Poly(ethylene glycol): An alternative solvent for the synthesis of cyclic carbonate from vicinal halohydrin and carbon dioxide

Article abstract of DOI:10.1071/CH08554

Poly(ethylene glycol) (PEG) in this work proved to be an efficient reaction medium for the reaction of vicinal halohydrin with carbon dioxide in the presence of a base to synthesise cyclic carbonates. Notably, PEG-400 as an environmentally friendly solvent exhibits a unique influence on reactivity compared with conventional organic solvents. Various cyclic carbonates were prepared in high yield employing this protocol. The process presented here has potential applications in the industrial production of cyclic carbonates because of its simplicity, cost benefits, ready availability of starting materials, and mild reaction conditions.

Full text of DOI:10.1071/CH08554

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2009, 62, 917–920
Poly(ethylene glycol): an Alternative Solvent
for the Synthesis of Cyclic Carbonate from
Vicinal Halohydrin and Carbon Dioxide
Jing-Lun Wang, Liang-Nian He,A,B Xiao-Yong Dou, and Fang WuA
A
A
AState Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University,
Tianjin 300071, China.
B
Corresponding author. Email: heln@nankai.edu.cn
Poly(ethylene glycol) (PEG) in this work proved to be an efficient reaction medium for the reaction of vicinal halohydrin
with carbon dioxide in the presence of a base to synthesise cyclic carbonates. Notably, PEG-400 as an environmentally
friendly solvent exhibits a unique influence on reactivity compared with conventional organic solvents. Various cyclic
carbonates were prepared in high yield employing this protocol. The process presented here has potential applications
in the industrial production of cyclic carbonates because of its simplicity, cost benefits, ready availability of starting
materials, and mild reaction conditions.
Manuscript received: 17 December 2008.
Final version: 27 March 2009.
Introduction
One of the most promising methodologies of CO2 chemical
fixation is the synthesis of five-membered cyclic carbonates,
which have been widely used for various purposes, such as
polar aprotic solvents, intermediates for organic and polymeric
synthesis, chemical ingredients for pharmaceutical/fine chem-
icals in biomedical applications, and electrolytic elements of
lithium secondary batteries.[ Therefore, great efforts have
been devoted to producing cyclic carbonate through the cyclo-
addition of an epoxide with CO2 as a replacement of the conven-
tional phosgene route.[ However, such a method requires the
initial synthesis of an epoxide, which generally involves toxic or
costly reagents and a tedious workup for separation.
The correct choice of reaction media is considered as one of
the central problems in chemical reactions, not only because
unique reactivity and selectivity are often observed in the right
solvent, but also because in many cases the general harm to the
environment as well as to human beings of a organic solvent has
a pivotal influence on its use on both a laboratory and industrial
12]
[
1]
scale. With increasing regulatory pressure on using organic
solvents, the development of an environmentally benign process
is so desirable that various kinds of alternative solvents such as
13]
[
2]
[3]
[4]
[5]
scCO2, fluorous media, ionic liquids, and water have
[6]
been explored as well as solvent-free processes. Furthermore,
one of the key areas of green chemistry is the elimination of
solvents in chemical processes or the replacement of a hazardous
solvent with an environmentally benign one.[
Recently, we reported an environmentally benign synthesis
of styrene carbonate directly from styrene and CO2 catalyzed
7]
by a binary system composed of sodium phosphotungstate and
n-Bu4NBr using 30% H2O2 as an oxidant.[
14]
In terms of
Poly(ethylene glycol)s (PEGs), also known as poly(ethylene
oxide)s (PEOs) or poly(oxyethylene)s (POEs), are a family
of water-soluble linear polymers formed by the interaction of
ethylene oxide with water, ethylene glycol, or ethylene gly-
col oligomers. They have applications as textile auxiliaries,
dispersants in toothpastes, oligomers in the manufacture of
polyurethanes, andpackingmaterialsforfood, etc.[ Ourinterest
in PEG is as its use as an inexpensive, non-volatile, biologically
acceptable, and eco-friendly solvent, which represents an inter-
esting reaction medium for conventional solvent replacement.[
It has been discovered that its application as a reaction medium
in organic syntheses has unique characters, as demonstrated by
recently published reports.[
Carbon dioxide is an easily available and renewable C1
building block as it has the advantages of high functional-
ity, abundance, low cost, non-toxicity, and non-flammabilty.
Nowadays, chemical transformation of CO2 into useful organic
chemicals has attracted ever-increasing attention from the point
of view of environment protection and resource utilization.[
mechanistic considerations, a bromohydrin is assumed to be
a intermediate in the single operation, thereby leading to the
formation of cyclic carbonate with the aid of a base. We envis-
aged that there would be an alternative route to cyclic carbonate
through the coupling of halohydrin and CO2, thereby avoiding
the pre-preparation of epoxides, which could still be obtained
8]
[
15]
from the chlorohydrin route in most commercial processes.
Indeed,Venturello et al. found that the reaction[
16a]
of halohydrin
9]
with tetramethylammonium hydrogen carbonate in acetonitrile
was preferentially carried out under a carbon dioxide atmo-
sphere.Very recently, Kawanami and Ikushima[
16b]
reported that
10]
organiccarbonatesweresuccessfullypreparedfromvicinalhalo-
hydrins and CO2 in the presence of sodium hydroxide using
◦
ionic liquids as the reaction media at 120 C and a CO2 pressure
of 20 MPa. In a continuation of our work on the development
of practical synthetic methodologies and green processes for
organic carbonates and their derivatives using CO2 as a synthon
11]
[17]
through molecular activation,
we demonstrate in the present
©
CSIRO 2009
10.1071/CH08554 0004-9425/09/080917

9
18
J.-L. Wang et al.
O
Table 2. Synthesis of various cyclic carbonates
Reaction conditions: substrate (1 mmol), K2CO3 (0.069 g, 0.5 mmol),
X
PEG-400/K CO
3
O
OH
2
ϩ
CO2
◦
2
PEG-400 2 mL, PCO 2 MPa, 50 C, 3 h
O
50ЊC, 3 h, 2 MPa
R
R
Entry
1
Substrate
Product
Conv. [%]
100
Yield [%]A
R: -Ph, -CH , -CH Cl, H
Yield: 72–100%
3
2
X: -Cl, -Br
O
O
Cl
>99
OH
O
Scheme 1. Cyclic carbonates from halohydrin with CO2.
Ph
Ph
O
Table 1. Synthesis of styrene carbonate from 2-bromo-2-phenylethanol
and CO2
Reaction conditions: 2-bromo-2-phenylethanol (0.2 g, 1 mmol), K2CO3
Br
Ph
O
2
3
100
100
>99
>99
OH
O
Ph
(
0.069 g, 0.5 mmol), solvent (2 mL), PCO2 2 MPa
O
HO
Cl
O
Entry
Solvent
Base
mmol]
Time
[h]
Temp
[ C]
Conv.
[%]
YieldA
[%]
Cl
O
◦
[
O
1
2
3
4
5
6
7
8
CH2Cl2
THF
CHCl3
Dioxan
CH3CN
DMF
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0
3
3
3
3
3
3
3
3
3
3
6
3
3
3
3
3
50
50
50
50
50
50
50
50
50
25
25
50
50
50
50
50
0
0
0
0
0
0
4B
5C
6C
91
100
100
89
91
>99
>99
72
O
OH
O
0
0
O
45
72
23
100
95
75
100
25
53
0
45
72
23
>99
95
75
>99
25
53
0
Cl
O
OH
O
H2O
PEG-400
H2O/PEG-400
PEG-400
PEG-400
PEG-1000
PEG-400
PEG-400
PEG-400
PEG-400
O
B
9
OH
O
10
11
12
13
14
15
16
O
Cl
Cl
Cl
OH
Br
C
O
O
7D
O
D
E
0.5
0.5
67
100
67
>99
A
Determined by GC using biphenyl as an internal standard.
B
C
D
◦
A
The reaction temperature was 80 C.
K CO (0.138 g, 1 mmol) was used.
80 C, 12 h.
Determined by GC using biphenyl as an internal standard.
The volume ratio of H2O to PEG-400, 1:1.
Using NaOH as the base.
B
C
2
◦
3
D
Using Na2CO3 as the base.
Using Cs2CO3 as the base.
E
has a potential utility for the synthesis of styrene carbonate with
high yield under mild reaction conditions.
Subsequently, we investigated the effect of the reaction tem-
◦
perature and the molecular weight of PEG. At 50 C, a 99%
work that vicinal halohydrin can be conveniently converted into
cyclic carbonates by coupling with CO2 in the presence of
K2CO3 using PEG-400 (molecular weight 400) as an alternative
solvent under mild reaction conditions (Scheme 1).
yield for styrene carbonate was attained, whereas room tem-
perature showed low reaction rate (Table 1, entries 8, 10–12).
However, PEG-1000 gave poor activity (entry 12), being pre-
sumably ascribed to the increased mass transport limitation of
gaseous CO2 in the highly viscous PEG with a long chain.[
Moreover, the base as an acid scavenger could have a great influ-
ence on the reaction. Indeed, the reaction did not occur at all
without adding a base (entry 14). K2CO3 and Cs2CO3 performed
better than Na2CO3 and NaOH under the otherwise identical
conditions (entries 8, 13, 15, and 16). In the synthesis of cyclic
carbonates, we chose K2CO3 as a base in terms of excellent
yields, efficiency, and ease of workup.
19]
Results and Discussion
The cyclization of 2-bromo-2-phenylethanol with CO2 into
styrene carbonate was chosen as a bench reaction as shown in
Table 1. Initially, solvent screening was carried out by using the
◦
reaction conditions of 3 h, 50 C, PCO 2 MPa. No conversion of
2
vicinal bromohydrin was observed in the low polarity solvents
such as dioxan, CH3Cl, tetrahydrofuran (THF), and CH2Cl2
(
Table 1, entries 1–4). With the increasing polarity of the sol-
In order to test the utility and generality of this process, we
examined the coupling reaction of various vicinal halohydrins
with CO2 by performing the reaction with the established reac-
tion conditions. The results are listed in Table 2. This protocol
is easily found to be applicable to different types of vicinal
halohydrins such as chlorohydrins, bromohydrins, and phenyl
and alkyl-substituted halohydrins, to produce the correspond-
ing cyclic carbonates (Table 2, entries 1–5). Note that the only
side product was found to be the respective epoxide. Interest-
ingly, α,γ-dichlorohydrin, derived from a biomass glycerol,[
[18]
vents (H2O > N,N-dimethylformamide (DMF) > CH3CN),
the yield of styrene carbonate increased except for with water
entries 5–7).Water showed poor performance probably owing to
(
its poor solubility towards the reactants. PEG-400 as the reaction
media gave full conversion with excellent selectivity under the
otherwise identical reaction conditions (entry 8). Interestingly,
the biphasic system also gave excellent results for cyclic carbon-
ate synthesis with 95% yield under identical conditions (entry 9).
It is distinct that the environmentally benign solvent PEG-400
20]

Synthesis of Cyclic Carbonate
919
also gave excellent results by using this protocol (entry 6). It is
worth mentioning that the present method could offer an efficient
and feasible pathway for the internal carbonate (entry 7), which
is difficult to prepare through other methods. Notably, inter-
nal cyclic carbonate is obtained exclusively as the cis-isomer,
that contained the products.) The combined extracts were dried
over MgSO4 and concentrated under vacuum to give the product
cyclic carbonate. The structures of the isolated products were
also characterized by H NMR and C NMR spectroscopy.
Spectroscopic characteristics of the cyclic carbonates are as
follows:
1
13
1
13
−1
as determined by H NMR, C NMR, and IR (cm , KBr)
[
17a,21]
spectroscopies ν(C=O): 1788 (s).
4
-Phenyl-1,3-dioxolan-2-one
As a consequence, in addition to its environmentally benign
characteristics, the advantages of using PEG-400 as the reac-
tion medium in the present study could be outlined as follows.
First, it is assumed that PEG-400 can form complexes through
coordinating the potassium cation such as crown ether does,
δH 4.35 (400 MHz, CDCl3) (t, 1H, J 8.4, OCH2), 4.80 (t, 1H, J
8.4, OCH2), 5.70 (t, 1H, J 8.0, OCH), 7.36 (d, 2H, J 7.6, Ph), 7.44
(d, 3H, J 6.4, Ph). δC (100.4 MHz, CDCl3) 71.12, 77.95, 125.83,
−
1
129.22, 129.71, 135.78, 154.76. νmax (KBr)/cm 1779, 1162,
[
22]
+
which results in an increase in the basicity of K2CO3.
Sec-
1046, 756, 688. m/z (EI, 70 eV) 164 (M ), 119, 105, 90, 78, 65,
ond, the ‘CO2-expansion of PEG’ effect[
10a,23]
leads to changes
51, 39, 29.
in the physical properties of the reaction mixture, such as low-
ered viscosity, increased gas/liquid diffusion rates, and solubility
of the reactants, thereby improving the synthetic process. Third,
another merit of using PEG as a reaction media is the ease of
product separation. In a typical experiment, cyclic carbonates
were separated by extraction.
4
-Methyl-1,3-dioxolan-2-one
δH (400 MHz, CDCl3) 1.43 (d, 3H, J 6.0, CH3), 3.98 (t,
1H, J 8.4, OCH2), 4.51 (t, 1H, J 8.4, OCH2), 4.82 (m, 1H,
CHO). δC (100.4 MHz, CDCl3)19.15, 70.53, 73.49, 154.95. νmax
(KBr)/cm 1791, 1184, 1120, 1076, 1052, 776. m/z (EI, 70 eV)
03 (M ), 57, 43.
−
1
+
1
Conclusions
1
,3-Dioxolan-2-one
We have developed a viable alternative protocol for cyclic car-
bonate synthesis from vicinal halohydrins and CO2 employing
PEG-400 as a promising reaction medium.A high yield of cyclic
carbonates together with excellent selectivity was achieved in
mild reaction conditions. Moreover, the product can be easily
separated by extraction. We feel that this would be a cost-
effective route to cyclic carbonate in an environmentally friendly
manner. The broad scope of this method and further applications
of PEG as reaction media to a wide set of organic reactions is
currently under investigation in our laboratory.
δH (400 MHz, CDCl3) 4.50 (s, 4H, OCH2). δC (100.4 MHz,
−
1
CDCl3) 64.62, 155.55. νmax (KBr)/cm 1803, 1775, 1165,
+
1
113, 1075. m/z (EI, 70 eV) 89 (M ), 43.
4
-Chloromethyl-1,3-dioxolan-2-one
δH (400 MHz, CDCl3) 3.71 (dd, 1H, J 3.2, 12.0, ClCH2), 3.80
dd, 1H, J 5.2, 12.0, ClCH2), 4.39 (dd, 1H, J 6.0, 8.4, OCH2),
.58 (t, 1H, J 8.4, OCH2), 4.98 (m, 1H, CHO). δC (100.4 MHz,
(
4
−
1
CDCl3) 43.84, 66.83, 74.29, 154.28. νmax (KBr)/cm 1800,
+
1
168, 1112, 1073, 1044. m/z (EI, 70 eV) 137 (M ), 75, 43.
Experimental
Cyclohexene Carbonate
All vicinal halohydrins were prepared according to literature
δH (300 MHz, CDCl3) 1.40–1.46 (m, 2H), 1.55–1.62 (m, 2H),
.86–1.89 (m, 4H), 4.64–4.7 (m, 2H). δC (75 MHz, CDCl3) 19.1,
[
24]
methods.
Carbon dioxide with a purity of 99.99% was com-
1
2
1
mercially available. All of the other reagents and catalysts used
in this work were of analytical grade and were used as received
−1
6.8, 75.7, 155.3. νmax (KBr)/cm 1788, 1210, 1014. m/z (EI)
+
43 (M ), 97, 83, 79, 69, 55, 39.
1
13
without further purification. H NMR and C NMR spectra
were recorded on a Varian Mercury Plus 400 MHz or Bruker
Accessory Publication
1H NMR and 13C NMR spectra, selected mass spectra, and IR
spectra are available from the Journal’s website.
3
00 MHz spectrometer, and at 100.4 or 75 MHz, respectively,
in CDCl3. Chemical shifts (δ) are given in ppm relative to
tetramethylsilane (TMS). The solvent signals were used as ref-
erences and the chemical shifts converted into the TMS scale
Acknowledgements
Support of this work from National Science Foundation of China
no. 20421202, 20672504, and 20872073), the 111 project (B06005), and the
Tianjin Natural Science Foundation is gratefully acknowledged. The authors
also thank the referees for their valuable suggestions regarding revision.
(
CDCl3: δC 77.0 ppm; residual CHCl3 in CDCl3: δH 7.26 ppm).
Gas chromatography (GC) analyses were performed on a Shi-
madzu GC-2014, equipped with a capillary column (RTX-5,
(
3
0 m × 0.25 mm) using a flame ionization detector. The prod-
ucts were characterized by comparison of their spectroscopic
data with those of authentic samples.
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