Mo(vi) complex supported on Fe3O4 nanoparticles: magnetically separable nanocatalysts for selective oxidation of sulfides to sulfoxides

Article abstract of DOI:10.1039/c5ra08653a

A molybdenum complex, [MoO₂Cl₂(DMSO)₂], was immobilized on amino propyl and Schiff base modified magnetic Fe₃O₄@SiO₂ nanoparticles by covalent linkage. The resulting nanoparticles were used as efficient and recyclable catalysts for the selective oxidation of sulfides to sulfoxides using urea hydrogen peroxide as the oxidant. The complete characterization of catalysts was carried out by means of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), elemental analysis, FT-IR and Raman microprobe techniques.

Full text of DOI:10.1039/c5ra08653a

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Mo(VI) complex supported on Fe3O4 nanoparticles:
Magnetically separable nanocatalysts for selective
oxidation of sulfides to sulfoxides
Cite this: DOI: 10.1039/x0xx00000x
Hasan Keypour#,a, Masomeh Balalia, Mohammad Mehdi Haghdoostb, Mojtaba
Received 00th January 2012,
Accepted 00th January 2012
b
Bagherzadeh*,
DOI: 10.1039/x0xx00000x
A molybdenum complex, [MoO2Cl2(DMSO)2], was immobilized on amino propyl and Schiff base
modified magnetic Fe3O4@SiO2nanoparticles by covalent linkage. The resulting nanoparticles were
used as efficient and recyclable catalysts for the selective oxidation of sulfides to sulfoxides using
urea hydrogen peroxide as the oxidant. The complete characterization of catalysts was carried out
by means of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission
electron microscopy (TEM), vibrating sample magnetometer (VSM), Xꢀray photoelectron
spectroscopy (XPS), elemental analysis, FTꢀIR and Raman microprobe techniques.
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bonded to Fe3O4 nanoparticles surfaces. On the other hand, after
coating, grafting of the metal complexes on the surface of Fe3O4
1. Introduction
nanoparticles is also possible.9,15,16
Nanomagnetic catalyst is an exponentially growing research field in
modern science that exhibits unique properties and application of
nanoparticles of different sizes and shapes.1ꢀ3 They have been widely
applied to some important reactions such as Suzuki and Heck
couplings as well as oxidation of sulfides and thiols.4ꢀ8 Although
many catalytic oxidation reactions using homogeneous catalysts
have been successfully demonstrated, the difficulties in separating of
the catalysts greatly restrict their applications in practice.
Heterogeneous catalysts usually need tedious procedures such as
filtration and centrifugation for recycling after reactions. This
shortcoming could be overcome using magnetic nanoparticle
supports because these particles have unique magnetic properties
that allow simple separation from the reaction mixture using an
external magnet without filtration.9ꢀ10
The Schiff base moiety is one of the preferred functional groups for
anchoring different catalytic species on the magnetic
nanoparticles.4,19,20 In this study, new heterogeneous nanocatalysts
were synthesized by the covalent anchoring of [MoO2Cl2(DMSO)2]
complex on the amino propyl and Schiff base coated magnetic
nanoparticles as active, magnetically separable oxidation catalysts.
Furthermore, the obtained catalysts showed not only high catalytic
activity in oxidation reactions but also high degree of chemical
stability in various organic solvents.
2. Results and discussion
Iron oxides particles have been paid growing attention owing
to their unique properties and potential applications in various fields,
such as magnetic resonance imaging (MRI) contrast agents11,
magnetically assisted drug delivery12, hyperthermia13 and recycling
of catalysts.4ꢀ6 Magnetite (Fe3O4) is generally accepted as being
appropriate and safe for in vivo biomedical applications, nonꢀtoxic,
hydrophilic, and biocompatible, and they have to remain stable in
aqueous colloidal suspensions.14 However magnetic nanoparticles
must be stabilized by protective agent against the tendency towards
agglomeration.15 Therefore, the surfaces of Fe3O4nanomagnetic were
often coated by inert materials such as silica or titanium dioxides to
prevent their aggregation and improve their chemical stability.9,16ꢀ18
There are only a limited number of molecules that can be directly
As illustrated in Scheme 1, the synthesis of the MNPs is a multistep
procedure. First, superparamagnetic Fe3O4 (1) nanoparticles were
prepared by the coꢀprecipitation method.21 In the next step, the
surface of Fe3O4 was encapsulated with silica in order to increase the
functionality and stability of nanoparticles. For this purpose, the
silicaꢀcoated MNPs (Fe3O4@SiO2 (2)) were synthesized by basic
hydrolysis and condensation of TEOS on the surface of the
Fe3O4nanoparticles.21The silica coated Fe3O4 nanoparticles were
surfaceꢀmodified with 3ꢀaminopropyltriethoxysilane (APTS) which
introduced ꢀNH2 group on to the surface of support.22
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DOI: 10.1039/C5RA08653A
TEOS
APTS
NH2
Fe3O4 (1)
Fe3O4@SiO2 (2)
Fe3O4@SiO2ꢀNH2 (3)
dialdehyde (5)
MoO2Cl2(DMSO)2
Fe3O4@SiO2ꢀNH2ꢀMo (4)
N
O
O
Fe3O4@SiO2ꢀSB (6)
N
MoO2Cl2(DMSO)2
Fe3O4@SiO2ꢀSBꢀMo (7)
Scheme 1. Stepꢀbyꢀstep synthesis of the nanocatalyst
.
After functionalization by APTS, free amino groups on the surface
of Fe3O4@SiO2ꢀNH2 nanoparticles can act as monodentate ligands
and offer binding sites for immobilization of many metal complexes.
With this idea in mind, Fe3O4@SiO2ꢀNH2ꢀMo nanoparticle was
obtained by the reaction between Fe3O4@SiO2–NH2 (3) and
MoO2Cl2(DMSO)2 complex. The DMSO ligands in the
MoO2Cl2(DMSO)2 complex are highly labile toward substitution and
can be replaced by the amine group of the surface. It is noteworthy
that the release of DMSO was confirmed by GC analysis of reaction
mixture. The obtained nanoparticle was characterized by means of
FTꢀIR, EDX, SEM and TGA.
In FTꢀIR spectrum of APTSꢀcoated Fe3O4 NPs (3), the absorption
bands in 2916 and 2850 cmꢀ1 (Fig. 1 (b)) ascribed to CꢀH stretch of
the propyl group .22 In addition, the presence of magnetite is evident
at 610 cmꢀ1. The broad band at 1057 cmꢀ1 is the characteristic peak of
the SiꢀOꢀSi group.23
Fig. 1. FTꢀIR spectra of (a) MoO2Cl2(DMSO)2, (b) Fe3O4@SiO2ꢀNH2,
Compared with the FTꢀIR spectrum of Fe3O4@SiO2ꢀNH2 (3)
(c) Fe3O4@SiO2ꢀNH2ꢀMo.
(Fig. 1 (b)), the characteristic peaks at 922 and 892 cmꢀ1
corresponding to the vibration modes of cisꢀMoO2 moiety can
be clearly observed in the FTꢀIR spectrum of Fe3O4@SiO2ꢀ
The chemical identity of the Fe3O4@SiO2 (2) and Fe3O4@SiO2ꢀNH2
(3) nanoparticles were confirmed by EDX analysis (Fig. S1 and Fig.
S2). EDX analysis of the Fe3O4@SiO2ꢀNH2ꢀMo (4) nanoparticles
(Fig. 2) showed expected elements such as iron, oxygen, silicon,
carbon, nitrogen, chlorine and molybdenum. The EDX indicated the
presence of Cl within the nanoparticle structure, revealed that the
MoꢀCl bonds remain intact during the grafting process. In addition,
the molybdenum content of the nanoparticle (4) was determined by
the inductively coupled plasma optical emission spectroscopy
(ICP/OES) analysis to be about 1.6 mmol gꢀ1. This loading value is
much higher than that previously reported for similar system24,
suggesting that the immobilization method is very effective.
NH2ꢀMo (4) nanoparticles (Fig. 1 (c)). These absorption bands
were also observed in the FTꢀIR spectrum of starting
MoO2Cl2(DMSO)2 complex (Fig. 1 (a)) which proves that Moꢀ
dioxo core has successfully bonded to the surface of the
Fe3O4@SiO2ꢀNH2 nanoparticles.24
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Energy (keV)
Fig. 2. The energyꢀdispersive Xꢀray spectroscopy (EDX) of the
Fe3O4@SiO2ꢀNH2ꢀMo (4).
Temperature˚C
Fig. 4. TGA analysis of Fe3O4@SiO2ꢀNH2ꢀMo (4).
The particle morphology and textural properties of nanoparticles (4)
were studied by SEM and representative images are shown
respectively in Fig. 3.25 In the SEM image, nanoparticles with
spherical shapes are observed with particle diameter in the range of
70ꢀ100 nm.
After functionalization by APTS, free amino groups on the
nanoparticle surface can react not only with various transition metal
complexes but also with many different carbonyl compounds to form
Schiff base ligands. For preparation of Fe3O4@SiO2ꢀSB
nanoparticles (6), Fe3O4@SiO2ꢀNH2 (3) nanoparticles were reacted
with
1,2ꢀbis(2ꢀformylphenoxymethyl)benzenedialdehyde
(5).
Undoubtedly, the Schiff base ligand on the surface of Fe3O4@SiO2ꢀ
SB nanoparticles has a high ability to form complex with many
transition metal centers which makes the Fe3O4@SiO2ꢀSB
nanoparticles a suitable candidate for immobilization applications.
With respect to this, we made Fe3O4@SiO2ꢀSB (6) react with the
MoO2Cl2(DMSO)2 complex in dry CH2Cl2 to synthesize
Fe3O4@SiO2ꢀSBꢀMo (7).
The FTꢀIR spectrum of the Fe3O4@SiO2ꢀSBꢀMo nanoparticle (Fig.
5(c)) clearly showed the formation of molybdenum complex, as
exemplified by the appearance of ν(Mo=O) bands in 930 and 886
cmꢀ1. These two bands also exist in the FTꢀIR spectrum of the
unreacted MoO2Cl2(DMSO)2 complex (Fig. 5(a)).24 In addition, the
shift of absorption band assigned to the C=N bonds from 1639 in
Fe3O4@SiO2ꢀSB to 1664 cmꢀ1 in Fe3O4@SiO2ꢀSBꢀMo confirmed the
coordination of Schiff base ligand.
Fig. 3. SEM images of Fe3O4@SiO2ꢀNH2ꢀMo(4).
The thermogravimetric analysis (TGA) curve of the Fe3O4@SiO2ꢀ
NH2ꢀMo (4) shows the multistep mass loss of the organic materials
between 50ꢀ600 ºC (Fig. 4). Fig. 4 indicates that there exist three
distinct weight loss stages during the nanoparticle pyrolysis.
According to TGA analysis, the residual mass percent of silica
coated NPs is about 54% at 600 ºC. The weight loss of 27% from 50
to 200 ºC is mainly due to the loss of physically adsorbed water,
while the second and third weight loss peaks in the range of 200ꢀ600
ºC ascribe to the loss of organic amino propyl linkage.23
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DOI: 10.1039/C5RA08653A
Fig. 7. SEM images of nanoparticle (7).
Similar to the TGA curve of nanoparticle 4, that of Fe3O4@SiO2ꢀSBꢀ
Mo (7) shows the multistep mass loss of the organic materials as a
function of temperature (Fig. 8). The first weight loss of about 37%
between 100ꢀ220 ºC is due to the removal of physically adsorbed
water or solvent.23 The weight loss of about 6% between 200ꢀ300 °C
and of about 10% between 300ꢀ600 °C may be associated with the
thermal degradation of complex and organic groups. According to
this TGA analysis, the residual mass percent of nanoparticles is 50%
at 600 °C.
Fig. 5. FTꢀIR spectra of (a) MoCl2O2(DMSO)2 complex, (b) Fe3O4@SiO2ꢀSB
and (c) Fe3O4@SiO2ꢀSBꢀMo.
Transmission electron microscopy (TEM) and SEM images of
nanoparticle (7) are shown in Fig. 6 and Fig. 7, respectively. These
image revealed that the Fe3O4@SiO2ꢀSBꢀMo consist of hundreds of
nanometerꢀsized particles (< 100 nm) as the major component.26
Temperature˚C
Fig. 8. The TGA curve of Fe3O4@SiO2ꢀSBꢀMo (7)
.
In addition, the EDX survey of the Fe3O4@SiO2ꢀSBꢀMo
nanoparticles (Fig. 9) confirmed the presence of molybdenum in the
nanoparticles structure. The loading amount of molybdenum was
about 0.7 mmol gꢀ1, which is determined by ICP/OES analysis. The
amount of Mo contain is very similar to that of previously reported
study and would normally be sufficient for providing high catalytic
activity. 24 The EDX peaks were also observed for all other expected
elements such as; iron, oxygen, silicon, carbon, nitrogen and
chlorine.
Fig. 6. TEM images of nanoparticle (7).
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DOI: 10.1039/C5RA08653A
SiKα
3500
3000
2500
2000
1500
1000
500
O Kα
FeLα
N Kα
C Kα
FeKα
MoLβ
MoLα
ClKβ
ClKα
FeKβ
keV
0
0
5
10
Energy(kev)
Fig. 9. The EDX analysis of the nanoparticle 7.
Xꢀray photoelectron spectroscopy (XPS) was applied to determine
the oxidation state of the Mo content (Fig. 10 and Fig S3). The XPS
spectrum of Fe3O4@SiO2ꢀSBꢀMo nanoparticle revealed two binding
energy at 232.70 eV (3d5/2) and 235.90 eV (3d3/2) which were
Fig. 11. Raman Microprobe spectrum for of nanoparticle 7.
Table 1 shows comparative CHN analysis of three nanoparticles:
Fe3O4@SiO2ꢀNH2 (3), Fe3O4@SiO2ꢀSB (6) and Fe3O4@SiO2ꢀSBꢀ
Mo (7). According to the CHN analysis, the formation of Schiff base
is evident by significant increase in C/N ratio from 3.7 in
Fe3O4@SiO2ꢀNH2 to 29.1 in Fe3O4@SiO2ꢀSB. The C, N and H
percentages in Fe3O4@SiO2ꢀSBꢀMo (7) is lower than two other
nanoparticles, mostly due to the molybdenum content.21
assigned to Mo(VI) species coordinated to nitrogen or oxygen
28
groups.27,
In addition, the fact that the element of Fe can’t be
detected in XPS analysis (Fig. S3) confirms the Fe3O4 cores are
completely coated with silica layer.
Table 1. Elemental analysis of Fe3O4@SiO2ꢀNH2 (3), Fe3O4@SiO2ꢀSB (6)
and Fe3O4@SiO2ꢀSBꢀMo (7).
Elemental analysis
Fe3O4@SiO2ꢀNH2
Fe3O4@SiO2ꢀSB
%C
9.73
%N
%H
2.22
3.82
3.28
2.589
1.105
0.6419
32.18
13.66
Fe3O4@SiO2ꢀSBꢀMo
Fig. 10. The Mo3d XPS spectrum of Fe3O4@SiO2ꢀSBꢀMo nanoparticle.
Magnetic measurements of the samples were investigated by a
vibrating sample magnetometer (VSM) at room temperature (Fig.
12). According to the magnetization curves, the saturation of the
nanoparticles decreased from 60 emu/g in the initial Fe3O4 sample to
10 emu/g in the final Fe3O4@SiO2ꢀSBꢀMo nanoparticle (7). This
drop in saturation might very well be resultant of the surface coating
and surface functionalization of Fe3O4 nanoparticles.24 It is
noteworthy that the most significant magnetization decrease
occurred in the coating of Fe3O4 nanoparticles with silica layer.
The successful immobilization of molybdenum dioxo complex was
also confirmed by means of Raman spectroscopy. Fig. 11 shows the
Raman spectrum (from 200 to 1000 cmꢀ1) of final Fe3O4@SiO2ꢀSBꢀ
Mo nanoparticles. Raman bands at low wavenumbers (224 and 303
cmꢀ1) come from vibrations of FeꢀO bonds of Fe3O4 core.29 Beside,
the Fe3O4@SiO2ꢀSBꢀMo nanoparticles (7) possess a Raman band for
the stretching mode of the Mo=O bond at around 920 cmꢀ1 and 899
cmꢀ1. These two bands can be taken as an unambiguous evidence for
successful immobilization of molybdenum complex on the magnetic
nanoparticles.30,31
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solution of Fe3O4@SiO2ꢀSBꢀMo nanocatalyst was filtrated while
substrate and oxidant were immediately added to the filtrate to
initiate the reaction. The hot filtration indicated that some form of
soluble molybdenum species were leached from the nanocatalyst and
were active for oxidation reaction.
Table 2. Oxidation of sulfides by nanoparticles 4 and 7 in the presence of
UHP oxidant.a
Conv.b
(%)
Sel.c
(%)
Ent.
1
Substrate
Catalyst
Cycle
TON
43
ꢀ
methylphenyl
sulfide
methylphenyl
sulfide
methylphenyl
sulfide
methylphenyl
sulfide
methylphenyl
sulfide
methylphenyl
sulfide
methylphenyl
sulfide
4
4
7
7
7
7
7
1
2
1
2
3
4
5
75
ꢀ
90
ꢀ
2
3
86
83
80
81
80
92
95
90
89
89
49
47
46
46
46
Fig. 12. The VSM analysis of (a) Fe3O4, (b) Fe3O4@SiO2, (c) Fe3O4@SiO2ꢀ
4
SB and (d) Fe3O4@SiO2ꢀSBꢀMo.
5
The chemoselective oxidation of sulfides to their corresponding
sulfoxides is a fundamental chemical reaction because sulfoxides are
valuable synthetic intermediates for the synthesis of chemically and
biologically significant molecules.32 Table 2 shows results for
nanoparticles 4 and 7 used in the oxidation of sulfides to sulfoxides.
In the first cycle, it is thought that the catalytic activity and
selectivity of both catalysts are comparable. Using nanocatalysts 4
and 7, the oxidation of methylphenyl, diethyl, diphenyl and
ethylphenyl sulfide resulted in the formation of corresponding
sulfoxides in good yields (60ꢀ99%) and selectivities (90ꢀ100%).
Control experiments indicated that no oxidation occurred in the
absence of either nanocatalysts or oxidant. In addition, the use of
Fe3O4@SiO2 (2) or Fe3O4@SiO2ꢀNH2 (3) nanoparticles in place of
nanoparticles 4 and 7 did not promote oxidation.
In the case of dioctyl sulfide, both catalysts mutually showed a
reduced activity with respect to the conversion of substrate (Table 2,
entries 20 and 21). However, although these two nanocatalysts
exhibited high catalytic performance in the first use, each
nanocatalyst demonstrated clearly different stability and recyclability
results. As summarized in Table 2, the Fe3O4@SiO2ꢀNH2ꢀMo
nanoparticle (4) lost its catalytic activity completely at the second
catalytic cycle. In contrary, even after five successive usages, the
Fe3O4@SiO2ꢀSBꢀMo nanoparticle (7) retained its catalytic activity
as well as its magnetic property. These results indicate the higher
stability of the Schiff base containing Fe3O4@SiO2ꢀSBꢀMo compare
with the Fe3O4@SiO2ꢀNH2ꢀMo nanoparticles. We believe that the
formation of Schiff base on the surface of MNPs resulted in the
higher chelating ability of ligand and, of course, the higher stability
Fe3O4@SiO2ꢀSBꢀMo nanoparticles.
6
7
8
9
10
diethyl sulfide
diethyl sulfide
diethyl sulfide
4
4
7
1
2
1
75
ꢀ
99
90
ꢀ
100
43
ꢀ
57
11
diethyl sulfide
7
2
99
100
57
12
13
14
15
16
17
diethyl sulfide
diethyl sulfide
diphenyl sulfide
diphenyl sulfide
diphenyl sulfide
diphenyl sulfide
ethylphenyl
sulfide
ethylphenyl
sulfide
dioctyl sulfide
dioctyl sulfide
7
7
4
4
7
7
3
4
1
2
1
2
99
98
60
ꢀ
63
59
100
100
100
ꢀ
100
100
57
56
34
ꢀ
35
34
18
4
7
1
1
85
85
100
100
49
49
19
20
4
7
1
1
45
50
100
100
26
28
21
a
Reaction condition: sulfide (0.4 mmol), UHP (0.45 mmol), molybdenum
nanocatalyst (0.007 mmol), 0.5 mL CH2Cl2, 0.5 mL MeOH, room
temperature, 30 min.
b Determined by GC using chlorobenzene as an internal standard.
c
Determined by GC, Selectivity to sulfoxide = [sulfoxide %/(sulfoxide % +
sulfone %)] × 100.
Base on the previously reported study 33, we postulated a mechanism
for the oxidation of sulfides by nanocatalyst 7. The first step of the
mechanism involves the reaction between the molybdenum dioxo
complex and UHP oxidant to produce oxoꢀperoxo compound and
water. The nucleophilic attack of the sulfide on one oxygen atom of
the peroxo ligand, yielding sulfoxide and regenerating the
molybdenum(VI) dioxo complex, which reenters the cycle.
In order to evaluate the stability of Fe3O4@SiO2ꢀSBꢀMo (7)
nanocatalyst, after each catalytic reaction, the catalyst particles were
collected at the bottom of the test tube using a magnet, supernatant
carefully decanted and analyzed by ICPꢀOES analysis to determine
the amount of molybdenum leaching. ICPꢀOES analysis did not
show any leaching of molybdenum species into the solution. In
addition, hot filtration test was performed in which the heated
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H2O
HOOH
spectrophotometer. Measures of pH were carried out by a Mettler
Toledo S40 Seven MultiTM pHꢀmeter. Raman spectrum was
measured by Confocal depth profiling with True Focus BRUKER
(Germany) equipped with highꢀenergy laser diodes. Scanning
electron microscopy (SEM) was carried out on Philips XL30. The
TGA/DTA curves were determined using 851 Mettler Toledo
apparatus. The heating rate was 5 K/min. Xꢀray photoelectron
spectroscopy (XPS) was carried out by Dual anode (Mg and Al Kα)
a chromatic Xꢀray source. Magnetic measurement of materials was
investigated with a vibrating sample magnetometer VSM (4 inch,
Daghigh Meghnatis Kashan Co., Kashan, Iran) at room temperature.
Transmission electron microscopy (TEM) images were obtained on
an EM10C (Zeiss) transmission electron microscope at an
accelerating voltage of 80 kV. Samples dispersed in solution were
cast onto a carbonꢀcoated copper grid.
O
O
O
O
O
Mo
Mo
O
S
S
4.2. Preparation of MNPs(Fe3O4@SiO2-NH2) (3)
Scheme 2. The postulated mechanism for the oxidation of sulfides by
nanocatalyst 7 in the presence of UHP oxidant.
Fe3O4 (1) and Fe3O4@SiO2 (2) magnetic nanoparticles were prepared
according to the reported method.21The obtained Fe3O4@SiO2
nanoparticles were dried under vacuum and then modified with 3ꢀ
aminopropyltriethoxysilane (APTS).22
3. Conclusions
4.3. Synthesis of Fe3O4@SiO2-NH2-Mo nanocatalyst (4)
In summary, herein we report two methods for the immobilization of
molybdenum(VI) complex on silicaꢀcoated MNPs. The obtained
nanoparticles were characterized with various characterization
methods and employed as catalysts for the selective oxidation of
sulfides to corresponding sulfoxides using ureaꢀhydrogen peroxide
as the oxidant. The catalysts showed the similar catalytic activity but
different stability and recyclability. Immobilization of Mo(VI)
complex on the MNPs trough the Schiff base ligand resulted in the
formation of nanocatalyst that could be recycle more than four times.
In contrary, the immobilization through the amino propyl linkage did
not lead to the formation of a highly stable and fully recyclable
1 g of Fe3O4@SiO2ꢀNH2 (3) was suspended in CH2Cl2 (50 mL).
Then, MoO2Cl2(DMSO)2 (0.7 mmol) in 15 mL CH2Cl2 was added
and the mixture was stirred for 24 h under a nitrogen atmosphere.
After separation with an external magnet, the product was washed
with CH2Cl2 to remove unreacted molybdenum precursor.
4.4. Synthesis of 1,2-bis(2-formylphenoxymethyl)benzene (5)
Sodium salt of 2ꢀhydroxybenzaldehyde was prepared by adding
solution of NaOH (6.25 mmol in 20mL water) to a solution of
salicaldehyde (6.25 mmol) in 25 mL of ethanol and stirring at 60 ºC
for 30 min. To this, a solution of 1,2ꢀbis(bromomethyl)benzene
(0.822 g, 3.125 mmol) in EtOH (20 mL) was added and refluxed For
24 h. The solution was cooled and the solid product was filtered off
and recrystallized from acetonitrile.34 Yield: 0.629 g (58%). m.p. 114
nanocatalyst
.
4. Experimental section
1
°C; HNMR (90 MHz, CDCl3): 5.26 ppm (s, 4H, CH2), 7.05ꢀ7.98
ppm (m, 12H, ArH), 10.41ppm (s, 2H, CHO); 13CNMR (90 MHz,
CDCl3): 188.5, 160, 135.5, 133.9, 128.8, 128.5, 124, 120, 112, 68
ppm.
4.1. Materials
Tetraethoxysilane (TEOS), 3ꢀaminopropyltriethoxysilane (APTS), 2ꢀ
hydroxybenzaldehyde,
1,2ꢀbis(bromomethyl)benzene
were
4.5. Synthesis of Fe3O4@SiO2-SB (6)
purchased from Aldrich. All commercially available solvents and
tested compounds were of analyticalꢀreagent grade and used without
further purification.
Fe3O4@SiO2ꢀNH2 (3) was suspended in 100 mL of methanol with
sonication. 1,2ꢀbis(2ꢀformylphenoxymethyl)benzene (5) (0.8 mmol)
was added to this mixture and the resulted mixture was refluxed for
24 h. The resultant solid was separated magnetically and then
washed with methanol several times to remove the unreacted residue
of the dialdehyde and dried under vacuum at 303 K.
4.2. Characterization methods
Gas chromatographic (GC) analyses were performed on an Agilent
Technology 6890N, 19019Jꢀ413 HPꢀ5, 5% phenyl methyl siloxane,
capillary 60m×250mm×1mm. Elemental analyses (C, H, and N)
were performed using a Heraeus Elemental Analyzer CHNꢀOꢀRapid
(ElementarꢀAnalysesystem, GmbH). IR spectra were recorded as
KBr pellets using a Perkin Elmer Spectrum Version 10.01.00
4.6. Synthesis of Fe3O4@SiO2-SB-Mo nanocatalyst (7)
For the preparation of Mo(VI) nanocatalyst, MoO2Cl2(DMSO)2 (1
mmol) was dissolved in CH2Cl2 (50 mL). 1 g of Fe3O4@SiO2ꢀSB (6)
This journal is © The Royal Society of Chemistry 2012
RSC Advances., 2012, 00, 1-3 | 7

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ARTICLE
DOI: 10.1039/C5RA08653A
was then added to this solution and stirred for 24 h under a nitrogen 11. C. Sanjaia, S. Kothana, P. Gonilb, S. Saesoob and W.
atmosphere. After separation with an external magnet, the product Sajomsang, Carbohydr. Polym., 2014, 104, 231ꢀ237.
was washed with CH2Cl2 to remove unreacted molybdenum 12. J.M. Montenegro, V. Grazu, A. Sukhanova, S. Agarwal, J.M.
precursor.
Fuente, I. Nabiev, A. Greiner and W.J. Parak, Adv. Drug Deliv.
Rev., 2013, 65, 677ꢀ688.
4.7. General conditions for catalytic oxidation of sulfides
13. Q.L. Jiang, S.W. Zheng, R.Y. Hong, S.M. Deng, L. Guo, R.L.
Hu, B. Gao, M. Huang, L.F. Cheng, G.H. Liu and Y.Q. Wang,
Appl. Surf. Sci., 2014, 307, 224ꢀ233.
14. J. Si and H. Yang, Mater. Chem. Phys., 2011, 128, 519ꢀ524.
15. M. Khosroshahi and L. Ghazanfari, Mater. Sci. Eng. C, 2012, 32,
1043ꢀ1049.
16. S. Campelj, D. Makovec and M. Drofenik, J. Magn. Magn.
Mater., 2009, 321, 1346ꢀ1350.
17. X. Peng, Y. Wang, X. Tang and W. Liu, Dyes Pigm., 2011, 91,
26ꢀ32.
18. L. Wang, Y. Sun, J. Wang, J. Wang, A. Yu, H. Zhang and D.
Song, Colloids Surf. B, 2011, 84, 484ꢀ490.
19. M. MasteriꢀFarahani and Z. Kashef, J. Magn. Magn. Mater.,
2012, 324, 1431ꢀ1434.
20. M. Esmaeilpour, A.R. Sardariana and J. Javidi. Appl. Catal., A,
2012, 445, 359ꢀ367.
A typical reaction using the Mo(VI) nanocatalyst and sulfides is
described as follows: Chlorobenzene (40 mL, 0.4 mmol) as the
internal standard and nanocatalyst 7 (0.01 g, 0.007 mmol of
molybdenum complex) were added to a solution of sulfide (0.4
mmol) in (1:1) a mixture of CH3OHꢀCH2Cl2 (1 mL), then UHP
(0.042 g, 0.45 mmol) as the oxidant was added to the resulting
mixture and stirred at room temperature for 30 min. The
nanocatalyst was separated using a magnetic field and the formation
of products was monitored by GC. To clearly carry out the identity
of the products, the retention times and spectral data of the products
were compared with those of commercially available sulfoxides and
sulfones. At the end of reaction, the catalyst particles were washed
with methanol and DCM for several times, were dried in vacuum
and could be reused.22
21. M. Bagherzadeh, M.M. Haghdoost and A. Shahbazirad, J.
Coord. Chem., 2012, 65, 591ꢀ601.
Acknowledgements
22. M. Bagherzadeh, M.M. Haghdoost, F. MatlobiꢀMoghaddam, B.
KoushkiꢀForoushani, S. Sarazdi and E. Payab, J. Coord. Chem.,
2013, 66, 3025ꢀ2036.
23. M.Z. Kassaee, H. Masrouri and F. Movahedi, Appl. Catal. A,
2011, 395, 28ꢀ33.
We are grateful to the Faculty of Chemistry of BuꢀAli Sina
University for financial support. We also acknowledge the Research
Council of Sharif University of Technology for research funding of
this project.
24. M. MasteriꢀFarahani and N. Tayyebi. J. Mol. Catal. A: Chem.,
2011, 348, 83ꢀ87.
Notes
25. C.I. Fernandes, M.D. Carvalho, L.P. Ferreira, C.D. Nunes and
P.D. Vaz, J. Organomet. Chem., 2014, 760, 2ꢀ10.
26. S. Shylesh, J. Schweizer, S. Demeshko, V. Schꢀnemann, S. Ernst
and W.R. Thiel, Adv. Synth. Catal., 2009, 351, 1789ꢀ1795.
27. Z. Li, C. Chen, E. Zhan, N. Ta, Y. Li and W. Shen, Chem.
Commun., 2014, 50, 4469ꢀ4471.
aChemistry Department, BuꢀAli Sina University, Hamedan Department of
Chemistry, BuꢀAli Sina University, Hamadan. Eꢀmail:haskey1@yahoo.com
bChemistry Department, Sharif University of Technology, Tehran, Iran
Email:bagherzadeh@sharif.edu
.
28. L. Barrui, J.M. CamposꢀMartín, M.P. de Frutos and J.L.G.
Fierro, Ind. Eng. Chem. Res. 2008, 47, 8016ꢀ8024
29. C. Guo, Y. Hu, H. Qian, J. Ning and S. Xu, Mater. Charact.,
2011, 62, 148 .
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