Synthesis of dicationic alkyl imidazolium peroxopolyoxotungsten-based phase transfer catalyst and its catalytic activity for olefin epoxidation

Article abstract of DOI:10.1016/S1872-2067(12)60697-4

Peroxopolyoxotungsten-based hybrid catalysts modified by dicationic long-chain alkyl imidazolium cations have been synthesized and characterized. The catalytic activity of the catalysts was measured for the epoxidation of olefins with H₂O₂. These catalysts proved to be high catalytic activity phase transfer catalysts. In particular, for the catalyst [D₁₂min]_1.5PW₄O₂₄ modified by the dodecyl dicationic imidazolium cation, the conversion of cyclohexene and selectivity for epoxycyclohexane were 97.7% and 96.3%, respectively. After the reaction, the catalyst could be recovered simply by filtration and reused four times. The conversion of cyclohexene and selectivity for epoxycyclohexane were still 72.4% and 97.2%, respectively, after recycling the catalyst four times. In addition, this phase transfer catalyst can be applied to the epoxidation of a wide range of olefins.

Full text of DOI:10.1016/S1872-2067(12)60697-4

Chinese Journal of Catalysis 34 (2013) 2236–2244
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Synthesis of dicationic alkyl imidazolium peroxopolyoxotungsten‐
based phase transfer catalyst and its catalytic activity for olefin
epoxidation
Jianghao Wu, Pingping Jiang*, Yan Leng, Yuanyuan Ye, Xiaojie Qin
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University,
Wuxi 214122, Jiangsu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Peroxopolyoxotungsten‐based hybrid catalysts modified by dicationic long‐chain alkyl imidazolium
cations have been synthesized and characterized. The catalytic activity of the catalysts was meas‐
ured for the epoxidation of olefins with H2O2. These catalysts proved to be high catalytic activity
phase transfer catalysts. In particular, for the catalyst [D12min]1.5PW4O24 modified by the dodecyl
dicationic imidazolium cation, the conversion of cyclohexene and selectivity for epoxycyclohexane
were 97.7% and 96.3%, respectively. After the reaction, the catalyst could be recovered simply by
filtration and reused four times. The conversion of cyclohexene and selectivity for epoxycyclohex‐
ane were still 72.4% and 97.2%, respectively, after recycling the catalyst four times. In addition, this
phase transfer catalyst can be applied to the epoxidation of a wide range of olefins.
Received 17 June 2013
Accepted 21 August 2013
Published 20 December 2013
Keywords:
Dicationic ionic liquid
Polyoxometalate
Olefin
Epoxidation
Phase transfer catalyst
© 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
reaction‐controlled phase‐separation catalysts for olefin epox‐
idation, considerable effort has been focused on modifying
Epoxides are valuable organic raw materials and intermedi‐
ates for fine chemical and pharmaceutical synthesis [1–3].
H2O2‐based catalytic epoxidation efficiency and reusability
under mild conditions have received much attention from an
economic and environmental point of view [4]. A wide range of
catalysts for olefin epoxidation have been described, such as
heteroatomic molecular sieves, transition metal (Mo, W, Mn,
and V) compounds, and polyoxometalates (POMs) [5–11].
Tungsten‐based POM catalysts show high efficiency of hydro‐
gen peroxide use and high selectivity towards epoxides, typi‐
cally the Venturello‐Ishii ({PO4[WO(O2)2]4}3–) species, and have
attracted considerable attention as effective catalysts for the
H2O2‐based epoxidation of olefins [12,13]. Since Xi et al. [14]
reported that quaternary ammonium POMs can be used as
POMs with organic species to obtain phase transfer POM‐based
hybrid catalysts with improved catalytic activity, selectivity,
and convenient catalyst recovery and recycling that combine
the advantages of both homogeneous and heterogeneous cata‐
lysts [15–19].
In this work, we synthesized a series of POM‐based ionic
hybrid catalysts by combining dicationic long‐chain alkyl imid‐
azolium cations with Venturello‐Ishii anions. Characterization
was performed using Fourier transform infrared (FT‐IR) spec‐
troscopy, thermogravimetric analysis (TGA), 1H NMR, and CHN
elemental analysis. The obtained hybrid catalysts were used for
the solid‐liquid‐solid phase transfer catalytic epoxidation of
olefins with aqueous H2O2 in different solvents.
*Corresponding author. Tel: +86‐510‐85917090; Fax: +86‐510‐85913617; E‐mail: ppjiang@jiangnan.edu.cn
This work was supported by the National Key Technology R&D Program (2012BAD32B03) and the Cooperative Innovation Foundation of Industry,
Academy and Research Institutes (BY2013015‐10) in Jiangsu Province of China.
DOI: 10.1016/S1872‐2067(12)60697‐4 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 34, No. 12, December 2013

Jianghao Wu et al. / Chinese Journal of Catalysis 34 (2013) 2236–2244
2. Experimental
sure distillation on a rotary evaporator under reduced pressure
at 40–50 °C, which gave a yellow powder. This catalyst was
[D12mim]1.5PW4O24.
2.1. Preparation of catalysts
The procedure for the synthesis of the catalysts is shown in
Scheme 1. The preparation of [D12mim]1.5PW4O24 is used as an
example.
2.2. Characterization of catalyst structure
FT‐IR spectra were recorded on an ABB FTLA2000 FT‐IR
spectrometer (Canada) (KBr discs, 4000–500 cm–1). TGA was
carried out with a METTLER‐TOLEDO TGA/1100SF instrument
(Switzerland) in N2 at a heating rate of 10 °C/min. Elemental
analyses (C, H, and N) were performed on a CHN elemental
analyzer (Elementar Vario EL III, Germany). The 1H NMR spec‐
tra were recorded on an AVANCE III 400 MHz digital NMR
spectrometer (Bruker, Germany) using a CDCl3 solvent.
2.1.1. Synthesis of N‐alkylimidazole
The synthesis of N‐dodecylimidazole was used as an example.
N-dodecyl bromide (7 g, 28 mmol) was dissolved in dimethyl
formamide (DMF, 25 mL) and then added to a solution of the
sodium salt of imidazole, which was formed by the reaction of
imidazole (2.3 g, 33.9 mmol) with sodium hydride (1.4 g, 62
mmol) in DMF (25 mL). The mixture was heated at 60 °C for 6
h, cooled, and then filtered. The filtrate was washed with brine
and water, and then dried with sodium sulfate. The solvent was
separated by reduced pressure distillation and N‐alkylimidaz‐
2.3. Epoxidation procedure
Cyclohexene (9 mmol), CH3CN (10 mL), and catalyst (0.1 g)
were added to a 25 mL flask. The reaction started after the ad‐
dition of aqueous H2O2 (30 wt%, 3 mmol) at 60 °C within 10
min under vigorous stirring. After the reaction, the product
mixture was analyzed by gas chromatography (GC). The cata‐
lyst was recovered by filtration immediately after the reaction
ready for the next reaction (run). The conversion (X) and selec‐
tivity (S) were calculated as follows:
X = (mol epoxide product + mol byproducts) / (mol initial
H2O2) × 100%
S = (mol epoxide product) / (mol epoxide product + mol
byproducts) × 100%
1
ole was obtained as a pale yellow oily product. H NMR (400
MHz, CDCl3) δ = 7.45 (s, 1H, CH), 7.04 (s, 1H, CH), 6.90 (s, 1H,
CH), 3.91 (t, J = 7.1 Hz, 2H, CH2), 1.77 (m, J = 13.5 Hz, 2H, CH2),
1.27 (m, J = 13.1 Hz, 18H, CH2), 0.88 (t, J = 6.7 Hz, 3H, CH3).
2.1.2. Synthesis of dicationic imidazolium ionic liquids
Dicationic imidazolium ionic liquids were prepared by re‐
fluxing N‐dodecylimidazole (4.72 g, 20 mmol) and 1,4‐dibro‐
mobutane (2.16 g, 10 mmol) in isopropanol (25 mL) at 80 °C
for 24 h. Then, the products were washed with diethyl ether
four times under vacuum. 1H NMR (400 MHz, CDCl3) δ = 10.18
(s, 2H, CH2), 8.12 (s, 2H, CH), 7.29 (s, 2H, CH), 4.58 (s, 4H, CH2),
4.27 (t, J = 7.5 Hz, 4H, CH2), 2.19 (s, 4H, CH2), 1.90 (d, J = 6.4 Hz,
4H, CH2), 1.25 (m, 36H, CH2), 0.88 (t, J = 6.8 Hz, 6H, CH3).
All of the olefin substrates were tested using the same pro‐
cedure.
3. Results and discussion
2.1.3. Synthesis of dicationic alkyl imidazolium peroxopolyoxo‐
tungsten‐based catalyst [20]
3.1. Catalyst structure and thermal stability
A suspension of tungstic acid (2.50 g, 10 mmol) in 7.93 g (70
mmol) of 30% aqueous H2O2 was stirred and heated at 60 °C
until a colorless solution was obtained. After filtering and cool‐
ing the solution at room temperature, 40 wt% H3PO4 (0.62 g,
2.5 mmol) was added, and the solution was diluted with 30 mL
of water and then stirred for 30 min. Dicationic imidazolium
ionic liquid (3.75 mmol) in dichloromethane (40 mL) was add‐
ed dropwise to the resultant solution with strong stirring over
a period of more than 2 min. Stirring was continued for an ad‐
ditional 60 min. The organic phase was then separated, dried
over Na2SO4, filtered, and gently evaporated by reduced pres‐
The TGA curves of the catalysts are shown in Fig. 1. The hy‐
brid catalysts were stable up to 200 °C (region I), indicating
that these catalysts are thermally stable. The slight mass loss is
due to the removal of the combination water. The mass loss
between 250 and 600 °C is due to decomposition of the organic
components in the catalyst (region II), which is consistent with
the CHN elemental analysis (Table 1). Thus, these results con‐
firm that the molar of cantion and polyanion of the catalysts is
1.5:1, and the hybrids have the chemical formulas shown in
Scheme 1.
Br
(
)
CH2 4
R-Br
Br
N
N
N
N
N
N
N
NH
Br-
Br-
R
R
R
R:
CnH
2n+1 (n = 1, 4, 8, 12, 16)
H2WO4+H2O2+ H3PO4
(
)
CH2 4
[Dnmim]1.5PW4O24
(n = 1, 4, 8, 12, 16)
-
3
PW4O24
R 1.5
N
N
N
N
R
Scheme 1. Typical preparation procedure of the catalysts.

Jianghao Wu et al. / Chinese Journal of Catalysis 34 (2013) 2236–2244
imidazole, peaks at 2960, 2918, and 2848 cm–1 that are due to
105
100
95
90
85
80
75
70
65
60
55
50
the stretching vibration of the C–H bond in the alkyl chain, and
peaks at 1562 and 1464 cm–1 that are due to the skeletal vibra‐
tion of the imidazole ring. These observations confirm that the
combination of dicationic alkyl imidazolium organic cations
with the Venturello anion ({PO4[WO(O2)2]4}3–) via ionic bonds
produced a new type of organic POM salt. For all these cata‐
lysts, the bands at 852 cm–1 can be attributed to the peroxo‐
oxygen band (v(O–O)) of the peroxo‐W species, which is re‐
graded as the active center for {PO4[WO(O2)2]4}3–‐based epoxi‐
dation reactions [21,22] and demonstrates that the catalysts
we prepared have catalytic activity centers.
(1)
(2)
(3)
(4)
(5)
II
I
100
200
300
400
500
600
700
Temperature (oC)
3.3. Catalytic performance of different catalysts
Fig. 1. Thermogravimetric curves of catalysts. (1) [D1mim]1.5PW4O24;
(2) [D4mim]1.5PW4O24; (3) [D8mim]1.5PW4O24; (4) [D12mim]1.5PW4O24;
(5) [D16mim]1.5PW4O24.
The results using different peroxophosphatotung‐
state‐based hybrid catalysts for the epoxidation of cyclohexene
in acetonitrile with H2O2 are shown in Table 2. The results
show that the carbon chain length of the R groups attached to
the imidazolium ions significantly affects the catalyst activity
for epoxidation. [D1mim]1.5PW4O24 showed 69.2% conversion
and 98.6% selectivity. When the carbon chain length was in‐
Table 1
Results of CHN elemental analysis.
Test value (%)/Theoretical value (%)
Catalyst
C
H
N
[D1mim]1.5PW4O24
[D4mim]1.5PW4O24
[D8mim]1.5PW4O24
[D12mim]1.5PW4O24
[D16mim]1.5PW4O24
14.42/14.60
19.97/20.18
26.16/26.38
32.74/31.51
34.70/35.82
1.97/2.05
3.12/3.02
3.98/4.06
4.72/4.94
5.32/5.74
5.66/5.68
5.12/5.23
4.85/4.73
4.19/4.32
3.54/3.98
creased from
4
to 12 (from [D4mim]1.5PW4O24 to
[D12mim]1.5PW4O24), the conversion of cyclohexene increased
from 78.5% to 97.7%, while the selectivity of both catalysts
was greater than 96%. This means that the longer the alkyl
chain of the R group of the imidazolium ions, the more likely it
is that the reactant comes in contact with the catalytic center.
However, when the carbon chain length was further increased,
the catalytic performance of the catalyst ([D16mim]1.5PW4O24)
decreased (89.2% conversion and 97.2% selectivity). This low‐
er catalytic performance may result from the long alkyl chain
increasing the catalyst molecule steric hindrance and mass
transfer resistance between the reactants and catalyst. As can
be seen from the above results, [D12mim]1.5PW4O24 gives the
best performance, with 97.7% conversion and 96.3% selectivi‐
ty.
3.2. FT‐IR analysis
The FT‐IR spectra of the hybrid catalysts are shown in Fig. 2.
The characteristic bands of the Venturello anion structure
{PO4[WO(O2)2]4}3– appear at 1077 and 1039 (P–O), 942 (W=O),
889 (W–Ob–W), 852 (O–O), 811 (W–Oc–W), and 591 cm–1
(W–Ob–O). For all the hybrid samples, featured peaks as well as
bands of organic groups can be clearly observed. For example,
[D12mim]1.5PW4O24 has bands at 3145 and 3099 cm–1 that can
be attributed to the stretching vibration of the C–H bond in
Moreover, the catalysts prepared showed different catalytic
behavior
during
the
reaction.
[D4mim]1.5PW4O24,
[D8mim]1.5PW4O24, [D12mim]1.5PW4O24, and [D16mim]1.5PW4O24
all showed phase transfer behavior during the reaction process,
with the switch from heterogeneous to homogeneous catalysis
clearly observed. At the beginning of the reaction, the catalyst
itself was solid at bottom (Fig. 3(a)), but when H2O2 was added
to the reaction system the catalyst gradually dissolved in the
medium to form a homogeneous mixture (Fig. 3(b)). After the
reaction was complete, the system became turbid, and the cata-
(1)
(2)
(3)
(4)
(5)
Table 2
Epoxidation of cyclohexene with H2O2 and various catalysts.
Catalyst
X/%
69.2
78.5
92.1
97.7
89.2
S/%
98.6
97.9
96.4
96.3
97.2
[D1mim]1.5PW4O24
[D4mim]1.5PW4O24
[D8mim]1.5PW4O24
[D12mim]1.5PW4O24
[D16mim]1.5PW4O24
3200 3000 2800 1600 1400 1200 1000 800 600
Wavenumber (cm1)
Fig. 2. FT‐IR spectra of catalysts. (1) [D1mim]1.5PW4O24; (2)
[D4mim]1.5PW4O24; (3) [D8mim]1.5PW4O24; (4) [D12mim]1.5PW4O24; (5)
[D16mim]1.5PW4O24.
Reaction conditions: 0.1 g catalyst, 9 mmol cyclohexene, 3 mmol H2O2,
10 mL acetonitrile, 60 °C, 4 h.

Jianghao Wu et al. / Chinese Journal of Catalysis 34 (2013) 2236–2244
Table 3
(b)
(c)
(a)
Effect of reaction media of cyclohexene epoxidation reaction.
Catalyst state
Solvent
X/% S/%
After reaction
During reaction
soluble
Acetonitrile
Ethyl acetate
Dichloromethane
1,2‐Dichloroethane
Cyclohexane
insoluble
insoluble
insoluble
insoluble
insoluble
97.7 96.3
97.6 97.1
98.8 96.6
98.3 96.2
88.2 98.1
soluble
soluble
Fig. 3. Photographs of the epoxidation of cyclohexene with CH3CNover
the [D12mim]1.5PW4O24 catalyst. (a) [D12mim]1.5PW4O24 solid at bottom;
(b) Homogeneous phase during the reaction; (c) At the end of reaction
and the catalyst has precipitated.
soluble
insoluble
Reaction conditions: 0.1 g catalyst, 9 mmol cyclohexene, 3 mmol H2O2,
10 mL solvent, 60 °C, 4 h.
lyst finally separated from the media at room temperature (Fig.
3(c)). However, [D1mim]1.5PW4O24 was a heterogeneous cata‐
lyst in the reaction, which may explain why the
[D1mim]1.5PW4O24 epoxidation activity is lower than the other
catalysts.
ture‐controlled phase transfer system and combine the ad‐
vantages of both homogeneous and heterogeneous catalysts.
3.4. Catalytic performance of [D12mim]1.5PW4O24 in different
solvents and reaction phases
As in the chloroform solvent, quaternary ammonium heter‐
opolyoxotungstates can react with H2O2 to form peroxide reac‐
tive intermediates that are soluble in the reaction system. The
peroxide reactive intermediates gradually return to the original
catalyst structure as H2O2 is used up in the epoxidation reac‐
tion, and then precipitate at the end of the reaction, thereby
forming a reaction‐controlled phase transfer system [14]. To
confirm that the phosphotungstate catalysts we prepared react
with H2O2 to form the soluble peroxide reactive intermediates
{PO4[WO(O2)2]4}3– in acetonitrile, the hybrid‐catalyzed epoxi‐
dation was confirmed by the IR measurement of
[D12mim]1.5PW4O24 after reacting with 30% H2O2 in CH3CN at
60 °C for 10 min, which mimics the practical reaction but in the
absence of any olefin substrate (Fig. 4(2)). Compared with the
FT‐IR spectrum of the fresh catalyst (Fig. 4(1)), the peak at 840
cm–1 (peroxo‐oxygen band, v(O–O)) of the catalyst treated by
H2O2 was significantly larger. This means that after H2O2
treatment the catalyst forms peroxide reactive intermediates
{PO4[WO(O2)2]4}3–. Therefore, the catalyst gradually dissolved
to form a homogeneous system when the H2O2 was added to
the solution. However, the catalyst separates from the reaction
media and must be cooled to room temperature after the reac‐
tion is completed. This behavior is different from that discussed
in the literature [14]. Therefore, dicationic alkyl imidazolium
Table 3 shows the results of the effect of different solvents
on the [D12mim]1.5PW4O24 catalyzed epoxidation of cyclohex‐
ene. When acetonitrile, ethyl acetate, dichloromethane, and
1,2‐dichloroethane were used as the solvent, phase transfer
was observed, and cyclohexene conversion and selectivity for
epoxide cyclohexane were both greater than 96%. Further‐
more, when ethyl acetate was used as the solvent, the reaction
showed temperature‐controlled phase transfer. However,
when dichloromethane and 1,2‐dichloroethane were used as
the solvent, the catalyst gradually precipitated when the H2O2
was used up (Fig. 5). As a result, the system becomes turbid,
indicating completion of the epoxidation reaction, which does
not need to be cooled to room temperature. The reaction pro‐
cess is a solid‐liquid‐solid phase‐separation catalytic process
forming a reaction‐controlled phase transfer system, which is
different to when ethyl acetate and acetonitrile were used as
the solvent. In addition, [D12mim]1.5PW4O24 did not dissolve
when cyclohexane was used as the solvent, which may be due
to active peroxy intermediate that is difficult to dissolve in low
polarity solvents, resulting in low catalytic activity. Therefore,
the dicationic alkyl imidazolium peroxopolyoxotungsten‐based
catalysts we have designed and synthesized can act as temper‐
ature‐controlled phase transfer catalysts in common polar or‐
ganic solvents and reaction‐controlled phase transfer catalysts
in weakly polar organic solvents.
peroxopolyoxotungsten‐based catalysts cause
a tempera‐
(1)
3.5. Catalyst reusability
889
It is convenient to recover the hybrid catalyst by filtration or
centrifugation after a reaction, and then the solid catalyst can
(2)
(a)
(b)
(c)
852
840
3200
2800
1600 1400 1200 1000 800 600
Wavenumber (cm1)
Fig. 5. Photographs of the epoxidation of cyclohexene with CH2Cl2 over
the [D12mim]1.5PW4O24 catalyst. (a) [D12mim]1.5PW4O24 floating in the
solution; (b) Homogeneous phase during the reaction; (c) At the end of
reaction and the catalyst has precipitated.
Fig. 4. FT‐IR spectra of catalysts. (1) [D12mim]1.5PW4O24; (2)
[D12mim]1.5PW4O24 treated by H2O2.

Jianghao Wu et al. / Chinese Journal of Catalysis 34 (2013) 2236–2244
Table 4
Table 5
Reusability of [D12mim]1.5PW4O24 catalyst for the epoxidation of cyclo‐
hexene with H2O2 in acetonitrile and dichloromethane.
Epoxidation of various olefins with H2O2 over the [D12mim]1.5PW4O24
catalyst.
In acetonitrile
In dichloromethane
Olefin
X/%
97.7
≥99
87.2
68.1
S/%
96.3
≥99
80.2
97.2
Reuse
number
1
2
3
4
X/%
97.7
92.1
81.5
72.4
S/%
X/%
98.8
97.5
93.6
89.2
S/%
96.6
98.3
97.8
96.2
Cyclohexenea
Cyclooctene a
Styreneb
96.3
98.2
96.7
97.3
1‐Octeneb
Reaction conditions: 0.1 g catalyst, 9 mmol substrate, 3 mmol H2O2, 10
mL acetonitrile; a 60 °C, 4 h; b 70 °C, 6 h.
Reaction conditions: 0.1 g catalyst, 9 mmol cyclohexene, 3 mmol H2O2,
10 mL solvent, 60 °C, 4 h.
larger relative to the peaks of the heteropolyanion. The inten‐
sity of the peaks in the same range for the catalyst recovered
from dichloromethane were almost the same as the peaks in
the spectrum of the heteropolyanion, indicating that the heter‐
opolyanion leached into acetonitrile. In addition, the peak at
852 cm–1 in the heteropolyanion spectrum disappeared in the
recycled catalyst, indicating that the catalyst precipitates out of
the reaction system when H2O2 was used up.
be reused. Table 4 shows the reusability of [D12mim]1.5PW4O24
for the epoxidation of cyclohexene with H2O2 in acetonitrile and
dichloromethane. In dichloromethane, the catalyst gave 89.2%
conversion after four runs, and recovery of the catalyst was
greater than 80%, indicating good reusability. In acetonitrile,
the conversion decreased from 97.7% to 72.4% between the
first and fourth runs. Compared with dichloromethane, the
reusability in acetonitrile was relatively poor, which may be
due to the catalyst leaching into the highly polar reaction media
during the runs. To confirm this, an experiment was carried out
in acetonitrile under the reaction conditions. Conversion of
29.4% (calculated by the decrease in the amount of cyclohex‐
ene, Conversion = (mol epoxide product + mol byproducts) /
(mol initial cyclohexene) × 100%) was obtained for reaction
time of 4 h. Then, the solid catalyst was filtered, and the reac‐
tion was continued for another 4 h with excess H2O2 added to
the homogeneous filtrate, which resulted in conversion of
37.5% (calculated by the decrease in the amount of cyclohex‐
ene). This result confirms that the catalyst leached into the
reaction media, and the leached species act as active sites.
Therefore, the weakly polar organic solvent dichloromethane is
more suitable for the catalytic reaction system than acetoni‐
trile.
3.6. Catalytic performance of [D12mim]1.5PW4O24 for other
olefins
To investigate the scope of the [D12mim]1.5PW4O24 catalyst
for epoxidation reactions, the substrates cyclooctene, 1‐octene,
and styrene were also investigated, and the results are shown
in Table 5. During the reaction processes, phase transfer was
clearly observed, and high olefin conversion and epoxide
product selectivity were obtained. Therefore, the
[D12mim]1.5PW4O24 catalyst was successfully applied to the
epoxidation of various olefins using H2O2, and good to excellent
activity and selectivity were obtained in all cases. In particular,
for the difficult epoxidation of styrene, the [D12mim]1.5PW4O24
catalyst gave 87.2% conversion and 80.2% selectivity.
FT‐IR analysis shows that the IR spectra of the recovered
catalyst (Fig. 6(2) and (3)) were generally consistent with the
spectrum of the fresh catalyst (Fig. 6(1)). However, the intensi‐
ty of the peaks at 1150–1650 cm–1, which are due to the organic
components, of the catalyst recovered from acetonitrile were
4. Conclusions
We synthesized the POM‐based hybrid material
[Dnmim]1.5PW4O24 by combining the dicationic alkylimidazo‐
lium cation with the peroxopolyoxometalate anion, and meas‐
ured the catalytic activity of the material in the epoxidation of
olefins with H2O2. The catalysts proved to be tempera‐
ture‐controlled phase transfer catalysts in common polar or‐
ganic solvents and reaction‐controlled phase transfer catalysts
in weakly polar organic solvents. The chain length of the R
group of the imidazolium cation significantly affected the phase
transfer catalysis behavior and the catalyst activity for epoxida‐
tion. The [D12min]1.5PW4O24 catalyst modified by the dodecyl
dicationic imidazolium cation showed very high conversion
and selectivity, coupled with convenient recovery and good
reusability.
(1)
(2)
(3)
References
3200 3000 2800 1600 1400 1200 1000 800 600
Wavenumber (cm1)
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Fig. 6. FT‐IR spectra of fresh [D12mim]1.5PW4O24 (1), reused
[D12mim]1.5PW4O24 in CH3CN (2), and reused [D12mim]1.5PW4O24 in
CH2Cl2 (3).
[3] Lu X N, Lin H Q, Yuan Y Z. Chin J Catal, 2010, 31: 1457

Jianghao Wu et al. / Chinese Journal of Catalysis 34 (2013) 2236–2244
Graphical Abstract
Chin. J. Catal., 2013, 34: 2236–2244 doi: 10.1016/S1872‐2067(12)60697‐4
Synthesis of dicationic alkyl imidazolium peroxopolyoxotung‐
sten‐based phase transfer catalyst and its catalytic activity for
olefin epoxidation
O
3
3
3
O
O
O
WP
WP
WP
O
Jianghao Wu, Pingping Jiang*, Yan Leng, Yuanyuan Ye, Xiaojie Qin
Jiangnan University
Organic phase
Aqueous phase
Phase interface
3
O
W
O
O
3
O
O
O
O
O
W
O
O
O
O
W
O
O
O
3
O
P
O
O
O
P
Peroxopolyoxotungsten‐based hybrid catalysts modified by the
dicationic long‐chain alkyl imidazolium cation were synthesized
and used as the phase transfer catalyst for cyclohexene epoxida‐
tion reactions.
W
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
PW
insoluble
W
W
W
O
W
O
O
O
soluble
O
O
O
O
O
O
H2O
H2O2
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