Immobilization of MoO2Cl2 on polystyrene via different linkers and oxidation of sulfides in the presence of hydrogen peroxide

Article abstract of DOI:10.1007/s13738-011-0030-y

Chloromethylated polystyrene was oxidized to aldehydic polystyrene and by reaction of this aldehydic polystyrene resin with furfuryl amine and 2-(amino methyl) pyridine, imine-bounded polystyrene resins 1a and 1b were obtained. Amine-bounded polystyrene resins 1c-1f were also prepared by direct reaction of chloromethylated polystyrene and amines. These functionalized polystyrene resins were used to immobilize MoO₂Cl₂ on polystyrene. These functionalized polystyrene resins were characterized with elemental analysis (CHN) and FT-IR spectrum. Polymersupported catalysts were characterized with FT-IR and neutron activation analysis (NAA). These catalysts were used in oxidation of methyl phenyl sulfide in the presence of H₂O₂ as oxidant and the results showed that these catalysts were highly active and selective. The reusability of these heterogeneous catalysts was also investigated and the results showed that the supported MoO₂Cl ₂ catalyst on polystyrene via imidazole liker was highly reusable as it was used 15 times in oxidation of methyl phenyl sulfide in the presence of environmental benign oxidant (H₂O₂) and solvent (H ₂O) without any decrease in its activity. Then the catalytic activity of these supported catalysts was investigated in oxidation of some aliphatic and aromatic sulfides. Almost all of these supported molybdenum-based catalysts were highly active and selective in the conversion of these sulfides to their corresponding sulfoxides.

Full text of DOI:10.1007/s13738-011-0030-y

J IRAN CHEM SOC (2012) 9:349–355
DOI 10.1007/s13738-011-0030-y
ORIGINAL PAPER
Immobilization of MoO2Cl2 on polystyrene via different linkers
and oxidation of sulfides in the presence of hydrogen peroxide
•
G. Grivani N. Gholampoor
Received: 3 February 2011 / Accepted: 29 July 2011 / Published online: 3 January 2012
Ó Iranian Chemical Society 2011
Abstract Chloromethylated polystyrene was oxidized to
aldehydic polystyrene and by reaction of this aldehydic
polystyrene resin with furfuryl amine and 2-(amino methyl)
pyridine, imine-bounded polystyrene resins 1a and 1b were
obtained. Amine-bounded polystyrene resins 1c–1f were
also prepared by direct reaction of chloromethylated poly-
styrene and amines. These functionalized polystyrene resins
were used to immobilize MoO2Cl2 on polystyrene. These
functionalized polystyrene resins were characterized with
elemental analysis (CHN) and FT-IR spectrum. Polymer-
supported catalysts were characterized with FT-IR and
neutron activation analysis (NAA). These catalysts were
used in oxidation of methyl phenyl sulfide in the presence of
H2O2 as oxidant and the results showed that these catalysts
were highly active and selective. The reusability of these
heterogeneous catalysts was also investigated and the
results showed that the supported MoO2Cl2 catalyst on
polystyrene via imidazole liker was highly reusable as it
was used 15 times in oxidation of methyl phenyl sulfide in
the presence of environmental benign oxidant (H2O2) and
solvent (H2O) without any decrease in its activity. Then the
catalytic activity of these supported catalysts was investi-
gated in oxidation of some aliphatic and aromatic sulfides.
Almost all of these supported molybdenum-based catalysts
were highly active and selective in the conversion of these
sulfides to their corresponding sulfoxides.
Introduction
Sulfoxides are very important reagents in synthetic organic
chemistry; particularly, they are very useful synthetic inter-
mediates for the construction of various chemically and
biologically significant molecules [1–3]. Thus, increasing
interests have stimulated investigations on new methodolo-
gies of sulfoxide synthesis. Among those methods, oxidation
of sulfides to sulfoxides or sulfones is an attractive and
important method in organic synthesis. Catalytic oxidation
of sulfides with environmentally benign oxidant has become
increasingly important. Hydrogen peroxide is an ideal
oxidant because of high-efficient oxygen content, low cost,
safety in storage and operation, readily available, environ-
mentally benign and production of water as a byproduct [3].
In the recent years, many procedures have been developed
for hydrogen peroxide oxidation of sulfides catalyzed
by several transition metal complexes such as W(VI) [3],
Mo(VI) [4], V(V) [5], Ti(IV) [6], Mn(III) [7], Cu(II) [8].
Homogeneous catalysts often provide the best results but use
of these catalysts has some disadvantages such as contami-
nation of products with catalyst and difficult separation of
catalyst from reaction medium to reuse. In order to overcome
to these problems, much effort has been devoted to attach-
ment of homogeneous transition metal complexes to insol-
uble organic or inorganic solid supports and used as
sulfoxidation catalysts [9–15]. These heterogenized catalysts
may combine the ease of product separation with reactivity
and selectivity founded with homogeneous catalysts.
Recently Chand et al. [16] used MoO2Cl2 as effective
homogeneous catalyst in oxidation of sulfides. In this
article, we report the immobilization of MoO2Cl2 on
polystyrene via different linkers, and the catalytic activity
and reusability of supported catalyst in oxidation of
sulfides.
Keywords Polymer-support Á Supported catalyst Á
MoO2Cl2 Á Oxidation Á Sulfoxide
G. Grivani (&) Á N. Gholampoor
School of Chemistry, Damghan University,
Damghan 36715-364, Iran
e-mail: Grivani@du.ac.ir
123

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J IRAN CHEM SOC (2012) 9:349–355
Experimental
Material
materials were obtained by using Varian CP-3800 instru-
ment with silicon-DC 200 column.
Functionalization of polystyrene
Chloromethylated polystyrene purchased from Aldrich and
all other materials were used purchased from Merck.
MoO2Cl2(DMF)2 was prepared according to the literature
[20].
Preparation of imine-bounded polystyrenes (1a, 1b)
Polystyrene resin (2% DVB) was oxidized to aldehydic
polystyrene as described in Ref. [17]. In two separated
round-bottom flasks the aldehyde-bearing beads were
allowed to swell in methanol and a solution(0.5 M in 25 ml
methanol) of amine (furfuryl amine and 2-(amino methyl)
pyridine) was added drop-wise to this mixture over a period
of 1 h and then refluxed for 7 h. The content was cooled to
Apparatus and techniques
Infrared spectra were recorded using KBr disks on a FT-IR
Perkin–Elmer spectrophotometer. All yields for aliphatic
sulfides and methyl phenyl sulfide based on starting
Scheme 1 Preparation
procedures of functionalized
polstyrenes (1a–1f)
O
DMSO
NaHCO3
Cl
H
155 oC/ 6 h
(a)Imine bounded polystyrenes:
NH2
CH3CN/Ref
8 h
O
N
O
O
N
H
1a
CH3CN/Ref
8 h
O
N
N
H2N
H
1b
(b)
Amine bounded polystyrenes:
NH2
CH3CN/Ref
48 h
NH
Cl
Cl
Cl
Cl
O
O
1c
CH3CN/Ref
48 h
H2N
N
N
N
1d
CH3CN/Ref
48 h
H2N
NH2
HN
NH2
1e
CH3CN/Ref
48 h
HN
N
N
N
1f
123

J IRAN CHEM SOC (2012) 9:349–355
351
pyridine was carried out in similar route except in that furfuryl
amine and 2-(amino methyl) pyridine was used instead of
imidazole.
Table 1 Elemental analysis data of the functionalized polystyrenes
1a–1f and vC=N (cm-1) of imine-bounded polystyrenes 1a and 1b
Functionalize
polystyrene
%C
%H
%N
vC=N
Immobilization of MoO2Cl2(DMF)2 on polystyrene
1a
1b
1c
1d
1e
1f
89.40
87.95
89.17
88.3
8.58
8.70
8.72
8.41
8.61
7.43
2.02
3.35
2.11
2.42
2.29
3.01
1,640
1,645
To a solution of MoO2Cl2(DMF)2 (2.5 g) in DMF (100 ml)
was added functionalized polystyrene (1 g). The mixture
was vigorously stirred at 100 °C for 24 h. After cooling,
the obtained resin was collected by filtration, washed
thoroughly with CH2Cl2 and dried in vacuum at room
temperature for several hours.
–
–
–
–
89.1
87.09
room temperature, filtered off, washed thoroughly with
methanol and petroleum ether, and dried in vacuum.
General procedure for catalytic oxidation of sulfides
in different solvents
Preparation of amine-bounded polystyrenes (1c–1f)
All of the reactions were carried out at room temperature
under air in a 25 ml flask equipped with a magnetic stirrer
bar. In 10 ml of solvent, were added 1 mmol of sulfide,
5 mmol of H2O2 and 0.017 mmol/Mo of catalyst, and the
reaction mixture was stirred. The progress of reactions was
monitored by GLC or TLC.
The functionalized polystyrene resin (2% DVB) with
imidazole and ethylene diamine linkers was prepared as we
have described previously [18, 19]. Functionalization of
polystyrene with furfuryl amine and 2-(amino methyl)
Scheme 2 Immobilization of
MoO2Cl2 on polystyrene via
different imine and amine
linkers (2a–2f)
DMF/ 100oC
N
O
N
N
O
MoO2Cl2(DMF)2
MoO2Cl2
24 h
2a
1a
DMF/ 100oC
24 h
N
N
MoO2Cl2(DMF)2
N
MoO2Cl2
2b
1b
1c
DMF/ 100oC
24 h
NH
O
MoO2Cl2(DMF)2
MoO2Cl2(DMF)2
NH
O
MoO2Cl2
2c
DMF/ 100oC
24 h
NH
N
NH
N
MoO2Cl2
2d
1d
DMF/ 100oC
24 h
MoO2Cl2(DMF)2
MoO2Cl2(DMF)2
HN
NH2
HN
NH2
1e
MoO2Cl2
2e
DMF/ 100oC
24 h
N
N
N
1f
N
2f
MoO2Cl2(DMF)
123

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J IRAN CHEM SOC (2012) 9:349–355
Table 2 The results of neutron activation analysis and vMo=O (cm-1
of polymer-supported catalysts 2a–2f
)
by direct reaction of chloromethylated polystyrene with
amines in acetonitrile (Scheme 1b). By reaction of amines
with chloromethylated polystyrene, the peak at 1,266 cm-1
corresponded to wagging mode of HCCl of –CH2Cl
group on polystyrene in FT-IR spectrum of original chlo-
romethylated polystyrene resin, was diminished or very
decreased in its intensity. Further evidence for producing of
amines and imines on polystyrene obtained from elemental
analysis of amine- and imine-bounded polystyrenes. The
results of CHN analysis for functionalized polystyrenes
(1a–1f) and vC=N for imine-bounded polystyrenes (1a, 1b)
are given in Table 1. Reaction of these functionalized
polystyrene resins (1a–1b) with a solution of MoO2Cl2
(DMF)2 in DMF led to attachment of MoO2Cl2 onto the
functionalized polystyrene via covalent bond (Scheme 2).
The supported MoO2Cl2 catalysts were characterized by
FT-IR spectra and neutron activation analysis (NAA). In
FT-IR spectrums of supported catalysts, new peaks were
appeared in the 900–1,000 cm-1 region that attributed to
Polymer-supported catalyst
% Mo
vMo=O
2a
2b
2c
2d
2e
2f
5.3
7.6
1.5
3.9
9.3
6.2
903, 965
903, 970
903, 954
903, 971
903, 960, 926
903, 948
General procedure for reusability of catalysts
All reactions were carried out as described above. The
progress of reactions was monitored by GLC. At the end of
each reaction the mixture was filtered off and the obtained
resin beads washed with 4 9 10 ml of CH2Cl2 and then
were used in the next cycle.
v
Mo=O. In addition, the metal loading on polystyrene was
determined with NAA. The Mo (%) and vMo=O of
supported catalysts (2a–2f) are given in Table 2. These
data confirm the immobilization of MoO2Cl2 on polysty-
rene. Then we investigated the catalytic activities of
supported catalysts in oxidation of methyl phenyl sulfide.
We studied the oxidation of methyl phenyl sulfide with
each catalyst in different solvents in the presence of H2O2
(Table 3). Among the H2O, CH3OH, C2H5OH, THF,
CH2Cl2, CH3CN, and (CH3)2CO, protic solvents gave
better results, but water was the best solvent for almost all
supported catalysts 2a–2f. All catalysts showed high
activity and selectivity in oxidation of methyl phenyl
sulfide to the methyl phenyl sulfoxide in the presence of
H2O2 as oxygen donor in protic solvents (H2O, CH3OH,
C2H5OH). Catalyst 2f showed the highest activity in
oxidation of methyl phenyl sulfide in the presence of H2O2.
Results and discussion
Chloromethylated polystyrene resin was oxidized to the
aldehydic polystyrene by the reaction with DMSO in the
presence of NaHCO3. Imine-bounded polystyrenes (1a and
1b) were prepared by the reaction of this aldehydic poly-
styrene with amines (furfuryl amine and 2-(amino methyl)
pyridine) in acetonitrile in two separated reactions
(Scheme 1a). These functionalized polystyrenes were
finely characterized by disappearing of vC=O of aldehydic
polystyrene at 1,699 cm-1 and producing of new bands at
1,640 and 1,645 cm-1 that related to vC=N of new imine-
bounded formation of 1a and 1b, respectively (Table 1).
Other functionalized polystyrenes (1c–1f) were prepared
Table 3 Oxidation of methyl phenyl sulfide by polymer-supported catalysts 2a–2f in different solvents in the presence of H2O2 30%, at room
temperature
Solv
%Conversiona (%sulfoxide)
Catal 2a
tb
Catal 2b
tb
Catal 2c
tb
Catal 2d
tb
Catal 2e
tb
Catal 2f
tb
H2O
97 (100)
100 (100)
92 (100)
43 (100)
65 (100)
48 (100)
32 (100)
25
25
25
25
25
25
25
98 (100)
96 (100)
93 (100)
41 (100)
56 (100)
54 (100)
35 (100)
20
20
20
20
20
20
20
100 (100)
100 (100)
93 (100)
40 (100)
30 (81)
25
65
65
65
65
65
65
98 (100)
95 (100)
80 (100)
44 (100)
9 (100)
25
40
40
40
40
40
40
100 (92)
100 (100)
95 (100)
54 (100)
13 (64)
15
15
15
15
15
15
15
100 (100)
100 (100)
84 (100)
42 (100)
10 (100)
45 (100)
13 (100)
15
30
30
30
30
30
30
CH3OH
C2H5OH
THF
CH2Cl2
CH3CN
Acetone
57 (100)
42 (100)
45 (100)
8 (100)
55 (100)
38 (100)
Reaction conditions: Methyl phenyl sulfide 1 mmol, catalyst: 0.017 mmol/Mo, H2O2 5 mmol, solvent 10 ml
a
Based on starting materials
b
t = min
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J IRAN CHEM SOC (2012) 9:349–355
353
Table 4 Reusability of polymer-supported catalysts 2a–2f in oxidation of methyl phenyl sulfide in H2O in the presence of H2O2 30%, at room
temperature
Run
%Conversion (%sulfoxide)
Catal 2a
ta
Catal 2b
ta
Catal 2c
ta
Catal 2d
ta
Catal 2e
ta
Catal 2f
ta
1
97 (100)
25
25
25
–
98 (100)
20
20
20
–
100 (100)
25
25
25
25
25
25
25
25
25
–
98 (100)
98 (100)
98 (100)
98 (100)
98 (100)
98 (100)
93 (100)
90 (100)
56 (100)
18 (100)
–
25
25
25
25
25
25
25
25
25
25
–
100 (92)
15
15
15
15
15
–
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
100 (100)
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
2
53 (100)
33 (100)
100 (100)
100 (92)
3
8 (100)
12 (100)
100 (100)
92 (94)
4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
100 (100)
71 (95)
5
–
–
100 (100)
33 (95)
6
–
–
97 (100)
–
–
–
–
–
–
–
–
–
–
7
–
–
92 (100)
–
8
–
–
65 (100)
–
9
–
–
21 (100)
–
10
11
12
13
14
15
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Reaction conditions: Methyl phenyl sulfide 1 mmol, catalyst: 0.017 mmol/Mo, H2O2 5 mmol, solvent 10 ml
a
t = min
Blank experiments in the absence of catalysts (in the
solvents of Table 3) showed that only 3–11% of methyl
phenyl sulfoxide was produced.
a catalyst, it might make it sufficient for commercial
application. Therefore, we investigated the reusability of
polymer-supported catalysts (2a–2f). The reusability of the
catalysts was monitored by using multiple sequential
oxidation of methyl phenyl sulfide with H2O2 (Table 4).
The activity of catalysts 2a and 2b was decreased after
first run. It was related to hydrolyzing of imine bond in the
presence of water as a solvent or byproduct that was
produced from catalytic cycle of oxidation(in proposed
mechanism (Scheme 3)) and leaching of the catalyst from
the support. In the FT-IR spectrums of these supported
catalysts (2a and 2b) after the first using, the intensity of
peaks for imine and Mo=O bonds was decreased that
approved the hydrolyzing of imine bond and leaching of
catalyst from support. The catalyst 2e shows two times
reusability and catalysts 2c and 2d were highly active
about six times reusing in oxidation of methyl phenyl
sulfide. The supported catalyst 2f is highly reusable and it
was reused 15 times without a considerable change in its
activity. It can be attributed to strong coordination of
imidazole to Mo(VI) center.
The reusability of a supporting catalyst can be the most
important property and if this character was the better for
Cl
Cl
L
L
L
DMF
or
Mo
O
Mo
O
Cl
Cl
O
+
O
O
O
,
O
S
S
H2O2
S
+ H2O
In order to assess the scope of catalytic activities of
these supported molybdenum-based catalysts, we studied
the oxidation of some aliphatic and aromatic sulfides in the
presence of H2O2 (Table 5). We obtained that these cata-
lysts were highly efficient in oxidation of different sulfides.
Almost all sulfides were completely converted to their
oxidized product in low times. The main product for
aliphatic sulfides was sulfoxide and the selectivity of the
Cl
Mo
Cl
L
L
L
DMF
OH
S
OH
or
Mo
O
O
O
Cl
Cl
S
OH
OH
O
Scheme 3 Proposed mechanism of oxidation of sulfides by the
polymer-supported MoO2Cl2 catalysts in the presence of H2O2
123

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J IRAN CHEM SOC (2012) 9:349–355
Table 5 Oxidation of some aliphatic and aromatic sulfides by polymer-supported catalysts 2a–2f in the presence of H2O2 30%, at room
temperature
Run Sulfide
%Conversion (sulfoxide)a
Catala2a tb Catala 2b
tb
Catala 2c
tb
90 100 (100)
100 (100) 10 100 (100) 10 100 (100) 165 100 (100)
Catala2d
tb
Catala 2e
tb
Catala 2f
tb
1
100 (100) 10 100 (100) 25 100 (100)
45 100 (100)
5
100 (100)
5
S
2
3
60 100 (100) 10 100 (100) 10
S
100 (100)
5
100 (100)
5
100 (100)
25 100 (100)
25 100 (100) 10 100 (100)
5
S
4
100 (100)
5
100 (100)
5
100 (100)
50 100 (100)
50 100 (100)
25 100 (92)
5
100 (100)
5
S
OH
CH3
5
6
97 (100) 25
98 (100) 20 100 (100)
25
98 (100)
15 100 (100) 15
S
CH3
100 (100) 35 100 (100) 35
100 (100) 35 100 (100) 30
90 (10)
375 100 (100) 155 100 (100) 55 100 (100) 35
S
OH
7
8
90 (10)
80 (20)
285 100 (10)
250 100 (20)
120 100 (100) 40 100 (100) 45
205 100 (40) 65 100 (40) 70
S
S
100 (10)
45 100 (10)
50
HO
OH
Reaction conditions: sulfide 1 mmol, catalyst 0.017 mmol/Mo, H2O2 5 mmol, solvent 10 ml. The used solvent for catalysts 2a, 2b, 2d and 2e
was MeOH, for catalyst 2c was EtOH and for catalyst 2f was H2O
a
For runs 1–5 based on GLC and for runs 6–8 based on TLC
b
t = min
Acknowledgments The authors are grateful to Damghan University
Research Council for their financial support.
catalysts for these aliphatic sulfides was very high, but
some of these catalysts converted some of aromatic sulfides
to sulfone as main product.
In conclusion, we immobilized the MoO2Cl2 on poly-
styrene in simple routes via different linkers and found that
these catalysts were highly reactive and selective in
oxidation of sulfides to their corresponding sulfoxides.
Catalyst 2f in that active complex have been immobilized
on polystyrene via imidazole linker was highly reusable for
15 times without any change in its activity in oxidation of
methyl phenyl sulfide to the methyl phenyl sulfoxide in the
presence of environmental benign oxidant (H2O2) and
solvent (H2O) that could be very important in green
chemistry.
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