Phenol and Organic Bases Co-Catalyzed Chemical Fixation of Carbon Dioxide with Terminal Epoxides to Form Cyclic Carbonates

Article abstract of DOI:10.1002/adsc.200390035

Phenol can efficiently catalyze the reactions of terminal epoxides with carbon dioxide in the presence of catalytic amounts of various organic bases such as 4-dimethylaminopyridine (DMAP), pyridine, 1,8-diazabicyclo[5.4.0]undec- 7-ene, and triethylamine t

Full text of DOI:10.1002/adsc.200390035

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Phenol and Organic Bases Co-Catalyzed Chemical Fixation of
Carbon Dioxide with Terminal Epoxides to Form Cyclic
Carbonates
Yu-Mei Shen,a Wei-Liang Duan,b Min Shia,*
a
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 354 Fenglin Lu, Shanghai 200032, P. R. China
Fax: ( ‡ 86)-21-64166128, mshi@pub.sioc.ac.cn
b
East China University of Science andTechnology, 130 Mei Long Road, Shanghai 200237, P. R. China
Received: October 28, 2002; Accepted: December 9, 2002
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de or from the author.
solvent, or catalysts requiring special structures. Herein,
we wish to report an extremely simple andeco-safer way
to cyclic carbonate from the reactions of epoxide with
Abstract: Phenol can efficiently catalyze the reac-
tions of terminal epoxides with carbon dioxide in the
carbon dioxide in the presence of catalytic amounts of
presence of catalytic amounts of various organic
phenol andan organic base.
bases such as 4-dimethylaminopyridine (DMAP),
pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, and
triethylamine to give the corresponding five-mem-
beredcyclic carbonate in high yields (initial pressure
3.57 MPa; reaction temperature 120 8C). p-Methoxy-
phenol with DMAP is the best combination to give
the cyclic carbonate in the highest yield.
During our investigations, we foundthat the five-
memberedcyclic carbonate 2a couldbe obtainedin
excellent yieldfrom the phenol (0.4 mol %) andan
organic base (0.4 mol %) co-catalyzedreactions of
epoxides 1 with carbon dioxide under mild conditions
(3.57 MPa CO2, 120 8C, 48 h) (Scheme 1). Using either
phenol or the organic base as a sole catalyst, no reaction
occurred. The co-existence of phenol and organic base
must be required in order to get high yields of cyclic
carbonate 2a. This catalytic system for the chemical
fixation of CO2 is very efficient.
Keywords: chemical fixation of carbon dioxide;
epoxide; green chemistry; organic base; phenol
The scope andlimitations of catalysts andreaction
conditions have been carefully examined. Many phenols
Conversion of carbon dioxide to industrially useful (phenol: pKa ˆ 10.0, m-nitrophenol: pKa ˆ 7.15, p-meth-
compounds has been a challenge for synthetic chemists oxyphenol: pKa ˆ 10.21, binol: pKa ˆ 10.64, or naphthol:
andhas recently attractedmuch interest in view of the
pKa ˆ 10.12) with organic bases (DMAP, DBU, Et3N, or
[1]
so-called™sustainable society∫
and™green chemis-
pyridine) have catalytic abilities for this reaction. The
try∫[2] concepts. One of the most attractive synthetic results are summarizedin Table 1. 4-Dimethylamino-
goals starting from carbon dioxide is the five-membered pyridine (DMAP) is the best organic base in this
cyclic carbonate system because five-memberedcyclic
carbonates have many synthetic uses andhave generally
reaction (Table 1, entries 3, 7 10) and p-methoxyphe-
nol is the most effective phenol under otherwise the
been synthesized from the corresponding diols and same reaction conditions (Table 1, entries 1 6). These
[3 7]
phosgene or relatedcompounds.
phosgene-free methods to synthesize the corresponding structure of the organic base play important roles in this
five-memberedcyclic carbonates have been report- reaction. As the matter of fact, the combination of either
ed,[8,9] the reaction of oxirane 1 with carbon dioxide has alcohol or carboxylic acidwith organic base shows no
Although many results suggest that both pKa of the phenol andthe
receivedmuch attention because of its simple operation,
high yield, and the harmless nature of the reagents.
Furthermore, the reaction is one of the most effective
methods to incorporate carbon dioxide into organic
molecules. In the last decades of the twentieth century
numerous catalytic systems have been developed for
this transformation. While the advances have been
significant,[10 23] all suffer from either low catalyst
stability/reactivity, air sensitivity, the needfor co-
reactivity. We also examinedthe reaction system using
O
Phenol
O
O
+
CO2
Organic Base, 3.57 MPa, 120 oC, 48 h
O
1a
2a
Scheme 1.
Adv. Synth. Catal. 2003, 345, No. 3
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337

Yu-Mei Shen et al.
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p-toluenesulfonic acidas a co-catalyst with DMAP, but
foundthat the cyclic carbonate was obtainedin only
10% under the same condition for DMAP and phenol.
The best combination is p-methoxyphenol (0.4 mol %)
with DMAP (0.4 mol %) in this reaction.
Under the optimized reaction conditions (p-methoxy-
phenol/DMAP, 3.57 MPa, 120 8C, 48 h), we examined
the reactions of other epoxides 1 with carbon dioxide.
The results are summarizedin Table 2. We foundthat, by
using 4 mol % of p-methoxyphenol andDMAP, many
monosubstitutedterminal epoxides can be quantitative-
ly transformedto the corresponding cyclic carbonates 2
(Table 2).
C4H9
H
H
1) DIBAL, toluene
2) D2O
MCPBA
C4H9
H
CH2Cl2
D
3
Considering the reaction mechanism, Kim showed
that in the reaction of epoxide with CO2 in the presence
of ZnBr2 andpyridine, the epoxy ring, activatedby the
O
O
C4H9
H
H
D
phenol, DMAP
C4H9
O
O
H
CO2
Lewis acidZnBr , was openedby the pyridine on the
2
H
4
basis of the X-ray crystal structure.[16] Then, it further
D
5
reactedwith CO
to give the corresponding cyclic
2
32%
carbonate. However, it is also well known that an
Scheme 2.
organic base can activate CO2 as a Lewis base[24] andthe
zwitterion [R3N C(O)OÀ] can open the aziridinyl
‡
ring.[25] In order to clarify the reaction mechanism, we
synthesized trans-deuterioethylene oxide as shown in openedby amine (DMAP) andthen reacts with CO 2 to
Scheme 2 according to the literature (see supporting give the corresponding deuterated ethylene carbonate 5
information) andutilizedit as the substrate in the
DMAP andphenol co-catalyzedreaction of epoxides
because, if the reaction proceeded via path b, another
deuterated ethylene carbonate 8 having the opposite
with CO2 (Scheme 2). The deuterated ethylene carbo- configuration of deuterium atoms as 5 shouldbe
nate formedwas analyzedby comparison with authentic
exclusively formed(Scheme 3).
Basedon the above results, in Scheme 3 path a, we
samples preparedaccoridng to the literature (see
1
supporting information, H NMR). As the result, we propose the plausible mechanism for this chemical
foundthat deuteratedethylene carbonate 5 was exclu- fixation reaction of CO2. We believe that, in fact, this is a
sively formed(the lower yieldcomparedby analogy
Lewis base amine andLewis acidphenol (through
hydrogen bonding) co-catalyzed reaction system. The
with 2c may be causedby the seconadry isotope
effect).[26] This result suggests that the formation of Lewis base andLewis acidwork together to open the
cyclic carbonate in our reaction system proceeds via epoxy ring andthen react with CO
to give the
2
path a as shown in Scheme 3, namely, the epoxy ring corresponding cyclic carbonate via a ring opening and
activated by phenol through hydrogen bonding is first recyclization process. Previous reports also suggest the
338
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Chemical Fixation of Carbon Dioxide with Terminal Epoxides
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then cooledto ambient temperature, the pressure released,
andthe contents transferredto a 50 mL round-bottom flask.
Unreactedsubstrate andsolvent were removedunder vacuum,
andthe residue was purifiedby silica gel column chromatog-
raphy (eluent: petroleum ether/EtOAc ˆ 1/4) to give the cyclic
carbonate as a colorless liquid.
O
O
O
O
O
C
C
H
O-
H
O
H
O
H
O-
O
O
O
H
D
C4H9
H
O
C4H9
H
C4H9
H
H
C4H9
D
D
D
H
H
5
DMAP
DMAP
4
DMAP
+
+
Path a ( Plausible Reaction Mechanism )
Acknowledgements
O
O
O
+
H
O
H
O
O
C DMAP
We thank the State Key Project of Basic Research (Project 973)
(No. G2000048007), Shanghai Municipal Committee of Science
and Technology, and the National Natural Science Foundation
of China for financial support (20025206 and 20272069).
H
O-
O
O
O
D
O-
C4H9
C4H9
H
H
C4H9
H
H
D
D
C4H9
D
H
H
O
O
+
H
H
8
4
C
DMAP
Path b
O-
+
C
O
DMAP
N
DMAP: Me2N
References and Notes
Scheme 3.
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A 100 mL stainless pressure reactor was chargedwith p-
methoxyphenol (23 mg, 0.18 mmol), propylene oxide (2.6 g,
45 mmol), DMAP (22 mg, 0.18 mmol), andCH Cl2 (0.5 mL).
2
The reaction vessel was placedunder a constant pressure
(3.57 MPa) of carbon dioxide for 5 min to allow the system to
equilibrate andthen heatedto 120 8C for 48 h. The vessel was
Adv. Synth. Catal. 2003, 345, 337 340
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