Synthesis of new zirconium complex supported on MCM-41 and its application as an efficient catalyst for synthesis of sulfides and the oxidation of sulfur containing compounds

Article abstract of DOI:10.1002/aoc.4340

In the present work, we report synthesis of new zirconium complex supported on mesoporous silica by anchoring of adenine on the wall of functionalized MCM-41, then reacted with ZrOCl₂. The resultant MCM-41-Adenine-Zr was characterized by FT-IR, XRD, TEM, SEM, TGA, EDX, ICP and BET techniques. It was exhibited that the MCM-41-Adenine-Zr can be used as an efficient and thermally stable nanocatalyst for the oxidation of sulfides, oxidative coupling of thiols and synthesis of sulfides. Moreover, this heterogeneous catalyst can be easily recovered from the reaction mixture by simple filtration and reused for several consecutive cycles without noticeable change in its catalytic activity.

Full text of DOI:10.1002/aoc.4340

Received: 10 December 2017
DOI: 10.1002/aoc.4340
Revised: 2 February 2018
Accepted: 3 February 2018
F U L L P A P E R
Synthesis of new zirconium complex supported on MCM‐41
and its application as an efficient catalyst for synthesis of
sulfides and the oxidation of sulfur containing compounds
1
2
1
Taiebeh Tamoradi
| Arash Ghorbani‐Choghamarani
| Mohammad Ghadermazi
1
University of Kurdistan, Department of
Chemistry, Faculty of Science, Sanandaj,
Iran
In the present work, we report synthesis of new zirconium complex supported
on mesoporous silica by anchoring of adenine on the wall of functionalized
2
Department of Chemistry, Faculty of
MCM‐41, then reacted with ZrOCl . The resultant MCM‐41‐Adenine‐Zr was
2
Science, Ilam University, P.O. Box,
characterized by FT‐IR, XRD, TEM, SEM, TGA, EDX, ICP and BET techniques.
It was exhibited that the MCM‐41‐Adenine‐Zr can be used as an efficient and
thermally stable nanocatalyst for the oxidation of sulfides, oxidative coupling
of thiols and synthesis of sulfides. Moreover, this heterogeneous catalyst can
be easily recovered from the reaction mixture by simple filtration and reused
for several consecutive cycles without noticeable change in its catalytic activity.
6
9315516 Ilam, Iran
Correspondence
Arash Ghorbani‐Choghamarani,
Department of Chemistry, Faculty of
Science, Ilam University, P.O. Box
69315516, Ilam, Iran.
Email: arashghch58@yahoo.com;
a.ghorbani@ilam.ac.ir
KEYWORDS
Mohammad Ghadermazi, University of
Kurdistan, Department of Chemistry,
Faculty of Science, Sanandaj, Iran.
Email: mghadermazi@yahoo.com
disulfide, recoverability, sulfide, sulfoxide, zirconium
Funding information
University of Kurdistan
[
12–16]
1
| INTRODUCTION
and high concentration of surface Si–OH groups.
MCM‐41 is member of mesoporous molecular sieves with
During the recent increasing interest in the field of
organocatalysis, heterogeneous catalysts are attracted
attention over homogeneous catalysts because of their
hierarchical structure and hexagonally packed arrays that
[
17]
can be used as catalyst supports.
These nanoparticles,
because of their high surface area and good catalytic activ-
ity and high efficiency, have a wide range of applications
in the removal of chromate and arsenate, drug delivery
systems, extraction, adsorption, catalysis support and
[1–3]
simplicity in recovery and regeneration.
Various
approaches have been suggested for the immobilization
of homogeneous transition metal complexes on silica,
zeolites, alumina and other metal oxides. Despite their
easy synthesis, anchoring of homogeneous transition
metal catalysts on solid supports often decreases the cata-
[
18–21]
recycling of expensive homogeneous catalysts.
Sulfoxides, disulfides and sulfides are useful in the
chemical industries and play a vital role in some medicines
and biological processes. During the recent increasing inter-
est in synthesis of these compounds, varieties of catalysts
have been received considerable attention. However, the
drawback of catalysts is their separation from the reaction
mixture using tedious procedure. This problem can be over-
come using nanocatalysts which can be easily removed with
[4–7]
lytic activity or efficiency.
Therefore in the last few
years, nano‐catalysts have been used as ideal heteroge-
neous supports because they can act as efficient bridge
[
8–11]
between homogeneous and heterogeneous catalysts.
Silica mesoporous molecular sieves have specific advan-
tages, including ease of preparation, low cost, excellent
thermal and chemical stability, large internal surface area
[22–25]
simple and inexpensive procedure such as filtration.
Appl Organometal Chem. 2018;e4340.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.4340

2
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TAMORADI ET AL.
On the other hand, heterogeneous zirconium oxide
operating at 200 Kv. Fourier transform infrared (FT‐IR)
catalysts have been developed to promote the oxidation
reaction under relatively mild conditions. In spite of tre-
mendous effort dedicated to the development of heteroge-
neous zirconium oxide complexes, up to date, there are no
report researches about the synthesis of sulfides in the
spectra were recorded on a Bruker VERTEX 80 v model
‐1
using the KBr pellets in the range of 400−4000 cm . Melt-
ing points of products were determined with an Electro-
thermal 9100 apparatus. Powder X‐ray diffraction (XRD)
measurements were taken using Co radiation source with
a wavel ength l = 1.78897 Å, 40 kV.
[26–28]
presence above mentioned complex.
In the present study, as a part of our continuing inter-
est in the development of efficient and new heterogeneous
catalysts for organic synthesis, we present our results on
the preparation and characterization of novel MCM‐41‐
Adenine‐Zr nanoparticles, and its catalytic application
for the oxidation of sulfides, oxidative coupling of thiols
and synthesis of sulfides via reaction of aryl halides with
sulfur. The simple work up, excellent yield, use of easy
to handle procedure, short reaction time, inexpensive
and non‐toxic catalyst; makes this protocol both attractive
and economically viable for above mentioned reactions.
More importantly, up to date, there are no reported for
synthesis of sulfides in presence zirconium catalyst.
2
.2 | Preparation of mesoporous silica‐
anchored MCM‐41‐Adenine‐Zr
Mesoporous MCM‐41 was synthesized through the sol‐gel
method by mixing 1 g of cetyltrimethylammonium bro-
mide (CTAB), as structure directing template agent, to a
solution containing 3.5 ml of NaOH solution (2 M) and
deionized water (480 ml) and stirred at 80 °C, then 5 ml
of tetraethylorthosilicate (TEOS) as the silica source was
gradually added to the solution and the mixture stirred
at the same temperature for 2 h. Finally, the resulting
mixture was filtered and washed with deionized water
and dried in an oven at 60 °C followed by calcination at
2
2
| EXPERIMENTAL
823 K for 5 h at a rate of 2 °C/min to remove the residual
surfactants. The collected product affords pure silica
MCM‐41. Functionalization of MCM‐41 was performed
by adding 1 g of MCM‐41 to a solution of 3‐
chloropropyltrimethoxysilane (1.5 ml) in 25 ml of toluene
(30 ml). The reaction mixture was stirred under reflux
conditions and allowed to stand for 24 h. The white pre-
cipitate was collected (MCM‐41‐Cl) and washed with n‐
hexane and dried under vacuum. Then, adenine (0.27 g)
was added to a suspension of the MCM‐41‐Cl (1 g) in tol-
uene (30 ml). The resulting mixture stirred under reflux
conditions for 48 h, filtered, washed thoroughly with eth-
anol/water and dried in vacuum. For the synthesis of
MCM‐41‐Adenine‐Zr catalyst, MCM‐41‐Adenine and
ZrO Cl.8H O (0.8 g) were mixed in ethanol (30 ml). Then
.1 | Materials and physical
measurements
All solvents and materials used in this work are pur-
chased from Merck, Fluka and Sigma‐Aldrich and used
without further purification. TGA measurement of the
nanostructures was carried out on Shimadzu DTG‐60
instrument with a temperature range from 80 to 700 °C.
The amount of metal was determined by inductively
coupled plasma‐optical emission spectrometry (ICP‐
OES). The surface morphology of nanostructures was
investigated with measuring SEM using FESEM‐TESCAN
MIRA3. The elemental analysis of the samples was taken
by Energy‐dispersive X‐ray spectroscopy (EDAX,
TSCAN). Transmission electron microscopy (TEM) analy-
sis was obtained with a Philips CM10 microscope
2
2
the mixture was refluxed for 16 h, filtered, washed
thoroughly with ethanol and dried in vacuum (Scheme 1).
SCHEME 1 Synthesis of MCM‐41‐
Adenine‐Zr

TAMORADI ET AL.
3 of 12
2
.3 | General procedure for the
2.6.3 | 1,2‐Di‐p‐tolyldisulfane (Table 4,
entry 2)
preparation of sulfoxides
1
In this step, MCM‐41‐Adenine‐Zr catalyst (4 mg) was
H NMR (400 MHz, CDCl , ppm): δ = 2.36 (s, 6H), 2.41
3 H
added to mixture of sulfide (1 mmol) and H O (0.4 ml)
(s, 3H), 7.11‐7.59 (m, 8H).
2
2
and stirred at room temperature under solvent‐free condi-
tion for appropriate time. Upon completion of the reac-
tion progress as monitored by TLC, the catalyst was
filtered and washed with ethyl acetate. Finally, ethyl ace-
tate was removed to give the pure sulfoxides and the prod-
ucts were obtained in good to high yields.
2
.6.4 | 2,20‐Dimethoxy diphenyl sulfide
(Table 6, entry 1)
1
H NMR (400 MHz, DMSO, ppm): δ = 6.96–7.36 (m, 8H),
H
3.82 (s, 6H).
2
.6.5 | Diphenyl sulfide (Table 6, entry 2)
2
.4 | General Procedure for the oxidative
1
H NMR (400 MHz, DMSO, ppm): δ = 6.30–7.34 (m, 6H),
H
coupling of thiols
7.37–7.46 (m, 4H).
In summary, a mixture of thiol (1 mmol), H O (0.4 ml) and
2
2
MCM‐41‐Adenine‐Zr (3 mg) was stirred at room tempera-
ture under solvent‐free condition. Completion of the reac-
tion and the compound purity were monitored by TLC.
After the reaction was completed, the separation of catalyst
from reaction products was performed by the filtration pro-
cess and the catalyst washed with ethyl acetate. Finally, the
solvent of product was removed to give the pure disulfides.
3
| RESULTS AND DISCUSSION
3.1 | Catalyst preparation
In continuation of our previous efforts on the application
of supported metal catalyst on mesoporous silica in organic
reactions,
[12,29–31]
herein, we report for the first time the
synthesis and characterization an environmentally friendly
and novel MCM‐41‐Adenine‐Zr catalyst (Scheme 1), and
investigated its application as an efficient heterogeneous
and recoverable catalyst in the synthesis of sulfoxides
2
.5 | General procedure for the sulfides
synthesis
(
Scheme 2), disulfides (Scheme 3) and sulfides (Scheme 4).
A plausible reaction mechanism for the synthesis
A mixture of sulfur (1 mmol), aryl halide (1 mmol), KOH
(0.7 g) and MCM‐41‐Adenine‐Zr catalyst (0.05 g) in
MCM‐41‐Adenine‐Zr is shown in Scheme 2.
DMSO (2 ml) was stirred at 130 °C. Then the progress of
reaction was monitored by TLC. After the completion of
the reaction, the catalyst was separated by filtration and
the reaction mixture was extracted with ethyl acetate.
The organic extract was washed twice with water and
dried with anhydrous Na SO . Finally, the solvent was
3
.2 | Catalyst characterization
The resultant MCM‐41‐Adenine has been characterized
by XRD, FT‐IR, TEM, SEM, TGA, EDS, ICP and BET
techniques.
2
4
evaporated to give corresponding sulfide.
2
2
.6 | Selected spectral data
.6.1 | Dodecyl methyl sulfoxide: (Table 2,
entry 7)
1
H NMR (400 MHz, DMSO, ppm): δ = 0.87 (t, J=6.6, 3H),
H
1
.26–1.71 (m, 20H), 2.95(s, 3H), 3.09 (t, J=8, 2H).
2.6.2 | Methyl phenyl sulfoxide (Table 2,
entry 8)
1
H NMR (400 MHz, CDCl , ppm): δ = 2.75 (s, 3H), 7.52–
SCHEME 2 MCM‐41‐Adenine‐Zr catalyzed the oxidation of
3
H
7
.62 (m, 2H), 7.66–7.69 (m, 3H).
sulfides to sulfoxides

4
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TAMORADI ET AL.
The morphology of the MCM‐41 and MCM‐41‐Ade-
nine‐Zr were obtained using scanning electron micros-
copy (SEM) technique. SEM images of the MCM‐41 and
MCM‐41‐Adenine‐Zr are given in Figure 2. As shown
in this Figure, MCM‐41 and MCM‐41‐Zr was made up
of quite homogeneous and uniform spherical particles
and no significant changes in the morphology occurred
SCHEME 3 MCM‐41‐Adenine‐Zr catalyzed the oxidation of
sulfides to sulfoxides
SCHEME 4 Proposed mechanism for oxidation of sulfides in
presence of MCM‐41‐Adenine‐Zr as catalyst
The crystalline structures of the MCM‐41 (blue curve)
and MCM‐41‐Adenine‐Zr (red curve) catalyst were deter-
mined by powder X‐ray diffraction (XRD). As seen in
Figure 1, the XRD pattern of MCM‐41 shows the presence
of a single intense peak and two weak peaks assigned to (1
0
4
0), (1 1 0) and (2 0 0) reflections at 2θ= 2.38, 3.81 and
.69°, respectively. These spectra reflect hexagonal meso-
porous structure of MCM‐41. Also, an overall decrease in
diffraction (100) at 2θ= 2.26° upon post anchoring of zirco-
nium complex on the wall of functionalized MCM‐41 was
noticed which is due to the difference in the scattering con-
trast of the pores and the walls of nanochannels of MCM‐
4
1. More importantly, The XRD pattern of the MCM‐41‐
Adenine‐Zr catalyst and MCM‐41 were indicated which
the texture of initial material of the MCM‐41upon post
anchoring of zirconium complex on MCM‐41 was retained.
FIGURE 1 The XRD patterns of MCM‐41 (blue curve) and MCM‐
FIGURE 2 SEM images of a) calcined MCM‐41and b) MCM‐41‐
Adenine‐Zr catalyst
4
1‐Adenine‐Zr (red curve)

TAMORADI ET AL.
5 of 12
upon the insertion of zirconium complex group onto
MCM‐41.
The energy‐dispersive X‐ray spectroscopy (EDX) anal-
ysis is shown in Figure 3. In order to determine the kinds
of elements in MCM‐41‐Adenine‐Zr, the EDS analysis of
MCM‐41‐Adenine‐Zr was performed; which EDS patterns
of this catalyst shows the presence of peaks associated
with Si, O, N, C and Zr species in the catalyst. Also, in
order to determine the exact amount of Zr loaded on mod-
ified MCM‐41 nanoparticles, ICP‐OES analysis was per-
−
1
formed and it was found to be 0.29 mmol g .
As shown in Figure 4, the size of MCM‐41‐Adenine‐Zr
catalyst was determined with transmission electron micros-
copy (TEM). TEM analysis of the synthesized MCM‐41‐Ade-
nine‐Zr shows that particles have highly ordered long‐range
hexagonal arrangement. It should be mentioned that the
size of the MCM‐41‐Adenine‐Zr catalyst is around 125 nm.
Blue curve in Figure 5 is the spectrum of MCM‐41, red
curve is the spectrum of MCM‐41‐Cl, violet curve is the
spectrum of MCM‐41‐Adenine and green curve is the
spectrum of MCM‐41‐Adenine‐Zr. FT‐IR spectrum of
MCM‐41 (blue spectrum) shows a bending vibration at
‐1
4
63 cm . Furthermore, absorption peaks appearing at
−
1
−1
around 1100–1200 cm and 3000–3600 cm are due to
Si–O–Si asymmetric stretching and the silanol OH groups,
respectively. In FT‐IR spectra of MCM‐41‐Cl (red spec-
trum), the presence of the anchored (3‐choloropropyl)
trimethoxysilane is identified by C–H stretching vibra-
‐1
tions that appear at 2955 and 2851 cm . In the FT‐IR
spectra of MCM‐41‐Adenine (violet spectrum), stretching
vibrations of C=C and C=N has been identified by
‐
1
adsorption bands at 1311‐1436 and 1609‐1692 cm . FT‐
IR spectrum of MCM‐41 (green spectrum) obtained after
adsorption of Zr on to MCM‐41‐Adenine.
Thermo‐gravimetric analysis (TGA) of the organic
groups supported on the surface of bare MCM‐41 is
FIGURE 4 TEM images of MCM‐41‐Adenine‐Zr catalyst at
different magnifications
FIGURE 3 EDX spectrum of MCM‐41‐Adenine‐Zr

6
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TAMORADI ET AL.
FIGURE 5 FT‐IR spectrum for bare MCM‐41 (blue spectrum),
MCM‐41‐Cl (red spectrum), MCM‐41‐Adenine (violet spectrum)
and MCM‐41‐Adenine‐Zr (green spectrum)
FIGURE 7 Nitrogen adsorption/desorption isotherms of MCM‐
41 and MCM‐41‐Adenine‐Zr
TABLE 1 Texture parameters obtained from nitrogen adsorption
studies
presented in Figure 6. In all samples, the first step of
weight loss below 200 °C corresponds to the removal of
the physically and chemically adsorbed solvents or sur-
face hydroxyl groups, and the other weight loss in the
range of 200‐500 °C is related to the decomposition of
the organic layers on the surface of MCM‐41. TGA curve
of the MCM‐41‐Adenine‐Zr (blue curve) shows a weight
loss more than 29% from 200 to 500 °C, resulting from
the decomposition of immobilized organic spaces on the
MCM‐41 surface. On the basis of this result, the well
grafting of organic groups including Zr complex on the
MCM‐41 is verified.
Pore diameter
by BJH
method (nm)
Pore
SBET
(m g )
volume
2
‐1
3
‐1
Sample
(cm g )
MCM‐41
1113.7
313.90
2.39
1.12
1.39
MCM‐41‐Adenine‐Zr
0.446
attributed to the anchoring of zirconium complex on the
[
28]
inner surface of the pores.
As shown in Figure 8, the X‐ray mapping of MCM‐41‐
Adenine‐Zr was investigated in order to evaluate the dis-
persion of Zr active sites in the catalyst. It was found that
the elemental map images were indicated the good disper-
sion of Zr on surface of catalyst.
As shown in Figure 7, the N ‐adsorption and desorp-
2
tion isotherms results are measured in order to determine
the textural properties. MCM‐41‐Adenine‐Zr was
degassed at 100 °C under an argon gas flow for 3 h prior
to the measurements. These results are shown in Table 1
indicating the functionalized MCM‐41 have smaller BET
surface area, narrower pore diameter and lower absorp-
3.3 | Catalytic studies
tion volume. The results of N adsorption and desorption
isotherms of MCM‐41 and MCM‐41‐Adenine‐Zr are
In the first part of our program, the catalytic activity of
MCM‐41‐Adenine‐Zr catalyst was examined in oxidation
of sulfides to sulfoxides using H O (30%) as oxidant at
2
2
2
room temperature (Scheme 3). In order to find the best
reaction conditions, dipropyl sulfoxide was prepared as a
model compound in the presence of different amounts
of MCM‐41‐Adenine‐Zr catalyst using H O (30%) in var-
2
2
ious solvents as well as solvent‐free conditions (Table 2).
These reactions were tested in ethanol, acetonitrile and
ethyl acetate and solvent‐free condition. After optimizing
the solvent, catalyst amounts were varied from 0.003 to
0.007 g for reactions carried out at room temperature. It
was found that there is a general trend of increasing con-
version of sulfide to sulfoxide with increasing amount of
catalyst. As shown in Table 2, 0.004 g MCM‐41‐Adenine‐
Zr and 0.4 ml H O under solvent‐free condition at room
2
2
FIGURE 6 TGA curves of MCM‐41 (red curve) and MCM‐41‐
Adenine‐Zr (blue curve)
temperature was found to be ideal reaction conditions for
the conversion of dipropylsulfide to the dipropylsulfoxide.

TAMORADI ET AL.
7 of 12
FIGURE 8 The X‐ray map analysis of MCM‐41‐Adenine‐Zr catalyst
TABLE 2 Optimization of oxidation of sulfides to the corresponding sulfoxides using MCM‐41‐Adenine‐Zr nanoparticles under various
conditions
a
Entry
Solvent
H
2
O
2
Catalyst (mg)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
Acetonitrile
Ethanol
0.4
0.4
0.4
0.4
0.4
0.5
0.4
0.4
4
4
4
3
4
4
5
7
105
120
85
85
92
79
79
97
96
98
98
Ethyl acetate
Solvent‐Free
Solvent‐Free
Solvent‐Free
Solvent‐Free
Solvent‐Free
70
55
50
50
45
a
Isolated yields.
The generality of this approach has been demon-
high efficiency in the presence of MCM‐41‐Adenine‐Zr as
strated by facile oxidation of a wide range of sulfides with
different functional groups to their corresponding prod-
ucts in the presence of MCM‐41‐Adenine‐Zr catalyst as
summarized in Table 3. All products are obtained in the
short reaction time and in good to excellent yields.
A plausible reaction mechanism for oxidation of sul-
fides is shown in Scheme 4.
As the second part of our organic study, we turned our
attention towards the synthesis of disulfide compounds in
catalyst and H O as the oxidant at room temperature
under solvent‐free conditions (Scheme 5).
In order to optimize the reaction conditions, we
started our investigation under the influence of varying
the amount of MCM‐41‐Adenine‐Zr catalyst and different
2
2
amount of H O2 for the oxidative coupling of 4‐
2
[35]
methylbenzenethiol as a model substrate using various
solvents such as acetonitrile, ethanol, ethyl acetate as well
as solvent‐free conditions (Table 4).

8
of 12
TAMORADI ET AL.
a
TABLE 3 Oxidation of sulfides to the sulfoxides in the presence of MCM‐41‐Adenine‐Zr
b
Entry
Substrate
Product
Time (min)
Yield (%)
M.p.(°C)
Found
Reported
[
32]
32]
[
1
2
3
4
5
6
7
8
9
Dipropylsulfide
2a
2b
2c
2d
2e
2f
55
45
35
40
5
96
95
97
90
92
91
97
97
89
Oil
Oil
Oil
Oil
[
Diethylsulfide
32]
33]
Dibenzylsulfide
132
127‐129
117‐119
[
Benzylphenylsulfide
Tetrahydrothiophene
Dimethylsulfide
122
[
13]
Oil
Oil
Oil
[
34]
60
50
55
65
Oil
[
[
34]
Dodecylmethylsulfide
Methylphenylsulfide
2‐(Phenylthio)ethanol
2 g
2 h
2i
63‐65
30‐32
61‐65
33‐34
33]
[
34]
Oil
Oil
a
b
Reaction conditions: MCM‐41‐Adenine‐Zr (0.004 g), sulfide (1 mmol), H
2
O
2
(0.4 mL), solvent‐Free condition at room temperature. Isolated yields.
It is noteworthy that, systematic studies are carried
out in the presence of different amounts of the catalyst
to investigate the effect of the catalyst. We have found that
a higher yield was observed when the amount of the cat-
alyst was increased.
SCHEME
coupling of thiols into disulfides
5
MCM‐41‐Adenine‐Zr catalysed the oxidative
TABLE 4 Optimization of oxidative coupling of thioles using MCM‐41‐Adenine‐Zr nanoparticles under various conditions
a
Entry
Solvent
H
2
O
2
Catalyst (mg)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
Acetonitrile
Ethanol
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.5
3
3
3
2
3
4
5
3
180
115
165
85
91
94
94
83
96
95
96
95
Ethyl acetate
Solvent‐Free
Solvent‐Free
Solvent‐Free
Solvent‐Free
Solvent‐Free
65
60
55
60
a
Isolated yields.
a
2 2
TABLE 5 Oxidative coupling of thiols into disulfides using H O in the presence of MCM‐41‐Adenine‐Zr
M.p. (°C)
Time
(min)
Yield
(%)
b
Entry
Substrate
Product
Found Reported
[
[
[
[
[
[
[
[
36]
32]
32]
32]
32]
32]
32]
36]
1
2
3
4
5
6
7
8
Phenylmethanethiol
4‐Methylbenzenethiol
Naphthalene‐2‐thiol
2‐Mercaptobenzoic acid
Benzo[d]thiazole‐2‐thiol
2‐Mercaptoethanol
4a
4b
4c
45
65
30
40
15
30
55
60
96
96
97
89
94
98
89
93
68‐71
35‐38
69‐70
36–38
137
275
134‐136
278–284
174–176
Oil
4d
4e
4f
90‐93
Oil
4‐Bromothiophenol
4 g
4 h
89‐92
86–90
Benzo[d]oxazole‐2‐thiol
90‐92
94–96
a
b
Reaction conditions: MCM‐41‐Adenine‐Zr (0.003 g), thiol (1 mmol), H
2
O
2
(0.4 ml), solvent‐Free condition at room temperature. Isolated yields.

TAMORADI ET AL.
9 of 12
In order to gain further insight into this process and
with optimal conditions in hand, oxidation reactions for
a wide range of thiols with different functional groups
were performed in the presence of MCM‐41‐Adenine‐Zr
as catalyst under mild and completely heterogeneous con-
ditions at room temperature (Table 5). After reaction com-
pletion, the products were extracted by simple filtration
and prepared in the short reaction time and in good to
excellent yields.
The proposed mechanism for this process using H O
2
2
as oxidant in the presence MCM‐41‐Adenine‐Zr catalyst is
[
35]
outlined in Scheme 6.
We finally investigated the synthesis of sulfide deriva-
tives in moderate to excellent yields.
In this work, sulfur was selected for the direct synthe-
sis of organic sulfides from aryl halides using MCM‐41‐
Adenine‐Zr as catalyst (Scheme 7). In order to find the
best reaction conditions, the reaction of iodobenzene
and sulfur in the presence of MCM‐41‐Adenine‐Zr cata-
lyst was selected as a model reaction and influence of sol-
vent, temperature and amount of catalyst and the type of
base on the outcome of reaction has been investigated
SCHEME 6 Proposed mechanism for oxidative coupling of thiols
in presence of MCM‐41‐Adenine‐Zr as catalyst
(
Table 6).
The reaction of sulfur (1 mmol), iodobenzene (1 mmol)
SCHEME 7 MCM‐41‐Adenine‐Zr catalyzed the synthesis of
sulfides
and KOH (0.7 g) was optimized in presence of different
amount of catalyst using various solvents such as EtOH,
MCM‐41‐Adenine‐Zr catalyst (0.003 g) in the presence
of H O (0.4 ml) under solvent‐free conditions at room
temperature was found to be ideal reaction conditions
DMSO, DMF, CH CN and PEG. Among various solvents
3
screened (Table 1, entries 1–8), it is found that the reac-
tion was highly effected in polar aprotic solvents such as
DMSO and dimethylformamide (DMF).
2
2
for the oxidative coupling of 4‐methylbenzenethiol.
TABLE 6 Optimization of the reaction conditions for the C–S coupling using MCM‐41‐Adenine‐Zr catalyst
a
Entry
Solvent
Base
Temp. (°C)
Catalyst (mg)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
DMF
PEG
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
NaOH
130
130
130
130
130
130
80
50
50
50
50
50
50
50
50
50
30
70
100
50
50
50
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
11
N.R
N.R
N.R
N.R
N.R
10
CH
3
CN
EtOH
2
H O
Toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
100
130
130
130
130
130
130
130
15
66
10
11
12
13
14
15
23
68
69
N.R
N.R
21
2 3
Na CO
Et
3
N
a
Isolated yields.

1
0 of 12
TAMORADI ET AL.
a
TABLE 7 Synthesis of symmetrical sulfides via reaction of sulfur and aryl halides using DMSO in the presence of MCM‐41‐Adenine‐Zr
M.p. (°C)
Time
(min)
Yield
(%)
b
Entry
Substrate
Product
Found Reported
[
[
22]
37]
1
2
3
4
5
6
7
8
9
2‐Methoxyiodobenzene
Iodobenzene
6a
6b
6c
6d
6e
6f
210
240
80
61
66
52
65
59
50
41
33
28
50
Oil
Oil
Oil
Oil
[
38]
4‐Bromonitrobenzene
Bromobenzene
158‐161
Oil
159–161
[
37]
360
180
560
120
620
660
60
Oil
[
39]
Benzylbromide
44‐46
Oil
43
[
38]
4‐Iodotoluene
Oil
[
[
38]
38]
4‐Chloronitrobenzene
4‐Bromotoluene
Chlorobenzene
6 g
6 h
6i
160‐162
Oil
159–161
[
[
38]
37]
Oil
Oil
Oil
1
0
4‐Iodonitrobenzene
6j
157‐160
159–161
a
b
Reaction conditions: MCM‐41‐Adenine‐Zr (0.05 g), sulfur (1 mmol), aryl halide (1 mmol) and KOH (0.7 g), DMSO (2 ml) at 130 °C. Isolated yields.
SCHEME 8 Proposed mechanism for
synthesis of sulfides in the presence of
MCM‐41‐Adenine‐Zr
In order to optimize the catalyst amount, various
quantities of catalyst were used in synthesis of sulfides.
Therefore, we studied the outcome of the reaction with
various amounts of catalyst. It can be seen that an
increase in the quantity of catalyst from 0.03 to 0.05 g
enhances the product yield from 23 to 66%. It should be
mentioned that a greater amount of catalyst has substan-
tially less effect on the yield and time of the reaction
(
Table 6, entry 11, 12).
As shown in Table 6, we observed that the best results
were obtained in presence 0.05 g MCM‐41‐Adenine‐Zr
catalyst, 0.7 g KOH in DMSO (2 ml) at 130 °C.
With optimal conditions in hand, in order to explore
the generality and scope of this protocol, a variety of
aromatic halides were employed to the synthesis of
FIGURE 9 Reusability of MCM‐41‐Adenine‐Zr in the oxidati on
of dipropyl sulfide (red column), the oxidative coupling of 4‐
methylbenzenethiol (green column) and the synthesis of
diphenylsulfide (blue column)

TAMORADI ET AL.
11 of 12
TABLE 8 Comparison of MCM‐41‐Adenine‐Zr for the oxidation of methylphenylsulfide with previously reported procedure
a
Entry
Substrate
Catalyst
Time (min)
Yield (%)
[
25]
1
2
3
4
5
6
7
8
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Cd‐salen‐MCM‐41
150
240
150
120
75
98
88
[
41]
42]
TsOH
[
SiO
2
–W
2
–Im
91.9
[
[
[
[
13]
43]
44]
26]
VO‐2A3HP‐MCM‐41
Ni‐SMTU@boehmite
NBS
96
97
93
98
270
300
55
Zr‐oxide@MCM‐41
MCM‐41‐Adenine‐Zr
97 [this work]
a
Isolated yields.
sulfides derivatives in the presence of MCM‐41‐Adenine‐
Zr for the appropriate time in moderate to excellent
yields.
3.6 | Comparison of the catalyst
The efficiency of this nanocatalyst is demonstrated by
comparing our results on the synthesis of
methylphenylsulfoxde with the previous methods in the
literatures (Table 8). As it can be seen in Table 8, easy
catalyst/product separation and catalyst recycling, high
yield, easy preparation of the catalyst using cheap and
commercially available materials, short reaction time,
use of non‐toxic ligand, and stability are several benefits
of this protocol.
The results of this study are summarized in Table 7.
After successful synthesis of sulfides derivatives, a
plausible reaction mechanism for the synthesis of this
[40]
product is proposed in Scheme 8.
3.4 | Recyclability of the catalyst
In order to investigate the recyclability of the catalyst, syn-
thesis of sulfides via reaction of iodobenzene with sulfur,
oxidation
of
methylphenylsulfide
to
the
4 | CONCLUSION
methylphenylsulfoxide and oxidative coupling of 4‐
methylbenzenethiol to the corresponding disulfide were
examined. The catalyst was separated by filtration and
dried after each run, recycled and reused without consid-
erable decrease of its catalytic activity. Figure 9 shows the
yield of 3 times of synthesis of sulfides and 6 times for the
oxidation of sulfides and oxidative coupling of thiols. This
observation can simply describe that the leaching of zirco-
nium from MCM‐41‐Adenine‐Zr is very negligible for
these reactions. According to ICP‐OES analysis, the exact
amount of Zr loaded on modified mesostructured for the
conversion of dipropyl sulfide to the dipropyl sulfoxide
at least for six consecutive cycles was found to be
In summary, preparation of new zirconium complex
supported onto surface of mesoporous silica as a
reusable, green and highly efficient catalyst have been
performed. The structure of new catalyst was character-
ized by FT‐IR, TGA, EDS, TEM, ICP‐OES, XRD, BET
and SEM. MCM‐41‐Adenine‐Zr was separable from the
reaction mixture by filtration, reused for consecutive
several cycles and used for the oxidation of sulfides,
oxidative coupling of thiols and synthesis of sulfides in
a short time under mild conditions in moderate to high
yields.
0
.21 mmol/g. Decrease in the catalyst efficiency and
ACKNOWLEDGEMENTS
lengthening of the reaction time.
The authors are deeply grateful to Erfan Ghadermazi,
University of Kurdistan and University of Ilam for finan-
cial support of this research project.
3.5 | Catalyst leaching Study
The amounts of zirconium leaching in synthesis of
diphenyl sulfide was studied by checking the Zr loading
amount before and after recycling of the catalyst by ICP‐
OEIS technique. It was found that the amount of zirco-
nium in fresh catalyst and the recycled catalyst after 3
times recycling is 0.29 and 0.19 mmolg , respectively.
Therefore, ICP‐OEIS analysis indicated that zirconium
leaching of this catalyst is very low.
ORCID
Taiebeh Tamoradi http://orcid.org/0000-0002-8548-271X
Arash Ghorbani‐Choghamarani
0002-7212-1317
Mohammad Ghadermazi
8631-6361
http://orcid.org/0000-
‐
1
http://orcid.org/0000-0001-

12 of 12
TAMORADI ET AL.
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How to cite this article: Tamoradi T, Ghorbani‐
Choghamarani A, Ghadermazi M. Synthesis of new
zirconium complex supported on MCM‐41 and its
application as an efficient catalyst for synthesis of
sulfides and the oxidation of sulfur containing
compounds. Appl Organometal Chem. 2018;e4340.
https://doi.org/10.1002/aoc.4340
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