Mild and highly efficient method for the oxidation of sulfides and oxidative coupling of thiols catalyzed by Fe3O4@MCM-41@VO-SPATB as efficient and magnetically recoverable nanocatalyst

Article abstract of DOI:10.1007/s13738-018-1536-3

The use of oxo vanadium complex with s-propyl-2-aminobenzothioate ligand immobilized onto functionalized magnetic nanoporous MCM-41(Fe₃O₄@MCM-41@VO-SPATB) as efficient and magnetically recoverable nanocatalyst for oxidation of sulfides into sulfoxides and oxidative coupling of thiols into disulfides using H₂O₂ as green oxidant is presented. This method provides much improved modification of oxidation reactions in terms of mild reaction conditions, short reaction time and good-to-excellent yields of products. Another important feature of this method is the ability to reuse the magnetite nanocatalyst for several times with no loss of its catalytic activity.

Full text of DOI:10.1007/s13738-018-1536-3

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1536-3
ORIGINAL PAPER
Mild and highly efficient method for the oxidation of sulfides
and oxidative coupling of thiols catalyzed by Fe O @MCM-41@VO-
3
4
SPATB as efficient and magnetically recoverable nanocatalyst
Mohsen Nikoorazm1 · Farshid Ghorbani · Arash Ghorbani‑Choghamarani · Zahra Erfani
2
1
1
Received: 25 May 2018 / Accepted: 22 October 2018
©
Iranian Chemical Society 2018
Abstract
The use of oxo vanadium complex with s-propyl-2-aminobenzothioate ligand immobilized onto functionalized magnetic
nanoporous MCM-41(Fe O @MCM-41@VO-SPATB) as efficient and magnetically recoverable nanocatalyst for oxidation
3
4
of sulfides into sulfoxides and oxidative coupling of thiols into disulfides using H O as green oxidant is presented. This
2
2
method provides much improved modification of oxidation reactions in terms of mild reaction conditions, short reaction
time and good-to-excellent yields of products. Another important feature of this method is the ability to reuse the magnetite
nanocatalyst for several times with no loss of its catalytic activity.
Keywords Fe O @MCM-41@VO-SPATB · Sulfoxides · Disulfides · Oxidation · Magnetic
3
4
Introduction
to the mesoporous molecular sieve family, consisting of a
hexagonal array of unidirectional pore structures with high
surface area, high pore volume, excellent thermal, chemi-
cal, and mechanical stability which are ideal to use as sup-
port [10–14]. Magnetic nanoparticles (MNPs) have recently
appeared as a new type of catalyst support because of being
simple in synthesis, high surface area, facile recovery and
recyclability via magnetic force, low toxicity and possibly
low cost [15]. Among different magnetic nanoparticles as
the magnetic support, Fe O nanoparticles are surely the
Oxo vanadium complexes have been extensively studied
because of their potential applicability as catalyst or media-
tors for thiocyanation of organic compounds [1], synthesis
of 4,4′-(arylmethylene) bis (3-methyl-1-phenyl-1H-pyrazol-
5
-ols) [2], oxidation of hydrocarbons [3] and oxidation of
organic sulfides to sulfoxides [4, 5]. Some of these catalytic
systems operate in liquid media, whereas others involve VO-
catalysts immobilized on insoluble supports. Immobiliza-
tion of homogeneous catalysts on various insoluble supports
with the advantage of catalysts separation and recycling is
of great importance in catalyst science, because the reac-
tions are carried out under mild conditions and the products
are easily isolated [6–8]. However, immobilization strategy
usually decreases the catalytic activity or selectivity [9].
This drawback could be solved using nanomaterials as ideal
solid supports such as mesoporpus silica, especially MCM-
3
4
most extensively studied. In recent years, the consolidation
of functionalized mesoporous silica with magnetic nano-
particles (NPs) to form porous magnetic nanostructures has
undoubtedly gained much interest for practical applications
such as catalytic applications, for sensors, magnetic stor-
age and recording, environmental, and biomedical appli-
cations [13, 16]. This type of magnetic nanostructures has
the advantage and properties of both mesoporous silica and
magnetic nanoparticles by which magnetic separation via
magnetic force provides a proper and low-cost method for
separation and recovery of these magnetic catalysts in a
multiphase suspension without using extra organic solvents,
additional filtration steps and tedious work-up [17, 18].
The selective oxidation of organosulfur compounds such
as sulfides and thiols into their corresponding sulfoxides and
disulfides is of great importance in synthesis of new prod-
ucts, biological and industry [9]. In particular, sulfoxides are
4
1 and magnetic nanoparticles (MNPs). MCM-41 belongs
*
Mohsen Nikoorazm
e_nikoorazm@yahoo.com
1
2
Department of Chemistry, Faculty of Science, Ilam
University, Ilam, P. O. Box 69315516, Iran
Department of Environment, Faculty of Natural Resource,
University of Kurdistan, Sanandaj 66177-15177, Iran
Vol.:(0
1
123456789)
3

Journal of the Iranian Chemical Society
fine chemicals, pharmaceuticals and versatile intermediates
for synthesis of many drugs, vitamins and biologically active
products including therapeutic agents such as antibacterial,
antiulcer, antifungal, antihypertensive, and antiatheroscle-
rotic, as well as psychotropic and vasodilators [19–21].
Likewise, disulfides are a very useful class of organochal-
cogenium compounds with biological and industrial appli-
cations including DNA cleavage, stabilization of peptides
in proteins, combinatorial synthesis, vulcanizing agents for
rubbers and elastomers, in the design of rechargeable lithium
batteries and serve as versatile reagents in organic synthe-
sis [22]. Therefore in this study, we intend to combine the
advantages of Fe O nanoparticles with mesoporous MCM-
10 mL of deionized water under nitrogen atmosphere. The
resulting solution was added drop-wise to 100 mL of 1.0 mol
−
1
L
NH .H O solution containing 0.4 g of cetyltrimethyl-
3 2
ammonium bromide (CTAB) under sonication and nitrogen
atmosphere with continuous stirring for 30 min, the black
precipitate (Fe O nanoparticles) was isolated by magnetic
3
4
decantation, washed thoroughly with deionized water, and
finally dried at 80 °C under vacuum. For the preparation of
core–shell structured Fe O @MCM-41, 0.5 g of the mag-
3
4
netic Fe O nanoparticles were ultrasonically dispersed in
3
4
ethanol (20 mL) for 30 min. Then, the suspension was cen-
trifuged and the solid was redispersed in a solution mix-
ture of deionized water (10 mL), ethanol (20 mL), and NH
3
4
3
4
1 to form magnetic Fe O core/mesoporous MCM-41 shell
(0.5 mL). The system was kept under vigorous mechanical
stirring for 30 min, and then tetraethylorthosilicate (TEOS)
(0.03 g) was added drop-wise. Subsequently the mixture
was kept under well-mixed conditions at room temperature
for 6 h. The coated nanoparticles (Fe O @nSiO ) were col-
3
4
(
Fe O @ MCM-41) as useful and versatile solid support
3 4
for oxo vanadium complex as a simple, green and efficient
heterogeneous catalyst for the oxidation of sulfides and oxi-
dative coupling of thiols using H O as green oxidant under
2
2
3
4
2
neat conditions at room temperature.
lected by magnetic separation, washed with ethanol and
deionized water for several times. Then, the coated Fe O @
3
4
nSiO nanoparticles were dispersed in a solution composed
2
Experimental
of ethanol (30 mL), deionized water (40 mL), NH (0.6 mL)
3
and CTAB (0.15 g). After mechanical stirring at room tem-
perature for 30 min, 0.4 g of TEOS was added drop-wise to
the solution and kept under stirring at room temperature for
6 h. The solid products were separated, washed with plenty
of ethanol/deionized water and dried in a vacuum oven at
80 °C for 12 h. Finally, to remove organic template CTAB,
Materials and techniques
Solvents and all starting materials were purchased with
high purity from Sigma-Aldrich, Merck or Flucka Chemi-
cal Companies.
−
1
Crystalline structure of synthesized samples identi-
fied using a Holland Philips X’pert X-ray powder diffrac-
tion (XRD) diffractometer, with monochromatized Cu Ka
radiation under the conditions of 40 kV and 30 mA. TGA
measurement was recorded between 30 and 800 °C using
Shimadzu DTG-60 automatic thermal analyzer. Fourier
transform infrared (FT-IR) spectra were recorded on KBr
pellets on FT-IR spectrophotometer (Bruker, Germany) Ver-
ethanol(100 ml) and 2 mol L HCl (5 ml) were added to
0.1 g of obtained product, then the mixture was kept under
mechanical stirring at room temperature, for 48 h. The solid
products were separated by magnetic separation, and dried
in a vacuum oven at 80 °C for 24 h [23].
Functionalization of the magnetic mesoporous silica
with MPTMS
−
1
tex 70 in the range of 400–4000 cm . The morphology of
the catalyst was obtained using SEM with FESEM-TESCAN
MIRA3, and also transmission electron microscopy (TEM)
analysis was recorded using a Zeiss-EM10C TEM. Vibrating
sample magnetometer (VSM) measurements were performed
using a vibrating sample magnetometer (VSM) MDKFD.
The content of vanadium was measured using inductively
coupled plasma-optical emission spectrometry (ICP-OES).
The modification of Fe O @MCM-41 with (3-mercaptopro-
3
4
pyl) trimethoxysilane (MPTMS) was performed by refluxing
4.8 g of Fe O @MCM-41and 4.8 g MPTMS in n-Hexane
3
4
for 24 h. The resulting solid of the functionalized Fe O @
3
4
MCM-41 (Fe O @MCM-41@npr-SH) was collected by
3
4
magnetic separation, washed with n-hexane and dried under
vacuum.
Preparation of Fe O @MCM‑41@VO‑SPATB
3
4
Preparation of catalyst
For the preparation of Fe O @MCM-41@VO-SPATB,
3
4
Preparation of Fe O @MCM‑41
a solution of isatoic anhydride (1.2 mmol) in ethanol was
3
4
added to 0.5 g of functionalized Fe O @MCM-41. The
3
4
Initially, the magnetic Fe O cores were prepared using
obtained solution mixture was refluxed for 3 h. The result-
ing solid was collected by magnetic separation, washed with
ethanol and dried under vacuum and designated as Fe O @
3
4
chemical coprecipitation method. Typically, FeCl ·4H O
2
2
(
0.8 g) and FeCl ·6H O (2 g) were completely dissolved in
3 2
3
4
1
3

Journal of the Iranian Chemical Society
MCM-41@SPATB. Ultimately, VO (acac) (0.168 g) was
Results and discussion
2
added to 0.250 g Fe O @MCM-41@SPATB in ethanol
3
4
(
20 mL) and stirred at 80 °C for 24 h under reflux conditions.
Characterization of Fe O @MCM‑41@VO‑SPATB
3
4
The resulting product was separated by magnet, and washed
with ethanol and dried in vacuum (Scheme 1).
The structure of prepared catalyst was studied and fully char-
acterized by FT-IR, XRD, EDS SEM, VSM, TEM, ICP-
OES, and TGA analysis.
General procedure for the oxidation of sulfides
to sulfoxides
The morphology of the Fe O @MCM-41 and Fe O @
3
4
3
4
MCM-41@VO-SPATB were obtained using scanning elec-
tron microscopy (SEM) technique (Fig. 1). As shown in
these images, the Fe O @MCM-41 and Fe O @MCM-41@
A mixture of Fe O @MCM-41@VO-SPATB (10 mg),
3
4
sulfide (1 mmol) and 33% H O (0.4 mL) was stirred at
2
2
3
4
3
4
ambient temperature under solvent-free conditions for the
specified time, and the progress of the reaction was moni-
tored by thin-layer chromatography (TLC). After completion
of the reaction, water was added to the reaction mixture, the
catalyst was separated by an external magnet and the product
was extracted with ethyl acetate (3×10 mL), and then dried
over anhydrous Na SO (1.5 g). Finally organic solvent was
VO-SPATB materials were composed of nearly spherical
agglomerations composed of regular uniform nanoparticles.
The energy dispersive spectrum (EDS) evidently shows
the presence of V, Fe, Si, O, N, S, and C species in the cata-
lyst (Fig. 2). Also, to determine the exact amount of vana-
dium loaded on Fe O @MCM-41, ICP-OES analysis was
3
4
performed; the vanadium amount of the immobilized cata-
2
4
−
1
evaporated, and sulfoxides were obtained in good-to-high
yields.
lyst on Fe O @MCM-41 was found to be 0.37 mmol g .
3 4
The X-ray diffraction analysis (XRD) patterns of Fe O @
3
4
MCM-41 and Fe O @MCM-41@VO-SPATB are shown
3
4
General procedure for the oxidative coupling
of thiols into disulfides
in Fig. 3. As seen from the small-angle XRD patterns in
Fig. 3a, the XRD pattern of Fe O @MCM-41 shows three
3
4
characteristic peaks (an intense diffraction peak at 2θ=2.36°
A mixture of thiol (1 mmol), 33% H O (0.4 mL) and
for d plane) together with an additional peak (at 2θ=3.94°
2
2
100
Fe O @MCM-41@VO-SPATB (10 mg) in ethanol (3 mL)
for d plane) and a very weak peak (at 2θ=4.36° for d
200
3
4
110
was stirred for the specified time at ambient temperature (the
progress of reaction was monitored by TLC). After comple-
tion of the reaction, the catalyst was separated by apply-
ing an external magnet and the product was washed with
ethyl acetate, and then dried over anhydrous Na SO (1.5 g).
plane) respectively, typically confirming the presence of
ordered hexagonal mesoporous structure of MCM-41. Com-
parison of X-ray powder diffraction patterns of Fe O @
3
4
MCM-41 and Fe O @MCM-41@VO-SPATB shows when
3
4
the vanadyl ions are coordinate to the Fe O @MCM-41, the
2
4
3
4
Finally, Evaporation of the solvent gave the disulfides in
very high isolated yields.
intensity of the main peaks was decreased; these observa-
tions are due to the increase in vanadyl ions in the pores
Scheme 1 Synthesis of Fe O @
OH OH OHOH
OH
OH
3
4
MCM-41@VO-SPATB
FeCl .6H O NH OH, CTAB
EtOH
MCM-41
Fe O
3
2
4
NH3
CTAB
TEOS
3
4
N
2
atmosphere
Deionized water
FeCl .6H O
2
2
Magnetic Fe O
Fe
3
O
4
@MCM-41
3
4
S
M
OH
V
T
P
NH
2
N
2
M
S
S
O
O
O
O
NH2 NH2S
SH
SH
Si
S
Si
Si
OOO
MCM-41
Si
O
O
O
Si
OOO
Si
OOO
OOO
HN
OOO
MCM-41
Fe O
OOO
MCM-41
VO(acac)2
Fe O
Fe O
3
4
3
4
3
4
3 4
Fe O @MCM-41@VO-SPATB
1
3

Journal of the Iranian Chemical Society
Fig. 1 a SEM images of Fe O @MCM-41 and b Fe O @MCM-41@VO-SPATB
3
4
3
4
and interaction with the framework of Fe O @MCM-41
3
4
[
24]. As seen from the high-angle XRD patterns in Fig. 3b,
the characteristic peaks at 2θ=30.31°, 35.6°, 43.2°, 54.1°,
7.25°, and 62.95° which are in good agreement with the
5
standard Fe O XRD spectrum and shows that catalyst had
3
4
been successfully synthesized [25]. The broad peck appeared
in around 2θ=20–30° is related to amorphous silica [26].
Figure 4 shows FT-IR spectra of (a) Fe O (b) Fe O @
3
4
3
4
MCM-41(c) Fe O @MCM-41@nPr-SH (d) Fe O @MCM-
3
4
3
4
4
1@SPATB and (e) Fe O @MCM-41@VO-SPATB, respec-
3 4
tively. Spectrum (a) shows the strong absorptions near
−
1
−1
5
79 and 444 cm and 3000–3500 cm due to Fe–O and
O–H stretching vibrations, for the Fe O @MCM-41 sam-
3
4
−
1
ple. (spectrum b) three characteristic peaks at 460 cm
,
−
1
−1
9
58 cm and 1081 cm corresponding to bending, sym-
metric stretching, and asymmetric stretching, Si–O–Si vibra-
−
1
Fig. 2 The EDS spectrum of Fe O @MCM-41@VO-SPATB
tions, respectively. Also the peak at 3445 cm is due to the
3
4
Fig. 3 XRD patterns of a low
angle and b high angle of
Fe O @MCM-41 and Fe O @
3
4
3
4
MCM-41@VO-SPATB
1
3

Journal of the Iranian Chemical Society
stretching vibrating absorption of O–H band in the surfaced
hydroxyl groups. Immobilization of MPTMS on the sur-
face of Fe O @MCM-41 was indicated by the appearance
3
4
−
1
of two peaks at 2981 and 2936 cm , assigned to the C–H
stretching vibrations, also S-H stretch band in the spec-
−
1
tra of Fe O @MCM-41@nPr-SH is found at 2550 cm
3
4
which is very weak. In the spectra of Fe O @MCM-41@
3
4
SPATB, C-N stretching frequency is present in the region
−
1
1
380–1412 cm , also presence of carbonyl group is indi-
−
1
cated by the 1623 cm band in its FT-IR spectrum (Fig. 5d).
Figure 5e shows the FT-IR spectrum after covalent bonding
of vanadyl ions onto Fe O @MCM-41@SPATB, the char-
3
4
−
1
acteristic V=O stretching frequency appears at 980 cm ,
−
1
within the range of 970–997 cm reported for similar oxo
vanadium (IV) complexes [27].
The TEM images of the Fe O @MCM-41@VO-SPATB
3
4
are shown in Fig. 5. It can be seen that the catalyst was
formed of nanometer-sized particles. The TEM micrograph
showed agglomeration of many ultrafine sphere-like parti-
cles which display dark magnetite cores surrounded by a
mesoporous shell.
The magnetic properties of Fe O @MCM-41 (a) and
3
4
Fe O @MCM-41@VO-SPATB (b) are demonstrated from
3
4
VSM data (Fig. 6). VSM value for Fe O @MCM-41nano-
3
4
Fig. 4 FT-IR spectra of a Fe O , b Fe O @MCM-41, c Fe O @
3
4
3
4
3
3
4
4
−1
particles (13.02 emu g ) is higher than Fe O @MCM-41@
MCM-41@nPr-SH, d Fe O @MCM-41@SPATB and e Fe O @
3
4
3
4
−
1
MCM-41@VO-SPATB
VO-SPATB (10.23 emu g ). Decrease in magnetic prop-
erty of Fe O @MCM-41@VO-SPATB is due to the graft-
3
4
ing of organic layers including oxo vanadium complex on
Fe O @MCM-41 nanoparticles. These results indicate the
3
4
Fig. 5 TEM images of Fe O @
3
4
MCM-41@VO-SPATB catalyst
at different magnifications
1
3

Journal of the Iranian Chemical Society
grafting of oxo vanadium complex on the Fe O @MCM-41
3
4
is verified.
The thermal stability of Fe O @MCM-41 and Fe O @
3
4
3
4
MCM-41@VO-SPATB was studied by thermogravimetric
analysis (TGA) (Fig. 7). The thermogravimetric analysis
curves of the synthesized Fe O @MCM-41 shows about 3%
3
4
weight loss in one step at between 25 and 100 °C due to des-
orption of water. The three steps of weight losses at below
2
50, 250–450 and 450–800 °C in TGA curve of Fe O @
3 4
MCM-41@VO-SPATB sample may be associated to the
removal of physically adsorbed water and solvent inside the
pores channels, the decomposition of immobilized organic
moieties on the Fe O @MCM-41@VO-SPATB surface and
3
4
condensation of the silanol groups, respectively.
Fig. 6 Magnetic curves of a Fe O @MCM-41 and b Fe O @MCM-
3
4
3
4
4
1@VO-SPATB
Catalytic studies
After full characterization of the catalyst structure, in the
present work we wish to describe a highly efficient and sim-
ple method for the oxidation of sulfides to sulfoxides and
oxidative coupling of thiols into disulfides using hydrogen
peroxide in the present of these catalysts.
To achieve suitable conditions for oxidation of sulfide
to sulfoxide, a series of experiments were performed with
the variation of amount of catalyst, amount of oxidant and
solvent system for oxidation of methyl phenyl sulfide as a
model reaction (Table 1). When the model reaction was car-
ried out in the absence of catalyst under solvent-free con-
ditions, the reaction is incomplete even after 8 h (Table 1,
entry 1) and an excellent yield of the product (98%) was
obtained in the presence of (10 mg, 0.37 mol%) of catalyst
in 45 min (Table 1, entry 2). In the next step in the optimi-
zation study, the model reaction was performed in different
solvents such as ethanol, water, acetonitrile, ethyl acetate,
dichloromethane and also solvent-free conditions (Table 1,
Fig. 7 TGA thermograms of Fe O @MCM-41 and Fe O @MCM-
3
4
3
4
4
1@VO-SPATB
Table 1 Optimization of
Yield (%)a
Entry
Amount of cata- Solvent
lyst (mg)
Amount of oxi-
dant (mL)
Time (min)
oxidation of sulfides to the
corresponding sulfoxides using
Fe O @MCM-41@VO-SPATB
3
4
1
2
3
4
5
6
7
8
9
None
10
10
10
10
10
10
8
Solvent free
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.4
8 h
45
45
45
45
45
45
45
45
45
Trace
98
75
90
84
86
35
92
82
under various conditions
Solvent free
Dichloromethane
Acetonitrile
Ethyl acetate
Ethanol
Water
Solvent free
Solvent free
Solvent free
6
10
1
0
90
Reaction conditions: Methyl phenyl sulfide (1 mmol), H O (0.5 mL) and catalyst (10 mg, 0.37 mol %)
2
2
under solvent-free condition at room temperature
Isolated yield
a
1
3

Journal of the Iranian Chemical Society
entries 2–7). As the result shows, the reaction under solvent-
free conditions leads to the formation of product in higher
yield after shorter reaction time. Finally, the reaction was
performed using different amounts of H O , as shown in
diversely substituted sulfides was tested for oxidation under
the optimized condition and the results are summarized
in Table 2. As it was shown, both aliphatic and aromatic
sulfides were successfully oxidixed to the corresponding
sulfoxides in high yields with excellent chemoselectivity.
In the oxidation of thiols, to find optimal reaction condi-
tions, 4-methylthiophenol was selected as model substrate
and influence of various reaction parameters such as sub-
strate oxidant ratio, nature of the solvent and catalyst amount
have been studied (Table 3). Among the different solvents
listed in Table 3, ethanol was chosen as the best solvent
2
2
Table 1, in the synthesis methylphenyl sulfoxide, the best
results were obtained when the (10 mg, 0.37 mol%) Fe O @
3
4
MCM-41@VO-SPATB catalyst and 0.5 ml of hydrogen
peroxide was used under solvent-free conditions at room
temperature.
After optimization of the reaction conditions, to deter-
mine the efficiency and the scope of this method, a series of
Table 2 Oxidation of various sulfides to sulfoxides
O
Fe O @MCM-41@VO-SPATB
3
4
S
S
R1
R2
R1
R2
solvent-free, r.t.
Entry
R1
R2
PhCH2
CH CH CH
Time (min)
Yield (%)a
M. P. (°C) [Refs.]
1
2
3
4
5
6
7
8
9
PhCH2
CH CH CH
Ph
CH CHCH
Ph
Tetrahydrothiophene
P-Me-Ph
PhCH2
60
20
20
10
45
5
45
360
240
10
96
94
93
94
98
96
94
90
86
93
133–135 [28]
Oil [9]
Oil [9]
Oil [29]
30–32 [9]
Oil [30]
121–122 [9]
115–117 [31]
87–89 [32]
Oil [22]
3
2
2
3
2
2
CH CH OH
2
2
Me
Me
–
Me
Ph
2
2
C H
C H
1
2
25
12 25
1
0
CH CH
CH ·CH
3 2
3
2
Reaction conditions: substrate (1 mmol), H O (0.5 mL) and catalyst (10 mg, 0.37 mol%) under solvent-free conditions at room temperature
2
2
a
Isolated yield
Table 3 Comparison between
various conditions for
Yield (%)a
Entry
Amount of cata- Amount of oxi-
Solvent
Time (min)
lyst (mg)
dant (mL)
the oxidative coupling of
4
-methylthiophenol in 20 min at
1
2
3
4
5
6
7
8
9
None
12
10
8
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.4
Ethanol
Ethanol
Ethanol
Ethanol
n-Hexane
Dichloromethane
Acetonitrile
Water
Ethyl acetate
Ethanol
8 h
20
20
20
20
20
20
20
20
20
Trace
96
96
90
91
85
86
75
93
room temperature
10
10
10
10
10
10
1
0
78
Reaction conditions: 4-methylthiophenol (1 mmol), H O (0.5 mL) and catalyst (10 mg, 0.37 mol%) in
2
2
EtOH (3 mL) at room temperature
Isolated yield
a
1
3

Journal of the Iranian Chemical Society
due to the high yield and shorter reaction time (Table 3,
entry 2). To investigate the effect of different amounts of
H O the reaction was performed using different amounts
in oxidation of sulfides and 4-methylthiophenol in oxidative
coupling of thiol reaction. After each catalytic cycle, cata-
lyst was separated by an external magnetic field and reused
for subsequent experiments after washing with ethyl acetate
to remove residual product. The results for seven catalytic
cycles without significant loss of catalytic activity and with
excellent yields are shown in Fig. 8.
2
2,
of H O and the results showed that 0.5 mL of H O is the
2
2,
2
2
best. Finally, the effect of catalyst amount on the outcome of
the reaction was also evaluated, the best result was obtained
with (10 mg, 0.37 mol%) of catalyst. After optimizing the
reaction conditions, a variety of thiols including aromatic
thiols, aliphatic thiols, benzilic thiol and heteroaromatic
thiols including other functional groups such as alkyl, hal-
ide, carboxylic acid, and hydroxyl groups converted into
corresponding disulfides using H O and catalytic amounts
To investigate the efficiency of Fe O @MCM-41@VO-
3
4
SPATB nanocatalyst in comparison with the previously
reported procedures in the literature, we provide the results
of the oxidation of the methyl phenyl sulfide and oxidative
coupling of 4-methylthiophenol with various catalysts. As
2
2
of Fe O @MCM-41@VO-SPATB in ethanol with good to
3
4
excellent yields (Table 4). 2-Hydroxyethylthiol gave only
bis(2-hydroxyethyl) disulfide (Table 4, entry 7). Interestingly
primary hydroxyl group in this substrate remained intact
during the oxidation reaction. Also, other substrates such as
entries 3, 4 (Table 4) have 2 or more oxidizable positions.
This results shows that the mercapto group in the presence
of another oxidizable group was selectively oxidized by this
procedure.
Recyclability of the catalyst
The reusability of magnetic catalysts is one of their most
important advantages in green chemistry and heterogeneous
catalysis, making them useful for commercial applications.
Fig. 8 Reusability of Fe O @MCM-41@VO-SPATB in the oxidation
3
4
In this study, the recyclability of Fe O @MCM-41@VO-
3
4
of methyl phenyl sulfide and oxidative coupling of 4- methylthiophe-
SPATB was studied in the reaction of methyl phenyl sulfide
nol
Table 4 Selective oxidative coupling of thiols to disulfides
Fe O @MCM-41@VO-SPATB
3
4
R3
S
3
R -SH
R3
S
EtOH, r.t.
Entry
R3
Time (min)
Yield (%)a
MP (°C) [Refs.]
1
2
3
4
5
6
7
8
9
PhCH2-
30
20
35
45
30
35
20
50
50
20
92
98
94
88
94
96
90
96
94
95
65–68 [33]
40–42 [30]
173–175 [30]
77–79 [34]
60–61 [34]
Oil [9]
p-MeC H –
6
4
2-Benzothiazole
2-Benzoxazole
Ph
–CH COOH
2
HOCH CH –
Oil [30]
2
2
2-COOHC H –
277–280 [9]
133–136 [9]
90–92 [30]
6
4
2-Naphthyl
p-BrC H –
1
0
6
4
Reaction conditions: substrate (1 mmol), H O (0.5 mL) and catalyst (10 mg, 0.37 mol%) in EtOH (3 mL) at room temperature
2
2
a
Isolated yield
1
3

Journal of the Iranian Chemical Society
Table 5 Comparison of Fe O @
3
4
Entry Substrate
Catalyst
Time (min) Yield (%) Refs.
MCM-41@VO-SPATB for
the oxidation of methyl phenyl
sulfide and oxidative coupling
of 4-methylthiophenol with
previously reported procedure
1
2
3
4
5
6
7
8
9
1
1
1
Methylphenylsulfide Fe O @MCM-41@VO-SPATB
45
300
120
270
300
210
20
98
98
96
93
95
93
98
99
99
96
93
97
This work
[35]
[36]
[37]
[38]
[39]
This work
[40]
3
4
Methylphenylsulfide Zr-oxide@MCM-41
Methylphenylsulfide VO-2A3HP-MCM-41
Methylphenylsulfide NBS
Methylphenylsulfide VO F(dmpz)
Methylphenylsulfide Thiourea dioxide/TBHP
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
2
2
Fe O @MCM-41@VO- SPATB
3
4
Fe O -Adenine-Zn
90
3
4
[bmim][SeO (OCH )]
Co-Salophen
NaI
120
180
1440
70
[41]
[42]
[43]
[44]
2
3
0
1
2
Fe O -adenine-Ni
3
4
presented in Table 5, the results of this research project
verified good reaction time and higher yield than the other
catalysts which have been reported previously. Furthermore,
compared with other catalysts, simple and inexpensive pro-
cedure, easy separation of the catalyst, low cost and non-
toxicity are advantages of this organometallic nanocatalyst.
2. M. Safaiee, M.A. Zolfigol, F. Derakhshan-Panah, V. Khakyzadeh,
L. Mohammadi, Croat. Chem. Acta 89(3), 317 (2016)
3
.
H. Hosseini Monfared, V. Abbasi, A. Rezaei, M. Ghorbanloo, A.
Aghaei, Transition Met. Chem. 37, 85 (2012)
4. A. Coletti, P. Galloni, A. Sartorel, V. Conte, B. Floris, Catal.
Today 192, 44 (2012)
5
.
M.A. Zolfigol, A. Khazaei, M. Safaiee, M. Mokhlesi, R. Rosta-
mian, M. Bagheri, M. Shiri, H.G. Kruger, J. Mol. Catal. A: Chem.
3
70, 80 (2013)
6
.
M. Nikoorazm, A. Ghorbani-Choghamarani, H. Mahdavi, S.
Esmaeili, Microporous Mesoporous Mater. 211, 174 (2015)
Conclusion
7. A. Ghorbani-Choghamarani, B. Tahmasbi, F. Arghand, S. Faryadi,
RSC Adv. 5, 92174 (2015)
8
9
.
.
L. Guanghua, W. Mai, R. Jin, L. Jao, Synlett. 9, 1418 (2008)
A. Ghorbani-Choghamarani, Z. Darvishnejad, B. Tahmasbi, Inorg.
Chim. Acta. 435, 223 (2015)
In summary, an environmentally friendly, efficient and mag-
netically recoverable Fe O @MCM-41@VO-SPATB nano-
3
4
catalyst was prepared and its structure was characterized by
FT-IR, SEM, TGA, VSM, EDS, TEM, ICP-OES and XRD
analysis techniques. In addition, catalytic activity of this
catalyst was examined for oxidation of sulfides to sulfoxide
under solvent-free conditions and oxidation of thiols to their
corresponding disulfides in ethanol with aqueous hydrogen
peroxide as oxidant at room temperature. It is notewor-
thy that this procedure includes the use of a commercially
available, waste-free process, cheap and chemically stabile
reagents, simplicity in operation, short reaction time and
high efficiency under relatively mild conditions. This sup-
ported magnetic nanoparticle can be easily recovered with
an external magnetic field and reused seven times before any
considerable decrease in its catalytic activity.
10. M. Nikoorazm, A. Ghorbani-Choghamarani, F. Ghorbani, H.
Mahdavi, Z. Karamshahi, J Porous Mater. 22, 261 (2015)
1
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Acknowledgements The authors gratefully acknowledge Ilam Uni-
versity Research Council for partial financial support of this research
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