Cyclic carbonate synthesis from epoxides and CO2 over cyanocobalamin/n-Bu4NI

Article abstract of DOI:10.1002/aoc.2906

The synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by cyanocobalamin and n-Bu₄NI system was achieved under 0.8 MPa CO₂ pressure at 140°C without organic solvents. Propylene carbonate was obtained in 99% yie

Full text of DOI:10.1002/aoc.2906

Full Paper
Received: 24 April 2012
Revised: 8 July 2012
Accepted: 10 July 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2906
Cyclic carbonate synthesis from epoxides and
CO over cyanocobalamin/n-Bu NI
Dongsheng Bai *, Huanwang Jing and Guangjian Wang
2
4
a
b
a
The synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by cyanocobalamin and n-Bu NI system was
4
ꢀ
achieved under 0.8 MPa CO
2
pressure at 140 C without organic solvents. Propylene carbonate was obtained in >99% yield
within 6 h under the optimized reaction conditions. The cyanocobalamin catalyst could be recycled with water and retained
moderate catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.
Keywords: epoxides; carbon dioxide; coupling reaction; cyclic carbonates; cyanocobalamin
General Procedure for Coupling Reaction of Epoxides and CO2
Introduction
All coupling reactions were performed in a 100ml stainless steel au-
2
The chemical fixation of carbon dioxide (CO ) has received much
toclave equipped with a magnetic stir bar. The autoclave reactor
was successively charged with cyanocobalamin (0.025 mmol),
Lewis base (0.05 mmol) and epoxide (50 mmol). The reactor
attention in the last two decades in view of abundant, inexpen-
sive, non-toxic carbon sources and increasing concern regarding
[1–3]
the environment.
One of the methodologies for CO
2
fixation
was pressurized with CO to 0.8MPa and then heated and stirred
2
is the cycloaddition of CO
2
to epoxides (Scheme 1) to form five
ꢀ
at 140 C. When the CO
2
pressure fell to 0.1–0.15 MPa, the reactor
numbered cyclic carbonates (CC). Cyclic carbonates are excel-
lent organic synthetic intermediates, monomers, aprotic polar
ꢀ
was cooled quickly to 0 C in ice-water and then vented.
The remained mixture was distilled under reduced pressure or
recrystallized with ethanol to obtain the pure cyclic carbonate.
[
4–6]
solvents and pharmaceutical/fine chemical intermediates.
Various catalyst systems have been successfully developed for the
synthesis of cyclic carbonates from epoxides and CO with varying
yields and times of flight (TOFs), such as metal salts,
2
[7–16]
metal
ionic liquids
However, many of these catalytic systems
Results and Discussion
[
17–20]
[21–28]
[29–34]
complexes,
organometallic compounds,
[35]
Effect of Temperature on Cycloaddition of PO and CO2
and organic bases.
Catalyzed by VB -TBAI
12
suffer from high toxicity, low catalyst stability and selectivity,
or addition of organic solvent. Hence, from an environmentally
benign point of view, the quest for catalytic systems that
combine toxicity or even zero toxicity, higher catalyst stability and
selectivity without adding of any organic solvent remains a huge
challenge.
Temperature is one of the most important factors for cycloaddition
of CO2 to epoxides. The influence of reaction temperature on
propylene carbonate (PC) yield is shown in Fig. 1. There was no
product generated when the coupling reaction was carried out at
room temperature, so a higher temperature was desired. It can be
In this paper, a natural edible product (cyanocobalamin)
was explored as a greener biomimic catalyst for the synthesis
of cyclic carbonates from epoxides and CO2 under 0.8 MPa
ꢀ
seen from Fig. 1 that the PC yield increased up to >99% at 140 C
2
under 0.8MPa CO pressure within 6 h, after which the PC yield
remained almost constant with further increase of temperature,
ꢀ
CO2 pressure at 140 C without use of organic solvents. This
ꢀ
hinting that 140 C is the optimal temperature for the coupling
is a new, simple, greener and safer route for the synthesis
of cyclic carbonates.
reaction of propylene oxide and carbon dioxide.
Reaction Time Effect on PC Yield
The effect of reaction time on PC yield is presented in Fig. 2. The
results indicate that the reaction proceeded slowly within the
Experimental
Materials
Propylene oxide (PO) was distilled from CaH
N-dimethylaminopyridine (DMAP) and cyanocobalamin (VB12
2
. Other epoxides, N,
*
Correspondence to: Dongsheng Bai, College of Chemistry and Material Science,
Huaibei Normal University, 235000 Huaibei, Anhui, China. E-mail: baidsh06@
lzu.edu.cn
)
were purchased from Aldrich and used without further purifica-
tion. Tetrabutylammonium fluoride (TBAF), tetrabutylammonium
chloride (TBAC), tetrabutylammonium bromide (TBAB) and
tetrabutylammonium iodide (TBAI) were obtained from Sinopharm
Chemical Reagent Co. Ltd. Phenyltrimethylammonium tribromide
a College of Chemistry and Material Science, Huaibei Normal University, 235000
Huaibei, Anhui, China
b State Key Laboratory of Applied Organic Chemistry, College of Chemistry and
(PTAT) was purchased from Aladdin.
Chemical Engineering, Lanzhou University, 730000 Lanzhou, Gansu, China
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.

D. Bai et al.
O
a
Table 1. Co-catalyst effect on the synthesis of propylene carbonate
VB /n-Bu NI
O
12
4
À1 b
+
CO2
O
O
Entry
Co-catalyst
Time (h)
Yield (%)
TOF (h )
o
0
.8 MPa, 140 C
R
1
2
3
4
5
6
7
TBAF
TBAC
TBAB
TBAI
PTAT
DMAP
—
12
6.5
10
6
73
60
122
185
196
330
264
198
—
R
R=CH ,CH Cl, CH CH , Ph, PhOCH , (CH )
2 4
3
2
3
2
2
98
>99
>99
99
2
Scheme 1. Cycloaddition of epoxides and CO .
7.5
10
12
12
12
—
c
8
TBAI
TBAI
6
10
d
9
<1.0
—
a
Reaction conditions: VB12, 0.025 mmol; co-catalyst, 0.05 mmol; PO,
ꢀ
5
0 mmol; P(CO
2
) 0.8 MPa, T 140 C.
b
c
Moles of propylene carbonate produced per mole of catalyst per hour.
Without VB12
.
d
Room temperature.
system (Table 1, entry 8 vs. entries 1–6). The obtained PC yield
catalyzed by VB /PTAT was higher than with VB /TBAB, because
1
2
12
3À
À
17]
the large Br anion in PTAT was a better leaving group than Br
in TBAB, which corresponded to our previous research results.
[
DMAP as an organic base first activated CO to form an organic
2
Figure 1. Influence of reaction temperature on PC yield.
a
Table 2. Recycling of cyanocobalamin catalyst
-
1 b
Entry
Cycle
Yield (%)
TOF (h )
1
Fresh
>99
84
330
280
253
223
c
2
1
2
3
d
3
76
e
4
67
a
Reaction conditions: VB12, 0.025 mmol (34 mg); TBAI, 0.05 mmol; PO,
ꢀ
5
0 mmol; P(CO
2
) 0.8 MPa; T 140 C; reaction time, 6 h.
b
c
Moles of propylene carbonate produced per mole of catalyst per hour.
Amount of recycled cyanocobalamin = 31 mg.
d
Amount of recycled cyanocobalamin = 28 mg.
Amount of recycled cyanocobalamin = 25 mg.
e
Table 3. The coupling results of various epoxides and CO
by VB12/TBAI
2
catalyzed
a
Figure 2. Reaction time effect on PC yield.
Entry
1
Substrate
Product
Time (h) Yield (%)
first 2 h, but the yield of PC was lower than 20%. In a relatively
longer reaction time of 6 h, the reaction proceeded rapidly and
the PC yield exceeded 99%. The reaction rate slowed down after
6
1.5
8
>99
93
2
3
6
h, indicating that the reaction was completed. It can be seen
that the CO fixation onto PO was completed within 6 h.
2
73
Co-catalyst Effect on the Synthesis of PC
4
5
12.5
6.25
9
91
>99
9
The catalytic activity of various catalytic systems was tested using
the model coupling reaction of PO and CO . The results are
2
summarized in Table 1. The activities of co-catalyst on this cou-
pling reaction were found to be quite important, as seen from
Table 1. Among different co-catalysts, TBAI showed superior
activity: >99% PC yield was obtained within 6 h (Table 1, entry 4).
Although TBAI could catalyze the cycloaddition of CO2 to PO
separately, PC yield was lower than any two-component catalytic
6
a
Reaction conditions: VB12, 0.025 mmol; TBAI, 0.05 mmol; epoxide,
ꢀ
5
0 mmol; P(CO
2
) 0.8 MPa, T 140 C.
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2012)

Cyanocobalamin-catalyzed formation of cyclic carbonates
O
R
CN
Co
O
CN
O
H
Co
OH
R
O
X
O
CN
Co
CN
Co
O
O
OH
VB12
OH
R
C
O
O-
CN
-
-
-
-
-
-
X = F , Cl , Br , Br , I
3
HO
Co
O
R
X
O
CN
Co
R
O
HO
O
O C
O-
X
R
X
2
Scheme 2. Proposed mechanism of the cycloaddition of CO to epoxides.
base–CO
2
intermediate, which was different from quaternary
Proposed Mechanism for Coupling Reaction of PO and CO
2
ammonium salt. It can be seen from Table 1 that DMAP showed
almost the same catalytic activity as TBAB. The activity order of
co-catalysts was TBAI> PTAT> DMAP> TBAB> TBAC> TBAF.
Considering the mechanism of the coupling reaction of epoxides
[
19]
and CO
2
described by Lu,
a proposed general mechanism is
illustrated in Scheme 2, in which the epoxide was activated by
cobalt center, and then attacked by nucleophilic reagent
(
co-catalyst) to produce the requisite metal/heteroatom alkoxide
Recycling of Cyanocobalamin Catalyst
intermediates that was suffered insertion of CO to lead
2
corresponding cyclic carbonates. This mechanism insists that
Lewis acidic center and Lewis base center have the importance
To examine the reusability of cyanocobalamin, we performed the
recycling experiments under optimized reaction conditions using
PO as substrate. The recycling results are summarized in Table 2.
After a reaction recycle, cyanocobalamin was extracted with dis-
tilled water three times. The collected water layer was washed
with CH Cl three times, and then concentrated under vacuum.
for this coupling reaction. The higher activity of VB /n-Bu NI
12
4
catalyst systems is attributed to both good nucleophilicity and
leaving group.
2
2
After drying in a vacuum oven, cyanocobalamin was reused for
the next cycle directly, but TBAI was added for each run. The Conclusions
recycling results in Table 2 show that cyanocobalamin retained
moderate activity in the coupling reaction of PO and CO ,
2
although the catalytic activity slightly decreased along with
increased recycling.
In summary, we have developed a new, simple, greener and safer
catalytic system of VB /n-Bu NI for the synthesis of cyclic carbo-
12
4
nates from epoxides and CO2 without organic solvents under
ꢀ
0
.8 MPa CO2 pressure at 140 C. Cyanocobalamin could be
recycled three times and retained moderate activity.
Cycloaddition Reaction of Various Epoxides and CO
Catalyzed by VB12/TBAI
2
Acknowledgments
To extend the scope of the coupling reaction, various epoxides
were used as substrates and reacted with CO under optimized
We are grateful for the financial support of the Anhui University
Natural Science Fund (KJ2012A256), the Natural Science Fund of Anhui
2
and solventless reaction conditions. The cycloaddition results
are shown in Table 3. Propylene oxide (Table 3, entry 1) and
glycidyl phenyl ether (Table 3, entry 5) gave the relevant cyclic
carbonate with >99% yield. 4-(Chloromethyl)-1,3-dioxolan-2-one
was obtained with 93% yield from 2-(chloromethyl)oxirane and CO2
(
1208085QB36) and Huaibei Normal University Startup Funding.
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