Silica acetate complex of N2O4: A highly efficient reagent for the selective conversion of thioethers to their corresponding sulfoxides

Article abstract of DOI:10.1081/SCC-100104421

Complexation of gaseous N₂O₄ with acylated silica gel affords a molecular addition compound, which is a highly efficient oxidizing agent for the conversion of thioethers to sulfoxides.

Full text of DOI:10.1081/SCC-100104421

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SILICA ACETATE COMPLEX OF N O : A HIGHLY
2
4
EFFICIENT REAGENT FOR THE SELECTIVE
CONVERSION OF THIOETHERS TO THEIR
CORRESPONDING SULFOXIDES
a
b
a
H. Firouzabadi , N. Iranpoor & R. Heydari
a
Chemistry Department , College of Sciences, Shiraz University , Shiraz, 71454, Iran
b
Chemistry Department , College of Sciences, Shiraz University , Shiraz, 71454, Iran
Published online: 09 Nov 2006.
To cite this article: H. Firouzabadi , N. Iranpoor & R. Heydari (2001) SILICA ACETATE COMPLEX OF N O : A HIGHLY
2
4
EFFICIENT REAGENT FOR THE SELECTIVE CONVERSION OF THIOETHERS TO THEIR CORRESPONDING SULFOXIDES, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:13, 2037-2041,
DOI: 10.1081/SCC-100104421
To link to this article: http://dx.doi.org/10.1081/SCC-100104421
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SYNTHETIC COMMUNICATIONS, 31(13), 2037–2041 (2001)
SILICA ACETATE COMPLEX OF N O :
2
4
A HIGHLY EFFICIENT REAGENT FOR
THE SELECTIVE CONVERSION
OF THIOETHERS TO THEIR
CORRESPONDING SULFOXIDES
H. Firouzabadi,*, N. Iranpoor,* andR. Hey da ri
{
Chemistry Department, College of Sciences,
Shiraz University, Shiraz 71454, Iran
ABSTRACT
Complexation of gaseous N O with acylated silica gel affords
4
2
a molecular addition compound, which is a highly efficient
oxidizing agent for the conversion of thioethers to sulfoxides.
The oxidation of thioethers is the most widely used route for the syn-
1
thesis of sulfoxides. Sulfone formation, which is the cause of the over-
oxidation of sulfoxides, is an undesired product in these reactions. In
order to inhibit the formation of this side product the transformation reac-
tion requires a gentle and a selective oxidation method. Therefore, develop-
ment of the selective method for this purpose is a useful practical
achievement.
*
Corresponding authors. Fax: (0711) 2220027.
E-mail: firouzabadi@chem.susc.ac.ir
{
2
037
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
2
038
FIROUZABADI, IRANPOOR, AND HEYDARI
In our laboratories, we have developed and reported efficient reagents
ꢁ
2
þ
for this purpose. We have found reported that NO ꢀ18-crown- 6ꢀH(NO )
3
2
which is a stable complex, performs this oxidation very efficiently at room
temperature without the formation of the corresponding sulfones.
Now we report that silica acetate can be prepared by the addition of
3
b
silica gel to a solution of ZnCl in acetic anhydride, which under reflux
2
affords the desired silica acetate. The resulting silica acetate is suspended
ꢂ
in dry CH Cl and N O gas was bubbled through the suspension at ꢁ10 C.
2
2
2
4
The white solid material, which is a solid source of N O gas, could be
2
4
stored in a refrigerator for months without loss of its oxidizing ability.
Now we report that this new reagent can be used for the oxidation of
thioethers to their corresponding sulfoxides without formation of the unde-
sired sulfones. The reactions are fast and proceed to completion in less than
30 min. in CH Cl at room temperature (Scheme 1 andTable ).
2 2
This reagent shows high selectivity for the oxidation of structurally
Scheme 1.
different thioethers (Scheme 2).
In conclusion, we have introduced a new oxidant for the efficient
Scheme 2.
sulfoxidation of thioethers under mild reaction conditions. This reagent
shows high selectivity for the oxidation of structurally different thioethers.
EXPERIMENTAL
Products were characterized by comparison of their physical and spec-
tral data with those of authentic samples. The authentic samples were either
4
purchased from Fluka or prepared by known procedures. IR spectra were

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SILICA ACETATE COMPLEX OF N O
2
2039
4
Table. Oxidation of Thioethers to Their Corresponding Sulfoxides
by Silica Acetate/N in CH Cl at Room Temperature
2
O
4
2
2
a
b
Isolated yield. Benzylic thioether linkage is labile and aryl alde-
hyde is also formed as the by-product.
recorded on a Perkin Elmer 781 spectrometer. NMR spectra were recorded
on a Bruker DPX 250. Mass spectra were recorded on a Shimadzu
GCMS-QP 1000EX. TLC accomplished the purity determination of the
substrates and reaction monitoring on Silica gel polygram SILG/UV 254
plates.
Preparation of Silica Acetate/N O Complex
2
4
a) In a round-bottomed flask (500 ml), ZnCl (2 g) was dissolved in
2
Ac O (50 ml) by shaking on a water bath, and then silica gel
2
(
25 g) was added. The mixture was refluxed for 3 h on the boiling
water bath. The resulting mixture was poured to the ice water
500 ml) and stirred vigorously to assist the hydrolysis of
(
unreacted acetic anhydride. After 30 min, the mixture was filtered
and washed with water and then with acetone and dried in the
air. The silica acetate (27 g) was obtained as a white powder.

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2
040
FIROUZABADI, IRANPOOR, AND HEYDARI
ꢀ
b) To a stirring cold suspension (À10 C) of silica acetate (27 g) in
5
CH Cl (150 ml) N O gas was bubbled through the suspension
2
2
2
4
for about 1 h. The solvent was evaporated under reduced press-
ure to give silica acetate/N O complex as a white powder
2
4
(
33.5 g).
Oxidation of Methyl Phenyl Thioether to its Corresponding
Sulfoxide with Silica Acetate/N O Complex. A Typical Procedure
2
4
To a vigorously stirred solution of methyl phenyl thioether (0.124,
mmol) in CH Cl (5 ml) at room temperature, silica acetate/N O complex
1.2 g) was added. The reaction was completed after 5 minutes. After column
1
(
2
2
2
4
chromatography on silica gel eluted with petroleum ether: acetone (6:4),
methyl phenyl sulfoxide as a yellow oily material was obtained in 0.136 g
ꢂ
6
97%, b.p. 0.3 100–104 C, lit. 102 C. m.p. 25–28 C, lit. 26–29 C).
ꢂ
ꢂ
6
ꢂ
(
Competitive Reaction Between Methyl Phenyl
andDibutyl Thioethers
To a solution of methyl phenyl thioether (0.124 g, 1 mmol) and dibutyl
thioether (0.146 g, 1 mmol) in CH Cl (5 ml), silica acetate/N O complex
2
2
2
4
(
1.2 g) was added. The resulting mixture was stirred vigorously at room
temperature for 15 min. The unreacted thioethers were separated from sulf-
oxides by column chromatography on a silica gel column eluted with pet-
roleum ether: acetone (9:1). The NMR spectrum of the sulfoxides mixture
indicates the formation of methyl phenyl and dibutyl sulfoxides in 84 and
ꢂ
16% (32.6 C).
ACKNOWLEDGMENT
We are grateful to Shiraz University Research Council for the partial
support of this work.
REFERENCES
1. a) Madesclaire, M. Tetrahedron 1986, 42, 5459, b) Mata, E.G.
Phosphoros, Sulfur, and Silicon 1996, 117, 231.

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SILICA ACETATE COMPLEX OF N O
2
2041
4
2
. Firouzabadi, H.; Seddighi, M. Synth. Commun. 1991, 21, 211.
Firouzabadi, H.; Mohammadpour-Baltork, I. Bull. Chem. Soc. Jpn.
992, 65, 1131. Firouzabadi, H.; Sharifi, A.; Karimi, B. Iran. J. Chem.
Chem. Eng. 1993, 12, 32. Firouzabadi, H.; Sardarian, A.R.;
1
&
Badparva, H. Bull. Chem. Soc. Jpn. 1996, 69, 685. Firouzabadi, H.;
Iranpoor, N.; Zolfigol, M.A. Synth. Commun. 1998, 28, 377.
Firouzabadi, H.; Iranpoor, N.; Zolfigol, M.A. Synth. Commun. 1998,
2
8, 1179 and the references cited therein.
. a) Richard, S.; Audet, P.; Savoie, R. J. Molecular Structure 1998, 178,
35, b) Firouzabadi, H.; Iranpoor, N.; Heydari, R. unpublished results.
. Vogel’s Textbook of Practical Organic Chemistry, 5 Ed., Longman &
Scientific Technical, 1991, pp. 791–792.
3
4
1
th
5
6
. Mallakpour, S.E. J. Chem. Ed. 1992, 69, 238.
. Fluka ‘‘Chemika-Biochemika’’, 1993/94.
Received in the UK June 20, 2000

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