γ-PCC and γ-PCC-SiO2 as efficient reagents for oxidation of thiols to disulfides

Article abstract of DOI:10.1081/SCC-200032406

Oxidative coupling of thiols to the corresponding symmetrical disulfides was performed in the presence of γ-picolinium chlorochromate and its silica gel supported. The reactivity of silica gel supported γ-picolinium chlorochromate for thiophenol derivativ

Full text of DOI:10.1081/SCC-200032406

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γ‐PCC and γ‐PCC‐SiO2
as Efficient Reagents for
Oxidation of Thiols to
Disulfides
Mohammad Mehdi Khodaei a , Peyman Salehi b ,
Maryam Goodarzi a & Ateesa Yazdanipour a
a Department of Chemistry, Faculty of Science ,
Razi University , Kermanshah, 67149, Iran
b Department of Phytochemistry, Medicinal Plants
Research Institute , Shahid Beheshti University ,
Tehran, Iran
Published online: 19 Apr 2010.
To cite this article: Mohammad Mehdi Khodaei , Peyman Salehi , Maryam Goodarzi
& Ateesa Yazdanipour (2004) γ‐PCC and γ‐PCC‐SiO2 as Efficient Reagents for
Oxidation of Thiols to Disulfides, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 34:20, 3661-3666,
DOI: 10.1081/SCC-200032406
To link to this article: http://dx.doi.org/10.1081/SCC-200032406
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 20, pp. 3661–3666, 2004
g-PCC and g-PCC-SiO2 as Efficient
Reagents for Oxidation of Thiols
to Disulfides
2
Mohammad Mehdi Khodaei,1, Peyman Salehi,
*
Maryam Goodarzi,1 and Ateesa Yazdanipour1
1Department of Chemistry, Faculty of Science, Razi University,
Kermanshah, Iran
2Department of Phytochemistry, Medicinal Plants Research Institute,
Shahid Beheshti University, Tehran, Iran
ABSTRACT
Oxidative coupling of thiols to the corresponding symmetrical disulfides
was performed in the presence of g-picolinium chlorochromate and its
silica gel supported. The reactivity of silica gel supported g-picolinium
chlorochromate for thiophenol derivatives is more than the reactivity of
pyridinium and g-picolinium chlorochromates.
Key Words: Disulfides; Oxidative coupling; g-PCC-SiO2; Thiols.
*
Correspondence: Mohammad Mehdi Khodaei, Department of Chemistry, Faculty of
Science, Razi University, Kermanshah 67149, Iran; E-mail: mmkhoda@razi.ac.ir.
3661
DOI: 10.1081/SCC-200032406
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3662
Khodaei et al.
Selective oxidation of thiols to disulfides under mild conditions is import-
ant from both biological[1] and synthetic points of view.[2] Thiols can be easily
overoxidized; therefore, extensive studies have been carried out for their
control oxidation.[3–13]
Corey in 1975 introduced pyridinium chlorochromate (PCC) as an oxidiz-
ing agent for oxidation of primary and secondary alcohols.[14] Thenceforth,
many chlorochromate reagents have been used for synthetic organic
transformation.[15–19]
Recently we reported g-picolinium chlorochromate (g-PCC) as an effi-
cient catalyst for different organic reactions, including the oxidation of alco-
hols to ketones and aldehydes,[20]deprotection of oximes,[21] and deprotection
of acetals and ketals.[22] We now report the selective and efficient conversion
of a number of thiols to disulfides by g-PCC and silica gel supported g-PCC
under mild and nonaqueous conditions (Sch. 1).
Oxidative coupling of different types of mercaptans was investigated.
First, commercially aromatic thiols have been used and coupled in dichloro-
methane at room temperature using g-picolinium chlorochromate or silica
gel supported g-picolinium chlorochromate. Under these conditions, the
mercaptans were selectively and efficiently oxidized to the corresponding
disulfides in 0.3–2.2 h (Table 1, entries 1–6). Next, saturated linear and
cyclic mercaptans were subjected to oxidation, and the yields and reaction
times were satisfactory. 2-Hydroxyethanthiol did not oxidize in the presence
of g-PCC, and thiosalicylic acid did not proceed using g-PCC or g-PCC-SiO2
(Table 1, entries 11 and 12). In all reactions, equimolar amounts of the catalyst
were used, and no signs of overoxidation were observed. The selectivity of the
present method was evident by the oxidation of 2-mercaptoethanol, where
only mercaptan functionality was converted to the disulfide. The results
show that the oxidation reaction in the presence of silica gel supported
g-PCC is faster than the reaction using g-PCC. Also, the reactivity of aromatic
thiols in the presence of g-PCC-SiO2 is more than the reactivity of arylthiols
using PCC.[23]
Summing up, the supported and unsupported g-PCC efficiently and select-
ively oxidized thiols to the corresponding symmetrical disulfides. The
supported g-PCC is more reactive than g-PCC and PCC when thiophenol
and its derivatives are used.
Scheme 1.

Table 1. Oxidation of thiols to disulfides by g-PCC and g-PCC-SiO2.
g-PCC g-PCC-SiO2
mp (8C) or bp (8C)/Torr
Entry
1
Thiol
Time (h)
0.6
Yield (%)
85
Time (h)
Yield (%)
85
Found
Reported
60–61[24]
1.0
0.5
1.0
60–61
45–46
219
2
3
0.3
0.7
90
90
93
91
47–48[24]
220[8]
4
5
6
0.9
0.6
2.2
87
94
86
0.5
1.0
1.0
90
91
91
70–72
72–74[24]
92–95[24]
143–144[24]
90–92
142–143
7
8
2.8
4.0
83
96
4.0
95
83
70–71
71–72[24]
20.0
125–129
125–128[24]
9
10
11
12
1.8
1.3
0.8
94
81
38
10.0
7.0
87
75
203–205/14
116–118/19
139/0.8
198–199/10[11]
116–118/20[8]
140/0.8[9]
No reaction
No reaction
No reaction

3664
Khodaei et al.
EXPERIMENTAL
Products are known compounds and were characterized by comparison of
their spectral data [hydrogen nuclear magnetic resonance (1H-NMR), infrared
(IR)] and physical properties with those reported in the literature. Monitoring
of the reactions were accomplished by thin-layer chromatography (TLC) on
precoated silica gel 60 F254 sheets. All yields refer to isolated products.
General Procedure for Oxidative Coupling of Thiols to
Disulfides by g-Picolinium Chlorochromate
To a solution of thiol (1 mmol) in dichloromethane (5 ml), g-picolinium
chlorochromate (1 mmol) was added, and the mixture was stirred magnetically
at room temperature for the appropriate time (Table 1). The progress of
the reaction was followed by TLC (eluent: methanol/acetic acid: 5/1). The
mixture was then filtered on a sintered glass funnel, and the residue was
washed with ether three times (each 15 ml). Solvent evaporation gave the
corresponding disulfides, which were recrystallized from methanol to afford
the pure products in 75–95% yields.
General Procedure for Oxidative Coupling of Thiols to
Disulfides by Silica Gel Supported g-Picolinium
Chlorochromate
To a solution of thiol (1 mmol) in dichloromethane (5 ml), the oxidant
(1 mmol) was added. The mixture was stirred magnetically at room tempera-
ture for the appropriate time (Table 1). The progress of the reaction was
monitored by TLC (eluent: n-hexane/ethyl acetate: 5/1). The mixture was
then filtered on a sintered glass funnel, and the residue was washed with
dichloromethane (3 ꢀ 10 ml). Solvent evaporation gave the corresponding
disulfides, which were recrystallized from methanol to afford the pure
products in 38–96% yields.
ACKNOWLEDGMENT
We are grateful to the Research Council of Razi University for partly
financially supporting this work.

Efficient Reagents for Oxidation of Thiols to Disulfides
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Received in the UK January 12, 2004