Magnetic nanoparticles (CoFe2O4)-supported phosphomolybdate as an efficient, green, recyclable catalyst for synthesis of b-hydroxy hydroperoxides

Article abstract of DOI:10.1002/adsc.201300551

Magnetic nanoparticles (CoFe₂O₄)-sup-ported phosphomolybdate ([CoFe₂O₄@SiO₂-PrNH ₂-PMo]) was readily prepared and identified as an effi-cient catalyst for ring-opening of various epoxides w

Full text of DOI:10.1002/adsc.201300551

FULL PAPERS
DOI: 10.1002/adsc.201300551
Magnetic Nanoparticles (CoFe2O4)-Supported Phosphomolybdate
as an Efficient, Green, Recyclable Catalyst for Synthesis of
b-Hydroxy Hydroperoxides
Pei-He Li,a Bao-Le Li,a Zhi-Min An,a Li-Ping Mo,a Zhen-Shui Cui,a
and Zhan-Hui Zhanga,*
a
College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang 050024, Peopleꢀs Republic of China
Fax : (+86)-311-8963-2795; e-mail: zhanhui@mail.nankai.edu.cn
Received: June 20, 2013; Revised: July 31, 2013; Published online: October 9, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300551.
Abstract: Magnetic nanoparticles (CoFe2O4)-sup- droxy hydroperoxides (HHPs) in high yields at room
ported phosphomolybdate ([CoFe2O4@SiO2-PrNH2- temperature, and the catalyst could be magnetically
PMo]) was readily prepared and identified as an effi- separated and recycled.
cient catalyst for ring-opening of various epoxides
with ethereal hydrogen peroxide (H2O2). The reac- Keywords: epoxides; hydrogen peroxide; b-hydroxy
tion proceeded under mild conditions to give b-hy- hydroperoxides; magnetic nanoparticles
Introduction
Direct construction of the peroxy bond in organic
synthesis using hydrogen peroxide (H2O2) has long
Recently, the application of nanoparticles (NPs) in or- been one of the most challenging research targets.[5]
ganic reactions has attracted great interest because Particularly, the ring-opening reaction of epoxides
they can act as highly efficient catalysts. Nanocatalysts with H2O2 is an important means for preparing b-hy-
may effectively bridge the gap between homogeneous droxy hydroperoxides (HHPs). HHPs can convenient-
and heterogeneous catalysis due to their good disper- ly be converted into the corresponding 1,2,4-trioxanes,
sion properties, high catalytic activity and selectivity. a class of peroxide compounds that possesses antima-
However, the tedious and costly separation and re- larial activity as exemplified by qinhaosu (artemisi-
covery procedure of the powdery nanocatalysis is an nin) and its analogues.[6] HHPs wherein the hydroper-
obstacle hampering their industry-scale applications. oxy group is in an allylic position are considerably
To further address the issues of separation, recovery used as protecting groups for the carbonyl group as
and recycling of catalysts from the reaction mixture, 1,2,4-trioxanes.[7] The ring-opening reaction of epox-
magnetic nanoparticles (MNPs) have emerged as an ides with H2O2 [w8] as originally catalyzed by strong acid
ideal support because of their unique separable fea- such as HClO4 or CF3CO2H[9] under homogeneous
tures by magnetic forces. Magnetic separation is reaction conditions. In recent years, some new im-
a simple, economical, and green means and it makes proved methods have been reported in the presence
the removing and recycling of catalyst much easier of promoters, such as molybdenyl acetylacetonate,[10]
than filtration and centrifugation. Moreover, magneti- the molybdenum complex prepared from Na2MoO4
cally recyclable nanocatalysts (MRNCs) are easily and glycine,[7] phosphomolybdic acid (PMA),[11]
and SbCl3/SiO2.[13] However, some of the
[12]
tunable by appropriate structural surface modification SnCl4
to load various functionalities and they have been above approaches still have certain shortcomings such
used in many organic transformations.[1–3] Among the as the use of expensive[7] and unrecyclable cata-
various MRNCs, cobalt ferrite (CoFe2O4) with gener- lysts,[10–12] lack of substrate generality,[10] long reaction
al formula (AB2O4) is one of the most versatile mag- times,[11] and the requirement of ultrasound irradia-
netic materials as it has moderate saturation magneti- tion.[13] Thus, the design of a recyclable catalytic
zation, chemical stability, resistance to oxidation, in- system that promotes efficient ring-opening of epox-
expensiveness, and high mechanical strength.[4]
ides with H2O2 is still strongly desirable and of signifi-
cant value.
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Magnetic Nanoparticles (CoFe2O4)-Supported Phosphomolybdate as an Efficient, Green, Recyclable Catalyst
Scheme 1. Synthesis of b-hydroxy hydroperoxides.
In continuation with our research on the design of
magnetic nanocatalysts[14] and the development of
environmentally friendly synthetic methods,[15]
we
prepared
a
new
type
of
magnetic
nanoparticles (CoFe2O4)-supported phosphomolyb-
date ([CoFe2O4@SiO2-PrNH2-PMo]) and found that it
is a highly active and recyclable catalyst for the syn-
thesis of HHPs (Scheme 1).
Results and Discussion
Figure 1. EDS spectrum of CoFe2O4@SiO2-PrNH2-PMo.
At first CoFe2O4 nanoparticles were prepared accord-
ing to method reported in the literature with some
modifications.[4] Coating of a layer of silica on the sur-
face of CoFe2O4 nanoparticles was achieved by soni-
cation of a CoFe2O4 suspension in an alkaline etha-
nol-water solution of tetraethyl orthosilicate (TEOS).
The obtained CoFe2O4@SiO2 was then treated with 3-
aminopropyltriethoxysilane (APTES) in refluxing tol-
uene to afford aminated-CoFe2O4@SiO2 NPs. PMA
was added to
a
suspension of aminated-Co-
Fe2O4@SiO2 in dry THF, while being dispersed by
sonication. The MNP-supported PMA was isolated by
magnetic decantation and washed with THF and
dried (Scheme 2). The Mo metal amount of the im-
mobilized catalyst was found to be 19.2% based on
inductively coupled plasma mass spectrometry (ICP-
MS) analysis. Electron dispersive spectrometry (EDS)
confirmed the presence of Fe, Co, Si, P, O, C and Mo
in the nanocatalyst (Figure 1). Figure 2 shows Fourier
transform infrared (FT-IR) spectra of CoFe2O4@SiO2-
PrNH2-PMo. The bands at 460, 1065, 1619 and
3438 cmÀ1 are the characteristic absorptions of SiO2,
which shows evidence for the formation of a silica
Figure 2. IR spectra of (a) CoFe2O4@SiO2, (b) aminated-
CoFe2O4@SiO2 and (c) CoFe2O4@SiO2-PrNH2-PMo.
shell. The presence of Co O and Fe O bonds in the peaks near 1084 and 3300 cmÀ1 are characteristic ab-
magnetic particles is confirmed by the characteristic sorption bands of the vibration of OH moieties, which
peak appeared at 596 cmÀ1. The intense and broad overlap with the NH2 stretching vibration. The en-
hancement of the bands at 1543 cmÀ1 provides direct
À
À
À
evidence to verify the existence of the N H deforma-
tion vibration. The absorptions at 889, 964 and
1065 cmÀ1 are assigned to the Mo O Mo bridges, ex-
À À
À À
ternal Mo=O bond and inner P O Mo bond, respec-
À
tively. Alkyl C H stretches are found at 2927 and
2860 cmÀ1.
Using the Debye–Scherrer equation, the average
nanoparticle diameter was estimated to be 30 nm,
which was in a good agreement with the results from
TEM (Figure 3). The TEM image shows that
Scheme 2. Synthesis of CoFe2O4@SiO2-PrNH2-PMo.
CoFe2O4@SiO2-PrNH2-PMo NPs have a core-shell
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Figure 5. XRD pattern of CoFe2O4@SiO2-PrNH2-PMo.
which can be well indexed to the cubic spinel phase
of CoFe2O4 in good agreement with literature data
(JCPDS 22–1086). The specific surface area of Co-
Fe2O4@SiO2-PrNH2-PMo obtained by the N2 adsorp-
tion isotherms was 39m2 gÀ1.
The magnetic properties of the samples Co-
Fe2O4@SiO2 and CoFe2O4@SiO2-PrNH2-PMo were
measured by a vibrating sample magnetometery
(VSM) at room temperature (Figure 6). The prepared
Figure 3. TEM image of CoFe2O4@SiO2-PrNH2-PMo.
structure and good dispersity. Further observation samples CoFe2O4@SiO2 and CoFe2O4@SiO2-PrNH2-
confirmed the formation of a silica layer around the PMo are superparamagnetic and the saturation mag-
CoFe2O4 nanoparticles. The SEM image shows that netization values are 23.0 emugÀ1 and 19.0 emugÀ1,
morphology of the particles is spherical or quasi- respectively. That the saturation magnetization of
spherical and the surface configuration of NPs is samples changed might be because of the functionali-
quite rough with smaller subunits (Figure 4). The zation by PrNH2-PMo. Furthermore, the superpara-
XRD spectrum of CoFe2O4@SiO2-PrNH2-PMo magnetic behavior of the synthesized nanocatalyst is
(Figure 5) exhibited diffraction peaks at around 18.28, critical for their application, which prevents aggrega-
30.18, 35.58, 43.18, 57.08 and 62.68 corresponding to tion and enables them to redisperse rapidly when the
the (111), (220), (311), (400), (511) and (440), magnetic field is removed.
Figure 4. SEM image of CoFe2O4@SiO2-PrNH2-PMo: (a) “fresh” catalyst and (b) “recovered” catalyst.
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Magnetic Nanoparticles (CoFe2O4)-Supported Phosphomolybdate as an Efficient, Green, Recyclable Catalyst
due to higher surface areas of nanoscale heterogene-
ous catalysts. Various other nanomaterials such as
Fe3O4, g-Fe2O3, CoFe2O4 and CoFe2O4@SiO2-
H3PW12O40 were also tested for this transformation
and generated the product in lower yields. Morever,
CoFe2O4@SiO2 could not catalyze the transformation
efficiently (entry 7). The reactions were also success-
fully performed at large scales without significant loss
of yield (entry 13).
To investigate the scope of the catalyst application,
various sterically, electronically and functionally di-
verse epoxides were tested with ethereal H2O2 under
the optimized conditions and the results are presented
in Table 2. All reactions have been completed in 15–
30 min to afford the corresponding products in good
yields with high regioselectivity. The regioselectivity
1
was determined by H NMR and also by comparison
Figure 6. Magnetization curves of (a) CoFe2O4@SiO2 and
(b) CoFe2O4@SiO2-PrNH2-PMo.
with known samples. The perhydrolysis of epoxides
shows that structure of the epoxides exerts a signifi-
cant effect on the ring-opening direction. In the case
The activity of the prepared catalyst was tested for of 2-monosubstituted aryl epoxides, b-hydroperoxy al-
the ring-opening of epoxides using 2-phenyloxirane cohols were obtained as the major product (a/b=95/
(1 mmol) as the model substrate in ethereal H2O2 5) during the reaction, which was consistent with pub-
(5 mmol). As shown in Table 1, the reaction occurred lished report.[11] On the other hand, in the case of gly-
smoothly in the presence of CoFe2O4@SiO2-PrNH2- cidic ethers, the ring-opening likely occurred predomi-
PMo, affording 2-hydroperoxy-2-phenylethanol (2a) nantly through an attack by hydrogen peroxide group
in 92% yield (Table 1, entry 11). The optimum on the sterically less crowded terminal carbon atom
amount of catalyst was 0.1 g (20 mol% Mo). Increas- of the epoxide, which is in agreement with an SN2
ing the amount of catalyst did not improve the yield mechanism. The probable reason may be that in aryl
and the reaction time, while in the absence of the cat- epoxides the positive charge at the benzylic position
alyst only a trace amount of the target product was is stabilized due to conjugation with the phenyl ring,
observed (Table 1, entry 1). For comparison, using thus leading to the predominant product carrying the
pure phosphomolybdic acid and ammonium phospho- entering hydroperoxyl group at that carbon. Whereas
molybdate as the homogeneous catalysts, showed in case of glycidic ethers, the steric factor predomi-
a drop in reaction rate and gave 81% and 70% yields nates over electronic factors thereby facilitating the
in 50 min, repectively (Table 1, entries 2 and 3). The attack at the sterically less crowded carbon atom of
reason for the improved catalytic activity might be the epoxide ring. The alkyl chain at the 2-position in
Table 1. Influence of different catalysts on the perhydrolysis of 2-phenyloxirane (1a).[a]
Entry
Catalyst
Time [min]
Yield [%][b]
1
2
3
4
5
6
7
8
none
600
50
50
50
50
50
360
20
30
30
15
15
20
trace
81
70
21
25
22
trace
89
72
85
phosphomolybdic acid (20 mol%)
ammonium phosphomolybdate (20 mol%)
nano Fe3O4 (20 mol%)
nano g-Fe2O3 (20 mol%)
nano CoFe2O4 (20 mol%)
nano CoFe2O4@SiO2 (0.1 g)
nano CoFe2O4@SiO2-H3PW12O40 (20 mol%)
nano CoFe2O4@SiO2-NH2-PMo (5 mol%)
nano CoFe2O4@SiO2-NH2-PMo (10 mol%)
nano CoFe2O4@SiO2-NH2-PMo (20 mol%)
nano CoFe2O4@SiO2-NH2-PMo (30 mol%)
nano CoFe2O4@SiO2-NH2-PMo (20 mol%)
9
10
11
12
13
92
90
90[c]
[a]
Experimental conditions: phenyloxirane (1 mmol), ethereal H2O2 (5 mL, 5 mmol), room temperature.
Isolated yields.
50-mmol scale.
[b]
[c]
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Table 2. Synthesis of b-hydroperoxy alcohols 2.
Entry
Epoxide
Product
Time [min]
15
Yield [%][a]
92
mp [oC]
1
64–65 (63–64[13]
)
2
3
4
5
6
7
15
16
20
15
15
15
89
88
87
90
89
88
75–76
103–104 (102–104[13]
)
108–110
102–103
70–71 (67–68[13]
)
86–88
8
15
15
20
15
15
89
82
78
79
80
oil
9
oil
10
11
12
33–34
75–76 (74–75[13]
)
oil
13
20
30
90
88
oil[11]
14
93–95
[a]
Isolated yield.
epoxide 1j showed both isomers, but gave the main trans isomer (Table 2, entry 13). As a symmetrical 2,3-
product 2j with the hydrogen peroxide group being disubstituted epoxide 2,3-diphenyloxirane was also
added at the less hindered terminal carbon. The struc- subjected to ring opening with H2O2 under same ex-
1
ture of 2j was confirmed by H NMR, 13C NMR with perimental conditions and gave 2-hydroperoxy-1,2-di-
the assistance of DEPT, and HMQC experiments. Cy- phenylethanol in 88% yield (Table 2, entry 14).
clohexene oxide underwent perhydrolysis exclusively
After the completion of reaction, the catalyst was
via a trans-stereospecific pathway to provide only one separated magnetically from the reaction mixtures
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Magnetic Nanoparticles (CoFe2O4)-Supported Phosphomolybdate as an Efficient, Green, Recyclable Catalyst
in the presence of FeCl3, underwent a condensation
with cyclohexanone (3) to produce 1,2,4-trioxane 4 in
high yield (Scheme 3). Second, it was shown that 2a is
an excellent substrate for synthesis of 1,2,4-trioxan-3-
one (6) after reaction with bis(trichloromethyl)car-
bonate (5).
Conclusions
In conclusion, we have developed a novel, efficient,
robust and reusable nano magnetically CoFe2O4 sup-
ported phosphomolybdate catalyst, for ring-opening
of epoxides to yield b-hydroxy hydroperoxides. The
advantages displayed by the catalytic system such as
economic viability, easy preparation and separation,
Figure 7. Reusability of catalyst.
and washed with Et2O, air-dired and then reused di- high catalytic activity, stability and reusability, advo-
rectly in a model reaction for the next round without cate that the present catalyst should be considered as
further purification. The results showed that the cata- a viable alternative in organic reactions.
lyst exhibited high but slowly decreasing activity in 8
consecutive cycles, which might be attributed to the
slight loss of catalyst during the reaction and recovery
processes (Figure 7). In order to confirm that the re-
Experimental Section
action is heterogeneous, a hot filtration test was per-
formed in the model reaction. The model reaction
General Remarks
was carried out for 5 min in the presence of magnetic
nanocatalyst. At this stage the yield of the product
was 65%. The catalyst was then removed and the fil-
tered reaction mixture was then stirred for another
1 h. But no corresponding increase of product yield
was observed, indicating that no homogeneous cata-
lyst was involved. In addition, metal leaching in the
catalyst was determined and ICP-MS analysis of the
clear filtrate indicated that the Mo and Fe contents
were 0.12 and 0.18 ppm, respectively. These results
confirm that the heterogeneous nature of the magnet-
ic nanocatalyst in this reaction and only a slight loss
of the catalyst occurs during the course of the reac-
tion. SEM images of fresh and recovered catalysts in-
dicated that no significant change had occurred. This
indicates that MNP-supported Mo catalyst had a very
high chemical stability and can endure the oxidation
conditions (Figure 4).
Ethereal hydrogen peroxide was prepared using a literature
procedure by extracting the commercially available aqueous
H2O2 with Et2O.[11] Other solvents and chemicals were ob-
tained commercially and were used as received. X-ray dif-
fraction analysis was carried out using a PANalytical X’Pert
Pro X-ray diffractometer. Surface morphology and particle
size were studied using a Hitachi S-4800 SEM instrument.
Transmission electron microscope (TEM) observation was
performed using Hitachi H-7650 microscope at 80 kV. Ele-
mental compositions were determined with a Hitachi S-4800
scanning electron microscope equipped with an INCA 350
energy dispersive spectrometer (SEM-EDS) presenting
a 133 eV resolution at 5.9 keV. The ICP-MS analyses were
carried out with an X series 2 spectrometer. The magnetic
properties of nanoparticles were determined in a vibrating
sample magnetometer (VSM, RDK-415E, Japan). Melting
points were determined using an X-4 apparatus and are un-
corrected. IR spectra were recorded using
a Bruker-
TENSOR 27 spectrometer instrument. NMR spectra were
taken with a Bruker DRX-500 spectrometer at 500 MHz
(1H) and 125 MHz (13C) using CDCl3 as the solvent with
TMS as internal standard. Mass spectra were recorded on
a ThermoFinnigan LCQ Advantage instrument with an ESI
The synthetic utility of the b-hydroxy hydroperox-
ides was showcased by their further transformation.
First, it was demonstrated that 2-phenyloxirane (2a),
Scheme 3. Preparation of 1,2,4-trioxane and 1,2,4-trioxan-3-one.
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source (4.5 keV). Elemental analyses were obtained on
a Vario EL III CHNOS elemental analyzer.
(3ꢂ20 mL). The combined organic phases were washed in
turn with water (2ꢂ10 mL) and brine (2ꢂ10 mL), dried
over anhydrous Na2SO4 and concentrated at ambient tem-
perature to give a crude product. Further purification was
achieved by flash column chromatography on silica gel (n-
hexane/EtOAc).
Preparation of CoFe2O4@SiO2-PrNH2-PMo Magnetic
Nanoparticles
CoFe2O4 NPs were prepared by a chemical co-precipitation
technique using FeCl3·6H2O and CoCl2·6H2O as precursors.
FeCl3·6H2O (2.70 g) and CoCl2·6H2O (1.19 g) were dis-
solved in 50 mL distilled water. Then, the mixture solution
was transferred into a three-necked flask equipped with
a mechanical stirrer. 25 mL of 3 mol/L NaOH solution were
added into the flask under vigorous stirring. The mixture
was heated to reflux for 1 h to yield a black dispersion.
When the reaction had finished, the black product was
washed with double-distilled water for several times until
the pH value of the solution became neutral. The black pre-
cipitate was separated by a permanent magnet, followed by
washing three times with ethanol and drying at 1008C in
a vacuum for 24 h.
Coating of a layer of silica on the surface of the CoFe2O4
NPs was achieved by pre-mixing (ultrasonic) a dispersion of
the purified CoFe2O4 NPs (1 g) obtained previously with dis-
tilled water (80 mL) for 1 h at 408C. A concentrated ammo-
nia solution (1.5 mL) was added and the resulting mixture
stirred at 408C for 30 min. Subsequently, tetraethyl orthosili-
cate (TEOS, 1.0 mL) was charged to the reaction vessel and
the mixture continuously stirred at 408C for 24 h. The silica-
coated NPs were collected using a permanent magnet, fol-
lowed by washing three times with ethanol, diethyl ether
and drying at 1008C in a vacuum for 24 h.
The obtained CoFe2O4@SiO2 (1 g) was added to the solu-
tion of 3-aminopropyltriethoxysilane (2 mmol, 0.44 g) in dry
toluene (20 mL) and refluxed for 20 h. After the reaction
had finished, the aminated-CoFe2O4@SiO2 were separated
by a permanent magnet, washed with double-distilled water
and anhydrous ethanol, and dried at 1008C for 5 h to give
the surface bound amino group CoFe2O4@SiO2-PrNH2.
For the preparation of CoFe2O4@SiO2-PrNH2-PMo: a mix-
ture of CoFe2O4@SiO2-PrNH2 (0.5 g) and phosphomolybdic
acid (0.5 mmol, 0.93 g) in dry THF (30 mL) was sonicated
for 1 h. The solid was collected using a permanent magnet,
followed by washing three times with THF. Finally, the ob-
tained CoFe2O4@SiO2-PrNH2-PMo was dried under vacuum
at 608C for 24 h. The Mo content was determined by ICP-
MS and it was found to be 19.2 wt% (2.0 mmolgÀ1). Typi-
cally, a loading at ca. 30.4 wt% H3PMo12O40 was obtained.
Preparation of 3-Phenyl-1,2,5-trioxaspiro
decane (4)
ACHTUNGTRENN[UNG 5.5]un-
To a mixture of 2a (1 mmol) and cyclohexanone (1.5 mmol)
in CH2Cl2 (5 mL), anhydrous FeCl3 (0.1 mmol) and MgSO4
(0.12 g) was added and stirred at ambient temperature for
1.5 h. After completion of the reaction, as indicated by
TLC, the reaction was quenched with a saturated NH4Cl so-
lution. The aqueous layer was extracted with ethyl acetate
(3ꢂ10 mL). The combined organic phases was dried over
anhydrous Na2SO4. The solvent was evaporated under
vacuum and the residue was purified by column chromatog-
raphy over silica gel using EtOAc/petroleum as eluent to
afford 4 as a colorless oil; yield: 213 mg (91%). IR (KBr):
n=3385, 3064, 2935, 2862, 1718, 1635, 1494, 1448, 1384,
1276, 1161, 1103, 929, 758, 698 cmÀ1 1H NMR (CDCl3,
;
500 MHz): d=7.38–7.34 (m, 4H), 7.30 (t, J=7.0 Hz), 1H),
5.07 (dd, J=7.5, 6.5 Hz, 1H), 4.29 (dd, J=8.0, 6.5 Hz, 1H),
3.69 (dd, J=8.0, 7.5 Hz, 1H), 1.83–1.62 (m, 8H), 1.47–1.44
(m, 2H) ppm; 13C NMR (CDCl3, 125 MHZ): d=23.9, 24.0,
25.2, 35.6, 36.2, 71.5, 77.6, 110.3, 126.3, 128.0, 128.5, 139.3;
ESI-MS: m/z=257 (M+Na)+; anal. calcd. for C14H18O3: C
71.77, H 7.74; found: C 71.95, H 7.56.
Preparation of 6-Phenyl-1,2,4-trioxan-3-one (6)
A mixture of 2a (1 mmol) and bis(trichloromethyl) carbon-
ate (1.5 mmol) was placed in a 25-mL round-bottom flask
containing 5 mL dry CH2Cl2. Anhydrous FeCl3 (0.1 mmol)
and MgSO4 (0.12 g) were added to it and the reaction mix-
ture was stirred at ambient temperature for 3 h. After com-
pletion of the reaction, as indicated by TLC, the reaction
was quenched with a saturated NH4Cl solution. The aqueous
layer was extracted with ethyl acetate (3ꢂ10 mL). The com-
bined organic phases was dried over anhydrous Na2SO4.
Evaporation of the organic solvent afforded the crude prod-
uct, which was purified by column chromatography over
silica gel using EtOAc/petroleum as eluent to afford 6 as
a white solid; yield: 158 mg (88%); mp: 52–558C. IR (KBr):
n=3414, 3386, 2924, 2862, 1621, 1385, 1290, 1102, 986, 843,
750, 637 cmÀ1 1H NMR (CDCl3, 500 MHz): d=7.47–7.43
;
(m, 3H), 7.37–7.35 (m, 2H), 5.68 (t, J=8.0 Hz, 1H), 4.80 (t,
J=8.0 Hz, 1H), 4.35 (t, J=8.0 Hz, 1H); 13C NMR (CDCl3,
125 MHz): d=71.2, 78.1, 125.9, 129.3, 129.8, 135.8, 154.9;
ESI-MS: m/z=203 (M+Na)+; anal. calcd. for C9H8O4: C
60.00, H 4.48; found: C 59.86, H 4.65.
General Procedure for Synthesis of b-Hydroxy
Hydroperoxides
A mixture of epoxide (1 mmol), CoFe2O4@SiO2-PrNH2-
PMo (20 mol% Mo, 0.1 g) in ethereal H2O2 solution (ca. 1.0
mol·lÀ1, 5 mL) was stirred at ambient temperature. After
completion of the reaction, as indicated by TLC, a magnetic
stirrer (0.5–0.7T) was applied to the outside of the reaction
flask to separate the catalyst from the solution. The catalyst
was then washed with Et2O, air-dired, and used directly for
the next round of reactions without further purification.
After that, the reaction mixture was diluted with Et2O
(20 mL) and washed with H2O (5 mL). The phases were sep-
arated. The aqueous layer was back-extracted with EtOAc
Acknowledgements
We are grateful for financial support from the National Natu-
ral Science Foundation of China (Nos. 21272053, 21072042
and 20872025) and the Nature Science Foundation of Hebei
Province (No. B2011205031).
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 2952 – 2959

Magnetic Nanoparticles (CoFe2O4)-Supported Phosphomolybdate as an Efficient, Green, Recyclable Catalyst
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