Bifunctional Ionic Liquids for the Multitask Fixation of Carbon Dioxide into Valuable Chemicals

Article abstract of DOI:10.1002/cctc.201501044

A series of task-specific ionic liquids (ILs) such as mono-, dicationic, and polymer-supported ILs were synthesized. These ILs were applied as multitasking organocatalysts for transformations of carbon dioxide into valuable chemicals through a range of reactions, including (i) cycloaddition reactions of CO₂/CS₂ with epoxides to form cyclic carbonates and 1,3-oxathiolane-2-thiones, (ii) transesterification of cyclic carbonates with methanol to form dimethyl carbonate, and (iii) synthesis of quinazoline-2,4(1 H,3 H)-diones and quinazoline-2,4(1 H,3 H)-dithiones from 2-aminobenzonitriles and CO₂/CS₂. The developed methodology is transition-metal free, solvent free, and additive free. Remarkably, the developed ILs were recyclable in up to seven consecutive cycles; thus, making this protocol green and cost effective.

Full text of DOI:10.1002/cctc.201501044

DOI: 10.1002/cctc.201501044
Full Papers
Bifunctional Ionic Liquids for the Multitask Fixation of
Carbon Dioxide into Valuable Chemicals
Vitthal B. Saptal and Bhalchandra M. Bhanage*[a]
A series of task-specific ionic liquids (ILs) such as mono-, dicat-
ionic, and polymer-supported ILs were synthesized. These ILs
were applied as multitasking organocatalysts for transforma-
tions of carbon dioxide into valuable chemicals through
a range of reactions, including (i) cycloaddition reactions of
CO2/CS2 with epoxides to form cyclic carbonates and 1,3-oxa-
thiolane-2-thiones, (ii) transesterification of cyclic carbonates
with methanol to form dimethyl carbonate, and (iii) synthesis
of quinazoline-2,4(1H,3H)-diones and quinazoline-2,4(1H,3H)-
dithiones from 2-aminobenzonitriles and CO2/CS2. The devel-
oped methodology is transition-metal free, solvent free, and
additive free. Remarkably, the developed ILs were recyclable in
up to seven consecutive cycles; thus, making this protocol
green and cost effective.
Introduction
Excess of carbon dioxide from industrial processes and the
burning of fossil fuels in the atmosphere is the main cause of
global warming. Conversely, carbon dioxide is an abundant,
cheap, non-toxic, and renewable carbon source. In recent
years, the use of carbon dioxide as a sustainable C1 feedstock
for the synthesis of fine value-added chemicals has been
widely demonstrated.[1] The chemistry of carbon dioxide has
become one of the most important branches of chemistry.[1j]
The insertion of carbon dioxide as a raw material into epoxides
affords five-membered cyclic carbonates, which can serve as
monomers for polycarbonates and polyurethanes, polar aprotic
solvents, electrolytes in secondary batteries, and raw materials
in various reactions.[2]
attention; these have included functionalized ionic liquids,[8] si-
lanediols,[9] cyclodextrins,[10] bagasse,[11] alkanolamines,[12] cellu-
lose,[13] phenols,[14] fluorinated alcohols,[15] and formic acids.[16]
The presence of a hydrogen-bond-donor catalyst polarizes the
CÀO bond of the epoxide ring and also stabilizes the charge of
intermediates formed during cycloaddition reactions. However,
these reported catalytic systems are found to be effective for
the transformation of carbon dioxide into only one product.
Therefore, there is pressing need to develop an environmental-
ly friendly, sustainable, and highly efficient heterogeneous cat-
alyst for multitask conversion of carbon dioxide that operates
under mild reaction conditions.
Bifunctional 1,4-diazabicyclo[2.2.2]octane (DABCO)-based hy-
droxyl-functionalized ILs[17] present tunable properties such as
hydrogen-bond-donor ability as well as being basic in nature;
this bifunctional nature creates a co-operative effect for activa-
tion of the starting material. Herein, we report the synthesis of
tunable and task-specific ILs (Figure 1) and their catalytic appli-
cations for the fixation of carbon dioxide into various valuable
chemicals under mild reaction conditions. These functionalized
ILs were found to be highly efficient heterogeneous organo-
catalysts for the conversion of epoxides, cyclic carbonates, and
Ionic liquids (ILs) are ionic compounds (organic salts) with
poor coordination, which results in these materials being
liquid below 1008C, or even at room temperature. The use of
ILs in organic synthesis is considered a cutting-edge technolo-
gy because of their prominent features such as high thermal
and chemical stability, low vapor pressure, easy recyclability,
high solubility, and tunable properties.[3] It is well known that
ILs have the ability to capture carbon dioxide and convert the
carbon dioxide into a variety of materials.[4] In this context, the
design of task-specific ILs has attracted much attention in
recent years as they have the rare ability to capture carbon di-
oxide reversibly.[4a,f]
Various catalytic systems have been well documented for
the synthesis of cyclic carbonates including metal complexes,[5]
Schiff bases,[6] and ionic liquids.[7] Among them, the catalysts
bearing hydrogen-bond-donor moieties have attracted great
[a] V. B. Saptal, Prof. B. M. Bhanage
Institute of Chemical Technology
Nathalal parekh Marg, Matunga East
Mumbai, Maharashtra 400019, (India)
E-mail: bm.bhanage@gmail.com
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201501044.
Figure 1. Structures of the functionalized and polymer-supported ionic liq-
uids used as catalysts.
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2-aminobenzonitriles into cyclic carbonates, 1,3-oxathiolane-2-
thiones, dimethyl carbonate quinazoline-2,4(1H,3H)-diones,
and quinazoline-2,4(1H,3H)-dithiones. Additionally, the synthe-
sized polymer-supported ILs show interesting morphologies by
changing the basic substituent on the polymer. The synthe-
sized ILs were recyclable and give up to seven recycle uses
without loss of activity.
Results and Discussions
Characterization of ILs
The synthesized ILs (Figure 1) were characterized by using vari-
ous analytical techniques including Fourier-transform infrared
spectroscopy (FTIR), nuclear magnetic resonance spectroscopy
(NMR), scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDX), and thermogravimetric analysis
(TGA). The presence of hydroxyl functional groups such as pro-
pane diol (PDO) and hydroxyl ethanol (HE) in the synthesized
ILs were confirmed by FTIR, where a broad band was obtained
at approximately 3341 cmÀ1 (Figure S3a and b in the Support-
ing Information). The broad peaks at ꢀ3384 and ꢀ3372 cmÀ1
confirm the immobilization of DABCO and [DABCO–PDO][Br] IL
on the polymer (Figure S3a in the Supporting Information). In-
terestingly, the SEM images of the polymer-supported ILs
showed spherical morphology, but only once the basic sub-
stituent on the polymer had been altered (Figure 2). Initially,
the polymer (PS-Cl Merrifield peptide resin 2% cross-linked,
2.3 mmolClgÀ1) had a beaten ball-like morphology (Figure 2a),
which gets converted into a well-oriented spherical pearl-like
morphology after immobilization of tertiary amines such as 1-
methylimidazole (MIM), DABCO, and 4-dimethylaminopyridine
(DMAP) on the polymer (Figure 2b,c,d). The immobilization of
[DABCO][Br] IL on the polymer creates the holes and patches
on the sphere (Figure 2e). The synthesized polymer-supported
diol-functionalized IL was further characterized by using ele-
mental analysis through energy-dispersive X-ray spectroscopy
(EDX), which confirms the presence of bromine and chlorine el-
ements in the polymer (Figure 2 f). To avoid the contamination
of products as a result of degradation of catalyst, the thermal
stability of IL catalysts is very important; thus, the synthesized
ILs were further characterized by TGA. The ILs were found to
thermally stable up to 4008C (Figure 3).
Figure 2. SEM images of the polymer-supported ILs with different bases:
(a) PS-Cl, (b) [PS–MIM][Cl], (c) [Ps–DABCO][Cl], (d) [PS–DMAP][Cl], (e) [PS–
DABCO–PDO][Br–Cl], and (f) EDX data of [PS–DABCO–PDO][Br–Cl].
Initially, we applied these ILs as catalysts in the synthesis of
cyclic carbonates (Table 1). The cycloaddition reaction of pro-
pylene oxide (PO) with carbon dioxide to synthesis the propyl-
ene carbonate (PC) was chosen as a model reaction with the
synthesized ILs as catalyst (Table 1). In the absence of ionic liq-
uids, the formation of PC was not observed (entry 1, Table 1).
The use of [DABCO–PDO][Cl] as a catalytic system for the cy-
cloaddition reaction gave a moderate yield (entry 2, Table 1).
Interestingly, the use [DABCO–PDO][Br] led to the formation of
PC in good yield (entry 3, Table 1). No effect on the yield of PC
was noted when the reaction temperature was decreased to
110 8C (entry 4, Table 1). Surprisingly, a significant increase in
the yield of PC was noted when [DABCO–PDO][I] was used as
the catalyst (entry 5, Table 1). This may be due to the high nu-
Figure 3. Thermogravimetric analyses (TGA) of polymer-supported ILs, show-
ing the high stability up to 4008C.
cleophilicity of iodine. Next, the effect of mono-hydroxyl (etha-
nol) [DABCO–HE][Br] and di-hydroxyl [DABCO–DHE][Br–Br] (di-
cationic) ILs on the reaction system were studied, and they
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Furthermore, we studied the effect of catalyst loading. De-
creasing the amount of catalyst loading led to a decrease in
the yield of PC (entries 13–14, Table 1). The kinetic study shows
that 3 h was the optimum time for the synthesis of PC (Fig-
ure 4a). The effect of pressure of carbon dioxide plays a very
important role in accelerating the rate of the cycloaddition re-
action; 2 MPa CO2 pressure was the optimum pressure to
obtain excellent yields of PC. Pressure below 2 MPa only pro-
vided low yields. However, further increases in the pressure re-
sulted in no further increase in the yield of PC (Figure 4b).
Hence, 2 MPa of CO2 pressure and a reaction time of 3 h at
1008C and 0.100 g of catalyst loading were the optimal reac-
tion conditions for the synthesis of PC. The RTILs have higher
viscosity and slow down the mass transfer, which directly af-
fects the yield of reactions.
Table 1. Optimization of reaction parameters for the synthesis of propyl-
ene carbonate using ILs.[a]
Entry
IL
T
t
Conversion Selectivity
[8C] [h] [%][b]
[%][b]
1
2
3
4
5
6
7
8
–
120
120
120
110
110
110
110
110
110
110
110
6
6
6
3
3
3
3
3
3
3
3
3
3
3
3
1
–
60
93
91
99
99
96
86
80
83
98
98
76
58
98
92
–
99
99
99
99
99
99
99
99
99
99
99
99
99
99[8j]
99[8k]
[DABCO–PDO][Cl]
[DABCO–PDO][Br]
[DABCO–PDO][Br]
[DABCO–PDO][I]
[DABCO–HE][Br]
[DABCO–DHE][Br–Br]
[PS–DABCO][Cl]
[PS–MIM][Cl]
[PS–DMAP][Cl]
[PS–DABCO–PDO][Br–Cl]
[PS–DABCO–PDO][Br–Cl] 100
[PS–DABCO–PDO][Br–Cl] 100
[PS–DABCO–PDO][Br–Cl] 100
[HEBimBr]/EG[e]
9
10
11
12
13[c]
14[d]
15
16
After optimization of reaction conditions, we further extend-
ed this catalytic system to the synthesis of various cyclic carbo-
nates (Table 2). The developed method was applicable for the
synthesis of a variety of cyclic carbonates such as aliphatic, ali-
phatic cyclic, and aromatic carbonates with various substitu-
ents including F, Cl, and Br. All the substrates under the opti-
mized reaction conditions provided good to excellent yields
and selectivity towards the cyclic carbonates. Next, we exam-
ined this protocol for the cycloaddition reaction of epoxides
with carbon disulfide to 1,3-oxathiolane-2-thiones. Various ep-
oxides reacted with carbon disulfide and gave good yields of
1,3-oxathiolane-2-thiones (entries 10–13, Table 2).
140
120
[(CH2CH2OH)Bim]ZnBr3
[a] Reaction conditions: Propylene oxide (20 mmol), CO2 (2 MPa), IL
(0.1 g). [b] Yield and selectivity determined by GC. [c] IL 0.05 g. [d] IL
0.025 g. [e] HEBim: hydroxylethanol butylimidazole and EG: ethylene
glycol as HBD.
were also found to be effective (entries 6–7, Table 1). In the
next set of experiment, we studied the effect of polymer-sup-
ported ILs for cycloaddition reactions. Polymer-supported ILs
(PSIL) including DABCO, DMAP, 1-methylimidazole functionali-
ties, and dicationic, diol-functionalized, and DABCO-based ILs
were tested in the cycloaddition reaction and they were also
found to be reactive for this transformation (entries 9–12,
Table 1). The dicationic [PS–DABCO–PDO][Br–Cl] shows excel-
lent catalytic activity for the synthesis of PC at milder reaction
temperatures than the other polymer-supported ILs (en-
tries 11–12, Table 1).
To gain an insight into the multitask applications of the syn-
thesized ILs, we examined this catalytic system for the synthe-
sis of dimethyl carbonate (DMC) as this material is very impor-
tant in organic synthesis. DMC has drawn much attention as
a safe, eco-friendly building block for the production of poly-
carbonates and other chemicals.[18] Owing to its high dielectric
constant, DMC has applications as an electrolyte in lithium-ion
batteries[18b] and as an additive in fuels.[18c] For synthesis of
DMC, the two-step transesterification process (Table 3) utilizing
CO2 as a raw material[19] is considered as a more sustainable
method than other commercial processes, which involve the
Figure 4. (a) Kinetics of the cycloaddition of carbon dioxide with propylene oxide to make propylene carbonate by using ILs as the catalyst. (b) Effect of the
pressure of carbon dioxide on the synthesis of propylene carbonate.
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the DABCO-based ionic liquids for the transesterifica-
tion of cyclic carbonate. Under the general reaction
conditions, transesterification of ethylene carbonate
and methanol was first explored by using [DABCO–
PDO][Cl] as the catalytic system (ethylene carbonate
10 mmol, methanol 150 mmol, and ionic liquid 0.2 g,
at 808C).
Without the IL, only 7% of ethylene carbonate was
converted (entry 1, Table 3), whereas the functional-
ized IL [DABCO–PDO][I] gave the highest conversion
and yield of DMC (entry 4, Table 3). Next, we studied
the effect of various polymer-supported ILs to syn-
thesize DMC by using the optimized reaction condi-
tions (entries 6–9, Table 3). Among the polymer-sup-
ported ILs, the [PS–DABCO][Cl] gives the best yield
(entry 6, Table 3). This transesterification reaction of
ethylene carbonate and methanol was completed
easily, with excellent yield (93%).
Table 2. Substrate study for the synthesis of cyclic carbonates using ILs.[a]
Entry
Substrate
Product
Conversion
[%][b]
Selectivity
[%][b]
1
2
3
98
91
85
99
99
99
4
5
88
81
99
99
After the synthesis of cyclic carbonates and DMC,
we further extended the work of the DABCO-based
ILs for the synthesis of quinazoline-2,4(1H,3H)-
diones. Quinazoline-2,4(1H,3H)-diones synthesized
from carbon dioxide and 2-aminobenzonitrile
(Table 4) are gaining considerable attention as impor-
tant intermediates for the synthesis of pharmaceuti-
cals.[21]
6
7
8
9
95
89
81
83
99
99
99
99
Although, for this transformation, various catalytic
systems are reported, most of these require high
pressures and temperatures.[22] Hence, there is still
demand to develop a novel catalyst system that op-
erates at mild temperature and low pressure. The re-
actions of 2-aminobenzonitrile with carbon dioxide
were performed by using ionic liquid based catalysts
(Table 4). The reaction for the synthesis of quinazo-
line-2,4(1H,3H)-diones performed in the absence of
ILs resulted in negligible product formation (entry 1,
Table 4). The reaction with [DABCO–PDO][Cl] gave
a moderate yield owing to its highly viscous nature;
however, to our delight, addition of water to the IL
reaction mixture accelerated the rate of reaction,
which in turn increased the yield up to 92% (entry 3,
Table 4). Among the screened various ILs, [DABCO–
HE][Br] gave an excellent yield of up to 97% for the
synthesis of quinazoline-2,4(1H,3H)-diones. The
scope this protocol under the optimized reaction
conditions was further extended in a substrate study
of quinazoline-2,4(1H,3H)-diones and it was observed
that the developed system has wide functional
group tolerance, including methyl, chloro, and nitro
10[c]
11[c]
70
90
91
96
12[c]
13[c]
73
56
98
98
[a] Reaction conditions: Epoxide (20 mmol), CO2 (2 MPa), [Ps–DABCO–PDO][Br–Cl]
(0.1 g), 1008C, 3 h. [b] Determined by GC. [c] Epoxide (5 mmol), CS2 (6 mmol), THF
(1 mL), catalyst (0.025 g), 508C, 6 h.
use of toxic and corrosive phosgene.[20] Traditionally, for the
synthesis of DMC, basic catalysts were used to promote the
transesterification reaction of cyclic carbonate with metha-
nol.[19b,c] Encouraged by the above findings, we sought to as-
certain whether the developed ionic liquids have enough
active centers acting as basic sites to activate methanol as well
as hydrogen-bond-donor groups to polarize the cyclic carbon-
ate. Further, we have determined the reaction conditions in
functionalities on the aromatic ring, and gives good to excel-
lent yields (entries 9–11, Table 4). After the synthesis of quina-
zoline-2,4(1H,3H)-diones, we extended this catalytic protocol
to the synthesis of quinazoline-2,4(1H,3H)-dithiones (en-
tries 12–14, Table 4). The developed ILs were also capable of
synthesizing quinazoline-2,4(1H,3H)-dithone and provides
good yields.
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To ensure the reusability of the synthesized task-specific ILs,
we selected [PS–DABCO–PDO][Br–Cl] and [DABCO–PDO][I] as
model catalysts for the cycloaddition reaction of CO2 with pro-
pylene oxide to make propylene carbonate. The [PS–DABCO–
PDO][Br–Cl] and [DABCO–PDO][I] were found to be highly reac-
tive and could be recycled in up to seven cycles without loss
of catalytic activity (Figure 5).
Table 3. Transesterification of ethylene carbonate with methanol to syn-
thesis DMC using the ILs.[a]
Entry
IL
t
Conversion
[%][b]
DMC
[%][b]
[h]
1
2
3
4
5
6
7
8
9
–
5
4
4
4
4
6
6
6
6
7
91
96
98
94
70
50
53
60
7
81
88
93
91
63
45
44
50
[DABCO–PDO][Cl]
[DABCO–PDO][Br]
[DABCO–PDO][I]
[DABCO–HE][Br]
[PS–DABCO][Cl]
[PS–MIM][Cl]
Conclusions
We have developed a sustainable and novel catalytic concept
using heterogeneous ionic liquids for the multitask synthesis
of value-added chemicals from the greenhouse gas CO2. In this
report, we have established the first systematic investigation
focused on the multitask and comprehensive utilization of CO2,
which provides a novel and environmentally benign strategy
for the synthesis of important chemicals. The synthesized ILs
provide the following merits for chemical transformations of
CO2: i) simple and high-yielding method for the synthesis of
cyclic carbonates, which proceeded under additive-
[PS–DMAP][Cl]
[PS–DABCO–PDO][Br–Cl]
[a] Reaction conditions: Ethylene carbonate (10 mmol, 0.88 g), MeOH
(150 mmol, 6 mL), ILs (0.2 g), 808C. [b] Determined by GC based on EC
conversion.
as well as solvent-free conditions; ii) transesterifica-
tion of cyclic carbonate to synthesize DMC proceeds
at low temperature with excellent yields; iii) low pres-
sure and mild temperature required for synthesis of
quinazoline-2,4(1H,3H)-diones without any hazardous
solvents; iv) developed ILs can be easily separated
and recycled for up to seven cycles with excellent ac-
tivity. Additionally, the developed protocol is also ca-
pable of the insertion of carbon disulfide into 1,3-ox-
athiolane-2-thiones and quinazoline-2,4(1H,3H)-di-
thiones. This approach with functionalized ILs cataly-
sis is a promising strategy for the development of
highly efficient fixation of carbon dioxide into value-
added chemicals at very mild reaction conditions.
Table 4. Synthesis of quinazoline-2,4(1H,3H)-diones from carbon dioxide and 2-ami-
nobenzonitrile catalyzed by ILs.[a]
Entry
IL
Substrate
Product
Yield
[%][b]
1
2
–
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
–
30
92
94
91
97
33
[DABCO–PDO][Cl]
[DABCO–PDO][Cl]
[DABCO–PDO][Br]
[DABCO–PDO][I]
[DABCO–HE][Br]
[PS–DABCO][Cl]
3[c]
4[c]
5[c]
6[c]
8[c]
Experimental Section
All chemicals and reagents were purchased from firms of
repute in the highest purity available and were used
without further purification. Merrifield peptide resin (2%
cross linked, 2.3 mmolClgÀ1) was purchased from Sigma
Aldrich and used directly. The reactions for the synthesis
of quinazoline-2,4(1H,3H)-diones were monitored by
using thin layer chromatography with Merck silica gel 60
F254 plates. The yields for the cyclic carbonates as well
as DMC were confirmed by using PerkinElmer Clarus 400
gas chromatography equipped with a flame ionization
9[c]
[DABCO–HE][Br]
[DABCO–HE][Br]
[DABCO–HE][Br]
[DABCO–HE][Br]
[DABCO–PDO][I]
[DABCO–HE][Br]
88
92
10[c]
11[c]
12[d]
13[d]
14[d]
75
detector and
a
capillary column (elite-1, 30 m”
1a
1a
1a
83
0.32 mm”0.25 mm). The morphologies of the polymer-
supported ILs were examined by field-emission gun-
scanning electron microscopy (FEG-SEM) analysis using
a Tescan MIRA 3 model. The energy dispersive X-ray
spectrum (EDS) was recorded by using an INCA x-act
Oxford instrument (Model 51-ADD0007). Thermogravi-
metric analysis (TGA) was carried out by using a Perkin-
Elmer STA 6000. The isolated products were confirmed
by GC-MS, 1H NMR and 13C NMR spectroscopic tech-
niques. The properties of the GC-MS (Shimadzu QP 2010)
instrument (Rxt-17, 30 m”25 mm, film thickness 0.25 mm
67
trace
[a] Reaction conditions: 2-Aminobenzonitrile (2 mmol), ILs (1 g), 110 8C, 20 h, CO2
(2 MPa). [b] Isolated yields. [c] Water (6 mL). [d] 1a(2 mmol), CS2 (2.4 mmol), ILs (1 g),
508C, 20 h.
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synthesized ionic liquids (Table 3). The typical procedure was car-
ried out in a 100 mL stainless-steel autoclave with stirring at
600 rpm, equipped with an automatic temperature control system.
Ethylene carbonate (10 mmol) and methanol (6 mL) were added
with the ionic liquid (0.2 g), and heated to the specified tempera-
ture. After completion of the reaction, the reactor was cooled in
ice-cold water. In the case of the polymer-supported ILs, the reac-
tion mixture and catalyst were separated easily by simple filtration.
In the case of non-supported ILs, excess methanol and DMC were
separated under vacuum and ethylene glycol recovered by adding
ethyl acetate to the IL.
General method for the synthesis of quinazoline-
2,4(1H,3H)-diones
For the synthesis of quinazoline-2,4(1H,3H)-diones, the reaction
was carried out in a stainless-steel autoclave equipped with auto-
matic magnetic stirrer and temperature control system. The auto-
clave was charged with 2-aminobenzonitrile (2 mmol), ionic liquid
(1 g), and water (6 mL), then pressurized with carbon dioxide
(2 MPa) and heated at 110 8C for 20 h. After completion of the reac-
tion, the reactor cooled to room temperature and depressurized.
The solid product was obtained by simple filtration and the ionic
liquids were recovered by removing the water under vacuum.
Figure 5. Recyclability in the synthesis of cyclic carbonate from epoxide and
carbon dioxide using [PS–DABCO–PDO][Br–Cl] and [DABCO–PDO][I] as the
catalyst systems. Reaction conditions: propylene oxide (20 mmol), IL (0.1 g),
CO2 (2 MPa), 1008C, 3 h.
df) were: column flow=2 mLmin, at 1808C increasing to 2408C at
108CminÀ1. IR spectra were recorded with a Shimadzu IR Affinity-1,
Fourier-transform infrared spectroscopy (FTIR) was recorded on
1
a JASCO-FTIR-400 spectrometer. H and 13C NMR spectra were ob-
tained with a Bruker Avance 400 MHz NMR spectrometer with D2O
or DMSO as the solvent system.
General method for the synthesis of 1,3-oxathiolane-
2-thiones
In a typical experimental procedure, epoxide (5 mmol), IL (0.1 g),
THF (1 mL), and CS2 (6 mmol) were added in a Schlenk tube con-
taining a magnetic stirrer, and heated at 508C for 5 h. After com-
pletion of the reaction, the reaction mixture was cooled in ice-cold
water and the catalyst was separated from reaction mixture by fil-
tration. Any remained CS2 in the reaction mixture was removed by
using a vacuum pump and the product was confirmed by GC and
GCMS.
Synthesis of ILs
The various DABCO-based mono- and di-hydroxyl functionalized
mono- and dicationic ionic liquids were synthesized by alkylation
of DABCO with haloalcohols. The variation (exchange) of anion
was done by a simple anion exchange method (see Section S1 in
the Supporting Information). Four different polymer-supported
ionic liquids with various bases, comprised of tertiary amine
groups, were synthesized by alkylation of amines with polymer in-
cluding DABCO, DMAP, 1-methylimidazole. Diol-functionalized di-
cationic DABCO-based ILs were synthesized by using commercially
available polymer Merrifield peptide resin (2% cross linked,
2.3 mmolClgÀ1).
General method for the synthesis of quinazoline-
2,4(1H,3H)-dithiones
In a typical experimental procedure, 2-aminobenzonitrile (2 mmol),
CS2 (2.4 mmol), and ILs (1 g) were added to a Schlenk tube con-
taining a magnetic stirrer, and heated at 508C for 20 h. After com-
pletion of the reaction, the reaction mixture was cooled to room
temperature. The product and IL were separated by adding H2O.
The reactions were monitored by TLC.
General method for the synthesis of cyclic carbonates
The cyclic carbonate was synthesized by cycloaddition of carbon
dioxide with epoxides in the presence of the synthesized ionic liq-
uids (Table 1). All the reactions were carried out in a 100 mL stain-
less-steel autoclave with stirring at 600 rpm and equipped with an
automatic stirrer and temperature control system. In a typical reac-
tion procedure, the catalyst (0.1 g) was introduced into the reactor
containing propylene oxide (25 mmol) at room temperature and
then pressurized to 2 MPa of CO2 pressure and heated to a particu-
lar temperature. After completion of the reaction, the reactor was
cooled in an ice-cold water bath and then CO2 was released slowly.
The product was separated from the reaction mixture by simple fil-
tration and analyzed by GC analysis (PerkinElmer, Clarus 400, BP-10
GC column, 30 m”0.32 mm ID, film thickness 0.25 mm).
Acknowledgements
V.B.S. is greatly thankful to the University Grant Commission
(UGC), India for providing a Junior Research Fellowship (JRF).
Keywords: carbon dioxide
·
cycloaddition reaction
·
heterogeneous catalysis · ionic liquids · polymer
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Received: September 22, 2015
Revised: October 15, 2015
Published online on November 26, 2015
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