Metal-free imidazolium hydrogen carbonate ionic liquids as bifunctional catalysts for the one-pot synthesis of cyclic carbonates from olefins and CO2

Article abstract of DOI:10.1039/c9gc01088b

A direct route for the synthesis of cyclic carbonates from olefins and CO₂ has been achieved by using imidazolium hydrogen carbonate ionic liquids ([C_nC_mIm][HCO₃]) as bifunctional catalysts in the absence of a solvent. [C_nC_mIm][HCO₃] can convert into a carbene-CO₂ adduct spontaneously. The HCO₃^- anion and carbene-CO₂ can serve as catalysts for olefin epoxidation and CO₂ cycloaddition, respectively, which obviously simplifies the synthesis of cyclic carbonates. The reaction proceeds quite well under mild conditions. This cheap and simple method can be applied to various olefins with good to excellent yields of cyclic carbonates. The catalyst can be easily recycled at least four times without significantly losing its catalytic activity.

Full text of DOI:10.1039/c9gc01088b

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DOI: 10.1039/C9GC01088B
Journal Name
ARTICLE
Metal-free imidazolium hydrogen carbonate ionic liquids as
bifunctional catalyst for the one-pot synthesis of cyclic carbonates
from olefins and CO2
Received 00th January 20xx,
Accepted 00th January 20xx
†
†
DOI: 10.1039/x0xx00000x
Jia Liu , Guoqiang Yang , Ying Liu, Dongsheng Wu, Xingbang Hu* and Zhibing Zhang*
www.rsc.org/
2
A direct route for the synthesis of cyclic carbonates from olefins and CO has been achieved by using an imidazolium
hydrogen carbonate ionic liquids ([C
convert into carbene-CO
epoxidation and CO
n
C
m
Im][HCO
3
n m 3
]) as bifunctional catalyst in the absence of solvent. [C C Im][HCO ] can
-
2
adduct spontaneously. The HCO
3
anion and carbene-CO
2
can serve as the catalysts of olefins
2
cycloaddition respectively, which obviously simplify the synthesis of cyclic carbonates. The reaction
performs quite well at mild conditions. This cheap and simple method can be applied to various olefins with good to
excellent yield of cyclic carbonates. The catalyst can be easily recycled at least four times without significant losing its
catalytic activity.
production and unstability of epoxides hamper the application
of this process. Considering that epoxides are synthesized from
Introduction
Carbon dioxide (CO
reduction of CO
regarded as an important way to slow down the greenhouse
2
effect, has got a lot of attention . On the other hand, CO is
3
4
olefins, one-pot synthesis of cyclic carbonates from olefins
and CO has attracted many interestings, because the reaction
2
) is one of the main greenhouse gases. The
concentration in atmosphere, which is
2
2
uses readily available and low-priced chemicals olefins, and
avoids the preliminary synthesis of epoxides. Most of the
reported processes adopted the strategy using two different
catalysts in the one-pot synthesis (Scheme 1). One of the
catalyst (catalyst A) is for olefins epoxidation and another
1
-4
also an abundant, renewable, nontoxic and economical carbon
5
source . In this sense, using CO
2
as an eco-friendly feedstock to
synthesize industrial products is an ultimate solution that has
become one of the most important branches of green
chemistry and chemical engineering. Until now, many useful
3
5-44
(catalyst B) is for CO
2
cycloaddition
. Though these
reactions have achieved successes, the using of two different
catalysts makes the processes quite complicated, especially for
the catalyst recycling.
chemicals have been synthesized from CO
2
, such as formic
3
,5-7
6-8
carboxylic acid 10, ketone
9,
11, 12
acid
,
methanol
,
,
16
1
3
14
15
oxazolidinones , amides , methyl compounds , imines ,
1
7
18
1, 3
dimethyl carbonate , salicylic acid , urea, and others
.
Cyclic carbonates are important industrial products that
have been widely applied as polar aprotic solvent, organic
synthesis intermediates, electrolytes in lithium-ion batteries
1
, 19
and monomers of polymer . In recent decades, a number of
syntheses of cyclic carbonates from CO have been described.
Among them, a classical and industrial way is the cycloaddition
of CO with epoxides. Until now, many catalytic systems have
been developed for the cycloaddition of CO
2
2
2
with epoxides,
Scheme 1. Traditional strategy for one-pot synthesis of cyclic
2
0-25
26-
such as ionic liquid with halogen as anion
, metal halides
carbonates from olefins and CO
2
2
8
1, 29-31
32
,
organic-metal complexes
,
metal oxides , and
3
3
immobilized molecular catalysts . However, the complicated
Obviously, developing single catalyst with both catalytic
ability for olefins epoxidation and CO cycloaddition is more
2
attractive and challenging. However, only few examples were
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing
2
10093, PR China. Fax: +86 2583 336599; Tel: +86 2583 596665; E-mail:
45-48
reported.
Dupont et al. reported the one-pot synthesis of
at 150 ℃ using
BMim][Br] as catalyst and tert-butyl hydroperoxide (TBHP) as
huxb@nju.edu.cn; zbzhang@nju.edu.cn
cyclic carbonate from styrene and CO
[
2
†
Author contributed equally
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See oxidant. 90% conversion of styrene and 40% selectivity of
DOI: 10.1039/x0xx00000x
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cyclic carbonate were obtained. 45 Sun et al. reported the quite low and no SO is produced in the absence of any catalyst
View Article Online
DOI: 10.1039/C9GC01088B
2 3
synthesis of styrene carbonate from styrene and CO catalyzed (Entry 6). KHCO can slightly catalyze the reaction and the
by basic resin R201 supported Au catalyst, using TBHP as selectivity of SO can reach 78.7% (Entry 7). This result agrees
4
9-52
oxidant under 4.0MPa CO
was obtained at 150℃ (yield: 50.6%). Jain et al. reported the center of [C
2
. The best yield of styrene carbonate well with previous researches
and suggests that the active
4
6
-
n m 3 3
C Im][HCO ] for the epoxidation is the HCO
oxidative carboxylation of styrene catalyzed by Co(acac)
2
-
anion. It is worth noticing that the cation also has non-
+
QPB@MCS which contains both cobalt(II) acetylacetonate negligible influence on the catalytic ability. [C
n m
C Im] is better
4
7
+
complex and quaternary triphenylphosphonium bromide.
Duan et al. combined polyoxometalate ([ZnW12
compared with K .
6
-
O40] ), Zn ion,
amino bridge ligand and chiral functional group to produce a Table
1
The epoxidation of styrene catalyzed by the
a
n m 3
metal-organic framework catalyst (ZnW-PYls). ZnW-PYls can [C C Im][HCO ]/THBP system
catalyze the oxidative carboxylation of styrene by using TBHP
4
8
as oxidant at mild conditions.
Some pioneer researches had suggested that bicarbonate may
react with hyperoxide to produce peroxymonocarbonate which is
Selectivity(%)b
Entry Catalysts
Conv.(%)b
4
9-52
known as the active intermediate of olefins epoxidation
the other hand, carbene-CO adduct has shown catalytic ability for
the CO
cycloaddition reaction53-57. In our previous research,
we had reported that imidazolium hydrogen carbonate ionic
. On
BA
SO
1
2
3
4
5
6
7
[C
[C
[C
[C
[C
None
KHCO
KHCO
1
1
1
1
1
C
C
C
C
C
2
4
6
Im][HCO
Im][HCO
Im][HCO
12Im][HCO
4
Im][Br]
3
3
3
]
]
]
44.2
53.5
39.3
33.6
40.7
12.5
20.2
45.1
15.3
13.3
15.2
15.6
22.5
41.0
20.9
19.0
78.9
77.6
73.6
74.9
70.2
0.0
2
2
3
]
liquids ([C
n
C
m
Im][HCO
3
] ILs) can convert into carbene-CO
2
adduct
1
7
-
spontaneously . It means that there has both HCO
CO in [C Im][HCO
perform the one-pot synthesis of cyclic carbonates from olefins and
CO (Scheme 2 ). Herein, we report a simple direct synthesis of
cyclic carbonates from olefins and CO using a metal-free
Im][HCO ] as a bifunctional catalyst in the absence of
3
and carbene-
2
n
C
m
3
], which provides an interesting chance to
3
3
78.7
80.7
c
8
2
a
Conditions: Styrene: 20mmol, Catalysts: 1.25mmol, Oxidants:
2
TBHP 40mmol, Temp: 65℃, Time: 22h.
[
C C
n m
3
b
Products were identified by GC and GC-MS.
solvent under mild reaction conditons. Good to excellent yield
of cyclic carbonates were obtained and the catalyst
c
The reactor was pressurized with CO
2
up to 2.0 MPa.
n m 3
[C C Im][HCO ] is easy to be recycled.
Table 2 The cycloaddition of CO
by the [C C Im][HCO ]
n m 3
2
and styrene oxide catalyzed
a
Entry Catalysts
Conv.(%)b
92.3
94.5
94.2
94.2
72.4
0
Sel.(%)b
98.4
99.2
98.7
98.5
98.7
-
1
2
3
4
5
6
7
[C
[C
[C
[C
[C
None
KHCO
1
1
1
1
1
C
C
C
C
C
2
4
6
Im][HCO
Im][HCO
Im][HCO
3
3
3
]
]
]
12Im][HCO
Im][Br]
3
]
Scheme 2. The structure of catalyst used here, the equilibrium
between [C Im][HCO ] and carbene-CO (C -CO ) derived from
this IL is shown.
4
n
C
m
3
2
n
C
m
2
3
0
90.2
-
c
8
SMes-CO
2
98.8
a
Conditions: Styrene oxide: 20mmol, Catalyst: 1.25mmol,
Results and discussion
CO
2
: 2.0MPa, Temp: 60℃, Time: 30h.
Epoxidation of styrene catalyzed by the [C
Before the one-pot synthesis of cyclic carbonates from
olefins and CO was performed, it is necessary to investigate
the catalytic ability of [C Im][HCO ]. The epoxidation of
olefins to epoxides and the cycloaddition of CO with epoxides
to cyclic carbonates were separately investigated using
Im][HCO ] as catalyst.
The epoxidation of styrene was selected as a probe to
n m 3
C Im][HCO ]
b
Products were identified by GC and GC-MS.
c
CO : 4.0MPa, Temp: 100℃
2
2
n
C
m
3
Cycloaddition of CO
Im][HCO
A series of imidazolium hydrogen carbonate ILs were used to
catalyze the synthesis of styrene carbonate from CO and
2
and styrene oxide catalyzed by the
2
[
C
n
C
m
3
]
[
C C
n m
3
2
styrene oxide. As shown in Table 2 (Entries 1-4), the
conversions and the styrene carbonate selectivities were
higher than 92% and 98% respectively. Further experiments
revealed that no product was obtained in the absence of any
catalyst (Entry 6).
investigate the reactivity of different catalysts (Table 1). The
oxidation of styrene mainly produced styrene oxide (SO) and
benzaldehyde (BA). Among the [C
investigated here, [C Im][HCO ] shows the best catalytic
reactivity (Table 1, Entries 1-4). Obviously, the conversion is
n m 3
C Im][HCO ] catalysts
C
1 4
3
2
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To find out the catalytic species in the cycloaddition reaction, Table 3 The oxidative carboxylation of styrene catalysed by
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a
DOI: 10.1039/C9GC01088B
some control experiments were further performed. No [C
reaction happens when KHCO was used alone (Entry 7),
anion is not the active center for the
cycloaddition between CO and styrene oxide. Previous
researches have shown that carbene-CO adduct can serve as
catalyst for the CO
cycloaddition reaction53-57. Considering
that [C Im][HCO ] can transform quickly into a carbene-CO
adduct and there has about 35% carbene-CO in the
in the
ILs should be the catalyst. Herein, when the SMes-CO2, a well-
known carbene-CO adduct, was added into the reaction
1 4 3
C Im][HCO ]
3
-
indicating that HCO
3
2
Sel.(%) b
2
Temp(℃
Entry
Conv.(%) b
2
)
SC
BA
3.2
5.3
C
n m
3
2
1
2
3
4
5
50
55
60
65
70
65
56.4
73.0
79.1
91.2
92.8
79.4
88.7
86.3
87.3
82.3
75.7
64.7
2
1
7
1 4 3 2
[C C Im][HCO ], we rationalize that the carbene-CO
7.6
10.5
19.0
15.3
Im][HCO
2
system, 90.2% conversion of styrene oxide and 98.8%
selectivity of SC were obtained (Entry 8). Above results clearly
c
6
a
One-pot single step process: Styrene: 20mmol, [C
.25mmol, Oxidants: TBHP 40mmol, CO
1
C
4
3
]:
reveal that the equilibrium coexistence carbene-CO
Im][HCO ] catalyzes the cycloaddition between CO
styrene oxide.
2
in the
1
2
: 2.0MPa, Time: 30h.
Products were identified by GC and GC-MS.
[
C C
n m
3
2
and
b
c
1 4
Catalyst: 1.25mmol [C C Im][Br].
Oxidative carboxylation of styrene catalyzed by
Im][HCO
According to above results, [C
and selectivity for both epoxidation and cycloaddition reactions.
Then, [C Im][HCO ] was used as catalyst for the synthesis of
Table 4 The oxidative carboxylation of different olefins catalyzed by
the [C C Im][HCO ].
1 4 3
[
1
C C
4
3
]
a
1 4 3
C Im][HCO ] showed good activity
1
C
4
3
styrene carbonate in one-pot process. It is exciting to find that good
styrene conversion and styrene carbonate selectivity were obtained
in the one-pot process (Table 3). Especially, the styrene conversion
in the one-pot process is obviously higher than that in the
epoxidation. For example, 53.5% conversion of styrene was
obtained at 65 ℃ in the epoxidation reaction (Table 1, Entry 2),
whereas the conversion is 91.2% at the same temperature in one-
pot process (Table 3, Entry 4). To check the possible influence of
Conv.(%)b
Sel.(%)b
Entry
1
Substrate
Product
O
O
O
91.2
82.3
O
Cl
O
2
3
4
5
Cl
O
71.4
48.8
75.5
93.0
91.0
77.3
79.5
63.5
84.7
Cl
Cl
O
O
O
CO
catalyst was performed with and without CO
and 8). Higher conversion was obtained in the presence of CO
2
on the oxidation, the epoxidation reaction using KHCO
3
as
Cl
O
Cl
2
(Table 1, Entries 7
O
O
2
,
5
8, 59
indicating that CO
2
can enhance the oxidation.
From this
O
O
O
viewpoint, the one-pot direct synthesis can not only simplify the
process but also reduce the amount of oxidant for the epoxidation
reaction.
O
O
O
6
89.0
Temperature has important influence on the styrene conversion
and the styrene carbonate selectivity (Table 3). Low temperature is
a
Conditions: Substrate: 20mmol, [C
1
C
4
Im][HCO
3
]: 1.25mmol,
benefit for improving the selectivity. With the decreasing Oxidants: TBHP 40mmol, CO
2
: 2.0MPa, Temp: 65℃, Time: 30h.
b
temperature in the oxidative carboxylation process from 70 to 50
, the conversion of styrene gradually decreased from 92.8 to
6.4%, whereas the selectivity of styrene carbonate generally Oxidative carboxylation of various olefins catalyzed by
Products were identified by GC and GC-MS.
℃
5
1 4 3
increased from 75.7 to 88.7%. The main byproduct is benzaldehyde [C C Im][HCO ]
which is produced in the epoxidation reaction.
To explore the substrate scope of this new one-pot process for
the synthesis of cyclic carbonates, different olefins were
investigated (Table 4). The catalyst is reactive for all the substrates
presented in the table. However, the conversions and cyclic
carbonates selectivities depend strongly on the olefin structures.
For the oxidative carboxylation of 3-Methylstyrene and 4-
Methylstyrene, the conversions are high (>91%), and the cyclic
carbonates selectivities are 89.0 and 84.7% respectively, due to
electron-donating effect of methyl (Table 4, Entries 5 and 6).
Comparing with methylstyrenes, due to electron-withdrawing
effect, the conversions of chlorostyrenes and the cyclic carbonates
[
1
C C
4
Im][Br] has been reported as catalyst for the one-pot
synthesis of cyclic carbonate from styrene and CO at 150℃,
which showed 90% conversion of styrene and 40% selectivity
of cyclic carbonate. 45 At lower temperature, the performances
of [C C Im][Br] are poorer comparing with that of [C C Im][HCO ]
1 4 1 4 3
in not only the epoxidation and cycloaddition, but also the one-
pot process (Tables 1-3). Besides, the yield of cyclic carbonate
2
1
using [C C
4
Im][HCO
3
] as catalyst at 65℃ is also obviously higher
4
5
than that using [C
1
C
4
Im][Br] as catalyst at 150℃.
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selectivities are lower (Table 4, Entries 2-4). The non-aromatic
olefins have also been used as substrates, such as 1-hexene and 1-
octene. However, no cyclic carbonates were obtained in the one-
pot process.
Acknowledgements
View Article Online
DOI: 10.1039/C9GC01088B
This work was supported by National Natural Science
Foundation of China (No. 21878141, 21676134 and 21776122)
and the Fundamental Research Funds for the Central
Universities (020514380175).
Notes and references
1
2
3
4
5
6
7
8
9
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C
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2.0MPa), Temp. (65℃), Time (30h).
3
]. Reaction conditions: Styrene
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1
C
4
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2
(
2
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W. Y. Gao, H. F. Wu, K. Y. Leng, Y. Y. Sun and S. Q. Ma,
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1 4 3
application. Hence, the recycling studies of [C C Im][HCO ] were
1
1
2
3
investigated in the oxidative carboxylation of styrene. After the
reaction, the catalyst can be easily separated from the solution by
extraction and reused without further treatment except drying
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significantly losing its catalytic reactivity (Fig. 1).
1
1
1
1
5
6
7
8
Conclusions
T. Zhao, X. Hu, D. Wu, R. Li, G. Yang and Y. Wu,
ChemSusChem, 2017, 10, 2046-2052.
We have demonstrated a direct one-pot synthesis of cyclic
carbonates from olefins and CO
metal-free imidazolium hydrogen carbonates [C
Im][HCO
2
at mild conditions catalyzed by
T. Iijima and T. Yamaguchi, Appl. Catal. A: Gen., 2008, 345,
n
C
m
Im][HCO ]. The
3
1
2-17.
[
n
C C
m
3
] are active not only for the epoxidation but also for 19 Q. W. Song, Z. H. Zhou and L. N. He, Green Chem., 2017, 19,
3
707-3728.
the cycloaddition reaction. For the one-pot synthesis of styrene
carbonate, good conversion of styrene and selectivity of styrene
carbonate can be obtained at mild reaction conditions. The scope of
this new catalytic system can be extended to other substrates.
Compared with previous systems which contain two different
2
2
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22 B. Sarmah and R. Srivastava, Ind. & Eng. Chem. Res., 2017,
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the bifunctional catalyst reported here is easy to be
5
reused without significantly losing its catalytic reactivity. From the
viewpoint of green chemistry, the direct synthesis of cyclic
carbonates from olefins and CO
2
2
2
2
2
2
2
3
4
5
6
7
8
9
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2
catalyzed by the simple and cheap
[
n
C C
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Green Chemistry
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DOI: 10.1039/C9GC01088B
Table of contents entry:
A direct route for the synthesis of cyclic carbonates from olefins and CO has been achieved by
2
using an imidazolium hydrogen carbonate ionic liquids as bifunctional catalyst in the absence of
solvent.