A Ti-substituted polyoxometalate as a heterogeneous catalyst for olefin epoxidation with aqueous hydrogen peroxide

Article abstract of DOI:10.1039/c1nj20312f

The Ti-substituted polyoxometalates ([C₁₂mim] ₅PTiW₁₁O₄₀, [CTA]₅PTiW ₁₁O₄₀ and [TBA]₅PTiW₁₁O ₄₀) were prepared and characterized by FT-IR, NMR, UV-vis and ICP-AES. Then the polyoxometalates (POM) were used as catalysts for the epoxidation of various olefins. It was found that the organic countercations had a considerable effect on the catalytic performance. In addition, UV-vis and the FT-IR spectroscopy indicated that the peroxo structure regarded as the active site for oxygen transfer was present even after the reaction, which led to the increasing reaction rate in the second run due to the disappearance of the induction period, as compared with that in the first run. A heterogeneous reaction mechanism has been suggested in olefin epoxidation catalyzed by a Ti-substituted polyoxometalate ([C₁₂mim]₅PTiW ₁₁O₄₀) with aqueous hydrogen peroxide in ethyl acetate. The heterogeneous POM catalyst can be easily separated and recycled eight times without decreasing the catalytic activities.

Full text of DOI:10.1039/c1nj20312f

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PAPER
A Ti-substituted polyoxometalate as a heterogeneous catalyst for olefin
epoxidation with aqueous hydrogen peroxide
Li Hua, Yunxiang Qiao, Yinyin Yu, Wenwen Zhu, Ting Cao, Yu Shi, Huan Li,
Bo Feng and Zhenshan Hou*
Received (in Gainesville, FL, USA) 9th April 2011, Accepted 13th June 2011
DOI: 10.1039/c1nj20312f
The Ti-substituted polyoxometalates ([C12mim]5PTiW11O40, [CTA]5PTiW11O40 and
[TBA]5PTiW11O40) were prepared and characterized by FT-IR, NMR, UV-vis and ICP-AES.
Then the polyoxometalates (POM) were used as catalysts for the epoxidation of various olefins.
It was found that the organic countercations had a considerable effect on the catalytic
performance. In addition, UV-vis and the FT-IR spectroscopy indicated that the peroxo structure
regarded as the active site for oxygen transfer was present even after the reaction, which led to
the increasing reaction rate in the second run due to the disappearance of the induction period,
as compared with that in the first run. A heterogeneous reaction mechanism has been suggested in
olefin epoxidation catalyzed by a Ti-substituted polyoxometalate ([C12mim]5PTiW11O40) with
aqueous hydrogen peroxide in ethyl acetate. The heterogeneous POM catalyst can be easily
separated and recycled eight times without decreasing the catalytic activities.
because they are more thermally and oxidatively stable toward
1. Introduction
oxygen donors, as compared with organometallic complexes.
The selective catalytic oxidation of organic compounds with
Moreover, their acidic and redox properties can be controlled
environmentally benign, cheap and readily available catalysts
at the molecular or atomic level. Transition metal mono-
and oxidants is the most economic and ecological route to a
substituted polyoxometalates, as a prominent branch of the
wide variety of valuable oxygen-containing products and
polyoxometalates, are useful single-site catalysts where an
intermediates.1 Among these oxidations, the epoxidation of
active metal M is isolated in and strongly bound to an
alkenes has gained much attention for a few decades because
inorganic metal-oxide matrix and thus is prevented from
oligomerization and leaching.7 From the early stage of the
epoxides have been widely used as raw materials for epoxy
Ishii–Venturello system8,9 which focused on the Keggin-type
resins, paints, surfactants, and are intermediates in organic
synthesis. Although a number of epoxidation processes based
phosphotungstate to the later development of various kinds of
polyoxometalates, such as sandwich-type polyoxometalates,10
on organic peroxides and peracids are still used up to now,
divacant lacunary silicodecatungstate11 and so on, the poly-
these processes have disadvantages from the economical
viewpoint because they are very capital intensive. Obviously,
oxometalates have been always considered as excellent
homogeneous catalysts in olefin epoxidation.12–14 On the other
the catalytic epoxidation with hydrogen peroxide as a clean
oxidant might offer some advantages because (i) it generates
hand, the most representative heterogeneous catalyst for the
epoxidation is a titanium-silicalite molecular sieve (TS-1).15,16
only water as a by-product and (ii) it has a high content of
active oxygen species.2 With the hard efforts made by many
According to the present research, three features of the Ti sites
research groups, a great number of efficient catalysts for
lead to the remarkable catalytic activity of TS-1: the hydro-
homogeneous or heterogeneous epoxidation with hydrogen
phobic environment, the tetrahedral coordination of Ti centers
peroxide have been developed.3–6
and the constrained reaction sites.17,18 However, the application
As we have known, the polyoxometalates (POM) and
of the highly active catalyst is still confined by its microporous
polyoxoperoxometalates (POPOMs), as attractive homogeneous
structure. Later, titanium-containing mesoporous molecular
catalysts, have been widely studied in the olefin epoxidation
sieves which possessed active Ti centers accessible to large
molecules sprung up, such as Ti-SiO2, Ti-SBA-15, Ti-MMM-2
etc.19–21 Nevertheless, for some of the Ti-containing hetero-
Key Laboratory for Advanced Materials, Research Institute of
Industrial Catalysis, East China University of Science and
Technology, Shanghai 200237, People’s Republic of China.
E-mail: houzhenshan@ecust.edu.cn; Fax: +86 21 64253372;
Tel: +86 21 64251686
geneous catalysts, such as TS-1, Ti-Alb and Ti-MCM-41, the
leaching of Ti or the stability of these catalysts towards H2O2
under the reaction conditions still seems to be the considerable
problems.22
c
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Because Ti-substituted POM catalysts were considered as
useful single-site catalysts, they are often regarded as homo-
geneous oxidatively stable models for TS-1 and Ti-containing
heterogeneous catalysts. Furthermore, Ti-substituted POM
catalysts own the ability to activate hydrogen peroxide,23
and thus were normally utilized as efficient homogeneous
catalysts in olefin oxidation.24,25 On the basis of our previous
research on epoxidation,26 it was found that the separation of
a homogeneous POM catalyst from products and solvent was
conventionally problematic. As a result, there is no doubt that
the exploration of highly efficient, easy separable heterogeneous
POM catalysts for the epoxidation is of great importance, but is
also challenging. In this work, we attempted to prepare a stable,
recyclable and heterogeneous Ti-based POM catalyst for the
epoxidation reactions with aqueous H2O2. Herein, a Ti-substituted
polyoxometalate ([C12mim]5PTiW11O40) has been synthesized and
used for the epoxidation of various olefins. The POM catalyst has
been characterized by FT-IR, NMR, SEM and BET surface area
determination. It has been proved that the present POM catalyst
([C12mim]5PTiW11O40) behaved as a heterogeneous catalyst in
epoxidation reactions with H2O2 by using ethyl acetate as reaction
media. For the sake of comparison, we also examine the influence
of organic countercations on catalytic activity.
Fig. 1 31P NMR spectra of the catalysts: (a) fresh [C12mim]5PTi-
W
11O40
(c) [C12mim]5PTiW11O40 treated with 500-fold H2O2; (d) recovered
[C12mim]5PTiW11O40
; (b) [C12mim]5PTiW11O40 treated with 50-fold H2O2;
.
(3H, t); 1.164 (18H, m); 1.818 (2H, m); 3.868 (3H, s); 4.196
(2H, t); 7.489 (1H, s); 7.498 (1H, s); 8.919 (1H, s).
The Na7PW11O39 was prepared according to the method
reported by Brevard et al.28 The preparation of Q5PTi-
W11O40(Q = C12mim, CTA, TBA) was similar to the procedure
reported by Kholdeeva et al.29 Briefly, Ti(SO4)2 (0.169 g,
0.7 mmol; 1 M solution in 2 M H2SO4) was added to an
aqueous solution (2 mL) of Na7PW11O39 (2 g, 0.7 mmol).
After the pH of the resulting solution was adjusted to 5.5 by
adding small aliquots of NaHCO3, the mixed solution was
stirred at room temperature for another 12 h. The catalyst was
then precipitated by adding [C12mim]Br (1.15 g, 3.5 mmol).
The white solids were collected, washed with distilled water
several times and then dried under the vacuum. The white
powder was obtained as [C12mim]5PTiW11O40. Anal. calcd for
C80H155N10PTiW11O40: C, 24.03; H, 3.91; N, 3.50; Ti, 1.20; W,
50.58%. Found: C, 23.44; H, 3.38; N, 3.40; Ti, 1.38; W, 55.3%.
31P NMR (161.9 MHz; CD3CN): d = À13.97 (Fig. 1a).
[CTA]5PTiW11O40 was prepared by the same procedure
with cetyltrimethyl-ammonium bromide (CTAB) as the
precipitant and obtained as a white powder. Anal. Calcd for
C95H210N5PTiW11O40: C, 27.40; H, 5.08; N, 1.68; Ti, 1.15; W,
48.57%. Found: C, 26.89; H, 4.85; N, 1.64; Ti, 1.44; W,
50.6%. [TBA]5PTiW11O40 was prepared with tetrabutyl-
ammonium bromide (TBAB) as the precipitant and obtained
as a white powder. Anal. calcd for C80H180N5PTiW11O40: C,
24.30; H, 4.59; N, 1.77; Ti, 1.21; W, 51.15%. Found: C, 22.56;
H, 4.29; N, 1.63; Ti, 1.45; W, 50.8%. 31P NMR (161.9 MHz;
CD3CN): d = À14.11.
2. Experimental
2.1. General remarks
All manipulations involving air-sensitive materials were
carried out using standard Schlenk line techniques under an
atmosphere of nitrogen. All solvents were distilled before use
according to standard methods. The other chemicals were of
analytical grade, commercially available without further
purification, unless otherwise stated. The elemental analysis
of C, H, N was performed on an Elementar Vario EI III
Elementa and ICP-AES analysis of W on a TJA IRIS 1000
instrument, respectively. Scanning electron microscope (SEM)
images were obtained on a JSM-6360LV microscope. BET
surface areas were measured at the temperature of liquid nitrogen
using a NOVA 4200e Analyzer. All NMR spectra were recorded
on a Bruker Avance III 400 instrument (400 MHz for 1H;
161.9 MHz for 31P) using D2O or CD3CN. FT-IR spectra were
recorded at room temperature on a Nicolet Fourier transform
infrared spectrometer (Magna550). UV-vis absorption spectra
were recorded on a UV-3200PC spectrophotometer using a
quartz cell. The products were analyzed by GC equipped with
a HP-5 column with 1-octane as an internal standard and the
conversion of reaction was calculated on the basis of H2O2.
2.2. Preparation of Ti-substituted polyoxometalates
[C12mim]5PTiW11O40, [CTA]5PTiW11O40 and [TBA]5PTiW11O40
2.3. Typical procedure for epoxidation reaction
The 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br)
was synthesized according to the conventional method.27
1-Methyl imidazole (3.25 g, 13 mmol) was allowed to react
with dodecyl bromide (1.07 g, 13 mmol) at 90 1C for 48 h in an
autoclave under a 0.7 MPa N2 atmosphere. After the reaction,
the products were washed with diethyl ether and then dried at
50 1C under vacuum for 1 h. dH (400 MHz; D2O): 0.758
The reaction was carried out in a Schlenk flask equipped with
a reflux condenser and a thermometer. To 2 mL ethyl acetate
was added catalyst [C12mim]5PTiW11O40 (60 mg, 0.015 mmol),
cis-cyclooctene (0.17 g, 1.54 mmol), and 30% H2O2 (0.085 g,
0.75 mmol). The reaction mixture was stirred at 60 1C for
4 h. Then the reaction mixture was cooled down to 0 1C,
the catalyst was then precipitated and separated. After being
c
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washed with cold ethyl acetate two times and dried at 50 1C for
2 h under reduced pressure, the catalyst was then used for the
next catalytic recycle.
3. Results and discussion
3.1. Catalyst characterization
The starting material Na7PW11O39 was characterized with
31P NMR, and the chemical shift was found at À10.7 ppm,
which was in line with what reported by Wang et al.30 The
single 31P NMR resonance at À14.11 for the fresh catalyst
[C12mim]5PTiW11O40 (Fig. 1a) indicated that there only
existed the structure of [PTiW11O40]5À 31
Fig. 2a, IR spectra of the fresh catalyst [C12mim]5PTiW11O40
exhibited characteristic peaks at 1089 cmÀ1 and 1064 cmÀ1
961 cmÀ1, 889 cmÀ1, 804 cmÀ1, 704 cmÀ1 and 592 cmÀ1, which
were identical with that of the Keggin-type [PTiW11O40]5À
anion reported previously.29 All these characterization demon-
strated definitely the structure of as-synthesized Ti-substituted
polyoxometalates.
.
As shown in
Fig. 3 Time profile of epoxidation of cis-cyclooctene catalyzed with
different catalysts: [C12mim]5PTiW11O40 (squares); [CTA]5PTiW11O40
(circles); [TBA]5PTiW11O40 (triangles). Reaction conditions:
0.015 mmol catalyst, 1.54 mmol cis-cyclooctene, 0.75 mmol H2O2,
2 mL ethyl acetate, reaction temperature 50 1C. Conversion = the
amount of cis-cyclooctene converted (moles)/initial H2O2 (moles) Â
100%. The selectivity to cis-cyclooctene oxide was always over 99%.
,
3.2. Catalytic performance
3.2.1 Influence of the organic countercation. It has been
shown that the organic countercation had great effects on
the catalytic activities of POM anions in the homogeneous
epoxidation reaction.32,33 In the present work, a [PTiW11O40]5À
anion, combined with three different countercations, was
utilized to catalyze olefins to epoxides with H2O2 in ethyl
acetate under mild conditions. As shown in Fig. 3, the
Ti-substituted POM anions combined with a [C12mim]+ cation
showed the highest catalytic activity among three POM catalysts,
while the POM catalyst with a CTA countercation gave moderate
activity and the POM catalyst with a TBA countercation gave
lowest activity. In addition, it was found that [C12mim]Br,
CTAB and TBAB themselves afforded very poor activity for
the epoxidation reaction under same reaction conditions.
Although the exact mechanism why the countercations in
POM affected the catalytic reaction was not quite clear, we
believed that the length and structure of the alkyl chains of the
countercations played a very crucial role in the catalytic
performance. It was understandable that the longer alkyl
chains led to the higher catalytic activities, because the catalyst
Fig. 4 The SEM images of the fresh catalysts: (a) [CTA]5PTiW11O40
and (b) [C12mim]5PTiW11O40
.
with longer alkyl chains has stronger interaction with the
hydrophobic substrates by van der Waals force, which was
favorable to the adsorption and reaction of the substrates.34
Furthermore, from the SEM images of [CTA]5PTiW11O40 and
[C12mim]5PTiW11O40 shown in Fig. 4a and b, respectively, we
can see the slight differences in the surface morphology of two
catalysts, which resulted from the difference in the structure of
organic countercations between two catalysts. It was found
that the particles of the [CTA]5PTiW11O40 catalyst showed
more compact arrangement than those of [C12mim]5PTi-
W11O40, which implied that the latter is more accessible to
the substrates. Meanwhile, it was found that the BET surface
area of [C12mim]5PTiW11O40 (26.2 m2 gÀ1) was higher than
that of [CTA]5PTiW11O40 (5.7 m2 À1), which was well in
g
agreement with characterization by SEM. As a result, the
catalytic activity of [C12mim]5PTiW11O40 for the epoxidation
of cis-cyclooctene was higher than that of [CTA]5PTiW11O40,
despite the same anions for both of the catalysts. On the basis
of the results above, the following investigation was mainly
focused on the properties of [C12mim]5PTiW11O40 due to its
higher catalytic activity.
3.2.2 Reaction in different media: heterogeneous or
homogeneous?. It was worthy of notice that the fresh [C12mim]5-
PTiW11O40 catalyst was white powder; when the catalyst was
treated with H2O2, it became orange, which might be due to
Fig. 2 FT-IR spectra of the catalysts: (a) fresh [C12mim]5PTiW11O40
(b) [C12mim]5PTiW11O40 treated with 50-fold H2O2; (c) recovered
[C12mim]5PTiW11O40
;
.
c
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Fig. 5 Epoxidation of cis-cyclooctene with H2O2 catalyzed by
[C12mim]5PTiW11O40 in ethyl acetate at 60 1C. The selectivity to
cis-cyclooctene oxide was always over 99%.
Fig. 7 UV-vis spectra of (a) fresh catalyst [C12mim]5PTiW11O40
;
(b) after [C12mim]5PTiW11O40 treated with H2O2 in ethyl acetate at
60 1C; (c) After reaction, the [C12mim]5PTiW11O40 catalyst was
separated from ethyl acetate. (Acetonitrile was used as solvent for
(a), (b), (c) at 20 1C.)
the formation of Z2-peroxo active species at the catalyst.24,35 It
was observed that both of the fresh and treated catalysts
were quite well dispersed in ethyl acetate, but precipitated
completely at the bottom of the flask after the stirring was
stopped and then the reaction mixture stood still for 5 min.
According to the above observation, there soon came the idea
that whether the present catalytic reaction went through a
heterogeneous way or not. Thus, the fast hot filtration at the
reaction temperature was employed to examine the filtrate for
activity.17 As shown in Fig. 5, no further cis-cyclooctene was
converted to the corresponding epoxide in the filtrate after the
catalysts were removed, which proved unambiguously that the
catalytically active species was not present in the homogeneous
filtrate, and that the reaction occurred on the catalyst surface
rather than in solution. Indeed, the elemental analysis showed
that only about 10 ppm of W was leached after reaction under
the conditions used in this work. Even if very small amounts of
titanium or W species are leached from the solid matrix during
the oxidation process, the observed catalytic activity is not due
to these species. This result proved definitely that the catalytic
reaction proceeded by a heterogeneous mechanism.
why the heterogeneous catalyst in ethyl acetate exhibited much
higher catalytic activity than the homogeneous analogues in
acetonitrile is not clear, we suggested that the difference in solvent
acidity might affect the activation of side-on TiOO peroxo species
by hydrogen bonds, which has been indicated previously.25
To gain insight into the formation of a reactive intermediate
during the reaction, the fresh catalyst ([C12mim]5PTiW11O40)
(Fig. 7a) was treated with H2O2, and the resulting orange
powder was filtered out and further characterized by FT-IR,
UV-vis and 31P NMR spectroscopy. As shown in Fig. 2b, the
characteristic peaks at 714 cmÀ1 and 620 cmÀ1 of IR spectra
can be attributed to the symmetric and asymmetric Ti-peroxide
stretches.36 Also, the absorption with maxima around 400 nm
of the UV-vis spectra (Fig. 7b) can be attributed to the peroxo
species O2 - Ti ligand-to-metal charge-transfer band.36
The orange powder was further characterized by 31P NMR
spectroscopy. It was demonstrated that the formation of the
peroxo structure resulted in the chemical shift toward down-
field from À13.98 ppm to À13.70 ppm (Fig. 1a and b).37 In
addition, there were no other peaks in the range of +7 to
À22 ppm in 31P NMR, which indicated that no products
derived from degradation of the Keggin structure are detectable
after being treated with aqueous H2O2 in the present catalytic
system. According to our previous research,26 the lacunary-type
phosphotungstate [n-C16H33N(CH3)3]4Na3[PW11O39] was rapidly
degraded into the catalytically active Venturello complex
[PO4{W(O)(O2)2}4]3À in the presence of H2O2, while Keggin-
type phosphotungstate [n-C16H33N(CH3)3]3[PW12O40] gave a
much slower degradation rate, thus leading to lower activity.
To examine the possibility for degradation of [C12mim]5PTi-
W11O40 with H2O2 in an aqueous phase, the fresh catalyst was
mixed with 500-fold excess of 30% H2O2 and then continuously
stirred at 60 1C for 4 h. Then the mixture was filtered and the
amount of W leached in the filtrate was confirmed to be
negligible by ICP-AES. This is also in agreement with the
previous report, which indicated that Ti-substituted poly-
oxometalate is normally thermodynamically stable to oxidation
and hydrolysis.38 It was also confirmed by the 31P NMR spectra
(Fig. 1b and c) that the Keggin structure was maintained even
Different reaction media have also been screened for the
epoxidation reaction. It is surprising that [C12mim]5PTiW11O40
displayed low epoxidation activity in acetonitrile, even the pre-
sent catalytic system was homogeneous during the whole of the
reaction period, as shown in Fig. 6. Although the exact reason
Fig. 6 The epoxidation of cis-cyclooctene over catalyst [C12mim]5P-
TiW11O40 in different reaction media. Reaction conditions: 0.015 mmol
catalyst, 1.54 mmol cis-cyclooctene, 0.75 mmol H2O2, 2 mL acetonitrile
or ethyl acetate, reaction temperature 60 1C.
c
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when treated with 500-fold excess of 30% H2O2. As a result,
the degraded peroxotungstate species which is normally
regarded as active species is absent in the present catalytic
system. Thus we deduced that the Ti-hydroperoxo (TiIV–OOH) or
the Ti-peroxo (TiIV–OO) intermediate is the actual active
center in the present system.
plotted, respectively. It was found that the reaction rate of the
recovered catalyst was much faster than the fresh one and the
induction period observed in the first run can be hardly
observed in the second run, which proved further that the
peroxo form of the Ti-substituted polyoxometalate existing in
the recovered catalyst is the actual active site for epoxidation.
The stability of active Ti-based species has been examined
by various methods during the reaction. To our surprise, it
was found that the peroxo species is still present even though
the epoxidation reaction was complete. It could be seen from
the FT-IR spectra that the recovered catalyst after the eighth
3.2.3 The generality and reusability of the catalyst. The
scope of the substrates was also investigated, in which the
cycloalkenes, long-chain alkenes, styrene and allylic alcohols
were chosen as substrates. As shown in Table 1, in the
[C12mim]5PTiW11O40/H2O2/ethyl acetate catalytic system, excellent
conversion and selectivity were obtained for epoxidation of
cis-cyclooctene (entry 1, Table 1), and a moderate conversion
for epoxidation of cyclohexene, styrene and (R)-(+)-limonene
(entries 3–5, Table 1). The catalytic system can also be adopted
for the epoxidation of allylic alcohols and excellent conversion
can be obtained (entries 6 and 7, Table 1). However, the
present POM catalyst can hardly convert 1-octene to the
corresponding epoxide.
run (Fig. 2a and c, respectively) showed a peak at 714 cmÀ1
,
which was assigned to adsorption of the peroxo structure
(Ti–OO). Besides, both the catalyst treated with H2O2 and
the recycled catalyst showed UV-vis adsorption around
400 nm, which resulted from the peroxo structure (Fig. 7b
and c). Similarly, the 31P NMR spectra of the recovered
catalyst also indicated the presence of the peroxo structure
(Fig. 1d). As a result, it can be drawn that the peroxo structure
in the Ti-substituted polyoxometalate was quite stable during
the whole course of reaction.
The recyclability of the catalyst was also examined. It was
obvious that the catalyst could be employed at least eight
times without decreasing the catalytic activity in the epoxidation
of cis-cyclooctene (entries 1 and 2, Table 1). The amount of
leaching of W detected by ICP-AES was only about 10 ppm
after the reaction, in combination with previous filtration
experiments, which confirmed further that the present
Ti-substituted polyoxometalate was a heterogeneous catalyst
in the epoxidation reaction.
Interestingly, the presence of the Ti-based peroxo structure
has a considerable impact on the reaction rate. As shown in
Fig. 8, the time dependences of the cis-cyclooctene oxidation
with the fresh catalyst and the recovered catalyst by H2O2 were
4. Conclusion
In summary, a Ti-substituted polyoxometalate ([C12mim]5P-
TiW11O40) has been utilized as catalyst for epoxidation of
olefins and the heterogeneous nature of catalysis in ethyl
acetate media was confirmed by a hot catalyst filtration test.
The organic countercations of the POM catalysts affected the
catalytic activity significantly. In the epoxidation reaction, the
Ti-based peroxo structure was believed to be the active species,
which was quite stable and maintained the peroxo structure
even after the reaction, thus enhancing the rate of the catalytic
reaction in the following run. The catalytic system can convert
different kinds of olefins to the corresponding epoxides. The
heterogeneous catalyst was easily separated and recycled eight
times without decreasing remarkably the catalytic activity.
Fig. 8 Time profile of epoxidation of cis-cyclooctene catalyzed
by [C12mim]5PTiW11O40. Reaction conditions: 0.015 mmol catalyst,
1.54 mmol cis-cyclooctene, 0.75 mmol H2O2, 2 mL ethyl acetate,
reaction temperature 50 1C. The selectivity to cis-cyclooctene oxide
was always over 99%.
a
Table 1 The epoxidation of various substrates over catalyst [C12mim]5PTiW11O40
Entry
Substrates
Reaction time/h
Conversion/%
Selectivity/%
1
cis-Cyclooctene
cis-Cyclooctene
Cyclohexenec
4
4
6
6
20
3
Z 99
Z 99
79.7
45.2
79.5
Z 99
Z 99
Z 99
Z 99
89.4
43.4
60
2b
3
4
5
6
7
Styrened
(R)-(+)-Limonenee
3-Methyl-2-buten-1-ol
Geraniolf
Z 99
93.1
2
a
0.015 mmol catalyst, 1.54 mmol cis-cyclooctene, 0.75 mmol H2O2, 2 mL ethyl acetate, reaction temperature 60 1C. Conversion of olefins = the
b
c
amount of olefins converted (moles)/initial H2O2 (moles) Â 100%. The eighth catalytic recycle. The by-products were 2-cyclohexene-1-ol and
d
2-cyclohexene-1-one. Benzyl aldehyde and benzoic acid as main by-products. Selectivity to cis-limonene oxide, the other product is
e
f
7-oxabicyclo[4.1.0]heptane. Selectivity to 2,3-epoxy alcohol.
c
1840 New J. Chem., 2011, 35, 1836–1841
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J. A. Mayoral, B. Coq and A. Galarneau, Green Chem., 2009,
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Acknowledgements
The authors are grateful for the support from the National
Natural Science Foundation of China (No. 20773037, No.
21073058), and Research Fund for the Doctoral Program of
Higher Education of China (20100074110014). The authors
would also like to express their thanks to Prof. Walter Leitner
for helpful suggestion and Dr Nils Theyssen for assistance.
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