Oxo-vanadium complex immobilized on chitosan coated-magnetic nanoparticles (Fe3O4): A heterogeneous and recyclable nanocatalyst for the chemoselective oxidation of sulfides to sulfoxides with H2O2

Article abstract of DOI:10.1016/j.poly.2018.07.013

This article presents the synthesis of Schiff base oxo-vanadium complex immobilized on chitosan coated-magnetic Fe₃O₄ nanoparticles [VO(CS)@Fe₃O₄] as a new magnetic interphase nanocatalyst. This type of functionalizing the surface of magnetic particles is a graceful method for bridging the gap between two types of heterogeneous and homogeneous catalysis. The characterization of as-synthesized nanocatalyst was performed through Fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The chemoselective oxidation of sulfides to sulfoxides using green oxidant of hydrogen peroxide at ambient temperature in high-yield was catalyzed with VO(CS)@Fe₃O₄. The synthesized catalyst can be used up to 8 times with no considerable leaching and change in its activity. Both improvement of catalytic performance and easy separation for the reaction procedure were obtained because of the presence of oxo-vanadium and the magnetic core.

Full text of DOI:10.1016/j.poly.2018.07.013

Accepted Manuscript
Oxo-vanadium complex immobilized on chitosan coated-magnetic nanoparti-
cles (Fe O ): A heterogeneous and recyclable nanocatalyst for the chemoselec-
3
4
tive oxidation of sulfides to sulfoxides with H O
2
2
Hojat Veisi, Sami Sajjadifar, Parisa Mohammadi Biabri, Saba Hemmati
PII:
S0277-5387(18)30400-5
https://doi.org/10.1016/j.poly.2018.07.013
POLY 13278
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
14 May 2018
6 July 2018
10 July 2018
Please cite this article as: H. Veisi, S. Sajjadifar, P.M. Biabri, S. Hemmati, Oxo-vanadium complex immobilized
on chitosan coated-magnetic nanoparticles (Fe O ): A heterogeneous and recyclable nanocatalyst for the
3
4
chemoselective oxidation of sulfides to sulfoxides with H O , Polyhedron (2018), doi: https://doi.org/10.1016/
2
2
j.poly.2018.07.013
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Oxo-vanadium complex immobilized on chitosan coated-magnetic
nanoparticles (Fe O ): A heterogeneous and recyclable nanocatalyst for the
3
4
chemoselective oxidation of sulfides to sulfoxides with H O2
2
Hojat Veisi,* Sami Sajjadifar, Parisa Mohammadi Biabri, Saba Hemmati
Department of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran
Email: hojatveisi@yahoo.com
Abstract. This article presents the synthesis of Schiff base oxo-vanadium complex
immobilized on chitosan coated-magnetic Fe
3
O
4
nanoparticles [VO(CS)@Fe
3
4
O ] as a new
magnetic interphase nanocatalyst. This type of functionalizing the surface of magnetic
particles is a graceful method for bridging the gap between two types of heterogeneous and
homogeneous catalysis. The characterization of as-synthesized nanocatalyst was performed
through fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field
emission scanning electron microscopy (FE-SEM), high resolution transmission electron
microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric
analysis (TGA), vibrating sample magnetometer (VSM), and X-ray photoelectron
spectroscopy (XPS). The chemoselective oxidation of sulfides to sulfoxides using green
oxidant of hydrogen peroxide at ambient temperature in high-yield was catalyzed with
VO(CS)@Fe
3
4
O . The synthesized catalyst can be used up to 8 times with no considerable
leaching and change in its activity. Both improvement of catalytic performance and easy
separation for the reaction procedure were obtained because of the presence of oxo-vanadium
and the magnetic core.
Keywords: Vanadium, Magnetic, Chitosan, Sulfides, Sulfoxides, Hydrogen peroxide
1
. Introduction
Organic chemists have interested in sulfoxides for a longtime because these compounds as a
functional group can transfer into different type of organo-sulfur compounds through
different reactions. This property is valuable for synthesizing drugs and sulfur-substituted
1
,2
natural products. Even though there are variety types of oxidants with ability to convert
sulfides to the corresponding sulfoxides, the cautious control of the reaction conditions such
as the amount of oxidants is needed for most of reagents for minimizing the production of
3
sulfones as side products.
4
f,i,5
Nowadays, there are many types of traditional oxidants for oxidation of the sulfide,
but
aqueous hydrogen peroxide is mostly interested because it is clean, , cheap, readily accessible
4
d,e,6
and environmentally friendly as its side products is only water.
A suitable catalyst is
usually required for activating hydrogen peroxide as it is a relatively weak oxidant and
4
c,h,7
induces oxidations slowly.
Therefore, an enormous number of effective catalysts based
on transition metal have been offered for oxidizing sulfides using hydrogen
4
c,d,f,h,i,5,6,7,8
peroxide.
However, only a few of them can prevent production of sulfone at the
sulfoxide step. Moreover, most of protocols have one or more restrictions such as the difficult
4
c,d,i
recovery of the catalyst, expensive, requiring a promoter or a co-catalyst,
high
temperature, time-consuming reaction, using chloro-hydrocarbon solvents, using large
amount of hydrogen peroxide and low TON. Consequently, the efforts continue to find a
suitable alternative catalysts and protocols that obey green chemistry.
1

A recently kind of functional substance is surface functionalized magnetic iron oxide
nanoparticles (NPs), which have been infinitely used in the fields of biotechnology and
catalysis. Among different types of available magnetic nanoparticles (MNPs) utilized as the
core magnetic support, Fe
properties such as high surface areas, low toxicity and superparamagnetic behavior.
Moreover, all ferrites are metal oxides, which present a considerable amount of hydroxyl
3
O
4
nanoparticles are mostly interested because of their specific
9
-14
1
5
groups on the external surface of their particles. Therefore, well-defined shells of different
substances are formed for surrounding the ferrite core or, in those cases that the target is the
functional materials, suitable functional groups are formed to support various types of
1
6
actuators, ligands, and/or catalysts via covalent bonding. Crucially, the magnetic-supported
catalysts show excellent catalytic property and good chemical stability, and their swell is also
1
7-19
resistance in organic solvents.
There are several reports on the immobilization of Schiff base oxo-vanadium complex on
solid supports and use of the resultant materials in the liquid phase selective oxidation in the
2
0
presence of peroxides as oxidants. In the context of developing the effective and eco-
2
1
friendly heterogeneous catalysts, we conducted a study on the synthesis of oxo-vanadium
Schiff base complex supported on chitosan coated-MNPs (VO(CS)@Fe ) as a new catalyst
3
O
4
for oxidizing the sulfides to sulfoxides chemo-selectively using hydrogen peroxide as a green
oxidant (Scheme 1).
2
2
. Experimental Section
.2. Preparation of the magnetic Fe
3
4
O nanoparticles (MNPs(:
MNPs were synthesized through co-precipitation of Fe (III) and Fe (II) ions with a molar
ratio of 2:1 in the presence of ammonium hydroxide .In general, 100 mL solution containing
FeCl
heated at 85 C under N
NH OH was slowly injected into this mixture in one step. The black MNPs was instantly
3
.6H
2
O (5.838 g, 0.0216 mol) and FeCl
2
.4H
2
O (2.147 g, 0.0108 mol) was prepared and
º
2
atmosphere and strongly stirred (500 rpm). Then, 10 mL of 25%
4
2
+/ 3+
formed after addition the ammonia solution to the Fe Fe salt solution. The stirring the
mixture was continunied for 25 min and the mixture was cooled to ambient temperature.
Then, dark MNPs were magnetically separated from the solution and washed three times with
DI water.
2
.3. Preparation of the CS@Fe
3
O
4
(Chitosan@Fe
3
O
4
):
First, 100 mL of 2% (v/v) acetic acid solution containing 1.0 g of chitosan (98% NH
2
) was
prepared and stirred sonically for 1 h. Then, magnetic chitosan nanoparticles (CS@Fe
were synthesized as following. 400 mg of wet precipitated (frsh) magnetite was dispersed in
0 mL of prepared chitosan solution (weight ratio of chitosan to Fe = 2:1). The obtained
mixture was brought to 150 mL, stirred for 1 h, at ambient temperature and neutralized with
0% (w/v) solution of NaHCO . After subsiding the foam, the mixture was centrifuged to
3
4
O )
8
3
O
4
1
3
collect the precipitates and the obtained precipitates were washed twice with deionized water
and dried at room temperature by spreading on a glass plate.
2
5
2
.4. Preparation of the VO(CS)@Fe
00 mg of synthesized CS@Fe was sonically dispersed in EtOH-H
0 min. Then, 0.265 g of vanadyl acetylacetonate (0.001 mol) was dissolved in 20 mL water
3
O
4
:
3
O
4
2
O (1:1, 100 mL) for
and added to the obtained mixture. The resulted mixture was refluxed for 24 hours. In the
next step, VO(CS)@Fe
3
O
4
was magnetically separated and washed using ethanol, distilled
2

water and acetone, respectively for removing probable unattached substrates. Moreover, the
-1
vanadyl content of the catalyst was obtained 0.34±0.001 mmol.g using atomic absorption
spectroscopy.
2
1
.5. Typical experimental procedure for the preparation of sulfoxides:
.5 mmol 30% (w/w) H and 30 mg VO(CS)@Fe nanocatalyst (1 mol%) were
2
O
2
3
O
4
sequentially added, to sulfide (1 mmol) in a 5 ml round bottom flask and the resulted mixture
was magnetically stirred at ambient temperature for desired time. The reaction progress was
checked using TLC (EtOAc/n-hexane, 1/10). After completion of the reaction, the catalyst
was magnetically isolated from the product through only 5 s and was washed twice using %
mL Et
2
O, decanted and dried using anhydrous Na
2
SO and diethyl ether evaporation under
4
decreased pressure. The pure products were obtained in 80-96% yields.
3
3
. Results and discussion
.1. Preparation and Characterization of VO(CS)@Fe
3
4
O nanocatalyst
The synthesis of Fe
the prepared MNPs were subsequently coated with chitosan (CS) for preparing chitosan
coated-magnetic Fe nanoparticles (CS@Fe ). Then, the coordination of CS@Fe
using VO(acac) causes the corresponding oxo-vanadium complex supported on chitosan
coated-magnetic Fe nanoparticles (VO(CS)@Fe ). Lastly, an external magnet was used
3
O
4
particles was performed according to our previous report [21a], and
3
O
4
3
O
4
3
O
4
2
3
O
4
3
O
4
to collect the mixture and the separated mixture was dried in vacuum. The synthesis of the
nanocatalyst is demonstrated in Scheme 1. The vanadium (IV) content of the nanocomposite
-1
was 0.34±0.001 mmol.g as predicted via atomic absorption spectroscopy. The catalyst was
characterized through FTIR, XRD, XPS, FESEM, EDX, TEM, TGA, ICP and VSM.
O
S
R1
R2
S
R1
R2
OH
O
O
HO
n
H O (30%), r.t.
Solvent-free
2
2
NH2
VO
CS
OV
VO
CS
OV
VO
VO
VO(acac)2
Chitosane
Fe O NPs
Fe O NPs
Fe3O4 NPs
3
4
3
4
OV
H O-EtOH
2
OV
VO
Fe O NP
3
4
OV
VO
VO
Fe O NPs@CS
3
4
Fe O NPs@CS/VO
3
4
Scheme 1: Synthesis of VO(CS)@Fe
3
4
O and its application for oxidizing sulfides to
sulfoxides chemo-selectively using H
2
O
2
3

In order to prove the existence of the chitosan coating, FTIR spectra of Fe
CS@Fe
contributing in binding procedure. As can be observed, the naked Fe
3
O
4
, chitosan, and
nanoparticles
3
O nanoparticles were prepared (Fig. 1) to study the possible functional groups
4
3
O
4
-1
showed a strong stretching absorbance peak at 574.68 cm corresponding to Fe–O–Fe groups
(
Fig. 1a). In the spectrum of chitosan (Fig. 1b), the corresponded absorption bands of amide I
-1
-1
and -NH in amide group bending vibration was observed at 1641 cm and 1590 cm ,
respectively. The adsorption peaks of chitosan were appeared at 1376 cm (–C–O– stretching
of primary alcoholic group), 1151 cm (asymmetric stretching of –C–O–C– bridge) and 1027
2
-1
-1
-1
cm (C–N bond) [22,23]. The FTIR spectrum of CS@Fe
3
O
4
nanoparticles showed that the
characteristic peak of Fe–O–Fe shifted to 580 cm (Fig. 1c) and all characteristic peaks of
Fe nanoparticles and chitosan were observed in this spectrum indicating the successful
coating of Fe with chitosan. These outcomes are in accordance with literatures [24,25].
-
1
3
O
4
3
O
4
Fig. 1 FTIR of a) Fe
3
O
4
; b) CS; and c) CS@Fe
3
4
O .
The scanning electron microscopy was used to study size and morphology of
VO(CS)@Fe . The FESEM image of a) Fe ; and c) VO(CS)@Fe showed that the
prepared catalyst is nanometer quasi-spherical with an average diameter of 30±5 nm (Fig. 2).
Moreover, a continuous polymer layer can be seen on the VO(CS)@Fe catalyst surface
3
O
4
3
O
4
3
O
4
3
O
4
comparing to Fe
3
O
4
.
In addition, the EDX detector coupled to the SEM was used to
4

prove the presence of chitosan (CS) shell on the Fe
3
4
O NPs surface that the results
confirmed the existence of Fe, C, N, and O in Figure 2b. The observing the V(IV)
,
signal in the nanocatalyst s EDX (Fig. 2d) showed the effective coordination of
VO(acac)
2
salt on CS@Fe
3
4
O .
a
O K
3500
3000
2500
2000
1500
1000
b
EDS
FeL
N K
FeK
500
C K
FeK
keV
7.705
0
0
.0250
c
O K
VL
EDS
d
1
500
000
FeK
1
FeL
N K
500
VK
C K
FeK
VK
keV
7.705
0
0
.0250
Fig. 2 FESEM images of a) Fe
VO(CS)@Fe
3
O
4
; c) VO(CS)@Fe
3
O
4
; and EDX data for b) CS@Fe
3
4
O ; d)
3
4
O .
HRTEM image of VO(CS)@Fe
3
4
O was presented in Fig. 3. It clearly shows well dispersion
of the prepared catalyst and several larger structures, which can be attributed to the
aggregation/coalescence of each nanoparticles. It can be observed that grey VO(CS) shells
covered dark Fe
3
4
O cores, confirming the effective coating procedure of VO(CS) materials.
5

Fig. 3 HRTEM images of VO(CS)@Fe
3
O
4
X-ray photoelectron spectroscopy (XPS) is an influential instrument for investigating the
electronic characteristics of the species created on the surface, including the environment of
electron, state of oxidation, and the binding energy of the core electron of the metal. XPS
elemental survey scans of the surface of the VO(CS)@Fe
3
4
O catalyst was shown in Fig. 4.
The peaks related to oxygen, carbon, nitrogen, vanadium and iron are obviously observed in
this spectrum. XPS analysis was also performed to determine the oxidation state of the V. In
Fig. 5, the V binding energy of VO(CS)@Fe
3
O
4
shows two peaks centered at 524.3 and
5
17.2 eV contributing to V 2p1/2 and V 2p3/2, respectively. Based on the previous studies [27],
the Vanadium Oxides will have symmetric peak shapes and for V2p the V2p1/2 component is
much broader than the V2p3/2 peak. Accordingly, V2p1/2 peak is much shorter than estimated.
These outcomes show that the V is in the (IV) form. The position of N 1s peak is frequently
affected by the local chemical/physical environment around it, and its area showed two type
of nitrogen, C-NH
2
(402 ev) and N-V(IV) (399.5 ev), that confirmed the effective bending of
vanadium ions to the surface [28].
6

Fig. 4 XPS spectrum related to the elemental survey scan of VO(CS)@Fe
3
4
O .
Fig. 5 XPS spectrum of VO(CS)@Fe
3
4
O in the Fe2p, C1s, V2p, O1s, and N1s regions.
7

X-ray diffraction (XRD) analysis was used to study the structure and phase purity of
structures. XRD patterns of Fe NPs, pure chitosan, and as-prepared VO(CS)@Fe NPs
catalyst were shown in Fig. 6. The presence of six peaks at 2θ about 30.2º, 35.7º,43.4º, 53.7º,
7.4º and 62.8º corresponding to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) is in a
good agreement with standard patterns of inverse cubic spinel magnetite (Fe ) crystal
structure. The whole diffraction peaks are related to the magnetic cubic structure of Fe
JCPDS 65-3107). The XRD pattern (Fig. 6c) of as-prepared VO(CS)@Fe catalyst reveals
the same diffraction peaks to that of Fe NPs (Fig. 6a). By contrast with the XRD pattern
of chitosan (Fig. 6b), it was found that an envelope peak centered at 20.2° in the XRD pattern
of VO(CS)@Fe (Fig. 6c) is the peculiar diffraction peak of the amorphous chitosan [29].
3
O
4
3
O
4
5
3
O
4
3
O
4
(
3
O
4
3
O
4
3
O
4
According to the obtained results, the crystalline phase of Fe
amorphous VO(CS) coating.
3
4
O is not affected by the
Fig. 6. XRD patterns of a) Fe
3
O
4
, b) CS, and c) VO(CS)@Fe
3
4
O .
TGA analysis was used to determine the stability of the synthesized VO(CS)@Fe
3
4
O catalyst
as well as the percentage of organic functional groups on the surface of MNPs. The TGA
results (Fig. 7) show an initial weight loss of 4.3% up to 100 °C that can be assigned to the
physical adsorption of hydroxyl groups of the surface and solvent on the support. The catalyst
8

was thermally degraded above 200 °C that indicates the excellent thermo-stability of catalyst.
The second and third weight loss of 23% in the range of 200-540 °C was because of the CS
groups degradation. The man mass content of (CS)@Fe3O4 was expected 23% using the
results of TGA.
Fig. 7 TGA curve of VO(CS)@Fe
3
O
4
It was observing that that both prepared particles have minor coercivities, which show that
they have a superparamagnetic nature. As can be observed in Fig. 8, saturation
-1
magnetizations are 62.3 and 32.3 emu g for Fe
3
O
4
and VO(CS)@Fe
3
4
O , respectively. The
order is because of an increase in the level of non-magnetic materials on the particle surface
that results more percentage of the non-magnetic CS coating and the grafted catalyst layer. A
direct outcome of this impact is that it VO(CS)@Fe
Fe for separating from the solution.
3
4
O needs more time comparing to bare
3
O
4
Fig. 8 VSM spectra of a) Fe
3
O
4
and b) VO(CS)@Fe
3
O
4
9

3
.2. The catalytic application of VO(CS)@Fe
3
4
O in the oxidation of sulfides to sulfoxides
2
1
In the continuing of our previous studies, the catalytic activity of VO(CS)@Fe
studied as a reusable organic-inorganic hybrid catalyst for the chemo-selective oxidation of
sulfides to sulfoxides with 30% H under solvent-free conditions at ambient temperature
Scheme 1).
3
O
4
was
2
O
2
(
For optimization of the reaction conditions, the oxidation of methyl phenyl sulfide with 30%
as a model was studied under different reaction conditions in terms of time and product
efficiency (Table 1). As can be observed in Table 1, the reaction could not be performed
completely without VO(CS)@Fe even after 24 h (entries 1 and 2). H (2 equiv.) The
optimal conditions for the converting methyl phenyl sulfide to methyl phenylsulfoxide
effectively was found with catalytic amount of VO(CS)@Fe (30 mg, 0.9 mol%) under
solvent free condition at ambient temperature (Table 1, entry 5).
H
2
O
2
3
O
4
2
O
2
3
O
4
Table 1. Optimization of the amounts of H
oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide.
Entry Catalyst (mol%) (mmol) Solvent
Solvent-free 24 h
Solvent-free 24 h
2
O
2
and VO(CS)@Fe
3
O
4
for the selective
a
H
2
O
2
Time (min) Yield (%)
1
2
3
4
5
6
7
8
9
1
1
Catalyst-free
Fe (20)
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
VO(CS)@Fe
2.0
2.0
2.0
2.0
2.0
2.0
1.0
3.0
2.0
2.0
2.0
35
45
90
90
90
90
90
90
90
90
85
3
O
4
3
O
O
O
O
O
O
O
O
O
4
4
4
4
4
4
4
4
4
(0.3)
(0.6)
(0.9)
(1.2)
(0.9)
(0.9)
(0.9)
(0.9)
(0.9)
Solvent-free 2 h
Solvent-free 45
3
3
Solvent-free
Solvent-free
5
5
3
3
Solvent-free 30
3
Solvent-free
EtOH
5
3
45
45
2 h
0
1
3
CH
CH
3
CN
Cl
3
2
2
a
1
Determined by H NMR.
As summarized in Tables 2, the generality of this technique has been highlighted by a simple
oxidant of several aliphatic and aromatic sulfides. The reaction shows the proper general use
for synthesising sulfoxides. The intended products were achieved quickly in good yields and
with good turn over numbers (TON). It is important to understand that the chemoselectively
oxidation of the sulfides occurred in the presence of functional groups resistant to oxidation,
including OH, CHO, and COOMe (Table 2, entries 6-8).
Table 2. VO(CS)@Fe
solvent-free condition.
3
O catalyzed selective oxidation of sulfides to sulfoxides under
4
a
b
-1 c
Entry
Sulfide
Sulfoxide
Time (min) Yield (%) TON (h )
S
O
1
S
5
90 100
10

S
O
S
2
3
12
10
88
90
97.8
100
S
Ph
O
S
Ph
O
S
S
4
5
15
15
85
85
94.5
94.5
O
O
S
O
S
O N
2
O N
2
O
S
S
6
7
8
5
84
80
70
93.3
88.9
77.8
88.9
OH
OH
O
S
S
12
20
CHO
CHO
O
S
S
COOMe
COOMe
O
8
1
S
S
20
20
80
75
O
S
0
S
83.3
a
Reaction conditions: sulfide (1 mmol), 30% H
2
O
2
(2.0 mmol), VO(CS)@Fe
3
O
4
(30 mg, 0.9 mol%), rt.
b
c
1
Determined by H NMR.
TON, turn over numbers (TON = Yield/Amount of catalyst (mol)).
Scheme 3 shows a reasonable catalytic mechanism for oxidizing sulfides to sulfoxides, which
is the first step of the oxidation procedure. A can be observed, the formation of peroxo-
vanadyl species is first occurred and subsequently, the sulfur atoms in the sulfide
nucleophilically attack on the peroxo species. As known, the metal atom plays a role to create
peroxo-metal species, which can activate the H
2
2
O molecule [30, 31].
11

O
V
OV
VO
CS
OV
VO
VO
OV
Fe3O4
VO
O
S
OV
VO
R2
R1
OV
OV
VO
HOOH
O
O
H O
V
2
S
VO
R1
R2
CS
OV
VO
VO
OV
Fe3O4
OV
VO
OV
VO
VO
Scheme 3. Suggested mechanism for the sulfide oxidation using H
VO(CS)@Fe
2
2
O in the presence of
3
4
O .
In order to study the reusability of VO(CS)@Fe
3
4
O , it was magnetically isolated from the
reaction mixture and reused for the offered procedure after rinsing with acetone. As
estimated, the catalyst can be used 8 or more cycles for oxidizing methyl phenyl sulfide to the
corresponding sulfoxide (Fig. 9). Moreover, a hot filtration test was performed for checking
the leaching of V (IV) ions from the surface; however, the reaction progress was not
quantitative significantly after 2 mins of reaction, the leaching of V(IV) into the reaction
solution after 8 cycles was studied using ICP that was obtained 1.35% demonstrating the
stability of the catalyst during the reaction.
Fig. 9. Reusability of nanocatalyst.
The comparison between the obtained results for oxidizing methyl phenyl sulfide in current
study and other related academic report was performed to determine the catalytic power of
12

VO(CS)@Fe
3
4
O . According to Table 3, the previous reported processes have at least one of
the subsequent limitations: time-consuming reaction, using a transition metal and applying
volatile and/or toxic organic solvents. The results of current study show that VO(CS)@Fe
is an appropriate catalyst for oxidizing of sulfides to sulfoxides selectively.
3
O
4
Table 3. Comparison present methodology with literature in the oxidation of methyl phenyl
sulfide to methyl phenyl sulfuxide.
Entry Reaction conditions
Time (min) Yield% Ref.
1
2
3
4
5
6
7
8
VO(CS)@Fe
MNPs-based N-propylsulfamic acid, solvent-free, r.t.
MCM-Mo, CH CN,r.t., 40 ºC
Silica-based tungstate interphase, CH
Peroxotungstate supported on silica, CH
Tungstate-exchanged Mg–Al-LDH catalyst, H
Fe @SiO /Mo, CH CN, 50 ºC
VO(IV)–MCM-41, EtOH, r.t.
3
O
4
, solvent-free, r.t.
6
90
87
99
82
92
88
92
95
This work
[20d]
[32]
[33]
[34]
[35]
[36]
[20e]
80
60
90
3
3
OH/CH
OH/CH
O, r.t.
2
Cl
2
2
, r.t.
Cl
2
3
, 8 ºC 150
2
30
90
480
3
O
4
2
3
4
. Conclusion
In conclusion, the new magnetic interphase nanocatalyst of oxo-vanadium Schiff base
complex immobilized on magnetic Fe nanoparticles [VO(CS)@MNPs] was successfully
synthesized and characterized through different methods. It was also showed that
VO(CS)@Fe can be applied as a green, effective and reusable heterogeneous magnetic
3
O
4
3
O
4
nanocatalyst for oxidizing a variety of sulfides to sulfoxides selectively using hydrogen
peroxide under solvent-free conditions at ambient temperature. The advantages of this
protocol are the utilize of a commercially accessible, green, inexpensive and chemically
stabile oxidant, the mild conditions of reaction, easy operation, feasibility, short time of
reaction, good to excellent efficiency, appropriate and easy recovery of the catalyst trough a
suitable external magnetic field, reusability and excellent chemo-selectivity.
Acknowledgments. We are thankful to Payame Noor University for partial support of this
work.
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15

Graphical Abstract
Oxo-vanadium complex immobilized on chitosan coated-magnetic
nanoparticles (Fe O ): A heterogeneous and recyclable nanocatalyst for the
3
4
chemoselective oxidation of sulfides to sulfoxides with H O2
2
Hojat Veisi,* Sami Sajjadifar, Parisa Mohammadi Biabri, Saba Hemmati
O
S
R1
R2
S
R1
R2
OH
O
O
HO
n
H O (30%), r.t.
Solvent-free
2
2
NH2
VO
CS
OV
VO
CS
OV
VO
VO
VO(acac)2
Chitosane
Fe O NPs
Fe O NPs
Fe3O4 NPs
3
4
3
4
OV
H O-EtOH
2
OV
VO
Fe O NP
3
4
OV
VO
VO
Fe O NPs@CS
3
4
Fe O NPs@CS/VO
3
4
16