New metal complexes supported on Fe3O4 magnetic nanoparticles as recoverable catalysts for selective oxidation of sulfides to sulfoxides

Article abstract of DOI:10.1002/aoc.3429

Fe₃O₄ nanoparticles were coated with aminopropyltriethoxysilane and subsequently reacted with isatin to obtain imine-bonded Fe₃O₄ nanoparticles. The addition of ZrOCl₂·8H₂O or CuCl₂ led to the formation of complexes of Zr(IV)/isatin@Fe₃O₄ or Cu (II)/isatin@Fe₃O₄ as new magnetically separable catalysts. The synthesized catalysts were characterized using various techniques. These catalysts are shown to be efficient for chemo-selective oxidation of sulfides to sulfoxides using hydrogen peroxide as oxidative agent. This system has many advantages, such as excellent level of reusability of magnetic catalysts, high yields, simplicity of separation of catalysts using an external magnet, environmental benignity and ease of handling.

Full text of DOI:10.1002/aoc.3429

Full paper
Received: 18 November 2015
Accepted: 10 December 2015
Published online in Wiley Online Library: 29 January 2016
(wileyonlinelibrary.com) DOI 10.1002/aoc.3429
New metal complexes supported on Fe3O4
magnetic nanoparticles as recoverable catalysts
for selective oxidation of sulfides to sulfoxides
Maryam Hajjami* and Somaye Kolivand
Fe3O4 nanoparticles were coated with aminopropyltriethoxysilane and subsequently reacted with isatin to obtain imine-bonded
Fe3O4 nanoparticles. The addition of ZrOCl2Á8H2O or CuCl2 led to the formation of complexes of Zr(IV)/isatin@Fe3O4 or Cu (II)/
isatin@Fe3O4 as new magnetically separable catalysts. The synthesized catalysts were characterized using various techniques.
These catalysts are shown to be efficient for chemo-selective oxidation of sulfides to sulfoxides using hydrogen peroxide as oxi-
dative agent. This system has many advantages, such as excellent level of reusability of magnetic catalysts, high yields, simplicity
of separation of catalysts using an external magnet, environmental benignity and ease of handling. Copyright © 2016 John Wiley
& Sons, Ltd.
Keywords: Zr(IV) complex of Fe3O4; Cu(II) complex of Fe3O4; magnetic nanoparticles; sulfoxides
Sulfoxides have attracted considerable interest due to their wide
Introduction
spectra of biological and pharmacological activities.[20] Therefore
In recent years, the significant role of transition metals as catalysts
in organic reactions has been undeniable.[1] Among the different
types of transition metals in the periodic table of elements, zirco-
nium and copper have become outstanding catalysts in many
organic transformations and new bond formations. The fundamen-
tal role of zirconium as a catalyst has been reported in many papers.
Amino-functionalized Zr(IV) was used as a solid catalyst in the
Knoevenagel condensation reaction.[2] The introduction of Zr
increases the reducibility of Ni–Zr/SiO2 for CO2 reforming of
methane.[3] Biodiesel production has been carried out in the pres-
ence of Zr-SBA-15 as a catalyst.[4] Hexagonal Zr(HPO4)2ÁH2O nano-
particles catalysed the alkylation of phenol.[5] Mesoporous
zirconium phosphate was used in the Pechmann condensation
reaction for the synthesis of coumarins.[6] Modified zirconium
dichloride was used for the polymerization of styrene.[7] Various
types of modified zirconium materials have been used in reduction
of nitric oxide,[8] dehydration of glycerol,[9] aromatization of
Hantzsch 1,4-dihydropyridines,[10] synthesis of nitrogen-containing
pyrazine-based heterocycles[11] and synthesis of α-amino-
phosphonates.[12] Copper is an efficient and non-toxic metal moi-
ety in many heterogeneous and homogeneous catalysts
particularly for the synthesis of organic compounds. Briefly, among
the copper-catalysed systems can be noted copper (II)/diamine
complex for the asymmetric Henry reaction.[13] Cu(II) acetylaceto-
nate anchored onto amine-functionalized mesoporous silica was
produced and tested for aziridination of styrene.[14] The
enantioselective Mukaiyama aldol reaction,[15] Friedel–Crafts
hydroxyalkylation[16] and Suzuki–Miyaura coupling reactions[17] in
the presence of Cu(II) complexes have been reported. Also spheri-
cal Cu-MCM-41 nanoparticles were used for three-component
reaction of aldehydes, amines and alkynes.[18] Cu(II)-SBA-15 was
demonstrated as an efficient catalyst for the synthesis of 1,
4-triazoles via azide alkyne cycloaddition.[19]
selective oxidation of sulfides to sulfoxides is an important transfor-
mation in organic chemistry. In recent years, acceptable processes
involving the use of hydrogen peroxide in the presence of various
types of transition metal catalysts for selective oxidation of sulfides
to sulfoxides have been reported. A considerable number of
methods have been reported for the oxidation of sulfides to sulfox-
ides using H2O2 in combination with NiFe2O4,[21] Ti(IV) complex,[22]
V/TiO2,[23] cerium(IV) triflate,[24] molybdate-based catalyst,[25]
metalloporphyrins immobilized into montmorillonite,[26] Zn
complex,[27] Cu salen–Fe3O4,[28] Cu(II) Schiff base complex,[29] pre-
formed manganese complex,[30] tantalum(V) chloride[31] and zirco-
nium tetrachloride.[32]
According to green chemistry and in line with sustainable devel-
opment, nowadays the employment of heterogeneous catalysts in
organic reactions has become a large area of research. For this pur-
pose, nanoparticle supports have emerged as an alternative form of
support materials, especially because of their high surface areas
and catalyst loading capacity. Recently iron(III) oxide magnetic
nanoparticles (MNPs) have been attracting much attention due to
their properties, including simple separation using an external mag-
net enabling the recovery and prevention of loss of catalyst and
high surface area to improve active catalytic sites.[33] The presence
of hydroxyl groups on the surface of Fe3O4 MNPs allows reaction
with alkoxysilane derivatives and formation of Si–O bonds which
support specific functional groups on the shell of the Fe3O4 core.
These kinds of modification of Fe3O4 provide a wide range of
*
Correspondence to: Maryam Hajjami, Department of Chemistry, Faculty of Science,
Ilam University, PO Box 69315516, Ilam, Iran. E-mail: mhajjami@yahoo.com
Department of Chemistry, Faculty of Science, Ilam University, PO Box 69315516,
Ilam, Iran
Appl. Organometal. Chem. 2016, 30, 282–288
Copyright © 2016 John Wiley & Sons, Ltd.

Modified Fe3O4 MNPs as catalysts for oxidation of sulfides
catalytic systems. For instance, cobalt(II) salophen complex sup-
ported on imidazole-functionalized silica-coated cobalt ferrite,[34]
ionic tagged 1,4-diazabicyclo[2.2.2]octane grafted on Fe3O4
nanoparticles,[35] imidazole functionalized on MNPs,[36] Fe3O4 MNPs
coated with (3-aminopropyl)triethoxysilane,[37] organometallic Mo
complex anchored to silica core–shell magnetic iron oxide,[38]
polybasic ionic liquid-coated MNPs[39] and Fe3O4@silica sulfonic
acid[40] have been reported in the literature.
In the work reported here, we synthesized magnetic Zr(IV)/
isatin@Fe3O4 and Cu(II)/isatin@Fe3O4 nanoparticles as green and
new catalysts for the oxidation of sulfides to sulfoxides by H2O2
(30%) in ethanol (1).
(Bruker, Germany) in the range 400–4000 cmÀ1. Thermogravi-
metric analysis (TGA) was carried out with a Pyris Diamond
(PerkinElmer, UK) from ambient temperature to 800 °C, using
a ramp rate of 10 °C minÀ1. Supermagnetic properties of the
catalysts were measured using vibrating sample magnetome-
try (VSM; MDKFD). An energy-dispersive X-ray spectroscopy
(EDX; FESEM-TESCAN MIRA3) study of Zr (IV)/imine@Fe3O4
and Cu (II)/imine@Fe3O4 confirmed the presence of zirconium
and copper in the structure of the catalysts. Transmission
electron microscopy (TEM) analysis of the Zr catalyst was re-
corded using a Zeiss EM10C-80KV instrument. The Cu catalyst
morphology was examined using scanning electron micros-
copy (SEM) with a FESEM-TESCAN MIRA3.
Experimental
Synthesis of Schiff Base-Functionalized Fe3O4
Chemicals and Instrumentation
Fe3O4 nanoparticles were prepared by the co-precipitation
method. Typically, 5.86 g of FeCl3Á6H2O and 2.22 g of
FeCl2Á4H2O were dissolved in 100 ml of deionized water at
80 °C under nitrogen atmosphere. Then, 10 ml of 25% NH4OH
solution was injected into the mixture with vigorous mechan-
ical stirring. Black MNPs were formed in the last step. After-
wards, the reaction mixture was cooled and the resulting
black MNPs were isolated using an external magnet, washed
four times with deionized water and ethanol and then dried
at 60 °C under vacuum. The prepared Fe3O4 (2 g) was soni-
cated in ethanol–water (250 ml) for 30 min and then 4 ml
of 3-aminopropyltriethoxysilane was stirred with the Fe3O4
at room temperature for 8 h under nitrogen atmosphere.
All reactants were purchased from Aldrich and Merck and
used without further purification. Deionized distilled water
was used in the preparation of all solutions. The known prod-
ucts were characterized from physical data by comparison
with those of authentic samples. Unknown compounds were
identified from their spectra (1H NMR and 13CNMR, Bruker
FX 400Q NMR spectrometer). The crystalline structure of syn-
thesized samples was examined using X-ray diffraction (XRD)
with a GBC-Difftech MMA diffractometer. Nickel-filtered Cu
Kα radiation (λ = 1.54 Å) was used at an acceleration voltage
of 40 kV. Fourier transform infrared (FT-IR) analyses were car-
ried out using KBr pellets and a Vertex 70 spectrophotometer
Scheme 1. Representation of the formation of Zr(IV)/imine@Fe3O4 and
Cu/imine@Fe3O4 MNPs.
Figure 1. EDX spectra of (a) Zr/isatin@Fe3O4 and (b) Cu/isatin@Fe3O4 MNPs.
Appl. Organometal. Chem. 2016, 30, 282–288
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Hajjami and S. Kolivand
Finally, the obtained nanoparticles were separated from the
solution by magnetic decantation, washed several times with
distilled water and ethanol and then dried in a vacuum over-
night to yield NH2(CH2)3–Fe3O4. In the next step, isatin
(3 mmol) was added to a magnetically stirred mixture of
NH2(CH2)3–Fe3O4 (1 g) in ethanol (20 ml). After refluxing for
4 h, the mixture was cooled to room temperature. The
resulting brown Schiff base-functionalized Fe3O4 was sepa-
rated using an external magnet, washed with ethanol and
dried in an oven under vacuum.
Synthesis of Zr (IV)/imine@Fe3O4
The Zr(IV) complex grafted to Fe3O4 was synthesized by the reac-
tion of ZrOCl2Á8H2O (2 mmol) in acetone (20 ml) with the Schiff
base-functionalized Fe3O4 (1 g) for 6 h under nitrogen atmo-
sphere and reflux condition. After that, the solid was separated
using an external magnet, and washed with ethanol and water.
It was then dried in a vacuum oven at 60 °C overnight. Coordina-
tion of the zirconium fragment to the grafted ligand yields Zr(IV)/
imine@Fe3O4 MNPs.
Synthesis of Cu (II)/imine@Fe3O4
Treatment of Schiff base-functionalized Fe3O4 (1 g) with an etha-
nol solution (20 ml) of CuCl2 (2 mmol) for 15 h under reflux condi-
tion and nitrogen atmosphere led to a new Cu complex labelled
as Cu (II)/imine@Fe3O4. The obtained solid was magnetically
collected from the solution and washed with water and ethanol
and dried in vacuum overnight. The synthetic pathway adopted
is outlined in 1.
General Procedure for Selective Oxidation of Sulfides to
Sulfoxides
A 30% hydrogen peroxide solution (0.4 ml) was added to a
solution containing sulfide (1 mmol), Zr or Cu complex MNPs as
catalyst (0.03 g) and 3 ml of EtOH. The reaction mixture was
stirred at 35 °C for the Zr catalyst or 45 °C for the Cu catalyst until
completion of reaction as monitored using TLC. After complete
conversion of the reactant, the catalyst was easily separated using
an external magnet and washed with dichloromethane to remove
residual product. The product was extracted with CH2Cl2, and
then the organic layer was dried over anhydrous Na2SO4. The
solvent was removed under vacuum and the residue was purified
using chromatography.
Figure 2. XRD patterns of step-by-step preparation of catalysts and used
catalysts.
Figure 4. FT-IR spectra of Fe3O4, amine@Fe3O4, imine@Fe3O4, Zr/
Figure 3. TGA patterns of Fe3O4, Zr/imine@Fe3O4 and Cu/imine@Fe3O4.
imine@Fe3O4, Cu/imine@Fe3O4 and reused catalysts.
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 282–288

Modified Fe3O4 MNPs as catalysts for oxidation of sulfides
Results and Discussion
In continuation of our studies of the application of immobilized
metal complexes on supports in organic reactions,[41–43] herein
we report the preparation and characterization of a Schiff base
complex of Fe3O4 nanoparticles prepared by chemical co-
precipitation of FeCl2 and FeCl3 according to a previously reported
procedure. After dispersion, the Fe3O4 nanoparticles were treated
with aminopropyltriethoxysilane to prepare NH2-functionalized
Fe3O4 nanoparticles. Addition of isatin to these amine functional-
ized MNPs led to the formation of imine@Fe3O4. After that, in order
to prepare the final catalyst as a Schiff base complex of MNPs,
ZrOCl2Á8H2O or CuCl2 was added to the imine@Fe3O4.
The EDX spectrum of Cu/isatin@Fe3O4 (Fig. 1) shows that the
mass percent of C, Fe, Si, O, N and Cu is 16.28, 72.19, 0.46, 9.19,
1.02 and 0.87, respectively. Also the EDX spectrum of
Zr/isatin@Fe3O4 (Fig. 1) shows that the mass percent of C, N,
O, Si, Fe and Zr is 2.52, 0.95, 10.14, 1.14, 84.8 and 1.18, respec-
tively. These peaks suggest a successful attachment of copper
and zirconium on the particle surface.
The XRD patterns of Fe3O4 MNPs, NH2@Fe3O4, imine@Fe3O4, Zr
(IV)/imine@Fe3O4, Cu(II)/imine@Fe3O4 and recovered zirconium
and copper complex catalysts after the oxidation reaction are
shown in Fig. 2. The typical peaks at 21.32°, 35.28°, 41.59°, 50.68°,
63.18°, 67.56° and 74.51° corresponding to reflections of (111),
(220), (311), (400), (422), (511) and (440) indicate that immobiliza-
tion on the surface of Fe3O4 does not significantly affect the struc-
ture of the Fe3O4 nanoparticles, even after recovery, and they all
match well with data for the standard Fe3O4 sample. The average
crystal size (L) of the catalyst nanoparticles is calculated using the
Debye–Scherrer formula, L = Kλ/β cos θ, where K is the Scherrer
Figure 6. Magnetization curves of (a) Zr/isatin@Fe3O4 and (b) Cu/
Figure 5. TEM images of Zr(IV)/isatin@Fe3O4 and SEM images of Cu(II)/
isatin@Fe3O4.
isatin@Fe3O4.
Appl. Organometal. Chem. 2016, 30, 282–288
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M. Hajjami and S. Kolivand
constant (0.94), λ is the X-ray wavelength (0.178897 nm), and, for
Zr/isatin@Fe3O4 MNPs, β is the peak width of half-maximum
(0.01689 nm) and θ is the Bragg diffraction angle (20.7497°), from
which the average crystal size is found to be approximately 11 nm.
TGA experiments were performed by heating Fe3O4 nanoparti-
cles under nitrogen to 800 °C in order to investigate the amount
of functional groups on the surface of the Fe3O4 nanoparticles
and obtain information on their thermal stability. As seen in Fig. 3,
there are three stages of weight loss for Fe3O4. About 2.98% weight
loss is observed in the first stage (30–150 °C) due to the loss of phys-
ically adsorbed water. In the second stage (150–450 °C), the weight
loss is about 2.25%, which is attributed to thermal degradation of
trace amount of NH4OH that remains from the synthesis process.
The weight loss in the third stage (450–800 °C) is very slight and
is about 0.007%, which may be attributed to further decomposition
of the Fe3O4 structure. Therefore, these results suggest that the syn-
thesized Fe3O4 nanoparticles are stable below 150 °C. The TGA
curves of Zr/imine@Fe3O4 and Cu/imine@Fe3O4 exhibit a three-
stage degradation pattern over the range 30–800 °C. There is a
weight loss of 11.49% for the Zr complex and 6.38% for the Cu
complex between 150 and 550 °C, which is attributed to the
thermal decomposition of organic groups grafted to Fe3O4.
Figure 4 shows the FT-IR spectra of Fe3O4 MNPs, n-propylamine-
functionalized Fe3O4, imine@Fe3O4, Zr (IV)/imine@Fe3O4, Cu (II)/
imine@Fe3O4 and recovered catalysts after the oxidation of
sulfides. In all cases the Fe&bond;O stretching vibration band near
584 cmÀ1 can be seen. The stretching vibration band at 1012 cmÀ1
is attributed to Si&bond;O modes of silica after functionalization of
Fe3O4 with aminopropyltriethoxysilane. After imine formation the
C&dbond;N stretching band appears at 1618 cmÀ1. The charac-
teristic vibrations can also be observed in the spectra of final
immobilized catalysts Zr (IV)/isatin@Fe3O4 and Cu (II)/isatin@Fe3O4.
In both cases, the C&dbond;N stretching band shows an increase
in frequency (1618 to 1626 cmÀ1 for the Zr complex and to
1624 cmÀ1 for the Cu complex) due to complexation to metal
ion. Interestingly, the spectra of the recovered Zr and Cu complex
functionalized Fe3O4 MNPs show that the catalysts are stable
during the reaction.
Table 1. Oxidation of methylphenyl sulfide in various solventsa
Entry
Solvent
Yield (%)b
Zr(IV)/isatin@Fe3O4 Cu (II)/isatin@Fe3O4
1
2
3
4
5
6
n-Hexane
—
19
—
8
Ethyl acetate
Acetone
30
12
93c
30
95c
Dichloromethane
Acetonitrile
Ethanol
50
95c
99c
aReaction conditions: methylphenyl sulfide (1 mmol), H2O2 (0.4 ml), Zr
(IV)/imine@Fe3O4 (0.03 g) at 35 °C, 4.5 h and Cu(II)/imine@Fe3O4
(0.03 g) at 45 °C, 6 h.
bIsolated yields.
cPurification by preparative TLC.
TEM images of Zr(IV)/isatin@Fe3O4 and SEM images of Cu(II)/
isatin@Fe3O4 are shown in Fig. 5. The TEM images disclose the
spherical shapes of the MNPs with an average size of 12 nm which
shows a close agreement with the values calculated from XRD
analysis. The observation from the TEM images indicates that the
magnetic core is visible as a dark spot inside the bright spherical
Schiff base complex grafted to O&bond;Si material.
Scheme 2. Selective oxidation of sulfides to sulfoxides.
Table 2. Oxidation of sulfides to sulfoxides using H2O2 with Zr/isatin@Fe3O4 or Cu/isatin@Fe3O4 systema
Entry
Substrate
Product
H2O2 (ml, Zr/Cu)
Time (min, Zr/Cu)
Yield (%, Zr/Cu)b
M.p. found (°C, Zr/Cu)
1
2
Methylphenyl sulfide
Dibenzyl sulfide
2a
2b
2c
0.4/0.5
0.4/0.5
0.4/0.4
0.5/0.5
0.5/0.5
0.4/0.4
0.4/0.4
0.4/0.4
0.4/0.4
0.4/0.4
0.4/0.4
0.4/0.4
270/360
180/300
10/15
98/99
98/98
98/98
99/97
80c/53c
97/99
96/99
98/99
96/95
62c/83c
97/95
97/96
Oil/oil[28]
129–131/128–132[28]
115–121/110–114[44]
118–122/116–121[28]
65–69/66–69[28]
Oil/oil[28]
3
Benzylmethyl sulfide
Benzylphenyl sulfide
Diphenyl sulfide
4
2d
2e
2f
300/240
1200/1440
180/30
75/60
5
6
Methyl furfuryl sulfide
Dibutyl sulfide
7
2 g
2 h
2i
Oil/oil[45]
8
Dipropyl sulfide
35/80
Oil/oil[28]
Oil/oil[25]
9
Diethyl sulfide
30/5
10
11
12
Dodecyl sulfide
2j
120/120
35/5
88–89/87–89[28]
Oil/oil[28]
Tetrahydrothiophene
2-(Methylthio)ethanol
2 k
2 l
30/10
Oil/oil[45]
aReaction conditions: sulfide (1 mmol), Zr(IV)/imine@Fe3O4 (0.03 g) at 35 °C and Cu(II)/imine@Fe3O4 (0.03 g) at 45 °C.
bIsolated yields.
cPurification by preparative TLC.
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Appl. Organometal. Chem. 2016, 30, 282–288

Modified Fe3O4 MNPs as catalysts for oxidation of sulfides
sulfides (2). The results show that this reaction is best carried out
using aqueous H2O2 (30%, 0.4 ml) and sulfide (1 mmol) in the pres-
ence of 0.03 g of Zr/isatin@Fe3O4 (at 35 °C) or Cu/isatin@Fe3O4 (at
45 °C). During the optimization of the reaction conditions to choose
an appropriate solvent, methylphenyl sulfide was subjected to the
oxidation reaction by H2O2 in the presence of the MNP catalysts
in various solvents. As is evident from Table 1, the best solvent is
ethanol for both catalysts and it was used in the all reactions.
To investigate the efficiency and the scope of Zr/imine@Fe3O4-
or Cu/imine@Fe3O4-catalysed preparation of sulfoxides, sulfides
were oxidized by hydrogen peroxide under optimized conditions.
As evident from Table 2, the reaction can be successfully used with
various sulfides including aromatic (Table 2, entries 1–6) or aliphatic
(Table 2, entries 7–12) sulfides to furnish the desired sulfoxides in
high to excellent yields. To show the chemo-selectivity of this
method, a sulfide containing hydroxyl groups was subjected to
the sulfoxidation reaction. This functional group remains intact
during the conversion of sulfide to sulfoxide (Table 2, entry 12).
After establishing the versatility of Zr/isatin@Fe3O4 and
Cu/isatin@Fe3O4 for oxidation of sulfides, their recyclability was
subsequently tested by recycling and reusing the catalysts in the
oxidation of benzylphenyl sulfide and methylphenyl sulphide, re-
spectively, under the optimized reaction conditions. After comple-
tion of the reaction, the reaction mixture was dissolved in
dichloromethane. Then the catalysts were separated using an
external magnet and subjected to the next cycle. The
Zr/isatin@Fe3O4 catalyst can be reused up to ten cycles without
any significant loss of catalytic activity. Also the Cu complex catalyst
can be reused seven times without significant loss of catalytic activ-
ity (Figs 7, 8). In another study, to investigate the recyclability of
the catalyst on a large scale, the oxidation of methylphenyl sulfide
(33.3 mmol) was examined as a model reaction in ethanol using
1 g of Zr/isatin@Fe3O4. We find that this catalyst demonstrates
excellent reusability. After the completion of the reaction, the
catalyst was rapidly recovered from the reaction mixture using
an external magnet, and the remaining magnetic nanocatalyst
was washed with dichloromethane to remove residual product
followed by decantation of the reaction mixture. After recovering
the catalyst, the catalyst was dried in an oven at 60 °C and
subjected to the next run. The catalyst was used over five runs
without any significant loss of activity. The average isolated yield
for five successive runs is 95%, which clearly demonstrates the
large-scale practical recyclability of the catalyst.
Figure 7. Reusability of Zr/isatin@Fe3O4 in the oxidation of benzylphenyl
sulfide to corresponding sulfoxide.
Figure 8. Reusability of Cu/isatin@Fe3O4 in the oxidation of methylphenyl
sulfide to corresponding sulfoxide.
The magnetic property of the catalysts was studied using VSM.
On the basis of Fig. 6, the two examples both present excellent
paramagnetism and the saturation magnetic moment is measured
to be 42 emu gÀ1 for Zr/isatin@Fe3O4 and 54 emu gÀ1 for
Cu/isatin@Fe3O4.
The efficiency of our prepared catalysts is demonstrated by
comparison of our results for the oxidation of benzylphenyl sul-
fide with those for other reported systems (Table 3). Obviously
the proposed methodology (Table 3, entries 7 and 8) shows
higher yield and less amount of catalyst than other methods
used in the literature.
After characterizing Zr/isatin@Fe3O4 and Cu/isatin@Fe3O4, we in-
vestigated the catalytic properties of these MNPs for oxidation of
Table 3. Comparison results for Zr(IV)-salen-MCM-48 with other catalysts for the oxidation of benzylphenyl sulfide using H2O2
Entry
Catalyst (g)
Condition
Time (min)
Yield (%)
Ref.
[21]
[25]
[29]
[46]
[47]
[28]
1
2
3
4
5
6
7
8
NiFe2O4 (0.07 g)
H2O2 (0.6 ml), CH3CN, r.t.
150
240
300
180
10
88
85
87
83
95
98
99
97
Mo/SiO2@Fe3O4 (0.189 g)
H2O2 (3 mmol), CH3CN, r.t.
H2O2 (2.5 mmol), CH3CN, r.t.
H2O2 (5 mmol), CH2Cl2/MeOH, r.t.
H2O2 (0.5 g), solvent-free, r.t.
H2O2 (0.5 ml), EtOH, 60 °C
H2O2 (0.5 ml), EtOH, 35 °C
H2O2 (0.5 ml), EtOH, 45 °C
Copper–Schiff base complex (0.5 mol%)
Silica-based ammonium tungstate (0.067 g)
N-Propylsulfamic acid@Fe3O4 (0.05 g)
Cu salen/Fe3O4 (0.05 g)
360
300
240
Zr/isatin@Fe3O4 (0.03 g)
This work
This work
Cu/isatin@Fe3O4 (0.03 g)
Appl. Organometal. Chem. 2016, 30, 282–288
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M. Hajjami and S. Kolivand
[18] M. Abdollahi-Alibeik, A. Moaddeli, RSC Adv. 2014, 4, 39759.
[19] I. Jlalia, F. Gallier, N. Brodie-linder, J. Uziel, J. Auge, N. Lubin-Germain,
Conclusions
J. Mol. Catal. A 2014, 393, 56.
In this work we report the preparation of Zr (IV)/isatin@Fe3O4 and
Cu (II)/isatin@Fe3O4 MNPs. These materials were used as catalysts
for selective oxidation of sulfides to sulfoxides using H2O2 as oxi-
dant. The synthesized catalysts were confirmed using XRD, FT-IR
spectroscopy, TGA, TEM, SEM, EDX and VSM. The attractive features
of this method are ease of separation, recyclability of the catalysts,
high yield, cleanliness, ease of handling and simple workup. These
catalysts can be easily recovered from the reaction system using an
external magnet and reused ten times for the Zr-based complex
and seven times for the Cu-based complex without noticeable de-
terioration in catalytic activity.
[20] M. C. Carreno, Chem. Rev. 1995, 95, 1717.
[21] A. M. Kulkarni, U. V. Desai, K. S. Pandit, M. A. Kulkarni, P. P. Wadgaonkar,
RSC Adv. 2014, 4, 36702.
[22] Y. Kon, T. Yokoi, M. Yoshioka, S. Tanaka, Y. Uesaka, T. Mochizuki, K. Sato,
T. Tatsumi, Tetrahedron 2014, 70, 7584.
[23] S. S. Negi, K. Sivaranjani, A. P. Singh, C. S. Gopinath, Appl. Catal. A 2013,
452, 132.
[24] B. R. Raju, S. Sarkar, U. C. Reddy, A. K. Saikia, J. Mol. Catal. A 2009, 308,
169.
[25] A. Bayat, M. Shakourian-Fard, M. M. Hashemi, Catal. Commun. 2014,
52, 16.
[26] X.-T. Zhou, H.-B. Ji, Catal. Commun. 2014, 53, 29.
[27] X.-F. Wu, Tetrahedron Lett. 2012, 53, 4328.
[28] A. Ghorbani-Choghamarani, B. Ghasemi, Z. Safari, G. Azadi, Catal.
Commun. 2015, 60, 70.
[29] P. Gogoi, M. Kalita, T. Bhattacharjee, P. Barman, Tetrahedron Lett. 2014,
55, 1028.
[30] W. Dai, G. Li, L. Wang, B. Chen, S. Shang, Y. Lv, S. Gao, RSC Adv. 2014, 4,
46545.
Acknowledgment
Financial support of this work by Ilam University, Ilam, Iran, is grate-
fully acknowledged.
[31] M. Kiriharaa, J. Yamamoto, T. Noguchi, Y. Hirai, Tetrahedron Lett. 2009,
50, 1180.
[32] K. Bahrami, Tetrahedron Lett. 2006, 47, 2009.
[33] a) V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J. M. Basset,
Chem. Rev. 2011, 111, 3036; b) A. H. Lu, E. L. Salabas, F. Schuth,
Angew. Chem. Int. Ed. 2007, 46, 1222.
[34] M. Afshari, M. Gorjizadeh, S. Nazari, M. Naseh, J. Magn. Magn. Mater.
2014, 363, 13.
[35] A. Ying, S. Liu, Y. Ni, F. Qiu, S. Xu, W. Tang, Catal. Sci. Technol. 2014, 4,
2115.
[36] S. Nazari, S. Saadat, P. K. Fard, M. Gorjizadeh, E. R. Nezhad, M. Afshari,
Monatsh. Chem. 2013, 144, 1877.
[37] H. R. Shaterian, M. Mohammadnia, Res. Chem. Intermed. 2014, 40,
371.
[38] C. I. Fernandes, M. D. Carvalho, L. P. Ferreira, C. D. Nunes, P. D. Vas,
J. Organometal. Chem. 2014, 760, 2.
[39] A. Pourjavadi, S. H. Hosseini, S. A. AghayeeMeibody, S. T. Hosseini, C. R.
Chim. 2013, 16, 906.
[40] H. Naeimi, S. Mohamadabadi, Dalton Trans. 2014, 43, 12967.
[41] M. Hajjami, F. Ghorbani, F. Bakhti, Appl. Catal. A 2014, 470, 303.
[42] M. Hajjami, B. Tahmasbi, RSC Adv. 2015, 5, 59194.
[43] M. Hajjami, Z. Yousofvand, Catal. Lett. 2015, 145, 1733.
[44] C. Yang, Q. Jin, H. Zhang, J. Liao, J. Zhu, B. Yu, J. Deng, Green Chem.
2009, 11, 1401.
[45] M. A. Zolfigol, K. Amani, A. Ghorbani-Choghamarani, M. Hajjami,
R. Ayazi-Nasrabadi, S. Jafari, Catal. Commun. 2008, 9, 1739.
[46] B. Karimi, M. Ghoreishi-Nezhad, J. H. Clark, Org. Lett. 2005, 7,
625.
References
[1] a) B. C. G. Soderberg, Coord. Chem. Rev. 2003, 247, 79; b) X.-S. Zhang,
K. Chen, Z.-J. Shi, Chem. Sci. 2014, 5, 2146; c) C.-X. Zhou, C. Zheng,
S.-L. You, Acc. Chem. Res. 2014, 47, 2558.
[2] Y. Yang, H.-F. Yao, F.-G. Xi, E.-Q. Gao, J. Mol. Catal. A 2014, 390, 198.
[3] L.Yao,J.Zhu,X.Peng,D.Tong,C.Hu,Int.J.HydrogenEnergy2013,38,7268.
[4] J. Iglesias, J. A. Melero, L. F. Bautista, G. Morales, R. Sánchez-Vázquez,
Catal. Today 2014, 234, 174.
[5] A. R. Hajipour, H. Karimi, Appl. Catal. A 2014, 482, 99.
[6] A. Sinhamahapatra, N. Sutradhar, S. Pahari, H. C. Bajaj, A. B. Panda, Appl.
Catal. A 2011, 394, 93.
[7] M. L. Kantam, S. Ghosh, K. Aziz, B. Sreedhar, B. M. Choudary, J. Mol. Catal.
A 2005, 240, 103.
[8] F. Bin, C. Song, G. Lv, J. Song, S. Wu, X. Li, Appl. Catal. B 2014, 150–151, 532.
[9] W. Trakarnpruk, Mendeleev Commun. 2014, 24, 167.
[10] M. Sharbatdaran, L. J. Foruzin, F. Farzaneh, M. M. Larijani, C. R. Chim.
2013, 16, 176.
[11] R. Malakooti, G. R. Bardajee, H. Mahmoudi, N. Kakavand, Catal. Lett.
2013, 143, 853.
[12] S. Bhagat, A. K. Chakraborti, J. Org. Chem. 2008, 73, 6029.
[13] S. J. Canipa, A. Stute, P. O’Brien, Tetrahedron 2014, 70, 7395.
[14] A. R. Silva, K. Wilson, A. C. Whitwood, J. H. Clark, C. Freire, Eur. J. Inorg.
Chem. 2006, 1275.
[15] S. Orlandi, A. Mandoli, D. Pini, P. Salvadori, Angew. Chem. Int. Ed. 2001,
40, 2519.
[16] A. Corma, H. Garcia, A. Moussaif, M. J. Sabater, R. Zniber, A. Redouane,
Chem. Commun. 2002, 1058.
[17] A. Fodor, Z. Hell, L. Pirault-Roy, Appl. Catal. A 2014, 484, 39.
[47] A. Rostami, B. Tahmasbi, F. Abedi, Z. Shokri, J. Mol. Catal. A 2013, 378,
200.
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Appl. Organometal. Chem. 2016, 30, 282–288