Combined effect of ether and siloxane substituents on imidazolium ionic liquids

Article abstract of DOI:10.1039/c5ra07466e

Ionic liquids (ILs) in combination with ether and siloxane substituents on the imidazolium cation, comprising of bis(trifluoromethylsulfonyl)imide (NTf₂) anions, have been synthesized due to their low viscosities, high thermal stabilities and low melting or glass transition temperatures(T_g). The structural flexibility of the ether and siloxane substituents on the imidazolium center overcomes the effect of van der Waals forces and gives them desirable and unique physical properties. These novel ILs show low viscosities (～72 mPa s at 25 °C), high thermal stabilities up to 430°C, and a wide liquid range over 500°C. In addition, these ILs exhibit only an amorphous glassy state on cooling at T_g below -74°C and cannot order properly to afford crystallization. The detailed thermal stability, phase transitions and heat capacity were studied by TGA, DSC and temperature-modulated DSC analysis. More importantly, we have also reported the large-scale (one kilogram) microwave-assisted synthesis of ILs [BMIM]Br and [1O2O2-Im-2O1]I as efficient and greener processes.

Full text of DOI:10.1039/c5ra07466e

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Combined Effect of Ether and Siloxane Substituents on
Imidazolium Ionic Liquids†
Santosh N. Chavan,a and Debaprasad Mandal*a
Received 00th January 20xx,
Accepted 00th January 20xx
Ionic liquids (ILs) in combination with ether and siloxane substituents at the imidazolium cation comprising of
bis(trifluoromethylsulfonyl)imide (NTf2) anion have been synthesized for the purpose of low viscosity, high thermal
stability and low melting or glass transition (Tg). The structural flexibility of ether and siloxane substituents on imidazolium
center overcomes the effect of van der Waals force and exhibit desirable and unique physical properties. These novel ILs
show low viscosity (~72 mPa.s at 25 °C), high thermal stability upto 430 °C, and wide liquid range over 500 °C. In addition,
these ILs exhibit only amorphous glassy state on cooling at Tg below –74 °C and cannot order properly to afford
crystallization. The detailed thermal stability, phase transitions and heat capacity were studied by TGA, DSC and
temperature-modulated DSC analysis. More importantly, we have also reported the large scale (one kilogram) microwave
assisted synthesis of ILs [BMIM]Br and [1O2O2Im2O1]I as an efficient and greener processes.
DOI: 10.1039/x0xx00000x
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supporting electrolyte or during filtration, pumping,
dissolution, separation and mixing.
Introduction
During the last few decades numerous studies have been
Ionic liquids (ILs) were introduced initially as media for organic
transformations. However, in recent years their chemistry
have been developed remarkably due to their potential
applications like new media for material synthesis,
devoted in reducing the viscosity and melting points of ILs by
altering the anion employed. For example,
bis(trifluoromethylsulfonyl)imide [Tf2N; TFSI], and dicyanamide
[(CN)2N] are the optimum choice of anions to keep the
viscosity low.[19] However, recently the functionality of cations
also attracted a great attention for regulating the viscosity.
Attachments of hetero atom containing substituents, like
alkoxy (R-O-R) and siloxy (Si-O-Si) groups with imidazolium,
phosphonium or ammonium cations are shown to be effective
in decreasing the viscosity dramatically due to increase in free
rotation around the hetero atom.[20],[21],[22],[23],[24] Further, the
alkoxy chain effect on decreasing the viscosity was ascribed to
the high conformational flexibility of the ether moieties and
biocatalysts,[1]
nanotechnology,[2],[3]
separation
techniques,[4],[5],[6] handling radioactive wastes,[7],[8] lubricant
additives,[9],[10],[11] electrolytes in electrochemical devices[12],[13]
and many others.[14] These ILs offers endless opportunities due
to their unique properties like negligible vapour pressure (non-
volatility), non-flammability, high thermal stability and wide
liquid temperature range in combination with high ionic
conductivity, wide electrochemical stability window and their
ability to dissolve a wide variety of compounds.[1] Combination
of these properties empower ILs as “greener” solvents for
energy applications and industrial processes.[15],[16]
provides more available holes for the convenience of mass
transport and low viscosity.[21,
25]
For example, alkoxy
The unique properties of each IL is essentially governed by
the nature of both cationic and anionic constituents and their
interionic interactions. While much work has been devoted to
the applications of ILs, the basic understanding and study of
their structure–property relationship will be of immense
benefit to fine tune the ILs with specific type of “designer
medium”.[17],[18] In addition, the high viscosity (η) of ILs is the
major barrier for their use in most of applications. For
example, in electrochemical reactions and devices, where
charge carrying species essentially diffuse through the
functionalized quaternary ammonium ILs offer enough
flexibility to reduce the viscosity relative to the isoelectronic
alkyl chains and they have been used as high-conductive
electrolytes.[22a] However, thermal stability would be a major
concern due to favourable elimination reaction facilitated by
electron withdrawing nature of alkoxy groups. Whereas, the
attachment of siloxy group not only gives conformational
flexibility similar to alkoxy but also improves the thermal
stability. However, addition of siloxane or ether fragments to
ILs wouldn’t alter their toxicity significantly. Also, due to highly
hydrophobic nature of siloxanes, the solubility of the ILs in
different solvents is expected to be altered.
Given, the individual study on alkoxy and siloxy
substitutents to ILs, the studies on the combination of these
two in ILs are still not been reported. Hence, we consider the
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combined effect of these two functional moieties alkoxy and
siloxy in an ionic liquid to ascertain all-in-one aforementioned
essential features like low viscosity, good thermal stability and
a wide liquid range. In the present study, we have designed
four novel ILs combining both alkoxy and siloxy substituents on
imidazolium cation with TFSI anion as shown in Figure 1 and
reported the detailed studies on viscosity, thermal stability,
phase transitions and heat capacity.
ILs
1 and 2 are 1-alkoxy-3-siloxy imidazolium salts. The less
toxic silyl or siloxane polymers are extensively used in medical
applications (implants) and in personal care products like, in
baby bottle teats. ILs
3 and 4 are designed for the comparison
of physical properties and better understanding the structure-
property relationships. The physical properties of ILs 1-4 were
validated with respect to BMIM TFSI (5), which is considered as
the most studied IL reported in the literature.
More importantly, we have also explored an efficient
microwave (MW) assisted method for producing large
quantities of high quality ionic liquids in kilogram scale. To the
best of our knowledge, the large scale synthesis of ILs over a
kilogram scale was only reported using conventional heating
method by Burrell et. al.[26] Microwave assisted synthesis has
importance as a valuable, greener and efficient alternative for
functionalized IL.[27]
Scheme 1. Synthesis of ionic liquids 1-5.
Results and discussion
Synthesis
Five unsymmetrically substituted imidazolium ionic liquids (1-
Figure 1) with Tf2N anion were synthesized from
5,
corresponding imidazolium iodides (1a-5a) with more than
90% yield and >99% purity. The purity of all ILs were analyzed
primarily by 1H, 19F NMR and mass spectroscopic techniques.
ILs
deionized water offer high purity ILs and the halide removals
was confirmed by AgNO3 test. However, IL is less
1, 2, 4 are highly hydrophobic, therefore washing with
3
hydrophobic compared to other ILs due to the presence of
ether functionality on the both sides of imidazolium ring and
the yield tend to reduce during washing with deionized water.
Corresponding imidazolium iodides
(
1a
-
5a
)
were
5b
synthesized from respective N-substituted imidazole (1b
-
)
by microwave irradiation in a batch scale of ~50 mmol in the
presence of acetonitrile as solvent (solvent was added to fill
the minimum volume of microwave oven vials ~6 mL) for 40
min (Scheme 1). Large scale microwave synthesis 2000 mmol
of [1O2O2-Im-2O1]I (3a) and [BMIM]Br (5a) were also tested
in a batch of 8 Teflon vials rotor of 100 mL capacity in solvent
free condition to assess the scope of greener/scale-up
methods and ILs were synthesized at almost half a kilogram
scale with 99% yield and 77% of the excess halide used in
reaction was recovered by simple decantation and distillation.
It is also possible to scale-up the MW synthesis with 16 vial
rotor for more than a kilogram scale.
Figure 1. Ionic liquids used in this study.
ILs
substituted
iodomethyldimethyldisiloxane (
was prepared from chloromethyldimethylchlorosilane (
1
and
2
were prepared from the reaction of ether
imidazole 1b and 2b and
). The disiloxane precursor
(
)
6
6
7) by
iodination in presence of phase transfer catalyst, Aliquat 336®.
Phase transfer catalyst reduces the halide exchange reaction
time and also increases the yield. The chloromethyl silane
compound
7
when used for quaternization (1a and 2a) the
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obtained yield was poor along with impurities, whereas the
iodide precursor gives clean reaction with better yield (~90%).
Table 2. The dynamic viscosity (η /mPa∙s) with change in temperature of
ILs 1-5.
Me3Si1-
Im-1SiOSi
(4)
BMIM
(5)
Temp.
(°C)
1O2-Im-
1SiOSi (1)
1O2O2-Im-
1SiOSi (2)
1O2O2-Im-
2O1 (3)
Table 1. Density of ILs 1-5 at 25 °C.
ILs
Density (g/cm3 at
25 °C)
10
194.7
174.2
174.1
380.2
105.7
Mol. wt
20
25
30
106.5
81.9
64.3
96.97
74.7
59.2
94.0
71.9
56.3
202.4
144.9
111.4
68.0
52.3
43.2
1O2-Im-1SiOSi TFSI (1)
1O2O2-Im-1SiOSi TFSI (2)
1O2O2-Im-2O1 TFSI (3)
Me3Si1-Im-1SiOSi TFSI (4)
BMIM TFSI (5)a
1.3036
1.2935
1.4155
1.2520
1.4365
567.67
611.72
509.07
595.80
419.36
40
50
60
70
41.3
28.6
20.8
15.7
39.2
27.3
20.0
15.2
36.4
25.1
18.3
13.8
66.3
44.9
31.4
21.9
29.7
21.2
16.4
12.4
[a] (at 25 °C BMIM TFSI 1.436 g/cm3)[18b]
.
80
12.2
11.9
10.8
15.7
9.8
90
9.8
7.9
9.5
7.6
8.7
7.1
11.5
9.3
8.0
6.7
Solubility/miscibility
.
The ILs
1
-
5
are highly miscible in
100
chloroform, dichloromethane, THF, acetone and benzene but
immiscible in water and hexane and slightly miscible in ether.
ILs 1-5 are also freely miscible in propylene carbonate which is
Viscosity. ILs with low viscosity are desirable to facilitate the
mass transport when applied as media in most of their
applications. The viscosity of an ionic liquid is significantly
governed by the molecular symmetry, ion sizes and the
interionic interactions (such as van der Waals force and
electrostatic attractions).[28] The viscosities for ILs 1O2-Im-
a good solvent to aid electrochemical analysis.
Characterization
NMR. C2 proton (HC2) of imidazolium ring is a good measure to
ascertain reaction progress and purity. While HC2 appeared at
~10 ppm with the halide anion but exhibits upfield shift to ~8
ppm with TFSI. This is also a good indication of the interaction
between cation and anion which mainly reflects the unique
properties of ILs. Tf2N (CF3) appears at –78 ppm in 19F NMR for
1SiOSi TFSI (
1), 1O2O2-Im-1SiOSi TFSI (
2), 1O2O2-Im-2O1 TFSI
(
3), Me3Si1-Im-1SiOSi TFSI (
4
) and BMIM TFSI (5) with varying
temperature in an inert atmosphere are listed in Table 2 and a
plot of viscosity vs. temperature is shown in Figure 2. All five
ILs follow the Vogel–Tammann–Fulcher (VTF) equation[29] for
viscosity with variation in temperature.
ILs 1-5 and there is almost no shift observed for different Ils.
Density. The density of ILs 1-5 were measured with small
variation of temperature and the density values at 25 °C are
given in Table 1 and more details are provided in Figure S1
[supporting information (SI)].
η = η0 exp[B/(T-T0)]
Where η is viscosity,
T is the absolute temperature, η0 (mPa.s),
B
(K), and T0 (K) are adjustable parameters for VTF equation.
η0 is the pre-exponential parameter, (a reference viscosity at
which the exponential term approaches unity i.e., high
temperature asymptote),
B is called pseudoactivation energy,
and T0 is coincide to ideal glass transition temperature.
Table 3. VTF equation parameters of viscosity for the ILs.
ILs
ηo (mPa.s)
B (K)
T0 (K)
R2
1O2-Im-1SiOSi
TFSI (1)
0.192±0.01
725±12.7
184.4±0.23
0.9999
1O2O2-Im-1SiOSi
TFSI (2)
0.233±0.01
0.216±0.01
679.2±11.9
659.5±2.6
180.3±1.02
184.4±0.23
0.9999
0.9999
1O2O2-Im-2O1
TFSI (3)
Me3Si1-Im-1SiOSi
TFSI (4)
0.039±0.02
0.070±0.04
1196.5±185 152.6±11.1
1057±189 138.0±14.5
0.9996
0.9992
BMIM TFSI (5)
Figure 2. Plot of dynamic viscosity (η, estimated error ±3%) vs.
temperature for ILs
1-5.
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The best-fit parameters η0 (mPa.s), B (K), and T0 (K) are viscosity stems from high molar volume does not keep up
given in Table 3 along with corresponding fitting coefficient R2 here.
values. From tabular data of VTF equation it is clear that if T0
The viscosity in these imidazolium ILs seems to be
values are smaller, then B is bigger and the viscosity would be governed by two major factors 1) interionic interactions and 2)
more sensitive to temperature. ILs 1-3 has similar η0 and T0 side chain mobility. Since the primary interaction between the
values, but IL
the B and T0 values do not show a regular relation with the same, we consider the electronic and structural effect of the
structures of cations sidechains that are related to van der Waals forces. Hence, the
BMIM TFSI ( ) shows η as 52.3 mPa.s at 25 °C which are in contribution of each alkoxy and siloxy chains are important.
good agreement (51.7 mPa.s) with the reported literature.[25] The alkoxy groups in IL 1-3 were carefully chosen with two CH2
Viscosity of ILs and are 81.9, 74.7 and 71.9 mPa.s at 25 spacers (Im-2O1 or Im-2O2O1) at the imidazolium attachment
1 gives higher B values among ILs 1-3. However, TFSI anion with imidazolium core structure essentially remain
5
1,
2
3
°C respectively, which are reasonably less viscous in spite of to reduce the electron withdrawing effect of alkoxy group. The
their high molar mass. Although, the viscosities of ILs 1-3 are sidechain flexibility of alkoxy group effectively influence the
little higher than BMIM TFSI (
the viscosity of these double functionalized ILs (1-3) with low mobility but, the electron donating effect of CH2-Si-O-Si also
mol. wt. alkyl substituted BMIM. decreases the partial positive charge and consequently the
Further, IL (Mw = 505.5) shows the lowest viscosity but interionic interaction.
interestingly does not increase much for ILs and with The Newtonian behavior of these ionic liquids (1-5 and 1a
considerable increase in molecular weight (Mw) upon 5a) were also tested on Rheometer at 25 °C in ambient
attachment of Si-O-Si group [Mw = 567.7 (IL ), 611.7 (IL )]. atmosphere by varying shear rate and represented in Figure S2
Since the electronic and geometric structure of the (SI). ILs and with TFSI anion exhibit Newtonian behavior
imidazolium ring remains unaffected by the functionalization as the viscosity remains constant with varying shear rate. But
of the alkyl chains, the primary interaction between the ILs with halide anion (1a 3a) shows gel type shear thinning
5), but one should not compare viscosity. The siloxanes (Si-O-Si), not only imparts the sidechain
3
1
2
-
1
2
1-
3
5
-
imidazolium ring and TFSI anion will be quite similar among behavior as shown in Figure S3 (SI). The viscosity determined
these ILs 1-5. Due to minimum basicity and good charge by Rheometer shows lower values than measured by
delocalization of TFSI, van der Waals forces is expected to be viscometer due to the influence of moisture while carrying out
dominating over interionic electrostatic interaction between the measurement by Rheometer in open-air atmosphere.
imidazolium cation and TFSI. Again the van der Waals forces
mostly depend on the molar mass and the side chains. Thermal Characterization
Sufficient side chain mobility of ether and siloxane moieties in
Thermal stability. The thermal stability of these ILs were
ILs 1-3 out-weighs the increase in the molar mass. This is also
reflected in 1H NMR δ1HC2 (imidazole) which correlates well
with the cation/anion interaction. For example, δ1HC2
determined by thermogravimetric analysis and the TGA curves
are shown in Figure 3. The thermal decomposition
temperature (Td) is considered as the onset temperature in
(imidazole) shifted downfield by ~2 ppm in ILs 1-5 with TFSI
compared to halides (1a-5a). However, δ1HC2 (imidazole)
TGA curve. The dynamic TGA results as shown in Table 4
exhibits excellent short term stability over 400 °C at a scan rate
doesn’t show any noticeable shift within ILs
1-5 indicating
of 10 °C/min. The onset temperature of mass loss for ILs
1, 2, 3
similar interionic interactions. This signifies the effect of side
chain functionality on viscosities.
and 4 show the Td as 430.4, 430.4, 426.8 and 413.6
respectively, which are quite similar due to the basic
imidazolium structure of all four ionic liquids with TFSI as
Compare to IL
, the η value decreases by 10 mPa.s at 20 °C, which is
opposite to the trend from the literature reported ILs [Me-Im-
2O1]TFSI[25] vs. [Me-Im-2O2O1]TFSI[30]
It seems there is
considerable effect of Si-O-Si (siloxane) functionality on the
viscosity of IL and . Again, IL shows similar viscosity with
[Me-Im-1SiOSi]TFSI (η = 75.6 mPa.s at 25 °C)[31]. Whereas, the
η value increases almost 20 mPa.s in IL compare to [Me-Im-
1, with increasing the alkoxy chain length in
IL
2
anion. [BMIM]TFSI
(
5)
shows higher decomposition
temperature at 440.4 °C compare to other ILs. The observed
thermal decomposition of [BMIM]TFSI is well within the limits
as reported in the literature (Tonset = 442[32] or 439 °C[33]).
.
1
2
2
ILs
1
,
2
, and
3
have comparable Td, as was observed in the
and indicate that the
case of viscosity. Very high Td of ILs
1
2
3
electron withdrawing effect of alkoxy on imidazolium core is
cancelled out by the electron donating and hyperconjugation
effect of disiloxane, which causes improved thermal stability.
2O2O1]TFSI (η =70.3 mPa.s at 21 °C). These comparisons point
towards the fact that the viscosity remains similar in spite of
the increase in the molar mass in ILs 1-3
Surprisingly the IL , which is a combination of Me3Si1 and
Si-O-Si1 shows higher viscosity (η =144.9 at 25 °C) than ILs 1-3
In comparison to IL , the η values of Me-Im-1Si-O-Si TFSI and
.
IL
4 surprisingly shows slightly lower thermal decomposition
4
temperature Td.
.
Pyrolysis of the imidazolium salts with different halide
anions is known to proceed most likely via SN2 process
depending on the basicity and/or nucleophilicity of the
anions.[34] However, in presence of TFSI anion the pyrolysis
proceeds via SN1 reaction and the thermal stability is governed
4
Me-Im-1SiMe3 at 25 °C are 89.0 and 97.7 respectively. The
effect of CH2SiMe3 is not similar here to keep the viscosity low.
The molar volume (Mol. wt./density) of IL
4 is highest among
ILs 1-5 due to lower density. Possibly, the trend that low
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by the difference in inductive effects of the side chain attached
to N-atom.
Based on the DTG curves (first derivative of TGA, Figure 3)
Table 5. Isothermal TGA of ILs 1-5.
a stepwise decomposition was observed for all the ILs except
(BMIM TFSI). IL exhibits overlapping of two continuous
degradation steps. Whereas, ILs and clearly shows three
5
ILs
Temperature (°C) % wt Loss in 4 h
3
1
2
1O2-Im-1SiOSi (1)
1O2O2-Im-1SiOSi (2)
1O2O2-Im-2O1 (3)
Si1-Im-1SiOSi (4)
BMIM (5)
250
280
280
280
310
13.5
16.3
8.7
degradation steps which can be assigned to characteristic
decomposition reaction. Assuming SN1 type degradation, the
first step showing a small hump with 10% weight (wt.) loss in IL
13.9
10.6
2
is possibly due to evaporation of ether substituent. Next two
big humps corresponds to [Im-Si-O-Si]+ (accounts for 40% wt.
loss) and in the end TFSI (accounts for 50% wt. loss). IL shows
2
exactly similar degradation pattern with a small hump (17%
wt. loss) as first step. This was followed by two large humps of
37% and 46% wt. loss corresponding to [Im-Si-O-Si]+ and TFSI
respectively. Although, the thermogravimetric analysis does
not provide a mechanism of the evaporation process, the
weight loss indicates that the decomposition initiates at the
ether attachment at least in
1
and
2
under the prevailing
conditions. Simultaneously, IL
4
shows two steps of
decomposition which closely matches with the corresponding
% wt. loss of the components, Me3SiCH2 (15%), [Im-Si-O-Si]
and TFSI (85%). All samples preferably show dominant mass-
loss at Tendset (above 490 °C) with left over residue of 3-5%,
except for IL 3 where the residue was 8%.
Table 4. Dynamic TGA data of ILs 1-5.
T
T
T
T
endset
start
onset
peak
ILs
(°C)
(°C)
(°C)
(°C)
Figure 4. Isothermal TGA curves of ILs 1-5
.
1O2-Im-1SiOSi (1)
288.1
430.4
473.6
493.3
1O2O2-Im-1SiOSi (2)
1O2O2-Im-2O1 (3)
Si1-Im-1SiOSi (4)
307.4
309.7
309.3
430.4
426.8
413.6
483.0
480.5
471.2
498.1
494.7
486.4
The long term thermal stability was also investigated by
performing isothermal TGA in N2 atmosphere for 4 h at a given
temperature. The temperature chosen was ~30 °C below the
Tstart. The long-term stability of these ILs are important from
industrial application point of view.[35] The data and nature of
isothermal TGA curve are depicted in Table 5 and Figure 4
respectively. From the slope of isothermal TGA curves, it can
BMIM (5)[a]
326.1
440.4
489.6
503.9
[a] Literature reported BMIM TFSI data T
(330 °C[32]) and T
onset
start
(442 °C[32], 439 °C[33]
)
be predicted that IL
the studied ILs, even better than IL
Tonset, ILs and (ether/siloxane) are more stable than 3
3
has the best long term stability among
5
(BMIM TFSI). Comparing
1
2
(ether-ether); also, Tstart for
2
and
and
3
are comparable in TGA.
However, it is found that IL
1
2 exhibits lower long term
thermal stability than 3. It can be predicted from DTG curve,
where the ether group evaporated first in SN1 type
degradation leaving [Im-Si-O-Si]+. [Im-Si-O-Si]+ gain extra
stability due to the +I effect of [Si-O-Si] group and facilitate the
degradation than in IL 3
(Ether-Im-Ether) where the [Im-Ether]+
part is unstable due to –I effect of ether group.
Phase transitions and Heat Capacity (Cp) in DSC and
Temperature-Modulated DSC. The phase transitions like the
glass transition (Tg), cold crystallization (Tc), and melting
temperature (Tm) were observed during DSC measurement
from -90 to 20 °C and were further confirmed by performing
TOPEM® a temperature-modulated DSC analysis program. The
Figure 3. Dynamic TGA and DTG curves of ILs 1-5
.
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DSC measurement was performed from –90 to 20 °C and Even during the TOPEM measurement melting was not
TOPEM was carried out from –90 to 60 °C.
observed for IL 4.
The heating scans show only glass transitions (Tg) in DSC as
well as in temperature-modulated DSC scan for ionic liquids
1,
Table 7. Heat capacity (C ) values of ILs (1-5) in temperature-modulated
p
2,
3, and 4 and the respective Tg values are –74.4, –72.3, –74.6
DSC (TOPEM) at T , 25 and 50 °C.
g
and –63.2 °C respectively. The glass transitions (Tg) and
corresponding enthalpies relaxation (ΔHg) of ILs 1-5 are given in
Table 6 and the DSC curves are shown in Figure 5, and Figure S4
T
25 °C
50 °C
g
[a]
p
[b]
p
C
C
C
C
C
C
p
p
p
p
ILs
(SI). The enthalpy relaxation ΔHg of 1O2O2-Im-SiOSi TFSI (2) is
(J/g∙K) (J/mol∙K) (J/g∙K)
(J/mol∙K) (J/g∙K) (J/mol∙K)
8.56 KJ/mol, which is highest among these ILs. The siloxane
1O2-Im-
1SiOSi (1)
1O2O2-Im-
1SiOSi (2)
1O2O2-Im-
2O1 (3)
1.09
1.18
1.14
618.7
721.8
580.3
1.23
1.41
1.38
698.2
862.5
702.5
1.25
1.39
1.40
709.6
850.3
712.7
substituted ILs give higher ΔHg than ether or alkyl substituents.
BMIM TFSI (5) shows only Tg at –88.3 °C and we do not
observe the cold crystallization and melting during DSC
measurement. However, temperature-modulated DSC
(TOPEM) analysis clearly shows the cold crystallization (Tc),
and melting temperature (Tm) to be –40.9 and –5.0 °C
respectively. According to literature the Tg, Tc, and Tm for
BMIM TFSI are –87, –40 and –7 °C respectively.[18b, 32]
Si1-Im-
1.03
1.14
613.7
478.1
1.19
1.30
709.0
545.2
1.20
1.32
715.0
553.5
1SiOSi (4)
BMIM (5)
[a] specific heat capacity; [b] molar heat capacity
Table 6. DSC data of ILs 1-5 with the enthalpy relaxation at glass
Many ionic liquids tend to crystallize pretty slowly,
however, it is still possible to detect these phase transitions in
TOPEM by employing slow heating rates. DSC scans with
heating and cooling cycle for all four ILs show no signs of
freezing or melting transitions, even during TOPEM. It is
evident that the ILs remained in the liquid state for the entire
transition (ΔH ).
g
T
(°C)
ΔH (KJ/mol)
ILs
g
g
1O2-Im-1SiOSi (1)
1O2O2-Im-1SiOSi (2)
1O2O2-Im-2O1 (3)
Si1-Im-1SiOSi (4)
BMIM (5)[a]
–74.4
–72.3
–74.6
–63.2
–88.3
1.873311
8.56408
1.374489
5.24304
1.216144
dynamic ranges of study reported here. Therefore ILs
1, 2 and
3
depict the formation of only glassy state due to high mobility
of side chains, which could not orient properly even at 2
°C/min heating rate during TOPEM measurement. Owing to
lack of melting, the liquid range of these ILs (1-3), may be
considered as the difference between glass transition
temperature (Tg) and thermal decomposition temperature
(Td), which is over 500 °C.
[a] BMIM TFSI T (–86 °C[32], –87 °C[18b]), T (–44 °C[32]), T (–2 °C[32], –
g
c
m
6 °C[18b]).
Heat capacity (Cp): The heat capacity (Cp) of ILs
1-5 were
determined from TOPEM scan ranging from –90 °C to 60 °C at
a heating rate of 2 °C/min. The respective Cp values at Tg, 25
and 50 °C are given in Table 7 and the detail of TOPEM graphs
are shown in Figure S5 (SI). Since specific heat capacity is an
important parameter that ought to be considered for ILs since
they are good candidates as thermal fluids.[36] IL
highest heat capacity among all the ILs in present study
considering either the molar or specific heat capacity. IL has
lowest heat capacity (Cp) due to the presence of Si containing
groups on both side of imidazolium ring. Heat capacity of ILs
tend to increase with increase in temperature which is
2 exhibits the
4
Figure 5. The heating DSC thermograph of five ionic liquids.
Upward peaks are considered as exothermic
1
-
5
The DSC curves for ILs
position in low temperature region, which was not observed in
TOPEM. One peculiar observation is that IL gets solidified
1, 2 and 3 show artefact peaks at initial
obvious and follow the general trend. For example, molar heat
capacity increased by ~10 J/mol on increasing temperature
4
from 25 °C to 50 °C in 1-5. However, IL 2 exhibit some heat
under open atmospheric conditions and at ambient
temperature possibly due to absorption of moisture from
atmosphere. However, when DSC analysis was performed with
exchange incident close to 50 °C (Figure S5, SI) and shows
lower Cp during this process compare to 25 °C.
solid IL 4, only the first scan shows the sample melted in the
temperature range 26-28 °C but subsequent cooling or heating
cycles lack any further instances of solidification or melting.
Conclusions
Efficient microwave assisted bulk scale (Kg scale) synthesis of
ILs resulted in high yield along with excellent purity. The
6 | J. Name., 2012, 00, 1-3
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ether/siloxane ILs exhibited large liquid range over 500 °C from °C overnight and loaded without any atmospheric
–74 °C to 430 °C with a decent low viscosity (~72 mPa.s at 25 interference. Each test was repeated at least thrice.
°C). The combined effect of ether and siloxane substituent in Measurement of water content. The water content in ILs 1-5
imidazolium cation overcomes the columbic packing force, van were determined after vacuum drying at 60 °C and 10-3 mbar
der Waals force, size factor and conformational degree of for 8 h by Karl Fisher titration using a C20 Karl Fisher
freedom. Development of ILs while considering structure- Coulometer (Mettler Toledo), with diaphragmless cell and dual
activity relationship seems to be effective approach. In recent platinum electrode sensor. For an analytical process
work, we found that similar effect of substituents are also HYDRANAL® Coulomat AG anolyte water standards from Fluka®
effective on different ammonium and phosphonium cations analytical was used. The moisture content of these ILs
1-5 was
for controlling the desirable features of ILs and these systems determined by Karl-Fisher titration in the range 200 to 400
will be described in subsequent reports.
ppm.
Viscosity. Viscosity was measured in an inert atmosphere on
Lovis 2000M Microviscometer from Anton Paar with
temperature scan ranging from 10 °C to 100 °C at a heating
rate of 5 °C/min. Each measurement was repeated at least
thrice and presented data is averaged out with an error limit of
3% (standard deviation less than 2 mPa.s). Stainless steel balls
having diameter of 1.5 mm, density 7.7 g/cm3 and running
path of 20 cm were used in three different capillaries of
diameter 2.5 mm, 1.8 mm, and 1.59 mm respectively, with the
respective viscosity range being 700–1500 mPa.s, 30–700
mPa.s, and 2.5–60 mPa.s. The Newtonian test and viscosity
measurements were carried out under atmospheric condition
on an Anton Paar Rheometer Model: MCR102 SN81403820;
FW3.80; Slot (3,-1); Adj (9,0)d, Measuring System: PP25-
SN34217; [d=0.1 mm], Peltier temperature control. The
temperature range of analysis was from –5 °C to 120 °C at the
heating rate 0.2 °C/s.
Experimental
General. Glassware were oven-dried prior to use and all
reactions were conducted in an inert atmosphere unless
otherwise specified. Aqueous solutions were prepared with
deionized water (Millipore). All ILs were vacuum dried at 60 °C
and 10-3 mbar for 6-10 h before performing each test. The
microwave assisted reactions were carried out in Muiltiwave
Pro instrument from Anton Paar. In this system two standard
magnetrons of 850 W deliver up to 1500 W microwave power
in an unpulsed mode over the full power range.
Materials. Chemicals like hexane, chloroform, diethyl ether,
ethyl acetate were purified by simple distillation.
Tetrahydrofuran was passed through neutral alumina followed
by distillation over Na/benzophenone. Acetone was freshly
dried over KOH and CaH2 respectively followed by distillation.
Acetonitrile and dichloromethane distilled over P2O5.
Imidazole (Alfa, 99.5%); 2-Methoxymethanol (Spectrochem,
India, 99.5%); 2-(2-Methoxy-ethoxy)-ethanol (SD Fine, India,
98.0%); p-Toluene sulphonyl chloride (SD Fine, India, 99.0%);
Thermal Analysis. The thermal decomposition temperature
was recorded in nitrogen atmosphere by thermogravimetric
analysis (TGA) technique on a “TGA/DSC 1” instrument with
SDTA sensor from Mettler Toledo. The thermal data were
analyzed in STARe software. The temperature, weight and tau
lag was calibrated using the Aluminum/Zinc standard sample.
High purity nitrogen (99.999%) was passed at a flow rate of 40
mL/min throughout the experiments to avoid contamination
from the external atmosphere. The experiments were
performed using alumina pan for sample holder and as
reference by using 5-20 mg samples. Thermal stability was
investigated by heating from 30 °C to 800 °C at a heating rate
of 10 °C/min. Each sample was tested for at least three times
and the error limit is <2%. The measurement of phase-
transition temperature and heat capacities were recorded by
differential scanning calorimeter (DSC) using a DSC1/700W
with HSS8 high sensitivity sensor instrument (Mettler Toledo)
with Huber TC100MT Intercooler and Olympus microscope
attachments. Data were analyzed in the STARe software. The
temperature, heat change and tau lag was calibrated using the
pure Indium/Zinc standard sample (In/Zn 156.6/419.5 °C). The
DSC was also calibrated with deionized water for low
temperature measurements. Standard aluminum pan with pin
was used as reference. The samples were heated at 120 °C and
held for 10 min isothermally to allow the evaporation of
volatile impurity like moisture. The DSC measurements were
performed successively through a heat-cool-heat (either 3 or 5
steps) program to ensure the phase transitions, as follows:
Chlorotrimethylsilane
(TCI,
98%);
Chloro(chloromethyl)dimethylsilane (Sigma Aldrich, 98%); NaI
(Alfa, 99%); Bis(trifluoromethanesulfonyl)imide lithium salt
(TCI, 98%); and Chloroform-d (Sigma Aldrich, 99.8 atom % D)
were used as received.
Characterization methods
NMR spectroscopy. NMR spectra were recorded using a JEOL
JNM-ECS 400 spectrometer at ambient probe temperatures
and referenced as follows: 1H: residual internal CHCl3 (δ = 7.26
ppm); 13C internal CDCl3 (δ = 77.16 ppm); FT-IR. FT-IR spectra
were recorded as neat with ATR on BRUKER TENSOR-27
spectrometer in the range of 600-4000 cm–1 (Spectral
Resolution = 4 cm−1; Number of scans = 100). GC-MS
Spectrometry. The mass spectra was recorded by GC-MS
(QP2010 Ultra, Shimadzu Corporation). The direct probe EI-MS
mode was used for data collection with 50 eV ion electron
energy.
Density Measurement. The density measurements were
performed between 20 °C and 40 °C in an inert atmosphere
using DMA 35 portable density meter from Anton Paar, which
was calibrated using ultrapure water (0.99704 g/mL at 25 °C).
The IL samples were previously degassed under vacuum at 60
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Journal Name
step 1: cooling from 25 °C to –90 °C at a rate of 5 °C/min and 123.18 (s, NCHCHN), 122.80 (s, NCHCHN), 119.89 (q, J=321.1
held for 5 min; step 2: heating from –90 °C to 20 °C at a rate of Hz, CF ), 70.01 (s, NCH CH O), 58.95 (s, NCH Si), 49.90 (s,
3
2
2
2
5 °C/min and again held 5 min; step 3: cooling from 20 °C to – NCH CH O), 42.39 (s, OCH ), 1.73 (s, Si(CH ) ), –1.18 (s,
2
90 °C at a rate of 5 °C/min and held for 5 min; step 4: heating Si(CH ) ). Si { H}, CDCl ) δ ppm: not detected (s, Si(CH ) ),
2
3
3 2
29
1
3 3
from –90 °C to 20 °C at a rate 5 °C/min. These ILs were 2.86 (s, Si(CH ) ).
3
3 2
19
( F CDCl ) δ ppm: –78.91 (s, CF ). MS m/z
3 3
3 3
thermally annealed by repeatedly cycling and/or holding the (EI): 552.25, 287.35, 271.10, 257.80, 229.35, 183.74, 141.10,
samples at sub-ambient temperatures for varying period of 140.10, 83.10. IR (neat): 3150.9 w, 2959.2 w, 1562.7 w, 1350.4
time to allow a complete crystallization. The heat capacity and m, 1184.6 s, 1053.6 s, 843.1 s.
heat flow were calculated from TOPEM®, a temperature-
1-(2-(2-methoxyethoxy)ethyl)-3-((1,1,3,3,3-
modulated DSC technique by using a heating method –90 °C to
pentamethyldisiloxanyl)methyl)-1H-imidazol-3-ium
60 °C at a rate of 2 °C/min. The temperature-modulated DSC
bis((trifluoromethyl)sulfonyl)amide (2): The reaction/workup
(TOPEM®) technique allows non-reversing effect i.e. kinetic
given for
1 was repeated with 2a (8.129 g, 17.73 mmol), LiTFSI
events such as reorganization, crystallization, crystal
perfection, cure, decomposition and stress relaxation to be
separated from reversing effect such as glass transition.
(6.108 g, 21.28 mmol), and 25 mL of acetone. This gave
2 as
light yellow oil (9.767 g, 15.97 mmol, 90%).
1
NMR: ( H, CDCl ) δ ppm: 8.71 (s, 1H, NCHN), 7.47 (t, 1H, J=1.8
3
Hz, NCHC), 7.13 (t, 1H, J=1.8 Hz, NCHC), 4.36 (t, 2H, J=4.54 Hz,
Syntheses.
NCH CH ), 3.78 (t, 2H, J=4.56 Hz, NCH CH ), 3.74 (s, 2H,
2
2
2
NCH Si), 3.62 (m, 2H, OCH CH ), 3.52 (m, 2H, OCH CH ), 3.35
2
In a typical synthetic procedure for preparation of ionic liquid
1O2O2-Im-2O1 TFSI (3) as an example. A mixture of N-alkoxy
imidazole (2b), 1O2-I (10) and acetonitrile prepared in Ar/N2
atmosphere was transferred into microwave Teflon vials. The
sample was microwave irradiated by controlled temperature
programming at 150 °C by 2 min ramp and held for 40 min at
150 °C, under a limiting pressure of 18 bar and 500 W power.
The reaction progress was monitored by TLC, and 1H NMR.
After completion of reaction, concentrate the reaction mixture
via rotavac. A viscous precipitate was obtained by drop wise
addition of residue in cold ether. The biphasic system was kept
at 0 °C for 2 h. Ether layer was decanted and the residue
washed with cold ether (50 mL × 3). The yellow viscous liquid
was subsequently dried in vacuum at 60 °C. The obtained
product was then placed for anion exchange with LiTFSI at
ambient temperature in acetone. After completion of reaction
the product was washed with water (40 mL × 5) and the halide
ion concentration was anticipated by AgNO3 test. The color
2
(s, 3H, OCH ), 0.21 (s, 6H, Si(CH ) ), 0.08 (s, 9H, Si(CH ) ).
2
2
2
2
13
( C
3
3 2
3 3
{ H}, CDCl ) δ ppm: 135.7 (s, NCHN), 123.4 (s, NCHCHN), 122.6
1
3
(s, NCHCHN), 119.9 (q, J=321.1 Hz, (CF )), 71.6 (s, NCH Si), 70.3
3
(s, NCH CH O), 68.8 (s, NCH CH O), 59.0 (s, OCH CH O), 49.8
2
2
2
2
2
2
2
(s, OCH CH O), 42.5 (s, OCH ), 1.8 (s, Si(CH ) ), –1.1 (s,
2
Si(CH ) ).
2
3
3 2
29
1
( Si { H}, CDCl ) δ ppm: 6.55 (s, Si(CH ) ), 2.93 (s,
3 3 2
3 3
Si(CH ) ).
19
( F CDCl ) δ ppm: –78.19 (s, CF ). MS m/z (EI):
3 3
3 3
332.25, 331.25, 185.05, 154.10, 147.05, 96.00. IR (neat):
3150.6 w, 2959.3 w, 1562.5 w, 1350.3 m, 1183.3 s, 1052.7 s,
842.7 s.
1-(2-(2-methoxyethoxy)ethyl)-3-(2-methoxyethyl)-1H-
imidazol-3-ium bis((trifluoromethyl)-sulfonyl)imide (3): The
reaction/workup given for
1 was repeated with 3a (7.383 g,
20.72 mmol), LiTFSI (6.545 g, 22.79 mmol) and 25 mL of
acetone. This gave
3 as light yellow oil (7.290 g, 14.31 mmol,
69%).
1
NMR: ( H, CDCl ) δ ppm: 8.80 (s, 1H, NCHN), 7.46 (t, J=1.7 Hz,
3
1H, NCHCHN), 7.38 (t, J=1.7 Hz, 1H, NCHCHN), 4.37 – 4.34 (m,
impurity was removed by activated charcoal. Ionic liquid
1 and
2
containing siloxane and ether substituent has been prepared
4H, N(CH ) CH O), 3.84 (t, J=4.7 Hz, 2H, NCH CH OCH ), 3.71
2
2 2
(t, J=4.7 Hz, 2H, NCH CH OCH ), 3.66
2
2
3
3.63 (m, 2H,
similarly starting from 2b. The detailed procedure is given
–
2
2
OCH CH O), 3.53 – 3.51 (m, 2H, OCH CH O), 3.37 (s, 3H,
2
under preparation method.
2
NCH CH OCH ), 3.36 (s, 3H, OCH CH OCH ).
2
2
2
1-(2-methoxyethyl)-3-((1,1,3,3,3-
13
1
(
C { H},
2
CDCl ) δ ppm: 136.34 (s, NCHN), 122.99 (d, J=25.6 Hz,
2
3
2
2
3
pentamethyldisiloxanyl)methyl)-1H-imidazol-3-ium
3
NCHCHN), 119.88 (q, J=321.6 Hz, CF ), 71.63 (s), 70.37 (s),
bis((trifluoromethyl)sulfonyl)amide (1):
A RB flask was
3
69.98 (s), 68.66 (s), 59.07 (s), 50.03 (d, J=21.0 Hz, O(CH ) ).
charged with 1a (7.202 g, 17.38 mmol), LiTFSI (5.987 g, 20.85
mmol), and 25 mL of acetone. The reaction mixture was stirred
at ambient temperature for 24 h. Acetone was then
evaporated at reduced pressure. The product was washed with
cold water (5 mL × 4) and dried under high vacuum at 50 °C for
3 2
F CDCl ) δ ppm: 78.85 (s, CF ). MS m/z (EI): 229.20, 154.10,
3 3
19
(
140.10, 126.26, 59.56. IR (neat): 3153.9 w, 2938.2 w, 2883.6
w, 2822.8 w, 1564.9 w, 1453.6 w, 1349.1 m, 1181.4 s, 1133.3 s,
1053.4 s.
4 h to afford
1 (8.973 g, 15.81 mmol, 91%). Colour impurities
1-((1,1,3,3,3-pentamethyldisiloxanyl)
methyl)
-3-
bis
were removed by activated charcoal; anion exchange and
iodide removal was confirmed by AgNO3 test and chemical
((trimethylsilyl) methyl) -1H-imidazol-3-ium
shift of δHC2 in 1H and 19F NMR.
((trifluoromethyl) sulfonyl)amide (4): The reaction/workup
given for was repeated with 4a (9.294 g, 21.00 mmol), LiTFSI
1
1
NMR: ( H, CDCl ) δ ppm: 8.55 (s, 1H, NCHN), 7.42 (t, J=1.5 Hz,
3
1H, NCHCHN), 7.16 (t, J=1.6 Hz, 1H, NCHCHN), 4.33 (t, J=4.5 Hz,
(7.234 g, 25.2 mmol), and 30 mL of acetone. This gave
4 as
light yellow oil (11.761 gm, 19.74 mmol, 94%).
1
2H, NCH CH O), 3.74 (s, 2H, NCH Si), 3.77 (t, J=4.5 Hz, 2H,
2
NCH CH O), 3.33 (s, 1H, OCH ), 0.18 (s, 6H, Si(CH ) ), 0.06 (s,
2
2
NMR: ( H, CDCl ) δ ppm: 8.65 (s, 1H, NCHN), 7.16 (t, J=1.7 Hz,
3
1H, NCHCHCN), 7.10 (t, J=1.7 Hz, 1H, NCHCHCN), 3.84 (s, 2H,
2
9H, Si(CH ) ).
2
3
3 2
13
1
( C { H}, CDCl ) δ ppm: 135.48 (s, NCHN),
3
3 3
8 | J. Name., 2012, 00, 1-3
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NCH SiO), 3.78 (s, 2H, NCH Si), 0.18 (s, 6H, Si(CH ) ), 0.13 (s, reaction/workup given for 1a was repeated with 2b (4.058 g,
3 2
2
9H, OSi(CH ) ), 0.09 (s, 9H, Si(CH ) ).
2
13
1
( C { H, CDCl } δ ppm: 23.50 mmol), 2-methoxyethyl 4-methylbenzenesulfonate (8,
3
134.5 (s, NCHN), 123.1 (d, J=11.0 Hz, NCHCHCN), 119.88 (q, J 4.743 g, 25.50 mmol) and 30 mL acetonitrile. This gave 3a
3 3
3 3
=321.2 Hz, CF ), 42.2 (s, NCH SiO), 41.8 (s, NCH Si), 1.7 (s, (7.617 g, 21.38 mmol, 91% yield) as yellow viscous liquid.
2
3
Si(CH ) ), –1.3 (s, OSi(CH ) ), –3.3 (s, Si(CH ) ).
2
29
1
1
( Si { H}, NMR: ( H, CDCl ) δ ppm: 9.76 (s, 1H, NCHN), 7.61 (s, 1H,
3
3 2
CDCl ) δ ppm
3 3 3 3
3.61 (s, OSi(CH ) ), 3.04 (s, OSi(CH ) ), not NCHCHN), 7.53 (s, 1H, NCHCHN), 4.58
19
:
–
4.51 (m, 4H,
3
detected (CH -Si(CH ) ).
3 2 3 3
( F CDCl ) δ ppm: –78.77 (s, CF ). N(CH ) CH O), 3.97 (m, 2H, NCH CH OCH ), 3.78 (m, 2H,
2
MS m/z (EI): 329.23, 263.12, 229.45, 154.12, 125.56, 99.23, NCH CH OCH ), 3.67 – 3.64 (m, 2H, OCH CH O), 3.53 – 3.49
3 3
3
3
2 2
2
2
2
3
2
2
2
2
2
57.01, 51.23 IR (neat): 3146.5 b, 2960.9 w, 1559.7 w, 1350.3 (m, 2H, OCH CH O), 3.36 (s, 3H, NCH CH OCH ), 3.35 (s, 3H,
2
2
2
2
3
13
1
m, 1184.7 s, 1135.6 m, 1052.7 s, 841.8 b.
OCH CH OCH ). ( C { H}, CDCl ) δ ppm: 136.7 (s, NCHN),
2 2 3 3
122.9 (d, J=23.7 Hz, NCHCHN), 71.6 (s), 70.3 (d, J=26.5 Hz), 68.8
(s), 59.1 (d, J=11.4 Hz), 50.0 (d, J=21.2 Hz).
1-(2-methoxyethyl)-3-((1,1,3,3,3-
pentamethyldisiloxanyl)methyl)-1H-imidazol-3-ium
iodide
(1a): A mixture of 1b (4.002 g, 31.69 mmol),
mmol) and 30 mL acetonitrile prepared in inert atmosphere pentamethyldisiloxanyl)methyl)-1H-imidazol-3-ium
was transferred into 100 mL microwave Teflon vials. The (4a): The reaction/workup given for 1a was repeated with 4b
reaction mixture was microwave irradiated with controlled (3.548 g, 23 mmol), (7.963 g, 27.60 mmol) and 30 mL of
6 (10.963 g, 38.03 1-(trimethylsilyl)-3-((1,1,3,3,3-
iodide
6
temperature programming of 150 °C within 2 min ramp and acetonitrile. This gave 4a (8.94 g, 20.24 mmol, 88% yield) as
then held for 40 min at 150 °C, with pressure limit 18 bar, and yellow viscous liquid.
1
max power limit of 500 W. The reaction progress was NMR: ( H, CDCl ) δ ppm: 9.92 (s, 1H, NCHN), 7.18 (d, J=1.4 Hz,
1
3
monitored by H NMR after collecting the sample from vials. 2H, NCHCHCN), 4.03 (s, 2H, NCH SiO), 3.96 (s, 2H, NCH Si),
2
After completion, the reaction mixture was concentrated in 0.22 (s, 6H, Si(CH ) ), 0.17 (s, 9H, OSi(CH ) ), 0.08 (s, 9H,
2
3 2
3 3
13
1
rotavac. The viscous precipitate was obtained upon drop-wise Si(CH ) ).
( C { H, CDCl ) δ ppm: 135.1 (s, NCHN), 122.8 (s,
3
addition of residue in 50 mL cold ether. The two phase system OSiNCHCHNSi), 122.7 (s, OSiNCHCHNSi), 42.5 (s, NCH SiO),
3 3
2
was kept at 0 °C for 2 h. The ether layer was decanted and the 42.0 (s, NCH Si), 1.9 (s, Si(CH ) ), –0.8 (s, OSi(CH ) ), –2.7 (s,
2
3 2
3 3
29
1
residue was washed with cold ether (50 mL × 3). The yellow CH Si(CH ) ).
( Si { H}, CDCl ) δ ppm: 3.61 (s, Si(CH ) ), 3.04
3 3 2
2
3 3
viscous liquid was dried in vacuum at 60 °C to give 1a (8.863 g, (s, OSi(CH ) ), –135.90 (s, Si(CH ) ).
3 3
3 3
21.39 mmol, 91%).
1
Microwave synthesis of bulk scale [BMIM]+ Br– (5a):
A
NMR: ( H, CDCl ) δ ppm: 9.66 (s, 1H, NCHN), 7.62 (s, 1H,
3
NCHCHN), 7.20 (s, 1H, NCHCHN), 4.58 (t, J=4.6 Hz, 2H,
mixture of 1-Methyl imidazole (164.200 g, 2000.00 mmol, d =
1.03) and n-Butyl bromide (411.660 g, 3004.38 mmol) were
mixed in 1000 mL RB flask and stirred for 30 min at ambient
temperature under N2 atmosphere. The reaction mixture was
transferred equally (~60 mL) into eight microwave Teflon vials
of 100 mL capacity containing a stir bar. The reaction mixture
was microwave irradiated with controlled temperature
programming of 150 °C within 2 min ramp and then held for 10
min at 150 °C, with a pressure limit 18 bar, and max power
limit of 900 W. The reaction progress was monitored by 1H
NCH CH O), 3.89 (s, 2H, NCH Si), 3.77 (t, J=4.8 Hz, 2H,
2
NCH CH O), 3.34 (s, 3H, OCH ), 0.21 (s, 6H, Si(CH ) ), 0.06 (s,
2
2
2
9H, Si(CH ) ).
2
3
3 2
13
1
( C { H}, CDCl ) δ ppm: 136.1 (s, NCHN), 123.2
3
(s, NCHCHN), 122.3 (s, NCHCHN), 70.3 (s, NCH CH O), 59.1 (s,
3 3
2
2
NCH Si), 50.0 (s, NCH CH O), 42.6 (s, OCH ), 1.9 (s, Si(CH ) ), –
2
2
0.6 (s, Si(CH ) ).
2
1
3
3 2
29
( Si { H}, CDCl ) δ ppm: 6.00 (s, Si(CH ) ),
3 3 2
3 3
3.05 (s, Si(CH ) ).
3 3
1-(2-(2-methoxyethoxy)ethyl)-3-((1,1,3,3,3-
pentamethyldisiloxanyl)methyl)-1H-imidazol-3-ium
iodide NMR and TLC (80/20 dichloromethane/methanol in silica gel).
(2a): The reaction/workup given for 1a was repeated with 2b The NMR was taken after 10 min from vial containing
(4.001 g, 23.50 mmol),
(8.133 g, 28.21 mmol), and 30 mL of immersion temperature probe. The 1H NMR shows clean
acetonitrile. This gave 2a (9.150 g, 19.96 mmol, 85% yield) as product along with n-BuBr which was used in excess (Figure
yellow viscous liquid. S6, SI). After completion, excess n-Butyl bromide was
6
1
NMR: ( H, CDCl ) δ ppm: 9.50 (s, 1H, NCHN), 7.67 (t, J=1.7 Hz, recovered (60.105 g, 438.66 mmol, 43.8% of 137.62 g excess of
3
1H, NCHCHN), 7.18 (t, J=1.7 Hz, 1H, NCHCHN), 4.52 (t, J=4.6 Hz, nBuBr) by decanting from the reaction mixture. The viscous IL
2H, NCH CH O), 3.82 (s, 2H, NCH Si), 3.82 (t, J=4.3 Hz, 2H, residue was evacuated in vacuum (1×10-3 mbar) at 50 °C for 2
2
NCH CH O), 3.58 – 3.55 (m, 2H, OCH CH O), 3.43 – 3.41 (m, h and more nBuBr of 45.374 g, 331.15 mmol were collected
2
2
2
2H, OCH CH O), 3.25 (s, 3H, OCH ), 0.14 (s, 6H, Si(CH ) ), – from the trap (total 77.0% of 137.62 g). The residue was
2
2
2
2
2
0.02 (s, 9H, Si(CH ) ).
3
3 2
13
1
( C { H}, CDCl ) δ ppm: 135.7 (s, washed with ethyl acetate (1×100 mL) to remove any high
3
3 3
NCHN), 123.2 (s, NCHCHN), 122.2 (s, NCHCHN), 71.4 (s, boiling organic impurity. The obtained brown colour product
NCH Si), 70.1 (s, NCH CH O), 68.7 (s, NCH CH O), 58.8 (s, was dried in vacuum at 60 °C for 5 h to give >98% yield (433.35
2
2
2
2
OCH CH O), 49.5 (s, OCH CH O), 42.4 (s, OCH ), 1.7 (s, g, 1977.68 mol, 98.9%). The pure IL solidifies at ambient
2
2
Si(CH ) ), –0.8 (s, Si(CH ) ).
2
2
2
3
29
1
( Si { H}, CDCl ) δ ppm: 6.38 (s, temperature.
3
3 2 3 3
Si(CH ) ), 2.86 (s, Si(CH ) ).
1
NMR: ( H, CDCl ) δ ppm: 10.17 (s, 1H, NCHN), 7.60 (s, 1H,
3
NCHCHCN), 7.23 (s, 1H, NCHCHCN), 4.23 (t, J=7.4 Hz, 2H), 4.01
3 2
3 3
Preparation
of
1-(2-(2-methoxyethoxy)ethyl)-3-(2-
iodide (3a): The
(s, 3H), 1.79 (pent, J=12.8, 7.6 Hz, 2H), 1.26 (sext, J=14.8, 7.4
Hz, 2H), 0.83 (t, J=7.4 Hz, 3H).
methoxyethyl)-1H-imidazol-3-ium
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ARTICLE
Journal Name
Shirota, H. Y. Lee, C. S. Santos, N. S. Murthy, and E. W.
Castner, Jr., Chem. Commun. 2012, 48, 4959-4961.
23 Y. Jin, S. Fang, M. Chai, L. Yang, and S.-i. Hirano, Ind. Eng.
Chem. Res. 2012, 51, 11011-11020.
24 H. Shirota, J. F. Wishart, and E. W. Castner, J. Phys. Chem. B
2007, 111, 4819-4829.
25 Z. J. Chen, T. Xue, and J.-M. Lee, RSC Adv. 2012, 2, 10564-
Acknowledgements
This research is supported by the Department of Atomic
Energy (DAE), India (2013/37C/57/BRNS) for financial support
and Santosh Chavan thanks to UGC for Fellowship.
10574.
26 A. K. Burrell, R. E. D. Sesto, S. N. Baker, T. M. McCleskey, and
G. A. Baker, Green Chem. 2007, , 449-454.
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Trans. 2014, 43, 10023-10032; bA. Rout, K. Binnemans,
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10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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RSC Advances
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Journal Name
View Article Online
DOI: 10.1039/C5RA07466E
ARTICLE
[11]
[12]
J. Qu, D. G. Bansal, B. Yu, J. Y. Howe, H. Luo, S. Dai, H. Li, P. [36]
J. Blau, B. G. Bunting, G. Mordukhovich, D. J. Smolenski,
ACS Appl. Mater. Interfaces 2012, 4, 997-1002.
aA. Fernicola, B. Scrosati, H. Ohno, Ionics 2006, 12, 95-
102; bM. Galiński, A. Lewandowski, I. Stępniak,
Electrochim. Acta 2006, 51, 5567-5580; cM. Gorlov, L.
Kloo, Dalton Trans. 2008, 2655-2666.
N. Calvar, E. Gómez, E. A. Macedo, Á. Domínguez,
Thermochim. Acta 2013, 565, 178-182.
[13]
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Solvents, Vol. 6, Wiley/VCH, Weinheim, 2010, pp. 191-
201.
[14]
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M. J. Earle, K. R. Seddon, Pure Appl. Chem. 2000, 72, 1391-
1399.
[16]
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M. Armand, F. Endres, D. R. MacFarlane, H. Ohno, B.
Scrosati, Nat Mater 2009, 8, 621-629.
S. S. Mondal, H. Müller, M. Junginger, A. Kelling, U.
Schilde, V. Strehmel, H. J. Holdt, Chem. Eur. J. 2014, 20,
8170-8181.
[18]
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,
Z. Chen, S. Liu, Z. Li, Q. Zhang, Y. Deng, New J. Chem.
2011, 35, 1596-1606.
aL. J. A. Siqueira, M. C. C. Ribeiro, J. Phys. Chem. B 2009
,
113, 1074-1079; bA. Triolo, O. Russina, R. Caminiti, H.
Shirota, H. Y. Lee, C. S. Santos, N. S. Murthy, E. W.
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Y. Jin, S. Fang, M. Chai, L. Yang, S.-i. Hirano, Ind. Eng.
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H. Shirota, J. F. Wishart, E. W. Castner, J. Phys. Chem. B
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[25]
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Z. J. Chen, T. Xue, J.-M. Lee, RSC Adv. 2012, 2, 10564.
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aC. O. Kappe, A. Stadler, D. Dallinger, Microwaves in
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17-30; cV. V. Namboodiri, R. S. Varma, Tetrahedron Lett.
2002, 43, 5381-5383; dR. S. Varma, V. V. Namboodiri,
Chem. Commun. 2001, 643-644; eM. Deetlefs, K. R.
Seddon, Green Chem. 2003, 5, 181-186.
[28]
P. Bonhôte, A.-P. Dias, N. Papageorgiou, K.
Kalyanasundaram, M. Grätzel, Inorg. Chem. 1996, 35,
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[29]
[30]
C. A. Angell, Chem. Rev. 2002, 102, 2627-2650.
Z. Fei, W. H. Ang, D. Zhao, R. Scopelliti, E. E. Zvereva, S. A.
Katsyuba, P. J. Dyson, J. Phys. Chem. B 2007, 111, 10095-
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[31]
[32]
[33]
S. Bulut, M. A. Ab Rani, T. Welton, P. D. Lickiss, I. Krossing,
ChemPhysChem 2012, 13, 1802-1805.
C. P. Fredlake, J. M. Crosthwaite, D. G. Hert, S. N. V. K. Aki,
J. F. Brennecke, J. Chem. Eng. Data 2004, 49, 954-964.
J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D.
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D. M. Fox, W. H. Awad, J. W. Gilman, P. H. Maupin, H. C.
De Long, P. C. Trulove, Green Chem. 2003, 5, 724-727.
Y. Cao, T. Mu, Ind. Eng. Chem. Res. 2014, 53, 8651-8664.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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