Novel functionalized guanidinium ionic liquids: Efficient acid-base bifunctional catalysts for CO2 fixation with epoxides

Article abstract of DOI:10.1016/j.molcata.2013.06.024

A series of functional guanidinium-based ionic liquids (FGBILs) that contain both Lewis acid and basic sites was prepared by a simple method, and used as catalysts for the synthesis of cyclic carbonates through the cycloaddition of CO₂ to epoxi

Full text of DOI:10.1016/j.molcata.2013.06.024

Accepted Manuscript
Title: Novel functionalized guanidinium ionic liquids:
Efficient acid-base bifunctional catalysts for CO2 fixation with
epoxides
Author: Dai Wei-Li Jin Bi Luo Sheng-Lian Luo Xu-Biao Tu
Xin-Man Au Chak-Tong
PII:
S1381-1169(13)00264-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2013.06.024
MOLCAA 8803
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
6-4-2013
26-6-2013
28-6-2013
Please cite this article as: D. Wei-Li, J. Bi, L. Sheng-Lian, L. Xu-Biao, T. Xin-Man,
A. Chak-Tong, Novel functionalized guanidinium ionic liquids: Efficient acid-base
bifunctional catalysts for CO2 fixation with epoxides, Journal of Molecular Catalysis
A: Chemical (2013), http://dx.doi.org/10.1016/j.molcata.2013.06.024
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Novel functionalized guanidinium ionic liquids: Efficient acid-base
bifunctional catalysts for CO2 fixation with epoxides
Dai Wei-Li a, Jin Bi a, Luo Sheng-Lian a,*, Luo Xu-Biao a, Tu Xin-Man a, and Au
Chak-Tong a,b
a
Key Laboratory of Jiangxi Province for Persistant Pollutants Control and Resources Recycle,
Nanchang Hangkong University, Nanchang 330063, Jiangxi, China
b
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
Prof. Luo Sheng-Lian
Key Laboratory of Jiangxi Province for Persistant Pollutants Control and Resources
Recycle, Nanchang Hangkong University
Nanchang 330063, Jiangxi
China
Tel: 86-791-83953373
Fax: 86-791-83953373
E-mail: sllou@hnu.edu.cn
* Corresponding authors
1
Page 1 of 35

Novel functionalized guanidinium ionic liquids: Efficient acid-base
bifunctional catalysts for CO2 fixation with epoxides
Dai Wei-Li a, Jin Bi a, Luo Sheng-Lian a,*, Luo Xu-Biao a, Tu Xin-Man a, and Au
Chak-Tong a,b
a
Key Laboratory of Jiangxi Province for Persistant Pollutants Control and Resources Recycle,
Nanchang Hangkong University, Nanchang 330063, Jiangxi, China
b
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
*Corresponding authors. Sheng-Lian Luo, Tel (Fax): 86-791-83953373, E-mail: sllou@hnu.edu.cn
Abstract
A series of functional guanidinium-based ionic liquids (FGBILs) that contain both
Lewis acid and basic sites was prepared by a simple method, and used as catalysts for
the synthesis of cyclic carbonates through the cycloaddition of CO2 to epoxides in the
absence of co-catalyst and solvent. Propylene oxide conversion was near completion
o
at 130 C and 2.5 MPa in 2 h when [TMGC2H4NH2]Br was used as catalyst. The
effects of functional groups and counter anions on catalytic performance were
investigated. The synergistic effect of polarization by hydrogen bonding and the
nucleophilic attack by bromide anion account for the facile ring-opening of epoxide.
Furthermore, the protocol is applicable to a variety of terminal epoxides, producing
the corresponding cyclic carbonates in high yield and selectivity. It is envisaged that
the metal- and solvent-free process using a single catalyst has high potential for
large-scale fixation of CO2.
2
Page 2 of 35

Keywords: carbon dioxide fixation; cycloaddition reaction; guanidinium-based ionic
liquid; cyclic carbonate.
1. Introduction
Carbon dioxide is a renewable C1 resource that is abundant, inexpensive and
nontoxic. The fixation of CO2 for the generation of useful compounds has attracted
much attention [1]. There are over 20 known chemical reactions that involve CO2 as
starting material, but CO2 fixation in an industrial scale remains as a challenge [2].
One of the promising processes is the cycloaddition of CO2 to epoxides for the
formation of cyclic carbonates. Cyclic carbonates are valuable compounds that are
used as polar solvents, electrolytes in lithium secondary batteries, precursors for
synthesizing polycarbonates and polyurethanes, and intermediates for production of
pharmaceuticals, fine chemicals, and agricultural chemicals [1-4].
With an atom utilization ratio of 100%, the cycloaddition of CO2 to epoxides is in
accord with the concept of “green chemistry” and “atom economy” [5]. In the past
decades, numerous catalysts have been developed for the synthesis of cyclic
carbonates. In recent years, ionic liquids (ILs) have received more attention than the
other catalysts (such as alkali metal salts [6], metal oxide [7-9], modified molecular
sieve [10-11], and organometallic complexes [12-15]) because they are low-cost,
good in solvating ability as well as being variable in polarity and adjustable in
structure and acid-base properties. So far, imidazolium salts [16-23], quaternary
ammonium salts [22,24,25], quaternary phosphonium salts [26-27], pyridinium salts
[28], and gunidinium salts [29-31], and other ILs [32-33] have been reported as
3
Page 3 of 35

efficient catalysts for CO2 fixation through the synthesis of cyclic carbonates from
epoxides. Although the advances are significant, most of the ILs showed
shortcomings such as unsatisfactory activity, harsh reaction conditions, being water
and/or air sensitive, and the need of a metal salt as co-catalyst. From the viewpoints of
industrial production and environment friendliness, it is highly desirable to develop a
stable single-component catalyst that functions well under mild reaction conditions.
There is increasing investigation on guanidinium ILs because they are thermally as
well chemically stability. With tunable groups on the N atoms, they show excellent
catalytic activity for organic reactions [34]. Compared to the use of
imidazolium-based ILs for the cycloaddition of CO2 to epoxides, the use of
guanidinium-based ILs (GBILs) is rare. Xie et al. [29]. reported that
hexabutylguanidinium chloride showed certain activity for the cycloaddition reaction,
but the reaction time was long and large amount of catalyst was needed. Later on, the
researchers reported the observation of high activity over a hexabutylguanidinium
bromide/ZnBr2 binary system, but ZnBr2 is required as a co-catalyst [30]. Furthermore,
Dou et al. [31] synthesized PEG that was functionalized with guanidinium salt which
showed certain activity for cycloaddition reaction. Recently Sun et al. reported that
hydroxyl- and carboxyl-functionalized imidazolium-based ILs showed good catalytic
activity for cycloaddition reactions [22-23]. As far as we know, there is no report on
the synthesis of functionalized guanidinium-based ILs (FGBILs) and their use as
catalysts for the synthesis of cyclic carbonate.
4
Page 4 of 35

R
: R = NH , Y =Br; : R = COOH,
1a 1b
Y =Br; 1c: R = OH, Y =Br; 1d: R = CH3,
2
HN
Y
Y =Br; : R = H, Y = Br
1e
N
N
2a: R = NH2, Y = BF4;
: R = NH , Y = PF
3a
2
6
Scheme 1. Structures of FGBILs.
In the present work, a series of FGBILs (Scheme 1) were synthesized, and for the
first time used as catalysts for the cycloaddition of CO2 to epoxides in the absence of
solvent and co-catalyst. We studied in detail the roles of functional group attached to
the cation as well as the role of the counter anion. Furthermore, a systematic
investigation was conducted on the effects of reaction parameters (catalyst loading,
temperature, time and initial CO2 pressure) on the catalytic reaction.
2. Experimental
2.1 Chemicals
The tetramethylguanidine, 2-bromoethanol, 3-bromopropionic aicd, bromoethane,
1-bromopropane, NaBF4, and KPF6 were purchased from Shanghai Jingchun Industry
Co., Ltd. 2-Bromoethylamine hydrobromide was purchased from Aldrich Chemical
Co. Propylene oxide and ethylene oxide were produced by Sinopharm Chemical
Reagent Co., Ltd. The other epoxides were purchased from Alfa Aesar China Co., Ltd.
All chemicals were used as received. The CO2 (99.9% purity) purchased from
Nanchang Guoteng Gas Co. was used without any further treatment.
2.2 Charaterization
The products were analyzed on a gas chromatograph (Agilent 7890A) that was
equipped with a FID and a DB-wax capillary column (30 m × 0.53 mm × 1.0 μm).
5
Page 5 of 35

1
NMR spectra were recorded on a Bruker 400 spectrometer in DMSO-d6. H NMR
chemical shifts (δ) in ppm were downfield from tetramethylsilane. Elemental analysis
was performed over a Vario EL III analyzer. The FT-IR spectra were recorded using a
Bruker vertex 70 FT-IR spectrophotometer. All reagents were used as received.
2.3 Preparation and characterization of Guanidinium-based ILs
A typical procedure for preparation of [TMGC2H4NH2]Br (1a) is as follows: A
solution of tetramethylguanidine (TMG) (40 mmol) in MeCN (12 mL) was prepared
o
at 0 C under N2 atmosphere in a dry round-bottomed flask equipped with a reflux
condenser. Another solution of 2-bromoethylamine hydrobromide (40 mmol) in
MeCN (6 mL) was added dropwise to the flask, and the mixture was heated to room
temperature and stirred for 24 h. Afterward, the solvent was removed, and the resulted
solid was washed three times with triethylamine and ethyl acetate respectively, then
o
1
dried at 60 C under vacuum for 12 h to give product 1a as a white solid. H NMR
(400 MHz, DMSO-d6): δ = 7.84 (s, 1H), 3.14-3.08 (m, 2H), 2.92 (s, 12H), 1.23 (t, J =
7.2 Hz, 2H); Anal. calcd for C7H19N4Br: C 35.15, H 8.01, N 23.43, found: C 35.27, H
8.08, N 23.55.
Other guanidinium ILs (1b-e) were prepared following the same method but
without the procedure of washing with triethylamine. [TMGC2H4COOH]Br (1b):
1
1
White solid; H NMR (400 MHz, DMSO-d6): H NMR (400 MHz, DMSO-d6): δ =
7.80 (s, 1H), 3.28 (s, 4H), 2.90 (s, 12H); Anal. calcd for C8H18N3O2Br: C 35.83, H
6.77, N 15.67, found: C 35.72, H 6.72, N 15.51; [TMGC2H4OH]Br (1c): White
1
1
solid; H NMR (400 MHz, DMSO-d6): H NMR (400 MHz, DMSO-d6): δ = 7.80 (s,
6
Page 6 of 35

1H), 3.30 (s, 4H), 2.90 (s, 12H); Anal. calcd for C7H18N3OBr: C 35.01, H 7.56, N
17.50, found: C 34.96, H 7.50, N 17.64; [TMGC2H4CH3]Br (1d): Colorless liquid;
1H NMR (400 MHz, DMSO-d6): δ = 7.81 (s, 1H), 3.16-3.08 (m, 2H), 2.92 (s, 12H),
1.61-1.52 (m, 2H), 0.90-0.70 (m, 3H); Anal. calcd for C8H20N3Br: C 40.34, H 8.46, N
1
17.64, found: C 40.48, H 8.56, N 17.75; [TMGC2H5]Br (1e): Colorless liquid; H
NMR (400 MHz, DMSO-d6): δ = 7.76 (s, 1H), 3.27-3.15 (m, 2H), 2.92 (s, 12H), 1.13
(dt, J = 7.2 Hz, 3H); Anal. calcd for C7H18N3Br: C 37.51, H 8.09, N 18.75, found: C
37.78, H 7.92, N 18.91.
The ionic liquid 2a and 3a were synthesized by anion exchange between ionic
liquid 1a and the corresponding inorganic salt. A typical synthesis route to
[TMGC2H4NH2]BF4 (2a) is as follows: Solid NaBF4 (2 mmol) was added to a solution
of 1a (2 mmol) in H2O (10 mL), and the mixture was stirred vigorously at room
temperature for 10 h. The solution was extracted with CH2Cl2 (3 × 10 mL), and the
organic phase was collected and dried with anhydrous Na2SO4 for 24 h. The organic
solution was subject to evaporation for solvent removal, and the resulted product was
o
dried at 60 C under vacuum for 12 h to give product 2a as a white solid. 1H NMR
(400 MHz, DMSO-d6): δ = 7.77 (s, 1H), 3.13-3.07 (m, 2H), 2.90 (s, 12H), 1.20 (t, J =
7.0 Hz, 2H); Anal. calcd for C7H19N4BF4: C 34.17, H 7.78, N 22.77, found: C 34.35,
H 7.72, N 22.94.
The ionic liquid [TMGC2H4NH2]PF6 (3a) was prepared by the same method but
using KPF6 rather than NaBF4. [TMGC2H4NH2]PF6 (3a): White solid; 1H NMR (400
MHz, DMSO-d6): δ = 7.76 (s, 1H), 3.13-3.07 (m, 2H), 2.90 (s, 12H), 1.19 (t, J = 7.2
7
Page 7 of 35

Hz, 2H); Anal. calcd for C7H19N4PF6: C 27.64, H 6.30, N 18.42, found: C 27.92, H
6.41, N 18.57.
The
imidazolium
IL
(1-(2-hdyroxyl-ethyl)-3-methyl-imidazolium,
[MImC2H4OH]Br) and quaternary ammonium IL (hydroxyl-ethyl-triethylammonium
bromide, [TEAC2H4OH]Br) were prepared according to the procedures reported in ref
1
[22]. [MImC2H4OH]Br: White solid; H NMR (400 MHz, DMSO-d6): δ = 9.24 (s
1H), 7.79 (d, 2H), 5.17 (s, 1H), 4.26 (t, J = 8.2 Hz, 2H), 3.89 (s, 3H), 3.72 (t, J =
6.6Hz, 2H); Anal. calcd for C6H11N2OBr: C 34.38, H 6.89, N 16.70, found: C 34.26,
H 6.81, N 16.87; [TEAC2H4OH]Br: White solid; 1H NMR (400 MHz, DMSO-d6): δ
= 5.27 (s, 1H), 3.77 (t, J = 4.8 Hz, 2H), 3.34 (q, J = 7.55 Hz, 6H), 3.31 (t, J = 4.8 Hz,
6H), 1.18 (t, J = 14.4 Hz, 9H); Anal. calcd for C8H20NOBr: C 42.49, H 8.91, N 6.19,
found: C 42.63, H 8.85, N 6.37.
2.4 Procedure for cyclic carbonate formation from epoxides and CO2
The cycloaddition reactions were carried out in a 50 mL high-pressure
stainless-steel autoclave equipped with a magnetic stirring bar. In a typical run, the
reactor was charged with epoxide (35.7 mmol), and certain amount of catalyst. After
the reactor was fed with CO2 to a desired pressure, the autoclave with its contents was
heated to a designated temperature and stirred for a designated period of time. Then
o
the reactor was cooled to 0 C in an ice-water bath, and the remaining CO2 was
released. The resulting mixture was analyzed using a GC-mass spectrometer. The
products were quantitatively analyzed using GC with a flame ionization detector.
3. Results and discussion
8
Page 8 of 35

3.1 Effect of catalyts
The synthesis of propylene carbonate (PC) through the cycloaddition of CO2 to
propylene oxide (PO) was chosen as model reaction to evaluate the catalytic activity
of the as-synthesized acid-base FGBILs, and the results are depicted in Table 1.
Table 1. Performance of various catalystsa
Catalytic results
Entry
Catalyst
Yield [%]
1.8
Sel. [%]
88.5
99.8
99.9
99.8
99.8
99.7
99.6
99.7
99.7
99.0
98.6
99.1
99.1
99.0
99.6
1
TMG
2
[TMGC2H4NH2]Br (1a)
[TMGC2H4COOH]Br(1b)
[TMGC2H4OH]Br (1c)
[TMGC2H4CH3]Br (1d)
[TMGC2H5]Br (1e)
[TMGC2H5]Br/CH3(CH2)2NH2
[TMGC2H5]Br/CH3COOHb
[TMGC2H5]Br/CH3CH2OHb
CH3CH2CH2NH2
94.6
90.8
88.3
71.6
62.8
80.3
78.0
78.8
6.0
3
4
5
6
b
7
8
9
10
11
12
13
14
15
CH3COOH
1.6
CH3CH2OH
1.9
[TMGC2H4NH2]BF4 (2a)
[TMGC2H4NH2]PF6 (3a)
[MImC2H4OH]Brc
3.1
2.7
58.1
9
Page 9 of 35

16
17
18
[TEAC2H4OH]Brc
KBr
49.6
3.4
99.6
99.3
99.0
TMG/KBr b
48.5
a Reaction conditions: PO 35.7 mmol, Cat. 0.5 mol%, initial CO2 pressure 2.0
MPa, Temp. 130 oC, time 2 h.
b Equal catalyst amount (0.179 mmol).
c
[MImC2H4OH]Br (1-(2-hydroxyl-ethyl)-3-methylimidazolium bromide) and
[TEAC2H4OH]Br (2-hydroxyl-ethyl-triethylammonium bromide) were
prepared according to ref [22].
One can see that the organic base tetramethylguanidine (TMG) shows almost no
activity for the synthesis of PC (entry 1) whereas the FGBILs ([TMGC2H4NH2]Br
(1a), [TMGC2H4COOH]Br (1b) and [TMGC2H4OH]Br (1c)) prepared from TMG
exhibit high catalytic activity and selectivity (entries 2-4). In comparison, the
traditional ILs [TMGC2H4CH3]Br (1d) and [TMGC2H5]Br (1e) are less efficient for
the cycloaddition reaction (entries 5, 6). Nevertheless, in the presence of alkyl
compounds containing NH2, COOH or OH group, the activity of 1e is greatly
enhanced (entries 7-9), regardless that the alkyl compounds by themselves are almost
inactive (entries 10-12). The results indicate that the functional groups play an
important role in the promotion of the reaction. However, the species used to
functionalize the guanidinium cation has distinct effect on the catalytic activity. One
can see that the activity order of FGBILs is 1a (NH2) > 1b (COOH) > 1c (OH)
(entries 2-4). While adding certain compounds containing NH2, COOH, or OH to 1e
10
Page 10 of 35

(entries 7-9), the order of activity enhancement is n-propylamine > acetic acid ≈
ethanol, in consistent with the sequence of the FGBILs. Recently, it was reported that
carboxyl- or hydroxyl-functionalized imidazolium-based ILs exhibited good catalytic
activity for the cycloaddition reaction, a result of hydrogen bonding between the
carboxyl or hydroxyl hydrogen atom and the oxygen atom of epoxide [22-23, 35-36].
In the CO2-capture procedure, it is regarded that the primary amine (R-NH2) first
reacts directly with CO2 to form carbamic acid (R-NHCOOH), then the carbamic acid
reacts with other base or water to form carbamate or carbonic acid [37-39]. However,
because the epoxide is weakly basic, the carbamic acid may interact with epoxide
through hydrogen bonding, which has a positive effect on the opening of epoxide ring.
Due to the inductive effect of amine group, the hydrogen bonding between carbamic
acid and epoxide is stronger than that between carboxylic acid and epoxide [40].
Furthermore, the hydrogen bonding between carboxylic acid and epoxide is also
stronger than that between hydroxyl and epoxide. Hence, with the influence of
hydrogen bonding on the opening of epoxide ring, the activity sequence of FGBILs
(1a (NH2) > 1b (COOH) > 1c (OH)) may be correlated to the strength of hydrogen
bonding between FGBILs and epoxide.
Furthermore, the effect of counter anions on the catalytic performance was also
evaluated. One can see that individually TMG and KBr show very poor activity for
the cycloaddition reaction (entries 1, 17) whereas using a mixture of TMG and KBr as
catalyst, there is large rise of PC yield (entry 18). The results suggest that because of
excellent nucleophilic attack on the epoxide, Br– is crucial for the synthesis of PC.
11
Page 11 of 35

–
–
Compared with Br–, BF4 and PF6 as counter anions showed lower activity (entries
13, 14), probably due to their poorer leaving ability and nucleophilicity.
Furthermore, Sun et al. [22] reported that hydroxyl functionalized
imidazolium-based and quaternary ammonium ILs exhibited good activity for the
cycloaddition reaction. In order to make a direct comparison, we evaluated the
[MImC2H4OH]Br and [TEAC2H4OH]Br ILs reported by Sun et al. under the
conditions adopted in this study, and the PC yields observed were 58.1% and 49.6%,
respectively (entries 15, 16). It is noted that the yields are lower than those observed
when 1a, 1b and 1c were used as catalysts (94.6%, 90.8% and 88.3%, respectively,
entries 2-4). It is noted that using FGBILs as catalyst, the selectivity to PC is always
above 99.8%, and only a minute amount of 1,2-propanediol generated due to PO
hydrolysis is detected as by-product. It is apparent that the FGBILs show much better
performance, and have great potential for industrial application as a single-component
catalyst for the cycloaddition of CO2 to epoxides.
3.2 Effect of reaction parameters
We adopted [TMGC2H4NH2]Br (1a) for further investigation because of its good
activity in the cycloaddition reaction. The influence of catalyst loading on PC
synthesis was investigated under identical reaction conditions. As shown in Figure 1,
with increase of 1a to PO molar ratio from 0.1 to 0.5 mol%, there is a sharp increase
of PC yield from 12.9 to 94.6%. Further increase of 1a loading to 1.0 mol% does not
result in significant rise of PC yield. Obviously, even at a low loading of 1a (0.5
mol%), excellent PC yield (94.6%) and selectivity (99.8%) can be obtained, indicating
12
Page 12 of 35

the high activity of the catalyst. Furthermore, the PC selectivity remains almost
unaffected (> 97.0%) upon a change of catalyst loading from 0.2 to 1.0 mol%.
100
100
Yield
80
60
40
20
0
Selectivity
95
90
85
80
0.0
0.2
0.4
0.6
0.8
1.0
Catalyst loading (mol%)
Figure 1. Influence of catalyst loading on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, initial CO2 pressure 2.0 MPa, 130 oC, 2 h)
The dependence of PC yield and selectivity on reaction temperature is illustrated in
Figure 2. It is obvious that the reaction is temperature-sensitive. With increase of
o
temperature from 110 to 130 C, PC yield rapidly increased from 55.1% to 94.6%.
o
Further rise of temperature to 150 C would cause only a slight increase of PC yield
(to 97.3%). Striking a balance between energy consumption and PC yield, we chose
o
130 C as the reaction temperature for PC synthesis. It is noted that the selectivity to
PC is almost independent of temperature change within the 110-150 oC range: always
above 99.7%. It was reported that using hydroxyl- [35, 41] and carboxyl- [23]
o
functionalized imidazolium ILs as catalyst, temperature higher than 130 C would
cause a decrease of PC selectivity. Moreover, Yang et al. [33] reported that when
amidinium-based ILs (1,8-diazabicylo [5.4.0]undec-7-enium chloride) were used as
13
Page 13 of 35

o
catalysts, a lowering of temperature below 140 C would result in a decline of PC
selectivity. From the results, it can be seen that the as-synthesized 1a catalyst shows
superior performance.
100
90
80
70
60
50
100
98
96
94
92
90
Yield
Selectivity
110
120
130
140
150
o
Temperature( C)
Figure 2. Influence of reaction temperature on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa, 2 h)
It was observed that the PC yield is strongly affected by the initial CO2 pressure. As
shown in Figure 3, an increase of initial CO2 pressure would result in a rapid rise of
PC yield in the low-pressure range (1.5-2.5 MPa), but there was a moderate decrease
of yield in the high-pressure range (2.5-4.0 MPa). At an initial CO2 pressure of 2.5
MPa, PC yield was the highest (96.7%) under the reaction conditions of 130 oC and 2
h. Such an effect of CO2 pressure on catalytic activity was observed in other catalytic
systems [27, 42, 43]. The phenomenon can be explained based on the concepts of
reaction equilibrium and mass transfer of reactant. PC is in its liquid form under the
adopted reaction conditions and an increase of CO2 pressure should be a positive
factor for PO conversion. It is well known that acidic CO2 could dissolve in basic
14
Page 14 of 35

epoxide and liquefies due to CO2-epoxide complexing [43, 44]. In the low-pressure
range, an increase of CO2 pressure leads to moderate CO2-PO complexing in the
liquid phase, and there is enhancement of PC yield. However, in the high-pressure
range, rather than promoting interaction among CO2, PO and catalyst, heavy CO2-PO
complexing becomes a negative factor because it is getting difficult to separate CO2
and PO. Thus the competition between these opposite factors results in a decline of
catalytic activity in the high-pressure range. It is noted that PC selectivity is always
above 99.6% and can be consider as independent of CO2 initial pressure.
100
100
98
96
94
92
90
80
Yield
Selectivity
60
40
0
1
2
3
4
Initial CO pressure ( MPa)
2
Figure 3. Influence of initial CO2 pressure on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, 1a 0.5 mol%, 130 oC, 2 h)
The influence of reaction time on PC synthesis is depicted in Figure 4. One can see
that the cycloaddition reaction proceeds rapidly in the first 2 h, reaching a PC yield of
94.6%. After that, the increase of PC yield becomes gradual. Hence, 2 h was chosen
as the reaction time in this study. Furthermore, the selectivity to PC stays above
99.8% throughout.
15
Page 15 of 35

100
90
80
70
60
50
100
98
96
94
92
90
Yield
Selectivity
1
2
3
4
5
Time (h)
Figure 4. Influence of reaction time on PC yield and selectivity. (Reaction conditions:
PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa, 130 oC)
3.3 Catalytic activity towards other epoxides
In order to investigate the generality of [TMGC2H4NH2]Br (1a), the cycloaddition
of CO2 to different epoxides was examined at 130 oC and 2.0 MPa, and the results are
summarized in Table 2. As shown, the catalyst 1a exhibits high activity and
selectivity across a variety of terminal epoxides (4a-f) (entries 1-6). Within 3 h, the
corresponding cyclic carbonates (5a-f) were formed quantitatively. However, epoxide
4g showed poor reactivity, and the yield of the corresponding cyclic carbonate (5g)
was just 83.3% after a prolonged reaction period of 20 h. It is probably due to the fact
that the two rings of cyclohexene oxide hinder the nucleophilic attack of Br－, causing
the rate of ring-opening to decrease. It is well known that the epoxides with an
electron-withdrawing group are able to stabilize the intermediate structure formed
after ring-opening of epoxides, thus enhancing the reactivity [32]. Hence, epoxides 4a,
4c and 4f are preferred substrates for the cycloaddition reaction (entries 1, 3, 6) due to
16
Page 16 of 35

Table 2. Cycloaddition of CO2 to different epoxides catalyzed by 1aa
Catalytic results
Time
Entry Epoxide
Product
Yield
Sel.
(h)
(%)
(%)
O
O
1
3
99.8
94.6
99.8
1
2
(4a)
O
O
(5a)
O
O
O
O
99.8
CH3
(4b)
CH3
(5b)
O
O
O
O
2
5
99.2
99.0
99.7
99.5
3
4
Cl
(4c)
Cl
(5c)
O
O
O
O
CH3
( )3
(4d)
CH3
( )3
(5d)
O
O
O
O
3
4
99.4
99.7
5
(4e)
(5e)
O
O
O
O
98.9
83.3
98.9
99.7
O
6
7
Ph
(4f)
O
Ph
(5f)
O
O
O
20
O
(4g)
(5g)
a Reaction conditions: PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa,
Temp. 130 oC.
17
Page 17 of 35

the less sterical hindrance (4a) or the strong electron with-drawing groups (4c, 4f). In
these cases, reactions could complete within 1 h. Moreover, the sequence of reactivity
of the other epoxides (4b ≈ 4e > 4d, entries 2, 4, 5) is understandable based on similar
concepts.
3.4 Catalyt recycling
Yield
Selectivity
100
80
60
40
20
0
1
2
3
4
5
Run
Figure 5. Reusability of catalyst 1a. (Reaction conditions: PO 35.7 mmol, 1a 0.5
mol%, initial CO2 pressure 2.0 MPa, 130 oC, 2 h)
Catalyst 1a shows excellent activity towards the synthesis of cyclic carbonates. It is
well known that stability and reusability of a catalyst are key factors that determine
whether it is industrially applicable. We studied the reusability of 1a using PO as
model substrate in a series of runs. In the test, the catalyst was separated from the
reaction mixture by distillation under reduced pressure and then used for the next run
under the same conditions. As shown in Figure 5, there is no significant change of PC
yield and selectivity across the five runs. The results indicate that the catalyst 1a can
be reused with stable performance.
18
Page 18 of 35

3.5 Possible Mechanism
(a)
(b)
1776
1240
4000
3500
3000
2500
2000
1500
1000
-1
Wavenumber (cm )
Figure 6. FT-IR spectra of (a) 1a/CO2, and (b) 1a.
In the case of using carboxyl or hydroxyl functionalized imidazolium-based ILs, it
was regarded that hydrogen bonding between the hydrogen atom of carboxyl (or
hydroxyl) and the oxygen atom of epoxide would result in polarization of C-O bond,
which could facilitate the ring open of epoxide [22, 35-36].
Among the FGBILs (1a, 1b and 1c), the amino-functionalized IL (1a) exhibits the
best catalytic activity. In order to illustrate the role of amino group, we obtained the
1HNMR spectrum of 1a as well as that of 1a and PO mixture (molar ratio 1:10) using
DMSO-d6 as solvent. We observe no change of chemical shift of H atom of amino
group in both cases. We hence deduce that there is no significant interaction between
the amino group and epoxide. In general, primary amine (R-NH2) can react directly
with CO2 to form carbamic acid species (R-NHCOOH) [37-39]. To clarify the
interaction between amino group and CO2, we carried out FT-IR analysis of 1a and
19
Page 19 of 35

NH2
(1a)
TMG
Br
O
R
O
CO2
NHCOOH
O
O
O
R
TMG
Br
TMG
NHCOOH
O
TMG
NHCOOH
(I)
O
O
(III)
Br
R
R
Br
TMG
NHCOOH
O
Br
(II)
CO2
R
Scheme 2. Proposed mechanism for the cycloaddition reaction.
1a/CO2 (keeping 1a in 4 MPa of CO2 for 4 h). As shown in Figure 6, the spectra of
1a/CO2 exhibits the characteristic bands of C=O (1776 cm-1) and C-O stretching
(1240 cm-1), which indicates the formation of carbamic acid species. In cycloaddition
reaction, because of the weak basicity of epoxide, the carbamic acid may interact with
epoxide through hydrogen bonding; such an interaction has a positive effect on the
opening of epoxide ring. Based on such an understanding, a plausible mechanism is
proposed as shown in Scheme 2. First, coordination of the central C atom of cation
and the H atom of carbamic acid species with the O atom of epoxide results in
polarization of epoxide C-O bond and formation of intermediate I. Then, nucleophilic
attack of bromide ion on the less sterically hindered β-carbon atom of epoxide
furnishes ring opening and the formation of intermediate II. Second, the oxygen of
20
Page 20 of 35

intermediate II interacts with CO2 to form halocarbonate III that transforms to cyclic
carbonate through intermolecular displacement of the bromide ion.
4. Conclusions
We developed a facile, reliable, and highly selective catalytic protocol for the
synthesis of cyclic carbonate using a type of novel FGBILs as acid-base bifunctional
catalysts under solvent- and metal-free conditions. The FGBILs are easily synthesized,
air-stable, cheap and environment-benign. They perform well as catalysts in the
cycloaddition of CO2 to epoxides, especially the NH2-functionalized one. The
interaction of functional groups with epoxide through hydrogen bonding and Lewis
acid activation strengthens the polarization of epoxide C-O bond, facilitating
ring-opening of epoxide as a result. The bromide anion also plays an important role in
the ring-opening process through nucleophilic attack of epoxide. With excellent
performance, the FGBILs are potentially applicable for chemical fixation of CO2 in an
industrial scale. It is envisaged that the scientific findings are useful for the design of
new and efficient catalysts for cycloaddition reaction of epoxides.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of
China (Grant Nos. 51104089, 51238002, and 51272099), Jiangxi Province Science
and Technology Project (Grant Nos. 2010AIB00400); Jiangxi Province Science and
Technology Support Program (Grant Nos. 20111BBG70003-4); and Natural Science
Foundation of Jiangxi Province (Grant Nos. 20122BAB213013).
References
21
Page 21 of 35

[1] T. Sakakura, J. C. Choi, H. Yasuda, Chem. Rev. 107 (2007) 2365–2387.
[2] X. B. Lu, D. J. Darensbourg, Chem. Soc. Rev. 41 (2012) 1462–1484.
[3] M. North, R. Pasquale, C. Young, Green Chem. 12 (2010) 1514–1539.
[4] W. L. Dai, S. L. Luo, S. F. Yin, C. T. Au, Appl. Catal. A: Gen. 366 (2009) 2–12.
[5] Y. Du, F. Cai, D. L. Kong, L. N. He, Green Chem. 7 (2005) 518–523.
[6] T. Sako, T. Fukai, R. Sahashi, Ind. Eng. Chem. Res. 41 (2002) 5353–5358.
[7] B. M. Bhanage, S. I. Fujita, Y. Ikushima, M. Arai, Appl. Catal. A: Gen. 219 (2001)
259–266.
[8] W. L. Dai, S. F. Yin, R. Guo, S. L. Luo, X. Du, C. T. Au, Catal. Lett. 136 (2010)
35–44.
[9] K. Yamaguchi, K. Ebitani, T. Yoshida, H. Yoshida, K. Kaneda, J. Am. Chem. Soc.
121 (1999) 4526–4527.
[10] E. J. Doskocil, J. Phys. Chem. B, 109 (2005) 2315–2320.
[11] R. Srivastava, D. Srinivas, P. Ratnasamy, Catal. Lett. 91 (2003) 133–139.
[12] X. B. Lu, B. Liang, Y. J. Zhang, Y. Z. Tian, Y. M. Wang, C. X. Bai, H. Wang, R.
Zhang, J. Am. Chem. Soc. 126 (2004) 3732–3733.
[13] L. L. Jin, H. W. Jing, T. Chang, X. L. Bu, L. Wang, Z. L. Liu, J. Mol. Catal. A:
Chem. 261 (2007) 262–266.
[14] J. A. Osma, A. L. Sánchez, M. North, A. Otero, and P. Villuendas. Catal. Sci.
Technol. 2 (2012) 1021–1026.
[15] F. Ahmadi, S. Tangestaninejad, M. Moghadam, V. Mirkahani, I. M. Baltork, A. R.
Khosropour, Polyhedron, 32 (2012) 68–72.
22
Page 22 of 35

[16] J. J. Peng, Y. Q. Deng, New J. Chem. 25 (2001) 639–641.
[17] H. Kawanami, A. Sasaki, K. Matsui, Chem. Commun. 39 (2003) 896–897.
[18] J. M. Sun, S. I. Fujita, F. Y. Zhao, M. Arai, Green Chem. 6 (2004) 613–616.
[19] H. S. Kim, J. J. Kim, H. Kim, H. G. Jang. J. Catal. 220 (2003) 44–46.
[20] J. K. Lee, Y. J. Kim, Y. S. Choi, H. Lee, J. S. Lee, J. Hong, E. K. Jeong, H. S.
Kim, M. Cheong, Appl. Catal. B: Environ. 111–112 (2012) 621–627.
[21] J. Y. Kim, R. S.Varma, J. Org. Chem. 20 (2005) 7882–7891.
[22] J. Sun, S. J. Zhang, W. G. Cheng, J. Y. Ren, Tetrahedron Lett. 49 (2008)
3588–3591.
[23] J. Sun, L. J. Han, W. G. Cheng, J. Q. Wang, X. P. Zhang, S. J. Zhang,
ChemSusChem. 4 (2011) 502–507.
[24] V. Calo, A. Nacci, A. Monopoli, A. Fanizzi, Org. Lett. 4 (2002) 2561–2563.
[25] J. M. Sun, S. I. Fujita, F. Y. Zhao, M. Arai, Appl. Catal. A: Gen. 287 (2005)
221–226.
[26] L. N. He, H. Yasuda, T. Sakakura, Green Chem. 5 (2003) 92–94.
[27] S. S. Wu, X. W. Zhang, W. L. Dai, S. F. Yin, W. S. Li, Y. Q. Ren, C. T. Au, Appl.
Catal. A: Gen. 341 (2008) 106–111.
[28] H. Y. Ju, J. Y. Ahn, M. D. Manju, K. H. Kim, D. W. Park, Korean J. Chem. Eng.
25 (2008) 471–473.
[29] H. B. Xie, H. F. Duan, S. H. Li, S. B. Zhang, New J. Chem. 29 (2005) 1199–
1203.
[30] H. B. Xie, S. H. Li, S. B. Zhang, J. Mol. Catal. A: Chem. 250 (2006) 30–34.
23
Page 23 of 35

[31] X. Y. Dou, J. Q. Wang, Y. Du, E. Wang, L. N. He, Synlett. 19 (2007) 3058–3062.
[32] B. Ochiai, T. Iwamoto, T. Endo, Green Chem. 8 (2006) 138–140.
[33] Z. Z. Yang, L. N. He, C. X. Miao, S. Chanfreau, Adv. Synth. Catal. 352 (2010)
2233–2240.
[34] G. Ye, S. W. Arritt, B. Twamley, J. M. Shreeve, Inorg. Chem. 44 (2005)
1704–1712.
[35] R. A. Watile, K. M. Deshmukh, K. P. Dhake, B. M. Bhanage, Catal. Sic. Technol.
2 (2012) 1051–1055.
[36] S. G. Liang, H. Z. Liu, T. Jiang, J. L. Song, G. Y. Yang, B. X. Han, Chem.
Commun. 47 (2011) 2131–2133.
[37] Z. Zelenak, D. Halamova, L. Gaberova, E. Bloch, P. Llewellyn, Micro. Meso.
Mater. 116 (2008) 358–364.
[38] B. Arstad, H. Fjellvåg, K. O. Kongshaug, O. Swang, R. Blom, Adsorption 14
(2008) 755–762.
[39] F. S. Li, R. P. Lively, J. S. Lee, W. J. Koros, Ind. Eng. Chem. Res.
dx.doi.org/10.1021/ie3029224.
[40] S. Winiwater, N. M. Bonham, F. Ax, A. Hallberg, H. Lennernas, A. Karlen. J.
Med. Chem. 41 (1998) 4939–4949.
[41] J. Sun, W. G. Cheng, W. Fan, Y. H. Wang, Z. Y. Meng, S. J. Zhang, Catal. Today,
148 (2009) 361–367.
[42] W. L. Dai, L. Chen, S. F. Yin, W. H. Li, Y. Y. Zhang, S. L. Luo, C. T. Au, Catal.
Lett. 137 (2010) 74–80.
24
Page 24 of 35

[43] L. F. Xiao, F. W. Li, J. J. Peng, C. G. Xia, J. Mol. Catal. A: Chem. 253 (2006)
265–269.
[44] R. Nomura, M. Kimura, S. Teshima, A. Ninagawa, H. Matsuda, Bull Chem. Soc.
Jpn. 55 (1982) 3200–3203.
25
Page 25 of 35

Figure Captions
Figure 1. Influence of catalyst loading on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, initial CO2 pressure 2.0 MPa, 130 oC, 2 h)
Figure 2. Influence of reaction temperature on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa, 2 h)
Figure 3. Influence of initial CO2 pressure on PC yield and selectivity. (Reaction
conditions: PO 35.7 mmol, 1a 0.5 mol%, 130 oC, 2 h)
Figure 4. Influence of reaction time on PC yield and selectivity. (Reaction conditions:
PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa, 130 oC)
Figure 5. Reusability of catalyst 1a. (Reaction conditions: PO 35.7 mmol, 1a 0.5
mol%, initial CO2 pressure 2.0 MPa, 130 oC, 2 h)
Figure 6. FT-IR spectra of (a) 1a/CO2, and (b) 1a.
Scheme 1. Structures of FGBILs.
Scheme 2. Proposed mechanism for the cycloaddition reaction.
26
Page 26 of 35

Table 1. Performance of various catalystsa
Catalytic results
Entry
Catalyst
Yield [%]
1.8
Sel. [%]
88.5
99.8
99.9
99.8
99.8
99.7
99.6
99.7
99.7
99.0
98.6
99.1
99.1
99.0
99.6
99.6
99.3
99.0
1
TMG
2
[TMGC2H4NH2]Br (1a)
[TMGC2H4COOH]Br(1b)
[TMGC2H4OH]Br (1c)
[TMGC2H4CH3]Br (1d)
[TMGC2H5]Br (1e)
[TMGC2H5]Br/CH3(CH2)2NH2
[TMGC2H5]Br/CH3COOHb
[TMGC2H5]Br/CH3CH2OHb
CH3CH2CH2NH2
94.6
90.8
88.3
71.6
62.8
80.3
78.0
78.8
6.0
3
4
5
6
b
7
8
9
10
11
12
13
14
15
16
17
18
CH3COOH
1.6
CH3CH2OH
1.9
[TMGC2H4NH2]BF4 (2a)
[TMGC2H4NH2]PF6 (3a)
[MImC2H4OH]Brc
[TEAC2H4OH]Brc
KBr
3.1
2.7
58.1
49.6
3.4
TMG/KBr b
48.5
a Reaction conditions: PO 35.7 mmol, Cat. 0.5 mol%, initial CO2 pressure 2.0
27
Page 27 of 35

MPa, Temp. 130 oC, time 2 h.
b Equal catalyst amount (0.179 mmol).
c [MImC2H4OH]Br (1-(2-hydroxyl-ethyl)-3-methylimidazolium bromide) and
[TEAC2H4OH]Br (2-hydroxyl-ethyl-triethylammonium bromide) were
prepared according to ref [22].
28
Page 28 of 35

Table 2. Cycloaddition of CO2 to different epoxides catalyzed by 1aa
Catalytic results
Time
Entry Epoxide
Product
Yield
Sel.
(h)
(%)
(%)
O
O
1
3
99.8
94.6
99.8
1
2
(4a)
O
O
(5a)
O
O
O
O
99.8
CH3
(4b)
CH3
(5b)
O
O
O
O
2
5
99.2
99.0
99.7
99.5
3
4
Cl
(4c)
Cl
(5c)
O
O
O
O
CH3
( )3
(4d)
CH3
( )3
(5d)
O
O
O
O
3
4
99.4
99.7
5
(4e)
(5e)
O
O
O
O
98.9
83.3
98.9
99.7
O
6
7
Ph
(4f)
O
Ph
(5f)
O
O
O
20
O
(4g)
(5g)
a Reaction conditions: PO 35.7 mmol, 1a 0.5 mol%, initial CO2 pressure 2.0 MPa,
Temp. 130 oC.
29
Page 29 of 35