Convenient synthesis of ethylene carbonates from carbon dioxide and 1,2-diols at atmospheric pressure of carbon dioxide

Article abstract of DOI:10.1080/00397911.2015.1116583

An efficient and convenient synthesis of ethylene carbonates was achieved by the reaction of carbon dioxide with 1,2-diols in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), followed by treatment with 1-bromobutane. This DBU-promoted transformation proceeded at an atmospheric pressure of carbon dioxide at 25 °C and gave ethylene carbonates in good yields.

Full text of DOI:10.1080/00397911.2015.1116583

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Convenient synthesis of ethylene carbonates
from carbon dioxide and 1,2-diols at atmospheric
pressure of carbon dioxide
Tsugio Kitamura, Yusuke Inoue, Taisei Maeda & Juzo Oyamada
To cite this article: Tsugio Kitamura, Yusuke Inoue, Taisei Maeda & Juzo Oyamada (2016)
Convenient synthesis of ethylene carbonates from carbon dioxide and 1,2-diols at
atmospheric pressure of carbon dioxide, Synthetic Communications, 46:1, 39-45, DOI:
10.1080/00397911.2015.1116583
To link to this article: http://dx.doi.org/10.1080/00397911.2015.1116583
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Date: 31 December 2015, At: 01:37

SYNTHETIC COMMUNICATIONS1
2016, VOL. 46, NO. 1, 39–45
http://dx.doi.org/10.1080/00397911.2015.1116583
Convenient synthesis of ethylene carbonates from
carbon dioxide and 1,2-diols at atmospheric pressure
of carbon dioxide
Tsugio Kitamura, Yusuke Inoue, Taisei Maeda, and Juzo Oyamada
Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering,
Saga University, Hojo-machi, Saga, Japan
ABSTRACT
ARTICLE HISTORY
Received 18 September
2015
An efficient and convenient synthesis of ethylene carbonates was
achieved by the reaction of carbon dioxide with 1,2-diols in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), followed by
treatment with 1-bromobutane. This DBU-promoted transformation
proceeded at an atmospheric pressure of carbon dioxide at 25 °C and
gave ethylene carbonates in good yields.
KEYWORDS
Carbon dioxide; 1,2-diols;
ethylene carbonates
GRAPHICAL ABSTRACT
Introduction
Carbon dioxide (CO2) is a nontoxic and renewable carbon resource that exists abundantly on
the earth. However, CO2 is emitted in the atmosphere by combustion of petroleum, coal, and
natural gas, and it causes global warming because of the greenhouse gas effect. Therefore,
reduction of CO2 has become one of the urgent issues in the world. To reduce the amount
of CO2, effective utilization of CO2 as a carbon source for production of valuable materials is
an important subject. The development of such synthetic processes is expected to solve
environmental problems and to provide economically valuable materials. Although synthesis
of carbonic esters is conducted by using highly toxic phosgene, safer synthetic methods of
carbonic esters using CO2 have been developed in recent years.[1] In the near future, the
carbonic ester synthesis using phosgene may be replaced for the method of using CO2.
On the other hand, ethylene carbonates are also useful materials and the synthesis of cyclic
carbonic esters can be efficiently attained by the reaction of CO2 and oxiranes.[1a,1d,1f,2]
Several methods for preparing cyclic carbonates from 1,2-diols and CO2 have been
CONTACT Tsugio Kitamura
kitamura@cc.saga-u.ac.jp
Department of Chemistry and Applied Chemistry, Graduate
School of Science and Engineering, Saga University, Hojo-machi, Saga 840-8502, Japan.
Supplemental data for this article can be accessed on the publisher's website.
© 2016 Taylor & Francis

40
T. KITAMURA ET AL.
developed.[1a,3] Although 1,2-diols have the advantages of availability and stability, the
methods using 1,2-diols are inferior in respect to the yields or the experimental operations
compared with the methods using oxiranes. Therefore, the synthesis of ethylene carbonates
using 1,2-diols needs improvement in the process.
Previously, it was reported that carbonic esters could be prepared by the capture of carbon
dioxide with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) / alcohols, followed by alkylation
with an alkyl halide.[4] Because this carbonate synthesis promoted by DBU is convenient
and mild, we have attempted to apply it to the synthesis of bis-carbonates from 1,2-diols
and CO2. However, contrary to our expectations, the reaction of ethylene glycol (1a) with
CO2 in the presence of DBU followed by alkylation with 1-bromobutane did not give the
bis-carbonate of ethylene glycol but ethylene carbonate (2a), as shown in Scheme 1. This
unexpected result provided us with a new strategy for ethylene carbonate synthesis. Although
the formation of ethylene carbonates from 1,2-diols and CO2 was reported,[5] there are still
some drawbacks that should be solved. This procedure requires high pressure of CO2
(10 bar), heating at 70 °C, addition of expensive ionic liquids, and use of dibromomethane
as solvent. Because the reaction under the atmospheric pressure conditions of CO2 can avoid
dangerous high-pressure conditions, it is important for conducting a safe and convenient
synthetic reaction. Here we report for the first time an efficient and convenient synthesis
of cyclic carbonates from 1,2-diols and CO2 at atmospheric pressure of CO2.
Results and discussion
First, we examined the reaction of ethylene glycol (1a) and CO2, affording ethylene
carbonate (2a). The reaction was conducted by introducing CO2 gas into a solution of
1a in CH2Cl2 in the presence of 2 equivalents of DBU, followed by addition of 2.4 equiva-
lents of 1-bromobutane. The reaction mixture was stirred at room temperature for 24 h
under CO2 atmosphere using a balloon. After passing through a short column of silica
gel with CH2Cl2 to remove the resulting DBU salts, the product mixture was separated
by column chromatography on silica gel, giving ethylene carbonate (2a) and dibutyl car-
bonate (3) in 95 and 98% yields, respectively (Table 1, entry 1). Elevation of the reaction
temperature to 40 or 50 °C decreased the yield of ethylene carbonate to 64 or 45%, respect-
ively (entries 2 and 3). It is considered that the yield of ethylene carbonate decreases due to
decarboxylation as the reaction temperature increases. When the reaction was conducted in
toluene or acetonitrile as solvent, the yield was decreased (entries 4 and 5). Moreover,
trimethylamine (TEA) was used as base instead of DBU, but the reaction did not occur
at all (entry 6).
Scheme 1. Unexpected results of reaction from CO2 and ethylene glycol.

SYNTHETIC COMMUNICATIONS
41
Table 1. Synthesis of ethylene carbonate from ethylene glycol and CO2.a
Entry
Solvent
Temperature (°C)
Yield (%)b
1
CH2Cl2
CH2Cl2
CH2Cl2
Toluene
MeCN
25
40
50
25
25
25
95c
64
45
0
62
0
2
3
4
5
6d
CH2Cl2
aConditions: 1a (5 mmol), DBU (10 mmol), BuBr (12 mmol), and solvent (2 mL) at 25 °C.
1
bYields were determined by H NMR.
cDibutyl carbonate was also formed in 98% yield.
dTEA was used instead of DBU.
Next, we examined the reaction using 1,2-butanediol (1b) as the substrate bearing a sub-
stituent. Because 1,2-butanediol has a less acidic secondary OH group, the reaction con-
ditions needed to optimize again. When the reaction of 1b was conducted in 1,2-
dichloroethane (DCE) using 4.0 equivalents of DBU and 4.8 equivalents of 1-bromobutane,
3-ethylethylene carbonate (2b) was formed in 63% yield (Table 2, entry 1). Extension of the
reaction time to 48 h did not give a better yield of 2b (entry 2). Increasing the amount of 1-
bromobutane to 9.6 equivalents slightly improved the yield to 67% (entry 3). Finally, we
found that the yield of 2b increased with increasing the amount of DBU (entries 4 and 5).
The best yield (96%) of 2b was obtained when 8 equivalents of DBU were used (entry 5).
With the optimized conditions of 3-ethylethylene carbonate synthesis in hand, we exam-
ined the reaction of various 1,2-diols 1 bearing substituents in order to find the scope of the
reaction. The results are given in Table 3. When 1,2-propanediol (1c) was subjected to the
similar reaction conditions to the reaction of 1,2-butanediol (1b), 3-methylethylene
carbonate (2c) was formed in 90% yield (entry 1). Styrenediol (1d), 4-(methylphenyl)etha-
nediol (1e), 4-(chlorophenyl)ethanediol (1f), and naphthylethanediol (1 g) underwent
efficiently the transformation to cyclic carbonates, giving the corresponding ethylene car-
bonates 2 in 84–89% yields (entries 2–5). These reactions suggest that the cyclic carbonate
Table 2. Synthesis of 3-etylethylene carbonate from 1,2-butanediol and CO2.a
Entry
DBU (mmol)
BuBr (mmol)
Time (h)
Yield (%)b
1
2
3
4
5
10
10
10
15
20
12
12
24
24
24
24
48
24
24
24
63
62
67
71
96
aConditions: 1 (2.5 mmol) and 1-bromobutane in DCE (1 mL) at 25 °C.
1
bYield was determined by H NMR.

42
T. KITAMURA ET AL.
Table 3. Synthesis of cyclic carbonates 2 from 1,2-alkanediol 1 and CO2.a
Entry
1
1,2-Alkanediol
Product
Yield (%)b
90
2
3
89
84
4
5
81
88
6
7
8
95c
63
93
9
60
0d
10
aConditions: 1 (2.5 mmol), DBU (20 mmol), and 1-bromobutane (24 mmol) in DCE (1 mL) at 25 °C for 24 h.
1
bYield was determined by H NMR.
cA mixture of stereoisomers.
dCyclic carbonates were not formed, but trans-1,2-cyclohexanediyl bis(dibutylcarbonate) (4) was obtained in 53% yield.

SYNTHETIC COMMUNICATIONS
43
synthesis from CO2 efficiently takes place in the case of monosubstituted 1,2-ethanediols.
Next, we examined the transformation of disubstituted 1,2-ethanediols to cyclic carbonates.
When 2,3-butanediol (1h) was reacted with CO2 in the presence of DBU and then treated
with 1-bromobutane, 3,4-dimethylethylene carbonate (2h) was obtained in 95% yield
(entry 6). Because 2,3-butanediol was a mixture of erythro and threo isomers, the product
was also a mixture of cis and trans isomers. To learn the outcome of the stereochemistry,
we conducted the reaction of threo-1,2-diphenylethylene glycol (1i). When 1i was reacted
with CO2 in the presence of DBU and followed by treatment with 1-bromobutane, cis-3,4-
diphenylethylene carbonate (2i) was obtained in 63% yield (entry 7). The slightly
decreased yield of the product may be attributable to the steric congestion between two
phenyl groups in the product, but the reaction provides a pure cis isomer. The similar reac-
tion of erythro-1,2-diphenylethylene glycol (1j) selectively gave trans-3,4-diphenylethylene
carbonate (2j) in 93% yield (entry 8). These results suggest that the present carbonate reac-
tion proceeds stereospecifically, as shown in Scheme 2.
However, a cyclic 1,2-diol shows a different behavior from acyclic diols. cis-Cyclohex-
ane-1,2-diol (1k) gave cyclic carbonate 2k in 60% yield, while trans-cyclohexane-1,2-diol
(1 l) did not yield the corresponding cyclic carbonate 2 l but a double carbonated product 4
was obtained in 53% yield (entries 9 and 10). In the case of trans-isomer 1 l, carbonation
takes place readily at each OH groups before cyclization because the intramolecular cycli-
zation may be difficult due to the inherent steric repulsion (Scheme 3).
Although less volatile alkyl halides were suitable for the present reaction due to slow
evaporation, a few additional experiments of 1a–c using iodomethane were examined to
determine the effect of alkyl halides on the cyclic carbonate formation. The results are
shown in Scheme 4, suggesting that even iodomethane is effective in this reaction.
A possible mechanism for the formation of cyclic carbonates 2 from 1,2-diols 1 and
CO2 is proposed in Scheme 5. One OH group of the 1,2-diol undergoes deprotonation by
DBU to react with CO2, giving a carbonate ion.[6] This carbonate ion reacts with 1-bro-
mobutane to form a butylcarbonate. Then, another OH group is deprotonated by DBU
to form an alkoxide ion, which undergoes intramolecular nucleophilic addition to the
carbonyl carbon to give an ethylene carbonate. Because this intramolecular cyclization
is a favorable 5-exo-trig mode,[7] it is considered that the intramolecular process proceeds
more efficiently than the intermolecular substitution with 1-bromobutane. The liberated
butoxide anion reacts with CO2 to give dibutyl carbonate after the reaction with 1-
bromobutane.
Scheme 2. Stereospecific synthesis of cyclic carbonates.

44
T. KITAMURA ET AL.
Scheme 3. Reaction of trans-1,2-cyclohexanediol (1 l) with CO2.
Scheme 4. Reaction of 1,2-diols 1a–c with CO2 using iodomethane.
In conclusion, we have demonstrated that several cyclic carbonates can be prepared in
good yields directly from CO2 and 1,2-diols. This cyclic carbonate synthesis is promoted by
DBU. This synthesis can be conducted under atmospheric pressure of CO2 and with one-
pot operation. Therefore, this method is very convenient and efficient. It is promising to be
applied to synthesis of various useful compounds in the future.
Experimental
Typical procedure for synthesis of 2a from 1a and CO2
Compound 1a (5 mmol), DBU (10 mmol), and CH2Cl2 (2 mL) were placed in a 50-mL two-
necked flask and CO2 gas was flowed with stirring at 25 °C until the solution was changed
to a white suspension. After addition of 1-bromobutane (12 mmol), the flask was capped
Scheme 5. Possible mechanism for ethylene carbonate formation.

SYNTHETIC COMMUNICATIONS
45
with a rubber septum and equipped with a CO2 balloon. The mixture was stirred at 25 °C
for 24 h and then passed through a short pad of silica gel with CH2Cl2 as eluent to remove
the DBU salts. The eluent was concentrated under reduced pressure and subjected column
chromatography on silica gel. Elution with a mixed solvent of CH2Cl2 and hexane (3:7)
gave dibutyl carbonate (3). Elution with CH2Cl2 gave 2a. The yield of the products was
1
determined by H NMR using an internal standard.
General procedure for the synthesis of cyclic carbonates 2
Compound 1 (2.5 mmol) and DBU (20 mmol) in DCE (1 mL) were placed in a 50-mL two-
necked flask and CO2 gas was flowed with stirring at 25 °C until the solution was changed
to a white suspension. After addition of 1-bromobutane (24 mmol), the flask was capped
with a rubber septum and equipped with a CO2 balloon. The mixture was stirred at 25 °C
for 24 h and then passed through a short pad of silica gel with CH2Cl2 as eluent to remove
the DBU salts. The eluent was concentrated under reduced pressure and the yield of the pro-
duct was determined by 1H NMR using an internal standard. The product 2 was separated by
column chromatography on silica gel using hexane and/or CH2Cl2 as eluent.
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