Iodic acid (HIO3) in combination with tetraethylammonium bromide as a catalyst for selective and accelerated sulfoxidation

Article abstract of DOI:10.1080/00397910500290540

The article describes the use of iodic acid in combination with catalytic amounts of tetraethylammonium bromide (TEAB) as a mild and alternative reagent system for oxidation of sulfides to sulfoxides. The salient features of the developed system are room-

Full text of DOI:10.1080/00397910500290540

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Iodic Acid (HIO ) in
3
Combination with
Tetraethylammonium Bromide
as a Catalyst for Selective and
Accelerated Sulfoxidation
a
a
Paresh D. Salgaonkar , Vidyanand G. Shukla, & K.
a
G. Akamanchi
a
Department of Pharmaceutical Sciences and
Technology , UICT , Matunga, Mumbai, India
Published online: 22 Aug 2006.
To cite this article: Paresh D. Salgaonkar , Vidyanand G. Shukla, & K. G. Akamanchi
(
2005) Iodic Acid (HIO ) in Combination with Tetraethylammonium Bromide as a
3
Catalyst for Selective and Accelerated Sulfoxidation, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 35:21,
2805-2810
To link to this article: http://dx.doi.org/10.1080/00397910500290540
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Synthetic Communications , 35: 2805–2810, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500290540
Iodic Acid (HIO ) in Combination with
3
Tetraethylammonium Bromide as a Catalyst
for Selective and Accelerated Sulfoxidation
Paresh D. Salgaonkar, Vidyanand G. Shukla, and
K. G. Akamanchi
Department of Pharmaceutical Sciences and Technology, UICT,
Matunga, Mumbai, India
Abstract: The article describes the use of iodic acid in combination with catalytic
amounts of tetraethylammonium bromide (TEAB) as a mild and alternative reagent
system for oxidation of sulfides to sulfoxides. The salient features of the developed
system are room-temperature reactions, short reaction times, and compatibility with
a wide range of functional groups.
Keywords: Iodic acid, sulfides, sulfoxides, tetraethylammonium bromide (TEAB)
INTRODUCTION
The oxidation of sulfides to sulfoxides is one of the most important transforma-
tions in synthetic organic chemistry because the resultant sulfoxides find
applications in synthesis of drugs, drug metabolites, and sulfur-substituted
[1]
natural products. It is easier to achieve the oxidation of sulfides to
sulphones; however, the selective oxidation to sulfoxides requires careful
control of the reaction conditions to avoid overoxidation. Selective
oxidation of sulfides to sulfoxides with many hypervalent iodine-containing
[
2,3]
reagent systems is well reported.
selective oxidation of sulfides to sulfoxides. However, the iodic acid
Use of iodic acid is also known for
[
4]
Received in India May 26, 2005
Address correspondence to K. G. Akamanchi, Department of Pharmaceutical
Sciences and Technology, UICT, Matunga, Mumbai 400 019, India. Fax: 91-22-
2
4145614; E-mail: kgap@rediffmail.com
2
805

2806
P. D. Salgaonkar V. G. Shukla, and K. G. Akamanchi
method has few drawbacks; mainly, the reactions require heating in a steam
bath, as a result of which the different functional groups such as esters and
cyanide become vulnerable in the reaction condition employed. This
reaction is also not applicable for sulfoxidation of unsaturated sulfides.
RESULTS AND DISCUSSION
The literature method using iodic acid at room temperature was found to be
sluggish and took 8 h to complete. However, the same reaction carried out
in the presence of ꢀ5 mol% TEAB as catalyst at room temperature was
complete within 15 min. The reaction was also carried out in different
solvents such as DMSO, acetone–water, and chloroform–water, and all
were found to be equally effective. Upon addition of excess oxidizing
agent, no overoxidation to sulfones was observed even after 24 h.
A variety of sulfides were subjected to oxidation as illustrated in Table 1.
The developed method is highly chemoselective and compatible with a
wide variety of functional groups such as nitrile (entry 7), ester (entry 8),
acid (entry 9), and alcohol (entry 10). The reactions were comparatively
slow with p-chlorophenyl sulfides (entries 4 and 6) and with less nucleophilic
sulfides (entries 7–9). In the case of sterically hindered sulfides (entry 11), a
long reaction time was needed. In a mixed reaction of methyl phenyl sulfide
with 1-undecene (entry 12), selective quantitative oxidation of sulfide to
sulfoxide was observed and 1-undecene was recovered unreacted. To
further explore the selectivity of the reaction, allyl phenyl sulfide was used
to give the corresponding sulfoxide in 86% isolated yield within 1.5 h (entry 1,
Table 2). In the absence of TEAB at room temperature, a complex mixture
was obtained (entries 2 and 3). Further, the reaction was also performed
with other allyl sulfides (entries 4 and 5), and the corresponding sulfoxides
were obtained in 85 and 87% yield respectively after column chromatography.
In conclusion, we have demonstrated the use of commercially available
iodic acid in combination with catalytic amounts of TEAB, is a mild and
efficient method for selective sulfoxidation.
EXPERIMENTAL
1
All H NMR spectra were recorded on JEOL, JNM-MY 60 FT, 60 MHz.
Chemical shifts are expressed in d units relative to the tetramethylsilane
(TMS) signal as internal reference in CDCl . FTIR (Perkin-Elmer Spectrum
RX1) spectra were recorded in CHCl or as KBr pellets. Mass spectra were
3
3
recorded on Finnigan Mat 1020B, by EI (70 eV) ionisation. All the solvents
were purchased from commercial sources and used without further
purification.

Iodic Acid for Sulfoxidation
2807
using TEAB (cat.) in acetone : H
Table 1. Oxidation of sulfides with HIO
a
3
2
O
[
(10:1) v/v]
Yield
d
(%)
b,c
Entry
1
Sulfoxide
Time
25 min
91
e
2
3
4
15 min
15 min
2 h
93
93
e
89
5
6
30 min
92
e
2.5 h
95
7
8
3.2 h
94
e
92
4 h
(
continued)

2808
P. D. Salgaonkar V. G. Shukla, and K. G. Akamanchi
Table 1. Continued
Yield
d
(%)
b,c
Entry
Sulfoxide
Time
7.3 h
e
9
91
93
1
0
1
20 min
26 h
1
91
93
12
15 min
a
Reactions run at room temperature using 1.1 equiv. of HIO and catalytic amounts
3
of TEAB in acetone : H
b
2
O [(10 : 1) v/v].
Sulfides commercially available were used as such without further purification.
[
5]
Remaining sulfides were prepared using standard available literature procedures.
c
All the sulfides and sulfoxides were confirmed by their physical and spectral pro-
[
3b]
perties (IR, NMR, and mass spectroscopy).
d
Yields indicate isolated yields after column chromatography.
Reactions were repeated on gram scale and gave comparable results with regard to
time and yield.
e
Typical Experimental Procedure
Water (1 ml) and TEAB (21 mg, 0.10 mmol) were added to a stirred solution
of iodic acid (0.39 g, 2.22 mmol) in acetone (10 ml). The resultant solution
was stirred at room temperature for 5 min followed by addition of methyl
phenyl sulfide (0.25 g, 2.02 mmol). The mixture was stirred at room tempera-
ture for 15 min, diluted with chloroform, and washed successively with 10%
sodium bisulfite solution, 10% sodium bicarbonate, water, and brine. The
organic layer was dried over sodium sulfate and concentrated to give a
residue, which was purified on silica gel by EtOAc–hexane (1 : 1) to give

Iodic Acid for Sulfoxidation
Table 2. Chemoselectivity studies using allyl sulfides
2809
TEAB
(mol%)
Yield
a
(%)
Entry
R
Time/temp
1.5 h/rt
1.5 h/rt
1.5 h/Steam bath
1.5 h/rt
1
2
3
4
5
H
H
5
—
—
5
86
Mixt
b
b
H
CH
Mixt
3
85
87
OCH
3
5
1.5 h/rt
a
Yields indicate isolated yields after column chromatography.
No chemoselectivity was observed and yield not determined.
b
2
methyl phenyl sulfoxide (0.26 g, 93%). IR (CHCl , cm ): n 3013, 1041, 749.
1
3
1
H NMR (CDCl ): d 2.73 (s, 3 H), 7.45–7.75 (m, 5 H).
3
ACKNOWLEDGMENT
The authors thank CSIR, New Delhi, India, for financial support.
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1
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3
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5
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2810
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(
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