CH2O), 3.17 (2 H, t, CH2CH2N), 3.20 (2 H, t,
CH2CH2CN), 3.98 (2 H, t, CNCH2), 4.25 (2 H, t, OCH2CH2),
4.58 (2 H, t, NCH2CH2), 7.75 (2 H, s, CHN), 7.77 (1 H, s,
NCHN) ppm. 13C NMR (75 MHz; D2O) = 122.96, 122.53,
116.5245, 109.39, 67.84, 48.37, 47.7243, 45.07, 31.74, 29.49,
29.45, 29.23, 28.19, 25.94, 25.66, 22.43, 18.62, 13.17 ppm.
FTIR-ATR nmax/cmÀ1: 2250 and 1564 (CN), 2921 and 2872
(C–H), 1218 and 1163 (SO3).
[C2CN Bim]DOSS; dH (300 MHz; CDCl3): = 0.84 (15 H, t,
CH3CH2), 1.24 (16 H, br m, CH2), 1.38 (4 H, d, OCH2CH),
1.62 (2 H, t, CH2CH2N), 1.91 (2 H, d, COCH2CH), 3.19
(2 H, t, CH2CH2CN), 3.98 (2 H, t, CNCH2), 4.05 (4 H, d,
OCH2CH), 4.28 (2 H, t, NCH2), 4.71 (1 H, t, CHSO3), 7.34 (1 H,
s, CHN), 7.80 (1 H, s, CHN), 9.95 (1 H, s, NCHN) ppm.
13C NMR (75 MHz; CDCl3) = 171.26, 168.56, 136.68, 122.64,
116.67, 67.53, 66.92, 62.06, 48.21, 48.00, 47.78, 47.57, 47.36,
30.21, 28.81, 22.75, 19.15, 13.24, 13.20 ppm. FTIR-ATR
Elemental analysis: found C, 63.68; H, 10.37; N, 7.98; S,
6.01%. C28H54N3O4S requires C, 63.60; H, 10.29; N, 7.95;
S, 6.06%.
n
max/cmÀ1: 2248 and 1564 (CN), 2929 and 2871 (C–H), 1213
and 1035 (SO3), 1730 (CQO), 1161 (C–O–C).
Elemental analysis: found C, 59.89, H, 9.15; N, 6.90; S,
5.41%. C30H54N3O7S requires C, 59.97; H, 9.06; N, 6.99;
S, 5.34%.
1-Butyl-3-propanenitrile
imidazolium
benzenesulfonate
[C2CN Bim]BS. 1-butyl-3-propanenitrile imidazolium benzene-
sulfonate [C2CN Bim]BS was synthesised by following the same
procedure as that described for [C2CN Bim]DDS by adding
sodium benzenesulfonate C6H5SO3Na (0.04 mol, 7.21 g) to
(0.04 mol, 10.33 g) [C2CN Bim]Br.
[C2CN Dim]DOSS; dH (300 MHz; CDCl3): = 0.88 (15 H, t,
CH3CH2), 1.32 (28 H, br m, CH2), 1.55 (4 H, d, OCH2CH),
1.87 (2 H, t, CH2CH2N), 2.83 (2 H, d, COCH2CH), 3.21
(2 H, t, CH2CH2CN), 3.96 (2 H, t, CNCH2), 4.17 (4 H, d,
OCH2CH), 4.24 (2 H, t, NCH2), 4.72 (1 H, t, CHSO3), 7.34
(1 H, s, CHN), 7.88(1 H, s, CHN), 9.62 (1 H, s, NCHN) ppm.
13C NMR (75 MHz; CDCl3) = 171.40, 169.37, 137.32, 123.31,
121.93, 117.05, 68.01, 50.23, 45.32, 38.58, 31.82, 30.03, 29.22,
28.84, 26.26, 23.39, 22.90, 19.67, 13.99, 10.83 ppm. FTIR-ATR
[C2CN Bim]BS; dH (300 MHz; D2O): = 0.83 (3 H, t,
CH3CH2), 1.28 (2H, t, CH2CH3), 1.87 (2 H, t, CH2CH2N),
3.17 (2 H, t, CH2CH2CN), 4.23 (2 H, t, CNCH2CH2), 4.57
(2 H, t, NCH2CH2), 7.54 (3 H, d,CHCHCH), 7.58 (1 H, s,
CHN), 7.63 (1 H, s, CHN), 7.78 (1 H, s, NCHN), 8.98 (2 H, br d,
CHCSO3) ppm. 13C NMR (75 MHz; D2O) = 135.82, 131.53,
129.04, 125.41, 123.12, 117.93, 50.00, 44.84, 30.38, 29.10, 25.01,
21.82, 19.36, 13.32 ppm. FTIR-ATR nmax/cmÀ1: 2248 and 1562
(CN), 2960 and 2871 (C–H), 1190 and 1031 (SO3).
n
max/cmÀ1: 2250 and 1564 (CN), 2925 and 2873 (C–H), 1223
and 1037 (SO3), 1731 (CQO), 1159 (C–O–C).
Elemental analysis: found C, 63.03; H, 9.65; N, 6.04; S,
4.73%. C36H66N3O7S requires C, 63.12; H, 9.71; N, 6.13;
S, 4.68%.
Elemental analysis: found C, 57.22, H, 6.54; N, 12.57; S,
9.48%. C16H22N3O3S requires C, 57.12; H, 6.59; N, 12.49;
S, 9.53%.
1-Alkyl-3-propanenitrile imidazolium dodecylsulfate [C2CN
Cnim]DDS. [C2CN Bim]Br (0.04 mol) and sodium dodecyl-
sulfate C12H25OSO3Na (0.04 mol) were mixed in 40 mL of hot
deionized water (60 1C). The mixture was stirred at room
temperature for 48 h. The water was slowly removed under
vacuum at 80 1C then 50 mL of CH2Cl2 was added to the
precipitate and the mixture was filtrated. The viscous extract
was then washed with deionized water and the washing was
repeated until it was bromide-free. The remaining solvent was
removed at 80 1C under vacuum and then dried in a vacuum
oven for 48 h to afford the viscous gel product, 1-butyl-3-
propanenitrile imidazolium dodecylsulfate [C2CN Bim]DDS.
A similar procedure was repeated to synthesise 1-decyl-3-
propanenitrile imidazolium dodecylsulfate [C2CN Dim] by
replacing [C2CN Bim]Br with [C2CN Dim]Br.
1-Butyl-3-propanenitrile imidazolium trifluoromethanesulfo-
nate [C2CN Oim]TFMS. 1-butyl-3-propanenitrile imidazolium
trifluoromethanesulfonate [C2CN Oim]TFMS was synthesised
by following the same procedure by adding sodium trifluoro-
methanesulfonate CF3SO3Na (0.04 mol, 6.88 g) to (0.04 mol,
10.33 g) [C2CN Bim]Br.
[C2CN Bim]TFMS; dH (300 MHz; D2O): = 0.90 (3 H, t,
CH3CH2), 1.29 (2 H, t, CH2CH3), 1.852 (H, t, CH2CH2N),
3.15 (2 H, t, CH2CH2CN), 4.23 (2 H, t, CNCH2CH2), 4.56
(2 H, t, NCH2CH2), 7.54 (1 H, s, CHN), 7.61 (1 H, s, CHN),
8.94 (1 H, s, NCHN) ppm. 13C NMR (75 MHz; D2O) =
135.73, 123.04, 122.33, 121.34, 117.92, 49.71, 44.80, 31.17,
19.24, 18.77, 12.66 ppm. FTIR-ATR
n : 2254
max/cmÀ1
and 1564 (CN), 2964 and 2875 (C–H), 1249 and 1029 (SO3),
[C2CN Bim]DDS; dH (300 MHz; D2O): = 1.01 (6 H, t,
CH3CH2), 1.45 (20 H, br m, CH2), 1.98 (2 H, t, CH2CH2O),
3.30 (2 H, t, CH2CH2N), 3.33 (2 H, t, CH2CH2CN), 4.39 (2 H,
t, CNCH2), 4.70 (2 H, t, OCH2CH2), 4.79 (2 H, t, NCH2CH2),
7.75 (2 H, s, CHN), 7.81 (1 H, s, NCHN) ppm. 13C NMR (75
MHz; D2O) = 136.29, 123.32, 122.79, 118.04, 68.45, 49.8386,
45.12, 43.64, 32.23, 31.68, 30.13, 26.16, 22.87, 19.96, 19.59,
19.20, 14.05, 13.25 ppm.
1226 and 1159 (CF3).
Elemental analysis: found C, 40.29 , H, 4.94; N, 12.79; S,
9.73%. C11H16F3N3O3S requires C, 40.36; H, 4.93; N, 12.84;
S, 9.80%.
Density and viscosity measurements
The density and viscosity of all ionic liquids was measured
at 298.15 K at atmospheric pressure using a Stabinger visco-
meter (Anton–Paar model SVM3000). The temperature was
FTIR-ATR nmax/cmÀ1: 2252 and 1564 (CN), 2923 and 2865
(C–H), 1215 and 1163 (SO3).
c
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New J. Chem., 2011, 35, 1111–1116 1115

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controlled to within Æ0.01 1C. The repeatability of the
measurements was Æ5 Â 10À4 g cmÀ3 and 0.35% for density
and viscosity, respectively. The standard calibration fluid
provided by the supplier was used for the calibration of the
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An ATAGO programmable digital refractometer (RX-5000
alpha) with a measuring accuracy of Æ4 Â 10À5 was used to
measure the refractive index of various ILs at 298.15 K.
The temperature of the apparatus was controlled to within
Æ0.05 1C. The apparatus was calibrated and checked before
each series of measurements using pure organic solvents
with known refractive indices.14,28–30 Dried samples kept in
desiccators were directly placed into the measuring cell.
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Thermogravimetry measurements
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A PerkinElmer, Pyris V-3.81 was used to measure the decom-
position temperatures of the synthesised ILs. The samples
were placed in aluminium pans under a nitrogen atmosphere
at a heating rate of 5 1C minÀ1. The measured start temperature
(Ts) and decomposition temperature (Td) are presented in
Table 1.
The melting, crystallisation, and glass transition temperatures
were measured by differential scanning calorimetry using a
5 1C minÀ1 heating rate. A Mettler-Toledo differential scanning
calorimeter (DSC822e) with Mettler-Toledo STARe software
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Acknowledgements
The author would like to thank Universiti Teknologi
PETRONAS for the facilities provided in this work and
PETRONAS sponsorship for A. K. Ziyada.
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