Peroxometalates immobilized on magnetically recoverable catalysts for epoxidation

Article abstract of DOI:10.1002/cplu.201200246

Magnetically separable catalysts were prepared and employed for the epoxidation of olefins with hydrogen peroxide. In all cases the magnetic core was firstly covered with a silica layer to prevent iron ion-initiated decomposition of hydrogen peroxide. The catalytic active species, an ionic liquid-type peroxotungstate, was then immobilized either by hydrogen bonding (catalyst 1) or by covalent SiO linkage (catalyst 2). In addition to a thorough characterization by FT-IR, XRD, NMR, DRIFT, XPS, and TEM, the catalytic potential was evaluated in the epoxidation of a variety of olefins as well as allylic alcohols. Both catalysts showed essentially a constant activity after at least ten consecutive cycles. On the basis of the research above, a new type of magnetically separable catalyst was constructed by immobilization of lacunary-type phosphotungstate by hydrogen bonding between the sulfonate anion and silanol group on the surface of the core-shell magnetic nanoparticles. After the detailed characterization, the catalyst was used in the epoxidation of a variety of olefins and allylic alcohols and was found to possess high activity, selectivity towards epoxides, and a constant activity after at least ten catalytic recycles without solvent.

Full text of DOI:10.1002/cplu.201200246

DOI: 10.1002/cplu.201200246
Peroxometalates Immobilized on Magnetically
Recoverable Catalysts for Epoxidation
[a, b]
[a]
[a]
[b]
[b, c]
[a]
Yunxiang Qiao,
Huan Li, Li Hua, Lars Orzechowski, Kai Yan,
B[ao] Feng,
[a]
[b]
[b, c]
Zhenyan Pan, Nils Theyssen, Walter Leitner,
and Zhenshan Hou*
Magnetically separable catalysts were prepared and employed
for the epoxidation of olefins with hydrogen peroxide. In all
cases the magnetic core was firstly covered with a silica layer
to prevent iron ion-initiated decomposition of hydrogen perox-
ide. The catalytic active species, an ionic liquid-type peroxo-
tungstate, was then immobilized either by hydrogen bonding
consecutive cycles. On the basis of the research above, a new
type of magnetically separable catalyst was constructed by im-
mobilization of lacunary-type phosphotungstate by hydrogen
bonding between the sulfonate anion and silanol group on
the surface of the core–shell magnetic nanoparticles. After the
detailed characterization, the catalyst was used in the epoxida-
tion of a variety of olefins and allylic alcohols and was found
to possess high activity, selectivity towards epoxides, and
a constant activity after at least ten catalytic recycles without
solvent.
(catalyst 1) or by covalent SiÀO linkage (catalyst 2). In addition
to a thorough characterization by FT-IR, XRD, NMR, DRIFT, XPS,
and TEM, the catalytic potential was evaluated in the epoxida-
tion of a variety of olefins as well as allylic alcohols. Both cata-
lysts showed essentially a constant activity after at least ten
Introduction
Green chemistry has become an attractive field of research in
the 21st century. Ionic liquids (ILs) as novel solvents play an im-
netic force and reused several times with essentially no loss of
activity. In 2005, Mizuno and co-workers were the first to im-
mobilized peroxometalate-anion-based IL-type catalysts on the
[
1]
portant role in this modern field of research. They were dem-
onstrated as potential replacements for organic solvents in
many chemical reactions. However, owing to the highly com-
plex and hence very costly synthesis of many ILs, demanding
normally more than 20 synthesis steps for their preparation,
approaches in which the amount of IL needed are dramatically
[3e]
surface of SiO through covalent bonding. It was observed
2
that (365Æ18) mmol of C8-IL fragments per gram of catalyst
2
((0.85Æ0.04) IL fragments per nm ) existed and 49% of silanol
groups were allowed to react to form a covalent Si-O-Si link-
age, where the loading amount of active peroxotungstate
anion was (105Æ5) mmol per gram. Although many similar cat-
[
2]
lowered are of special interest. Supported IL phases, which
are much easier to separate, fulfill these demands and have
[5e,g]
alytic systems have been subsequently reported,
the disad-
[
3]
found numerous applications in catalytic design.
vantage resulting from low IL loading through covalent linkage
cannot be ignored. As a result, the approach of IL immobiliza-
tion which allows much easier tuning of the necessary IL
amount for a given transformation is highly desirable.
Likewise, magnetic nanoparticles (MNPs) have attracted
growing interest and are nowadays considered a new type of
catalyst support owing to their good stability, easy synthesis
and functionalization, high surface area, and facile separation
procedure by magnetic forces. The technique of magnetic sep-
aration has obvious advantages over the conventional separa-
tion methods which involve thermal, mechanical, or chromato-
graphic methods. Recently, MNPs have been successfully used
to immobilize enzymes, transition metal catalysts, and organo-
The catalytic epoxidation of olefins with hydrogen peroxide
as an oxidant constitutes an important research area and rep-
[
a] Y. Qiao, Dr. H. Li, L. Hua, Dr. B. Feng, Z. Pan, Prof. Z. Hou
Key Laboratory for Advanced Materials
Research Institute of Industrial Catalysis
East China University of Science and Technology
[
4]
catalysts. It was demonstrated that the MNP supported cata-
lysts fulfill demands concerning activity and selectivity in a re-
markable manner. Their unique separation procedure by an ex-
ternal permanent magnet allows a most easy recovery without
a significant loss of catalyst material if its dissolution is avoid-
ed. However, there are only a few studies published describing
1
30 Meilong Road, Shanghai 200237 (P. R. China)
Fax: (+86)21-64253372
E-mail: houzhenshan@ecust.edu.cn
[
b] Y. Qiao, Dr. L. Orzechowski, Dr. K. Yan, Dr. N. Theyssen, Prof. W. Leitner
Max-Planck-Institut fꢀr Kohlenforschung
Kaiser-Wilhelm-Platz 1, 45470 Mꢀlheim an der Ruhr (Germany)
[
3a,5]
[
c] Dr. K. Yan, Prof. W. Leitner
a combination of supported IL phase and MNPs.
For exam-
Institut fꢀr Technische und Makromolekulare Chemie
Lehrstuhl fꢀr Technische Chemie und Petrolchemie
RWTH Aachen, Worringerweg 1, 52064 Aachen (Germany)
ple, the MNP-supported IL catalysts immobilized by covalent
bonds have been used in oxidation, hydrogention, and con-
densation reactions as well as CO2 cycloaddition reac-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201200246.
[
3a,5e–g]
tions.
The catalysts could be easily recycled using a mag-
1128
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ChemPlusChem 2012, 77, 1128 – 1138

Catalysts for Epoxidation
resents the core of a variety of
chemical processes for produc-
ing bulk and fine chemicals
without creating substantial pol-
lution. But the difficult separa-
tion and successive leaching of
homogeneous catalysts during
epoxidation seriously impeded
industrial application. In our
continuing efforts towards ho-
[
6]
mogeneous
epoxidation,
herein we design and prepare
MNPs-supported IL-type peroxo-
metalate catalysts, and use
them for the epoxidation of al-
kenes. We expect that the de-
signed catalysts can combine
the advantages of highly active
homogeneous catalysts and
easy separation of MNPs. Be-
cause epoxidation reactions
using hydrogen peroxide as an
oxygen source are sensitive to-
wards iron centers in terms of
unproductive H O2 decomposi-
2
tion and leaching, an impermea-
ble dense silica layer was coated
on the ferrite-based MNP cores.
Such shielding has been rarely
reported for epoxidation cata-
[
7]
lysts.
Scheme 1. Illustration of the catalyst systems.
Metal–oxygen clusters, for ex-
ample, peroxometalates have at-
tracted much attention and
[6,8]
been widely used as active species in oxidation catalysis.
In
On the other hand, inspired by the studies of Horvath and
[10]
previous studies, IL-type structures with the combination of
imidazolium cations and polyoxometalate anions have been
employed as thermoregulated catalysts allowing easy phase-
Bianchini, there definitely exists hydrogen-bonding interac-
À
tions between the silanol groups of the support and the SO3
groups, where water acted as an immobilization agent for the
hydrogen bond. We continued to design and prepare another
new type of magnetically recoverable IL-type active species im-
mobilized on MNPs by strong hydrogen-bonding interaction,
and also used it for the epoxidation of alkenes and allylic alco-
[
6,9]
separation and catalyst recovery.
During the reaction at ele-
vated temperatures, such catalysts are well dissolved in the re-
action medium, while they self-separate after the reaction in
an own phase when the systems reach room temperature
again. Although excellent activity and selectivity were obtained
by this approach, the recycling of catalysts is often still a prob-
lem as its unwanted leaching in the product mixture phase
lowers the catalytic performance after several runs. Therefore,
more effective immobilization approaches are desired.
Herein, we report the preparation of two different magneti-
cally separable catalysts which are employed for the epoxida-
tion of olefins with hydrogen peroxide. In the first case, the
catalytically active IL-type peroxotungstate is expected to be
immobilized by hydrogen bonds (catalyst 1 in Scheme 1). In
contrast, the immobilization in catalyst 2 (Scheme 1) is be-
lieved to be realized by covalent bonds. Both catalysts have
been tested to perform the epoxidation of olefins, whereby
the immobilization by hydrogen bonds allows higher IL load-
ings.
7
À
hols. The lacunary-type PW O
39
anion was chosen as the
11
[11]
active species owing to its high activity for epoxidation. The
as-synthesized materials were characterized by NMR, FT-IR,
DRIFT, MS, elemental analysis, and TEM.
Results and Discussion
We first prepared the magnetic Fe O cores, which were then
3
4
coated with a dense SiO layer. This material was treated with
2
À
an imidazolium-based IL, for which the initial PF6 anion was
exchanged with a catalytically active peroxotungstate anion.
The immobilization of the catalytically active IL was achieved
by both hydrogen bonding (catalyst 1) and covalent linkage
(catalyst 2).
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Z. Hou et al.
For obtaining catalyst 2, the silica-coated magnetite nano-
the high condensation of silanol groups under H2 reducing
conditions (Figure S1a vs. S1b), and all six materials exhibited
nearly the same reflections, which revealed that the Fe O core
particles were first treated with [SDMIM]PF in toluene at reflux
6
to afford a covalent linkage between the two reactants. After
3
4
+
anion exchange, catalyst 2 was then obtained with a [SDMIM]
in the MNP behave in a very stable manner. The asterisks can
be indexed to the face-centered cubic phase of Fe O , which is
À1
2À
loading of 160 mmolg
and
a
[W O ]
loading of
2
11
3
4
À1
4
4.1 mmolg (Scheme 1). These loadings are close to that re-
in agreement with the reported JCPDS card no. 19-0629.
Figure 2a,b shows transmission electron microscopy (TEM)
images of the synthesized Fe O /SiO MNPs before and after
[
3a,e]
ported in the literature.
Owing to the low IL loading obtained and the incomplete
anion exchange, relatively large amounts of catalyst needed to
be used in the reactions. Therefore the question arises of how
an increase in loading of the active species can be achieved.
Thus we attempted to prepare a catalyst in which the immobi-
lization of the active species is realized through hydrogen
bonds between the terminal SiÀOH groups of the silica layer
and silanol functionalities in the cationic imidazolium chain.
And indeed the preparation of MNP-[HDMIM] [W O ] (cata-
3
4
2
reduction. Clear core–shell architectures can be observed as
2
2
11
+
lyst 1) resulted in an increased [HDMIM]
loading of
À1
2À
À1
3
22.7 mmolg and a [W O ] loading of 156.8 mmolg if
2
11
20 wt% of the IL was applied (Scheme 1).
Figure 1a–c shows the FT-IR spectra of the as-prepared
À1
MNPs. The presence of additional bands centered at 804 cm ,
À1
À1
9
58 cm , and around 1047–1248 cm (broad band) all corre-
Figure 1. The FT-IR spectra of (a) reduced Fe
c) catalyst 2, (d) PW11, (e) DSPIM-PW11, (f) freshly prepared catalyst 3, (g) cata-
lyst 3 after ten consecutive cycles in the condition of no solvent, (h) cata-
lyst 3 after seven consecutive cycles with CH OH as reaction solvent.
3 4 2
O /SiO MNP, (b) catalyst 1,
(
3
Figure 2. TEM images of (a) Fe
SiO MNPs after reduction, (c) hydrogen-bonding catalyst MNP-[HDMIM]
[W O ] (1) before reaction, (d) 1 after ten consecutive runs, (e) covalently
3 4 2 3 4
O /SiO MNPs before reduction, (b) Fe O /
2
2
-
spond to the symmetric and asymmetric stretching vibration
2
11
of the silica framework including terminal SiO groups. Band at
2 2
linked catalyst MNP-[SDMIM] [W O11] (2) before reaction, (f) 2 after ten con-
secutive runs, (g) EDX of a2 in (d), (h) EDX of a4 in (f). Insets of (g) and (h)
are enlarged EDX images for W between 8–10 eV).
À1
1
3
610 cm
and the broad band at approximately
À1
400 cm correspond to water molecules. Furthermore, the
À1
bands at 1446, 2854, and 2927 cm are attributed to CÀH
À1
stretching absorptions, and the band at 1562 cm CÀC ab-
a result of a sufficient intensity contrast between the Fe O
3
4
sorption, which arisen from the IL part of the magnetic cata-
lysts. As seen in Figure 1a–c, the CÀH stretching bands in
MNP-[HDMIM] [W O ] (catalyst 1) are much stronger than
cores and the silica shells based on the electron density differ-
ence. The presence of this composite is also supported by
energy-dispersive X-ray spectrometry (EDX) because neither
bare Fe O nor core-free silica NPs can be seen in these sam-
2
2
11
those of MNP-[SDMIM] [W O ](catalyst 2), and is most likely
2
2
11
3
4
the result of a higher IL loading in the first case. Overall, the
FT-IR spectra provide supportive evidence for the Fe O /SiO
2
ples. The TEM images reveal that most of the Fe O MNPs are
3 4
quasispherical with an average diameter of 13 nm, surrounded
by a silica shell with a thickness of around 10 nm. The MNPs
with well-defined core–shell structures are clearly observed,
even though silica shells had trapped more than one magnetic
core in most cases. The principal idea for the formation of the
outer silica shell is to avoid corrosion of Fe O MNPs and un-
3
4
MNP structure and the successful grafting of the functionalized
ILs onto the Fe O /SiO MNP surface.
3
4
2
The XRD patterns of the Fe O /SiO MNPs before and after
3
4
2
reduction, catalysts 1 and 2 before reaction as well as after ten
runs are shown in Figure S1a–f in the Supporting Information.
3
4
We observed that SiO peaks became smaller likely owing to
productive H O2 conversion at the iron centers. Figure 2e,f
2
2
1130
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ChemPlusChem 2012, 77, 1128 – 1138

Catalysts for Epoxidation
shows TEM images of catalyst 2 before reaction and after ten
cycles. Likewise, images of catalyst 1 are depicted in Fig-
ure 2c,d. Importantly, the catalysts show no qualitative differ-
ence in their morphologies after recycling (TEM images with
the large scale bar (200 nm) for Figure 2a–c,e are shown in Fig-
ure S2).
as well as the coating layer of functionalized IL for catalysts 1
and 2. In addition, the MNPs mainly showed super-paramag-
netic behaviors, thus indicating that MNPs still undergo strong
magnetization in the composite particles. This behavior is ideal
for application in catalysis as it allowed an efficient magnetic
separation on one hand and a rapid redispersion of these par-
ticles if the applied magnetic field was removed on the other.
The diffuse reflectance infrared Fourier transform spectrosco-
py (DRIFTS) is a powerful surface sensitive technique. Here it
was used to obtain spectroscopic information in the OH
stretching region and evaluate the effect of [HDMIM] [W O ]
The components of the two functionalized catalysts 1 and 2
after the tenth recycle were assayed by EDX and elemental
mapping analysis. The presence of Si, O, and Fe in Figure 2g,h
confirm the presence of multiple layers of SiO on the surface
2
of the Fe O MNPs. The signal of Cu is from the Cu grid. The
3
4
2
2
11
characteristic peaks for element W are 8.4 and 9.6 keV, originat-
ing from modified MNPs (Figure 2d,f), thus indicating that the
active species for the functionalized ILs were immobilized suc-
cessfully on the surface of the Fe O /SiO MNPs. The peaks
addition on the silica support. Because DRIFTS cannot be ap-
plied easily for dark-colored materials owing to strong absorp-
tion, uniform SiO NPs were synthesized to replace the mag-
2
[13]
netite containing counterparts, which were also performed
with the same procedures as made during the preparation of
3
4
2
were not so obvious mainly owing to the low W content in
the whole MNPs.
catalyst 1. Consequently, the SiO NPs was coated by silica to
2
Figure 3 shows the XPS spectra of W from the prepared
K W O , the two fresh catalysts 1 and 2 as well as from the
produce silica-coated SiO , then it was further reduced at high
2
temperature (3008C) to obtain SiO /SiO NPs, followed by treat-
2
2
11
2
2
used catalyst 1 after three runs. The spectra of the catalysts
ing with [HDMIM] [W O ] to afford SiO /SiO -[HDMIM] [W O ].
2 2 11 2 2 2 2 11
DRIFT spectra of the SiO /SiO2 NPs and SiO /SiO -[HDMIM] -
2
2
2
2
[
W O ] at different pre-treatment temperatures (508C, 1008C,
2 11
and 1508C) are presented in Figure 4. Changes in the OH-
stretching region by the co-presence of [HDMIM] [W O ] can
2
2
11
be clearly revealed: the relative intensity of the bands centered
À1
at 3738 cm , which corresponds to isolated silanol groups, is
significantly decreased in material SiO /SiO -[HDMIM] [W O ].
2
2
2
2
11
Figure 3. XPS spectra of W in (a) K
2 2
W O11, (b) catalyst 2, (c) catalyst 1, and (d)
catalyst 1 after three consecutive runs.
contain the characteristic peaks for C 1s, O 1s, and Si 2p at 285,
33, and 104 eV, respectively (not shown). In addition, a signal
5
at 167.8 eV, corresponding to Fe 2p, was detected weakly
owing to the dense silica shell as well as the IL coating. The
only difference between the samples are shifts in the position
VI
VI
of the W signal: Whereas the peaks of W 4f and W 4f
5/2
7/2
were located at 36.7 and 38.8 eV for K W O , both catalysts 1
2
2
11
and 2 showed similar peaks at 35.2 and 37.4 eV, although the
peaks were rather weak because of the low W content in the
whole MNPs. This observation is comparable with those report-
[
12]
ed for polyoxometalate tungsten-containing ions. Consisten-
cy in the XPS spectra of catalyst 1 before reaction and after
three runs further confirmed the stability of the active species.
The magnetic property of Fe O /SiO MNPs, catalysts 1 and 2
3
4
2
were studied by a vibrating-sample magnetometer. As shown
in Figure S3, the saturation magnetization (Ms) of Fe O /SiO
2
3
4
À1
MNPs reached 26.10 emug , catalyst 2 reached 23.40 and cat-
À1
alyst 1 reached 8.5 emug . The relatively low Ms values were
Figure 4. DRIFT spectra in the OH vibration region of SiO
2 2
/SiO NPs (top),
less than the reference value for the pure MNPs (Fe O ), which
3
4
SiO /SiO -[HDMIM] [W 11] (middle) and SiO /SiO -(DSPIM-PW11) (bottom) de-
2
2
2
2
O
2
2
can be explained by considering the diamagnetic contribution
of the silica shells surrounding the MNPs for all three materials,
gassed at different pretreatment temperatures: (a) 508C, (b) 1008C,
(c) 1508C.
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1131

Z. Hou et al.
Simultaneously, the relative intensity of the broad band
and the catalytic activities in alcohols were superior to those
obtained in water or EtOAc. Interestingly, a solvent mixture of
methanol and water (volume ratio 10:1) was proven to be suit-
able again. Overall, the data in Table 2 showed that a significant
solvent effect on the performance of the peroxometalate cata-
À1
around 3681 cm increases owing to the formation of hydro-
gen-bonding between the support and the active species, and
is attributed to the OH vibration of hydrogen-bonded hydroxy
[
14]
29
groups.
Moreover, Si CP/MAS (cross-polarization magic
[6a,17]
angle spinning) NMR spectra showed no significant changes of
Q3 components during the preparation of SiO /SiO -[HDMIM] -
lyst could be identified.
2
2
2
[
W O ] (Figure S4). Therefore, the covalent linkage between IL-
2 11
type peroxotungstate and surface silanol is highly impossible.
Both observations argued for an immobilization of [HDMIM]2-
Table 2. Epoxidation of cyclooctene catalyzed by catalyst 1 in different
solvents.
[
a]
[
W O ] on the silica surface by hydrogen bonding.
2 11
Solvent
Conversion [%]
Selectivity [%]
Through our previous study, we found that the direct combi-
CH
CH
3
OH
CH
>99
>99
68.6
59.5
77.0
>99
>99
>99
>99
>99
>99
>99
nation of the magnetite core and the IL resulted in low catalyt-
ic activity due to the decomposition of hydrogen peroxide on
the unprotected Fe O surface. In contrast, SiO -coated mag-
3
2
OH
3
CH COOCH CH
2
3
H
2
O
3
4
2
no solvent
O/CH OH=1:10
volume ratio)
netite in conjunction with the proper ILs showed excellent ac-
tivity. The subsequent reduction by hydrogen is not only favor-
able to form a tight silica shell due to the condensation of sur-
face silanol groups at high temperature but may also prevent
H
2
3
(
2
À
[
3
a] Reaction conditions: cyclooctene (1.5 mmol), catalyst ([W
0 mmol, 2 mol% with respect to cyclooctene), 30% aqueous
2
O
H
11
]
:
2
O
2
[
15]
agglomeration of the MNPs.
(
0.5 mmol), solvent (2 mL), 333 K, 3 h. Conversion and selectivity were de-
termined by GC analysis. Conversion (%)=products (mol)/initial H
mol)ꢁ100.
Catalyst 2 was employed in the epoxidation of cyclooctene
2 2
O
(
using H O (Table 1). Notably, the catalyst could be recycled at
2
2
least seven times without any loss of activity in a mixed sol-
vent of methanol and water, which argues for a successful im-
mobilization of the catalytically active species on the surface of
The recyclability of catalyst 1 was investigated in the epoxi-
[
3a,c,4d,16]
silica by covalent bonds.
Interestingly, if the reaction
dation of cyclooctene using several solvents. As shown in
Table 3, the conversions dropped rapidly even after the first
cycle if methanol or ethanol was used as a reaction medium.
This outcome is in agreement with the observation that
[HDMIM] [W O ] was found to be leaching out considerably
was performed in pure methanol, the epoxide yield dropped
to nearly 90% after the third run—this outcome argues for the
[
17]
importance of the chosen solvent system. This result is also
in agreement with the determination of leaching W in the re-
action solvent: only 11 ppm W was found in mixed solvent
2
2
11
during catalytic recycling: A quantification of the W content by
ICP-AES analysis gave 48 and 152 ppm in methanol and etha-
nol, respectively. Nevertheless, the solubility of [HDMIM]2-
[W O ] in CH OH at room temperature was measured to be
(
CH OH/H O=10:1), but 25 ppm in methanol.
3 2
Similar to catalyst 2, a screening in different solvents was
also performed first with catalyst 1 choosing again cyclooctene
as a model substrate. As shown in Table 2, the selectivities to
cyclooctane epoxide were all found to be higher than 99%
2
11
3
À1
0.90 mmolmL (333 ppm W in CH OH), much higher than that
3
Table 1. Conversions in cyclooctene epoxidations using catalyst 2 in pure
methanol or in a mixture with water.
Table 3. Results from catalyst recycling experiments of 1 in different sol-
vents.
[
a]
[a]
Run
Conversion [%]
CH OH
CH
3
OH
CH
3
2
H
2
O/CH
volume ratio)
:20 1:10
3
OH
(
1
Run
Conversion [%]
1
2
3
4
5
6
7
8
9
10
>99
85.8
72.6
27.0
–
–
>99
64.2
>99
99
95.8
85.2
87.9
77.6
–
–
–
>99
>99
>99
CH
3
OH
H
2
O/CH
3
OH=1:10
(volume ratio)
–
–
–
–
–
–
–
–
1
2
3
4
5
6
7
>99
>99
89.8
90.8
85.6
77.4
–
>99
>99
>99
>99
>99
>99
>99
94.8
93.6
97.8
96.7
>99
>99
>99
–
–
–
–
–
2
À
2À
2 11
O ] :
[
3
(
a] Reaction conditions: cyclooctene (1.5 mmol), catalyst ([W
0 mmol, 2 mol% with respect to cyclooctene), 30% aqueous
2
O
H
11
]
:
[a] Reaction conditions: cyclooctene (1.5 mmol), catalyst ([W
30 mmol, 2 mol% with respect to cyclooctene), 30% aqueous
(0.5 mmol), solvent (2 mL), 333 K, 3 h. Conversion and selectivity were de-
2
O
2
2 2
H O
0.5 mmol), solvent (2 mL), 333 K, 3 h. Conversion and selectivity were de-
termined by GC analysis. Conversion (%)=products (mol)/initial H
mol)ꢁ100. All epoxide selectivities were >99%.
2
O
2
termined by GC analysis. Conversion (%)=products (mol)/initial H
(mol)ꢁ100. Selectivities of all the epoxide products were >99%.
2 2
O
(
1132
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ChemPlusChem 2012, 77, 1128 – 1138

Catalysts for Epoxidation
leached during each reaction, which proved the significance of
the support.
Table 4. Recycling behavior of catalysts derived from 1 in which the cata-
lyst loading ([HDMIM]
in %.
2
[W
2
O
11]) was varied. Conversion values are given
[
a]
Interestingly, in solvent mixtures consisting of methanol and
water, catalytic stability could be improved dramatically. In-
creasing the water content from 1:20 to 1:10, a loss of activity
could not be observed after ten cycles. A possible reason for
such a good leaching resistance might be based upon the sta-
bilization of the hydrogen bonds owing to the water mole-
cules present (Scheme 1) as demonstrated by previous re-
Run
Catalyst loading [wt%]
30
20
15
10
5
1
2
3
4
5
6
7
8
9
>99
>99
>99
>99
>99
>99
98.0
97.1
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
94.2
>99
>99
>99
>99
96.9
87.3
69.8
58.1
–
–
–
–
–
–
–
–
94.8
[
18]
93.6
97.8
96.7
>99
>99
>99
search.
when water is present owing to the negligible solubility of
HDMIM] [W O ] in H O at room temperature. Consistently,
In addition, the catalyst solubility was decreased
–
–
–
–
–
[
2
2
11
2
a W leaching of only 19 ppm could be detected in the mixture
of H O and CH OH (1:10).
85.9
87.1
10
–
2
3
2
À
Furthermore the most effective weight loading of [HDMIM]2-
W O ] was screened in detail. Figure 5 shows the effect of
2 11
[a] Reaction conditions: cyclooctene (1.5 mmol), catalyst ([W O ] :
[
[
30 mmol corresponding to 20 wt% IL loading, 2 mol% with respect to cy-
clooctene), 30% aqueous H (0.5 mmol), solvent (H O/CH OH volume
ratio 1:10, 2 mL), 333 K, 3 h. catalyst loading=“IL” (mg)/total amount of
(mg)ꢁ100. Conversion and selectivity were determined by GC analysis.
2
11
2
O
2
2
3
HDMIM] [W O ] loading on the conversion of cyclooctene ep-
2
2
11
1
2 2
Conversion (%)=products (mol)/initial H O (mol)ꢁ100. The selectivity of
epoxide products was >99%.
catalyst stability in the case of low catalyst loadings. To gain
some insight into the catalyst stability, hot filtration experi-
ments were performed to examine the involvement of dis-
solved catalyst fractions of 1. Here, both the unfiltered and fil-
tered partitions were monitored for continued activity in cyclo-
octene epoxidation. One can conclude from Figure 6 that it is
not very likely that dissolved catalyst fractions dominate the
transformation. Or, if they do have some effect, then they
would deactivate quite fast and the solid catalyst fraction
would function as a continuous reservoir for the active spe-
Figure 5. Cyclooctene conversion as a function of catalyst loading
2À
(
[HDMIM]
responding to 20 wt% IL loading, 2 mol% with respect to cyclooctene), 30%
aqueous H (0.5 mmol), reaction medium=H O/CH OH (volume
ratio=1:10, 2 mL), 333 K, 3 h. Catalyst loading=“IL” (mg)/total amount of
(mg)ꢁ100.
2
[W O11]). Cyclooctene (1.5 mmol), catalyst ([W O ] : 30 mmol cor-
2
2
1
1
2
O
2
2
3
[19]
cies.
1
oxidation, which argues for a first order dependence. Under
given reaction conditions, a loading of 10 wt% is sufficient to
reach a conversion of >99% after 3 hours. Results from recy-
cling of MNP-[HDMIM] [W O ] (catalyst 1) are given in Table 4
2
2
11
as well. It can be clearly seen that higher catalyst loading of
0 wt% is necessary to maintain the initial activity after ten
2
runs. The reason for that lies in an almost constant leaching
rate after each cycle which was quantified by ICP-AES analysis
of the W content with an average value of 19 ppm (0.34% of
the initial amount). Besides, a higher catalyst loading can pre-
vent the decomposition of hydrogen peroxide in a supportive
manner by further coating of the MNP surface. Good argu-
ments in this direction were collected from checking the stabil-
ity of H O in the absence of the olefin by titration analysis: no
Figure 6. Epoxidation of cyclooctene by catalyst 1 at 608C in H
CH OH=1:10 (volume ratio), reaction time profiles of the hot filtration ex-
3
periment. The filtration was performed after 20 min reaction time.
2
O/
Catalyst 1 was also tested in the epoxidation of other al-
kenes. As shown in Table 5, the catalyst was applied successful-
ly in the epoxidation of both olefins and allylic alcohols with
30% H O as an oxidant. Under optimized conditions, cyclo-
2
2
H O was present after 3 hours stirring using 5 wt% catalyst
2
2
loading, whereas 74.7% H O of the initial concentration re-
2
2
mained when using 20 wt% catalyst loading under similar con-
ditions.
2
2
heptene and 1,5-cyclooctadiene were converted into the corre-
sponding epoxide completely (with respect to the dosed H O
From the data shown in Table 4 (the fifth and sixth column
from the left), we initially got the impression that leaching W
species could also be one of the reasons for the very limited
2
2
amount) within 1 hour and with perfect selectivity. Also, cyclo-
hexene could be converted in a similar level, albeit with
ChemPlusChem 2012, 77, 1128 – 1138
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chempluschem.org
1133

Z. Hou et al.
tion rates were obtained in cyclooctene epoxidation (Figure 7),
which verifies once again the crucial role of the [W O ] anion
[
a]
Table 5. Epoxidation of various substrates catalyzed by 1.
2
11
Entry
1
Substrate
t [h]
Conv. [%]
Sel. [%]
as the active species. Moreover, Figure 7 shows the stability of
cycloheptene
cyclohexene
1,5-cyclooctadiene
styrene
decene
3-methyl-2-buten-1-ol
geraniol
1
3
1
6
>99
>99
>99
31.8
11
>99
>99
>99
>99
48
[
[
[
b]
2
3
4
5
6
7
8
c]
>99
27.8
>99
>99
93
d]
3
1.5
1.5
1.5
[
[
e]
f]
cinnamyl alcohol
79.6
2
À
[
2
(
a] Reaction conditions: substrate (1.5 mmol), catalyst ([W
mol% with respect to substrate), 30% aqueous H
O/CH OH volume ratio 1:10, 2 mL), 333 K. Conversion and selectivity
were determined by GC analysis. Conversion (%)=products (mol)/initial
(mol)ꢁ100. [b] The selectivities to 2-cyclohexene-1-ol, 2-cyclohex-
ene-1-one, and cyclohexane-1,2-diol are 9.6, 33.5, and 8.8%, respectively.
c] In aqueous H (0.5 mmol), the products were 5,6-epoxycyclooctene
with 95.8% selectivity and 1,2-5,6-di-epoxycyclooctadiene with 4.2% se-
lectivity. In aqueous H (1.0 mmol), the products were 5,6-epoxycy-
clooctene with 85.8% selectivity and 1,2-5,6-di-epoxycyclooctadiene with
4.2% selectivity. [d] The selectivities to benzoic acid and benzaldehyde
2
O
11
]
: 30 mmol,
2 2
O (0.5 mmol), solvent
H
2
3
2 2
H O
[
2
O
2
Figure 7. Comparison of reaction profiles from catalysts 1 and 2 with the
2À
same [W
2
O
11
]
loading (30 mmol). Solid points: fresh catalyst 1 (&) and 2
(~); open points: fresh catalyst 1 (&) and 2 (~) have been preserved in air
2
O
2
for 18 months, and then recycled ten consecutive times. Reaction condi-
2
À
1
tions: n (cyclooctene)/n (H
tion medium: H O/CH OH=1:10 (volume ratio).
2 2 2 11
O )/n ([W O ] )=50:17:1, T=608C, t=3 h; reac-
are 49.2 and 23.0%, respectively. [e] The selectivities to 2,3-epoxygeraniol
and 2,3-6,7-diepoxygeraniol are 93 and 7%, respectively. [f] The selectivi-
ties to cinnamaldehyde and 1-methoxypropyl-benzene are 13.0 and
2
3
7.4%, respectively.
both fresh catalysts 1 and 2 after being stored under ambient
conditions for one and a half years, then recycled ten times,
which is demonstrated by the time profile of cyclooctene ep-
oxidation. Only slight deactivation was observed for catalyst 1,
82.5% conversion after 1 hour was preserved. Meanwhile the
conversion of catalyst 2 dropped to 54.6% after 1.5 hours. This
observation proves again that catalyst 1 is much more stable
than catalyst 2.
a lower epoxide selectivity (48%; Table 5, entry 2). Styrene is
less reactive under the reaction conditions applied: styrene ep-
oxide was achieved in 31.8% conversion and 27.8% selectivity
(Table 5, entry 4). The conversion of 1-decene was also not effi-
cient although the selectivity was perfect, which reflected the
electrophilic mechanism for the epoxidation reaction. More-
over, the catalyst showed good transformation activity for allyl-
ic alcohols. Both 3-methyl-2-buten-1-ol and geraniol were com-
pletely converted within 1.5 hours. The corresponding epox-
ides were obtained with 99% and 93% selectivities, respective-
ly. Furthermore, cinnamyl alcohol could also be converted
completely within 1.5 hours, but the desired product was built
with a lower selectivity of 79.6%. The catalytic reaction mecha-
nism for the epoxidation of allylic alcohols including the ex-
change of the water ligand to form the tungsten-alcoholate
species followed by the insertion of oxygen to the carbon–
carbon double bond, and the regeneration of the dinuclear
On the basis of the research above, we attempted to devel-
op another type of magnetically separable catalyst loaded with
an ionic liquid-type zwitterion 1-dodecyl-3-(3-sulfopropyl)-imi-
dazolium (DSPIM), coupling with a lacunary-type polyoxometa-
late Na PW O (PW ). The finally obtained MNP supported
7
11 39
11
PW11 was also applied to epoxidation reactions.
The starting material PW was synthesized and character-
1
1
31
31
ized by IR and P NMR, and the signal observed in P NMR
spectrum (162 MHz; D O) at a chemical shift of À10.84 ppm
2
[11a,b]
was in accordance with that reported.
In addition, as
shown in Figure 1d,e, the IR spectra of the prepared ionic salt
[
20]
À1
peroxotungstate with hydrogen peroxide is proposed. This is
possibly the reason why allylic alcohols oxidized easily as com-
pared with simple electron-deficient olefins (Table 5, entries 4
and 5 vs. Table 5, entries 6–8).
DSPIM-PW11 exhibited characteristic bands at 1076 cm and
À1
À1
À1
À1
1040 cm (PÀO), 940 cm (WÀO ), 881 cm and 848 cm
d
À1
À1
(W-O -W), and 795 cm and 718 cm (W-O -W), which were
b
c
all identical to IR bands of the Na PW O salt. The presence of
7
11 39
À1
À1
Derived catalytic systems of higher simplicity were also in-
vestigated for cyclooctene epoxidation under standard condi-
additional bands at 2922 cm , 2852 cm
(alkyl CÀH),
À1
À1
À1
1633 cm (CÀN), 1562 cm (CÀC), and 1465 cm (alkyl CÀH)
correspond to the organic part of the catalyst. All these charac-
teristic bands were preserved very well in the spectra of cata-
2
À
tions ( [W O ] (30 mmol), cyclooctene (1.5 mmol), 30% H O2
2
11
2
(
0.5 mmol), solvent (H O/CH OH volume ratio 1:10, 2 mL),
2 3
3
33 K, 3 h). An impregnation of K W O salt on reduced MNPs
lyst 3 MNP-(DSPIM-PW ) (Figure 1f). The broad band centered
2
2
11
11
À1
À1
resulted in a conversion of only 9%. Simple mixing of [DMIm]2-
W O ] with reduced MNPs led to 34% conversion in the first
at 1038–1248 cm overlaps with PÀO bands (1076, 1040 cm )
and correspond to the symmetric and asymmetric stretching
vibration of the silica oxide in Figure 1f. Overall, the FT-IR spec-
tra also provided supportive evidence of the Fe O /SiO MNP
[
2
11
[
6a]
and 5.6% in the second run. These observations verify the
importance of an intense interaction between the surface of
MNPs and the functionalized IL.
3
4
2
structure and the successful coating of the functionalized zwit-
terion onto the Fe O /SiO MNP surface.
Comparative tests of catalysts 1 and 2 with the same
3
4
2
2À
[W O ] loading were conducted. Here, nearly the same reac-
2 11
1134
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ChemPlusChem 2012, 77, 1128 – 1138

Catalysts for Epoxidation
7À
To supplement to our IR results, the Raman analysis of re-
active species (PW O ) were immobilized successfully by or-
11 39
duced Fe O /SiO MNPs and catalyst 3 was carried out. Because
ganic zwitterions on the surface of the Fe O /SiO MNPs.
3 4 2
3
4
2
overheating of the Raman laser would change the maghemite
The magnetic properties of catalyst 3 was also studied (Fig-
ure S3). The saturation magnetization (Ms) of catalyst 3
reached 8.5 emug . The relatively low Ms value can also be
[
21a]
À1
to hematite,
the bands centered at 362 and 667 cm are
À1
attribute to hematite formed during measurement, as shown
Figure S5. The hematite phase weakened in catalyst 3 owing
to the dispersion of hybrid material DSPIM-PW , and the new
explained by considering the diamagnetic contribution of the
silica shells surrounding the MNPs, as well as the coating layer
of hybrid material (DSPIM-PW ) for catalyst 3.
11
À1
band centered at 972 cm is probably due to the existence of
11
[
21]
PW11 in the sample. In addition, the bands centered at 1429
The epoxidation of cyclooctene using aqueous H O was
2 2
À1
and 2878 cm prove the existence of the organic part of
chosen as the model reaction to investigate the catalytic per-
formance of catalyst 3 in different solvents. As shown in
Table 6, the selectivities to cyclooctane epoxide were all found
DSPIM.
DRIFT spectroscopy was also used to prove the presence of
hydrogen bonding in catalyst 3 (Figure 4, top and bottom).
After the adsorption of DSPIM-PW11 on SiO /SiO , it was clearly
2
2
À1
observed that the band centered at 3738 cm
became
[
a]
Table 6. Epoxidation of cyclooctene catalyzed by 3 in different solvents.
À1
weaker, while the broad band around 3681 cm did not
change obviously. This observation is possibly due to the co-
existence of the hybrid material with the surface silanol
groups. The changes in the spectra of the OH stretching
region upon adsorption of DSPIM-PW11 were very similar with
those of SiO /SiO -[HDMIM] [W O ] as discussed before, which
Entry
Solvent
Conversion [%]
Selectivity [%]
1
2
3
4
5
6
7
ethyl acetate
acetonitrile
water
methanol
methanol/acetate (1:1)
methanol/cyclohexane (1:1)
no solvent
79.1
85.1
56.8
>99
60.9
61.7
>99
>99
>99
>99
>99
>99
>99
2
2
2
2
11
therefore, suggests that DSPIM-PW11 has a strong hydrogen-
bond interaction with silanol groups on the surface of MNPs.
In other words, the IL-type compound has been immobilized
by hydrogen bonding (Scheme 2).
>99
397À
=10 mmol), cyclooc-
[
a] Reaction conditions: catalyst 3 (108 mg; PW11
O
tene (0.5 mmol), 30% aqueous H O (0.17 mmol), solvent (2 mL), T=
2
2
608C, t=3 h.
to be higher than 99%. The solvents EtOAc, CH CN, and H O
3
2
were found to be poor solvents for the epoxidation. Interest-
ingly, the conversion can reach >99% in CH OH which is
3
a polar organic solvent. Meanwhile only moderate conversions
were obtained in the mixture of CH OH and cyclohexane, or
3
CH OH and EtOAc. These results imply that the solvent has
3
Scheme 2. Catalytically active species immobilized on the surface of MNPs
by hydrogen bonding.
a significant effect on the catalytic performance, as observed
[5g,17]
by several other research groups.
Because organic solvents
such as acetonitrile, dichloromethane, and alcohols always lead
to the leaching of POM catalysts during the separation of
products from catalysts (resulting from dissolution of catalysts
The XRD patterns of PW , MNP-PW , and catalyst 3 MNP-
11
11
[22]
(
DSPIM-PW ) were measured (Figure S1). The XRD pattern of
in these solvents ), therefore solvent-free epoxidation reac-
tions are highly desirable in view of clean separation. As
a result, the present catalyst 3 was used to carry out the epoxi-
dation reaction in the absence of solvent and the outcome is
also showed in Table 6, entry 7. Interestingly, it was observed
that catalyst 3 resulted in emulsification between H O and cy-
11
MNP-PW11 indicated weak diffraction peaks centered at 17.58
and 26.48 diffraction angles arising from that of PW , even
11
À1
a high loading of PW11 (185 mmolg MNPs equivalent to
6.8 wt%) was employed. However, the diffraction peaks re-
3
sulting from PW11 disappeared completely in catalyst 3, which
demonstrates that PW11 can be dispersed more uniformly on
the core–shell structure MNPs owing to the introduction of the
organic zwitterions.
2
2
clooctene during the reaction. After the reaction, the emulsion
was broken by adding ethyl acetate and then catalyst 3 was
conveniently separated from the reaction mixture by applying
an external magnetic field. It is highly probable that the emul-
sion induced by the zwitterionic-modified catalyst 3 can accel-
erate the reaction by increasing the interface area and facilitat-
Figure S6a,b shows TEM images of the as-synthesized cata-
lyst 3. Core–shell architectures can be observed as Fe O MNPs
3
4
surrounded by a silica shell. The EDX and elemental mapping
analysis were used to show the components of the magnetic
[23]
ing transfers between the two phases.
catalyst. The presence of multiple layers of SiO on the surface
Furthermore, we screened the loading of DSPIM-PW on the
2
11
À1
of the Fe O MNPs was also confirmed by the presence of Si,
reduced Fe O /SiO MNP (mmolg MNPs) with respect to cata-
3
4
3
4
2
O, and Fe elements (Figure S6c). The characteristic peaks for el-
ement W originating from modified MNPs, indicated that the
lytic activity of the core–shell MNPs. The catalytic activity in-
creased with increased loading of DSPIM-PW . It was illustrat-
11
ChemPlusChem 2012, 77, 1128 – 1138
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chempluschem.org
1135

Z. Hou et al.
À1
ed that about 185 mmolg MNPs on the catalyst was enough
As a comparison, fast hot filtration was also employed at the
reaction temperature to examine the filtrate under the condi-
tion of no solvent. As shown in Figure 8, no further cyclooc-
to convert all cyclooctene into epoxide, as shown in Figure S7.
The recyclability of the catalyst MNP-(DSPIM-PW ) (cata-
11
lyst 3) was investigated by choosing the epoxidation of cyclo-
octene as a model reaction under various conditions. As
shown in Table 7, in CH OH the conversion dropped rapidly
3
[
a]
Table 7. Recycling of catalyst 3 under different conditions.
Run
Conversion [%]
[
b]
CH
3
OH
No solvent
1
2
3
4
5
6
7
8
9
>99
31
–
>99
>99
96.5
>99
95.7
99.4
>99
>99
>99
>99
–
–
–
–
–
–
–
Figure 8. Fast hot filtration test for MNP-(DSPIM-PW11) (catalyst 3) without
solvent at 608C. Vertical axis C represents the concentration of cyclooctane
epoxide in ethyl acetate (mgmL ethyl acetate). a) Original liquid phase
À1
with catalyst inside. b) Filtrate from hot filtration.
1
0
7
À
[
a] Reaction condition: catalyst 3 (108 mg; PW11
tene (0.5 mmol), 30% aqueous H (0.17 mmol), CH
h, all selectivities >99%. [b] After catalyst 3 was separated by a magnet-
O
39 =10 mmol), cyclooc-
tene was converted into the corresponding epoxide in the fil-
trate after the catalysts were removed—even when new sub-
strate and H O were added, thus confirming that the catalyti-
2
O
2
3
OH (2 mL), 608C,
3
2
2
ic field, it was further washed by CH
the next run.
3
OH three times and used directly for
cally active species was not present in the homogeneous fil-
trate or the concentration of the leached active species in the
filtrate is so low that it did not contribute to the catalytic activ-
ity. In other words, the reaction occurred dominantly on the
catalyst surface rather than in solution. From the discussion
above, it can be seen that the solvent affects the activity for
epoxidation by its polarity, hydrophobicity, and coordinated
even after the first cycle when CH OH was used to wash the
3
catalyst after the reaction (Table 7, column 2). This outcome
implies that the catalytically active species might leach into
the liquid phase during the consecutive runs. The quantitative
analysis by ICP-AES indicates that 867 ppm W was leached into
the methanol solution in each consecutive run.
[5g,17]
ability with active center as reported previously.
As we were encouraged by the good activity, selectivity, and
stability obtained by using 3 as a catalyst for the epoxidation
of cyclooctene, the MNP-supported IL-type catalyst was ex-
tended to the epoxidation of several types of olefins (such as
cyclic olefins, terminal olefins, and allylic alcohols). As shown in
Table 8, catalyst 3 was applicable to the epoxidation of both
In the next step, the conversion of cyclooctene was carried
out without solvent. As shown in Table 7, the present active
species immobilized by hydrogen bonding interactions (cata-
lyst 3) is highly stable and the conversion remained >99%
with >99% selectivity, even after ten consecutive cycles. The
reason for these positive outcomes lies in the fact that nearly
no leaching was detected after each cycle—where the amount
of W found in liquid phase was only 2.8 ppm, which was quan-
tified by ICP-AES analysis. These results were also in good
agreement with the observation that after ten consecutive cat-
alytic cycles without solvent, the absorption band of the
DSPIM-PW11 species in catalyst 3 was almost same as that of
the fresh catalyst. Meanwhile there was nearly no absorption
of DSPIM-PW11 species in catalyst 3 only after two times cycles
olefins and allylic alcohols with 30% H O2 as the oxidant.
2
Under optimized conditions, cycloheptene and cyclohexene
were converted into the corresponding epoxide with moderate
conversion (Table 8, entries 1 and 2). The transformation of an
Table 8. Epoxidation of various substrates catalyzed by MNP-(DSPIM-
[a]
PW ) (catalyst 3) without solvent.
11
Entry
1
Substrate
Conversion [%]
Selectivity [%]
when using CH OH as solvent (Figure 1f–h).
cycloheptene
cyclohexene
1-decene
3-methyl-2-buten-1-ol
geraniol
67.2
65.3
4.5
85.8
>99
95.3
53.2
>99
19.8
>99
>99
93.6
95.0
>99
3
[
b]
2
3
4
5
6
7
To demonstrate if the leached W species played a crucial
role in catalytic epoxidation carried out in CH OH, the fast hot
3
filtration test was performed at the reaction temperature (Fig-
ure S8). It was observed that further cyclooctene was convert-
ed into the corresponding epoxide in the filtrate when new
substrate and H O were added. This finding proved that the
[c]
crotyl alcohol
methyl oleate
7
À
2
2
[a] Reaction condition: catalyst 3 (108 mg; 10 mmol PW O ), substrate
11 39
(
1
0.5 mmol), 30% aqueous H
,2-diol was detected as the by-product. [c] Geranial (E-citral) was detect-
2
O
2
(0.17 mmol), 608C, 3 h. [b] Cyclohexane-
catalytically active species was present in the homogeneous fil-
trate, and further explained why the catalyst could not be recy-
ed as the by-product.
cled when the reaction was carried out in CH OH solvent.
3
1136
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPlusChem 2012, 77, 1128 – 1138

Catalysts for Epoxidation
n-alkene was also examined (Table 8, entry 3). The relatively
low conversion of 1-decene resulted from the possible strong
hydrophobic nature of the alkene and the electrophilic reac-
tion mechanism of epoxidation. However, the catalyst showed
good transformation activity for allylic alcohols. For example,
Rev. 2009, 38, 2532–2542; f) S. Laurent, D. Forge, M. Port, A. Roch, C.
Robic, L. V. Elst, R. N. Muller, Chem. Rev. 2008, 108, 2064–2110; g) A. H.
Lu, E. L. Salabas, F. Schꢅth, Angew. Chem. 2007, 119, 1242–1266; Angew.
Chem. Int. Ed. 2007, 46, 1222–1244; h) R. L. Oliveira, P. K. Kiyohara, L. M.
Rossi, Green Chem. 2010, 12, 144–149.
[5] a) A. Taher, J. B. Kim, J. Y. Jung, W. S. Ahn, M. J. Jin, Synlett 2009, 15,
2
2
477–2482; b) R. Abu-Reziq, D. S. Wang, M. Post, H. Alper, Chem. Mater.
008, 20, 2544–2550; c) Y. Y. Jiang, C. Guo, H. S. Xia, I. Mahmood, C. Z.
3
-methyl-2-buten-1-ol, geraniol, and crotyl alcohol were con-
verted into the corresponding epoxide with over 85% conver-
sion and over 93% selectivity. In addition, methyl oleate was
also converted into the epoxide with 53.2% conversion with-
out any solvent.
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In summary, we have demonstrated simple preparation proto-
cols for epoxidation catalysts which are easy to recover by
magnetic forces. The obtained catalysts were characterized ex-
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of IL-type compounds immobilization by hydrogen bonds
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