Silica chloride/NaNO2 as a novel heterogeneous system for production of thionitrites and disulfides under mild conditions

Article abstract of DOI:10.1080/10426500307872

Thiols can be readily converted to their corresponding thionitrites with a combination of silica chloride (I), wet SiO₂ and sodium nitrite in dichloromethane at room temperature. Disulfides result from the homolytic cleavage of the sulfur-nitrogen bond of the unstable thionitrite and subsequent coupling of the resultant thiyl radicals.

Full text of DOI:10.1080/10426500307872

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Phosphorus, Sulfur, and Silicon and the Related
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Silica Chloride/NaNO 2 as a Novel Heterogeneous
System for Production of Thionitrites and Disulfides
Under Mild Conditions
a
b
a
Mohammad Ali Zolfigol , Farhad Shirini , Arash Ghorbani Choghamarani & Efat Ghofrani
a
a
Bu-Ali-Sina University , Hamadan, Iran
b
Gilan University , Rasht, Iran
Published online: 27 Oct 2010.
To cite this article: Mohammad Ali Zolfigol , Farhad Shirini , Arash Ghorbani Choghamarani & Efat Ghofrani (2003) Silica
Chloride/NaNO 2 as a Novel Heterogeneous System for Production of Thionitrites and Disulfides Under Mild Conditions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 178:7, 1477-1481, DOI: 10.1080/10426500307872
To link to this article: http://dx.doi.org/10.1080/10426500307872
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Phosphorus, Sulfur, and Silicon, 178:1477–1481, 2003
Copyright �C Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390212573
SILICA CHLORIDE/NaNO AS A NOVEL
2
HETEROGENEOUS SYSTEM FOR PRODUCTION
OF THIONITRITES AND DISULFIDES UNDER
MILD CONDITIONS
a
b
Mohammad Ali Zolfigol, Farhad Shirini, Arash Ghorbani
a
a
Choghamarani, and Efat Ghofrani
Bu-Ali-Sina University, Hamadan, Iran and Gilan University,
Rasht, Iranb
a
(Received December 3, 2002; in final form January 9, 2003)
Thiols can be readily converted to their corresponding thionitrites with
a combination of silica chloride (I), wet SiO2 and sodium nitrite in
dichloromethane at room temperature. Disulfides result from the ho-
molytic cleavage of the sulfur-nitrogen bond of the unstable thionitrite
and subsequent coupling of the resultant thiyl radicals.
Keywords: Disulfides; silica chloride; thiols; thionitrites (S-nitro-
sothiols)
There currently is a general interest in heterogeneous systems because
of the importance that such systems have in industry and in develop-
1
,2
ing technologies. In continuation of our studies on the application
3,4
of heterogeneous systems we found that silica chloride (I) is an ex-
cellent source for generation of HCl. It is interesting to note that the
addition of wet SiO2 to the reaction mixture containing silica chloride
generates HCl in situ. Therefore, We used it for a different purpose.5,6
We also were interested in using reagent (I) for the nitrosation of thiols
+
via in situ generation of HNO2 and NO , respectively, when used in
conjunction with NaNO2, wet SiO2 in an organic solvent (Scheme 1).
On the other hand thionitrites have not been as widely studied as their
oxygen counterparts alkyl nitrites, generally because of their reduced
This research project has been supported by grant No. NRCI 32-296 of National
Research Projects and with support of National Research Council of Islamic Republic
of Iran.
Address correspondence to Mohammad Ali Zolfigol, Chemistry Department, College
of Science, Bu-Ali-Sina University, Hamadan 65174, PO Box 4135, Iran. E-mail:
zolfi@sadaf.basu.ac.ir
1
477

1
478
M. A. Zolfigol et al.
SCHEME 1
7
stability. However, in recent years there has been much interest gen-
erated in the chemistry and biochemistry of nitrosothiols,7
� 14
since (a)
they are being examined as possible drugs to effect vasodilatation and
to reduce platelet aggregation, (b) they are now believed to play an
important part in some of the physiological processes involving nitric
7
oxide, (c) they are being used as a source of thiyl radicals or as ni-
trosating agents. The vital role of thiols and disulfides in living sys-
tems has focused on their interconversion reactions. Intense interest
in the chemistry of thionitrites has been generated in connection with
the newly discovered remarkable physiological roles of nitric oxide, in-
cluding particularly vasodilation and cytotoxic action of macrophages.
Thiols and thionitrites (S-nitrosothiols) are believed to be involved in in
vivo processes, possibly in the mechanism of NO transfer reactions.11
The most general reagent is nitrous acid, generated from sodium ni-
trite and mineral acid in water or in mixed alcohol-water solvents. Other
nitrosating agents have been used successfully to synthesize thioni-
trites, notably alkyl nitrites, nitrosyl salts, dinitrogen trioxide, dini-
7
� 10
11
12
trogen tetroxide,
trichloronitromethane, oxalic acid dihydrate,

Silica Chloride/NaNO2 as a Novel Heterogeneous System
1479
inorganic acidic salts,13 or silica sulfuric acid14 and sodium nitrite. Very
recently, we among many others, have demonstrated that heteroge-
neous reagent systems have many advantages such as simple experi-
mental procedures, mild reaction conditions and minimization of chemi-
cal wastes as compared to the liquid phase counterparts.1
3� 16
Therefore,
we decided to apply silica chloride (I)/NaNO2 as a new heteroge-
neous system for the nitrosation of thiols. We wish to report a simple,
cheap and convenient method for the effective nitrosation of thiols
and production of disulfides under mild and heterogeneous conditions
(
Scheme 1).
Different kinds of thiols were subjected to the nitrosation reaction
in the presence of NaNO2, wet SiO2 (50% w/w), and silica chloride (I)
in dichloromethane. The nitrosation reactions were performed under
mild and completely heterogeneous conditions at room temperature. A
bright-red heterogeneous solution was obtained immediately due to the
formation of thionitrite. Disulfides result from the homolytic cleavage
of the sulfur-nitrogen bond of the unstable thionitrite and subsequent
1
1
coupling of the resultant thiyl radicals. Therefore, this method also
could be used for conversion of thiols to their corresponding disulfides
quantitatively with increasing temperature (Scheme 1 and Table I).
Although the reaction occurs without wet SiO2, the reaction time is
very long and the reaction is completed only after several days. There-
fore we think that the presence of wet SiO2 will act as a media and will
TABLE I Nitrosation of Thiols to Their Corresponding Unstable
Nitrosothiols (2) and Production of Disulfides (3) with a Combination of Silica
Chloride (I), NaNO
2
(II), and Wet SiO
2
(50% w/w) in Dichloromethane at
Room Temperature
Reagent/Substratea
b
Entry
Substrate
Product
I (g)
II (mmol)
Time (min)
Yields (%)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
3a
3b
3c
3d
3e
3f
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.54
0.27
2
2
2
2
2
2
2
2
2
60
60
60
30
45
20
35
35
25
99
92
90
60
99
98
95
3g
c
c
—
—
91
3i
a
Wet SiO2:substrate (1) (0.2 g:1 mmol).
Isolated yields.
b
c
Polymerization occurred.

1
480
M. A. Zolfigol et al.
provide a heterogeneous effective surface area for in situ generation of
HNO2. It also will make easy work-up.
In conclusion, practical and efficient nitrosation-oxidation of thiols
were achieved by the present methodology. The low cost and availability
of the reagents, easy procedure, and easy work-up make this method
attractive for the organic chemists.
EXPERIMENTAL SECTION
General
Chemicals were purchased from Fluka, Merck, Riedel-deHaen AG and
Aldrich Chemical companies. Silica chloride was synthesised according
3
,4
to the reported procedures. Disulfides were characterized by compar-
1
ison of their spectral (IR, H-NMR, UV, and TLC) and physical data
8
� 14,17,18
with authentic samples.
A Typical Experimental Procedure
To a solution of thiophenol [(1f) 0.220 g, 2 mmol] in CH2Cl2 (10 mL),
I (0.54 g), wet SiO2 (50% w/w) (0.4 g) and NaNO2 (0.257 g, 4 mmol)
were added. The resulting mixture was stirred at room temperature; a
bright-red heterogeneous solution was obtained immediately. Thion-
itrites were characterized by comparison of their UV spectra with
1
7,18
those reported in the literature.
CH2Cl2): PhSNO, 380, 529, 570 nm]. A pale yellow solution was also
Typical spectra are as follows: �max
(
obtained after 20 min and then filtered. The residue was washed with
CH2Cl2 (2 � 10 ml). Anhydrous Na2SO4 (3 g) was added to the filtrate.
After 15 min, the resulting mixture was filtered again. Dichloromethane
was evaporated. The yield was 0.213 g (98%) of crystalline brownish
�
17,18
�
solid (3f), m.p. 58–59 C [Lit.
m.p. 58–60 C].
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