Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable catalysts for the synthesis of cyclic carbonates from CO2 and expoxides

Article abstract of DOI:10.1016/j.cattod.2014.02.042

Polymer grafted with asymmetrical dication ionic liquid (IL) based on imidazolium and phosphonium ([P-Im-C₄H₈Ph ₃P]Br₂) was fabricated, and for the first time evaluated as catalyst for the synthesis of cyclic ca

Full text of DOI:10.1016/j.cattod.2014.02.042

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Polymer grafted with asymmetrical dication ionic liquid as efficient
and reusable catalysts for the synthesis of cyclic carbonates from CO2
and expoxides
a
a
a,∗
a
a
a,b
Dai Wei-Li , Jin Bi , Luo Sheng-Lian , Luo Xu-Biao , Tu Xin-Man , Au Chak-Tong
a
Key Laboratory of Jiangxi Province for Persistant Pollutants Control and Resources Recycle, Nanchang Hangkong University, Nanchang 330063, Jiangxi,
China
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online xxx
Polymer grafted with asymmetrical dication ionic liquid (IL) based on imidazolium and phosphonium
([P-Im-C4H8Ph3P]Br2) was fabricated, and for the first time evaluated as catalyst for the synthesis of
cyclic carbonates from epoxides and CO2 without using any co-catalyst and solvent. The catalyst showed
much superior activity than monocation imidazolium and phosphonium ILs. At a low catalyst loading
Keywords:
Carbon dioxide
Epoxide
Cyclic carbonate
Asymmetrical dication ionic liquid
Heterogeneous catalysis
(
0.38 mol%), high yield (96.8%) and selectivity (99.5%) of propylene carbonate can be obtained over [P-
◦
Im-C4H8Ph3P]Br2 at 130 C and 2.5 MPa in 4 h. The cooperation of nucleophilic attack of bromine anions as
well as the activation of the two cations may contribute to the good activity of the catalyst. Furthermore,
the catalyst shows excellent stability and reusability. It can be reused for up to five runs without any
significant loss of catalytic activity after simple filtration.
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
liquids (ILs) [23–30] were studied for cycloaddition reactions.
At present, most of the ILs used are traditional monocation ILs
such as imidazolium [31–35], quaternary ammonium [36–39], and
quaternary phosphonium [3,13,23,26] ILs. The homogeneous and
hetergeneous catalyst systems developed so far are unsatisfactory
in activity and/or reusability, and there are disadvantages such as
harsh reaction conditions, water and/or air sensitivity of the metal-
containing catalysts, and the use of organic solvents (e.g. DMF,
toluene, CH Cl ). From the viewpoints of industrial application and
It is well known that the current chemical industry depends
heavily on fossil-based carbon sources, in particular petroleum,
that are only available for a few more decades [1]. Despite being
blamed for global warming, CO2 is a renewable carbon source that
is economical, nontoxic and abundant [2–5]. Hence, CO is an alter-
native, and is considered as a renewable feedstock for the chemical
industry. There are over 20 reaction processes that use CO2 as a
2
2
2
raw material [1,6]. One of them is the cycloaddition of CO to epox-
ides which is considered to be promising and feasible for industrial
application.
environment friendliness, there is a need to develop metal- and
solvent-free catalysts that show high stability and activity under
mild reaction conditions.
2
Cyclic carbonates are valuable chemicals that can be used as
aprotic polar solvents, electrolytic elements of lithium secondary
batteries, monomers for polycarbonates, ingredients for pharma-
ceutical as well as fine chemical intermediates [3–5,7–9]. In the
past decades, a wide range of catalysts such as alkali metal salts
Recently, it was reported that the introduction of functional
groups (such as carboxyl, hydroxyl, and amino groups) into the
adopted cations is a strategy to enhance the catalytic activity of
traditional monocation ILs [30,35,40–45]. However, due to the lack
of proper functional groups and methods for functionalization, it
is difficult to further improve the performance of traditional ILs.
Compared to traditional monocation ILs, geminal dication ILs have
advantages in term of thermal stability and volatility, as well as
tenability of physical and chemical properties [46]. Potentially,
they can be used as lubricants [47] and solvents [48–50] for high-
temperature uses, gas chromatography stationary phases [51], and
catalysts for esterification [52] and transesterification reactions
[53,54]. To the best of our knowledge, the use of dication ILs as
[
10,11], metal oxides [12,13], modified molecular sieves [14,15],
organic bases [16–18], organometallic complexes [19–22] and ionic
∗ Corresponding author at: College of Environmental and Chemical Engineering,
Nanchang Hangkong University, Nanchang 330063, Jiangxi, China.
Tel.: +86 791 83953373; fax: +86 791 83953373.
E-mail address: sllou@hnu.edu.cn (L. Sheng-Lian).
http://dx.doi.org/10.1016/j.cattod.2014.02.042
0
920-5861/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
lysts for the synthesis of cyclic carbonates from CO and expoxides, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.042
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Scheme 1. Procedure for the preparation of polymer grafted with dication IL.
catalysts for the synthesis of cyclic carbonates has not been
reported before. It is envisaged that dication ILs can be synthesized
as high efficient catalysts through proper selection of cations and
modification with functional groups. In this study, we developed a
simple, feasible and effective method to immobilize imidazolium
with phosphonium on a polymer. The as-synthesized asymmetri-
cal dication IL was used for the first time as heterogeneous catalyst
for the cycloaddition of CO2 to epoxides.
the polymer. On the other hand, using methylimidazole instead
of P-Im we prepared 1-(3-methylimidazolium-1-yl) butane-
(triphenylphosphonium) bibromide ([MIm-C H Ph P]Br ).
4
8
3
2
2.3. Characterization
Scanning electron microscopic (SEM) observations were carried
out over a Nova NanoSEM 450 microscope. Energy dispersive X-
ray spectroscopy (EDS) analysis was performed using accessory
(INCA 250) of Nova NanoSEM 450 instrument. Thermogravimetric-
differential scanning calorimetry (TG-DSC) analysis was performed
on a SDT Q600 (TA Instruments-Waters LLC) at a heating rate
2
. Experimental
2.1. Chemicals
◦
of 10 C/min in a N2 flow. NMR spectra were recorded on
The poly-divinylbenzene (PDVB) grafted with 1-(3-amino-
propyl)imidazole (denoted as P-Im; QuadraPure ImDAZ;
00–400 ␮m particle size, extent of labeling: 1.5 mmol/g load-
ing, 1% cross-linked with divinylbenzene) was purchased from
Sigma–Aldrich Chemical Reagent Co., Ltd. Propylene oxide
a Bruker 400 spectrometer using DMSO-d6 as solvent. High-
resolution mass spectra (HRMS) were conducted on a Waters
Xevo G2-S Q-Tof equipped with an ESI source. The FT-IR spectra
were recorded using a Bruker vertex 70 FT-IR spectrophotome-
ter.
1
(
PO), 1,4-dibromobutane, triphenylphosphine (Ph P) and 1-
3
Bromobutane were purchased from Sinopharm Chemical Reagent
Co., Ltd. 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.
2.4. General procedure for synthesis of cyclic carbonates
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), catalyst (0.38 mol%, calculated based on the amount
of IL), and an appropriate amount of biphenyl (as internal stan-
dard for GC analysis). 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
2
.2. Preparation of polymer grafted with dication ILs
The procedure for grafting the polymer
with
asymmetrical dication IL is shown in Scheme 1. First, (4-
bromobutyl)triphenylphosphonium bromide) ([Ph PC H Br]Br)
◦
time. Then the reactor with its content was cooled to 0 C in an
3
4
8
ice-water bath, and the remaining CO2 was released. The result-
ing mixture was analyzed using a GC (Agilent 7890 A) that was
equipped with a flame ionization detector (FID) and a DB-wax cap-
illary column (30 m × 0.45 mm × 0.85 ␮mm). The products were
identified by GC–MS and NMR (TMS as internal standard) meth-
ods.
was synthesized according to the following procedure (Scheme 1a):
A mixture of triphenylphosphine (10 mmol), 1,4-dibromobutane
(
10 mmol), and toluene (20 mL) was under reflux in a round bottom
flask (100 mL) for 24 h in a nitrogen atmosphere. The as-resulted
mixture was cooled down and subject to filtration. The obtained
residue was washed three times with diethyl ether, followed by
◦
drying at 60 C for 12 h in vacuum to give [Ph PC H Br]Br as a
3
4
8
1
white solid. H NMR (400 MHz, DMSO-d ): ı = 7.90–7.73 (m, 15 H),
.63–3.32 (m, 4 H), 2.49–2.47 (m, 2 H), 1.99–1.64 (m, 2 H).
3. Results and discussion
6
13
3
C
NMR (100.6 MHz, DMSO-d ): ı = 135.4, 130.8, 119.3, 40.2, 34.2,
3.1. Characterization
6
3
1
3.2, 20.8, 19.6. IR (neat): n = 3074, 3057, 2931, 2885, 2862, 1585,
485, 1436, 750, 690 cm . HR-MS (QTOF): m/z = 399.0864, calcd.
−1
The polymer grafted with asymmetrical dication IL ([P-
Im-C H Ph P]Br ) was prepared through grafting monocation
for C22H25PBr (M + H): 399.0877. We also synthesized butylt-
riphenylphosphonium bromide ([Ph P-C H ]Br) using the same
method.
4
8
3
2
phosphonium cation onto the surface of P-Im that was grafted with
an imidazole group via covalent bonding. The [P-Im-C H Ph P]Br
3
4
9
4
8
3
2
According to Scheme 1b, we grafted the dication IL onto the
polymer to produce the heterogeneous catalyst (denoted as [P-
and P-Im were characterized by FT-IR analysis. As shown in
Fig. 1, compared with P-Im, [P-Im-C H Ph P]Br exhibits the
4
8
3
2
−
1
Im-C H Ph P]Br ). First a mixture of [Ph PC H Br]Br (6.0 mmol),
C-P stretching band (1411 cm ) and the characteristic skele-
4
8
3
2
3
4
8
−
1
P-Im (2.0 g), and toluene (20 mL) was added to a 100 mL flask,
and the as-obtained mixture was refluxed for 24 h in a nitrogen
atmosphere. The obtained solid was filtered out, washed three
ton stretching bands of benzene (1562, 1494 and 1436 cm ).
It is hence evidenced that there is the successful grafting of
imidazolium and phosphonium dication IL onto the polymer sur-
face.
◦
times with ethyl acetate, and dried at 60 C for 12 h in vacuum to
give the [P-Im-C H Ph P]Br . Following the same procedure, we
The morphology of P-Im and [P-Im-C H Ph P]Br was studied
4
8
3
2
4
8
3
2
separately grafted 1-(4-bromobutyl) imidazolium bromide ([P-Im-
C H Br]Br), and 1-butylimidazolium bromide ([P-Im-C H ]Br) on
by SEM. As shown in Fig. 2a and b, the surface of P-Im is smooth.
With the grafting of IL on the material, there is clear roughening of
4
8
4
9
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
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(
a)
(
b)
1
494
3396
1
411
1
562
1436
Fig. 3. EDS spectrum of [P-Im-C4H8Ph3P]Br2.
3
.2. Catalytic performance
4
000
3500
3000
2500
2000
1500
1000
-
1
Wavenumber (cm )
To investigate the effects of molecular composition (imid-
azolium, phosphonium cation, and bromide anion) on the
cycloaddition reaction, we studied the activity of the prepared
catalysts, and the results are summarized in Table 1. One can
see that the imidazole-grafted polymer (P-Im) shows poor cat-
alytic activity (entry 1). With the introduction of monocation
imidazolium-based IL onto the polymer, there is improvement
of catalytic activity, but the yield of propylene carbonate (PC)
over [P-Im-C H ]Br and [P-Im-C H Br]Br is not satisfactory (76.5%
Fig. 1. FT-IR spectra of (a) P-Im and (b) [P-Im-C4H8Ph3P]Br2.
surface (Fig. 2c and d). The EDS spectrum of [P-Im-C H Ph P]Br
2
4
8
3
(
Fig. 3) shows the presence of phosphorus and bromine, suggesting
the successful grafting of dication onto the support.
Depicted in Fig. 4 are the TG and DSC curves of P-Im and [P-
4
9
4
8
Im-C H Ph P]Br . It is clear that both materials are stable up to
4
◦
8
3
2
and 75.1% respectively, entries 2 and 3). Furthermore, the use
of monocation phosphonium-based IL ([Ph P-C H ]Br and [Ph P-
◦
3
[
00 C. Upon heating to 450 C, there is the pyrolysis of P-Im and
3
4
9
3
P-Im-C H Ph P]Br . The decomposition of the latter involves two
4
8
3
2
C H Br]Br) as homogeneous catalysts also result in poor activity
4 8
◦
endothermic steps at 338 and 420 C, plausibly due to the decompo-
sition of dication IL and polymer support, respectively. The results
(74.3% and 75.5% PC yield, respectively, entries 4 and 5). However,
superior catalytic activity is observed over the polymer grafted
with the dication IL prepared from imidazolium with phospho-
nium; PC yield of 96.8% and PC selectivity of 99.5% are achieved over
reveal that [P-Im-C H Ph P]Br can tolerate a temperature as high
4
8
3
2
◦
as 260 C (Fig. 4b).
Fig. 2. SEM images of (a, b) P-Im and (c, d) [P-Im-C4H8Ph3P]Br2.
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
lysts for the synthesis of cyclic carbonates from CO and expoxides, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.042
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system, especially at the initial stage. On the other hand, under
stirring the [P-Im-C H Ph P]Br particles are well dispersed.
4
8
3
2
To further investigate the effects of molecular composition
on the catalytic activity of polymers that are grafted with dica-
tion IL, we evaluated the activities of [P-Im-C H Ph P]Br that
4
8
3
2
were formed by different combinations of ingredients. One can
see that the P-Im/[Ph P-C H Br]Br having both imidazole group
3
4
8
and monocation phosphonium IL shows lower activity than
P-Im-C H Ph P]Br (entry 8 versus 6). Moreover, over [P-Im-
[
4
8
3
2
C H Br]Br/Ph P having both monocation imidazolium IL and Ph P,
4
8
3
3
the PC yield is only 78.5% which is much lower than that over
P-Im-C H Ph P]Br (entry 9 versus 6). However, a combined use
[
4
8
3
2
of [P-Im-C H ]Br and [Ph P-C H ]Br that includes two momoca-
4
9
3
4
9
tion ILs results in activity almost equal that of [P-Im-C H Ph P]Br
4
8
3
2
(entry 10 versus 6). The fact that the activity of dication IL is
much superior than that observed in the case of combined use
of ingredients indicates that both cations of [P-Im-C H Ph P]Br
4
8
3
2
are beneficial to the cycloaddition reaction. It was reported that
nucleophilic attack on the epoxide by a halide anion of ILs is cru-
cial [28,41,55,56]. Compared to [P-Im-C H ]Br, [P-Im-C H Br]Br
4
9
4
8
containing one more bromine as substituent group is similar in
activity (entry 2 versus 3). Such phenomenon is also observed over
[
Ph P-C H ]Br and [Ph P-C H Br]Br (entry 4 versus 5). The results
3 4 9 3 4 8
demonstrate that it is the bromine anions that are participating
in the cycloaddition reaction. Hence, the superior activity of [P-
Im-C H Ph P]Br is ascribed to the imidazolium and phosphonium
4
8
3
2
cations as well as to the availability of bromine anions in doubled
amount.
Before, Zhang et al. [41] and Dai et al. [45] reported that PDVB
grafted with hydroxyl- and carboxyl-functionalized imidazolium-
based IL (denoted as [P-HEIm]Br and [P-CEIm]Br) show good
catalytic activity for the synthesis of cyclic carbonates. In order to
make a direct comparison, we evaluated the [P-HEIm]Br and [P-
CEIm]Br catalysts under the conditions adopted in this study, and
the PC yields were found to be 88.1% and 85.6%, respectively (entries
Fig. 4. TG and DSC curves of (a) P-Im and (b) [P-Im-C4H8Ph3P]Br2.
1
1 and 12), lower than that observed over [P-Im-C H Ph P]Br
4 8 3 2
(
96.8%). It is apparent that the polymer grafted with dication IL has
[
P-Im-C H Ph P]Br at low catalyst loading of 0.38 mol% under rel-
4 8 3 2
greater potential for industrial application as a heterogeneous cat-
alyst for the cycloaddition of CO to epoxides. Moreover, It is noted
that while using monocation or dication ILs as catalysts, only a
minute amount of 1,2-propanediol generated due to PO hydrolysis
is detected as by-product in the cycloaddition reaction.
atively mild reaction conditions (entry 6). Based on the results,
we attribute the superior activity of [P-Im-C H Ph P]Br to the
presence of dication IL. Moreover, the performance of [P-Im-
C H Ph P]Br is better than that of the homogeneous dication
2
4
8
3
2
4
8
3
2
IL[MIm-C H Ph P]Br catalyst (entry 6 versus 7). The main reason
4
8
3
2
for such a phenomenon is that due to the poor miscibility of [MIm-
C H Ph P]Br in PO, the IL does not disperse well in the reaction
3
.3. Effects of reaction parameters on catalytic activity of
4
8
3
2
[P-Im-C H Ph P]Br
4
8
3
2
The results so far indicate that [P-Im-C H Ph P]Br is an effec-
4
8
3
2
Table 1
Catalytic performance of catalysts .
tive catalyst for the cycloaddition of CO2 to epoxide. It is generally
accepted that reaction parameters such as temperature, time and
initial CO2 pressure have a significant effect on product yield. We
investigated the dependence of PC yield and selectivity on reaction
parameters. As shown in Fig. 5, the temperature has a pronounced
positive effect on the cycloaddition reaction when it rises from
a
Entry
Catalyst
Catalytic results
Yield (%)
Sel. (%)
1
2
3
4
5
6
7
8
9
P-Im
[P-Im-C4H9]Br
[P-Im-C4H8Br]Br
[Ph3P-C4H9]Br
8.9
76.5
75.1
74.3
75.5
96.8
90.6
88.8
82.6
95.1
88.1
85.6
96.2
99.1
99.7
99.6
99.5
99.5
99.6
99.7
99.4
99.7
99.8
99.7
◦
◦
110 to 130 C, but a further rise from 130 to 150 C causes a slight
decrease of PC yield and selectivity. It is plausible that the decrease
[Ph3P-C4H8Br]Br
[P-Im-C4H8Ph3P]Br2
[MIm-C4H8Ph3P]Br2
P-Im/[Ph3P-C4H8Br]Br
◦
of PC yield and selectivity above 130 C is a result of side reac-
tions, such as PC polymerization, PO isomerization, and a reaction
between PO and water [24,40,44,57,58]. Therefore, from a practical
b
[P-Im-C4H8Br]Br/Ph3Pb
◦
standpoint the optimal reaction temperature is 130 C.
b
1
1
1
0
1
2
[P-Im-C4H9]Br/[Ph3P-C4H9]Br
The effect of CO pressure on the cycloaddition reaction is shown
2
c
[P-HEIm]Br
in Fig. 6. It was found that an increase of CO2 pressure results in a
moderate rise of PC yield (from 49.5% to 96.8%) in the low-pressure
range (1.0–2.5 MPa), but a decrease of yield in the high-pressure
range (2.5–3.0 MPa). Such an effect of CO2 pressure on catalytic
activity was reported before [41,45,59,60]. It is known that under
the adopted reaction conditions PC is in its liquid form, and an
c
[P-CEIm]Br
a
Reaction conditions: PO 35.7 mmol, catalyst 0.38 mol%, CO2 pressure 2.5 MPa,
◦
temperature 130 C, time 4 h.
b
Equal catalyst amount (0.136 mmol).
c
[
[
P-HEIm]Br was prepared according to Ref. [45].
P-CEIm]Br was prepared according to Ref. [41].
d
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
lysts for the synthesis of cyclic carbonates from CO and expoxides, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.042
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Fig. 7. Effect of time on PC yield and selectivity. Reaction conditions: PO 35.7 mmol,
catalyst 0.38 mol%, CO2 pressure 2.5 MPa, temperature 130 C.
Fig. 5. Effect of temperature on PC yield and selectivity. Reaction conditions: PO
◦
3
5.7 mmol, catalyst 0.38 mol%, CO2 pressure 2.5 MPa, time 4 h.
increase of CO2 pressure should be a positive factor for PO con-
version. A possible explanation of this phenomenon is that acidic
CO2 dissolves in basic epoxide and liquefies due to the formation
of CO -epoxide complexes [43,45]. Thus rather than promoting the
2
interaction of CO , PO and catalyst, the high CO pressure results
2
2
in heavy CO -PO complexing, consequently leading to difficulty of
2
CO and PO separation. In other words, the dicline in catalytic activ-
2
ity is a net result of these two opposite factors. It is noted that PC
selectivity is almost independent of CO2 initial pressure. It is con-
sidered that an CO2 pressure of 2.5 MPa is the most suitable for the
cycloaddition reaction.
The dependence of PC yield and selectivity on reaction time was
also investigated. As depicted in Fig. 7, with extension of reaction
time from 1 to 4 h, PC yield sharply increases from 27.7 to 96.8%.
Further prolong of reaction time to 5 h results in only a slight rise
of PC yield. It is noted that the selectivity to PC stays above 99.3%
throughout.
3.4. Catalyst recycling
Fig. 8. Recyclability of [P-Im-C4H8Ph3P]Br2. Reaction conditions: PO 35.7 mmol,
catalyst 0.38 mol%, CO2 pressure 2.5 MPa, temperature 130 C, time 4 h.
◦
From environmental and economical viewpoints, it is good to
have a catalyst that is stable and recyclable. We studied the sta-
bility and recyclability of the ([P-Im-C H Ph P]Br ) catalyst. After
runs by FT-IR (Fig. 9) and TG-DSC (Fig. 10) analysis. In both cases,
the recovered catalyst showed results similar to those of the fresh
one, demonstrating that [P-Im-C H Ph P]Br is highly stable under
4
8
3
2
each run, [P-Im-C H Ph P]Br was recovered by simple filtration.
4
8
3
2
4
8
3
2
As shown in Fig. 8, the catalyst exhibits stable activity across the
five consecutive runs. To further investigate the stability of [P-Im-
C H Ph P]Br , we characterized the recovered catalyst after five
the adopted reaction condition.
4
8
3
2
Fig. 6. Effect of CO2 pressure on PC yield and selectivity. Reaction conditions: PO
◦
3
5.7 mmol, catalyst 0.38 mol%, temperature 130 C, time 4 h.
Fig. 9. FT-IR spectra of [P-Im-C4H8Ph3P]Br2: (a) fresh, and (b) recovered.
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3.5. Cycloaddition of CO2 to various epoxides
The above results indicate that [P-Im-C H Ph P]Br is an effi-
4
8
3
2
cient, stable and reusable catalyst for the cycloaddition of CO2 to
PO. To study the efficiency and generality of the catalytic system, we
used [P-Im-C H Ph P]Br for the cycloaddition of CO2 to different
4
8
3
2
epoxides under the optimized reaction conditions. The results are
summarized in Table 2. It was observed that the catalyst is applica-
ble to a variety of terminal epoxides, producing the corresponding
cyclic carbonates with remarkable yield and selectivity. Among the
epoxides surveyed, epichlorohydrin (entry 2) is the most reactive,
and the reaction comes to near completion in 3 h. In the cases of
1
,2-hexene oxide (entry 3) and glycidyl phenyl ether (entry 5), the
substrates show low activity due to steric hindrance and electronic
effects. As for cyclohexene oxide (an internal epoxide, entry 6),
it takes much longer time (24 h) to reach 82.3% yield due to the
hindrance of the rings. It is noted that the selectivity to the cor-
responding cyclic carbonates is ≥99.5%, including epichlorohydrin
that always shows low selectivity (<97%) in other catalyst systems
[
54,61,62].
3.6. Possible reaction mechanism
Taking account of the mechanism for the cycloaddition reaction
catalyzed by onium salt, i.e. alkylimidazolium halide [63] or tetra-
butylammonium bromide [64], it was proposed that the reaction
involves the ring opening of epoxide through nucleophilic attack
of a halide anion, leading to an oxy-anion species that forms cyclic
carbonate upon reaction with CO . However, the results obtained
2
by us indicate that both cation and anion play an key role in the
facilitation of cycloaddition reaction. Furthermore, Xie et al. [65]
and Han et al. [58] proposed that the opening of an epoxy ring can
be attributed to the cooperation of nucleophilic attack by an anion
and the activation by onium cation through electronic interaction.
According to experimental and theoretical evidences, a plausible
mechanism is suggested and shown in Scheme 2. The opening of
two epoxy rings is facilitated by nucleophilic attack of bromine
anions as well as by activation of imidazolium and phosphonium
Fig. 10. TG and DSC curves of [P-Im-C4H8Ph3P]Br2: (a) fresh, and (b) recovered.
Scheme 2. Proposed mechanism for the cycloaddition reaction.
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
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2

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Table 2
Foundation of Jiangxi Province (Grant Nos. 20122BAB213013). CTA
thanks NCHKU for an adjunct professorship.
Cycloaddition of CO2 to various epoxides catalyzed by [P-Im-C4H8Ph3P]Br2a.
Entry Epoxide
Product
Time (h) Catalytic results
Yield (%) Sel. (%)
References
O
O
[
1] T. Sakakura, K. Kohno, Chem. Commun. (2009) 1312–1330.
O
O
1
4
96.8
99.5
[2] B.Y. Li, Y.H. Duan, D. Luebke, Appl. Energ. 102 (2013) 1439–1447.
CH3
[
[
3] Q.W. Song, L.N. He, J.Q. Wang, H. Yasuda, T. Sakakura, Green Chem. 15 (2013)
110–115.
4] N. von der Assen, J. Jung, A. Bardow, Energ. Environ. Sci. 6 (2013) 2721–2734.
CH3
O
[5] M.Y. He, Y.H. Sun, B.X. Han, Angew. Chem. Int. Ed. 52 (2013) 9620–9633.
[
[
[
6] T. Sakakura, J.C. Choi, H. Yasuda, Chem. Rev. 107 (2007) 2365–2387.
7] K. Nakanv, T. Kamada, K. Nozaki, Angew. Chem. Int. Id. 45 (2006) 7274–7277.
8] S.J. Zhang, Y.H. Chen, F.W. Li, X.M. Lu, W.B. Dai, R. Mori, Catal. Today 115 (2006)
61–69.
O
2
3
O
O
3
6
98.9
96.7
99.5
99.6
Cl
Cl
[
9] J. Sun, S. Fujita, M. Arai, J. Organoment. Chem. 690 (2005) 3490–3497.
[
[
[
10] B. Barkakaty, K. Morino, A. Sodo, T. Endo, Green Chem. 12 (2010) 42–44.
11] J.W. Huang, M. Shi, J. Org. Chem. 68 (2003) 6705–6709.
12] W.L. Dai, S.L. Luo, S.F. Yin, C.T. Au, Appl. Catal. A: Gen. 366 (2009) 2–12.
[13] 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.
14] E.J. Doskocil, J. Phys. Chem. B 109 (2005) 2315–2320.
15] R. Srivastava, D. Srinivas, P. Ratnasamy, Catal. Lett. 91 (2003) 133–139.
16] H. Kawanami, Y. Kushima, Chem. Commun. (2000) 2089–2090.
17] A. Barbarini, R. Maggi, A. Mazzacani, G. Mori, G. Sartori, R. Sartorio, Tetrahedron
Lett. 44 (2003) 2931–2934.
18] J.L. Jiang, R.M. Hua, Synth. Commun. 36 (2006) 3141–3148.
19] 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.
O
O
CH3
O
O
O
( )3
CH3
(
)3
[
[
[
[
O
O
O
4
5
4
99.3
99.8
[
[
[
20] F. Ahmadi, S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-
Baltork, A.R. Khosropour, Polyhedron 32 (2012) 68–72.
O
[
21] C.J. Whiteoak, N. Kielland, V. Laserna, Escudero-Adán, E. Martin, A.W. Kleij, J.
Am. Chem. Soc. 135 (2013) 1228–1231.
O
O
O
O
6
98.6
82.3
99.9
99.9
[22] D.Y. Jang, H.G. Jang, G.Y. Kim, G.J. Kim, Catal. Today 185 (2012) 306–312.
[23] F. Bellina, C. Chiappe, M. Lessi, Green Chem. 12 (2012) 148–155.
[24] J. Sun, S.J. Zhang, W.G. Cheng, J.Y. Ren, Tetrahedron Lett. 49 (2008) 3588–3591.
Ph
O
Ph
[
[
[
25] L.N. Han, H.Q. Li, S.J. Choi, M.S. Park, S.M. Lee, Y.J. Kim, D.W. Park, Appl. Catal.
A: Gen. 429–430 (2012) 67–72.
26] J. Sun, S.J. Zhang, Z.X. Li, X.P. Zhang, W.B. Dai, R. Mori, J. Mol. Catal. A: Chem.
O
O
O
6
24
256 (2006) 295–300.
O
27] J.K. Lee, Y.J. Kim, Y.S. Choi, H. Lee, J.S. Lee, J. Hong, E. Jeong, H.S. Kim, M. Cheong,
Appl. Catal. B: Environ. 111–112 (2012) 621–627.
a
Reaction conditions: PO 35.7 mmol, catalyst 0.38 mol%, CO2 pressure 2.5 MPa,
[28] Y.N. Zhao, Z.Z. Yang, S.H. Luo, L.N. He, Catal. Today 200 (2013) 2–8.
[29] Y.C. Zhao, C.Q. Yao, G.W. Chen, Q. Yuan, Green Chem. 15 (2013) 446–452.
[30] W.L. Dai, B. Jin, S.L. Luo, X.B. Luo, X.M. Tu, C.T. Au, J. Mol. Catal. A: Chem. 378
◦
temperature 130 C.
(
2013) 326–332.
[31] H.C. Cho, H.S. Lee, J. Chun, S.M. Lee, H.J. Kim, S.U. Son, Chem. Commun. 47 (2011)
17–919.
through electronic interaction to give the corresponding interme-
diates. Then the intermediates react with CO2 to form the cyclic
carbonates together with the release of catalyst.
9
[
[
32] L.N. Han, S.W. Park, D.W. Park, Energ. Environ. Sci. 2 (2009) 1286–1292.
33] Y. Xie, Z.F. Zhang, T. Jiang, J.L. He, B.X. Han, T.B. Wu, K.L. Ding, Angew. Chem.
Int. Ed. 46 (2007) 7255–7258.
[
[
[
34] S. Ghazali-Esfahani, H.B. Song, E. P a˘ unescu, F.D. Bobbink, H.Z. Liu, Z.F. Fei, G. Lau-
renczy, M. Bagherzadeh, N. Yan, P.J. Dyson, Green Chem. 15 (2013) 1584–1589.
35] T.Y. Shi, J.Q. Wang, J. Sun, M.H. Wang, W.G. Cheng, S.J. Zhang, RSC Adv. 3 (2013)
4
. Conclusions
3
726–3732.
36] Y.X. Zhou, S.Q. Hu, X.M. Ma, S.G. Liang, T. Jiang, B.X. Han, J. Mol. Catal. A: Chem.
84 (2008) 52–57.
[37] Y. Zhao, J.S. Tian, X.H. Qi, Z.N. Han, Y.Y. Zhuang, L.N. He, J. Mol. Catal. A: Chem.
71 (2007) 284–289.
38] J.Q. Wang, K. Dong, W.G. Cheng, J. Sun, S.J. Zhang, Catal. Sci. Technol. 2 (2012)
480–1484.
Polymer grafted with asymmetrical dication IL ([P-Im-
C H Ph P]Br ) was fabricated and demonstrated as effective
4
8
3
2
2
catalyst for the synthesis of cylclic carbonates from epoxides and
CO2 in the absence of co-catalyst and solvent. Compared with
the monocation IL and homogeneous dication IL catalyst system,
2
[
1
[
P-Im-C H Ph P]Br showed superior activity. Moreover, the cata-
[39] D.W. Sun, H.J. Zhai, Catal. Commun. 8 (2007) 1027–1030.
[40] J. Sun, L.J. Han, W.G. Cheng, J.Q. Wang, X.P. Zhang, S.J. Zhang, ChemSusChem 4
4
8
3
2
lyst shows good stability and recyclability. After 5 runs, there was
almost no loss of catalytic activity, and the physico-chemical prop-
erties of catalyst kept unchange. The high activity and selectivity
of the polymer grafted with dication IL is attributed to the syn-
ergistic effects of bromide anions as well as both imidzolium and
phosphonium cations. From the viewpoint of large-scale produc-
tion and green chemistry, the catalyst is attractive because of its
activity, simplicity, stability, and recyclability.
(
2011) 502–507.
[
[
41] Y.Y. Zhang, S.F. Yin, S.L. Luo, C.T. Au, Ind. Eng. Chem. Res. 51 (2012) 3951–3957.
42] R.A. Watile, K.M. Deshmukh, K.P. Dhake, B.M. Bhanage, Catal. Sci. Technol. 2
(2012) 1051–1055.
43] W.L. Dai, L. Chen, S.L. Luo, S.F. Yin, C.T. Au, Catal. Lett. 135 (2010) 295–304.
44] J. Sun, W.G. Cheng, W. Fan, Y.H. Wang, Z.Y. Meng, S.J. Zhang, Catal. Today 148
[
[
(
2009) 361–367.
[45] 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.
(
[
[
[
46] T. Payagala, J.M. Huang, Z.S. Breitbach, P.S. Sharma, D.W. Armstrong, Chem.
Mater. 19 (2007) 5848–5850.
47] C.M. Jin, C. Ye, B.S. Phillips, J.S. Zabinski, X. Liu, W. Liu, J.M. Shreeve, J. Mater.
Chem. 16 (2006) 1529–1535.
Acknowledgments
48] X. Han, D.W. Armstrong, Org. Lett. 7 (2005) 4205–4208.
This work was financially supported by the National Natural Sci-
ence Foundation of China (Grant Nos. 51104089, 51238002, and
[49] J.C. Xiao, J.M. Shreeve, J. Org. Chem. 70 (2005) 3072–3078.
[
[
[
50] R. Wang, C.M. Jin, B. Twamley, J.M. Shreeve, Inorg. Chem. 45 (2006) 6396–6403.
51] J.L. Anderson, D.W. Armstrong, Anal. Chem. 19 (2005) 6453–6462.
52] D.S. Zhao, M.S. Liu, J. Zhang, J.P. Li, P.B. Ren, Chem. Eng. J. 221 (2013) 99–104.
5
1272099), Jiangxi Province Science and Technology Project (Grant
Nos. 2010AIB00400); Jiangxi Province Science and Technology Sup-
port Program (Grant Nos. 20111BBG70003-4); and Natural Science
[53] M.M. Fan, J. Yang, P.P. Jiang, P.B. Zhang, S.S. Li, RSC Adv. 3 (2013) 752–756.
[54] H. Zhao, G.A. Baker, J. Chem. Technol. Biotechnol. 88 (2013) 3–12.
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
lysts for the synthesis of cyclic carbonates from CO and expoxides, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.042
2

G Model
CATTOD-8935; No. of Pages8
ARTICLE IN PRESS
D. Wei-Li et al. / Catalysis Today xxx (2014) xxx–xxx
8
[
55] J. Sun, J.Q. Wang, W.G. Cheng, J.X. Zhang, X.H. Li, S.J. Zhang, Y.B. She, Green
[61] D.S. Bai, Q. Wang, Y.Y. Song, B. Li, H.W. Jing, Catal. Commun. 12 (2011) 684–688.
[62] J. Tharun, M.M. Dharman, Y. Hwang, R. Roshan, M.S. Park, D.W. Park, Appl. Catal.
A: Gen. 419–120 (2012) 178–184.
[63] J.I. Yu, H.Y. Ju, K.H. Kim, D.W. Park, Korean J. Chem. Eng. 27 (2010) 446–451.
[64] V. Caló, A. Nacci, A. Monopoli, A. Fanizzi, Org. Lett. 4 (2002) 2561–2563.
[65] H.B. Xie, H.F. Duan, S.H. Li, S.B. Zhang, New J. Chem. 29 (2005) 1199–1203.
Chem. 14 (2012) 654–660.
[56] J.N. Appaturi, F. Adam, Appl. Catal. B: Environ. 136–137 (2013) 150–159.
[57] C.X. Miao, J.Q. Wang, Y. Wu, Y. Du, L.N. He, ChemSusChem 1 (2008) 236–241.
[58] J. Sun, J.Y. Ren, S.J. Zhang, W. Cheng, Tetrahedron Lett. 50 (2009) 423–426.
[59] L. Han, H.J. Choi, S.J. Choi, B. Liu, D.W. Park, Green Chem. 13 (2011) 1023–1028.
[60] L.F. Xiao, F.W. Li, J.J. Peng, C.G. Xia, J. Mol. Catal. A: Chem. 253 (2006) 265–269.
Please cite this article in press as: D. Wei-Li, et al., Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable cata-
lysts for the synthesis of cyclic carbonates from CO and expoxides, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.042
2