Polystyrene-bound diethanolamine based ionic liquids for chemical fixation of CO2

Article abstract of DOI:10.1016/j.tetlet.2012.03.058

Polystyrene-bound diethanolamine based ionic liquids (PS-DHEEAB and PS-THEAB) were synthesized and applied for the chemical fixation of CO ₂ into cyclic carbonates without any additional co-catalyst and solvent. The effect of the catalysts with different number of hydroxyl group in the cation of the IL on the reaction was systematically investigated. Highest activity and selectivity were achieved in the presence of polystyrene supported diethanolamine ethyl bromide (PS-DHEEAB) in comparison with other catalysts employed. The catalyst was tough in stability and also found to be extended to a variety of terminal epoxides and aziridines. The relationship between high catalytic reactivity and the -OH functional groups was proposed.

Full text of DOI:10.1016/j.tetlet.2012.03.058

Tetrahedron Letters 53 (2012) 2684–2688
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Polystyrene-bound diethanolamine based ionic liquids for chemical fixation
of CO2
Xi Chen a,b, Jian Sun a, Jinquan Wang a, Weiguo Cheng a,
⇑
a Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences,
Beijing 100190, PR China
b Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Polystyrene-bound diethanolamine based ionic liquids (PS-DHEEAB and PS-THEAB) were synthesized
and applied for the chemical fixation of CO2 into cyclic carbonates without any additional co-catalyst
and solvent. The effect of the catalysts with different number of hydroxyl group in the cation of the IL
on the reaction was systematically investigated. Highest activity and selectivity were achieved in the
presence of polystyrene supported diethanolamine ethyl bromide (PS-DHEEAB) in comparison with other
catalysts employed. The catalyst was tough in stability and also found to be extended to a variety of ter-
minal epoxides and aziridines. The relationship between high catalytic reactivity and the –OH functional
groups was proposed.
Received 6 December 2011
Revised 12 March 2012
Accepted 20 March 2012
Available online 24 March 2012
Keywords:
Cyclic carbonate
Ionic liquids
Polystyrene resin
Diethanolamine
Ó 2012 Elsevier Ltd. All rights reserved.
Cyclic carbonates, which can serve as excellent aprotic polar
solvents and extensively as intermediates in the production of
pharmaceuticals and fine chemicals, have drawn much more atten-
tion recently.1 Their current synthesis routes by cycloaddition of
CO2 to epoxides are regarded as an effective way of utilizing CO2
as a Cl resource (Scheme 1).1
Diethanolamine and its N-substituted derivatives, which are
currently used for CO2 industrial absorption,10 could also serve as
valuable intermediates,11 group protective agent,12 and excellent
ligand for organometallic catalysts.13 However, studies on the uti-
lization of diethanolamine based ILs for chemical fixations of CO2
to produce cyclic carbonates are scarce. The synthesized ILs con-
tains a large amount of –OH groups that may show excellent activ-
ity with respect. Herein, we report the first examples of supported
diethanolamine based ILs for the synthesis of cyclic carbonates.
Polystyrene resin was chosen as a support due to its high mechan-
ical and chemical stability as well as good anti-swelling properties
in various solvents.14 Based on the comparison in activity and
stability of ClÀ, BrÀ, and IÀ in our previous work,5 BrÀ was chosen
as the best anion of the IL catalysts. The corresponding catalyst
structures (PS-DHEEAB and PS-THEAB) were described in Scheme 2.
The synthesis procedures of the catalysts were illustrated in
Various catalysts have been employed for this transfor-
mation.2–8 Among which, ionic liquids (ILs) and their immobiliza-
tion catalysts are especially highlighted.3–6 This is because that
as a novel substitute, ILs can be tailored by designing functional
groups in their cations or anions to adapt different applications.9
Besides, ILs can also be chemically immobilized onto solid supports
such as silica, molecular sieves, chitosan, and polystyrene (PS) re-
sin with the advantages of high activity and separability. Among
the above functionalized groups, –OH group is widely investigated
for enhancing the activity of catalysts for the synthesis of cyclic
carbonates.3–6 Our recent works proposed that –OH group in the
ILs could exhibit a positive behavior on the ring opening of epox-
ides.5 This effect combined with the nucleophilic synergetic effect
of halide anion could make the cycloaddition reaction proceed
smoothly.5 Since most natural building blocks, such as carbohy-
drates, amino acids, and nucleic acids, offer a rich source of H-bond
donors, hydrogen bonding resulted in many diverse and flexible
‘platform’ to establish a highly effective catalytic system.
Scheme 315–17
.
Using propylene oxide (PO) as a model substrate, the activities
of the synthesized catalysts on the synthesis of propylene carbon-
ate (PC) were investigated without any additional Lewis acid re-
agent and solvent18. For comparison, we also investigated the
O
Cat.
O
O
+
CO2
R
O
T,P
R
R = H, CH3, C4H9, C6H13, CH2Cl, Ph, etc
⇑
Corresponding author. Tel./fax: +86 10 8262 7080.
E-mail address: wgcheng@home.ipe.ac.cn (W. Cheng).
Scheme 1. Synthesis of cyclic carbonates from CO2 and epoxides.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.058

X. Chen et al. / Tetrahedron Letters 53 (2012) 2684–2688
2685
OH
R
N+
=
Br-
R = CH2CH3
PS-DHEEAB
R = CH2CH2OH PS-THEAB
OH
Scheme 2. Structures of PS-DHEEAB and PS-THEAB.
OH
+
N
-
Br
Br
OH
OH
OH
OH
PS-DHEEAB
a: Acetonitrile, 80oC, 24h
b: Toluene, 80oC, 24h
HN
+
N
Cl
OH
+
OH
OH
N
HO
Br
-
Br
PS-DHEA
OH
PS-THEAB
Scheme 3. Synthesis procedure of PS-DHEEAB and PS-THEAB.
activities of the corresponding homogeneous IL (DHEDEAB) and
the catalysts we synthesized in our previous work (PS-HEIMB
and PS-EIMB).5 All of the PS supported IL catalysts were used with-
out grinding (particle size: 1 mm, 18 mesh). The structures of the
PS supported IL catalysts are shown in Scheme 4, and the corre-
sponding results are listed in Table 1.
OH
OH
N+
N+
OH
Br-
Br-
OH
OH
PS and diethanolamine (Table 1, entries 1 and 2) are ineffective
catalysts as respected. DHEDEAB (entry 3), which was the homoge-
neous state of PS-DHEEAB, showed excellent activity. The main
reason for this was that the homogenous IL had a better miscibility
in the substrate. The catalytic activities of PS-DHEEAB (entry 4), PS-
THEAB (entry 7) and PS-HEIMB (entry 8), which have different
number of –OH groups, were also investigated in our experiment.
PS-DHEEAB and PS-THEAB showed higher activities than PS-
HEIMB, which may be due to the role of more –OH groups in the
ring opening of epoxides. PS-THEAB showed a little lower activity
than PS-DHEEAB, which possibly because that the two –OH groups
in the cation of PS-DHEEAB could form two hydrogen bonding ef-
fect with the O atom of the epoxide, which was calculated by
molecular simulation in our previous work,5 by which the ring
opening of epoxide could be promoted. This similar effect could
also be found in the other work.8a However, the excess –OH group
in the cation of PS-THEAB might prefer to form intramolecular
hydrogen bond with halide anion, by which the nucleophilic
behavior of the anion was weakened.19 The catalytic activity of
PS-EIMB (entry 9) was significantly lower than that of the –OH
containing catalysts, and it further proved the synergistic catalysis
role of –OH groups.
PS-THEAB
PS-DHEEAB
OH
N+
N+
Br-
N
N
Br-
PS-HEIMB
PS-EIMB
Scheme 4. Structures of the PS supported IL catalysts.
Table 1
Synthesis of PC catalyzed by different catalystsa
Entry
Catalyst
Conversionb (%)
Selectivityb (%)
1
2
3
4
5
6
7
8
9
PS
—
4
—
99
99
99
99
99
99
99
99
Diethanolamine
DHEDEAB
PS-DHEEAB
PS-DHEEABc
PS-DHEEABd
PS-THEAB
PS-HEIMB
PS-EIMB
86
69
92
99
65
52
35
According to the above results, a proposed mechanism was
exhibited in Scheme 5. As proposed in Scheme 5, the coordination
of H atoms in the –OH groups with the O atom of the epoxide
through a hydrogen bond resulted in the polarization of C–O
bonds, and the Br anion made a nucleophilic attack on the less ste-
rically hindered carbon atom of the epoxide at the same time. As a
a
Reaction conditions: PO (0.1 mol), catalyst (2.0 mmol), temperature: 110 °C,
CO2 pressure: 2.0 MPa, reaction time: 2 h.
b
Determined by GC.
Reaction time: 3 h.
Reaction time: 4 h.
c
d

2686
X. Chen et al. / Tetrahedron Letters 53 (2012) 2684–2688
O
H
R
N+
O
O
R
O
H
Br-
2.
1.
R
O-
H
OH
OH
O
Br
N+
N+
Br-
O
O
H
H
O-
O
O
O
O
R
4.
3.
O
N+
Br
CO2
R
O
H
Scheme 5. Proposed mechanism.
result, the ring of the epoxide was opened easily. Then, the interac-
tion occurred between the oxygen anion and CO2, forming an alkyl-
Table 2
Synthesis of other products catalyzed by PS-DHEEABa
carbonate anion which would be transformed into
a cyclic
Time Conversionb Selectivityb
carbonate by the intramolecular substitution of the halide in the
next step. From the viewpoint of exhibiting improved yield of PC,
increased number of –OH groups might reinforce the ring opening
effect.
Entry Substrate
Product
(h)
(%)
(%)
O
O
O
O
Due to the high activity and selectivity for the coupling reaction
of PO and CO2, PS-DHEEAB was used for further investigation. In
the recycling experiment, we used PS-DHEEAB for six times. As
shown in Figure 1, no significant decrease in PO conversions and
selectivity for six repeated runs indicates the high stability of the
catalyst.
The highly efficient PS-DHEEAB catalyst was also found to be
extended to a variety of terminal substrates under the optimal
reaction conditions, including epoxides and aziridines20. The re-
sults are summarized in Table 2. Aromatic 1a, 1b, 1c, 1d, and 1e
O
1
2
99
99
1a
2a
O
O
O
O
O
2
4
3
99
99
99
99
1b
2b
O
Cl
O
O
3
Cl
1c
2c
PO conversion
O
PC selectivity
100
O
(
O
(
)
5
4c
6
6
99
96
99
99
)
5
1d
80
60
40
20
0
2d
O
O
O
Ph
O
O
O
5
1e
Ph
2e
O
O
6c
24
87
99
1
2
3
4
5
6
1f
Runs
2f
Figure 1. Recycling experiments for PS-DHEEAB. Reaction conditions: PO (0.1 mol),
catalyst (2.0 mmol), temperature: 110 °C, CO2 pressure: 2.0 MPa, reaction time: 3 h.

X. Chen et al. / Tetrahedron Letters 53 (2012) 2684–2688
2687
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Table 2 (continued)
Entry Substrate
Product
Time Conversionb Selectivityb
(h)
(%)
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O
O
N
N
O
O
7d
0.5 99
97e
Ph
Ph
Ph
1g
2g
N
N
8d
2
99
98f
Ph
1h
2h
a
Reaction conditions: epoxides (0.1 mol), catalyst (2.0 mmol), 110 °C, CO2
2.0 MPa.
b
Determined by GC.
Reaction temperature: 120 °C.
Reaction temperature: 50 °C.
c
d
e
f
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epoxides were the preferred substrates for the reaction and these
reactions could be completed in less than 6 h. While 1f, which
needs 24 h to reach 87% yield due to the higher hindrance origi-
nated from the two rings. The selectivity of all the reactions to
the cyclic carbonates was more than 99%. The catalyst also showed
excellent activity to the reactions of 1g, 1h aziridines and CO2 to
produce 5-aryl-2-oxazolidinones. The reactions could be processed
at mild conditions to achieve high conversion and regioselectivity.
In conclusion, a series of PS-bound diethanolamine based ionic
liquids were developed and used for the synthesis of cyclic carbon-
ates under mild conditions without any co-catalyst and any co-sol-
vents. Catalysts with different number of hydroxyl groups in the
cation of the IL had a remarkable influence on the reaction. Among
all the supported IL catalysts investigated, PS-DHEEAB was the
most effective. The catalyst could be applicable to a series of termi-
nal epoxides and aziridines with good activities. Moreover, the cat-
alyst could be recycled for six times without significant loss in
activity and selectivity. The result of this work is an example of
the application of diethanolamine based ILs as environmentally be-
nign alternatives in organic synthesis and catalysis.
15. Typical synthesis procedure of hydroxyl-functionalized ionic liquids: (a) For the
synthesis of PS-DHEEAB,
a mixture of PS (10.0 g, 53.4 mmol, 18.05% Cl
content), diethanolamine (5.6 g, 53.5 mmol) and acetonitrile (50 mL) was
heated at 80 °C for 24 h in a 125 mL three-necked flask with vigorous stirring.
After cooled down to room temperature, the solid residue was collected by
filtration and washed separately with water and acetone. Then, the solid was
dried under vacuum at 60 °C for 12 h and PS-DHEA was obtained. The loading
of diethanolamine attached on the PS was 3.7 mmol/g determined by nitrogen
content from elementary analysis (Vario EL, Elementar Analysensysteme
GmbH), 98% of the –Cl was reacted through the calculation. (b) Bromoethane
(5.9 g, 54.1 mmol), PS-DHEA (10.0 g) and acetonitrile (70 mL) were added into
a 125 mL three-necked flask equipped with a magnetic stirrer, the mixture was
heated at 80 °C for another 24 h. After reaction, the reaction mixture was
cooled down to room temperature. The liquid phase was poured off, and the
solid residue was washed with ethyl acetate three times. Then, the solid was
dried under vacuum at 60 °C for 12 h and PS-DHEEAB was obtained. Based on
the similar procedure, PS-THEAB was synthesized respectively, using 2-
bromoethanol instead of bromoethane.
Acknowledgments
16. The amount of ionic liquid attached on the PS was determined from elemental
analysis: PS-DHEEAB (loading, 2.6 mmol/g), PS-THEAB (loading, 2.6 mmol/g),
PS-HEIMB (loading, 3.2 mmol/g), and PS-EIMB (loading, 3.2 mmol/g).
17. FT-IR spectroscopic studies were firstly carried out with PS-DHEEAB, support
PS and the active specie DHEDEAB. The results were compared with those of
the corresponding monomeric analogues. The samples were dried over
phosphorus pentoxide under vacuum at 70 °C for 48 h before detecting. Both
DHEDEAB and PS-DHEEAB display a typical strong peak corresponding to –OH
stretching frequency centered at about 3420 cmÀ1, and a typical peak centered
at 1265 cmÀ1 in PS corresponding to the stretching frequency of the functional
group –CH2Cl disappears in the spectra of PS-DHEEAB, suggesting the complete
modification of PS.
This work was supported by the National Basic Research Pro-
gram of China (2009CB219901), and the National Science Fund of
China (21006117 and 20936005). The authors gratefully acknowl-
edge Professor Suojiang Zhang for his guidance and meaningful
discussion in this work.
References and notes
18. Cycloaddition procedure for the reaction of propylene oxide (PO) with CO2: All the
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2008, 1, 236–241; (d) Melendez, J.; North, M.; Pasquale, R. Eur. J. Inorg.
Chem. 2007, 3323–3326.
coupling reactions were conducted in
a 100 mL stainless-steel reactor
equipped with a magnetic stirrer and automatic temperature control system.
A typical reaction was carried out as follows: In the reactor, an appropriate CO2
(ꢀ1.0 MPa) was added to a mixture of PO (7.0 mL, 0.1 mol), and catalyst
(2.0 mmol) at room temperature. Then, the temperature was raised to 110 °C
with the addition of CO2 from a reservoir tank to maintain a constant pressure
(2.0 MPa). After the reaction had proceeded for 2.0 h, the reactor was cooled to
ambient temperature, and the remaining CO2 and PO were removed and
absorbed in the saturation solution of Na2CO3. The catalyst was separated by
filtration, and the products were isolated and analyzed by Agilent 6890/5973
GC–MS equipped with a FID detector and a DB-wax. The catalyst was washed
3. (a) Wong, W. L.; Cheung, K. C.; Chan, P. H.; Zhou, Z. Y.; Lee, K. H.; Wong, K. Y.
Chem. Commun. 2007, 2175–2177; (b) Wong, W. L.; Chan, P. H.; Zhou, Z. Y.; Lee,
K. H.; Cheung, K. C.; Wong, K. Y. ChemSusChem 2008, 1, 67–70; (c) Haak, R. M.;

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X. Chen et al. / Tetrahedron Letters 53 (2012) 2684–2688
with acetone for three times and dried under vacuum for the recycling
experiment.
19. (a) Xie, H. B.; Zhang, S. B.; Li, S. H. Green Chem. 2006, 8, 630–633; (b)
Yamaguchi, M. J. Phys. Chem. A 2011, 115, 14620–14628.
77.49, 155.35 (C@O); Anal. Calcd for 2d: C, 62.77; H, 9.36; O, 27.87. Found: C,
62.70; H, 9.38; O, 27.92. 4-phenyl-1,3-dioxolan-2-one (2e): 1H NMR (CDCl3,
TMS, 400 MHz): 4.34 (t, J = 8.4 Hz, 1H); 4.80 (t, J = 8.4 Hz, 1H); 5.68 (t,
J = 8.0 Hz, 1H); 7.35–7.44 (m, 5H); 13C NMR (CDCl3, TMS, 100 MHz): 71.10,
77.92, 125.81, 129.12, 129.63, 135.70, 154.81 (C@O); Anal. Calcd for 2e: C,
65.85; H, 4.91; O, 29.24. Found: C, 65.72; H, 4.92; O, 29.36. 4,5-tetramethylene-
1,3-dioxolan-2-one (2f): 1H NMR (CDCl3, TMS, 400 MHz): 1.80–1.86 (m, 2H);
1.97–2.05 (m, 2H); 2.28 (d, J = 4.8 Hz, 4H); 5.06–5.11 (m, 2H); 13C NMR (CDCl3,
TMS, 100 MHz): 19.00, 26.61, 75.65, 155.27 (C@O); Anal. Calcd for 2f: C, 59.14;
H, 7.09; O, 33.77. Found: C, 59.06; H, 7.14; O, 33.80. 3-Ethyl-5-phenyloxazolidin-
2-one (2g): 1H NMR (400 MHz, CDCl3) d 1.19 (t, J = 9.2 Hz, 3H), 3.30–3.51 (m,
3H), 3.89 (t, J = 11.5 Hz, 1H), 5.47 (t, J = 6.9 Hz, 1H), 7.33–7.40 (m, 5H); 13C NMR
(100 MHz, CDCl3) d 12.7, 39.0, 51.7, 74.4, 125.6, 129.0, 129.2, 138.7, 157.8;
Anal. Calcd for 2g: C, 69.09; H, 6.85; N, 7.32; O, 16.73. Found: C, 68.92; H, 6.95;
N, 7.28; O, 16.85. 3-Isopropyl-5-phenyloxazolidin-2-one (2h): 1H NMR
(400 MHz, CDCl3) d 1.16 (d, J = 9.2 Hz, 3H), 1.21 (d, J = 9.0 Hz, 3H), 3.40 (t,
J = 6.0 Hz, 1H), 3.89 (t, J = 11.4 Hz, 1H), 4.11–4.22 (m, 1H), 5.48 (t, J = 10.5 Hz,
1H), 7.34–7.40 (m, 5H); 13C NMR (100 MHz, CDCl3) d 20.0, 21.0, 41.6, 48.5, 74.4,
125.5, 128.3, 128.8, 138.7, 158.3; Anal. Calcd for 2h: C, 71.21; H, 7.81; N, 6.39;
O, 14.59. Found: C, 71.12; H, 7.85; N, 7.23; O, 14.69.
20. Spectral characteristics of the products (2a–h) in Table 2 were provided as
follows: 1,3-Dioxolan-2-one (2a): 1H NMR (CDCl3, TMS, 400 MHz): 4.2 (t,
J = 10 Hz, 4H); 13C NMR (CDCl3, TMS, 100 MHz): 63.3, 155 (C@O); Anal. Calcd
for 2a: C, 40.92; H, 4.58; O, 54.50. Found: C, 40.82; H, 4.56; O, 54.62. 4-methyl-
1,3-dioxolan-2-one (2b): 1H NMR (CDCl3, TMS, 400 MHz):1.49 (d, J = 6.0 Hz,
3H); 4.05 (t, J = 8.8 Hz, 1H); 4.60 (t, J = 8.0 Hz, 1H); 4.86–4.94 (m, 1H); 13C NMR
(CDCl3, TMS, 100 MHz): 18.95, 70.46, 73.51, 154.95 (C@O); Anal. Calcd for 2b:
C, 47.06; H, 5.92; O, 47.02. Found: C, 46.93; H, 5.94; O, 47.13. 4-chloromethyl-
1,3-dioxolan-2-one (2c): 1H NMR (CDCl3, TMS, 400 MHz): 1.490 (d, J = 6.0 Hz,
3H); 4.05 (t, J = 8.4 Hz, 1H); 4.60 (t, J = 8.0 Hz, 1H); 4.86–4.94 (m, 1H); 13C NMR
(CDCl3, TMS, 100 MHz): 18.95, 70.46, 73.51, 154.95 (C@O); Anal. Calcd for 2c:
C, 35.19; H, 3.69; Cl, 25.97; O, 35.15. Found: C, 35.11; H, 3.72; Cl, 25.88; O,
35.29. 4-hexyl-1,3-dioxolan-2-one (2d): 1H NMR (CDCl3, TMS, 400 MHz): 0.84 (t,
J = 13.1 Hz, 3H); 1.24–1.28 (m, 7H); 1.34 (t, J = 9.6 Hz, 1H); 1.65 (t, J = 11.7 Hz,
2H); 4.08 (t, J = 15.8 Hz, 1H); 4.53 (t, J = 15.8 Hz, 1H); 4.74 (t, J = 6.9 Hz, 1H); 13
NMR (CDCl3, TMS, 100 MHz): 14.29, 22.52, 24.45, 28.87, 31.63, 33.44, 69.69,
C