Green route for selective gram-scale oxidation of sulfides using tungstate/triazine-based ionic liquid immobilized on magnetic nanoparticles as a phase-transfer heterogeneous catalyst

Article abstract of DOI:10.1002/aoc.3953

Tungstate ions were successfully loaded onto triazine-based ionic liquid-functionalized magnetic nanoparticles through an anion exchange process. The use of triazine core for creating ionic liquid led to the immobilization of high amounts of WO₄

Full text of DOI:10.1002/aoc.3953

Received: 13 April 2017
DOI: 10.1002/aoc.3953
Revised: 6 May 2017
Accepted: 17 June 2017
F U L L P A P E R
Green route for selective gram‐scale oxidation of sulfides
using tungstate/triazine‐based ionic liquid immobilized on
magnetic nanoparticles as a phase‐transfer heterogeneous
catalyst
Seyed Hassan Hosseini1 | Maryam Tavakolizadeh2 | Nasrin Zohreh2
| Rouhollah Soleyman3
1 Department of Chemical Engineering,
Tungstate ions were successfully loaded onto triazine‐based ionic liquid‐func-
tionalized magnetic nanoparticles through an anion exchange process. The
use of triazine core for creating ionic liquid led to the immobilization of high
amounts of WO42−. The resulting catalyst showed high activity and selectivity
in the oxidation of sulfides to sulfoxides with H2O2 as a green oxidant at room
temperature. In addition, due to the presence of ammonium groups in the cat-
alyst structure, water dispersibility of the catalyst was increased. More impor-
tant, the catalyst was magnetically recovered and reused for up to six runs
without any marked decrease of activity and selectivity. Finally, easy gram‐
scale oxidation of methylphenyl sulfide as well as fast separation of catalyst
and product makes the protocol economical and industrially applicable.
University of Science and Technology of
Mazandaran, Iran
2 Department of Chemistry, Faculty of
Science, University of Qom, PO Box 37185‐
359, Qom, Iran
3 Polymer Science and Technology
Division, Research Institute of Petroleum
Industry (RIPI), Tehran, Iran
Correspondence
Nasrin Zohreh, Department of Chemistry,
Faculty of Science, University of Qom, PO
Box 37185‐359, Qom, Iran.
Email: nasrin.zohreh@gmail.com;
n.zohreh@qom.ac.ir
KEYWORDS
heterogeneous catalyst, ionic liquid, oxidation of sulfide, trichlorotriazine, tungstate
1 | INTRODUCTION
permanganate,[6] NaIO4[7] and HNO3,[8] suffers from sev-
eral disadvantages. The use of large amounts of high‐
Catalytic oxidation reactions are important processes due
to their wide application in the conversion of raw petro-
leum materials, such as alkenes, alcohols and sulfides, to
useful commercial derivatives.[1] In addition, due to the
increasing demand for oxidation products, today, great
efforts are being made to design and prepare appropriate
catalysts aiming to obtain products with more selectivity
and higher yield, and especially minimizing the cost of
production and environmental pollutions.[2] Among the
oxidation reactions, selective oxidation of sulfides to sulf-
oxides has been significantly developed in recent years
because sulfoxides are widely used for the synthesis of
various chemicals in the laboratory and industry.[3] Oxi-
dation of sulfides to sulfoxides usingtraditional methods
and reagents, such as the use of potassium hydrogen car-
valent oxidizing agent, production of unwanted toxic
waste and by‐products, difficult and time‐consuming sep-
aration and purification of desired product from reaction
mixture[9] and, importantly, overoxidation of sulfoxides
to sulfones are some examples.[10] H2O2 has been found
to be an efficient and green promising oxidant for sul-
phides[11] because it offers benefits such as low cost, high
content of active oxygen and production of water as envi-
ronmentally benign by‐product.[12] Several transition
metals have been also applied in order to increase activity
and selectivity of hydrogen peroxide for sulfide oxida-
tion.[13] Recently, catalytic systems based on tungsten spe-
cies have been widely applied in combination with H2O2,
owing to high activity and selectivity of tungsten.[14]
Noyori and co‐workers were the first to use Na2WO4/
H2O2 combination as a homogeneous catalytic system
bonate,[4]
m‐chloroperbenzoic
acid,[5]
potassium
Appl Organometal Chem. 2017;e3953.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.3953

2 of 10
HOSSEINI ET AL.
for oxidation reactions.[15] However, it seems that the use
of a phase transfer catalyst accompanied with aqueous
Na2WO4/H2O2 is inevitable because of the organic iden-
tity of reactants. On the other hand, although this cata-
lytic system has shown high activity and selectivity,[16] it
still suffers from the disadvantages of homogeneous cata-
lysts, especially their recoverability and reusability prob-
lems. Immobilization of tungstate‐based homogenous
catalysts onto solid supports such as silica,[17] mesoporous
silica,[18] polymers[19] and magnetic nanoparticles[20] is a
promising route to overcome these problems. In addition,
minimization of tungsten contamination of the final prod-
uct is another highlight of these protocols.[21]
ray diffraction (XRD) patterns were recorded with a
Rigaku D/Max‐3c X‐ray diffractometer. X‐ray fluores-
cence (XRF) spectra of samples were taken using a Phil-
lips 1404 XRF instrument. Atomic absorption
spectrometry (AAS; Shimadzu 680 A) or inductively
coupled plasma (ICP) optical emission spectrometry
(Perkin‐Elmer DV 4300) were used for elemental mea-
surements. Conversions and yields were measured using
a 6890 GC with an Agilent Technologies HP‐Innowax.
2.2 | Preparation of amine‐functionalized
magnetic nanoparticles (MNP@APTS)
One of the most interesting modifications based on
this approach is the immobilization of tungstate ions on
Silica‐coated Fe3O4 nanoparticles (MNPs) were synthe-
sized based on our previously reported method.[28] MNPs
(1.50 g) were ultrasonically dispersed in 50 ml of ethanol–
water (4/1) mixture. Then, APTS (5 ml) was added and
the mixture was stirred at 80 °C for 24 h. MNP@APTS
was magnetically separated and washed several times
with methanol (3 × 30 ml) and dried under vacuum at
50 °C (1.43 g).
ionic liquid (IL)‐modified nanosupports.[22] This strategy
2− [23]
allows a high loading of WO4
.
Also, ILs could serve
as excellent phase transfer catalysts because of their lipo-
philic backbone and hydrophilic ionic nature[24] which
results in increased dispersity of nanoparticles in various
solvents.[25] ILs also increase the thermal stability of a cat-
alyst and reduce leaching of tungstate ions to the reaction
solution or to product structure.[26]
2.3 | Functionalization of MNP@APTS
with TCTA (MNP@TA)
Based on this strategy, in this paper, we present a sim-
ple route for the preparation of an oxidation catalyst com-
2−
posed of immobilized bis(aminoethylammonium)/WO4
In a round‐bottom flask, MNP@APTS (1.20 g) was ultra-
sonically dispersed in 50 ml of dry tetrahydrofuran
(THF). Then, TCTA (10 mmol, 1.8 g) and DIEA (15 mmol,
1.9 g) were added and the flask was put in an ice bath. The
mixture was stirred for 7 h under nitrogen atmosphere.
The product (MNP@TA) was magnetically separated
and washed with THF (3 × 10 ml) and MeOH
(3 × 10 ml) and dried under vacuum at room temperature
(1.13 g).
IL, derived from triazine,[27] on magnetic nanoparticles
for the first time. The resulting system was used as a het-
erogeneous, magnetic and phase transfer catalyst for the
selective oxidation of sulfides to sulfoxides in the presence
of aqueous H2O2.
2 | EXPERIMENTAL
2.1 | Materials and methods
2.4 | Preparation of MNP@TA‐IL/W
catalyst from MNP@TA
Ferric chloride hexahydrate (FeCl3⋅6H2O), ferrous chlo-
ride tetrahydrate (FeCl2⋅4H2O), ammonia (25%),
tetraethyl
orthosilicate
(TEOS),
(3‐aminopropyl)
In a three‐necked round‐bottom flask, MNP@TA (1.0 g)
was dispersed in dry THF (10 ml) and DIEA (15 mmol,
1.9 g) was added. Then, an excess amount of
ethylenediamine (EDA; 25 ml) was slowly added and mix-
ture was stirred at 90 °C for a day to produce
MNP@DATA ligand. The product was separated using
an external magnet and washed with methanol
(5 × 10 ml) and dried under vacuum at 50 °C (1.0 g).
MNP@DATA (1.0 g) was then ultrasonically dispersed
in water (15 ml). Then, HCl (37 wt%, 1 ml) was added
and the mixture was stirred for 30 min at room tempera-
ture. The MNP@TA‐NH3/Cl nanoparticles were magneti-
cally separated and washed three times with water to
remove any excess of acidic reagent. For exchange of chlo-
ride with tungstate ions, the residue was dispersed in
trimethoxysilane (APTS), 2,4,6‐trichloro‐1,3,5‐triazine
(TCTA) and diisopropylethylamine (DIEA) were obtained
from Sigma‐Aldrich and used without further purifica-
tion. Na2WO4⋅4H2O, H2O2 (30 wt%) and various organic
solvents were purchased from Merck.
Fourier transform infrared (FT‐IR) spectra of samples
were taken using an ABB Bomen MB‐100 FT‐IR spec-
trometer. Thermogravimetric analysis (TGA) was con-
ducted under a nitrogen atmosphere with a TGA Q 50
thermogravimetric analyser. Transmission electron
microscopy (TEM) images were taken with a Philips
CM30 electron microscope. Magnetization of the catalyst
was measured using vibrating sample magnetometry
(VSM; Meghnatis Daghigh Kavir Co., Kashan, Iran). X‐

HOSSEINI ET AL.
3 of 10
deionized water (25 ml) and Na2WO4⋅4H2O (3.3 g) was
added to the mixture. The mixture was stirred for two
days at room temperature. The final catalyst (MNP@TA‐
IL/W) was magnetically separated and washed with water
(5 × 10 ml) and methanol (2 × 10 ml) and dried under vac-
uum at 50 °C (0.91 g).
with methanol and dried at 60 °C. The product mixtures
were extracted using CHCl3 or EtOAc (3 × 40 ml). The
combined organic layer was then concentrated to 30 ml.
The resulting mixture was kept in a freezer for 24 h. Dur-
ing this time, the crude product was solidified. Then, the
remaining solvent was quickly decanted in another flask.
The crude product was further dried at 30 °C under
vacuum.
2.5 | General procedure for oxidation of
sulfides catalysed by MNP@TA‐IL/W
Substrate (1 mmol), water (2 ml) and 30% H2O2
(1.5 mmol) were loaded into a 25 ml round‐bottom flask
and then MNP@TA‐IL/W (0.4 mol%, 10 mg) was added
to the mixture. The reactants were vigorously stirred at
room temperature (25 °C) for the required time. After
completion of the reaction, the catalyst was magnetically
separated, washed with methanol and dried for another
run. The product mixtures were extracted using ethyl ace-
tate and analysed by GC.
3 | RESULTS AND DISCUSSION
MNP@TA‐IL/W was synthesized according to the proce-
dure outlined in Scheme 1. In the first step, MNPs were
prepared by co‐precipitation method from Fe3+ and Fe2+
salts under basic conditions. Then, Fe3O4 nanoparticles
were protected from oxidative and harsh reaction condi-
tions by SiO2 coating of the Fe3O4 surface through basic
hydrolysis of TEOS. The surface of the MNPs was func-
tionalized by APTS to provide amine functional groups
required for the next step. TATC was anchored easily onto
the surface of the amine‐functionalized MNPs (second
step) using an ice bath and dry THF in the presence of
non‐nucleophilic base DIEA. This strategy also allowed
substitution of only one Cl with amine groups. After-
wards, EDA reacted with the triazine core via substitution
reaction of two remaining Cl under reflux conditions
2.6 | General procedure for gram‐scale
oxidation of Methylphenyl sulfide catalysed
by MNP@TA‐IL/W
In a 250 ml round‐bottom flask, MNP@TA‐IL/W
(0.4 mol%, 0.48 g) was ultrasonically dispersed in water
(100 ml). Methylphenyl sulfide (6 g, 48 mmol, 6 ml) was
added and the flask placed in an ice bath. To this, 30%
H2O2 (72 mmol, 7.4 ml) was added dropwise. After addi-
tion of H2O2, the mixture was vigorously stirred at room
temperature (25 °C) for 1.5 h. After completion of the
reaction, the catalyst was magnetically separated, washed
2−
(MNP@DATA). Immobilization of WO4 was carried
out by acidifying the terminal amines of MNP@DATA
to produce MNP@TA‐NH3/Cl followed by chloride
exchange process with tungstate to produce the final sup-
ported catalyst.
SCHEME 1 Preparation of MNP@TA‐IL/W catalyst

4 of 10
HOSSEINI ET AL.
3.1 | Characterization of catalyst
Characterizations of the catalyst and other nanoparticle
intermediates were achieved using various analyses,
namely FT‐IR spectroscopy, TGA, TEM, XRD, energy‐dis-
persive X‐ray spectroscopy (EDX), VSM, AAS, ICP and
XRF. FT‐IR spectra of MNP, MNP@APTS, MNP@TA,
MNP@TA‐NH3/Cl and MNP@TA‐IL/W are shown in
Figure 1. Obviously, all samples exhibited characteristic
vibration bands associated with Fe‐O (630 cm−1) and Si‐
O (1097 cm−1) suggesting the presence of silica‐coated
Fe3O4 (Figure 1). The FTIR spectrum of MNP@APTS
displayed stretching vibrations of C‐N of APTS at 1557
and 1496 cm−1 (Figure 1b). Appearance of sharp and
strong stretching bands of C‐N at 1612, 1560 and
1510 cm−1 is a strong evidence for loading of TA
(MNP@TA; Figure 1c). After substitution of Cl with
EDA, these characteristic bands appeared blue‐shifted in
the spectrum of MNP@TA‐NH3/Cl (Figure 1d) as com-
pared with those of MNP@TA (Figure 1c). The FT‐IR
spectrum of the final catalyst (Figure 1e) showed a clear
band at 899 cm−1 (W‐O) that strongly confirmed the
2−
anion exchange process and immobilization of WO4
on the nanoparticle surface.
TGA was used to monitor the organic content coating
on each intermediate, as well as stability and decomposi-
tion profiles for comparison. The obtained results are
depicted in Figure 2. The weight loss at around 90–
150 °C is attributed to the physically adsorbed water
molecules on the surface of nanoparticles in all sam-
ples.[29] The TGA curve of MNP@APTS (Figure 2Ib) shows
a weight loss at 250 °C attributed to the decomposition of
FIGURE 2 TGA curves of bare MNPs (Ia), MNP@APTS (Ib),
MNP@TA (Ic), MNP@TA‐NH3/cl (id) and MNP@TA‐IL/W (Ie);
and DTG/TG curves of MNP@TA‐IL/W (IIa/Ie)
aminopropyl groups (Figure 2Ib). From this weight loss
(3.2 wt%), the loading of APTS on the surface of MNP
was calculated to be 0.54 mmol g−1. The weight loss
increased to 9.6 wt% in the TGA curve of MNP@TA
(Figure 2Ic) confirming the loading of TA on amine‐func-
tionalized nanoparticles. Subtracting the 3.2 wt% from this
value gave the loading of TCTA (0.43 mmol g−1). Substitu-
tion of EDA with both chlorides followed by acidifying the
terminal amine groups led to an increased weight loss of
21.7 wt% for MNP@TA‐NH3/Cl (Figure 2Id). After chlo-
ride exchange with tungstate, the degradation of the
organic segment in the MNP@TA‐IL/W catalyst occurred
at 380 °C (Figure 2Ie) and the content of organic compo-
nents was calculated to be 10.05 wt%. The DTG analysis
of the catalyst also showed three peaks mainly at 90, 375
and 460 °C, which are attributed to the loss of water mol-
ecules and decomposition of organic components (Figure
2IIa and 2Ie). Surprisingly, TGA also showed that the
catalyst is stable up to 380 °C which makes the catalyst
applicable under thermal reaction conditions.
FIGURE 1 FT‐IR spectra of MNPs (a), MNP@APTS (b),
MNP@TA (c), MNP@TA‐NH3/cl (d) and MNP@TA‐IL/W (e)

HOSSEINI ET AL.
5 of 10
Figure 3 shows the XRD patterns of Fe3O4 and
magnetization is sufficient for easy separation of the
catalyst with an external magnet.
To identify the constituent elements of the MNP@TA‐
IL/W catalyst, EDX was used. The EDX spectrum showed
the presence of tungsten and other elements such as C, N,
Si, Fe and O (Figure 5). Importantly, it was found that there
MNP@IL/W accompanied with the standard diffraction
lines of Fe3O4. The typical peaks corresponded to crystal
planes of Fe3O4 nanoparticles and are compatible with
the standard Fe3O4 (JCPDS 19–0629). These results
revealed that the crystalline phase of Fe3O4 nanoparticles
did not changed during the catalyst preparation steps.[30]
The broad peak at 20–30° is the characteristic peak of
amorphous silica.[31]
The magnetism of MNP@TA‐IL/W (Figure 4a) was
investigated in comparison with MNPs (Figure 4b) using
VSM analysis at room temperature. As shown in Figure 4
, the saturated magnetism of MNP@TA‐IL/W was found
to be 63 emu g−1 which was less by 11.0 emu g−1 compared
to MNPs because of the presence of organic materials
around the MNPs. However, a value of 52 emu g−1 for
is only a trace of Cl element in the catalyst structure demon-
2−
strating that all chlorides are exchanged with WO4
.
Additionally, XRF analysis was also performed to deter-
mine the content of Cl and Na (Table 1). Values of 2.41,
2.73 and 0.09 wt% were found for chloride in MNP@TA,
MNP@TA‐NH3/Cl and MNP@TA‐IL/W, respectively
(corresponding to 0.68, 0.77 and 0.025 mmol g−1 loading of
Cl). These values confirmed (1) substitution of one Cl with
amine groups in the second step, (2) exchange of all Cl with
2−
EDA in the third step and (3) exchange of all Cl with WO4
in the final step of catalyst preparation. Negligible amount
of Na obtained from EDX and XRF (Table 1) also showed
−
that two Cl were exchanged with one WO42− and NaWO4
is not immobilized. In addition, the loading of Cl in
MNP@TA‐NH3/Cl was measured by the standard method
(titration by AgNO3, according to the Moher method) and
it was found that the loading of Cl was 0.8 mmol g−1
(Table 1, along with XRF data). Finally, W loading was
calculated to be 0.39 mmol g−1 using AAS and ICP analysis
and this value was selected for calculation of catalyst
loading in oxidation reactions.
Figure 6 displays a TEM image of MNP@TA‐IL/W. As
can be seen in the TEM image, black Fe3O4 nanoparticles
were surrounded by grey silica and organic components.
Also the size of the catalyst nanoparticles was found to
be around 12 nm with a uniform size and dispersity.
3.2 | Oxidation of sulfides to sulfoxides
using MNP@TA‐IL/W catalyst
FIGURE 3 XRD patterns of (a) Fe3O4 and (b) MNP@TA‐IL/W
To investigate the catalytic efficiency of MNP@TA‐IL/W,
oxidation of methylphenyl sulfide in the presence of H2O2
as final oxidant was chosen as a model reaction. The effect
of various parameters including solvent, temperature, cat-
alyst loading and molar ratio of H2O2 was investigated to
obtain the best reaction conditions (Table 2). Initially, the
effect of tungstate catalyst was investigated. As outlined in
Table 2 (entries 1 and 2), reaction conversion and selectiv-
ity are low without MNP@TA‐IL/W or with MNP@TA‐
NH3/Cl. Investigations of effect of solvent revealed the
vital role of solvent in conversion (Table 2, entries 3–7).
Compared to other solvents, MNP@TA‐IL/W showed
the highest conversion for methylphenyl sulfide in water
(entry 4). It seems that water provides a polar protic
medium for phase transfer activity of the catalyst. Increas-
ing the amount of H2O2 to 1.5 eq. led to increased selectiv-
ity up to 89% for sulfoxides 2a (entries 8–10). To obtain
FIGURE 4 VSM curves for MNPs (a) and MNP@TA‐IL/W (b)

6 of 10
HOSSEINI ET AL.
FIGURE 5 EDX analysis of MNP@TA‐IL/W
TABLE 1 Elemental analysis of cl, Na and W
Loading cl
(mmol g−1 a
Loading Na
(mmol g−1 a
Loading cl
(mmol g−1 b
Loading W
(mmol g−1 c
)
Sample
Cl (wt%)a
)
)
)
MNP@ta
2.41
0.68
—
—
—
0.8
—
—
MNP@ta‐Eda
<0.01
2.73
<0.002
0.77
—
—
MNP@TA‐NH3/cl
MNP@ta‐Il/W
—
—
0.09
0.025
<0.06
0.39
aBased on XRF analysis.
bBased on titration experiment.
cBased on AAS analysis.
the highest conversion and selectivity, increasing the cat-
alyst loading was evaluated while keeping the other
parameters constant. Excellent conversion and selectivity
(98 and 99%) were obtained using 0.4 mol% catalyst and
this condition (entry 12) was chosen as optimum for the
selective oxidation of sulfides to sulfoxides in the presence
of 1.5 eq. of H2O2. Surprisingly, higher temperature (entry
13) or catalyst loading (entries 14 and 15) reduced the
selectivity of the reaction.
Considering the inherent activity and phase transfer
capability of the catalyst and optimized reaction condi-
tions, the applicability of MNP@TA‐IL/W catalytic sys-
tem was tested for selective oxidation of various sulfides
in the presence of H2O2 (Table 3). MNP@TA‐IL/W
showed excellent catalytic efficiency at room temperature,
giving almost quantitative conversion (83–99%) and yield
(91–90%) for alkylaryl (Table 3, entries 1–5 and 7–11),
dialkyl (entries 12 and 13) and diaryl (entry 6) sulfides.
It seems that diphenyl sulfide and aryl sulfides with elec-
tron‐withdrawing groups (entries 9–12) exhibited longer
reaction time and lower conversion (entry 6). Apparently,
the resonance of electron pair of sulfur with aromatic ring
is effective. Alkyl sulfides with longer alkyl chains (entries
4, 12 and 13) also showed reduced conversion. These
results are probably due to the substrates being insoluble
in water. Poor water solubility of the sulfides lowered
the concentration of substrate in aqueous phase, which
thus decreased the reaction rate of the aqueous phase
FIGURE 6 TEM image of MNP@TA‐IL/W

HOSSEINI ET AL.
7 of 10
TABLE 2 Optimization of sulfide oxidation catalysed by MNP@TA‐IL/Wa
Entry
Catalyst
(mol%)
Solvent
H2O2
(mmol)
Time
(h)
Conversion
(%)b,c
Yield (%)c
2a 3a
29 71
Solvent
1
2
3
4
5
6
7
—
—
—
—
4
4
4
4
4
4
4
24
24
18
4
4
4
31
54
65
71
64
69
44
MNP@TA‐NH3/Cld
25
35
48
50
39
53
75
65
52
50
61
47
0.1
0.1
0.1
0.1
0.1
H2O
MeOH
MeCN
Toluene
4
H2O2
8
9
10
0.1
0.1
0.1
H2O
H2O
H2O
3
1.5
1.2
3.5
3
3.5
75
72
65
55
89
85
45
11
15
Catalyst loading
11
12
13
14
15
0.3
0.4
0.4
0.4
0.5
H2O
H2O
H2O (50 °C)
MeCN
1.5
1.5
1.5
1.5
1.5
2
1
1
1
0.5
89
98
99
85
99
90
99
88
80
96
10
1
12
20
4
H2O
aReaction conditions: methylphenyl sulfide (1 mmol), solvent (2 ml), 25 °C.
bConversions were calculated based on initial mmol of methylphenyl sulfide.
cAfter extraction with EtOAc, conversions and yields were determined by GC using p‐xylene as internal standard.
dMNP@TA‐NH3/Cl: 15 mg.
a
TABLE 3 Selective oxidation of various sulfides to the corresponding sulfoxides with MNP@TA‐IL/W and H2O2
Entry
R1
R2
Time (h)
Conversion (%), yield of
2 (%) (yield of 3, %)
1
Ph
Me
1
98, 99 (1)
99, 99 (1)
98, 96 (4)
96, 96 (4)
98, 97 (3)
83, 91 (9)
97, 98 (2)
97, 95 (5)
96, 95 (5)
95, 97 (3)
90, 93 (7)
95, 97 (3)
91, 98 (2)
2
Ph
Et
1
3
Ph
CH2CH2OH
CH2(CH2)2Me
Allyl
2
4
Ph
2.5
1
5
Ph
6
Ph
Ph
5.5
1.5
1.5
2
7
Ph
C6H5CH2
p‐BrC6H4CH2
Et
8
Ph
9
p‐BrC6H4
p‐BrC6H4
p‐BrC6H4
CH2(CH2)2Me
Allyl
10
11
12
13
Allyl
2.5
3
C6H5CH2
CH2(CH2)2Me
CH2(CH2)2Me
1
1
aReaction conditions: sulfide (1 mmol), H2O (2 ml), MNP@TA‐IL/W (0.4 mol%), H2O2 (30%, 1.5 eq.), 25 °C.
bConversions were calculated based on initial mmol of sulfide.
cAfter extraction with EtOAc, conversions and yields were determined by GC using p‐xylene as internal standard.

8 of 10
HOSSEINI ET AL.
catalysis. However, the water solubility of substrate had a
smaller effect on the selectivity. Interestingly, allylic
(entries 5, 10 and 13) and alcoholic (entry 3) sulfides were
selectively oxidized to corresponding sulfoxides without
epoxidation of the double bond or oxidation of alcohol
group. All of these findings showed that the MNP@TA‐
IL/W catalyst has high activity and selectivity in the green
oxidation reaction of sulfides in the presence of H2O2 at
room temperature.
SCHEME 2 Gram‐scale oxidation of methylphenyl sulfide using
MNP@TA‐IL/W
To further demonstrate the practicality and efficiency
of the developed protocol, a scaled‐up reaction was per-
formed using methylphenyl sulfide (1a) as substrate on a
48 mmol scale (Scheme 2). The reaction was initially car-
ried out in an ice bath with slow addition of hydrogen per-
oxide in order to control the exothermic reaction. After
stirring for another 1.5 h at room temperature, the prod-
uct 2a was obtained with 96% conversion and 98%
selectivity.
An important issue associated with the performance
of a heterogeneous catalyst is its recovery and reusability.
The MNP@TA‐IL/W catalyst could be easily separated
using an external magnet after reaction. To investigate
the recyclability of the MNP@TA‐IL/W catalyst, the cata-
lyst was recycled six times. After the completion of the
reaction in each run, the catalyst was magnetically col-
lected at the bottom of the flask and the solution was
poured in another flask for workup and GC analysis.
The catalyst was washed with EtOH and used in the next
fresh run. As summarized in Figure 7(I), the reaction
exhibited no obvious decline in the conversion of
methylphenyl sulfide and the selectivity of sulfoxide dur-
ing all six runs. Increasing of reaction time after each
run could be attributed to the loss of some of the catalyst
during recovery experiments. In order to confirm that the
FIGURE 7 Recycling experiment (I), and leaching experiment
(II)
TABLE 4 Comparing catalytic activity of MNP@TA‐IL/W with tungsten‐ and non‐tungsten‐based heterogeneous catalysts in the selective
oxidation of sulfides
Tungsten‐based catalysts
PW4‐Zn(0.8)/SnO2
WO42−@PMO‐IL (1 mol%), H2O2
(1.2 eq.), r.t., H2O/MeOH, 0.5–5 h,
recoverable (filtration, 9 runs)[33]
C8‐AP‐WO42−@SBA‐15
(1.5 mol%), H2O2 (1 eq.),
30 °C, H2O/MeCN, 1–10 h,
recoverable (filtration, 7
runs)[18]
PILW (1.2 mol%), H2O2 (3 eq.),
r.t., solvent‐free, 2–5 h,
recoverable (filtration, 8
runs)[19]
(3.5 mol%), H2O2 (4 eq.),
96 °C, DMC, 5–7 min,
recoverable (filtration)[32]
Other catalysts
PS‐Mo and PA‐Mo
(0.1 mol%), H2O2 (4 eq.), r.
t., H2O, 5–150 min,
recoverable (filtration, 10
runs)[34]
SiO2‐chit@vanadium (enantioselective Si@asp (100 mg), H2O2
Fe3O4@chit/cu (0.47 mol%),
H2O2 (1 eq.), r.t., solvent‐free,
5 min–24 h, recoverable
reaction, 10 mol%), H2O2 (1.5 eq.),
0 °C, HOAc (1.5 eq.), 12 h,
(1.15 eq.), r.t., H2O, 24 h,
recoverable (filtration, 6
runs)[36]
recoverable (filtration, 5 runs)[35]
(external magnet, 4 runs)[37]
This work MNP@TA‐IL/W (0.4 mol%), H2O2 (1.5 eq.), r.t., H2O (2 ml), 1–5.5 h, recoverable (external magnet, 6 runs)

HOSSEINI ET AL.
9 of 10
active species are not WO42− leaking from the MNP@TA‐
IL/W catalyst in the oxidation reaction, a leaching exper-
iment was carried out using the model reaction (Figure 7
(II)). In a typical experiment, after 30 min reaction time,
the catalyst was filtered, and the reaction solution was
kept on stirring under the same experimental conditions
without catalyst (Figure 7(II)). However, the conversion
of methylphenyl sulfide increased 5% after 2.5 h from cat-
alyst removal; this was attributed to the presence of H2O2
(and not leached WO42−) in the reaction mixture. This
claim was confirmed by investigation of the yield of sulf-
oxide during the reaction process (green curve in
Figure 7(II)). Apparently, the lack of selective tungsten
catalyst led to the overoxidation of sulfides to sulfoxides
in the presence of H2O2. Additionally, AAS analysis of
the reaction solution after removal of catalyst detected
no significant amount of tungsten. AAS analyses of the
recovered MNP@TA‐IL/W catalyst also showed no signif-
icant (<0.001 mmol g−1 of W) differences compared with
the fresh catalyst, indicating the heterogeneous behaviour
and good reusability of the catalyst in the reaction. Com-
bined with the results of catalytic performance of the
reused catalyst, leaching tests and AAS, it is evident that
the MNP@TA‐IL/W catalyst is highly recoverable and
recyclable. Table 4 compares the activity of the present
catalyst with those of the most recently reported tungsten‐
and non‐tungsten‐based catalysts in selective oxidation of
sulfides.
[2] a) A. N. Bilyachenko, M. M. Levitsky, A. I. Yalymov, A. A.
Korlyukov, A. V. Vologzhanina, Y. N. Kozlov, L. S. Shul'Pina,
D. S. Nesterov, A. J. Pombeiro, F. Lamaty, RSC Adv. 2016, 6,
48165; b) G. Liu, X. Bai, H. Lv, Appl. Organomet. Chem. 2017,
31, e3587.
[3] a) B. Karimi, M. Ghoreishi‐Nezhad, J. H. Clark, Org. Lett. 2005,
7, 625; b) B. Yu, A.‐H. Liu, L.‐N. He, B. Li, Z.‐F. Diao, Y.‐N. Li,
Green Chem. 2012, 14, 957; c) R. Das, D. Chakraborty, Tetrahe-
dron Lett. 2010, 51, 6255.
[4] J. Drabowicz, W. Midura, M. Mikołajczyk, Synthesis 1979, 1979,
39.
[5] A. Dishington, S. Fillery, M. R. V. Finlay, Tetrahedron Lett.
2010, 51, 4211.
[6] G. W. Gokel, H. M. Gerdes, D. M. Dishong, J. Org. Chem. 1980,
45, 3634.
[7] N. J. Leonard, C. R. Johnson, J. Org. Chem. 1962, 27, 282.
[8] A. R. Suárez, L. I. Rossi, S. E. Martín, Tetrahedron Lett. 1995, 36,
1201.
[9] a) D. H. Barton, W. Li, J. A. Smith, Tetrahedron Lett. 1998, 39,
7055; b) G. W. Breton, J. D. Fields, P. J. Kropp, Tetrahedron Lett.
1995, 36, 3825.
[10] C. G. Venier, T. G. Squires, Y. Y. Chen, B. F. Smith, J. Org.
Chem. 1982, 47, 3773.
[11] a) C. Yuan, H. Liu, X. Gao, Catal. Lett. 2014, 144, 16; b) S. P.
Das, J. J. Boruah, N. Sharma, N. S. Islam, J. Mol. Catal. A
2012, 356, 36; c) J. J. Boruah, S. P. Das, S. R. Ankireddy, S. R.
Gogoi, N. S. Islam, Green Chem. 2013, 15, 2944; d) H.‐M. Shen,
W.‐J. Zhou, H.‐K. Wu, W.‐B. Yu, N. Ai, H.‐B. Ji, H.‐X. Shi, Y.‐B.
She, Tetrahedron Lett. 2015, 56, 4494; e) H.‐M. Shen, W.‐J.
Zhou, X. Ma, H.‐K. Wu, W.‐B. Yu, N. Ai, H.‐B. Ji, H.‐X. Shi,
Y.‐B. She, Molecules 2015, 20, 16709.
4 | CONCLUSIONS
[12] a) K. Bahrami, M. M. Khodaei, B. H. Yousefi, M. S. Arabi, Tet-
rahedron Lett. 2010, 51, 6939; b) M. Hajjami, L. Shiri, A.
Jahanbakhshi, Appl. Organomet. Chem. 2015, 29, 668.
In this paper, we introduced a novel and effective hetero-
geneous catalyst for selective oxidation of sulfides to sulf-
oxides with excellent conversion and yield without any
significant overoxidation. The catalyst was easily prepared
through immobilization of tungstate ion on triazine‐
derived IL supported on MNPs via an anion exchange pro-
cess and characterized using various methods. Compared
to previously reported catalysts (Table 4) the use of green
solvent and oxidant, low catalyst loading, mild conditions,
short reaction time, easy and high recoverability and reus-
ability, and performance of the reaction on a gram scale
make this catalyst particularly applicable for environmen-
tally friendly syntheses.
[13] H. Srour, P. Le Maux, S. Chevance, G. Simonneaux, Coord.
Chem. Rev. 2013, 257, 3030.
[14] a) B. Sreedhar, P. Radhika, B. Neelima, N. Hebalkar, A. Mishra,
Cat. Com. 2008, 10, 39; b) X.‐Y. Shi, J.‐F. Wei, J. Mol. Catal. A
2008, 280, 142; c) T. Yamaura, K. Kamata, K. Yamaguchi, N.
Mizuno, Catal. Today 2013, 203, 76; d) N. Mizuno, K. Kamata,
K. Yamaguchi, Catal. Today 2012, 185, 157; e) K. Suzuki, J.
Jeong, K. Yamaguchi, N. Mizuno, New J. Chem. 2016, 40, 1014.
[15] K. Sato, M. Aoki, R. Noyori, Science 1998, 281, 1646.
[16] a) T. Hida, H. Nogusa, Tetrahedron 2009, 65, 270; b) K. Sato, J.
Takagi, M. Aoki, R. Noyori, Tetrahedron Lett. 1998, 39, 7549.
[17] K. Kawamura, T. Yasuda, T. Hatanaka, K. Hamahiga, N.
Matsuda, M. Ueshima, K. Nakai, Chem. Eng. J. 2016, 285, 49.
REFERENCES
[18] B. Karimi, M. Khorasani, ACS Catal. 2013, 3, 1664.
[1] a) M. Ghorbanloo, R. Tarasi, J. Tao, H. Yahiro, Turk. J. Chem.
2014, 38, 488; b) T. Punniyamurthy, S. Velusamy, J. Iqbal,
Chem. Rev. 2005, 105, 2329; c) W. Al Zoubi, Y. G. Ko, Appl.
Organomet. Chem. 2017, 31, e3574; d) S. Keshipour, N. Kalam
Khalteh, Appl. Organomet. Chem. 2016, 30, 653; e) Q. Zhou, Z.
Wan, X. Yuan, J. Luo, Appl. Organomet. Chem. 2016, 30, 215.
[19] A. Pourjavadi, M. Nazari‐Chamazkoti, S. H. Hosseini, Chem
2015, 39, 1348.
[20] J. Zhu, P. C. Wang, M. Lu, Chem 2012, 36, 2587.
[21] N. Zohreh, S. H. Hosseini, A. Pourjavadi, R. Soleyman, C. Ben-
nett, J. Ind. Eng. Chem. 2016, 44, 73.

10 of 10
HOSSEINI ET AL.
[22] D. Elhamifar, S. Kazempoor, B. Karimi, Cat. Sci. Technol. 2016,
6, 4318.
[29] H. Masrouri, F. Movahedi, Appl. Catal. A 2011, 395, 28.
[30] M. Tajbakhsh, M. Farhang, R. Hosseinzadeh, Y. Sarrafi, RSC
Adv. 2014, 4, 23116.
[23] A. Pourjavadi, S. H. Hosseini, F. M. Moghaddam, B. K.
Foroushani, C. Bennett, Green Chem. 2013, 15, 2913.
[31] A. Ying, S. Liu, Y. Ni, F. Qiu, S. Xu, W. Tang, Cat. Sci. Technol.
2014, 4, 2115.
[24] a) A. Ying, S. Liu, Y. Ni, F. Qiu, S. Xu, W. Tang, Cat. Sci.
Technol. 2014, 4, 2115; b) A. Ying, S. Liu, Z. Li, G. Chen, J.
Yang, H. Yan, S. Xu, Adv. Synth. Catal. 2016, 358, 2116; c) A.
Ying, H. Hou, S. Liu, G. Chen, J. Yang, S. Xu, ACS Sustain.
Chem. Eng. 2016, 4, 625.
[32] S. Nojima, K. Kamata, K. Suzuki, K. Yamaguchi, N. Mizuno,
ChemCatChem 2015, 7, 1097.
[33] B. Karimi, M. Khorasani, F. Bakhshandeh Rostami, D.
Elhamifar, H. Vali, ChemPlusChem 2015, 80, 990.
[25] a) D. Liu, J. Gui, Z. Sun, Y.‐K. Park, Catal. Lett. 2012, 142, 1330;
b) G. Chatel, C. Monnier, N. Kardos, C. Voiron, B. Andrioletti,
M. Draye, Appl. Catal. A 2014, 478, 157; c) F. Hosseini Eshbala,
F. Mohanazadeh, A. Sedrpoushan, Appl. Organomet. Chem.
2017, 31, e3597; d) B.‐X. Tang, X.‐N. Fang, R.‐Y. Kuang, J.‐H.
Wu, Q. Chen, S.‐J. Hu, Y.‐L. Liu, Appl. Organomet. Chem.
2016, 30, 943; e) J. Wu, Y. Gao, W. Zhang, Y. Tan, A. Tang, Y.
Men, B. Tang, Appl. Organomet. Chem. 2015, 29, 96.
[34] J. J. Boruah, K. Ahmed, S. Das, S. R. Gogoi, G. Saikia, M.
Sharma, N. S. Islam, J. Mol. Catal. A 2016, 425, 21.
[35] C. Shen, J. Qiao, L. Zhao, K. Zheng, J. Jin, P. Zhang, Cat. Com.
2017, 92, 114.
[36] H.‐M. Shen, W.‐J. Zhou, W.‐B. Yu, H.‐K. Wu, Q.‐P. Liu, H.‐B. Ji,
Y. Wang, Y.‐B. She, Chem 2016, 40, 4874.
[37] A. Fakhri, A. Naghipour, Mater. Technol. 2017, 846.
[26] a) B. Karimi, F. B. Rostami, M. Khorasani, D. Elhamifar, H.
Vali, Tetrahedron 2014, 70, 6114; b) Y. Leng, J. Wang, P. Jiang,
Cat. Com. 2012, 27, 101; c) T. Lu, L. Zhang, Z. Ge, Y. Ji, M. Lu,
Appl. Organomet. Chem. 2015, 29, 276.
How to cite this article: Hosseini SH,
Tavakolizadeh M, Zohreh N, Soleyman R. Green
route for selective gram‐scale oxidation of sulfides
using tungstate/triazine‐based ionic liquid
immobilized on magnetic nanoparticles as a phase‐
transfer heterogeneous catalyst. Appl Organometal
Chem. 2017;e3953. https://doi.org/10.1002/aoc.3953
[27] a) N. Zohreh, M. Tavakolizadeh, S. H. Hosseini, M. Jahani, A.
Pourjavadi, C. Bennett, Chem 2016, 40, 10325; b) N. Zohreh,
M. Jahani, J. Mol. Catal. A 2017, 426, 117; c) N. Zohreh, M.
Tavakolizadeh, S. H. Hosseini, A. Pourjavadi, C. Bennett, Poly-
mer 2017, 112, 342.
[28] A. Pourjavadi, S. H. Hosseini, F. Seidi, R. Soleyman, Polym. Int.
2013, 62, 1038.