Silica-supported bis (trimethylsilyl) chromate: Oxidation of thiols to their corresponding disulfides

Article abstract of DOI:10.1080/00397910601039267

An efficient and convenient method for the oxidation of thiols mediated by silica-supported bis (trimethylsilyl) chromate (BTSC) in acetonitrile is reported. Copyright Taylor & Francis Group, LLC.

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Silica‐Supported bis (Trimethylsilyl)
Chromate: Oxidation of Thiols to Their
Corresponding Disulfides
a
a
a
Majid M. Heravi , Fatemeh Derikvand , Hossein A. Oskooie , Rahim
a
b
Hekmat Shoar & Mahmood Tajbakhsh
a
Department of Chemistry , School of Sciences, Azzahra University , Vanak,
Tehran, Iran
b
Department of Chemistry , Mazandaran University , Babolsar, Iran
Published online: 06 Feb 2007.
To cite this article: Majid M. Heravi , Fatemeh Derikvand , Hossein A. Oskooie , Rahim Hekmat Shoar &
Mahmood Tajbakhsh (2007) Silica‐Supported bis (Trimethylsilyl) Chromate: Oxidation of Thiols to Their
Corresponding Disulfides, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:3, 513-517, DOI: 10.1080/00397910601039267
To link to this article: http://dx.doi.org/10.1080/00397910601039267
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Synthetic Communications , 37: 513–517, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601039267
Silica-Supported bis (Trimethylsilyl)
Chromate: Oxidation of Thiols to Their
Corresponding Disulfides
Majid M. Heravi, Fatemeh Derikvand, Hossein A. Oskooie,
and Rahim Hekmat Shoar
Department of Chemistry, School of Sciences, Azzahra University,
Vanak, Tehran, Iran
Mahmood Tajbakhsh
Department of Chemistry, Mazandaran University, Babolsar, Iran
Abstract: An efficient and convenient method for the oxidation of thiols mediated by
silica-supported bis (trimethylsilyl) chromate (BTSC) in acetonitrile is reported.
Keywords: BTSC, disulfides, oxidation, solid-supports, thiols
[
1,2]
Disulfides are useful reagents in organic synthesis.
They are also used in
and they are essential
moieties of biologically active compounds for peptide and protein stabili-
[3]
sulphenylation of enolates and other anions,
[
4]
zation. Because disulfides are relatively more stable to organic reactions
such as oxidation, alkylation, and acylation compared to the corresponding
free thiols, the thiol group can be protected as a disulfide. The desired thiol
can be generated from the disulfide either by reduction or by other sulfur–
2
2
[5]
sulfur bond cleavage reagents such as CN , OH , or hydrazines. Various
reagents for oxidative coupling of thiols to disulfides are described (e.g., per-
[
manganates, sodium perborate, ferric chloride, sodium chlorite,
6]
[7]
[8]
[9]
[
10]
[11]
[12–17]
hydrogen peroxide,
the difficulty of product handling and isolation, Some of these methods
halogens,
and others,
but they encounter
Received in the U.K. June 12, 2006
Address correspondence to Majid M. Heravi, Department of Chemistry, School of
Sciences, Azzahra University, Vanak, Tehran, Iran. E-mail: mmh1331@yahoo.com
5
13

5
14
M. M. Heravi et al.
Scheme 1.
suffer from disadvantages such as long reaction times, limited availability of
oxidant, toxicity of reagents, and difficulty of product handling and isolation.
However, there is still an interest in developing a clean, mild, and efficient
method to synthesize aliphatic, aromatic, and heteroaromatic disulfide.
We have recently used bis (trimethylsilyl) chromate (BTSC) as a versatile
[
18–26]
oxidizing agent.
reactions using solid supports,
for the oxidation of thiols to disulfides using bis(trimethylsilyl) chromate
In connection with our studies to implement organic
[27–32]
herein we report experimentation
(
BTSC) in acetonitrile.
The use of supported reagents,
[33–35]
has attracted interest because of
improved selectivity, reactivity, and associated ease of manipulation. In
[27–32]
view of ongoing research using solid supports in our laboratory,
we
used silica-supported BTSC as an efficient oxidizing agent to effect thiols-
to-disulfides conversions.
The present method (Scheme 1) is equally applicable for the oxidative
coupling of alkyl, aryl, and heterocyclic thiols. As expected, thiols with
electron-withdrawing groups took slightly longer time to complete the
reaction. Acetonitrile is the solvent of choice in this conversion for the
optimum yield. The results of attempted oxidation reactions of these thiols
are presented in Table 1.
The reactions promoted by silica-supported BTSC are usually carried out
under mild conditions with good yields and simple workup: ønly filtration is
required to remove the catalyst, and often evaporation of the filtrate
Table 1. Oxidation of thiols to disulfides using silica-supported BTSC
a
Entry
R
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
Ph-
2-NH -ph-
4-Me-ph-
15
12
12
10
15
40
9
98
98
94
95
93
90
95
92
90
2
2
Ph-CH -
2-naphtalyl-
2-1,3-benzodiazole-
1-Octyl-
HOOCCH2-
Cyclochexyl-
9
12
a
Products were identified from comparison of physical and spectro-
scopic properties with authentic compounds.

Oxidation of Thiols
515
Table 2. Comparison of silica-supported BTSC with some of the other reagents for
oxidation of thiophenol and sulfides
Entry
Reagent
Time (min)
Yield
References
1
2
3
4
5
Bu
PCC
3
SnOMe/FeCl
3
120
114
10
99
97
79
93
98
[13]
[14]
[15]
[16]
—
(NH )S O
2 8
4
Caro’s acid/SiO2
Silica-supported BTSC
270
15
afforded pure products. The procedure involves simple stirring of thiols and
silica-supported BTSC in acetonitrile.
In conclusion, we have shown that silica-supported BTSC is an efficient,
rapid, mild, and inexpensive reagent for the oxidation of aliphatic, aromatic,
and heteroaromatic thiols to the corresponding disulfides. To show the advan-
tages and drawbacks of this reagent over some other oxidants, we have
compared some of our results with those reported in the literature with
respect to reaction times and yields in Table 2.
EXPERIMENTAL
General Procedure for Oxidation of Thiols with Silica-Supported
BTSC
A solution of thiol (1 mmol) in MeCN (5 mL) was treated with silica-
supported BTSC (2 mmol), and the mixture was stirred at room temperature.
The progress of the reaction was monitored by gas chromatography or thin-
layer chromatography. The reaction mixture was filtered and washed with
MeCN (5 mL). The filtrate was evaporated to give the corresponding
disulfide in almost pure form. If necessary, the product was purified by
column chromatography (eluent:hexane/CH Cl ).
2
2
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