Reductive cleavage of S-S bond by Zn/AlCl3 system: A novel method for the synthesis of sulfides from alkyl tosylates and disulfides

Article abstract of DOI:10.1081/SCC-120039486

Alkyl and aryl disulfides are reduced by zinc powder in the presence of AlCl₃ in aqueous media to yield zinc thiolates. These thiolate anion species then react with alkyl tosylates to give sulfides in high to excellent yields.

Full text of DOI:10.1081/SCC-120039486

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Reductive Cleavage of S–S
Bond by Zn/AlCl System:
3
A Novel Method for the
Synthesis of Sulfides from
Alkyl Tosylates and Disulfides
a
a
Barahman Movassagh & Amir Mossadegh
a
Department of Chemistry , K. N. Toosi University
of Technology , P.O. Box 15875‐4416, Tehran, Iran
Published online: 30 Mar 2009.
To cite this article: Barahman Movassagh & Amir Mossadegh (2004) Reductive
Cleavage of S–S Bond by Zn/AlCl System: A Novel Method for the Synthesis
3
of Sulfides from Alkyl Tosylates and Disulfides, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry,
34:13, 2337-2343, DOI: 10.1081/SCC-120039486
To link to this article: http://dx.doi.org/10.1081/SCC-120039486
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SYNTHETIC COMMUNICATIONS
Vol. 34, No. 13, pp. 2337–2343, 2004
Reductive Cleavage of S–S Bond by
Zn/AlCl System: A Novel Method for
3
the Synthesis of Sulfides from Alkyl
Tosylates and Disulfides
*
Barahman Movassagh and Amir Mossadegh
Department of Chemistry, K. N. Toosi University of Technology,
Tehran, Iran
ABSTRACT
Alkyl and aryl disulfides are reduced by zinc powder in the presence
3
of AlCl in aqueous media to yield zinc thiolates. These thiolate anion
species then react with alkyl tosylates to give sulfides in high to excellent
yields.
3
Key Words: Alkyl tosylates; Zn/AlCl system; Reductive cleavage of
disulfides; Zinc thiolates; Sulfides.
*
Correspondence: Barahman Movassagh, Department of Chemistry, K. N. Toosi
University of Technology, P.O. Box 15875-4416, Tehran, Iran; E-mail: movassagh@
kntu.ac.ir.
2
337
DOI: 10.1081/SCC-120039486
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker Inc.

2
338
Movassagh and Mossadegh
INTRODUCTION
Historically the chemistry of sulfides has been relatively well studied.
Nevertheless the chemistry of sulfides is still important from both theoretical
[
1]
and practical viewpoints. Sulfides are the starting compounds for the
preparations of other sulfur compounds, such as sulfoxides, sulfones, sulfonium
[1]
compounds, etc. Several procedures for the preparation of sulfides have
been reported including: reduction of sulfoxides and sulfones; desulfuriza-
tion of disulfides, aryllithium or organocuprate addition to thiocarbonyl
[
2,3]
[4]
compounds;
displacement of aryl halides by thiolate ion; treatment of alkyl halides
treatment of thiols and alkyl halides with DBU; nucleophilic
5]
[
[
with sodium sulfide, thiourea, or thiocarbonate; use of bis-(tributyltin)
6]
[7]
[8]
[
9]
[10]
sulfide as a sulfur transfer agent; reaction of halides with thiosilanes.
Recently, sulfides have been prepared from thiols using montmorillonite-
[
11]
3
sulfides from an organosamarium reagent and disulfides has been reported.
-aminopropyltriethoxysilane as a catalyst.
Also, the synthesis of allyl
[12]
[13]
Lu and Zhang
synthesized benzyl sulfides via reaction of benzyl bromide
with disulfides promoted by Sm/BiCl system in aqueous media. Very recently,
3
we introduced Zn/AlCl system in aqueous media for the preparation of sulfides
3
[
14]
from disulfides and organic halides.
offer numerous advantages over common reactions in organic solvents.
Such reactions in aqueous media
[13]
From a synthetic point of view, there are some major limitations to the
preparation of sulfides by S–S bond cleavage in disulfides, including: (i) the
need for anhydrous organic solvents, (ii) the necessity to prepare an organo-
metallic complex, (iii) strong base catalysis, and (iv) loss of half unit of
[
13,15]
disulfide.
circumvents these problems.
But, the S–S bond cleavage in disulfides by a Zn/AlCl system,
3
As part of our ongoing work on Zn/AlCl system, here we report that
3
alkyl tosylates can react with various disulfides promoted by the above system
in CH CN–H O mixed solvent at 658C to afford sulfides in high to excellent
yields (Sch. 1).
3
2
A series of symmetrical alkyl and aryl disulfides were treated with various
primary alkyl tosylates in the presence of Zn/AlCl system with a molar
3
ratio of disulfide : AlCl : tosylate ¼ 0.5 : 1 : 1.5. The presence of aluminum
3
chloride is quite essential, and in the absence of this Lewis acid, the reaction
slows down considerably. The disappearance of zinc powder during the
Scheme 1.

Reductive Cleavage of S–S Bond by Zn/AlCl System
3
2339
preliminary treatment of disulfides with Zn/AlCl is attributed to the forma-
3
[
14]
tion of a zinc thiolate intermediate which further undergoes nucleophilic
displacement with alkyl tosylates in the presence of AlCl to afford the sulfide.
3
The reactions of diaryl disulfides with benzyl tosylates (entries 1–3,
Table 1) were rather fast and gave the corresponding benzyl–aryl sulfides
in excellent yields. The results also show the need for relatively longer
reaction times and sometimes lower yields for symmetrical alkyl disulfides
(
entries 4, 8, and 9, Table 1).
In conclusion, the present method introduces an alternative with shorter
[
14]
reaction times to the ones reported previously.
Also, it offers some advan-
tages over earlier reported procedures in that it avoids the need to apply thiol,
the manipulation of air-sensitive transition metal complexes, and the use of
dry solvent, as well as being carried out under mild conditions.
EXPERIMENTAL
Disulfides and alkyl tosylates were readily prepared according to the
22]
[
[23]
procedures given by Fristad
and Choudary,
respectively. All products
were identified by comparison of their spectra and physical data with those
of the known samples. IR spectra were recorded using a Shimadzu IR-408
1
instrument. H-NMR spectra were determined by a Bruker DRX-500 Avance
5
9
00 MHz spectrometer. Melting points were obtained by an Electrothermal
100 apparatus.
General Procedure for Preparation of Sulfides
In a 50 mL two-neck flask fitted with a reflux condenser, AlCl (1 mmol),
3
zinc powder (2 mmol), acetonitrile (10 mL), and disulfide (0.5 mmol) were
placed. The mixture was stirred at 658C for about 2 hr until the zinc powder
disappeared. Alkyl tosylate (1.5 mmol), and water (2.5 mL) were then added
at once to the solution and stirring was continued at that temperature for
3
.5–15 hr in air atmosphere. Progress of the reaction was monitored by
TLC (eluent: petroleum ether/EtOAc, 2 : 1). After completion of the reaction,
the solution was filtered and washed with ether. The combined ether/CH CN
3
solution was then washed with water and dried over anhydrous sodium sulfate.
The solvent was evaporated in vacuo to give the corresponding sulfide, which
was purified either by column chromatography using silica gel (petroleum
ether/EtOAc, 2 : 1), or recrystallized from ethanol.
1
Selected H-NMR (in CDCl ) spectral data for product 1: d 3.65 (s, 2H),
3
7
.20–7.50 (m, 10H). 6: d 0.86 (t, 3H, J ¼ 7.5 Hz), 1.22–1.29 (m, 2H),

2
340
Movassagh and Mossadegh

Reductive Cleavage of S–S Bond by Zn/AlCl System
3
2341
1
.40–1.46 (m, 2H), 2.87 (t, 2H, J ¼ 7.8 Hz), 7.21–7.34 (m, 5H). 10: d 0.91
t, 3H, J ¼ 7.4 Hz), 1.37–1.48 (m, 4H), 2.90 (t, 2H, J ¼ 7.6 Hz), 7.33 (d, 2H,
J ¼ 8.0 Hz), 7.78 (d, 2H, J ¼ 8.0 Hz). 12: d 0.88 (t, 3H, J ¼ 7.5 Hz),
.21–1.49 (m, 6H), 1.52–1.79 (m, 2H), 2.91 (t, 2H, J ¼ 7.6 Hz), 7.34 (d, 2H,
(
1
J ¼ 8.0 Hz), 7.44 (d, 2H, J ¼ 8.0 Hz). 14: d 0.87 (t, 3H, J ¼ 7.5 Hz), 1.20–
1
.48 (m, 6H), 1.50–1.77 (m, 2H), 2.91 (t, 2H, J ¼ 7.8 Hz), 7.23–7.38 (m, 5H).
ACKNOWLEDGMENT
We thank the K. N. Toosi University of Technology Research Council for
financial support.
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Received in India February 26, 2004