MCM-41 grafted quaternary ammonium salts as recyclable catalysts for the sequential synthesis of dimethyl carbonate from epoxides, CO2, and methanol

Article abstract of DOI:10.1246/cl.2010.1277

One kind of novel heterogenous bifunctional catalyst, MCM- 41 grafted quaternary ammonium salts with terminal amino group, was prepared. These catalysts exhibited excellent catalytic performance and good reusability in the sequential synthesis of dimethyl carbonate from epoxides, CO₂, and methanol.

Full text of DOI:10.1246/cl.2010.1277

doi:10.1246/cl.2010.1277
Published on the web November 6, 2010
1277
MCM-41 Grafted Quaternary Ammonium Salts as Recyclable Catalysts for the Sequential
Synthesis of Dimethyl Carbonate from Epoxides, CO , and Methanol
2
Jian Li,1,2 Liguo Wang,1,2 Shimin Liu,1,2 Xueli Li,1,2 Feng Shi,* and Youquan Deng*
1
1
1
Centre for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, P. R. China
2
Graduate University of the Chinese Academy of Sciences, Beijing 100039, P. R. China
(
Received September 10, 2010; CL-100782; E-mail: ydeng@licp.cas.cn)
One kind of novel heterogenous bifunctional catalyst, MCM-
1 grafted quaternary ammonium salts with terminal amino group,
was prepared. These catalysts exhibited excellent catalytic
performance and good reusability in the sequential synthesis of
dimethyl carbonate from epoxides, CO2, and methanol.
Cl
4
OH
OH
OH
O
O
(
MeO)3SiCH2CH2CH2Cl
Refluxing toluene, 6 h
Si
O
TMEDA
Refluxing toluene, 24 h
OH
MCM-41-pr-Cl
MCM-41
N
N
Cl-
N+
O
N
TMEDA
With the development of industrial production, environ-
Si
O
O
mental problems caused by CO such as the greenhouse effect
N
2
N
OH
have attracted wide attention. Meanwhile, CO2 is an abundant,
renewable, and economic carbon resource. Therefore, trans-
TMHDA
+
MCM-41-pr-TMEDA Cl-
formation of CO to other useful compounds has important
2
1
significance. However, CO2 is the most oxidized state of carbon
Scheme 1. Preparation route of MCM-41 grafted quaternary ammonium
salts with terminal amino groups.
and acts as a relatively inert molecule. Therefore, the activation
of CO2 is a challenging topic in catalysis and high-energy
starting materials such as epoxides are generally needed for the
high-efficient conversion of CO2.
ammonium salts with terminal amino groups. These novel bi-
functional catalysts exhibited excellent catalytic performance and
good reusability in the sequential synthesis of dimethyl carbonate
Dimethyl carbonate (DMC) is considered to be a safe, non-
corrosive, and environmentally benign chemical and energy
source. It can be used as carbonyl source and alkylating reagent
in pharmaceuticals and agricultural chemicals. Additionally,
DMC also can be used as solvent, fuel oil additive, and
from epoxides, CO , and methanol. To the best of our knowledge,
2
no MCM-41 grafted quaternary ammonium salts with terminal
amino groups as catalysts for the sequential synthesis of DMC has
been reported. In a typical organo-functionalization, N,N,N¤,N¤-
tetramethylethylenediamine (TMEDA) was grafted onto MCM-
41 in two steps as shown in Scheme 1. 10 g of MCM-41 was
reacted with 6 mL of 3-(chloropropyl)trimethoxysilane in 100 mL
of dry toluene for 6 h under refluxing. The anchored moiety
MCM-41-pr-Cl was filtered and washed with dichloromethane
(30 mL © 3). 14 g of MCM-41-pr-Cl was obtained after drying at
110 °C (elemental analysis %: C, 7.505; H, 1.463; Cl, 6.890%).
Then 2.5 g of MCM-41-pr-Cl was treated with 2.5 mL of
TMEDA in 60 mL of toluene for 24 h also under refluxing. After
being filtered, washed with dichloromethane (15 mL © 3) and
2
electrolyte. Up to now, several routes have been developed for
DMC synthesis. Among them, transesterification is a commer-
cialized and environmentally friendly route for massive produc-
tion of DMC, and this method is also considered to be one of
the most valuable and promising routes for large-scale CO2
3
utilization. The transesterification process can be divided into a
one-step and a two-step methods. The two-step method has the
advantages of mild reaction conditions, high selectivity, and low
investment, while the complicated operation process is one of the
main drawbacks for this route due to the separation of cyclic
carbonate intermediates. As for the one-step method, although
it eliminates the drawback of separations, most of catalysts
are difficult to recover owing to the solubility of the active
component and the occurrence of side reactions is unavoidable.
Moreover, rigorous reaction conditions are usually required. To
solve all these problems, a sequential transesterification process
is reported, in which the cycloaddition of epoxide with CO2 and
the transesterification of cyclic carbonate with methanol proceeds
step by step catalyzed by the same catalyst without the separation
+
¹
dried at 100 °C, 2.8 g of MCM-41-pr-TMEDA Cl was obtained
(elemental analysis %: C, 14.122; H, 3.284; N, 3.230; Cl,
+
¹
6.295%). MCM-41-pr-TMHDA Cl , MCM-41-pr-n-Bu N, and
2
+
¹
silica gel anchored TMEDA (SG-pr-TMEDA Cl ) were ob-
tained in the same manner.
To gain insight into the elemental chemical states of catalyst,
+
¹
MCM-41-pr-TMEDA Cl was characterized by X-ray photo-
electron spectroscopy. C, O, Si elements for MCM-41 and C, N,
+
¹
O, Si, Cl elements for MCM-41-pr-TMEDA Cl were observed
in XP full spectra analysis, indicating the obvious changes in
4
of intermediates. However, for reported catalyst K CO /
2
3
6
BrBu3PEG6000PBu3Br, the only defect is that the loss of K2CO3
is inevitable due to its solubility in methanol. Hence, efficient and
recyclable catalysts are highly desired for this process.
elemental composition (Figure S3 ). The N 1s spectrum can be
divided into two peaks at 399.8 and 402.6 eV as shown in
Figure 1, which could be assigned to nitrogen in the tertiary
As mentioned in the literature,3d quaternary ammonium salts
are active for the cycloaddition of epoxide and CO2, and tertiary
amines can promote the transesterification reaction. Inspired by
this work, herein, we synthesized MCM-41 grafted quaternary
amino moiety and quaternary ammonium group, respectively.
5
Therefore, MCM-41 grafted TMEDA with bifunctional groups
was successfully prepared. The peak area ratio of quaternary
ammonium to tertiary amino moiety was 1.45, this suggesting
Chem. Lett. 2010, 39, 1277­1278
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1
278
Table 1. Synthesis of DMC catalyzed by MCM-41 grafted quaternary
ammonium salts with terminal amino groups
N 1s
a
O
O
Cat.
Cat.
HO
R
OH
O
O
O
+
CO2
O
O
+
CH3OH
R
CH3 CH3
R
Cyclic carbonate
DMC
yield/%
Entry
Substrate
Con./%
Sel./% Yield/%
410
405
400
395
Binding Energy/eV
b
O
O
O
O
1
61
73
99
99
99
99
99
99
98
99
98
99
96
99
60
72
99
99
99
90
97
99
98
99
34
97
52
58
85
72
68
55
70
+
¹
Figure 1. N 1s XP spectrum of MCM-41-pr-TMEDA Cl .
c
2
3
>99
>99
>99
90
d
4
O
5
6
7
8
9
O
O
98
Ph
O
e
36
Figure 2. ¹TEM images of (a) MCM-41 and (b) MCM-41-pr-
PhO
>99
99
+
TMEDA Cl .
O
iPrO
74
79
that a fraction of bis(quaternary ammonium salt) was also formed
during the reaction of MCM-41-pr-Cl with TMEDA.
O
1
1
1
0
1
2
>99
35
O
O
+
¹
TEM images of MCM-41 and MCM-41-pr-TMEDA Cl
f
—
O
confirmed the mesoporous structure even after grafting of the
organic functionality as shown in Figure 2, indicating the long-
range ordering and mesostructural arrangement of MCM-41 are
not significantly disturbed after organo-functionalization.
The catalytic performance of MCM-41 grafted catalyst
was investigated for the sequential synthesis of DMC. As
g
98
75
a
Reaction procedure: epoxide, 30 mmol; methanol, 750 mmol; MCM-
1-pr-TMEDA Cl , 10 wt % epoxide. Operation procedures: synthesis
of carbonates at 120°C, 2 MPa, and 6 h. After cooling and
depressurization, methanol was added and then the mixture was
refluxed for 4 h at 120°C. MCM-41-pr-n-Bu N was used as catalyst.
SG-pr-TMEDA Cl as catalyst. MCM-41-pr-TMHDA Cl as
catalyst. 12 h. Not detected. MCM-41-pr-TMEDA Cl was used
for the sixth time.
+
¹
4
+
¹
b
shown in Table 1, MCM-41-pr-TMEDA Cl and MCM-41-pr-
2
+
¹
c
+
¹
d
+
¹
TMHDA Cl exhibited better catalytic activity than MCM-41-
e
f g + ¹
+
¹
pr-n-Bu2N and SG-pr-TMEDA Cl using ethylene oxide as the
substrate (Entries 1­4), which may be due to the special organic
groups and mesoporous structure of the designed catalyst.
+
¹
Meanwhile, for most substrates, MCM-41-pr-TMEDA Cl
dimethyl carbonate. Compared with amine-grafted catalysts,
these catalysts exhibited excellent catalytic performance and
good reusability. We believe that these bifunctional catalysts
will lead to further applications in carbon dioxide fixation
reactions, and additional studies are underway.
exhibited excellent catalytic activity for cycloaddition and very
good catalytic effect for transesterification with 36­79% DMC
yields observed (Entries 5­11). DMC yields were influenced
by the substituent of oxide with different electron-supplying
capacity and a sequence of alkoxyl > phenyl > alkyl was
obtained. However, only 36% yield for glycidyl phenyl ether
was observed because of the poor solubility of corresponding
cyclic carbonate in methanol. A low DMC yield was also
predicted for cyclohexene oxide, the reason for which may be
that its special cyclic molecular structure hampered the
nucleophilic attack from the chloride and therefore decreased
the rate of ring opening. Experiments were also carried out to
examine the recyclability of the catalyst using ethylene oxide as
the substrate (Entry 12). A slight decrease in the yield of DMC
was observed, indicating that catalyst was not only insoluble in
the reaction mixture but also can be reused.
References and Notes
1
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1
997, 11, 2.
3
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Supporting Information is available electronically on the CSJ-Journal Web
site, http://www.csj.jp/journals/chem-lett/index.html.
In conclusion, one kind of novel bifunctional catalyst,
MCM-41 grafted quaternary ammonium salts with terminal
amino groups, was prepared for the sequential synthesis of
Chem. Lett. 2010, 39, 1277­1278
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/