Highly efficient and reusable polystyrene-supported copper(II) catalytic system for S-arylation of potassium thiocyanate by aryl halides in water

Article abstract of DOI:10.1002/aoc.3471

An inexpensive, efficient and environmentally friendly copper(II) catalyst supported on polystyrene was successfully synthesized and used as a heterogeneous catalyst for S-arylation of potassium thiocyanate by aryl halides. Also this catalyst could be recovered and reused several times without any noticeable decrease in its catalytic activity. Copyright

Full text of DOI:10.1002/aoc.3471

Full paper
Received: 8 December 2015
Revised: 14 January 2016
Accepted: 9 February 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3471
Highly efficient and reusable polystyrene-
supported copper(II) catalytic system for
S-arylation of potassium thiocyanate by aryl
halides in water
a,b
a
Abdol R. Hajipour * and Saeideh Jajarmi
An inexpensive, efficient and environmentally friendly copper(II) catalyst supported on polystyrene was successfully synthesized
and used as a heterogeneous catalyst for S-arylation of potassium thiocyanate by aryl halides. Also this catalyst could be recov-
ered and reused several times without any noticeable decrease in its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.
Keywords: copper(II) catalyst; C–S coupling; symmetric diaryl sulfides; heterogeneous catalyst; aryl halides
Moreover, heterogeneous catalysis has the benefits of easy prod-
uct purification, reusability and high activity. Among these hetero-
Introduction
The making of carbon–sulfur bonds is a significant instrument in
geneous catalysts, copper immobilized on polystyrene has
appeared as an interesting material because of its numerous uses
in organic synthesis.
organic synthesis, because of broad applications of organo-sulfur
[
1–3]
[24]
compounds in various fields of science.
Diaryl thioethers and
their oxidized forms exist in a large number of polymeric mate-
rials, biologically active molecules and pharmaceutical materials,
for example in antiasthmatic, antiallergy, antibipolar disorder,
Also, during the last few years there has been an interest in stud-
ies of green chemical systems. Lately, the employment of water as
solvent in chemical reactions has attracted much notice because of
its nontoxicity, low price and high accessibility compared with
[
4–10]
antidiabetes, antischizophrenia and anti-HIV agents.
There-
[
25,26]
fore, the creation of carbon–sulfur bonds is of much interest and
forms a very important part in the preparation of numerous phar-
maceutical, biological and chemical molecules.
other organic solvents.
Water as a solvent was used by Carril and co-workers for the
preparation of diaryl sulfides from the reaction of thiophenol deriv-
atives with aryl halides catalyzed by a mixture of a 1,2-diamine de-
In conventional techniques, severe and difficult conditions are
used for the creation of carbon–sulfur bonds. For example, reduc-
tion of aryl sulfoxides or aryl sulfones with powerful reducing
[
27]
rivative and a copper salt.
Zhou and co-workers reported an
extremely impressive procedure for the formation of carbon–sulfur
bonds between potassium thiocyanate and aryl halides using
CuCl /1,10-phenanthroline and (n-Bu) NF in water, with no recov-
[
11]
agents is one technique for the preparation of sulfides.
In 1985, Migita and co-workers reported the synthesis of aryl sul-
fides via reaction of thiols and aryl halides using a palladium
2
4
[14]
ery and reusability being described for this catalytic system.
[12]
catalyst. The employment of unstable and costly thiols with very
unpleasant odors represents a dangerous and serious problem. Fur-
thermore, sulfur-containing compounds can behave as destroyers
of metal catalysts due to their powerful coordinative characteristics,
Hence, the design of a stable, efficient, inexpensive and heteroge-
neous copper catalyst that permits very proficient carbon–sulfur
bond creation reactions of a broad range of aryl halides is useful.
In continuing done efforts to expand green synthetic paths and
[
13]
[28–33]
frequently rendering catalytic reactions useless.
Also, some recently developed procedures involve costly ligands,
heterogeneous catalysis for organic reactions,
herein we re-
port the 4-amino-5-methyl-3-thio-1,2,4-triazole-functionalized poly-
styrene resin-supported Cu(II) (PS-tazo-Cu(II)) complex
[
14]
[15]
solvents and catalytic systems, long reaction times, metal pol-
lution of final products and inability to recycle the catalysts. These
reasons restrict the use of reactions on large scales. Hence, it is nec-
3
[16–18]
essary to discover new catalytic systems with cheap metals,
*
Correspondence to: Abdol R. Hajipour, Pharmaceutical Research Laboratory,
ligands and solvents and with capability for reuse, for the prepara-
tion of these very valuable and useful materials.
Department of Chemistry, Isfahan University of Technology, Isfahan 84156, IR
Iran. E-mail: haji@cc.iut.ac.ir
Recently, substantial developments have been reported in the
scope of heterogeneous catalysis for a wide range of organic
a Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan
University of Technology, Isfahan 84156, IR, Iran
[19–21]
reactions.
Generally, heterogeneous catalysts present lower
coordinating sites, higher surface area and facile functionalization
which account for the high catalytic activity of these catalysts.
b Department of Pharmacology, University of Wisconsin, Medical School, 1300
University Avenue, Madison, WI, 53706-1532, USA
[
22,23]
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

A. R. Hajipour and S. Jajarmi
In the FT-IR spectrum of PS-tazo-Cu(II) complex 3 (Fig. 1) can be
À1
seen an absorption band at 3434.6 cm , which is attributed to
À1
the N–H bond. Also the band at 1115.62cm corresponds to the
stretching vibrations of the C–N bonds. SEM (Fig. 2) was used to
characterize the morphologies of PS-tazo-Cu(II) 3. As can be seen,
the pure polystyrene bead has a flat and smooth surface, while
the anchored complex shows coarseness of the top layer. The
EDX spectrum (Fig. 3) clearly shows the presence of copper in the
synthesized complex. ICP analysis indicates that the amount of cop-
per loaded into the triazole-functionalized polystyrene is 0.46%
À1
(
0.72 mmol g ).
To determine the potency of the triazole-functionalized polysty-
rene resin-supported Cu(II) complex 3, it was used in the reaction
Scheme 1. Synthesis of heterogeneous catalyst PS-tazo-Cu(II) (3).
between iodobenzene and potassium thiocyanate in water at
1
35°C for 7 h (Table 1). First, we examined the effects of bases
[24]
and additives on this reaction. Among the studied bases, KOH
is the best and the corresponding product 6a is obtained in 95%
yield (Table 1, entry 2). Also, among the studied additives,
cetyltrimethylammonium bromide (CTAB) is the best (Table 1, en-
tries 2, 5 and 6). Then the effect of temperature was investigated
(
Scheme 1), as an inexpensive and efficient catalytic system for the
preparation of diaryl sulfides using potassium thiocyanate as the
sulfur source in water as solvent.
(
Table 1, entry 9). As is evident from Table 1, 135°C is the best tem-
perature. Finally, the amount of Cu(II) complex was also studied. A
.05 mmol loading of Cu(II) is found to be optimal, since a lower
Results and discussion
0
yield is obtained when the amount of complex is decreased
(Table 1, entry 8).
4
-Amino-5-methyl-3-thio-1,2,4-triazole (1) was prepared
[
31]
according to the procedure reported in a literature.
The
After we determined the optimized conditions, the PS-triazole-
Cu(II) complex 3 was used as a catalyst for the reaction of potassium
thiocyanate with aryl halides containing electron-donating or
electron-withdrawing substituents. The results obtained are sum-
marized in Table 2. On the whole, all the reactions give correspond-
ing products (Table 2, 6a–6 l) in good to excellent yields ranging
from 55 to 100%. Aryl iodides with electron-withdrawing substitu-
structure of the produced polystyrene-bound triazole (PS-tazo)
was characterized using elemental analysis (CHN). The
amount of nitrogen of PS-tazo 2 is obtained as 5.6%. Based
2
on this, the amount of triazole attached to the
À1
chloromethylated polystyrene is 1 mmol g
of the polymer.
This means that 79.4% of the whole chlorine content is
replaced by triazole. Then stirring of polymer-bound triazole
ents such as NO
sponding products in higher yields compared with those
containing electron-donating groups such as CH and OCH
Table 2, entries 6 and 7). Therefore we these reactions are affected
2
, Br and Cl (Table 2, entries 2–5) give the corre-
2
with a solution of CuCl
2
Á5H
2
O in dimethylformamide (DMF)
at room temperature for 6 h (Scheme 1) results in the prepa-
ration of PS-tazo-Cu(II) (3). The synthesized catalyst 3 was
characterized using Fourier transform infrared (FT-IR) spectros-
copy, scanning electron microscopy (SEM), energy dispersive
X-ray spectroscopy (EDX) and inductively coupled plasma
3
3
(
by electronic effects. In addition to aryl iodides, aryl bromides can
react with potassium thiocyanate with longer times (Table 2, entries
8–14). Also, aryl chlorides react under these conditions, although
(
ICP) analysis.
their reactivity is lower than that of aryl iodides and bromides
(Table 2, entries 15–18).
We propose a mechanism for thioetherification of aryl halides
with KSCN as shown in Scheme 2. At first, aryl halide connects to
the catalyst and chloride ions leave. In the next step, thiocyanate
ion replaces halide ion on the catalyst and an aryl thiocyanate is
produced as the first cycle product. Then this product goes into
the next cycle and C–S bond is broken in aryl thiocyanate. Second,
aryl halide adds to the catalyst and then the product of this cycle
(aryl thiocyanate) is obtained through an elimination step and the
catalyst enters the next cycle.
Moreover, we investigated the recovery and reusability of the
catalyst using the reaction of iodobenzene with potassium thiocya-
nate as a model system. After completion of this reaction, the cop-
per catalyst from the first run of the reaction was filtered and
washed several times with water and ethyl acetate. After drying un-
der vacuum for 6 h, we reused the recovered catalyst in the reaction
under the same conditions. As evident from Table 3, the recovered
catalyst can be employed successfully for five subsequent runs and
exhibits excellent reusability.
To determine the amount of leaching of the copper from the het-
erogeneous catalyst, after completion of the reaction the catalyst
was separated by simple filtration and the copper content of the
Figure 1. FT-IR spectrum of PS-tazo-Cu(II) complex.
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Cross-coupling of aryl halides with potassium thiocyanate
Figure 3. EDX spectrum of polymer-anchored PS-tazo-Cu(II).
filtrate was determined using ICP analysis. It is found that less than
0.15% of the whole amount of the initial copper species is lost into
the solution during the reaction. This degree of leaching is unim-
portant and is confirmed from the excellent reusability of this het-
erogeneous copper catalyst.
Conclusions
We successfully prepared an inexpensive and efficient
polystyrene-supported triazole copper(II) complex, which was
employed as a heterogeneous catalyst for the synthesis of
diaryl thioethers in water as solvent. The catalyst showed high
activity for this reaction within 7 h, and could be easily recov-
ered and reused five times without significant loss in its activ-
ity. The high catalytic efficiency, low cost and excellent
recyclability means that it is a preferable catalyst compared
with the large number of heterogeneous copper catalysts re-
ported to date.
Experimental
General
All chemicals used were of commercial reagent grade and were
used without further purification. Chloromethylated polystyrene
(4–5% Cl and 2% crosslinked with divinylbenzene) was a product
of Merck. The aryl halides and potassium thiocyanate were ob-
tained from Merck or Fluka.
Preparation of polymer-anchored PS-tazo-Cu(II) (3)
The triazole-functionalized polymer 2 was prepared according to
[
31]
the procedure reported in a literature. PS-tazo 2 (1g) was treated
with DMF (20 ml) for 30 min. Then CuCl Á5H O (0.2g) was added,
2
2
and the resulting mixture was stirred at room temperature for 6 h.
The resulting polymer, impregnated with the copper complex,
was filtered and washed with ethyl acetate and an ethanol–water
mixture and dried at 50°C for 6 h to afford PS-tazo-Cu(II) 3
(Scheme 1).
General procedure for synthesis of diaryl thioethers
A glass flask equipped with a magnetic stirrer was charged with
KOH (4.0mmol), potassium thiocyanate (1.0mmol), aryl halide
Figure 2. SEM images of chloromethylated polystyrene (A and C) and
PS-tazo-Cu(II) complex (B and D).
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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A. R. Hajipour and S. Jajarmi
Table 1. Optimization of conditions for reaction of aryl halides and po-
a
tassium thiocyanate
b
Entry Base
Additive Catalyst (mmol of Cu) Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
NaOH
KOH
CTAB
CTAB
CTAB
CTAB
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.04
0.05
0.05
0.05
0.06
7
7
7
7
7
7
7
7
7
5
8
7
90
95
80
85
75
83
72
75
70
72
95
95
Na
2
CO
CO
3
K
2
3
c
KOH PEG-400
d
KOH
KOH
KOH
KOH
KOH
KOH
KOH
TBAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
e
f
0
1
2
a
Reaction conditions: iodobenzene (2 mmol), KSCN (1 mmol), base
O (3 ml), additive (0.2 mmol), 135°C, aerobic conditions.
Isolated yield.
(
4 mmol), H
2
b
c
PEG-400: poly(ethylene glycol) 400.
d
TBAB: tetrabutylammonium bromide.
Reaction was done by CTAB (0.1 mmol).
e
f
Reaction was done in 120°C.
Table 2. Scope of reaction of aryl halides and potassium thiocyanate,
a
catalyzed by PS-tazo-Cu(II)
Scheme 2. Proposed mechanism for thioetherification of aryl halides with
KSCN.
b
Entry
X
Y
Time (h)
Product
Yield (%)
1
2
3
4
5
6
7
8
9
I
I
H
7
7
6a
6b
6c
95
100
100
100
100
90
4-NO
2
a
Table 3. Recyclability of catalyst under optimum reaction conditions
I
3-NO
4-Cl
2
7
b
Entry
Cycle
Yield (%)
I
7
6d
6e
6f
I
4-Br
7
1
2
3
4
5
1
2
3
4
5
95
95
93
90
89
I
4-CH
3
7
I
4-OCH
H
3
7
6 g
6a
6b
6 h
6i
88
Br
Br
Br
Br
Br
Br
1-Br
Cl
Cl
Cl
Cl
I
10
10
10
10
10
10
10
12
12
12
12
4
83
4-NO
4-COCH
2
85
10
11
12
13
14
15
16
17
18
19
20
3
80
a
Reaction conditions: iodobenzene (2 mmol), KSCN (1 mmol), KOH
O (3 ml),
4-CHO
4-CN
78
(
1
b
4 mmol), PS-tazo-Cu(II) (0.05 mmol of Cu), CTAB (0.2 mmol), H
35°C, aerobic conditions.
2
6j
88
4-OCH
Naphthalene
H
3
6f
80
Isolated yield.
6 k
6a
6b
6d
6 l
6a
6a
77
62
4-NO
4-Cl
2
69
66
(
2.0mmol), CTAB (0.2mmol), PS-tazo-Cu(II) (0.05 mmol of Cu) and
4-NH
H
2
55
c
3 ml of water. The mixture was heated under reflux at 135°C in
an oil bath for 7 h under aerobic conditions. The progress of
the reaction was monitored using TLC (n-hexane). After comple-
tion of the reaction, the copper catalyst was separated from the
mixture by simple filtration, washed with water and ethyl acetate
and reused in the next run. The organic layer was extracted
using saturated brine solution. The solvent was removed under
vacuum, and the product was purified using silica gel column
chromatography with ethyl acetate–methanol as eluent.
95
d
Br
H
7
90
a
Reaction conditions: aryl halide (2 mmol), KSCN (1 mmol), KOH
O (3 ml),
(4 mmol), PS-tazo-Cu(II) (0.05 mmol of Cu), CTAB (0.2 mmol), H
2
1
35°C, aerobic conditions.
b
Isolated yield.
c
Reaction of iodobenzene with thiophenol.
d
Reaction of bromobenzene with thiophenol.
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Cross-coupling of aryl halides with potassium thiocyanate
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