Halide aided synergistic ring opening mechanism of epoxides and their cycloaddition to CO2 using MCM-41-imidazolium bromide catalyst

Article abstract of DOI:10.1016/j.molcata.2014.02.008

Imidazole was immobilized on MCM-41 using 3-chloropropyltriethoxysilane (CPTES) as the anchoring agent followed by alkylation with 1,2-dibromoethane at 110 C. The resulting catalyst was designated as MCM-41-Imi/Br. The catalyst was used for the synthesis of cyclic carbonates via cycloaddition of CO₂ with several epoxides under solvent free condition. The use of MCM-41-Imi (without bromide ion) to catalyze the reaction led to the elucidation of the reaction mechanism involved in the synergistic catalysis. The catalyst was used in the cycloaddition of styrene oxide, epichlorohydrine, glycidol, allyl glycidyl ether and phenyl glycidyl ether. A high yield and excellent selectivity of cyclic carbonates were obtained under optimized conditions. The yields of the respective cyclic carbonates were 98.8% for styrene oxide, 97.0% for epichlorohydrin, 98.3% for glycidol, 97.5% for allyl glycidyl ether, 96.7% for phenyl glycidyl ether and 100% for 1,2-epoxyhexane.

Full text of DOI:10.1016/j.molcata.2014.02.008

Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Halide aided synergistic ring opening mechanism of epoxides and
their cycloaddition to CO2 using MCM-41-imidazolium
bromide catalyst
Farook Adam∗, Jimmy Nelson Appaturi, Eng-Poh Ng
School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Imidazole was immobilized on MCM-41 using 3-chloropropyltriethoxysilane (CPTES) as the anchoring
agent followed by alkylation with 1,2-dibromoethane at 110 ◦C. The resulting catalyst was designated as
MCM-41-Imi/Br. The catalyst was used for the synthesis of cyclic carbonates via cycloaddition of CO2 with
several epoxides under solvent free condition. The use of MCM-41-Imi (without bromide ion) to catalyze
the reaction led to the elucidation of the reaction mechanism involved in the synergistic catalysis. The
catalyst was used in the cycloaddition of styrene oxide, epichlorohydrine, glycidol, allyl glycidyl ether
and phenyl glycidyl ether. A high yield and excellent selectivity of cyclic carbonates were obtained under
optimized conditions. The yields of the respective cyclic carbonates were 98.8% for styrene oxide, 97.0%
for epichlorohydrin, 98.3% for glycidol, 97.5% for allyl glycidyl ether, 96.7% for phenyl glycidyl ether and
100% for 1,2-epoxyhexane.
Received 25 September 2013
Received in revised form 10 January 2014
Accepted 9 February 2014
Available online 18 February 2014
Keywords:
Cycloaddition
Carbon dioxide
Ring opening of Epoxide
Imidazole
Synergistic effect
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
epoxides remains inadequately explained and are actively being
investigated.
Cyclic carbonates have been produced conventionally by reac-
ting phosgene (COCl2) with ethane-1,2-diol in the presence of an
excess amount of dichloromethane as solvent. Hydrochloric acid
and chlorinated solvents are produced as byproducts that are harm-
ful to human and the environment [1]. Due to the extreme toxicity
attributed to phosgene, CO2 seems to be the most appropriate sub-
stitute. Carbon dioxide is a greenhouse gas found to be present in
the atmosphere at a concentration of 398.58 ppm [2]. The rising
demand of cyclic carbonates has also resulted in the need to look
for safer and greener techniques for its synthesis. Scheme 1 shows
the reactions used to synthesize cyclic carbonates using the tradi-
tional route and the new green route. The use of carbon dioxide
will also help to reduce the amount of carbon dioxide in the atmo-
sphere. Although this will not be enough to reduce global warming,
it will at least help to reduce the amount of carbon dioxide in the
environment. It has been known that CO2 can be incorporated into
epoxides without the formation of byproducts [3]. However, due
to the inert nature of CO2, its activation and incorporation into
One of the main factors that can accelerate the reaction between
CO2 and epoxide are the catalysts that are used in the reac-
tion. A wide range of homogeneous and heterogeneous catalysts
has been developed to catalyze the reaction between CO2 and
epoxides to form cyclic carbonates. Homogeneous catalysts, such
as CoCl2/onium salt [4], diimine Ru(II) complex [5], Al-salen-
PEA [6], betaine-based quaternary ammonium ion and carboxylic
acid [7], DMF [8,9], Au/Fe(OH)3–ZnBr2/Bu4NBr [10], ionic liq-
uid with highly cross linked polymer [11], BrBu3PPEG600PBU3Br
[12], cellulose/KI [13], and Au/R201 [14] have been stud-
ied. Several heterogeneous catalysts, such as metal oxides;
MgO [15,16], Nb2O5 [1], Mg–Al oxide [17], guanidine-MCM-41
[18], Adeine-Pr-Al-SBA-15 [19], Cr-salen-SiO2 [20], Mn-salen-
SiO2 [21], ClAlPC-MCM-41 [22], as-synthesized MCM-41 [23],
Ti-SBA-15-Pre-Ade [24], 3-(2-hydroxyl-ethyl)-1-propyl imidaz-
olium bromide-SBA-15 [25] and zeolite based organic-inorganic
hybrid catalyst [26] have also been investigated. Both homoge-
neous and heterogeneous catalysts have their own advantages
and disadvantages. The major problem associated with most
homogeneous catalyst is the difficulty in the separation of the
catalyst from the reaction mixture and recycling of the catalyst.
These drawbacks has been overcome in heterogeneous catalyst
system.
∗
Corresponding author. Tel.: +60 46533567; fax: +60 46574854.
E-mail addresses: farook@usm.my, farook dr@yahoo.com, farookdr@gmail.com
(F. Adam).
http://dx.doi.org/10.1016/j.molcata.2014.02.008
1381-1169/© 2014 Elsevier B.V. All rights reserved.

F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
O
43
mechanism of the cycloaddition reaction. This paper describes
the role of the quaternary imidazolium center and bromide ion
which is shown to play a synergistic role in the activation of
the CO2 and the subsequent ring opening of the epoxide. To the
best of our knowledge, this is the first report that also show
the important role of water molecules in the formation of inter-
mediates and byproducts under CO2 free condition. Based on
the data obtained, a most likely reaction mechanism has been
proposed.
Traditional route
CH2Cl2
O
2HCl
COCl2
+
+
+
O
OH
HO
O
Greener route
O
O
O=C=O
O
Scheme 1. The synthesis of cyclic carbonates via traditional route and greener route.
2. Experimental
2.1. Material
The rice husk (RH), for the preparation of MCM-41 was obtained
from a rice mill in Penang. Other materials used were nitric
acid (Qrec, 65.0%), sodium hydroxide pellets (R&M Chemicals,
99.0%), acetone (Qrec, 99.5%), cetyltrimethylammonium bromide
(CTAB) (Riedel-de Haen, 98.0%), 3-chloropropyltriethoxysilane
(CPTES) (Sigma-Aldrich, 95.0%), toluene (Qrec, 99.5%), acetoni-
trile (Qrec, 99.5%), 1,2-dibromoethane (Merck, >99.0%), imidazole
(Scharlau, 99.0%), styrene oxide (SAFC, >97.0%), epichlorohydrin
(FlukaChemika,99%), glycidol (Aldrich, 96%), allylglycidyl ether
(Aldrich, >99%), phenyl glycidyl ether (Aldrich, 99%) and 1,2-
epoxyhexane (Aldrich, 97%). The carbon dioxide was purchased
from CAMBREX-HENKEL, Penang and used as received. All other
reagents used were of analytical grade and used without further
purification.
The catalyst is crucial to activate the CO2 in the chemical
reaction. Lu et al. [22] had used MCM-41 supported aluminium
phthalocyanine (AlPc) complex for the reaction of CO2 and epox-
ides. It required a co-catalyst, n-Bu4NBr which enhanced the
reaction as well as gave high catalytic activity. The activation
of CO2 was initiated by nucleophilic attack of the alcoholate
(
OCH2CH2Br) on the carbon atom of CO2 which was aided by
the weak interaction between the central metal ion of (ClAlPc) and
the lone pair electron of one of the oxygen of CO2. The catalyst
showed a synergistic effect during the reaction that resulted in the
insertion of CO2 to the Al O bond of Pc(Cl)Al OCH2CH2Br. This
formed a linear carbonate, which converted into cyclic carbonates
by the intramolecular substitution of the halides. Nevertheless, the
mechanism for the formation of cyclic carbonates by this binary
catalyst has not been reported. Qiao et al. [27] had reported that
imidazolium-styrene copolymer supported zinc catalyst which was
denoted as Zn/PS-IL[X] (X = Br−, Cl−, BF4−, PF6−) was a suitable cat-
alyst for the cycloaddition of CO2 to styrene oxide (SO). Among
the catalyst investigated, Zn/PS-IL[Br] was the most efficient, which
2.2. Synthesis of MCM-41-Imi/Br
gave 97.5% yield with a TOF of 3800 h−1
.
The preparation of MCM-41-Imi/Br was carried out accord-
ing to published method [35]. 2.0 g of MCM-41-Imi and 1.4 mL
of 1,2-dibromoethane was refluxed at 110 ◦C for 24 h. The excess
alkyl halide was filtered off, followed by repeated washing with
dichloromethane. The resulting solid was dried in an oven at 100 ◦C.
The yield of MCM-41-Imi/Br was 2.1 g with a BET surface area of
130 m2 g−1 [35].
In 1992, researchers at the Mobil Oil Cooperation successfully
synthesized MCM-41 (hexagonal) [28] and MCM-48 (cubic) materi-
als from silica [29]. These materials had amorphous silica wall with
long range ordered framework with uniform mesopores. These
materials have been used in catalysis, as adsorbents and recently in
drug delivery systems. Due to the tremendous interest in the area of
catalysis, MCM-41 has been utilized for various chemical reactions
and has shown remarkable catalytic activity. These materials are
of particular interest due to the well-ordered mesopores with high
accessibility for reactants as well as products. Moreover, this mate-
rials can be used to synthesize hybrid organic-inorganic materials
with an ionic liquid functionality unit as part of the solid network.
The ionic liquid being connected to the surface of MCM-41 through
an appropriate linker.
In this study, the silica from RHA [30–34] was converted to
MCM-41 and used as support for heterogeneous catalyst to synthe-
size cyclic carbonates. The production of cyclic carbonates in high
yield not only depends on the catalyst, but also on other reaction
parameters such as temperature, pressure, catalyst amount and
reaction time. The optimized conditions vary depending on the type
of epoxide and the active site of the catalyst. In the past 10 years,
there has been much research using a wide range of homogeneous
and heterogeneous catalysts with different epoxides. However,
none of them studied the detailed reaction parameters for various
epoxides with the same catalyst.
2.3. Cycloaddition reaction and the analysis
In a typical catalytic reaction, epoxide (30 mmol) and 300 mg of
the catalyst (MCM-41-Imi or MCM-41-Imi/Br) were charged into a
high pressure laboratory autoclave, equipped with a magnetic stir-
rer and a heating mantle system. The reactor was carefully flushed
once with CO2. About 30 bar of CO2 was dosed into the reactor, and
heating and stirring started. Once the temperature reached 100 ◦C,
the reaction was allowed to proceed for 4 h.
After the reaction was complete, the autoclave was allowed to
cool down to room temperature, and the excess CO2 was released
by opening the outlet valve. After depressurization, the autoclave
was opened slowly, and the reaction mixture was separated by fil-
tration. To a 0.5 mL of the reaction product, 20 ␮L of cyclohexanol or
acetophenone as internal standard was added. The resulting mix-
ture was analyzed with gas chromatography (Clarus 500 Perkin
Elmer) equipped with Elite Wax or Elite 1 capillary column (Perkin
Elmer) and flame ionization detector. The reaction mixture was also
analyzed by GC–MS (Clarus 600 Perkin Elmer) with a mass selective
detector and helium as the carrier gas to identify the formation of
products.
Recently, the synthesis and catalytic activity of MCM-41-Imi/Br
[35] was reported. It was found that MCM-41-Imi/Br catalyzed
the cycloaddition reaction between CO2 and styrene oxide effec-
tively under solvent free condition. As an extension to this work,
herein we describe the systematic investigation leading to the

44
F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
(b)
100
100
95
90
85
80
75
70
65
(a)
100
95
90
85
80
75
70
100
95
90
95
90
85
80
75
70
85
80
75
70
65
80
(d)
90
100
110
120
130
140
0
1
2
3
4
5
6
Temperature (0C)
Time (hr)
(c)
100
95
90
85
80
75
70
100
95
90
85
80
75
70
100.0
99.6
99.2
98.8
98.4
98.0
97.6
97.2
100.0
99.6
99.2
98.8
98.4
98.0
97.6
97.2
100
150
200
250
300
20
25
30
35
40
Catalyst amount (mg)
CO2 pressure (bar)
Fig. 1. The effect of different parameters on the synthesis of styrene carbonate (SC) from CO2 under solvent free conditions. (a) The effect of reaction time (reaction conditions:
temperature = 140 ◦C, pressure = 40 bar, catalyst amount = 300 mg), (b) The effect of temperature, (reaction conditions: time = 4 h, pressure = 40 bar, catalyst amount = 300 mg),
(c) The effect of CO2 pressure, (reaction condition: time = 4 h, temperature = 100 ◦C, catalyst amount = 300 mg), (d) The effect of catalyst amount, (reaction conditions: time = 4 h,
temperature = 100 ◦C, pressure = 30 bar). In all the cases, the amount of styrene oxide = 3.5 mL (30 mmol).
3. Results and discussion
reaction temperature was raised from 80 to 100 ◦C, and remained
unchanged at 120 ◦C (Fig. 1(b). It is known that, the activation
energy for the synthesis of polycarbonates is usually lower than
that for the thermodynamically favored cyclic carbonates.
Thus, at lower temperature (80 ◦C), the reaction rate was low
but enhanced the selectivity toward the polycarbonates. The yield
increased with the reaction temperature up to 140 ◦C. However, a
slight reduction in the selectivity was observed at 140 ◦C as com-
pared to 100 ◦C. The main reason may be that the high temperature
might be favorable for the increase in the byproducts.
3.1. Catalytic performance of MCM-41-Imi/Br
3.1.1. Catalytic synthesis of styrene carbonate
The catalytic performance of MCM-41-Imi/Br was evaluated in
the cycloaddition of CO2 (40 bar) with styrene oxide (SO) (30 mmol)
for 0.5–6 h to produce styrene carbonate (SC) as shown in Eq. (1).
The influence of CO2 pressure on the styrene oxide conversion
and product yield are shown in Fig. 1(c). At 20 bar, the conversion
of styrene oxide was 98.4% and achieved 100% at 30 bar. However,
further increase in the pressure to 40 bar caused a decrease in the
conversion. Thus, 30 bar was the optimum CO2 pressure resulting
in high yield. In addition, the CO2 pressure and reaction temper-
ature for optimum performance was dependent on the catalyst
amount used. The use of 100 mg of the catalyst yielded lower con-
version and SC yield compared with 200 and 300 mg (Fig. 1(d)).
The higher catalyst mass (300 mg) led to maximum conversion of
100%. The complete conversion is not only due to the higher num-
ber of imidazolium units (1.03 mmol g−1) but also to the influence
of the electron density, the high surface area of the host material
(1115 m2 g−1), and the ease of formation of ionic interactions with
the styrene oxide, leading to favorable adsorption onto the active
sites [35,36]. Therefore, the optimized conditions of the reaction
was determined to be 100 ◦C, 30 bar CO2 pressure, 300 mg catalyst
and 4 h reaction time.
O
O
MCM-41-Imi/Br
100 oC, 30 bar, 4h
solvent free
+
CO2
O
O
styrene oxide (SO)
styrene carbonate (SC)
Conversion : 100 %
Selectivity : 98.8 %
(1)
The effect of time, temperature, CO2 pressure and catalyst amount
on the cycloaddition of carbon dioxide with styrene oxide was
investigated. No solvent was used in these reactions. The results are
summarized in Fig. 1. As shown in Fig. 1(a), the SC yield increased
with the reaction time up to a period of 4 h, after which no increase
in SC yield was achieved. The results suggested that the CO2 fixa-
tion of SO was completed within 4 h. On this basis, the experiment
to assess other reaction parameters were performed for 4 h. Note
that, a further increase in the reaction time led to a slight decrease
in SC yield. This may be due to the formation of styrene glycol as
byproduct. The yield of SC increased from 69.7 to 97.9% when the
As comparison, a similar experiment was carried out with MCM-
41-Imi (without bromide ion). MCM-41-Imi performed poorly

F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
45
Table 1
Cycloaddition of CO2 with epoxides catalyzed by MCM-41-Imi/Br under different optimized conditions.a
Entry
Substrate
Temperature (◦C)
Pressure (bar)
Time (h)
Conversion (mol %)b
Selectivity (mol %)b
Yield (mol %)b
TOFc
Cl
O
1
90
25
4
100
97.0
97.0
23.5
23.9
(EPCH)
HO
O
2
90
20
4
100
98.3
98.3
(GOH)
O
3
4
120
100
60
20
6
3
99.0
96.7
98.5
97.5
96.7
15.8
31.3
O
(AGE)
O
O
100
(PGE)
O
5
100
20
3
100
100
100
32.4
(EH)
a
Reaction conditions: 30 mmol substrate, 300 mg MCM-41-Imi/Br.
Determined by GC.
Turnover frequency: moles of cyclic carbonate produced per mole of quaternary imidazolium ion per hour.
b
c
(yield: 16.0%). The MCM-41-Imi/Br gave higher yield due to the
synergistic effect of the quaternary imidazolium ion with the active
(free) bromide ion. Such a free bromide ion is not present in MCM-
41-Imi. Thus, we can conclude that the presence of the quaternary
imidazolium ion and the Br− ion helped to promote a synergistic
effect to enhance the reaction. Note that a previously reported het-
erogeneous catalyst, MCM-41-TBD (a guanidine catalyst) required
higher temperature (140 ◦C), 50 bar CO2 pressure, with acetoni-
trile as solvent and took about 70 h to give 90.0% yield of styrene
carbonate [18].
Lately, Zalomaeva et al. [37] had developed metal–organic-
framework (MOF), i.e. Cr-MIL-101 as a heterogeneous catalyst for
the production of styrene carbonate. The catalytic activity required
a low temperature of 25 ◦C and low pressure of CO2 (8 bar). How-
ever, a longer reaction time of 48 h was needed to obtain a yield
of 95% with tetrabutylammonium bromide as the co-catalyst. This
makes the MOF catalyst unfavorable from the points of view of
reaction time.
Table 1 clearly show that epichlorohydrin (entry 1) and glycidol
(entry 2) converted to chloropropene carbonate (CC) and glycerol
carbonate (Gc) with the yield of 97.0 and 98.3% respectively with
the TOF values of ∼24 h−1. Both epoxides needed a lower reaction
temperature of 90 ◦C and a reaction time of 4 h to attain the respec-
tive yields. However, the CO2 pressure for optimal performance
for both reactions were significantly lower than for SO. Epichloro-
hydrin required slightly higher CO2 pressure as compared with
glycidol. The selectivity of both cyclic carbonates was lower due
to CO2 pressure or temperature employed for the reaction. At low
temperature, the CO2 dissolves in the epoxides and liquefies, lead-
ing to the formation of a CO2-epoxide complex. This will indirectly
reduce the interaction between epoxide-catalyst or CO2-catalyst
and lead to low catalytic activity. Such observation of CO2 pressure
and temperature in catalysis has been observed by others [7,25].
In order to verify the advantage of this study, MCM-41-Imi/Br
was compared with ZIF-8 functionalized ethylenediamine which
was developed recently by Miralda et al. [38]. The ZIF-8 system
consists of organic–inorganic active sites with a surface area of
1096 m2 g−1. However, it has a major drawback due to the large
number of byproducts at the optimum condition and thus the sys-
tem still remains unfavorable.
3.1.2. Parametric studies for other epoxides
The effect of temperature, CO2 pressure, catalyst amount and
reaction time on the cycloaddition of CO2 with epichlorohydrin
(EPCH), glycidol (GOH), allyl glycidyl ether (AGE), phenyl glycidyl
ether (PGE) and 1,2-epoxyhexane (EH) were investigated using
MCM-41-Imi/Br as the catalyst. The number of moles of reactant
was set at 30 mmol for all the respective epoxides. The result of the
study is shown in Table 1.
The rate at which the cyclic carbonates are synthesized is given
as turnover frequencies (TOF), calculated on the assumption that
the imidazolium ion were the active site. The results shown in
In contrast, a relatively longer reaction time (6 h) and a much
higher pressure (60 bar) was needed to convert AGE into allyl gly-
cidyl carbonate (AGC) (Table 1, entry 3). When the reaction was
carried out at low temperature (80 ◦C), about 67.1% yield was
achieved. However, when the reation temperature was increased
to 120 ◦C, AGC selectivity dramatically increased from 67.1% to
98.5%. The results indicated that a reaction temperature of 120 ◦C
was necessary for the complete conversion (∼99.0%) of AGE using

46
F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
Table 2
3.2. The systematic steps leading to the mechanism of the
cycloaddition
Influence of the catalyst amount on the yield of the cycloaddition of CO2 with
epoxides.
Catalyst amount (mg)
Yield (mol %)
3.2.1. Ring opening of epoxides using MCM-41-Imi/Br
EPCHa
GOHa
AGEb
PGEc
EHd
98.3
99.1
100
It is well known that the ring opening of the epoxide involves
two pathways: (i) cleavage by Lewis acids and (ii) cleavage by
Lewis base. Pescarmona et al. [40] in their recent review described
the ring opening of SO via the ␣-carbon due to the electron-
withdrawing inductive effect of the phenyl group. Thus, the
electron-withdrawing nature of the aromatic ring favors the back-
biting reaction after the insertion of CO2 to an intermediate to form
the SC [41]. However, in this work the ring opening of SO occurred
at the less sterically hindered carbon atom of SO ring (␤-carbon)
(Schemes 2 and 3).
100
200
300
91.2
92.4
97.0
83.6
92.6
98.3
72.0
100
97.5
88.1
97.9
99.2
Reaction condition: Substrate: 30 mmol, solvent less.
Temperature: 90 ◦C, pressure: 25 bar, time: 4 h.
Temperature: 120 ◦C, pressure: 60 bar, time: 6 h.
Temperature: 100 ◦C, pressure: 20 bar, time: 6 h.
Temperature: 100 ◦C, pressure: 20 bar, time: 4 h.
a
b
c
d
In order to demonstrate the opening of the epoxide ring by a
nucleophilic reagent (Br− ion) at the ␤-carbon, the MCM-41-Imi/Br
was heated at 100 ◦C together with SO in the absence of CO2 for
4 h. The resulting products were analyzed by GC–MS. The reaction
between MCM-41-Imi/Br with styrene oxide showed two peaks in
the GC–MS which correspond to 2-bromo-1-phenylethanol (as the
major product) and a minor byproduct, styrene glycol (Fig. 1 of the
Supplementry Information).
A possible reason for the presence of the hydroxyl group in the
reaction intermediate and byproduct may be due to the interac-
tion of H OH molecules present in the catalyst. Recently, Dai et al.
[25] reported the use of 3-(2-hydroxyethyl)-1-propyl imidazolium
bromide-SBA-15 (HEPIMBr) catalyst for the synthesis of cyclic car-
bonates. They proposed that, the intermediate formation occurred
when the H atom of the silyl-hydroxyl group coordinated with the
O atom of epoxide through hydrogen bonding. Then, the halide
anion makes a nucleophilic attack on the sterically less hindered
MCM-41-Imi/Br as the catalyst. The TOF value (15.8 h−1) for this
reaction is the lowest compared with other epoxides. As can be
seen from (Table 1, entry 4 and 5) 100% selectivity of phenyl gly-
cidyl carbonate (PGC) and 4-butyl-1-3-dioxolan-2-one could be
obtained from PGE and EH respectively under the same reaction
conditions, i.e. 100 ◦C, 20 bar and 3 h reaction time. These results are
unexpected because both epoxides contain different substituents
and different chemical and physical properties. However, a small
decline in the conversion of PGE was observed possibly due to
the side reaction of the cyclic carbonate. Similar work was carried
out by Xiao et al. [39] and Zhou et al. [7] using immobilized ionic
liquid–ZnCl2 and betaine based catalyst respectively under harsher
reaction conditions as compared with the present work.
Apart from the influence of temperature and pressure, the
cycloaddition reaction was also affected by the amount of catalyst.
Table 2 shows the influence of the catalyst amount on the yield
for each epoxide. Increasing the amount of MCM-41-Imi/Br from
100 mg to 300 mg enhanced the catalytic activity. This is certainly
due to the amount of quaternary imidazolium ion per unit sur-
␤-carbon atom of the epoxide, due to the polarization of the C
O
bonds. Nevertheless, no evidence was given for the ring opening
process.
In the case of aliphatic terminal epoxide (EH), the nucleophilic
attack also happens at the less sterically hindered carbon atom
of the epoxide ring (␤-carbon). This is due to higher accessibil-
ity and the electron-donating effect of the alkyl group. Thus, EH
is more easily converted to 4-butyl-1,3-dioxolan-2-one without
any byproducts in a shorter reaction time. On the other hand, for
epoxide such as AGE, the ether group influenced the course of
the reaction leading toward cyclic carbonate formation. However,
harsher reaction condition was needed for the conversion of AGE to
attain maximum yield. Surprisingly, milder reaction condition was
observed for PGE in comparison with AGE. One plausible reason for
this is the electronic ␲-system of the benzene ring in PGE is able
to form a stable interaction with the quaternary imidazolium ion
on the catalyst. This leads to a stable intermediate, thereby reduc-
ing the temperature and a shorter reaction time. Since the role of
face area (7.92 × 10–3 mmol m−2) and bromide ion (0.44 mmol g−1
)
would increase, resulting in higher yield of the desired products, as
shown in Table 2.
The influence of reaction time on the yield was also investigated
as MCM-41-Imi/Br could offer a higher yield of product for the CO2
cycloaddition with different epoxides. The results (Table 1) indi-
cated that the reaction time of 4 h was necessary for the complete
conversion of EPCH and GOH under the selected reaction condi-
tions.
A relatively long reaction time (6 h) was needed to complete the
reaction for AGE, resulting in a product yield of 97.5% (AGC). Inter-
estingly, with PGE and EH, 96.7 and 100% conversion was achieved
in 3 h. However, no plausible explanation can be put forward for
this fast reaction time with respect to their chemical structure.
Br
OH
N
N
Br-
Br
OH
β
HO
HO
α
Br-
R
+
O
O
R
R
H
H
R = alkyl or aryl group
Scheme 2. Reaction of MCM-41-Imi/Br with epoxide in the absence of CO2: Most likely position for a nucleophilic attack of the ring and possible role of water molecule in
the formation of intermediate and/or byproduct.

F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
47
δ +
H
δ −
N
H
N
N
N
O
O
H
H
O
O
R
R
OH
N
OH
N
R
R = alkyl or aryl group
Scheme 3. Reaction of MCM-41-Imi with epoxide in the absence of CO2: The role of water molecule in the formation of byproduct.
the quaternary imidazolium ion is also to fix the carbon dioxide on
the catalyst, the proximity thus generated between the CO2 and
the epoxide would have reduced the activation energy much more
significantly to afford much milder condition for the reaction of
PGE with the CO2. However, this needs to be investigated in more
detail.
supplementary Information). However, the GC–MS was not able
to separate these isomers under the analytical condition used.
3.2.3. Effect of water
The effect of water in the cycloaddition reaction (CO2 with SO)
over MCM-41-Imi/Br was investigated to further proof the reac-
tion mechanism. In the absence of water in the reaction, the SC
yield was maximum at 98.8%. Further addition of water results
in decline in SC yield; when the ratio of H2O/SO was 0.3, the SC
yield was found to be 86.3%. It can be concluded that, the addi-
tion of water has a negative effect on the selectivity to SC. The
byproduct of styrene glycol was found to be higher in the pres-
ence of water in this reaction. A systematic investigation was
conducted by Dai et al. [25] on the effect of water on the cycload-
dition reaction over SBA-15-HEPIMBr. They found that when the
ratio of H2O/PO was 0.01, the PC yield was higher, and when it
was 0.2, the PC yield decreased. A trace amount of water had
3.2.2. Ring opening of epoxides using MCM-41-Imi
The MCM-41-Imi (without Br− ion) was employed as a con-
trol catalyst in the same manner to study the process of the ring
opening of styrene oxide. The reaction between MCM-41-Imi and
styrene oxide shows the formation of styrene glycol as a major
product. However, a mixture of minor products, 2-phenylethoxy-
1-phenylethanol and its isomer, 2-phenylethoxy-2-phenylethanol
were also identified which could be formed due to the reac-
tion between styrene oxide and styrene glycol (Fig. 6 of the
Br
Br
O
C
O
C
O
O
R
N
N
O
N
N
Br-
O
R
Br
O
Br
R = alkyl or aryl group
O
O
N
Br
+
N
R
Scheme 4. The proposed reaction mechanism for cycloaddition of epoxide and CO2 catalyzed by MCM-41-Imi/Br: The simultaneous activation of epoxide and CO2 on the
catalyst.

48
F. Adam et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 42–48
positive effect on PO conversion. It is proposed that the OH groups
of water play a similar role to that of hydroxyl-functionalized ionic
liquid (HIL) in the cycloaddition reaction.
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We would like to thank the Malaysian Government for a FRGS
Grant (Ac. No. 203/PKIMIA/6711316) and USM-RU-PRGS grant
(1001/PKIMIA/844075), which partly supported this work. We
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Appendix A. Supplementary data
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Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.02.008.