Organic-inorganic hybrid polyionic liquid based polyoxometalate as nano porous material for selective oxidation of sulfides

Article abstract of DOI:10.1016/j.molstruc.2017.03.041

Organic-inorganic hybrid nano porous materials based on poly(ionic liquid)-polyoxometalate (PIL-POM) were reported. These hybrid materials were synthesized by the reaction of 4-vinyl pyridine with 1,3-propanesultone, followed by the polymerization and also sulfonate-functionalized cross-linked poly(4-vinylpyridine) and combining these polymers with H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂). Activity of prepared PIL-PMo₁₀V₂ hybrids were investigated as catalysts for oxidation of sulfides with H₂O₂ as oxidant. For understanding catalytic activities of the PIL-PMo₁₀V₂ hybrids in oxidation of sulfides, effect of catalyst composition, substrate, and reaction conditions were studied. The results show that the PIL-PMo₁₀V₂ hybrids are active as selective heterogeneous catalysts for oxidation of sulfides and can be recovered and reused. The catalyst was characterized by FT-IR, TGA-DSC, XRD, SEM/EDX, BET, CV and zeta potential measurement. Also, average molecular weight of prepared catalysts were measured.

Full text of DOI:10.1016/j.molstruc.2017.03.041

Journal of Molecular Structure 1139 (2017) 255e263
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Organic-inorganic hybrid polyionic liquid based polyoxometalate as
nano porous material for selective oxidation of sulfides
, b,
Ezzat Rafiee a *, Shabnam Shahebrahimi a
a Department of Inorganic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, 67149, Iran
b Institute of Nano Science and Nano Technology, Razi University, Kermanshah, 67149, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Organic-inorganic hybrid nano porous materials based on poly(ionic liquid)-polyoxometalate (PIL-POM)
were reported. These hybrid materials were synthesized by the reaction of 4-vinyl pyridine with 1,3-
propanesultone, followed by the polymerization and also sulfonate-functionalized cross-linked poly(4-
vinylpyridine) and combining these polymers with H5PMo10V2O40 (PMo10V2). Activity of prepared
PIL-PMo10V2 hybrids were investigated as catalysts for oxidation of sulfides with H2O2 as oxidant. For
understanding catalytic activities of the PIL-PMo10V2 hybrids in oxidation of sulfides, effect of catalyst
composition, substrate, and reaction conditions were studied. The results show that the PIL-PMo10V2
hybrids are active as selective heterogeneous catalysts for oxidation of sulfides and can be recovered and
reused. The catalyst was characterized by FT-IR, TGA-DSC, XRD, SEM/EDX, BET, CV and zeta potential
measurement. Also, average molecular weight of prepared catalysts were measured.
Received 6 December 2016
Received in revised form
8 March 2017
Accepted 8 March 2017
Available online 16 March 2017
Keywords:
Polyoxometalates
Poly(ionic liquid)
Nano porous catalysts
Organic-inorganic hybrids
Sulfoxidation
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
potentially have both of IL and polymer properties, such as high
thermal stability, easily molding, corrosion resistance, and multi-
In 1914 Paul Walden synthesized ionic liquid (IL). ILs are
generally defined as organic/inorganic salts that are composed of
cations and anions which melt below 100 ꢀC [1]. These compounds
are liquid because there is weak interactions between oppositely
charged ions in ionic structures. Also, there are light intermolecular
interaction (only electrostatic interactions, hydrogen bonds, or
vander Waals interactions are involved) and asymmetric chemical
structures. Phosphonium, ammonium, pyrrolidinium, imidazolium,
and pyridinium are common IL cations. IL properties related to the
kind of anion part more than cations, and anions commonly used
are mineral acid, halides, metal oxide clusters such as poly-
oxometalates (POM) and polyatomic inorganics (PFꢁ6 , BF4ꢁ) [2]. Their
negligible volatility, remarkable solubility, and potential recycla-
bility of such ILs make these compounds as good solvents and
catalysts for chemical reactions [3e7].
plicity of available structures [2,9]. PILs have different applications
including energy and environmental applications. These com-
pounds are used in analytical chemistry, materials science,
biotechnology, and surface science also using as catalysts [10e16].
Polymer supported catalysts are used as heterogeneous and
recyclable catalysts in organic transformation that make reaction
methods more convenient, economic and environmentally
benign [17].
POMs are family of anionic inorganic metal oxide clusters.
Because of their acidic and redox properties, POMs have received
specific attention in the field of acidic or oxidation catalyst [18].
Many nano porous carriers with high surface areas, such as silica,
active carbon, zeolite, and so on are used as support to impregnate
onto or encapsulate POMs. Produced heterogeneous catalysts show
higher efficiency compare to homogeneous ones [19e22]. Much
attention has been focused on modification of POMs with organic
species to produced POM-based hybrid catalysts with improved
catalytic activity and convenient catalyst recovery and reusability.
Hybrid organic POM could be produced by exchanging of the pro-
tons of the POM by ILs [23e25]. Nevertheless, catalytic stability of
these catalysts needs to be improved. For this purpose POM based
polymeric hybrid nano porous catalysts by combining SO3H-func-
tionalized IL polymer with POMs were produced. Because of the
Polymerization of ionic liquids produce poly(ionic liquid)s
(PILs), in these materials IL species are repeating units. Thus, the
cationic or anionic centers are compelled to the repeating units in
the polymer chain. PILs unlike ILs are solid in most cases [8]. PILs
* Corresponding author. Department of Inorganic Chemistry, Faculty of Chemis-
try, Razi University, Kermanshah, 67149, Iran.
E-mail addresses: ezzat_rafiee@yahoo.com, e.rafiei@razi.ac.ir (E. Rafiee).
http://dx.doi.org/10.1016/j.molstruc.2017.03.041
0022-2860/© 2017 Elsevier B.V. All rights reserved.

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E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
involvement of a polymeric framework these catalyst should
possess a more structural stability. Also its catalytic performance
increase for selective oxidation of organic sulfur compounds in a
short time and mild conditions. In addition, in this work, we
compared catalytic activity of H5PMo10V2O40 (PMo10V2) based
poly(4-vinylpyridine) (PVPy) in two form not cross-link polymer
and cross linked polymer with 2% divinyl benzene (DVB).
2.2.4. Preparation of cross-linked poly(4-VPyPS)-PMo10V2
1,3-propane-sultone (20 mmol) was slowly added to a disper-
sion of poly(4-vinylpyridine) cross-linked with 2% DVB (2.1 g) in
toluene at ambient temperature, and the resulting mixture was
stirred for 2 h. The temperature was then raised to 60 ꢀC and the
mixture was stirred for 24 h. The mixture was cooled to ambient
temperature and the resulting solid was filtered then washed
sequentially with dichloromethane and methanol before being
dried under vacuum at 55 ꢀC. The solution of PMo10V2
(0.528 mmol) was added dropwise into the obtained cross-link poly
(VPyPS) (0.3 g) in methanol, followed by refluxing for 24 h. On
completion, methanol was removed in vacuum to give the final
product cross-link poly(VPyPS)-PMo10V2 (CPVPyPSPMo10V2) as a
dark green solid.
2. Experimental
2.1. General
All used reagents and solvents were purchased from Fluka,
Aldrich or Merck Company and used without further purification.
Poly(4-vinyl pyridine) cross-linked with 2% DVB (100e200 mesh,
MW: 60000) was obtained from Fluka. PMo10V2 from Aldrich was
used. FT-IR spectra were recorded as KBr pellets using a Shimadzu
470 spectrophotometer. Scanning electron microscopy (SEM) and
energy dispersive X-ray spectroscopy (EDX) were used to know the
morphology and composition of the catalyst on a model XL30
Philips. X-ray diffraction (XRD) patterns were collected on the STOE
powder diffraction system. Differential scanning calorimetry (DSC)
measurements were done on a METTLER with a scanning rate of
10 ꢀC/min in air. Thermogravimetric analysis was carried out using
a Shimadzu TGA-50H spectrometer at heating rate of 10 ꢀC/min
under flowing rate nitrogen 30 mL/min. Brunauer Emmett-Teller
(BET) surface areas and pore volumes were evaluated on a sorp-
tometer kelvin 1042 using nitrogen adsorption at 77 K. The elec-
trochemical reduction of catalyst was studied in phosphate buffer
(0.1 M), pH ¼ 2. A glassy carbon electrode was used as the electrode
2.3. Oxidation of liquid sulfides
To a stirred mixture of the sulfide (5 mmol), and catalyst
(0.036 g) in EtOH (10 mL), 30% aq. H2O2 (1.68 mL, 15 mmol) was
added in one portion. The slurry was stirred at room temperature.
After completion of the reaction followed by TLC, the catalyst was
separated by filtration. Corresponding sulfoxide was extracted with
Et2O from the reaction mixture. Evaporation of the solvent afforded
the crude product. The crude product was purified by column
chromatography on silica gel using EtOAc/hexane as eluent.
3. Results and discussion
3.1. Catalyst characterization
and Ag/AgCl as the reference electrode. Cyclic voltammograms (
n
,
The precursor poly(VPyPS) was prepared by reaction of 4-
vinylpyridine with 1,3-propane sultone, followed by the polymer-
ization with AIBN. The average molecular weight of the synthesized
polymer has been characterized by light scattering technique that
was 32300 g (Fig. S1a). Ultimately, methanol solution of the ob-
tained poly(VPyPS) with an aqueous solution of PMo10V2 was
refluxed, which afforded [poly(VPyPS)]5PMo10V2 catalyst,
(PVPyPSPMo10V2) (Scheme 1).
0.1 V sꢁ1) were obtained at ambient temperature (20 ꢀC).
5
Measurements of charge distribution (Zeta potential measure-
ments) and average molecular weight of the polymer synthesized
were carried out using HPPS5001, Malvern, UK. The products of
sulfoxidation were characterized by 1H NMR and melting point
using a Bruker Avance 200 MHz NMR spectrometer and Barnstead
electro thermal 9200 respectively.
The CPVPyPSPMo10V2 catalyst was readily prepared in two steps
via the reaction of cross-link poly(4-VPy) with 1,3-propane sultone
to render a positive charge, followed by acidification of the
resulting product with PMo10V2 (Scheme 2).
For the synthesis of hybrid materials, two different molar ratios
of PVPyPS and PMo10V2 were used: PVPyPS to PMo10V2 molar ratio
is 5/1 to produce PVPyPSPMo10V2 and 5/4 for PVPyPS4PMo10V2.
Elemental analysis carried out using EDX (Fig. 1a) revealed the
presence of several elements including C, Mo, V, and S which
confirmed the formula of PILs-PMo10V2 compounds (Table 1).
Based on the data, it seems that there is an active species of
PMo10V2 in PVPyPSPMo10V2 and PVPyPS4PMo10V2 per 10 and
almost 7 monomer units respectively.
2.2. Preparation of the catalysts
2.2.1. Preparation of 4-vinylpyridine propane sulfone
To a solution of 1, 3-propane-sultone (0.1 mol, 12.2 g) in dry
toluene (50 mL), 4-vinyl pyridine (0.1 mol, 10.5 g) was slowly added
at room temperature and the mixture was stirred overnight until
the solid formed. It was washed with ether and dried in vacuum at
room temperature. The solid was used in next step without further
purification.
2.2.2. Preparation of poly 4-vinylpyridine propane sulfone
The obtained 4-vinylpyridine propane sultone (VPyPS) (2.5 g)
was dissolved in methanol (20 mL), and azobisisobutyronitrile
(AIBN) (0.05 g) was added under nitrogen atmosphere, and the
mixture was refluxed at 60 ꢀC for 24 h with stirring. Then the sol-
vent was removed by distillation, and the residue was washed with
ethanol to give a white solid hereafter named poly(VPyPS).
Morphology of the catalysts was investigated by SEM. It could be
seen from Fig. 1b that the surface of the polymers is distinctly
altered in each hybrid organic-inorganic catalysts. Particles of
PVPyPS4PMo10V2 as compared to other samples have more uni-
form distribution and less agglomeration.
Measurement of average molecular weights of PVPyPSPMo10V2
and PVPyPS4PMo10V2 (1740000, 1730000 g respectively) showed
that with increasing of the amount of polar species PMo10V2, the
average molecular weight of organic-inorganic hybrid polymer has
been decreased (Figs. S1b and c). The reason of this reduction of
molecular weight may be because of this fact that PIL is full of
charges along the polymer chains and can be easily self-stabilized
by Coulomb repulsion once nanoparticles are formed. So if ionic
strength change this would induce PIL chains to aggregate, the PIL
2.2.3. Preparation of poly(VPyPS)-PMo10V2
The solution of PMo10V2 (1 or 4 mmol) was added dropwise into
the obtained poly(VPyPS) (monomer molar quantity 5 mmol) in
methanol, followed by the refluxing for 24 h. On completion,
methanol was removed in vacuum to give final products poly(-
VPyPS)-PMo10V2 (PVPyPSPMo10V2) (1 mmol PMo10V2) and poly(-
VPyPS)-4PMo10V2 (PVPyPS4PMo10V2) (4 mmol PMo10V2) as green
solids.

E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
257
Scheme 1. Synthesis of the PVPyPSPMo10V2 catalyst.
Scheme 2. Preparation of CPVPyPSPMo10V2.
might collapse into nanoparticles stably dispersed in the solution
[26]. This could be confirmed by SEM images.
Keggin bands for hybrid catalyst appeared which are resulted from
the strong ionic interaction between the polymeric cations and
PMO10V2. Therefore the FT-IR spectra of the PILs- PMO10V2 showed
that the basic structure and geometry of the Keggin anion are
preserved.
The XRD patterns of PVPyPSPMo10V2, PVPyPS4PMo10V2,
CPVPyPSPMo10V2 and PMo10V2 were also investigated (Fig. S3).
PMo10V2 possess the characteristic peak of the Keggin anions.
However, all of the peaks disappeared in the XRD pattern of PIL-
PMo10V2. This phenomenon demonstrates that the rearrangement
took place between POM and polymeric cations by self-assembly.
All these results suggest that PIL-PMo10V2 has the structure illus-
trated in Schemes 1 and 2.
As shown in the DSC traces of Fig. 2a, upon heating PVPyPSP-
Mo10V2, PVPyPS4PMo10V2 and CPVPyPSPMo10V2 exhibit a glassy
transition temperature (Tg) at 105, 115 and 100 ꢀC.
TGA analysis was carried out to investigate the thermal stability
of PVPyPS4PMo10V2 (Fig. 2b). The bulk PMo10V2 catalyst experi-
enced considerable weight loss in the low temperature region due
to the removal of water molecules, and then finally decomposed
Also, the measured BET specific surface areas and pore volume
of the catalyst particles are reported in Table 2. There is an
increasing of specific surface area and pore volume of PVPyPS4P-
Mo10V2. It is therefore expected that the catalytic activity of
PVPyPS4PMo10V2 may be more than PVPyPSPMo10V2.
The FT-IR spectroscopy was employed to identify structural and
bonding changes in the Keggin unit present in the PILs-PMO10V2.
The spectra of 4VPyPS (Fig. S2a), PVPyPS (Fig. S2b) PVPyPSPMo10V2
(Fig. S2c), PVPyPS4PMo10V2 (Fig. S2d) and CPVPyPSPMo10V2
(Fig. S2f) CPVPyPS (Fig. S2g) exhibit the peaks around 1040 and
1205 cmꢁ1 could be due to the symmetric and asymmetric
stretching vibrations of S]O respectively. The broad and asym-
metric peak around 3424 cmꢁ1 could be due to OeH vibrations and
quaternization stretching frequency at 1640 cmꢁ1. Also PMo10V2
(Fig. S2e) shows typical bands for absorptions at 1064, 964, 873 and
794 cmꢁ1 attributed to PeO, Mo¼Oa, MoeOb and MoeOc, respec-
tively. But vibration bands of PMo10V2 in PILs-PMO10V2 are slightly
shifted in comparison with free PMo10V2. These slight shifts of the

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E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
Fig. 1. (a) EDX patterns of (I) PVPyPSPMo10V2, (II) PVPyPS4PMo10V2, and (III) CPVPyPSPMo10V2, (b) SEM images of (I) PVPyPSPMo10V2, (II) PVPyPS4PMo10V2, and (III)
CPVPyPSPMo10V2.

E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
259
Table 1
The presence of several elements of PIL-PMo10V2.
Entry
Type of catalyst
C%
S%
Mo%
V%
Mol % Mo
Mol % V
Mol % S
1
2
3
PVPyPSPMo10V2
PVPyPS4PMo10V2
CPVPyPSPMo10V2
33.009
28.689
48.164
7.793
8.084
2.625
22.889
31.845
16.466
2.54
3.38
1.748
0.238
0.332
0.171
0.049
0.066
0.034
0.243
0.252
0.082
Table 2
The parameters of BET surface area, pore size, and pore volume of PIL-PMo10V2.
Entry
Type of catalyst
BET surface area [m2 gꢁ1
]
Pore volume [cm3 gꢁ1
]
Pore Size [nm]
1
2
3
PVPyPSPMo10V2
PVPyPS4PMo10V2
CPVPyPSPMo10V2
2.2286
6.8253
1.5879
0.010042
0.019226
0.0023927
18.024
11.267
6.0273
around 395 ꢀC. Also the TG curve indicates that the decomposition
of PVPyPS4PMo10V2 was in three steps, about 100, 410 and 550 ꢀ
PVPyPS4PMo10V2 the N2 adsorptionedesorption isotherm were
conducted and shown in Fig. 3. The isotherm curve of PVPyPS4P-
Mo10V2 is close to type IV that is characterized mesoporous
adsorbent with strong affinities. Also Nano porous materials refer
to a class of porous materials having pore diameters from 100 nm
down to around 1 nm. Based on the International Union of Pure and
Applied Chemistry (IUPAC) definition, a pore size range of <2, 2e50
and > 50 nm are related to micro-/meso- and macropores,
respectively. According to these pore size ranges and results in
Table 2, prepared catalysts are mesopores compounds.
C
which are water molecules, decomposition temperature of polymer
(organic part) and PMo10V2 respectively. According to TGA curve,
10 wt% of this sample contains organic part. This fact indicates
PVPyPS4PMo10V2 produced by ionic interaction between PVPyPS
moiety with PMo10V2 and this interaction is increased thermal
stability of PMo10V2. So there is not just a physical mixture of
PVPyPS with PMo10V2 in the molecular hybrid material.
In order to investigate the porous structure and surface area of
Fig. 2. (a) DSC curves, (b) TGA patterns of (I) PMo10V2 and (II) PVPyPS4PMo10V2.

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E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
Fig. 4. Oxidation of MPS in the presence of PILs-PMo10V2 at reaction conditions: MPS:
5 mmol, H2O2: 15 mmol, and catalyst: 0.036 gr, in EtOH at room temperature.
Fig. 3. N2 adsorptionedesorption isotherm of PVPyPS4PMo10V2.
because of the amphipathic property of this inorganic-organic
composite catalyst, and thus, it could be activated Mo10V2 [30,31].
The effect of the amount of H2O2 on the reaction was also investi-
gated (Fig. 6) and it was found that with using 3 M ratio of H2O2/
sulfide (O/S) the yield of the reaction is high, but reducing O/S to 1
reduces yield of the reaction (Fig. 6a and b). Increasing of O/S up to
8 has not considerable effect on time of the reaction (Fig. 6d). O/
S ¼ 3 is selected as optimized amount of oxidant.
3.2. Catalytic reaction
Catalytic activity of synthesized PIL-POMs were studied by
oxidation reaction of methyl phenyl sulfide (MPS) as model sub-
strate using H2O2 as oxidant (Scheme 3).
As a result from Fig. 4, PVPyPS4PMo10V2 was selected as the best
catalyst in terms of catalytic activity. According to our knowledge
this reaction was proceeded based on electron transfer property of
PMo10V2 as catalyst.
To investigate the electron transfer ability of the catalysts cyclic
voltammetry was recorded for PMo10V2, PVPyPSPMo10V2 and
PVPyPS4PMo10V2. The cyclic voltammograms of the PILs- PMo10V2,
pure PILs, and pure PMo10V2 were shown in Fig. 5. As it could be
seen in voltammograms redox wave attributed to the electron-
transfer reaction of V(IV)/V(V) of PILs-PMo10V2 voltammogram
showed shift toward pure PMo10V2.
It seems that higher active site according to Table 1, in
PVPyPS4PMo10V2 is the main reason for this higher activity
compare to two other IL-POMs. Lower activity of CPVPyPSPMo10V2
as catalyst is possibly because of cross link in network of this
polymer which obtained longer reaction time.
For more investigation charge distribution of these catalysts
should be measured. Zeta potential measurements of samples are
illustrated in Fig. S4. As can be seen from Fig. S4a, before interaction
between PVPyPS moiety with PMo10V2, surface charge of PVPyPS
was a few negative (ꢁ7.37). In particles of PVPyPSPMo10V2 and
PVPyPS4PMo10V2, the negative potential of particles increased, as
shown in Figs. S4b and S4c. Increasing of negative potential may be
because of increasing of electron density of samples not solely
negative charge [27]. Therefore, on account of the negative catalyst
surface (Fig. S4b compare with Fig. S4c), adsorption of substrate on
the catalyst surface gets harder, consequently the reaction time
increased that can be compared with the results of other papers
[28,29].
The influence of other reaction parameters on the selectivity and
efficiency of oxidation of MPS as a model substrate using aqueous
H2O2 was examined using PVPyS4PMo10V2 as the best catalyst
(Table 3).
Activity was investigated by using several solvents in the reac-
tion, such as EtOH, n-heptan, H2O and mixture of n-heptan with
EtOH or MeCN. With increasing polarity of the solvent, time of the
reaction was dramatically decreased (Table 3, entry 1e4) in
contrast, catalytic performance in n-heptan as nonpolar solvent
showed very low yield (Table 3, entry 5). It is therefore proposed
that the substrate is more easily available to the PMo10V2 moiety in
the presence of a polar solvent and reacts readily with the activated
hydrogen peroxide therein. Also, different amount of the catalyst
was examined. The results of Table 3 indicated that optimum
amount of PVPyPS4PMo10V2 was 0.036 g.
Selective producing of sulfone was also investigated. Results
showed that with increasing of the temperature, solubility of
PVPyPS4PMo10V2 was increased that is unsuitable for recyclability
of the catalyst (Table 4).
H2O2 as oxidant could diffuse into the bulk of PVPyS4PMo10V2
Fig. 5. Cyclic voltammograms for the PMo10V2, PVPyPSPMo10V2 and PVPyPS4PMo10V2
in phosphate buffer (0.1 M), pH
¼
2, scan rate: 0.1 V/s, ambient temperature
Scheme 3. Oxidation of MPS to sulfoxide.
(20
5
ꢀC).

E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
261
Fig. 6. Influence of different O/S ratios on yield and time of the reaction using PVPyPS4PMo10V2 as catalyst in reaction conditions: 5 mmol, and catalyst: 0.036 gr, in EtOH at room
temperature.
Table 3
Influence of catalyst amount and solvent on oxidation of MPS in the presence of PVPyPS4PMo10V2.a
Entry
PVPyPS4PMo10V2 (g)
Solvent
Time (min)
Conv. (%)
Yield (%) of sulfoxide
1
2
3
4
5
6
7
8
9
10
0.036
0.036
0.036
0.036
0.036
0.036
0.072
0.072
0.072
0.018
EtOH
10
45
25
15
30
20
25
30
25
40
100
95
95
98
80
70
90
90
100
97
98
80
90
96
65
70
90
75
90
95
75% n-Heptan þ 25% EtOH
50% n-Heptan þ 50% EtOH
50% n-Heptan þ 50% MeCN
n-Heptan
H2O
EtOH
n-Heptan
50% n-Heptan þ 50% EtOH
50% n-Heptan þ 50% MeCN
a
Reaction conditions: MPS: 5 mmol, O/S:3, solvent (10 mL), room temperature.
A series of sulfides was subjected to oxidize under the optimized
reaction conditions obtained for sulfoxide production (Table 5).
Some types of sulfides were oxidized to the sulfoxide with excellent
selectivities.
Reusability of the catalyst is an important advantage when it is
introduced for practical application in catalytic processes. The
recycling performance of PVPyPS4PMo10V2 was investigated in
several runs of oxidation reaction of MPS to corresponding sulf-
oxide with 30% aq. H2O2 (Fig. S5). At the end of the reaction,
PVPyPS4PMo10V2 was separated by centrifuging, washed with
mixture of n-heptan/EtOH and dried under vacuum. The yield of
Table 4
Effect of temperature on reaction in the presence of PVPyPS4PMo10V2 as catalyst.a
Entry Temperature Time (min) Yield of sulfoxide % Yield of sulfone %
1
2
3
25 ꢀC (O/S ¼ 3) 10
98
2
2
2
98
98
60 ꢀC (O/S ¼ 6) 35
60 ꢀC (O/S ¼ 8) 35
a
Reaction conditions: MPS: 5 mmol, H2O2 (30%), EtOH (10 mL), catalyst: 0.036 g.

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E. Rafiee, S. Shahebrahimi / Journal of Molecular Structure 1139 (2017) 255e263
Table 5
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Selective oxidation of sulfides to sulfoxides with 30% aq. H2O2 using PVPyPS4P-
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a
Isolated yield; Reaction conditions: Sulfide: 5 mmol, O/S: 3, and catalyst: 0.036 g
in EtOH (10 mL) at r.t; all products were identified by comparing their 1H NMR with
those in authentic samples [S].
98% for the first run decreased down to 90% after fourth run, mostly
due to the unavoidable leaching of the catalyst during the reaction.
To investigate the amount of leaching of PMo10V2, a mixture of
PVPyPS4PMo10V2 (0.036 g) in solvent of model reaction (10 mL
ethanol) was stirred and UVevis spectra of diluted solution was
recorded after removal of the catalyst. The content of PMo10V2 in
solution was determined with the aid of calibration curves and was
only 4.1 wt% (Fig. S6). Because ionic bond established between
PVPyPS and PMo10V2, in intensively polar environment of the re-
action existing PMo10V2 in outer surfaces polymer be leached but
PMo10V2 on inner surfaces polymer remains. Moreover, there is no
significant change in the FT-IR spectrum (Figs. S7a and S7b).
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4. Conclusion
In conclusion, a poly(4-vinylpyridine) supported oxidative ionic
liquid is developed as nano porous structure catalyst, and use in
sulfoxidation reaction in heterogeneous media. The prepared
samples are synthesized by sulfonated of 4-vinylpyridine, then
polymerization and pairing poly(VPyPS) with PMo10V2 anion.
Average molecular weight of PVPyPSPMo10V2 and PVPyPS4P-
Mo10V2 are measured. The glass transition point (Tg) of the poly-
mers have been determined by using DSC measurements. The
catalyst of PVPyPS4PMo10V2 has been successfully applied for se-
lective oxidation of sulfides to the sulfoxides with dilute H2O2, in
EtOH. The results show that this catalyst in comparison with other
two catalysts exhibited excellent redox property of PMo10V2 and
could be reused at least three times with a slight decrease in cat-
alytic activity.
Acknowledgements
The authors thank the Razi University Research Council for
support of this work.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
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