Caro's acid supported on silica gel. IV. Facile synthesis of sulfones by the oxidation of various sulfides in aprotic solvent

Article abstract of DOI:10.1081/SCC-120002692

Oxidation of sulfides with Caro's acid supported on silica gel in acetonitrile gave sulfones in high to excellent yields under mild condition.

Full text of DOI:10.1081/SCC-120002692

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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CARO's ACID SUPPORTED ON SILICA GEL. IV. FACILE
SYNTHESIS OF SULFONES BY THE OXIDATION OF
VARIOUS SULFIDES IN APROTIC SOLVENT
Moslem M. Lakouraj , B. Movassagh & K. Ghodrati
To cite this article: Moslem M. Lakouraj , B. Movassagh & K. Ghodrati (2002) CARO's ACID
SUPPORTED ON SILICA GEL. IV. FACILE SYNTHESIS OF SULFONES BY THE OXIDATION OF
VARIOUS SULFIDES IN APROTIC SOLVENT, Synthetic Communications, 32:6, 847-850, DOI:
10.1081/SCC-120002692
To link to this article: http://dx.doi.org/10.1081/SCC-120002692
Published online: 16 Aug 2006.
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SYNTHETIC COMMUNICATIONS, 32(6), 847–850 (2002)
CARO’S ACID SUPPORTED ON
SILICA GEL. IV. FACILE SYNTHESIS
OF SULFONES BY THE OXIDATION
OF VARIOUS SULFIDES IN
APROTIC SOLVENT
Moslem M. Lakouraj,1, B. Movassagh,2, and
K. Ghodrati
*
*
1Institute of Chemistry, Mazandran University,
Babolsar 47415, Iran
2Department of Chemistry, Razi University,
Kermanshah 67149, Iran
ABSTRACT
Oxidation of sulfides with Caro’s acid supported on silica gel
in acetonitrile gave sulfones in high to excellent yields under
mild condition.
Sulfones are important intermediates in organic synthesis,2 which are
most generally prepared either by oxidation of corresponding sulfides3 or by
a displacement reaction using sodium sulfonates as a nucleophile.4
A
number of former-type methods have been developed.3,5 However, most
of these products work well for simple sulfides, or suffer from laborious
preparation of oxidizing agent, the use of potentially explosive oxidants,
*Corresponding authors. E-mail: Lakouraj@umcc.ac.ir
847
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

848
LAKOURAJ, MOVASSAGH, AND GHODRATI
employment of heavy metal based reagents, requirement of aqueous media,
or low yields, which make them synthetically unattractive.
In connection with our studies on oxidation reactions carried out with
Caro’s acid supported on silica gel,1 we present here a simple, mild and
efficient synthesis of sulfones by using this heterogeneous oxidizing agent.
O
Caro’s acid/SiO
2
1
2
1
2
R S R
R —S—R
acetonitrile, 40oC
O
81–99%
Table 1 summarizes the results obtained for a variety of sulfides which
was treated with Caro’s acid/SiO2 in acetonitrile at 40ꢀC. As evident, the use
of atleast three equivalents of the oxidant is necessary to obtain sulfone as a
sole product. Practically, using a lower amount of the oxidant produces a
mixture of sulfoxide and sulfone, and attempts to drive the product forma-
tion exclusively toward sulfoxide are unsuccessful. A sulfoxide/sulfone
selectivity of 65 : 35 is obtained in oxidation of p-chlorophenyl benzyl sulfide
Table 1. Oxidation of Sulfides to Sulfones with Caro’s Acid/SiO2 in CH3CNa
Mol Ratio
Oxid./Sub.
Reaction
Time (h)
Yieldb
(%)
Entry
R1
PhCH2
PhCH2
R2
a
b
c
d
e
f
g
h
i
Ph
3
3
3
3
3
3
3
3
3
3
5
5
97
96
91
98
94
92
91
84
87
81
99
4-MeC6H4
4-ClC6H4
Ph
4-MeC6H4
CH3
CH3
CH3(CH2)3
CH3(CH2)5
CH3(CH2)3
4-MeC6H4
5.5
5.5
6.5
6.5
4.5
5
4.5
6.5
5.5
9
PhCH2
4-NO2C6H4
4-NO2C6H4
Ph
4-MeC6H4
CH3(CH2)3
4-ClC6H4
4-MeC6H4
2,4-(NO2)2C6H3
j
k
aReaction carried out at reflux condition.
bYields refer to the pure and isolated product.

CARO’S ACID SUPPORTED ON SILICA GEL. IV
849
using one molar ratio of oxidant. The method described here is easy to carry
out and does not require any aqueous work-up. Yields are high to excellent,
and work-up is exceedingly simple only involving filtration and evaporation.
EXPERIMENTAL
Sulfides were either prepared in our laboratory6 or purchased from
Fluka and Merck companies. All products were characterized by compar-
ison of their spectral and physical data with those of known samples. IR
1
spectra were obtained using a shimadzu 470 instrument. H NMR spectra
were recorded on JEOL JNM-PMX 60 MHz or Bruker 200 MHz NMR
spectrometer.
Preparation of Silica gel Supported Caro’s Acid
To an ice cooled 98% sulfuric acid (4.7 g) is added in small portions
potassium persulfate (4.5 g) with stirring; to this is added crushed ice (13 g)
and the temperature is kept below 15ꢀC. Silica gel (5 g, Kieselgel 60G,
70–230 mm) is then added in portions to the mixture and stirred for 4 h in
ice-water bath. The mixture is filtered under suction and dried in a desicca-
tor to give a white free flowing powder.
Preparation of Benzyl Phenyl Sulfone; As a Typical Procedure
Caro’s acid-silica gel (1.8 g, Caro’s acid content 3 mmol),1 is slowly
added to a solution of benzyl phenyl sulfide (200 mg, 1 mmol) in acetonitrile
(10 ml). The resulting mixture was stirred magnetically for 5 h at 40ꢀC. The
progress of reaction is monitored by T.L.C. (eluent: n-hexane/ether; 1 : 1).
On completion of the reaction, the mixture is filtered. Evaporation of the
solvent gave the crude product which was recrystallized from ethanol-water
to afford the pure benzyl phenyl sulfone (225 mg, 97%); m.p.144–145.5ꢀC
(lit.7 146–146.5).
ACKNOWLEDGMENTS
The authors thank Dr. J. Ghasemi for helpin analytical determination
of Caro’s acid and are grateful to the Razi University Research Council for
the financial support of this work.

850
LAKOURAJ, MOVASSAGH, AND GHODRATI
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Received in Japan December 18, 2000