Chemo-selective oxidation of sulfide to sulfoxides with H2O2 catalyzed by oxo-vanadium/Schiff-base complex immobilized on modified magnetic Fe3O4 nanoparticles as a heterogeneous and recyclable nanocatalyst

Article abstract of DOI:10.1016/j.poly.2018.09.034

In this study, a schiff-base oxo-vanadium complex supported on magnetic Fe₃O₄ nanoparticles [VO(BINE)@Fe₃O₄] is prepared as a novel magnetically interphase nanocatalyst and its structural features are evaluated using different methods of TEM, SEM, EDX, ICP, VSM, TGA and FT-IR. Catalytic investigations demonstrate that this catalyst can catalyze chemoselective oxidation of sulfides to sulfoxides in high yields and short times at room temperature using hydrogen peroxide, as a green oxidant. The catalyst can be recovered up to 8 cycles without noticeable leaching and loss of catalytic activity.

Full text of DOI:10.1016/j.poly.2018.09.034

Accepted Manuscript
Chemo-selective oxidation of sulfide to sulfoxides with H2O2 catalyzed by oxo-
vanadium/Schiff-base complex immobilized on modified magnetic Fe3O4 nano-
particles as a heterogeneous and recyclable nanocatalyst
Hojat Veisi, Asra Rashtiani, Amin Rostami, Mohadeseh Shirinbayan, Saba
Hemmati
PII:
S0277-5387(18)30586-2
https://doi.org/10.1016/j.poly.2018.09.034
POLY 13433
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
7 June 2018
15 September 2018
Please cite this article as: H. Veisi, A. Rashtiani, A. Rostami, M. Shirinbayan, S. Hemmati, Chemo-selective
oxidation of sulfide to sulfoxides with H2O2 catalyzed by oxo-vanadium/Schiff-base complex immobilized on
modified magnetic Fe3O4 nanoparticles as a heterogeneous and recyclable nanocatalyst, Polyhedron (2018), doi:
https://doi.org/10.1016/j.poly.2018.09.034
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Chemo-selective oxidation of sulfide to sulfoxides with H2O2 catalyzed by
oxo-vanadium/Schiff-base complex immobilized on modified magnetic
Fe3O4 nanoparticles as a heterogeneous and recyclable nanocatalyst
Hojat Veisi,*,a Asra Rashtiani,a Amin Rostami,b,c Mohadeseh Shirinbayan,b Saba Hemmatia
aDepartment of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran
Email: hojatveisi@yahoo.com
bDepartment of Chemistry, Faculty of Science, University of Kurdistan, 66177-15175, Sanandaj, Iran
cResearch Centre of Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj, Iran
Abstract. In this study, a schiff-base oxo-vanadium complex supported on magnetic Fe3O4
nanoparticles [VO(BINE)@Fe3O4] is prepared as a novel magnetically interphase nanocatalyst
and its structural features are evaluated using different methods of TEM, SEM, EDX, ICP,
VSM, TGA and FT-IR. Catalytic investigations demonstrate that this catalyst can catalyze
chemoselective oxidation of sulfides to sulfoxides in high yields and short times at room
temperature using hydrogen peroxide, as a green oxidant. The catalyst can be recovered up to
8 cycles without noticeable leaching and loss of catalytic activity.
Keywords: Sulfides, Sulfoxides, Hydrogen peroxide, Oxo-vanadium complex, Magnetically
catalyst
Introduction
Though selective oxidation of sulfides and converting them to sulfoxides or sulfones is so
invaluable in organic chemistry, it has remained an endeavor [1,2]. Consequently, scientists
have attempted to propose and confirm an innovative method to oxidize sulfides. The first
sulfoxide procurement approach refers to Maercker’s work, in 1865. Since then, many
procedures have been developed to conduct transformation of sulfides into sulfoxides [3]. For
this purpose, several oxidants have been widely applied including concentrated HNO3, high-
valence metal salts [4], sodium metaperiodate, m-chloroperoxybenzoic acid [5], halogens and
nitrogen pentoxide [6-10]. Unfortunaly, many of the developed procedures require hazardous
and toxic reagents [11], are complicated methods [12] or involve overoxidation of sulfoxides,
which results in unexpected sulfones or undesired by-products [13,14]. That is why many
researchers have focused on developing innovative and effective catalytic systems that use an
alternative oxidant, are able to surpass the outlined restrictions and satisfy eco-sustainability
and green chemistry requirements, particularly atom economy. An appropriate oxidant
candidate is aqueous 30% H2O2, which is known as an ecological oxidant, since it demonstrates
several extraordinary advantages such as being low cost and eco-friendly, possessing an
efficient-oxygen content and generatig water as an oxidation side product [15].
If the devised catalytic system employs a homogeneous catalyst, then it will be necessary to
remove the expensive catalyst from the reaction vessel and use a chromatographic technique
to retrieve the catalyst [16]. Therefore, manufactured catalytic arrangements should be
considered to contain supported organic and metal based catalyst materials to activate hydrogen
peroxide [17]. Such catalyst can be retrieved from the reaction vessel and reused, conveniently.
Though this research area has advanced over years, most devised methods have failed in
controlling the reaction process to gain selective and excellent yields of sulfoxide or sulfone
products. A class of catalysts that has attracted much interest corresponds to vanadium (V)
1

Schiff base complexes due to their noticeable functional compatibilities and provision of high
selectivity in oxidation reactions of sulfides [18].
To enhance reusability of the utilized catalyst, magnetic property can be included. Magnetic
organic-inorganic nanocomposites have become popular among academic and industrial
scholars as magnetic catalysts. Using such catalytic magnetic nanoparticles (NPs) can facilitate
catalyst isolation and recycling, which is a common problem in many homogenous and
heterogeneous catalytic processes [19-21]. Furthermore, magnetic catalysts can be recovered
after several subsequent catalytic runs by application of an external magnetic field while
conserving their catalytic efficiencies [22].
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 presence
of peroxides as oxidants [23]. In continue of our attempts towards developing efficient and
ecofriendly heterogeneous catalysts [23], herein, we synthesize a new oxo-vanadium Schiff
base complex supported on magnetic nanoparticles, i.e. VO(BINE)@Fe3O4, characterize it and
explore its catalytic features in chemoselective oxidation of sulfides to sulfoxides using green
H2O2 oxidant (Figure 1).
2. Experimental
2.1. Preparation of Fe3O4/Pr-NH2
Fe3O4/Pr-NH2 was synthesized according to the synthesis method described in our previous
report [23d].
2.2. Preparation of VO(BINE)@Fe3O4
500 mg of the prepared Fe3O4/Pr-NH2 NPs were dispersed in 70 mL ethanol through 20 mon
sonication. Then, 1 mmol 1,2-bis(2-formyl naphthoxy)ethane was added to the obtained
solution and the solution was stirred for 24 h under N2 atmosphere, at 80 ºC. In the next step,
the heated reaction mixture was permitted to cool down to room temperature. The resultant
NPs, i.e. Fe3O4/Schiff base (BINE) particles, were washed several times with ethanol, removed
from the solution via magnetic decantation and dried up at room temperature. After that, the
resulted 500 mg BINE NPs were dispersed in 50 mL EtOH-H2O (1:1) solution for 20 min, in
an ultrasonic bath. Next, a 20 mL aqueous solution of vanadyl acetylacetonate (0.265 g; 0.001
mol) was mixed with the BINE mixture and refluxed for 24 h. In this way, VO(BINE)@Fe3O4
particles formed. The produced NPs were removed by magnetic decantation and washed using
ethanol, water and acetone, subsequently, to eliminate any unattached substrate. According to
atomic absorption spectroscopy measurements, the obtained catalyst had 0.29±0.001 mmol g-
1 vanadyl content.
2.3. Typical experimental procedure for sulfoxide preparation
A 5-mL round bottom flask was used as the reactor. At each synthesis trial, 30 mg
VO(BINE)@Fe3O4 nanocatalyst (0.9 mol%) and 30% (w/w) H2O2 oxidant (2.0 mmol) were
added to 1 mmol sulfide, successively, and the prepared reaction mixture was stirred for the
desired time on a magnetic stirrer, at room temperature. TLC (EtOAc/n-hexane, 1/10) and GC
were employed to track progress of the reaction. After reaction completion, an external magnet
was applied to separate the catalyst from the reaction products (within 5 s) and the reaction
mixture was washed two times with diethyl ether (3 mL) and decanted. The mixture of organic
2

compounds was dried over anhydrous Na2SO4. Then, Et2O was evaporated under reduced
pressure to achieve pure products in 80% to 96% yields.
3. Results and discussion
3.1. Preparation and characterization of VO(BINE)@Fe3O4
VO(BINE)@Fe3O4 nanocatalyst was prepared in several subsequent steps. First, Fe3O4 was
synthesized based on our previous work [23e]. Then, the iron oxide particles were coated with
3-aminopropyltriethoxysilane (APTES) to give aminopropyl-functionalized magnetic NPs.
Next, the functionalized amino groups reacted with 1,2-bis(2-formyl naphthoxy)ethane to form
Fe3O4/Schiff base (BINE). At the end, the Fe3O4 immobilized Schiff base (BINE@Fe3O4) was
coordinated with VO(acac)2 to generate oxo-vanadium complex supported on magnetic NPs
(VO(BINE)@Fe3O4). Finally, the VO(BINE)@Fe3O4 NPs were separated by an external
magnet and vacuum dried. The synthesis steps carried out to produce the catalyst are depicted
in Scheme 1. Elemental analysis determined that ~0.32 mmol of Schiff base has linked to 1 g
of Fe3O4. Moreover, t hese values declared that all anchored BINE ligand have efficiently and
approximately coordinated with V ions giving the required catalytic active sites. The catalyst
was characterized by FTIR, CHN, XRD, FESEM, TEM, EDS, ICP and VSM analysis methods.
O
O
NH2
EtO
EtO
S
i
NH2
S
i
O
EtO
NH4OH, N2
FeCl3.6H2O
Fe3O4 NP
Fe3O4 NP
FeCl2.4H2O 85 oC, 30 min
O
S
O
i
NH2
O
O
O
H
CHO
OHC
1,2-bis(2-formyl
naphthoxy)ethane
O
O
N
S
i
O
O
O
Fe3O4 NP
O
S
O
VO(acac)2
i
N
O
H2O-EtOH
reflux, 24 h
H
H
O
O
N
S
i
O
O
O
V
Fe3O4 NP
O
O
S
O
i
N
O
H
3

Fig. 1. Preparation of VO(BINE)@Fe3O4 nanocatalyst.
To confirm successful functionalization of the Fe3O4 NPs with BINE Schiff base groups,
Fourier transform infrared (FT-IR) spectroscopy was performed. Figure 2 shows FTIR spectra
of (a) magnetic Fe3O4 NPs, (b) amino-functionalized magnetic NPs, i.e. Fe3O4/Pr-NH2, and (c)
Fe3O4/Schiff base (BINE). FT-IR spectrum for Fe3O4 NPs (Figure 2a) contains a peak at 3437
cm-1, which refers to symmetric and asymmetric stretching vibrational modes of O-H bonds
attached to surface of the iron atoms [24]. Also, it outlines several bands with low
wavenumbers (≤700 cm-1) corresponding to Fe-O bonds of Fe3O4. Fe-O vibrational bands
related to bulk Fe3O4 should appear at 570 cm-1 and 375 cm-1. However, as size of the particles
is reduced and we have Fe3O4 NPs, the peaks are accompanied with a blue shift and have
peaked at 634 cm-1 and 568 cm-1 [23e]. FT-IR spectra of Fe3O4/Pr-NH2 and Fe3O4/ BINE
(Figures 2b and 2c, respectively), outline almost similar peak positions for Fe-O bond
vibrations. Meantime, observation of a vibrational band at 1000 cm-1 approves presence of
APTMS on surface of the Fe3O4 NPs, which is associated with Fe-O-Si stretching vibrations
[25, 26]. In Figures 1b and 1c, the peaks positioned at 2959 cm-1 and 3085 cm-1 are assigned to
aliphatic and aromatic C-H bonds of Fe3O4/Pr-NH2 and Fe3O4/Schiff base (BINE),
respectively. The ∼1080 cm-1 peak is attributed to Si-O-Si stretching modes of Fe3O4/Pr-NH2
and Fe3O4/BINE. These vibrational bands approve successful coating of the Fe3O4 NPs by
silica and the Schiff base precursor. Furthermore, the 1624, 1581, 3028 and 1436 cm-1 peaks,
which are ascribed to C=NH, C=C, aryl C-H stretches and C-N stretching of amine
respectively, verify attachment of primer of Schiff base groups to surface of the Fe3O4/Pr-NH2
NPs [23c]. All these peaks clarify that surface of the Fe3O4 NPs has been modified by BINE
groups, successfully, and the NPs are ready for metal-ligand coordination.
4

Fig. 2. FT-IR spectrum of (a) magnetic Fe3O4 nanoparticles, (b) amino-functionalized
magnetic (Fe3O4/Pr-NH2) nanoparticles, and (c) Fe3O4/Schiff base (BINE).
FESEM and TEM identified morphology and size of the hybrid organic-inorganic catalyst
(VO(BINE)@Fe3O4). According to FESEM image of VO(BINE)@Fe3O4, its particles are
uniform and nanometer-sized (Figure 3). Also, the TEM image indicates successful production
of the modified Fe3O4 magnetic NPs with a homogenous distribution of particles (Figure 4).
Magnification of the TEM image, unravels slight aggregation and a stacking texture, which is
an outcome of attractive magnetic interaction between the catalyst NP structures. Mean
diameter of the Fe3O4 core in the NPs is about 10 to 15 nm.
5

Fig. 3. FESEM image of VO(BINE)@Fe3O4 nanocatalyst.
Fig. 4. a) TEM image of VO(BINE)@Fe3O4 nanocatalyst.
6

Successful immobilization of oxo-vanadium Schiff base complex on Fe3O4 surface was also
approved using an EDX detector coupled with FESEM. In this way, Fe, V, C, N, O and
Si were detected (Figure 5).
Fig. 5. EDX data for VO(BINE)@Fe3O4 nanocatalyst.
Figure 6a displays XRD pattern of VO(BINE)@Fe3O4 nanocatalyst. In this pattern, several
diffraction peaks can be distinguished at 2θ of 30.2º, 35.8º, 43.4º, 53.6º, 57.2º and 62.8º. These
peaks can be ascribed to (220), (311), (400), (422), (511) and (440) planes of cubic Fe3O4
structure (JCPDS 65-3107). Consequently, it can be inferred that presence of oxo-vanadium
complex has not altered crystalline phase of Fe3O4. VSM was applied to measure magnetization
of VO(BINE)@Fe3O4 NPs, at room temperature. According to the measured VSM curve, no
hysteresis can be observed and remanence and coercivity are negligible. These evidences
indicate super-paramagnetism of these NPs (Figure 6b). Saturation magnetization of
VO(BINE)@Fe3O4 (29.2 emu g-1) is less significant than saturation magnetization of Fe3O4
(62.3 emu g-1) [23e] since the coated Schiff base oxo-vanadium complex layer is non-magnetic.
Nevertheless, the obtained catalyst is sufficiently magnetic sensitive to enable its efficient and
convenient separation from reaction mediums
Fig. 6. a) XRD pattern and; b) VSM spectra of VO(BINE)@Fe3O4.
7

TGA analysis helped to evaluate stability of the synthesized VO(BINE)@Fe3O4 catalyst and
percentage of organic functional groups bound to surface of the magnetic NPs. TGA curve of
the catalyst (Figure 7) demonstrates 3.2% initial weight loss at temperatures lower than 200
°C. This weight loss is related to evaporation of physisorbed solvent molecules and loss of
surficial hydroxyl groups of the support. Degradation of the organic groups is observed in the
range of 250 to 520 °C, based on the identified second and third weight losses that sum up to
19%. Therefore, no catalyst weight loss, except solvent loss, is observed by elevating the
temperature up to 200 ºC and only at temperatures above 250 °C the catalyst degrades
thermally, which implies its high thermal stability. Such high thermal stability is advantageous
since many organic compounds should be synthesized at high temperatures.
Fig. 7. TGA diagram for VO(BINE)@Fe3O4.
Nitrogen adsorption desorption isotherm was used for deter-mining the surface properties (Fig.
8). VO(BINE)@Fe3O4 shows type IV isotherm which exhibits the mesoporous structure and
presence of nano-voids in this system. BET analysis of VO(BINE)@Fe3O4 demonstrates the
specific surface area is estimated at about 55.2 m2g-1. Moreover, BJH pore size distribution of
the catalyst shows a narrow mesopore size distribution centered at 25.8 nm. Its pore volume
was estimated as 0.404 cm3g-1 by BJH analysis. VO(BINE)@Fe3O4 represents the good BET
surface area with the great pore volume, which makes it as a suitable option for catalytic
system.
8

Fig. 8. BET Ads Des isotherm and pore size distribution of VO(BINE)@Fe3O4.
3.2. Catalytic application of VO(BINE)@Fe3O4 in oxidation of sulfides to sulfoxides
Solvent free catalytic activation of 30% H2O2 by VO(BINE)@Fe3O4, as a reusable organic-
inorganic hybrid catalyst, and performance of the catalyst in chemo-selective oxidation of
sulfides to sulfoxides was investigated at room temperature (Figure 9).
S
H
R1
R2
O
O
N
S
i
O
O
H2O2 (30%), r.t.
Solvent-free
O
V
Fe3O4 NP
O
O
S
O
S
O
i
N
O
R2
R1
H
Fig. 9. VO(BINE)@Fe3O4 catalyzed the oxidation of sulfides to sulfoxides using H2O2.
In this respect, first the reaction conditions were optimized by concentrating on oxidation of
methyl phenyl sulfide, as a model sulfide, using 30% H2O2 under different reaction conditions.
The obtained reaction times and product yields are listed in Table 1. As Table 1 implies, the
oxidation reaction cannot complete without VO(BINE)@Fe3O4 catalyst even after 24 h (entries
1 and 2). On the other hand, complete oxidation of methyl phenyl sulfide to methyl phenyl
9

sulfoxide can be achieved using 2 eq. H2O2 and 30 mg VO(BINE)@Fe3O4 (0.9 mol%) at room
temperature and under solvent free condition (Table 1, entry 5).
Table 1. Optimization of the amounts of H2O2 and VO(BINE)@Fe3O4 for the selective
oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide.
Entry Catalyst (mol%)
H2O2 (mmol) Solvent
Time (min) Yield (%)a
Solvent-free 24 h 35
1
Catalyst-free
2.0
2.0
2.0
2.0
2.0
2.0
1.0
3.0
2.0
2.0
2.0
2
Fe3O4 (20)
Solvent-free 24 h
Solvent-free 2 h
Solvent-free 45
Solvent-free
Solvent-free
Solvent-free 30
Solvent-free
EtOH
CH3CN
CH2Cl2
45
96
96
96
96
75
80
96
96
90
3
4
5
6
7
8
9
10
11
VO(BINE)@Fe3O4 (0.3)
VO(BINE)@Fe3O4 (0.6)
VO(BINE)@Fe3O4 (0.9)
VO(BINE)@Fe3O4 (1.2)
VO(BINE)@Fe3O4 (0.9)
VO(BINE)@Fe3O4 (0.9)
VO(BINE)@Fe3O4 (0.9)
VO(BINE)@Fe3O4 (0.9)
VO(BINE)@Fe3O4 (0.9)
5
5
5
30
30
2 h
aDetermined by GC and no sulfone was observed..
Table 2 highlights generality of the proposed synthesis approach as an easy but efficient
method to oxidize aliphatic and aromatic sulfides. So that, this catalyzed reaction is an
appropriate method that can be utilized for general synthesis of sulfoxides. As Table 2
demonstrates, the intended products can be acquired in excellent yields, at minimal reaction
times and with good turnover numbers (TON) and turnover frequencies (TOF). It should be
noted that the sulfides oxidize chemoselectively regardless of the nature of sulfide functional
groups, such as OH, CHO and COOMe (Table 2, entries 6-8).
Table 2. VO(BINE)@Fe3O4 catalyzed selective oxidation of sulfides to sulfoxides under
solvent-free condition.a
Sulfide
Sulfoxide
Time Yield
(min) (%)b
Entry
TOF TON
(h-1)c (h-1)d
O
S
S
1
5
10
6
96
95
96
1280 106.7
633.3 105.5
1066.7 106.7
S
O
S
2
3
S
O
S
Ph
Ph
O
S
S
4
5
10
10
88
92
586.7 97.8
613.3 102.2
O
O
S
O
S
O2N
O2N
10

O
S
S
6
7
8
5
90
85
78
1200
100
OH
OH
O
S
S
10
15
566.7 94.4
346.7 86.7
CHO
CHO
O
S
S
COOMe
COOMe
O
S
S
S
8
15
15
85
80
377.8 94.4
355.5 88.9
O
S
10
aReaction conditions: sulfide (1 mmol), 30% H2O2 (2.0 mmol), VO(BINE)@Fe3O4 (30 mg, 0.9 mol%), rt.
bDetermined by GC and all products are known and were characterized by IR and NMR spectra as
compared with those reported in the literature [27-30].
cTOF, turnover frequencies (TOF) = (Yield/Time)/Amount of catalyst (mol).
dTON, turnover number (TON) = Yield/Amount of catalyst (mol).
Figure 10 illustrates a proposed mechanism for oxidative conversion of sulfides to sulfoxides
by the title catalyst. This conversion is the first stage of sulfide oxidation process. At the first
step, hydrogen peroxide binds to the vanadium ion and peroxo-vanadyl species form. Then, the
generated peroxo-vanadyl species undergoes a nucleophilic attack by sulfur atom of the sulfide.
As it is known, the metal atom plays a role in formation of peroxo-metal species and activates
H2O2 molecules [31-33].
H
O
O
N
S
i
O
O
O
V
Fe3O4 NP
O
O
S
O
i
N
O
S
O
H
R2
R1
H2O2
H2O
H
S
R1
R2
O
i
S
N
O
O
O
O
O
Fe3O4 NP
V
O
O
i
S
O
N
O
H
Fig. 10. Proposed mechanism for the sulfide oxidation with H2O2 in the presence of
VO(BINE)@Fe3O4.
11

To test reusability of the catalyst, VO(BINE)@Fe3O4 was collected from the reaction mixture
by applying a magnetic device, rinsed in acetone and reused in further catalytic runs. As it was
expected, VO(BINE)@Fe3O4 can be employed for 8 or more subsequent catalytic cycles of
methyl phenyl sulfide oxidation to its associated sulfoxide (Fig. 11). Also, a hot filtration test
was conducted to explore leaching of V(IV) ions from surface of the catalyst. A negligible
quantity of reaction progress was observed, even after 2 min reaction time. ICP analysis
determined 1.35% V(IV) leaching into the reaction solution, after 6 catalytic runs. This
insignificant leaching value verifies stability of the catalyst, under the reaction conditions.
Fig. 11. Reusability of nanocatalyst.
Finally, activity of VO(BINE)@Fe3O4 in catalytic oxidation of methyl phenyl sulfide is
compared with performance of other reported catalysts in Table 3. Accordingly, the previously
reported catalytic procedures have exhibited one of the following disadvantages, at least: using
transition metal, longer reaction times and requiring volatile and/or toxic organic solvents.
Based on Table 3, it can be stated that VO(BINE)@Fe3O4 is a proper catalyst for
chemoselective oxidation of sulfides to sulfoxides.
Table 3. Comparison present methodology with literature in the oxidation of methyl phenyl
sulfide to methyl phenyl sulfuxide.
Entry Reaction conditions
Time Yield TOF
Ref.
(min)
5
%
96
(h-1)c
1280
78.9
839
1
2
3
4
5
6
7
8
9
10
VO(BINE)@Fe3O4, solvent-free, r.t.
MNPs-based N-propylsulfamic acid, solvent-free, r.t.
MCM-Mo, CH3CN,r.t., 40 ºC
Silica-based tungstate interphase, CH3OH/CH2Cl2, r.t.
Peroxotungstate supported on silica, CH3OH/CH2Cl2, 8 ºC 150
VO(acac)2-exchanged polymer resin catalyst, H2O, r.t.
Fe3O4@SiO2/Mo, CH3CN, 50 ºC
VO(IV)–MCM-41, EtOH, r.t.
This work
[23e]
[35]
[36]
[37]
[38]
[39]
[23f]
[40]
[18c]
80
60
100
99
90
82
92
98
27.3
24.5
98
10
90
480
10
92
20.4
d
95
-
d
VO(IV) Schiff base complexes, EtOH, r.t.
100a
-
b
d
oxovanadium(IV) Schiff base complex, solvent-free,45 °C 50
-
-
aConversion (%).
bThe major product is sulfone.
cTOF, turnover frequencies (TOF) = (Yield/Time)/Amount of catalyst (mol).
dThe catalyst’s mol% is not reported in the paper.
4. Conclusion
12

This paper introduces an oxo-vanadium Schiff base complex supported on Fe3O4 nanoparticles
[VO(BINE)@Fe3O4] as a novel magnetically interphase nanocatalyst and evaluates its
properties by different techniques. It has also been demonstrated that VO(BINE)@Fe3O4 can
be employed as a green, reusable and efficient heterogeneous nanocatalyst to oxidize a wide
range of sulfides to sulfoxides, selectively, using H2O2 at room temperature and solvent free
conditions. This protocol has several advantages including mild reaction conditions, using an
eco-friendly, commercially available, cheap and chemically stable oxidant, simplicity of
operation, short reaction times, practicability, good to high yields, convenient catalyst
recyclability through applying an external magnetic field and excellent chemoselectivity.
Acknowledgement
We are thankful to Payame Noor University (PNU) and Kurdistan University of Iran for
financial supports.
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Graphical Abstract
15

Chemo-selective oxidation of sulfide to sulfoxides with H2O2 catalyzed by oxo-
vanadium/Schiff-base complex immobilized on modified magnetic Fe3O4
nanoparticles as a heterogeneous and recyclable nanocatalyst
Hojat Veisi, Asra Rashtiani, Amin Rostami, Mohadeseh Shirinbayan, Saba Hemmati
S
H
R1
R2
O
O
N
S
i
O
O
H2O2 (30%), r.t.
Solvent-free
O
V
Fe3O4 NP
O
O
S
O
S
O
i
N
O
R2
R1
H
16