Highly efficient epoxidation of cyclohexene with aqueous H2O2 over powdered anion-resin supported solid catalysts

Article abstract of DOI:10.1016/j.molcata.2016.07.038

Resin supported solid acid catalysts have extended the application of conventional solid acid catalysts in the field of selective oxidations. The present work describes selectively catalytic epoxidation of cyclohexene with aqueous 30% H₂O₂ over powdered anion-resin supported peroxo phosphotungstic acid heterogeneous catalysts prepared through a simple anion-exchange from powdered chloride-form anion resin without any special pre-exchanged treatment. Among these powdered solid catalysts, anion-exchanged resin D201 supported peroxo phosphotungstic acid exhibits the best activity for the titled reaction to obtain 92.4?mol% conversion and 98.1% selectivity of epoxide, for which D201-PWAR(4) behaves as a truly heterogeneous catalyst. Some factors such as various peroxo phosphotungstic acid concentrations, the oxidants, the solvents, the molar ratios of H₂O₂/cyclohexene, the catalyst amount, the reaction temperature and time play important roles in controlling the epoxidation.

Full text of DOI:10.1016/j.molcata.2016.07.038

Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Highly efficient epoxidation of cyclohexene with aqueous H O over
2
2
powdered anion-resin supported solid catalysts
C. Penga,c, X.-H. Lu
Q.-H. Xia
a
a,c,∗
, X.-T. Ma
b,∗∗
, Y. Shen , C.-C. Weia,c, J. Hea,c, D. Zhoua,c
,
b
a,c,∗
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei University, Wuhan 430062, PR China
Hubei Collaborative Innovation Center of Targeted Antitumor Drug, Jingchu University of Technology, Jingmen 448000, PR China
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Resin supported solid acid catalysts have extended the application of conventional solid acid cata-
lysts in the field of selective oxidations. The present work describes selectively catalytic epoxidation
of cyclohexene with aqueous 30% H2O2 over powdered anion-resin supported peroxo phosphotungstic
acid heterogeneous catalysts prepared through a simple anion-exchange from powdered chloride-form
anion resin without any special pre-exchanged treatment. Among these powdered solid catalysts, anion-
exchanged resin D201 supported peroxo phosphotungstic acid exhibits the best activity for the titled
reaction to obtain 92.4 mol% conversion and 98.1% selectivity of epoxide, for which D201-PWAR(4)
behaves as a truly heterogeneous catalyst. Some factors such as various peroxo phosphotungstic acid
concentrations, the oxidants, the solvents, the molar ratios of H2O2/cyclohexene, the catalyst amount,
the reaction temperature and time play important roles in controlling the epoxidation.
Received 2 November 2015
Received in revised form 18 July 2016
Accepted 20 July 2016
Available online 21 July 2016
Keywords:
Powdered chloride-form anion resin
Peroxo phosphotungstic acid
Epoxidation
Cyclohexene
H2O2
© 2016 Elsevier B.V. All rights reserved.
1
. Introduction
The epoxidation reaction of olefins is one of the most impor-
cleanness and economic consideration [9]. So far, the epoxida-
tion reactions have involved in the use of Schiff base complexes,
metal phthalocyanine, metal porphyrins, heteropoly acids and Ti-
containing zeolites as the catalysts [1,10–12].
Anion resin is commonly used for water treatment, so as to
improve the water quality [13,14]. The modified anion resin as
the catalyst in recent years has been widely used in the synthesis
of nitrile and ether [15,16], alkylation, aldol condensation, olefin
hydration, elimination, rearrangement, and so on [17–19].
Currently, rhenium- and tungsten-based homogeneous com-
pounds are the most active catalyst for the epoxidation using
tant catalytic oxidation processes, the epoxy products of which
as intermediates can be used in the synthesis of polymers, phar-
maceuticals, fine chemicals and biological materials [1–3]. Epoxy
compounds can be converted to a series of chiral compounds
through ring-opening reaction, therefore receiving much attention
[
4].
Traditionally, the production of epoxy compounds is mainly
conducted in the presence of organic peroxides [5] and inorganic
hypochlorite [6]. However, these systems will generate a lot of low-
value by-products and hazardous wastes to increase the cost. In
order to overcome these disadvantages, hydrogen peroxide (H O )
and molecular oxygen/air have been used as the oxidizing agents
for the epoxidation of alkenes [7,8]. Among these oxygen donors,
H O is an important oxidant with respect to environmentally
aqueous H O2 [20]. In the case of tungsten chemistry, the most
2
significant developments were made in the 1980s by Venturello
et al. [21] and Ishii et al. [22], who used phosphotungsten-based
catalysts in biphasic reaction media for the epoxidation of apolar
olefins. Most of the tungsten catalysis reported is homogeneous and
liquid biphasic system, with a quaternary ammonium compound
enhancing phase transfer of peroxo W compound from aqueous to
the organic layer [23–27]. In 1999 and 2000, PW-Amberlite cat-
alyst, was prepared by ion-exchange of a peroxo PW-anion onto
a specially-preformed nitrate form of a commercial macroreticular
resin Amberlite IRA-900, in the presence of H O [28,29]. However,
2
2
2
2
∗ Corresponding authors at: Hubei Collaborative Innovation Center for Advanced
Organic Chemical Materials, Hubei University, Wuhan 430062, PR China
∗
∗
2
2
Corresponding author at: Hubei Collaborative Innovation Center of Targeted
the preparation process is slightly complicated since anion resin
must be transferred into a special nitrate form prior to the ion-
Antitumor Drug, Jingchu University of Technology, Jingmen 448000, PR China.
E-mail addresses: xinhuan003@aliyun.com (X.-H. Lu), mxtjmhb@163.com
(
X.-T. Ma), xiaqh518@aliyun.com (Q.-H. Xia).
http://dx.doi.org/10.1016/j.molcata.2016.07.038
381-1169/© 2016 Elsevier B.V. All rights reserved.
1

3
94
C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
O
Tungsꢀc acid
Phosphoricacid
catalyst, H
2
O
2
OH
+
OH
OH
O
+
3
0%H O
+
2
2
(
D201, D261 or 201)
CHCH
*
2
*
*
CHCH
2
*
Scheme 2. Catalytic oxidation of cyclohexene with H2O2.
C H OH
2
5
D201-PWAR
D261-PWAR
H PW O
4 24
+
3
2
01-PWAR
n
n
◦
8
0 C for 2 h. In the meantime, 7.80 mmol tungstic acid, 1.95 mmol
phosphoric acid, and 15 ml 30% H O , and 40 ml water were added
CH
N
2
CH
N
2
2
2
2 4 24
H PW O
H
3
C
CH
3
Cl
H
3
C
CH
3
into a 100-ml 3-necked flask to obtain a mixture solution, which
Cl
◦
was stirred at 60 C overnight. Subsequently, the powdered anion
CH
3
CH
3
resin was added into a solution of preformed peroxo phospho-
◦
ric acid and aged at 60 C for 1 h under shaking, which was then
Scheme 1. Preparation route of the catalysts.
◦
heated to 80 C for the anion-exchange treatment for 5 h. Finally,
the powder resin catalyst was recovered by filtration, washed with
deionized water until neutral, and then washed by acetone, fol-
lowed by drying at 60 C for 2 h. Besides, D201-PWAR catalysts with
different P contents (0.70, 0.78, 0.84, 0.99 and 1.23 wt%) were pre-
pared through above-said anion-exchange treatment of anion resin
D201 with aqueous solutions of different P concentrations, and
named as D201-PWAR(1), D201-PWAR(2), D201-PWAR(3), D201-
PWAR(4) and D201-PWAR(5) (Scheme 1). Other anion resins (D261
and 201) underwent the same anion-exchange procedure to obtain
the catalysts D206-PWAR and 201-PWAR.
exchange, and the catalytic activity of the resulting catalyst for the
epoxidation of cyclohexene is poor. In 2015, PW -Zn(x)/SnO was
prepared by using zinc-modified SnO2 as the support, which could
act as an efficient and reusable heterogeneous catalyst for selective
4
2
◦
oxidation with aqueous H O2 oxidant [30]. The catalytic perfor-
2
mance of PW -Zn(0.8)/SnO2 was much superior to those of the
4
corresponding homogeneous analogue THA PW and the previ-
3
4
ously reported tungstate-based heterogeneous catalysts; however,
no any report has approached its use in the epoxidation of cyclo-
hexene.
In the present work, a simple synthesis route of peroxo phos-
photungstic acid anion-exchanged resin (PWAR) heterogeneous
catalysts is firstly developed. Through a simple anion-exchange of
only chloride-form powdered anion-resin with peroxo phospho-
tungstic acid, an active solid catalyst is achieved, which has shown
a very good catalytic activity for the epoxidation of cyclohexene
2
.3. Characterization
X-ray diffraction (XRD) patterns of samples were recorded
on a Rigaku D/MAX-IIIC diffractometer with Cu K␣ radiation
␭ = 1.54184 Å) operating at 30 kV and 25 mA. The average crystal
(
sizes were estimated from SEM images, which were observed using
a JEOL JSM 6500 F scanning electron microscope (SEM) operating at
an accelerating voltage of 25 kV and a tube current of 100 ␮A under
with 30% H O to obtain of 92.4 mol% conversion of cyclohexene
2
2
and 98.1% selectivity of epoxide.
−
6
vacuum at 10 mbar, where the setup was coupled to an Energy
Dispersive Spectrometer (EDS) for micro-analysis. UV–vis spectra
of samples was determined on a Shimadzu UV-2550 spectrometer.
The Kubelka–Munk function was used to convert reflectance mea-
surements into equivalent absorption spectra using the reflectance
of BaSO4 as a reference, and to obtain absorption edge energies
directly from the curves. Thermogravimetric analysis (TGA) of the
catalysts was performed on a Mettler Toledo TGA/SDTA851e under
2
. Experimental
2.1. Materials
Chloride-form anion resins (D201, D261, 201) are commercial
products and ground into fine powder from ball before use. Note
that three resins are styrene-divinylbenzene type ones containing
exchangeable chloride anions. D201 and D261 are macroporous
anion resins similar to Amberlite IRA-900, and 201 is gelatinous
resin similar to Amberlite IRA-400, for which the compositions
and anion-exchange capacities of these anion resins are shown in
Scheme 1 and Table 2. Various alkenes and solvents underwent
re-distillation treatment prior to use, inclusive of cyclohexene,
cyclooctene, 1-hexene, styrene, 1-dodecene, allyl alcohol, chloro-
◦
◦
N2 flowing of 60 ml/min at heating rate of 20 C/min up to 800 C.
2.4. Epoxidation of cyclohexene
The catalytic epoxidation of cyclohexene (Scheme 2) was carried
out in a 25-mL single-necked round-bottom glass flask equipped
with a cryogenic-liquid condenser under atmospheric pressure.
Typically, 10.0 mmol of cyclohexene, 12.0 mmol of H O , 5.0 g of
acetonitrile and 350 mg of the catalyst were added into the reactor.
Note that H O2 was added by four times and each time lasted ten
minutes. The mixture was vigorously stirred by a magnetic stir-
rer and heated to desired temperature in a water bath. After the
completion of the reaction, the solid powder catalyst was recov-
ered by filtration and washed thoroughly with acetone and ethanol,
propene, ␣-pinene, acetonitrile (CH CN), ethyl alcohol (EtOH),
3
ꢀ
ethyl acetate, acetone, methylbenzene, N,N -dimethyl formamide
DMF), 1,4-dioxane, cyclohexane and dichloroethane. All other
2 2
(
reagents were used as received without further purification,
including hydrogen peroxide (30%, H O ), tungstic acid (H WO ),
2
2
2
3
4
phosphoric acid (85%, H PO ), aqueous tert-butyl hydroperoxide
3
4
(
65%, TBHP), sodium hypochlorite (NaClO) and cumyl hydroperox-
ide (>70%, CHP).
◦
and dried at 60 C overnight for the next use. The liquid filtrate
was analyzed by a gas chromatograph equipped with a capillary
column (SE-30, 30 m × 0.25 mm × 0.25 ␮m) and an FID detector, in
which chlorobenzene was used as an internal standard to quantify
all the components. The cyclohexene conversion and the epoxide
selectivity were calculated by using Eqs. (1) and (2).
2
.2. Preparation of catalysts
Anion resins that had been ground into fine powders required
one pretreatment for the removal of impurities prior to use [31]. In a
1
5
was recovered by filtration and washed thoroughly with deionized
water. Note that above-said two steps were repeated once. The
recovered powder resin was washed by acetone, and then dried at
00-ml 3-necked flask, the mixture of 2.5 g anion resin powder and
0 ml ethanol was refluxed at 80 C for 24 h. Then, the solid powder
◦
moles of cyclohexene reacted
Cyclohexene conversion(mol%) =
total moles of cyclohexene
×100
(1)

C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
395
Table 1
Chemical composition of as-synthesized catalysts (weight%).
1.6
.4
1.2
Catalyst
C%
O%
P%
Cl%
W%
1
D201
82.97
69.37
67.59
64.87
61.87
57.07
62.25
67.82
13.15
12.97
12.14
11.60
11.26
10.87
11.35
12.28
–
3.88
3.33
3.10
2.78
2.20
1.41
2.36
3.21
–
D201-PWAR(1)
D201-PWAR(2)
D201-PWAR(3)
D201-PWAR(4)
D201-PWAR(5)
D261-PWAR
0.70
0.78
0.84
0.99
1.23
0.92
0.75
13.63
16.39
19.91
23.68
29.42
23.12
15.94
D201-PWAR(4)
1.0
0.8
0.6
0.4
2
01-PWAR
peroxo phosphotungstic
acid
D201 resin
D201-PWAR(2)
moles of cyclohexene oxide formed
moles of cyclohexene oxidereacted
Cyclohexene oxide selectivity(%) =
100
0.2
D201-PWAR(1)
300 400
×
(2)
0
.0
2
00
500
Wavelength (nm)
600
700
3
. Results and discussion
Fig. 1. UV–vis spectra of various samples.
3.1. Characterstics of catalysts
3
00 nm, different from those of peroxo phosphotungstic acid and
D201 resin itself. The blue shifts are observed, possibly due to the
effect of peroxo phosphotungstic acid anions introduced into the
framework of D201 resin on coordinative environments.
The XPS measurements were performed to identify elemental
compositions of multilayer films deposited on the D201-PWAR(4)
The SEM images of catalysts are shown in Fig. S1, indicating
that the morphologies of catalysts are still similar to that of par-
ent anion resin after the anion-exchange treatment. This means
that the framework structure of anion resin D201 is not destroyed
and the active sites have been highly dispersed on its surface.
The EDX (energy-dispersive X-ray) analysis confirms a uniform
distribution of active components in this composite material. As can
be seen from Table 1, with increasing the loading concentration of
peroxo phosphotungstic acid, the contents of P and W in the catalyst
are increased stepwise. As shown in Table 1, the contents of P and
W are the highest in the D201-PWAR(5) catalyst; however, those
of P and W in D261-PWAR and 201-PWAR are less at the same
conditions.
catalyst. The survey spectrum of the film shows the presence of C1s
(
(
BE = 286.08 eV), N1s (BE = 403.08 eV), W4f (BE = 34.08 eV) and O1s
BE = 533.08 eV) core levels with no evidence of impurity (in Fig. 2a).
The 403.08 eV peak is attributed to the carbon bound to N atom of
D201-PWAR(4). Fig. 2b shows the W4f core-level spectrum with
two peaks centered at binding energies of 35.28, and 37.38 eV. The
W4f7/2 (35.28 eV) is ascribed to the HPW species. Fig. 2c shows the
spectrum of the C1s core level. The 284.68 eV peak can be assigned
to the alkyl carbon of D201-PWAR(4). Fig. 2d shows the O1s spec-
trum, where the 530.58 eV and 532.28 eV BE peaks are ascribed to
the W–O and W–O–W bands in HPW. These XPS results confirm the
existence of the D201 and HPW in the multilayer film in conjunction
with the results of EDX and UV–vis spectra.
Table 2 presents the BET surface areas and total pore volumes
of various catalysts determined by the BET analysis. Both values of
the catalyst D201-PWAR (D201 as the support) are the largest. The
BET surface area of the support D261 and the catalyst D261-PWAR
2
2
is 19.7 m /g and 18.0 m /g. However, it is difficult to detect specific
surface area and pore volume of the support 201 and the catalyst
2
01-PWAR. The TGA curves of different catalysts in N2 are shown
3.2. The epoxidation of cyclohexene over various
anion-exchanged catalysts
in Fig. S2, where shows highly thermal stability of peroxo phospho-
tungstic acid species. The weight loss between room temperature
and 300 C is due to the evaporation of water, while that between
◦
Various anion-exchanged catalysts have been applied to cat-
alyze the epoxidation of cyclohexene with H O , as demonstrated
◦
3
00 and 650 C is attributable to the decomposition of organics.
The XRD patterns of catalysts are shown in Fig. S3, where shows
2
2
in Table 3. Under identical experimental conditions, various cat-
alysts show different catalytic properties in the epoxidation of
cyclohexene. When no catalyst is added (blank), only 2.9 mol%
of cyclohexene is converted with 100% selectivity of cyclohex-
ene oxide. 201-PWAR merely converts 34.6 mol% of cyclohexene
with only 55.7% selectivity of cyclohexene oxide. The byproducts
(others) of the reaction include cyclohexenol, cyclohexenone and
the peak positions of peroxo phosphotungstic acid locating in the
◦
◦
range from 27 to 30 . The UV–vis spectra of various samples is
shown in Fig. 1, in which peroxo phosphotungstic acid shows the
absorption bands at 233 and 263 nm. As for the D201 resin itself,
the maximal absorption appears at 303 nm. D201-PWAR samples
exhibit broad and strong absorptions in the range from 200 to
Table 2
BET surface areas and pore volumes of different materials.
2
3
Material
D201
Anion exchange capacity (meq/g) dry (meq/ml) wet
1.1
Surface area (m /g)
Total pore volume (cm /g)
22.3
0.065
3.7
D201-PWAR(4)
D261
21.6
19.7
0.062
0.048
1.1
.6
3
D261-PWAR
18.0
<0.1
0.047
–
2
01
1.4
.6
3
2
01-PWAR
–
–

3
96
C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
(
a)
C
1s
(b)
Wf7/2
Wf5/2
O
1s
N
1s
W
4f
0
200
400
600
800 1000 1200
27
30
33
36
39
42
45
48
Binding Energy (eV)
Binding Energy (eV)
(
c)
(d)
O1s
C1s
278 281 284 287 290 293 296 299
522 525 528 531 534 537 540 543 546
Binding Energy (eV)
Binding Energy (eV)
Fig. 2. XPS core level spectra recorded for D201-PWAR(4) catalyst (a) survey, (b) W4f, (c) C1s, (d) O1s.
Table 3
100
a
Effect of various catalysts on the epoxidation of cyclohexene .
Catalyst
Conversion(mol%)
Selectivity(%)
80
Cyclohexene oxide
Others
None
2.9
100
0
D201-PWAR(4)
D261-PWAR
92.4
75.2
34.6
98.1
94.5
55.7
1.9
5.5
44.3
60
40
2
01-PWAR
a
Reaction conditions: catalyst (350 mg), CH3CN (5.0 g), cyclohexene (10 mmol),
◦
Conversion
selectivity
H2O2 (12 mmol), 50 C, 6 h.
cyclohexanediol. However, D261-PWAR can convert 75.2 mol% of
cyclohexene, along with the selectivity of 94.5%. In contrast, D201-
PWAR(4) presents an excellent catalytic activity with 92.4 mol%
conversion and 98.1% selectivity, remarkably higher than those
over other catalysts. Based on the above results, powdered D201
anion resin is considered to be an effective support for the prepa-
ration of catalyst in high activity.
2
0
0
0
.65
0.75
0.85
0.95
1.05
1.15
1.25
P content (wt%)
In order to test the effect of the P content on the epoxidation, a
series of D201-PWAR catalysts with different contents of P is pre-
pared and applied in the epoxidation of cyclohexene (Fig. 3). As
the content of P is lower than 0.95 wt%, the conversion of cyclo-
hexene is lower than 72.0 mol%. When the content of P is increased
from 0.99 to 1.23 wt%, the conversion of cyclohexene shows a slight
increase from 92.4 to 94.5 mol%, while the selectivity of the epox-
ide has kept an inconspicuous fluctuation of around 97.5–98.1%.
However, when the content of P is 1.23 wt%, the selectivity of cyclo-
hexene oxide is sharply reduced to 94.3%. In general, the catalyst
with 0.99 wt% P is the most active.
Fig. 3. Effect of various P contents in D201-PWAR on the epoxidation of cyclohex-
ene. (Reaction conditions: catalyst (350 mg), CH CN (5.0 g), cyclohexene (10 mmol),
3
◦
H2O2 (12 mmol), 50 C, 6 h).
further shows the excellent activity of our epoxidation system
using D201-PWAR(4) as the catalyst. According to the methods
reported in the literature [32–36], the conversion gradually
decreases in the order of D201-PWAR(4) (92.4%) > MnTPPS-
3−
3−
Ad
(88.0%) > PW-Amb
(84.0%) > Q3+{PO [W(O)(O ) ] }
4
2
−
2 4
2
(52.8%) > [␲-C5H5N(CH2)15CH ] [PW O ] (47.5%) > WO4 /PO
3
3
4
16
4
A comparison of our results with the earlier data reported for
the epoxidation of cyclohexene is summarized in Table 4, which
association (29.4%), slightly different from the descending
order of the epoxide selectivity: Q3+{PO [W(O)(O ) ] }
3−
4
2 2 4

C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
397
Table 4
Comparison of different catalysts for the epoxidation of cyclohexene.
Catalyst
Reaction conditions
Subs. amount (mmol)
Conv. (%)
Sele. (%)
Ref.
◦
Tempt., time ( C, h)
H2O2 (mmol)
PW-Amb
MnTPPS-Ad
3
1
400
32, 24
25, 4
70, 0.75
3
2
120
84.0
88.0
29.4
99.0
70.0
88.0
[32]
[33]
[34]
WO42-/PO43- association
ꢀ
ꢁ
3−
+
Q3
PO4[W(O)(O2)2]4
100
60, 1
60
52.8
100
[35]
[36]
This work
[
␲-C5H5N(CH2)15CH3]3[PW4O16]
D201-PWAR(4)
16
10
35, 4
50, 6
8
12
47.5
92.4
97.0
98.1
Table 5
Effect of various oxidants on the epoxidation of cyclohexene over D201-PWAR(4)
100
a
.
Oxidant
Conversion (mol%)
Selectivity (%)
9
8
7
6
0
0
0
0
Cyclohexene oxide
Others
TBHP
H2O2
CHP
3.5
92.4
37.4
2.2
3.6
–
35.6
98.1
4.9
17.3
34.5
–
64.4
1.9
95.1
82.7
65.5
–
NaClO
b
Air
None
selectivity
conversion
a
Reaction conditions: catalyst (350 mg), CH3CN (5.0 g), cyclohexene (10 mmol),
◦
oxidants (12 mmol), 50 C, 6 h.
b
◦
50
Flow rate of air (30 ml/min), 50 C.
4
0
0
(
100%) > PW-Amb
(99.0%) > D201-PWAR(4)
(98.1%) > [␲-
C5H5N(CH2)15CH ] [PW O16] (97.1%) > WO42 /PO4
−
3−
association
3
3
4
3
(
88.0%) > MnTPPS-Ad (70.0%).
1.0
1.1
1.2
1.3
1.4
n
(
H2O2)/n(cyclohexene)
3
.3. Effect of different reaction conditions
.3.1. Effect of different oxidants
Fig. 4. Effect of H2O2/cyclohexene molar ratios on the epoxidation of cyclohex-
ene. (Reaction conditions: catalyst (350 mg), CH3CN (5.0 g), cyclohexene (10 mmol),
3
◦
Various oxidants including TBHP, H O , CHP, NaClO and air
50 C, 6 h).
2
2
◦
are tested to epoxidize cyclohexene over D201-PWAR(4) at 50 C.
◦
When no any oxidant is added, no epoxidation occurs below 60 C.
Table 6
a
Effect of various solvents on the epoxidation of cyclohexene .
As compared with H O , TBHP, CHP, NaClO and air are less efficient
2
2
for the epoxidation of cyclohexene under the present experimental
conditions (Table 5). When TBHP is used as the oxidant, the conver-
sion of cyclohexene is 3.5 mol% with 35.6% selectivity of epoxide,
similar to the result of air as the oxidant. NaClO achieves 2.2 mol%
conversion and about 17.3% selectivity of epoxide. Using CHP as the
oxidant, 37.4 mol% conversion of cyclohexene is obtained with only
Solvent
Conversion (mol%)
Selectivity (%)
Cyclohexene oxide
Others
CH3CN
92.4
86.5
56.5
72.0
72.5
99.9
5.2
98.1
86.8
95.3
97.6
8.6
50.2
36.7
46.2
1.9
13.2
4.7
1,4-dioxane
DMF
acetone
ethyl acetate
EtOH
toluene
2.4
4
.9% selectivity of epoxide.
91.4
49.8
63.3
53.8
3
.3.2. Effect of H O /cyclohexene molar ratios
2
2
dichloroethane
19.6
Fig. 4 describes the effect of H O /cyclohexene molar ratios
2
2
a
Reaction conditions: catalyst (350 mg), solvent (5.0 g), cyclohexene (10 mmol),
on the catalytic epoxidation of cyclohexene. With the increase
of the n(H O )/n(cyclohexene) molar ratio from 1:1 to 1.4:1,
◦
H2O2 (12 mmol), 50 C, 6 h.
2
2
the conversion of cyclohexene is speedily increased from 87.9
to 95.6 mol%, but the selectivity to cyclohexene oxide is vigor-
ously decreased from 98.1 to 75.5%, ascribable to the oxidation
only 50.2%. This is because the epoxide can be readily ring-opened
by EtOH to form ether. Obviously, CH3CN is the optimal solvent for
the selective epoxidation of cyclohexene.
of ␣-H in cyclohexene in the presence of the excess H O2 and
2
the hydrolysis of cyclohexene oxide. When the molar ratio of
n(H O )/n(cyclohexene) is 1.2:1, the maximal yield of epoxide is
attained.
3.3.4. Effect of catalyst amount
2
2
The effect of the catalyst amount on the conversion and
selectivity is illustrated in Fig. 5. When the amount of catalyst
D201-PWAR(4) is increased from 100 to 350 mg, the conversion
of cyclohexene is speedily increased from 30.2 to 92.4 mol%, while
the selectivity of cyclohexene oxide is slightly decreased from 99.9
to 98.1%. With a further increase in the catalyst amount from 350
to 400 mg, the conversion of cyclohexene is continuously increased
from 92.4 to 94.4 mol%, but the selectivity of cyclohexene oxide is
sharply decreased from 98.1 to 89.2%. This shows that the addi-
tion of excess catalyst is unbeneficial to the selective epoxidation
of cyclohexene.
3.3.3. Effect of various solvents
Further investigations have shown the importance of
suitable solvent for the titled epoxidation (Table 6).
a
The conversion of cyclohexene decreases in the sequence
of EtOH (99.9 mol%) > CH CN (92.4 mol%) > 1,4-dioxide
86.5 mol%) > ethyl acetate (72.5 mol%) > acetone (72.0 mol%) > DMF
56.5 mol%) > dichloroethane (19.6 mol%) > methylbenzene
5.2 mol%). Although a high cyclohexene conversion of 99.9 mol%
3
(
(
(
can be achieved in the solvent of EtOH, the selectivity of epoxide is

3
98
C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
00
1
100
9
8
0
0
90
80
70
60
50
40
30
70
conversion
selectivity
conversion
selectivity
control experiment
6
5
4
3
0
0
0
0
0
.10 0.15 0.20 0.25 0.30 0.35 0.40
0
1
2
3
4
5
6
7
8
9
Time(h)
Catalyst amount (g)
Fig. 7. Effect of reaction time on the epoxidation of cyclohexene. (Reaction con-
Fig. 5. Effect of catalyst amount on the epoxidation of cyclohexene. (Reaction con-
ditions: CH3CN (5.0 g), cyclohexene (10 mmol), H2O2 (12 mmol), 50 C, 6 h).
◦
ditions: catalyst (350 mg), CH3CN (5.0 g), cyclohexene (10 mmol), H2O2 (12 mmol),
◦
50
C.).
100
con.%
sel. %
1
00
9
8
7
6
5
4
3
0
0
0
0
0
0
0
80
60
40
20
0
conversion
selectivity
30
40
50
60
70
1
2
3
4
5
o
Temperature ( C)
Number of reuses
Fig. 6. Effect of reaction temperature on the epoxidation of cyclohexene. (Reac-
tion conditions: catalyst (350 mg), CH3CN (5.0 g), cyclohexene (10 mmol), H2O2
Fig. 8. Recycling results of the catalyst D201-PW(4). (Reaction conditions: catalyst
◦
(
350 mg), CH3CN (5.0 g), cyclohexene (10 mmol), H2O2 (12 mmol), 50 C, 6 h).
(
12 mmol), 6 h).
decreased to 98.0% in 2 h, to 97.0% in 4 h, to 96.0% in 6 h, and to
3
.3.5. Effect of reaction temperature
The effect of reaction temperature on the epoxidation of cyclo-
9
2.8% in 8 h.
Furthermore, control experiments are carried out according to
hexene with H O over D201-PW(4) is studied, as illustrated
in Fig. 6. With increasing the reaction temperature from 30 to
5
9
of cyclohexene oxide from 99.3 to 98.1%. When the temperature
is increased from 50 to 70 C, the conversion of cyclohexene is
gradually increased from 92.4 to 96.8 mol%, but the selectivity of
cyclohexene oxide is sharply decreased from 98.1 to 75.1%, possi-
bly attributed to the formation of by-products at higher reaction
temperatures.
2
2
the method described in the literature [7,37]. As shown in Fig. 7,
after the epoxidation reaction is initially conducted for 1 h, the con-
version of cyclohexene reaches 35.4 mol%. Then, the solid catalyst
is filtered off and the reaction is continued for another 7 h. The
final conversion analyzed by GC merely shows a small increment
of 3.5 mol% on D201-PWAR(4), attributable to the non-catalytic
oxidation of cyclohexene by H O , which further confirms the char-
◦
0 C, the conversion of cyclohexene is increased from 41.2 to
2.4 mol%, accompanied with a slight decrease of the selectivity
◦
2
2
acteristics of heterogeneous catalysis.
3.4. Recycling studies
3.3.6. Effect of reaction time
The recycling experiments of D201-PWAR(4) catalyst for the
Fig. 7 shows the effect of reaction time on the epoxidation
epoxidation of cyclohexene are conducted. As observed from Fig. 8,
the activity of catalyst is still maintained at a high level, even if the
catalyst has been used five times, and all the reactions maintain
almost a high cyclohexene conversion of >90 mol% and a constant
level of ca. 98.0% selectivity, which suggests recyclable stability of
the catalyst. For the first recycle, ICP analyses of the reaction mix-
of cyclohexene with H O2 over D201-PWAR(4). Within the reac-
2
tion time of 1 h, the conversion of cyclohexene is about 35.4 mol%,
then sharply increased to 72.0 mol% in 2 h, to 90.0 mol% in 4 h, to
4.0 mol% in 6 h and to 97.5 mol% in 8 h with prolonging the reaction
9
time. However, the selectivity of epoxide is 99.3% in 1 h, stepwise

C. Peng et al. / Journal of Molecular Catalysis A: Chemical 423 (2016) 393–399
399
Table 7
Acknowledgements
a
The epoxidation of various alkenes with H2O2 over D201-PWAR(4) .
Substrate
Conversion (mol%)
Selectivity (%)
Epoxide
This work was supported by National Natural Science Foun-
dation of China (21173073, 21273064, 21503074, 21571055),
by Natural Science Fund for Creative Research Groups of Hubei
Province of China (2014CFA015), and by 2014 Sci-tech Sup-
port Project of the Science and Technology Department of Hubei
Province of China (2014BAA098).
Others
1.9
9
9
2.4
3.2
98.1
90.2
b
9.8
6
3
3
7.9
5.3
9.4
79.1
35.1
36.9
21.9
64.9
63.1
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molcata.2016.07.
0
38.
1
3
8.4
0.4
78.6
86.4
21.4
13.6
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Reaction condition: catalyst (350 mg), CH3CN (5.0 g), alkene (10 mmol), H2O2
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powdered anion resin is used. Thus-synthesized catalyst D201-
PWAR(4) shows an excellent activity for the epoxidation of
cyclohexene with aqueous 30% H O oxidant, with 92.4 mol% con-
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molar ratio of 1 (cyclohexene): 1.2 (30% H O ) under ambient
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2
2
pressure. And, this catalyst is heterogeneous recyclable. Some fac-
tors like the type of anionic resins, solvents, oxidants, temperature
and time exert notable impacts on the epoxidation reaction. Also,
this catalyst shows good catalytic activity for the epoxidation of
cyclooctene, but relatively poor ones for other alkenes.