Synthesis and characterization of oxo-vanadium complex anchored onto SBA-15 as a green, novel and reusable nanocatalyst for the oxidation of sulfides and oxidative coupling of thiols

Article abstract of DOI:10.1007/s11164-018-3367-3

Abstract: The present work describes the synthesis of a new oxo-vanadium complex immobilized on SBA-15 nanostructure as an efficient catalyst for oxidation of sulfides and oxidative coupling of thiols. Characterization of the resultant AMPD@SBA-15 nanostructure was performed by various physico-chemical techniques such as Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, energy-dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, thermal gravimetric analysis, and N₂ adsorption and desorption. The results of the developed procedure bring several benefits such as the use of commercially available, ecologically benign, operational simplicity, and cheap and chemically inert reagents. It shows good reaction times, practicability and high efficiency, and is easily recovered from the reaction mixture by simple filtration and reused for several consecutive cycles without noticeable change in its catalytic activity. More importantly, high efficiency, simple and an inexpensive procedure, commercially available materials, easy separation, and an eco-friendly procedure are the several advantages of the currently employed heterogeneous catalytic system.

Full text of DOI:10.1007/s11164-018-3367-3

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3367-3
Synthesis and characterization of oxo-vanadium
complex anchored onto SBA-15 as a green, novel
and reusable nanocatalyst for the oxidation of sulfides
and oxidative coupling of thiols
Taiebeh Tamoradi1 Mohammad Ghadermazi1
•
•
Arash Ghorbani-Choghamarani2 Somayeh Molaei1
•
Received: 4 December 2017 / Accepted: 1 March 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract The present work describes the synthesis of a new oxo-vanadium complex
immobilized on SBA-15 nanostructure as an efficient catalyst for oxidation of sulfides
and oxidative coupling of thiols. Characterization of the resultant AMPD@SBA-15
nanostructure was performed by various physico-chemical techniques such as Fourier
transform infrared spectroscopy, transmission and scanning electron microscopies,
energy-dispersive X-ray spectroscopy, inductively coupled plasma optical emission
spectroscopy, X-ray diffraction, thermal gravimetric analysis, and N2 adsorption and
desorption. The results of the developed procedure bring several benefits such as the use
of commercially available, ecologically benign, operational simplicity, and cheap and
chemically inert reagents. It shows good reaction times, practicability and high effi-
ciency, and is easily recovered from the reaction mixture by simple filtration and reused
for several consecutive cycles without noticeable change in its catalytic activity. More
importantly, high efficiency, simple and an inexpensive procedure, commercially
available materials, easy separation, and an eco-friendly procedure are the several
advantages of the currently employed heterogeneous catalytic system.
&
&
&
Taiebeh Tamoradi
t.tabss@yahoo.com
Mohammad Ghadermazi
mghadermazi@yahoo.com
Arash Ghorbani-Choghamarani
arashghch58@yahoo.com; arashghch@gmail.com; a.ghorbani@ilam.ac.ir
1
2
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
123

T. Tamoradi et al.
Graphical Abstract
Keywords SBA-15 Á Vanadium complex Á Oxidation reaction Á Sulfoxide Á
Disulfide
Introduction
In recent years heterogeneous catalysts are more important because of their
recyclability, performance in activity and separation [1]. A homogeneous catalyst
can be converted to a heterogeneous catalyst through support, such as organic and
inorganic acids and bases supported on alumina, zeolite, silica gel, carbon
nanotubes and magnetic nanoparticles. Supporting action modulates the perfor-
mance of homogeneous catalysts in terms of selectivity and catalytic activity. It also
makes all the beneficial properties of solid catalysts, such as easy separation and
recycling available on homogeneous catalysts [2–6]. Among the existing substrates,
those in nano levels are better candidates for the support of homogeneous catalysts
due to their advantages such as very small size, which produces a high surface to
volume ratio [7–9]. The use of pre-fabricated large porosity silicates has recently
attracted the attention of researchers. Among these are the mesoporous patterns such
as MCM-48, MCM-41 and SBA-15 [10]. Large porosities (Mesopores) are
nanoparticles of diameter (2–50 nm) and have good properties such as high surface
absorption, high specific surface, structural order and narrow pore distribution.
123

Synthesis and characterization of oxo-vanadium complex…
Meanwhile, SBA-15 mesoporous silica with a high specific surface area (about
782.46 m2/g), cavity size (normally 4–6 nm), and high thermal resistance, is known
as the best large porosity silica with two-dimensional symmetry having equal
ventures with hexagonal arrangement [11]. Oxidation of sulfides and thiols are
important reactions in organic chemistry [12], they are used as valuable synthetic
intermediates in the production of a wide range of chemicals, active molecules and
pharmaceuticals [13, 14]. Certain sulfoxicides play an important role in antifungal,
anti-hypertensive and vasodilator drugs [15–17]. The rich chemistry of sulfoxides
makes them highly useful reagents in syntheses. Sulfoxides are interesting active
groups that are widely used to form carbon–carbon bonds, especially in organic
reactions, and the transformation of functional groups and molecular redistribution
[18]. On the other hand, the formation of disulfide bonding in peptides and active
biochemical molecules, as well as in the processing of sweet oil, is important. The
low sulfur-sulfur bond leads to high reactivity of these compounds. Additionally, in
the chemical and industrial fields, disulfides are used as a volcanizing agent for
rubbers and elastomers, as well as modifying the surface of precious metals such as
gold, silver, platinum, palladium and some semiconductors [19, 20]. Among
methods for synthesizing sulfoxides and disulfide, the oxidation of sulfides and
thiols to the corresponding sulfoxides and disulfide is very common and, of course,
desirable. The study of different oxidation methods shows that the attention of
chemists is more to achieve superior methods than the old ones. These methods are
more appropriate in terms of reaction time, greater yield, easier product separation,
and they are cheaper and more selective. Herein, new oxovanadium complex
immobilized on SBA-15 has been reported as a recoverable nanocatalyst for the
oxidation of sulfides to sulfoxides and oxidative coupling of thiols into
corresponding disulfides under neat conditions.
Experimental
General
The cationic surfactant Pluronic P123 triblock copolymer (EO20PO70EO20, MW
5800), tetraethyl orthosilicate (TEOS; 98%), 3-chloropropyltrimethoxysilane
(CPTMS), triethylamine, ethanol, ethyl acetate, acetonitrile, H2O2 (33%), n-Hex-
ane, vanadyl acetylacetonate (VO(acac)2), toluene, 2-amino-2-methyl-1,3-propane-
diol (AMPD) and all reagents were purchased from Merck, Sigma-Aldrich and
Fluka. IR spectra were examined for characterization of prepared samples by KBr
disc using a VERTEX 70 model BRUKER FT-IR spectrophotometer. Powder X-ray
diffraction (XRD) patterns were collected to obtain the crystallographic structure of
nanocatalysts by X-ray diffraction patterns using a Cu radiation source with a
˚
wavelength l = 1.54060 A, 40 kV. SEM and TEM images were recorded using
FESEM-TESCAN MIRA3 and Zeiss-EM10C TEM, respectively. The thermal
stability of the nanocatalyst was also studied by TGA using a Shimadzu DTG-60
instrument in the temperature range of 50–750 °C. Melting points of products were
determined with an Electrothermal 9100 apparatus. Inductively coupled plasma
123

T. Tamoradi et al.
optical emission spectrometry (ICP-OES) was used to obtain the vanadium content
of the nanocatalyst.
General procedure for the preparation of the VO-AMPD@SBA-15
The SBA-15 mesoporous silica has been successfully prepared according to a very
recently reported method [21]. Initially, SBA-15 nanoparticles were prepared by
adding 4g of pluronic 123 as the surfactant template to a solution containing 90 mL
of HCl solution (2 M) and deionized water (30 mL). The resulting mixture was
stirred at 35 °C for 5 h, and then 9.04 mL of tetraethylorthosilicate (TEOS) as the
silica source was gradually added to the solution, and the mixture stirred at the same
temperature for 20 h. Finally, the collected product was washed with deionized
water followed by calcination at 823 K for 5 h at a rate of 2 °C/min to remove the
residual surfactants. The white powders were designated that affords pure silica
SBA-15. Then, 1 g of the obtained SBA-15 with 1.5 mL of 3-chloropropy-
ltrimethoxysilane (CPTMS) refluxed in dry toluene (20 mL) for 24 h. The final
product was separated by simple filtration, washed with hexane and dried at 50 °C
to give the SBA-15 coated with CPTMS. AMPD@SBA-15. nanoparticles were
subsequently produced by the reaction of the CPTMS supported on SBA-15 (1 g)
with 0.21 g of 2-Amino-2-methyl-1,3-propanediol (AMPD) and triethylamine
(1.5 mmol) in dry toluene under reflux conditions for 48 h. AMPD@SBA-15 was
separated by filtration, washed with deionized water and ethanol and dried at 50 °C.
Then, VO-AMPD@SBA-15 was successfully obtained through coordination of
AMPD@SBA-15 ligand with vanadium. Furthermore, AMPD@SBA-15 (1 g) and
VO(acac)2 (0.672 g) were mixed in 30 mL ethanol, and then the mixture was
refluxed for 16 h. The nanosolid VO-AMPD@SBA-15 was separated from the
solution by filtration. The final product was washed with copious amounts of ethanol
and dried under vacuum at room temperature.
General procedure for the oxidation of sulfides
In a typical experimental procedure, a round-bottomed flask was charged with
sulfide (1 mmol), H2O2 (30% aqueous, 0.3 mL) and VO-AMPD@SBA-15
(0.004 g). Then the mixture was stirred at room temperature under solvent-free
conditions and the progress of the reaction was monitored by TLC. After
completion of the reaction, the catalyst was removed by filtration, and the residue
was extracted with ethyl acetate. The organic extract was dried over anhydrous
Na2SO4 then evaporated to give the desired product without further purification.
General procedure for the oxidation of thiols to disulfides
In another study, a mixture of the VO-AMPD@SBA-15 (0.004 g), thiol (1 mmol)
and H2O2 (0.4 mL) was stirred at room temperature in ethyl acetate (2 mL). The
progress was monitored by TLC. After completion of the reaction, VO-
AMPD@SBA-15 catalyst was separated from the mixture by filtration. Then
123

Synthesis and characterization of oxo-vanadium complex…
products were extracted with ethyl acetate and dried, and the solvent was removed
to give the pure disulfides.
Results and discussion
Catalyst preparation
Brieflly, 3 chloropropyltrimethoxysilane was first loaded on the surface of SBA-15
nanoparticles. Then surfaces of Sba-15 nanoparticles were coated using 2-amino-2-
methyl-1,3-propanediol (AMPD) ligand as a green and available diol by reaction of
chloride groups of CPTMS supported on SBA-15 nanoparticles and amine groups of
AMPD ligand. Finally, treatment of AMPD@SBA-15 with VO(acac)2 provides
VO-AMPD@SBA-15through a stable interaction between the metal ions and
functional groups of the diol (Scheme 1).
Catalyst characterization
SEM images of VO-AMPD@SBA-15 are depicted in Fig. 1. According to these
images, micrographs of the prepared samples show uniform particle size distribution
and particles with diameters of about 300 nm, retaining the well-defined wheat-like
macrostructure clusters of pure SBA-15.
The TGA curve of the VO-AMPD@SBA-15 shows the quantitative determina-
tion of the organic groups decreases supported on the surface of SBA-15
nanostructure. It should be noted that the mass of the organic functional groups
decomposes upon heating. As shown in Fig. 2, the small amount of weight loss
happens below 200 °C, which is due to removal of physically adsorbed solvent and
surface hydroxyl groups, and the other weight loss of about 27% between 200 and
600 °C is related to decomposition of functional groups chemisorbed onto the
surface of SBA-15 nanoparticles [22]. On the basis of the results of the TGA curve,
Scheme 1 Synthesis of VO-AMPD@SBA-15 nanocatalyst
123

T. Tamoradi et al.
Fig. 1 SEM image of calcined SBA-15 (a) and SEM images of VO-AMPD@SBA-15 (b)
Fig. 2 TGA thermogram of VO-AMPD@SBA-15
the well grafting of vanadium 2-Amino-2-methyl-1,3-propanediol complex onto
mesoporous SBA-15 silica is verified.
One indication of bond formation between the nanoparticles and the vanadium
complex can be inferred from FTIR. FTIR spectra within the range of 400–4000 nm
for SBA-15, SBA-15-Cl, AMPD@SBA-15 and VO-AMPD@SBA-15 nanoparticles
were demonstrated (Fig. 3). As shown in Fig. 3a, the FTIR spectrum of the SBA-15
sample displays characteristic absorption peaks at 1099, 842 and 480 cm-1
corresponding to Si&bond;O&bond;Si asymmetric stretching, Si&bond;O&bond;Si
symmetric stretching and Si&bond;O&bond;Si bending vibrations, respectively.
Also, the presence of C&bond;H stretching vibration at 2912 cm-1 in the SBA-15-
Cl spectrum is due to the anchored (3-choloropropyl) trimethoxysilane [23].
Furthermore, in the spectrum of AMPD@SBA-15, bands in the range of 1550 and
13,250 cm-1 are attributed to the N–H and C–N vibrations, confirming grafting of
the organic groups onto the SBA-15 nanoparticles. Also, in order to determine the
exact amount of vanadium loaded on modified magnetic nanoparticles, ICP-OES
analysis was performed, and it was found to be 0.41 mmol g-1
.
123

Synthesis and characterization of oxo-vanadium complex…
Fig. 3 FTIR spectrum of bare SBA-15 nanoparticles, SBA-15-Cl, AMPD@SBA-15 and VO-
AMPD@SBA-15
TEM images of VO-AMPD@SBA-15 at different magnifications are depicted in
Fig. 4. It can be seen that the catalyst was formed of nanometer-sized particles. It
should be mentioned that the images are indicative of uniform particle size and
hexagonal shape.
The N2 adsorption/desorption isotherm for VO-AMPD@SBA-15 nanocatalyst is
shown in Fig. 5. As seen in Table 1, the Brunauer–Emmett–Teller surface area
(SBET), the Barret–Joyner–Halenda average pore diameter (DBJH) and the total pore
volumes (Vtotal) of VO-AMPD@SBA-15 are summarized. It can be seen that a
decrease in the SBET, DBJH and Vtotal for VO-AMPD@SBA-15 nanocatalyst
upon post anchoring of vanadium complex on the wall of functionalized SBA-15
was observed, which is due to the presence of a pendant group on the pore surface
that partially blocks the adsorption of nitrogen molecules [24]. Also, the N2
adsorption/desorption isotherm of SBA-15 and VO-AMPD@SBA-15 indicated that
the texture of initial material of the SBA-15 upon post anchoring of vanadium
complex on SBA-15 was retained.
123

T. Tamoradi et al.
Fig. 4 TEM images of VO-AMPD@SBA-15 catalyst at different magnifications (a, b and c)
Fig. 5 Nitrogen adsorption/desorption isotherms of VO-AMPD@SBA-15
123

Synthesis and characterization of oxo-vanadium complex…
Table 1 Texture parameters obtained from nitrogen adsorption studies
Sample
SBET (m2 g-1
)
Pore diameter by BJH method (nm) Pore volume (cm3 g-1
)
SBA-15
874
6.168
3.52
1.049 [24]
0.662
VO-AMPD@SBA-
15
360.19
The crystalline structures of the VO-AMPD@SBA-15 catalyst were determined
by powder X-ray diffraction (XRD). The peak positions in the sample remained
constant after the functionalization process as compared to the SBA-15. The intense
peak corresponding to the pore family and the two additional weak reflections
assigned to the family planes, which are indicative as (100), (110), and (200)
reflections are associated with a hexagonal space group symmetry P6mm and high
hexagonal mesoscopic order (Fig. 6) [23].
Catalytic studies
In this research, we developed the preparation of a recyclable, green and efficient
nanocatalyst. Then, in order to investigate the catalytic activity of the prepared
nanohybrid, we investigated it for the oxidation of sulfides (Scheme 2) and
oxidative coupling of thiols (Scheme 3). In this regard, the oxidation of
Fig. 6 The XRD patterns of VO-AMPD@SBA-15
123

T. Tamoradi et al.
Scheme 2 VO-AMPD@SBA-15 catalyzed the oxidation of sulfides to sulfoxides
Scheme 3 Proposed mechanism for oxidation of sulfides in presence of VO-AMPD@SBA-15 as catalyst
methylphenylsulfide was selected as a model reaction. In order to optimize the
reaction conditions, the effects of solvent, amount of catalyst and H2O2 were studied
for the model reaction. Our observations are summarized in Table 2. Because of
mild conditions of described heterogeneous systems, there is no overoxidation to
sulfone for oxidation of sulfides.
In order to gain further insight into this process and with optimal conditions in
hand, we also decided to examine the wider applicability of the catalyst for the
oxidation of a wide range of sulfides with different functional groups. The results of
the investigation are summarized in Table 3.
In continuation of this research work, a reaction mechanism for oxidation of
sulfides in the presence of VO-AMPD@SBA-15 is proposed on the basis of the
literature [25]. Initially, reaction of H2O2 with VO-AMPD@SBA-15 leads to the
intermediate A. The intermediate A is converted to active oxidant B and then
nucleophilic attack of the sulfide on this intermediate (C1) produced corresponding
sulfoxide (Fig. 7).
It should be mentioned that the catalytic activity of VO-AMPD complex in
comparison with VO-AMPD@SBA-15 is investigated for the conversion of
methylphenylsulfide to the methylphenylsulfoxide under optimized conditions. As
123

Synthesis and characterization of oxo-vanadium complex…
Table 2 Optimization of oxidation of sulfides to the corresponding sulfoxides using VO-AMPD@SBA-
15 nanoparticles under various conditions
Entry
Solvent
H2O2 (mL)
Catalyst (mg)
Time (min)
Yield (%)a
b
1
2
3
4
5
6
7
8
9
10
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Ethanol
0.3
0.2
0.3
0.3
0.3
0.4
0.5
0.3
0.3
0.3
0
3
4
3
5
4
4
4
4
4
140
85
–
87
98
89
98
97
91
90
89
91
60
75
55
55
50
85
Ethyl acetate
Acetonitrile
120
140
aIsolated yields
bControl experiment in the absence of catalyst
Table 3 Oxidation of sulfides to the corresponding sulfoxides in the presence of VO-AMPD@SBA-15
Entry
Substrate
Product
Time (min)
Yield (%)a
1
Dodecyl methylsulfide
Dipropylsulfide
2a
2b
2c
2d
2e
2f
45
35
25
5
97
98
97
99
98
92
97
98
96
92
90
93
98
91
92
89
96
90
93
98
2
3
Dibenzylsulfide
4
Tetrahydrothiophene
Propylenesulfide
5
30
45
20
25
20
15
30
50
60
40
55
50
30
45
55
25
6
Diethylsulfide
7
Ethylphenylsulfide
Benzylmethylsulfide
Diphenylsulfide
2g
2h
2i
8
9
10
11
12
13
14
15
16
17
18
19
20
Benzylphenylsulfide
Bis(4-hydroxyphenyl)sulfide
Dimethylsulfide
2j
2k
2l
Methylphenylsulfide
Allyl(methyl)sulfide
2-Furfurylmethylsulfide
Dibutylsulfide
2m
2n
2o
2p
2q
2r
4-Chlorophenyl(methyl) sulfide
2-(Methylthio)ethanol
n-Dodecylsulfide
2s
2t
2-(Phenylthio)ethanol
aIsolated yields
123

T. Tamoradi et al.
Fig. 7 Reusability of VO-AMPD@SBA-15 for the oxidation of tetrahydrothiophene (green column) and
the oxidative coupling of 4-methylthiophenol (blue column). (Color figure online)
shown in Table 4, the products were obtained in 92 and 98% yield in the presence of
VO-AMPD complex and VO-AMPD@SBA-15, respectively.
After successfully synthesizing a series of sulfoxides with high efficiency, the
catalytic activity of VO-AMPD@SBA-15 was also investigated in the oxidative
coupling of thiols. In order to optimize the reaction conditions, we investigated the
oxidative coupling of 4-methylthiophenol as a model substrate in the absence and
presence of various solvents and in the presence of different amounts of VO-
AMPD@SBA-15 using different amounts of hydrogen peroxide (H2O2). The results
of the investigation are summarized in Table 5.
With the optimal reaction conditions in hand, we extended the scope of the
method for the wide range of aromatic and aliphatic thiols. The results of the
chemoselective oxidation of thiols to disulfides are summarized in Table 6. It
should be mentioned that the thiols afforded the corresponding products in short
times with good to excellent yields (Scheme 4).
The proposed mechanism for this process using H2O2 as oxidant in the presence
VO-AMPD@SBA-15 catalyst is outlined in Scheme 5 [24].
Recyclability of the catalyst
In addition, according to the green chemistry viewpoint, the recovery and reusability
of catalyst is an outstanding issue in modern catalysis researches. In this regard, the
Table 4 Effect of VO-AMPD complex in comparison with VO-AMPD@SBA-15 in oxidation of
methylphenylsulfide as a model compound under optimized conditions
Entry Substrate
Catalyst
Time (min) Catalyst (mg) Yield (%)a
1
2
Methylphenylsulfide VO-AMPD complex
60
4
4
92
Methylphenylsulfide VO-AMPD@SBA-15 60
98 [this work]
aIsolated yields
123

Synthesis and characterization of oxo-vanadium complex…
Table 5 Optimization of oxidative coupling of thiols to disulfides using VO-AMPD@SBA-15 under
various conditions
Entry
Solvent
H2O2 (mL)
Catalyst (mg)
Time (min)
Yield (%)a
b
1
Ethyl acetate
Ethyl acetate
Solvent-free
Ethyl acetate
Ethyl acetate
Ethyl acetate
Ethanol
0.4
0.4
0.4
0.4
0.3
0.5
0.4
0.4
0.4
0
4
3
5
4
4
4
4
4
180
50
70
45
65
45
95
70
85
–
3
98
87
98
90
98
91
93
89
4
5
6
7
8
9
Solvent-free
Acetonitrile
10
aIsolated yields
bControl experiment in the absence of catalyst
Table 6 Oxidative coupling of thiols to disulfides using H2O2 in the presence of VO-AMPD@SBA-15
Entry
Substrate
Product
Time (min)
Yield (%)a
1
Mercaptosuccinic acid
2-Mercaptobenzoic acid
Phenylmethanethiol
4a
4b
4c
4d
4e
4f
35
20
25
45
50
40
35
65
60
35
70
30
35
40
50
85
80
30
25
40
99
95
94
97
98
96
96
92
89
98
93
95
90
97
92
97
98
90
93
99
2
3
4
Benzo[d]thiazole-2-thiol
4-Methylbenzenethiol
2-Mercapto-6-methylpyridine
Benzenethiol
5
6
7
4g
4h
4i
8
2-Mercaptopyridine
9
2-Mercaptoacetic acid
2,6-Dichlorobenzenethiol
4-Mercaptopyridine
10
11
12
13
14
15
16
17
18
19
20
4j
4k
4l
4-Phenylimidazole-2-thiol
4,6-Dimethyl-2-pyrimidinethiol
2-Mercaptoethanol
4m
4n
4o
4p
4q
4r
2-Mercaptoimidazole
2-Aminothiophenol
1-Ethyl-1H-imidazole-2-thiol
4-Bromothiophenol
Naphthalene-2-thiol
4s
4t
Benzo[d]oxazole-2-thiol
aIsolated yields
123

T. Tamoradi et al.
Scheme 4 VO-AMPD@SBA-15 catalyzed the oxidative coupling of thiols into disulfides
Scheme 5 Proposed mechanism for oxidative coupling of thiols in presence of VO-AMPD@SBA-15 as
catalyst
prepared catalyst has the potential for efficient recycling for nine additional reaction
cycles without significant loss of catalytic activity, establishing the reusability of the
catalyst. As evident in Fig. 8, this experiment obviously proves that vanadium is
covalently anchored to the organic functional groups on the SBA-15 nanostructure
surface.
The nature of the recovered catalyst was investigated by EDX (Fig. 8) XRD
patterns (Fig. 9), SEM (Fig. 10) and ICP-OES analysis. The results indicate that the
catalyst can be recycled without any significant change in its structure or
mesoporousity of the silicate parent.
The energy-dispersive X-ray spectroscopy (EDX) analysis of the recovered
catalyst shows the presence of peaks associated with Si, O, N, C and V specie in the
catalyst. In order to determine the exact amount of V loaded on modified SBA-15
nanoparticles, ICP-OES analysis of recovered catalyst was performed, and it was
found to be 0.37 mmol g-1. Therefore, the catalytic activity has been decreased
slightly because the leaching of metal from VO-AMPD@SBA-15 is very negligible.
As seen in Fig. 9, the X-ray diffraction analysis (XRD) patterns of recovered
catalyst were recorded by powder X-ray diffraction (XRD). It can be seen that the
XRD pattern of the catalyst has not been changed in the recovered catalyst.
123

Synthesis and characterization of oxo-vanadium complex…
Fig. 8 EDX spectrum of recovered VO-AMPD@SBA-15
Fig. 9 The XRD patterns of recovered VO-AMPD@SBA-15
The morphology of the recovered VO-AMPD@SBA-15 was also obtained using
the scanning electron microscopy (SEM) technique (Fig. 10).
Hot filtration test
Also, the oxidation of 4-methylbenzenethiol in the presence of VO-AMPD@SBA-
15 has been investigated by carrying out a hot filtration test in order to find whether
the catalyst is truly heterogeneous in nature or whether vanadium is leaching out
from the solid catalyst to the solution. In this experiment, after continuing the
reaction under optimized conditions, we found the yield of product in a half time of
123

T. Tamoradi et al.
Fig. 10 SEM images of
recovered VO-AMPD@SBA-15
the reaction to be 67%. Then the reaction was repeated and in a half time of the
reaction, the catalyst was separated from the reaction mixture and allowed the
filtrate to react further under identical reaction conditions. The yield of reaction in
this stage was 73% that confirmed the leaching of vanadium had not occurred.
Comparison of the catalyst
In order to examine the efficiency of overall performance of the catalyst reactions,
we compared the results of the synthesis of methylphenylsulfoxde in the presence of
our catalyst with previously reported catalysts in the literature (Table 7). It should
be noted that the prepared catalyst showed shorter reaction times, easier purification
and better yields than the other catalysts. Also, in comparison with other catalysts,
easy catalyst/product separation and catalyst recycling, easy preparation using
cheap and commercially available materials in a short period of time, use of non-
toxic ligands, easy separation, and stability are several benefits of this protocol.
Conclusion
In the present work, a VO-AMPD@SBA-15 nanohybrid was successfully obtained
via a simple and versatile procedure, which was confirmed with FT-IR, TGA, SEM,
ICP-OES, XRD, BET and TEM. Also, the performance of VO-AMPD@SBA-15 as
an efficient, green and reusable catalyst for the oxidation of sulfides and oxidative
coupling of thiols was investigated. The prepared catalytic system can combine the
advantages of homogeneous and heterogeneous catalysts, and; therefore ,they can
123

Synthesis and characterization of oxo-vanadium complex…
Table 7 Comparison of VO-AMPD@SBA-15 for the oxidation of methylphenylsulfide with previously
reported procedures
Entry
Catalyst
Time (min)
Yield (%)a
1
(CH3)4N?CrO3F-
75
120
120
210
150
120
155
360
150
300
120
60
82 [26]
92 [27]
57 [18]
93 [28]
90 [29]
84 [30]
95 [17]
92 [31]
98 [17]
35 [32]
94 [33]
98 [this work]
2
Alumina-supported nanoruthenium/H2O2
3
2NaBO3Á4H2O(I)/KBr
Thiourea dioxide/TBHP
SiO2–W2–Py/H2O2
4
5
6
(C2H5)3NH?[CrO3F]-
8
Ni(II)-Salen-MCM-41/UHP
Borax/H2O2
9
10
11
12
13
Cd(II)-Salen-MCM-41/UHP
Clay-supported ceric ammonium nitrate (CAN)/O2
Iron(II)-catalyzed
VO-AMPD@SBA-15
aIsolated yields
be readily separated from the solution by simple filteration, allowing straightforward
recovery and reuse. More importantly, this method offers several advantages
including the use of commercially available materials, short reaction times, clean
reactions, operational simplicity, high efficiency under relatively mild conditions, a
waste-free process, and cheap and chemically stabile reagents.
Acknowledgements The authors are deeply grateful to Erfan Ghadermazi, University of Kurdistan and
Ilam University for financial support of this research project.
References
1. A. Masahiko, Z. Fengyu, Catalyst 5, 868 (2015)
2. F. Havasi, A. Ghorbani-Choghamarani, F. Nikpour, Microporous Mesoporous Mater. 224, 26 (2016)
3. C.E. Song, J.S. Lim, S.C. Kim, K. Lee, D.Y. Chi, Chem. Commun. 24, 2415 (2000)
4. T. Tamoradi, A. Ghorbani-Choghamarani, M. Ghadermazi, New J. Chem. 41, 11714 (2017)
5. M.A. Zolfigol, V. Khakyzadeh, A.R. Moosavi-Zare, A. Zare, P. Arghavani-Hadi, Z. Mohammadi,
M.H. Beyzavi, J Chem. 65, 280 (2012)
6. M. Darabi, T. Tamoradi, M. Ghadermazi, A. Ghorbani-Choghamarani, Transit Metal Chem. 42, 703
(2017)
7. S. Shylesh, V. Schunemann, W.R. Thiel, Angew. Chem. Int. Ed. 49, 3428 (2010)
8. P. Movaheditabar, M. Javaherian, V. Nobakht, React. Kinet. Mech. Catal. 122, 217 (2017)
9. C.W. Lim, I.S. Lee, Nano Today 5, 412 (2010)
10. J. Kulys, R. Vidziunate, J. Mol, Catal. B Enzym. 37, 79 (2005)
11. D. Zhao, J. Feng, Q. Hou, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky, Science 279,
548 (1998)
12. X.B. Li, Z.J. Li, Y.J. Gao, Q.Y. Meng, S. Yu, R.G. Weiss, G.H. Tung, L.Z. Wu, Angew. Chem. Int.
Ed. 53, 2085 (2014)
13. E. Rattanangkool, W. Krailat, T. Vilaivan, P. Phuwapraisirisan, M. Sukwattanasinitt, S. Wacha-
rasindhu, Eur. J. Org. Chem. 22, 4795 (2014)
14. H.B. Jeon, K.T. Kim, S.H. Kim, Tetrahedron Lett. 55, 3905 (2014)
123

T. Tamoradi et al.
15. A. Shaabani, A.H. Rezayan, Catal. Commun. 8, 1112 (2007)
16. A. Sreedhar, P. Radhika, B. Neelima, N. Hebalkar, A.K. Mishra, Catal. Commun. 10, 39 (2008)
17. M. Nikoorazm, A. Ghorbani-Choghamarani, H. Mahdavi, S. Mostaffa Esmaeili, Microporous
Mesoporous Mater. 211, 174 (2015)
18. D. Habibi, M.A. Zolfigol, M. Safaiee, A. Shamsian, A. Ghorbani-Choghamarani, Catal. Commun. 10,
1257 (2009)
19. H. Firouzabadi, N. Iranpoor, M. Abbasi, Tetrahedron Lett. 51, 508 (2010)
20. Y. Liu, H. Wang, C. Wang, J.P. Wan, C. Wen, RSC Adv. 3, 21369 (2013)
21. J. Davarpanah, A.R. Kiasat, Catal. Commun. 46, 75 (2014)
22. A. Ghorbani-Choghamarani, B. Tahmasbi, P. Moradi, Appl. Organometal. Chem. 30, 422 (2016)
23. M. Nikoorazm, A. Ghorbani-Choghamarani, M. Khanmoradi, Appl. Organometal. Chem. 30, 236
(2016)
24. M. Hajjami, F.Ghorbani, Z. Yousofvand, Appl. Organometal. Chem. 2017
25. T. Tamoradi, M. Ghadermazi, A. Ghorbani-Choghamarani, Appl. Organometal. Chem. 2017
26. H. Imanieh, S. Ghamami, M.K. Mohammadi, A. Jangjoo, Russ. J. Gen. Chem. 77, 282 (2007)
27. P. Veerakumar, Z. Lu, M. Velayudham, K.L. Lu, S. Rajagopal, J. Mol. Catal. A 332, 128 (2010)
28. S. Kumar, S. Verma, S.L. Jain, B. Sain, Tetrahedron Lett. 52, 3393 (2011)
29. S. Xian-Ying, W. Jun-Fa, J. Mol. Catal. A Chem. 280, 142 (2008)
30. S. Ghammamy, M.K. Mohammadi, A.H. Joshaghani, Maced. J. Chem. Chem. Eng. 27, 117 (2008)
31. S. Hussain, S.K. Bharadwaj, R. Pandey, M.K. Chaudhuri, Eur. J. Chem. 42, 3319 (2009)
32. A. Dhakshinamoorthy, K. Pitchumani, Catal. Commun. 10, 872 (2009)
33. B. Li, A.H. Liu, L.N. He, Z.Z. Yang, J. Gao, K. Hong, ChenGreenChem 14, 130 (2012)
123