Synthesis of organic sulfides via Zn/AlCl3 system in aqueous media

Article abstract of DOI:10.1081/SCC-120003615

An efficient procedure for preparation of various sulfides has been introduced through a simple reaction of disulfides with suitable alkyl or aryl halides which is promoted by commercial zinc powder in the presence of AlCl₃ in aqueous media at 65°C.

Full text of DOI:10.1081/SCC-120003615

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SYNTHESIS OF ORGANIC SULFIDES VIA Zn/AlCl3 SYSTEM
IN AQUEOUS MEDIA
M. M. Lakouraj a , B. Movassagh a & Z. Fadaei b
a Department of Chemistry, Mazandaran University, Babolsar, 47415, Iran
b Department of Chemistry, Razi University, Kermanshah, 67149, Iran
Version of record first published: 16 Aug 2006.
To cite this article: M. M. Lakouraj, B. Movassagh & Z. Fadaei (2002): SYNTHESIS OF ORGANIC SULFIDES VIA Zn/AlCl3 SYSTEM
IN AQUEOUS MEDIA, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 32:8, 1237-1242
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SYNTHETIC COMMUNICATIONS, 32(8), 1237–1242 (2002)
SYNTHESIS OF ORGANIC SULFIDES VIA
Zn/AlCl3 SYSTEM IN AQUEOUS MEDIA
M. M. Lakouraj,1, B. Movassagh,1 and Z. Fadaei2
*
1Department of Chemistry, Mazandaran University,
Babolsar 47415, Iran
2Department of Chemistry, Razi University,
Kermanshah 67149, Iran
ABSTRACT
An efficient procedure for preparation of various sulfides
has been introduced through a simple reaction of disulfides
with suitable alkyl or aryl halides which is promoted by com-
mercial zinc powder in the presence of AlCl3 in aqueous
media at 65ꢀC.
Recently, organometallic-type reactions in aqueous media have
attracted considerable interest in organic synthesis.1 If one can perform
these reactions in aqueous media just as generally and easily as in organic
solvent, such reactions may offer a number of advantage: i) practical con-
venience and environmental benefits due to the omission of inflammable and
anhydrous solvents; ii) protection and deprotection process for certain func-
tional groups can possibly be simplified; iii) water-soluble compounds and
substrates bearing active functional groups can be reacted directly without
*Corresponding author. E-mail: lakouraj@umcc.ac.ir
1237
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

1238
LAKOURAJ,MOVASSAGH,AND FADAEI
the need of derivatization; iv) the rate and stereochemical outcomes of the
reactions may offer new opportunities in synthesis.
Most commonly, zinc, indium, tin and bismuth or BiCl3/Al,
BiCl3/Zn and BiCl3/Fe systems are used.1,2 However, the application of
aqueous organometallic reactions seems to have been somewhat limited
mainly to allylation and propargylation of carbonyl compounds.
Sulfides are useful synthetic reagents and intermediates in organic syn-
thesis. Many methods are known for the formation of sulfides including
desulfurization of disulfides, reduction of sulfoxides and sulfones, aryllithium
or organocuprate addition to thiocarbonyl compounds;3 the treatment of
halides with sodium sulfides,4 thiourea;5 the use of electrophilic sulfur
species;6 the use of bis(tributyltin)sulfide as a sulfur transfer agent;7 treatment
of thiols and alkyl halides with DBU.8 Under the action of phosphorus(III)
compounds disulfides are subjected to partial desulfurization leading to sul-
fides.9 A number of complexes of iron, nickel and other transition metals
have been studied rather extensively as reagents for desulfurization of various
compounds.10 But, all methods mentioned above lack in general applicability
because of severe reaction conditions and complicated procedures and/or
activated reactants are required. The traditional method for preparation of
unsymmetrical sulfides and the alkylation of thiols suffer from drawbacks
such as foul smelling of thiols and elevated temperature. Recently, montmor-
illonite-3-aminopropyl triethoxysilane and Ce exchanged zeolite catalyzed
synthesis of sulfides has been reported.11 Also, in a more recent study Lu
and Zhang reported the formation of benzyl sulfides catalyzed by a Sm/BiCl3
system in aqueous media, in which disulfides were used as a thiolating
source.12 Disulfides are important reagents in synthetic chemistry, and
many methods have been published for synthesis of disulfides.9,13 Among
them, oxidative coupling of thiols to disulfides is the most important one.14
In connection with our ongoing work on Zn/AlCl3 system, we wish to
report a convenient route to the preparation of different sulfides through a
simple coupling of disulfides with alkyl and aryl halides promoted by cheap
and reactive metallic zinc dust in the presence of AlCl3 in DMF-H2O-mixed
solvent (Scheme 1).
The results are summarized in Table 1. The treatment of symmetrical
aryl disulfides with benzyl bromides (Entries 1–7, Table 1) and primary alkyl
bromides (Entries 8 and 9, Table 1) affords the corresponding aryl–alkyl
Scheme 1.

SULFIDE SYNTHESIS VIA Zn/AlCl3 SYSTEM
1239
sulfides in excellent yields. Under the same conditions tertiary alkyl halide
(Entry 10, Table 1) does not produce the expected sulfide even after 27 h. This
represents the SN2 type nucleophilic reaction (Scheme 2). In the case of aryl
halides containing strong electron withdrawing substituents (Entries 11–17,
Table 1), the reactions proceed more easily to afford diaryl sulfides in good to
excellent yields, but simple aryl halides (Entries 18–20, Table 1) and those
having electron donating substituents (Entry 21, Table 1) do not react at all.
As a result, an SNAr mechanism is proposed for these halides (Scheme 2).
While symmetrical dialkyl disulfides react conveniently with alkyl halides
(Entries 24–27, Table 1) to give the corresponding sulfides, the reaction of
symmetrical dialkyl disulfides (Entries 22 and 23, Table 1) with aryl halides
failed due to fast formation of an unknown complex. Also, under the same
conditions, a-cyanothioethers (Entries 28 and 29, Table 1) were easily synthe-
sized in high yields, using chloroacetonitrile as alkyl halide.
Scheme 2.
It is worth mentioning that zinc powder was also examined with dif-
ferent Lewis acids such as BF3-Et2O, AlCl3, FeCl3, and ZnCl2 in different
solvents, but the best result was obtained with the Zn/AlCl3 system in DMF-
H2O mixed solvent. The presence of AlCl3 and H2O is essential in this
procedure.
To conclude, this method is attractive since it offers some advantages
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 were prepared according to the method reported by Rieke
et al.15 Zinc powder and AlCl3 were purchased from Merck company.

1240
LAKOURAJ,MOVASSAGH,AND FADAEI
Table 1. Preparation of Sulfides from Disulfides with Zn/AlCl3 in DMF/H2O
Time Yielda
M.P. (ꢀC) (obs.)/M.P. or
B.P. (ꢀC/mm) (lit.)ref
No.
RR
0X or ArX
(h)
(%)
1
2
3
4
5
6
7
8
Ph
p-ClC6H4
p-MeC6H4 PhCH2Br
m-MeC6H4 PhCH2Br
Ph
p-MeC6H4 p-NO2C6H4CH2Br 10.5
p-ClC6H4 p-NO2C6H4CH2Br 14
p-MeC6H4 CH3(CH2)2CH2Br 17
PhCH2Br
PhCH2Br
13
90
90
94
94
95
93
85
95b
(41.5–42.5)/40–4212
(53)/5311
15
11
12
(45–45.5)/45–4616
(30–32)/3117
(79)/7918
p-NO2C6H4CH2Br 12
(94–94.5)/9019
(70–70.5)/66–6720
(80–82/1 mm)/
135–138/15 mm21
(oil)/175–6/12 mm22
–
(120–121)/12023
(125–126)/123–12424
(102–103.5)/102.5–10425
(100–101)/100–101.525
(120–121)/12025
(125–126)/12425
(100–101)/100–101.525
–
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
p-ClC6H4
p-MeC6H4 Me3CCl
Ph
p-ClC6H4
p-MeC6H4 2,4-(NO2)2C6H4Cl
m-MeC6H4 2,4-(NO2)2C6H4Cl
Ph 2,4-(NO2)2C6H4F
p-ClC6H4 2,4-(NO2)2C6H4F
m-MeC6H4 2,4-(NO2)2C6H4F
Ph
Ph
Ph
Ph
Cyclohexyl 2,4-(NO2)2C6H4Cl 19
CH3(CH2)3 2,4-(NO2)2C6H4Cl 19
CH3(CH2)3 CH3(CH2)2CH2Br 18
CH3(CH2)7 PhCH2Br
PhCH2 PhCH2Br
CH3(CH2)3 PhCH2Br
CH3(CH2)4CH2Br 18
100b
0
27
6
8
4.5
5.5
3
3.5
2
2,4-(NO2)2C6H4Cl
2,4-(NO2)2C6H4Cl
95
85
95
75
92
92
73
0
0
0
0
0
C6H5-F
C6H5-Cl
C6H5-Br
m-MeC6H4Br
18
18
19
17
–
–
–
–
0
–
88b
86
55b
100b
87
85
(oil)/187/5 mm23
(oil)/175/12 mm26
(50)/49–5123
(oil)/130/5 mm27
(oil)/133–13528
(89–90)/88–9029
19
21
16
3.5
6
Ph
p-ClC6H4
ClCH2CN
ClCH2CN
aYields based on pure isolated product.
bG.C. Yields.
All products were characterized by comparison of their spectral and physi-
cal data with those of known samples. IRspectra were obtained using a
Shimadzu 470 instrument. 1H NMRspectra were determined by Jeol JNM-
PMX 60 MHz or Bruker 200 MHz NMRspectrometer. Melting points were
obtained by a Gallen-Kamp apparatus and were corrected.

SULFIDE SYNTHESIS VIA Zn/AlCl3 SYSTEM
1241
General Procedure for Preparation of Sulfides from Corresponding
Diaryl Disulfides (Method A). A mixture of diaryl disulfide (0.5 mmol),
zinc powder (130 mg, 2 mmol), aluminum chloride (133 mg, 1 mmol),
DMF (10 ml), and water (2.5 ml) was stirred at 65ꢀC for 1 h until the zinc
powder disappeared; alkyl halide and/or aryl halide (1.5 mmol) was then
added at once to the solution and stirring was continued at that temperature
for 2–19 h in air atmosphere. After completion of the reaction, the solution
was filtered and washed with diethyl ether. The combined ether/DMF sol-
ution was then washed with water and dried over sodium sulfate. The sol-
vent was evaporated in vacuo to give the corresponding sulfide in high yield
which recrystallized from ethanol.
General Procedure for Synthesis of Sulfides from Corresponding Dialkyl
Disulfides (Method B). A mixture of dialkyl disulfide (0.5 mmol), aryl or
alkyl halide (1.5 mmol), zinc powder (130 mg, 2 mmol), aluminum chloride
(133 mg, 1 mmol), DMF (10 ml), and water (2.5 ml) was stirred at 65ꢀC for
3.5–19 h in air atmosphere. After completion of the reaction, the solution
was filtered and washed with diethyl ether. The combined ether/DMF sol-
ution was then washed with water and dried (Na2SO4). The solvent was
evaporated in vacuo to afford desired sulfide.
ACKNOWLEDGMENT
Authors are thankful to Razi University Research Council for finan-
cial support, and also grateful to Institute of Chemistry of Mazandran
University for complementary assistance of this work.
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Received in the UK January 18, 2001