Polystyrene and silica gel-supported, AlCl3-catalyzed preparation of diaryl sulfoxides from arenes and thionyl chloride

Article abstract of DOI:10.1080/10426500903496721

A simple, chemoselective, and efficient method has been developed for direct conversion of arenes to symmetrical diaryl sulfoxides using thionyl chloride in the presence of a catalytic amount of cross-linked polystyrene-supported aluminium chloride (Ps-AlCl₃) and silica gel-supported aluminium chloride (SiO₂-AlCl₃). These solid acid catalysts are stable and can be easily recovered and reused without appreciable change in their efficiency. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500903496721

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Phosphorus, Sulfur, and Silicon and the
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Polystyrene and Silica Gel–Supported,
AlCl3-Catalyzed Preparation of Diaryl
Sulfoxides from Arenes and Thionyl
Chloride
Kaveh Parvanak Boroujeni a
a Department of Chemistry , College of Science, Shahrekord
University , Shahrekord, Iran
Published online: 24 Sep 2010.
To cite this article: Kaveh Parvanak Boroujeni (2010) Polystyrene and Silica Gel–Supported, AlCl3-
Catalyzed Preparation of Diaryl Sulfoxides from Arenes and Thionyl Chloride, Phosphorus, Sulfur, and
Silicon and the Related Elements, 185:10, 2085-2091, DOI: 10.1080/10426500903496721
To link to this article: http://dx.doi.org/10.1080/10426500903496721
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Phosphorus, Sulfur, and Silicon, 185:2085–2091, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903496721
POLYSTYRENE AND SILICA GEL–SUPPORTED,
AlCl3-CATALYZED PREPARATION OF DIARYL
SULFOXIDES FROM ARENES AND THIONYL CHLORIDE
Kaveh Parvanak Boroujeni
Department of Chemistry, College of Science, Shahrekord University,
Shahrekord, Iran
A simple, chemoselective, and efficient method has been developed for direct conversion of
arenes to symmetrical diaryl sulfoxides using thionyl chloride in the presence of a catalytic
amount of cross-linked polystyrene-supported aluminium chloride (Ps-AlCl3) and silica
gel–supported aluminium chloride (SiO2-AlCl3). These solid acid catalysts are stable and
can be easily recovered and reused without appreciable change in their efficiency.
Keywords Arene; polystyrene; silica gel; sulfinylation; sulfoxide
INTRODUCTION
Sulfoxides are highly important intermediates in organic synthesis1 and in the field
of drugs and pharmaceuticals.2,3 They often play an important role as therapeutic agents
such as antihypertensive,4 anthelmintic,5 and cardiotonic agents.6 Optically active sulfox-
ides have received much attention as important chiral auxiliaries in asymmetric synthesis7
and in carbon–carbon bond forming reactions.8 In addition, syntheses of diaryl sulfoxides
provide a convenient route to triarylsulfonium salts, which are used as photoactive cationic
initiators9 and for the photogeneration of protonic acids in the lithographic resist field.10
Usually, sulfoxides are prepared by indirect methods, which involve oxidation of sul-
fides,11,12 reduction of sulfones,13 and the reaction of organometallic reagents with sulfinic
acid esters, mixed anhydrides, or sulfines.14 A literature survey shows that less attention
has been paid to the use of direct methods for the preparation of sulfoxides. Addition of
aryl Grignard reagents to thionyl chloride,14 the Friedel–Crafts sulfinylation of arenes with
benzenesulfinyl chloride using a Lewis acid catalyst such as AlCl3,15 the reaction of arenes
with FSO3H-SbF5 (Magic acid)/SO2,16 and the reaction of arenes with thionyl chloride in
the presence of a catalyst such as trifluoromethane sulfonic acid,17 scandium triflate,18 ionic
liquid,19 heteropoly acid,20 and sulfated zirconia21 are some of the reported direct methods
of preparation of diaryl sulfoxides. Except for a few, many of the above methods suffer from
Received 24 September 2009; accepted 18 November 2009.
Dedicated to the memory of Professor Ahmad Banihashemi.
The author thanks the Research Council of Shahrekord University for partial support of this work.
Address correspondence to Kaveh Parvanak Boroujeni, Department of Chemistry, College of Science,
Shahrekord University, Shahrekord 115, Iran. E-mail: parvanak-ka@sci.sku.ac.ir
2085

2086
K. P. BOROUJENI
the drawbacks such as disturbance to other functional groups, less selectivity, the formation
of a mixture of products containing sulfonium salts and chlorinated byproducts along with
desired sulfoxide, environmental pollution, tedious work-up, a need for stoichiometric or
excess amounts of catalyst in some reactions, and the use of moisture-sensitive, expen-
sive, hazardous, difficult to handle, or unreusable catalysts. In view of these, the search
for finding a cost effective, mild, and simple chemoselective protocol for the synthesis of
sulfoxides is still relevant.
In recent years, the use of heterogeneous catalysts has received considerable attention
in different areas of organic synthesis. The high selectivity, nontoxicity, noncorrosiveness,
easy separation from the reaction media, recyclability, moisture and air tolerance, and easier
handling make the use of heterogeneous catalysts attractive alternatives to conventional
homogeneous catalysts.22,23 Although the catalytic applications of heterogeneous catalysts
for organic synthesis have been well established, relatively few examples are reported on
the use of polymer-supported Lewis acid catalysts.24
Over the last several years, Ps-AlCl3 and SiO2-AlCl3 have been reported to catalyze
Friedel–Crafts acylation of aromatic compounds.25,26 In a previous study, we also reported
the use of Ps-AlCl3 and SiO2-AlCl3 as remarkably efficient heterogeneous catalysts for
the Friedel–Crafts sulfonylation of arenes.27 Along this line, we report in this article that
Ps-AlCl3 and SiO2-AlCl3 are also highly efficient and chemoselective catalysts for the
electrophilic sulfinylation of arenes with thionyl chloride under mild reaction conditions
(Scheme 1).
O
S
Cat. / SOCl2
CH2Cl2 / r.t.
R
R
2
R
Cat.:
Ps-AlCl3 or SiO2-AlCl3
Scheme 1
RESULTS AND DISCUSSION
Ps-AlCl3 was prepared by the addition of AlCl3 to polystyrene (8% divinylbenzene)
in carbon disulfide under reflux conditions. SiO2-AlCl3 was prepared by treating silica gel
with AlCl3 in refluxing carbon tetrachloride. Sulfinylation of different kinds of arenes with
thionyl chloride in the presence of these catalysts was carried out at room temperature in
CH2Cl2, which proved to be the solvent of choice among other organic solvents (Table I).
The optimum molar ratio of Ps-AlCl3 to arene was 0.15:2 and for SiO2-AlCl3 was 0.1:2.
It was observed that both activated and weakly deactivated arenes gave the corresponding
sulfoxides in high to excellent yields (Table I, entries 1–12). It is worth noting that acid-
sensitive substrate pyridine was converted into the corresponding sulfoxide in excellent
yield (entry 13). However, highly deactivated arenes failed to give sulfoxide under the
same conditions (entries 14 and 15). The methodology showed the excellent positional
selectivity, as the para substituted product was formed exclusively. It is probable that
mild catalytic activity and steric crowding of the supported catalysts influence higher para
selectivities observed in the sulfinylation reactions. Side product formation was not observed
in the reactions we have studied. Ps-AlCl3 and SiO2-AlCl3 are stable under the reaction

PREPARATION OF DIARYL SULFOXIDES
2087
a
Table I Sulfinylation of arenes using SOCl2 catalyzed by Ps-AlCl3 and SiO2-AlCl3
Entry
1
Arene
Product
Time (h)
Yield (%)b
1.51
1.42
9011,28
9111,28
2
3
4
5
6
7
1.41
1.32
9316
9316
1.31
1.22
9220
9320
11
0.82
9318
9218
1.21
1.22
9118
9118
1.21
1.12
9316
9216
1.21
1.22
9216
9216
8
9
2.51
2.32
8718,29
8918,29
2.21
2.12
9018
9018
(Continued on next page)

2088
K. P. BOROUJENI
Table I Sulfinylation of arenes using SOCl2 catalyzed by Ps-AlCl3 and SiO2-AlCl3a (Continued)
Entry
10
Arene
Product
Time (h)
Yield (%)b
1.61
1.52
9118
9218
11
12
13
31
9030
9230
2.92
31
32
8816
9016
1.41
1.22
9231
9231
14
15
No reaction
No reaction
101
102
–
–
101
102
–
–
aThe molar ratio of the arene: SOCl2:Ps-AlCl31 is 2:1.2:0.15 and for SiO2-AlCl32 is 2:1.2:0.1.
bYields refer to pure isolated products, and all sulfoxides prepared are known compounds and were characterized
by comparison of their physical and spectral data with those of the authentic samples.
conditions, and there is no leaching of acid moieties during the reactions. The results show
that the order of sulfinylation activity of these catalysts is SiO2-AlCl3 > Ps-AlCl3.
When Ps-AlCl3 was used as catalyst for sulfinylation, no band corresponding to S O
stretching in the IR spectrum of Ps-AlCl3 was observed after the sulfinylation reaction
in either the presence or absence of substrate, indicating that polystyrene itself does not
undergo sulfinylation under the experimental conditions used.
To evaluate the selectivity of this method, we investigated competitive reactions for
sulfinylation of a variety of arenes using SOCl2 in the presence of Ps-AlCl3, SiO2-AlCl3,
and AlCl3. As shown in Table II, Ps-AlCl3 and SiO2-AlCl3 are able to discriminate arenes
containing electron-donating and electron-withdrawing groups from each other, a trans-
formation that is difficult to accomplish via conventional methods (Table II, entries 1–3).
Benzene was selectively converted to the sulfoxide in the presence of naphthalene (entry
4). From the results, it is clear that Ps-AlCl3 and SiO2-AlCl3 are superior to AlCl3 from the
view of higher chemoselectivity and efficiency in sulfinylation reactions. We also observed
that the AlCl3-catalyzed reaction produces the corresponding sulfonium salt as a byproduct

PREPARATION OF DIARYL SULFOXIDES
2089
Table II Competitive sulfoxide formation reactions using SOCl2 in the presence of Ps-AlCl3, SiO2-AlCl3, and
a,b
AlCl3
Entry
1
Sub. 1
Sub. 2
Prod. 1 (Yield)c
Prod. 2 (Yield (%))c
Time (h)
1.5
2
3
4
1.7
1.5
1.6
aThe molar ratio of Subs. 1:Subs. 2:SOCl2 is 2:2:1.1.
bAll reactions were carried out in CH2Cl2 at room temperature in the presence of Ps-AlCl3 (0.15 mmol),1
SiO2-AlCl3 (0.1 mmol),2 and AlCl3 (0.32 mmol).3
cGC yield.
in addition to the sulfoxide.14 Moreover, AlCl3 might be required for use in reagent quanti-
ties due to its complexation of product molecules. The higher chemoselectivity of Ps-AlCl3
and SiO2-AlCl3 over AlCl3 may be attributed to the mild catalytic activity of these solid
catalysts. To the best of our knowledge, these chemoselectivities are new and have not been
reported in the literature.
A comparison of the efficiency of Ps-AlCl3 and SiO2-AlCl3 catalysts with some of
those reported in the literature is given in Table III. As is shown in Table III, in addition
to having the general advantages attributed to the solid supported catalysts, Ps-AlCl3 and
SiO2-AlCl3 have a good efficiency compared to other recently reported catalysts.
In conclusion, we have developed the use of Ps-AlCl3 and SiO2-AlCl3 as inexpensive,
easy to handle, noncorrosive, stable (as bench top catalysts), reusable (at least five times
with negligible loss in their catalytic activity), and environmentally benign catalysts for
the synthesis of diaryl sulfoxides from arenes using SOCl2. High chemoselectivity, mild
reaction conditions, easy workup, short reaction times, and high to excellent yields are
other obvious advantages of the present method.

2090
K. P. BOROUJENI
Table III Comparison of some of the results obtained using Ps-AlCl3 and SiO2-AlCl3 with some other catalysts
used for direct sulfinylation of arenes with SOCl2
Arene
Catalyst
TfOH
Solvent
Temp. (◦C)
Time (h)
Yield (%)
Anisole
Neat
CH2Cl2
Neat
CH2Cl2
CH2Cl2
Neat
CH2Cl2
CH2Cl2
Neat
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
2
1.5
2.5
1.2
1.3
5 min
1.4
1.5
1.5
1.3
1.4
9517
9018
9420
93
92
8519
91
90
9021
93
Sc(OTf)3
a
H3PW12O40
SiO2-AlCl3
Ps-AlCl3
[Bmim]Cl.AlCl3
SiO2-AlCl3
Ps-AlCl3
Sulfated zirconia
SiO2-AlCl3
Ps-AlCl3
b
Benzene
Toluene
CH2Cl2
CH2Cl2
93
aTungstophosphoric acid (heteropoly acid).
b1-Butyl-3-methylimidazolium chloroaluminate (ionic liquid).
EXPERIMENTAL
Chemicals were either prepared in our laboratory or were purchased from Merck
and Fluka. Polystyrene (8% divinylbenzene, prepared via suspension polymerization,
polyvinylpyrrolidone 90 K as suspension agent, grain size range: 0.25–0.6 mm) was ob-
tained from Iran Polymer and Petrochemical Institute. Gas chromatography was recorded
on a Shimadzu GC 14-A. IR spectra were run on a Shimadzu model 8300 FT-IR spectropho-
1
tometer. H NMR spectra were recorded on a Bruker DPX-300 (300 MHz) spectrometer
using CDCl3 as solvent and TMS as the internal standard. Capacities of the catalysts were
determined by gravimetric method and atomic absorption technique using a Philips atomic
absorption instrument. Melting points were determined on a Fisher-Jones melting-point ap-
paratus and are uncorrected. Reaction monitoring and purity determination of the products
were accomplished by GLC or TLC on silica-gel polygram SILG/UV254 plates.
Preparation of Ps-AlCl3 and SiO2-AlCl3
These catalysts were prepared as reported in the literature.27 The capacities of Ps-
AlCl3 and SiO2-AlCl3 obtained by gravimetric method and checked by atomic absorption
technique were 0.4 and 1.3 mmol AlCl3 per gram, respectively.
Typical Procedure for Sulfinylation of Anisole with SOCl2
To a solution of anisole (2 mmol) and Ps-AlCl3 (0.15 mmol) or SiO2-AlCl3 (0.1
mmol) in CH2Cl2 (10 mL), SOCl2 (1.2 mmol) was added dropwise, and the resulting
mixture was stirred at ambient temperature under N2 atmosphere. Progress of the reaction
was monitored by TLC and GC. After completion of the reaction, the catalyst was filtered off
and washed with CH2Cl2 (2 × 10 mL). The filtrate was then treated with saturated sodium
bicarbonate (15 mL), extracted with CH2Cl2 (2 × 10 mL), and dried over anhydrous
Na2SO4. Evaporation of the solvent on a rotary evaporator under reduced pressure gave di-
(4-methoxyphenyl) sulfoxide.20 Whenever required, the products were purified by column

PREPARATION OF DIARYL SULFOXIDES
2091
chromatography so as to afford the pure diaryl sulfoxide. The spent catalyst from different
experiments was washed with ether and used again without further drying.
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