Fast, efficient and convenient method for the preparation of arylazo sulfides using aryl diazonium silica sulfates under mild and solvent-free conditions

Article abstract of DOI:10.1016/j.dyepig.2011.02.010

An efficient, fast, and straightforward procedure for the synthesis of arylazo sulfides and arylazo thiosulfonates is described in the present paper by using aryl diazonium silica sulfates and sodium thiolates. Using the present method, different kinds of

Full text of DOI:10.1016/j.dyepig.2011.02.010

Dyes and Pigments 91 (2011) 44e48
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Fast, efficient and convenient method for the preparation of arylazo sulfides
using aryl diazonium silica sulfates under mild and solvent-free conditions
,
b
c,
Amin Zarei a , Leila Khazdooz , Abdol R. Hajipour d, Hamidreza Aghaei e
*
a Department of Science, Islamic Azad University, Fasa Branch, Post Box No. 364, Fasa 7461713591, Fars, Iran
b Department of Science, Islamic Azad University, Khorasgan Branch, Isfahan 81595-158, Iran
c Department of Pharmacology, University of Wisconsin, Medical School, USA
d Pharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan, Iran
e Department of Chemistry, Islamic Azad University, Shahreza Branch, Shahreza 311-86145, Isfahan, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient, fast, and straightforward procedure for the synthesis of arylazo sulfides and arylazo thio-
sulfonates is described in the present paper by using aryl diazonium silica sulfates and sodium thiolates.
Using the present method, different kinds of aryl diazonium silica sulfates, containing electron-with-
drawing groups as well as electron-donating groups, were rapidly converted to the corresponding ary-
lazo sulfides in good yield and short reaction time. These reactions were carried out at room temperature
under mild and solvent-free conditions. The use of non-toxic and inexpensive materials, simple and clean
work-up, short reaction times and good yields are the advantages of this method.
Received 3 November 2010
Received in revised form
28 December 2010
Accepted 16 February 2011
Available online 9 March 2011
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Aryl diazonium silica sulfates
Sodium thiolates
Arylazo sulfides
Arylazo thiosulfonates
Solvent-free
Mild conditions
1. Introduction
with using aryl mercaptans, tedious work-up, and low yields
because of disulfide formation. In continuation of our studies on the
Aryl diazonium salts have been prepared and studied as
powerful intermediates in classical and modern organic synthesis
due to their easy availability and high reactivity [1e4]. Therefore,
there is always an interest in the field of aromatic diazonium salts.
Arylazo sulfides have been studied from their thermal [5,6] and
photochemical [7,8] behavior as well as their applications in
organic synthesis [9e20]. For example, it is known that the ther-
molysis of these compounds is an important method for the
preparation of arydiazenyl radicals [5,6]. Moreover, arylazo sulfides
are one of the important precursors for SRN1 reactions to produce
a number of variously functionalized aromatic compounds [9e20].
Furthermore, some of the chlorinated phenylazo phenyl sulfides
are used as agricultural pesticides and miticides. One of the useful
procedures for the preparation of arylazo sulfides is the reaction of
aryl diazonium salts with aryl mercaptans [21e24]. Although some
of these methods are convenient protocols with good yields, some
of them suffer from disadvantages such as the stench associated
stabilization of diazonium salts on silica sulfuric acid and their
applications in organic synthesis [25e28], we report herein an
efficient, fast, and convenient procedure for the synthesis of arylazo
sulfides employing aryl diazonium silica sulfates in the presence of
sodium thiolates under solvent-free conditions. In spite of the
traditional methods, these reactions were carried out at room
temperature and there was no need to employ low temperature
(Scheme 1).
2. Experimental
2.1. General
All reagents were purchased from Merck and Aldrich and used
without further purification. Aryl diazonium silica sulfates were
synthesized according to the previous works [25e28]. All yields
refer to the isolated products after purification. The products were
characterized by comparison with authentic samples and by spec-
troscopic data (IR, 1H NMR, 13C NMR spectra and melting point). All
melting points were taken on a Gallenkamp melting apparatus and
were uncorrected. UV spectra were recorded on a JASCO V-570
* Corresponding author. Tel.: þ98 917 1302528; fax: þ98 311 2289113.
E-mail address: aj_zarei@yahoo.com (A. Zarei).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.02.010

A. Zarei et al. / Dyes and Pigments 91 (2011) 44e48
45
2.3.5. 3-Nitrophenylazo methanethiosulfonate (Table 1, entry 19)
Grinding
r.t., 5-10 min
ArN2 OSO3-SiO2
R = Ph, CH3SO2
ArN=NSR
RSNa
+
Orange solid; UV (lmax in acetone): 334 nm. Decomposed at
121 ꢁC; FTIR (KBr) cmꢂ1: 3084, 2935, 1607, 1531, 1493, 1356, 1335,
1160, 1086, 916, 872, 819, 793, 741. 1H NMR (500 MHz, CDCl3)
Scheme 1. An efficient, fast, and convenient procedure for the synthesis of arylazo
sulfides employing aryl diazonium silica sulfates in the presence of sodium thiolates
under solvent-free conditions.
d
¼ 8.71 (1 H, s), 8.48 (1 H, d, J ¼ 7.87 Hz), 8.25 (1 H, d, J ¼ 7.77 Hz),
7.80 (1 H, t, J ¼ 8.04 Hz), 3.25 (3 H, s). 13C NMR (125 MHz, CDCl3)
d
¼ 149.65, 149.41, 131.40, 130.09, 129.16, 35.48. Anal. Calcd for
C7H7N3O4S2: C, 32.18; H, 2.70; N, 16.08; S, 24.54. Found: C, 32.11; H,
2.77; N, 15.99; S, 24.45.
UV/vis/NIR spectrophotometer. IR spectra were recorded on
a JASCO FT/IR-680 PLUS spectrometer. 1H NMR spectra were
recorded on a Bruker 500 MHz.
2.3.6. 2-Nitrophenylazo methanethiosulfonate (Table 1, entry 20)
Orange solid; UV (lmax in acetone): 338 nm. Mp 74e76 ꢁC; FTIR
(KBr) cmꢂ1: 3070, 3022, 2940, 1599, 1525, 1339, 1199, 957, 893, 857,
2.2. General procedure for the synthesis of arylazo sulfides
778, 746. 1H NMR (500 MHz, CDCl3)
d
¼ 8.14 (1 H, d, J ¼ 7.62 Hz),
7.88-7.83 (2 H, m), 7.71 (1 H, d, J ¼ 7.14 Hz), 3.23 (3 H, s). 13C NMR
Sodium thiolate (1.2 mmol, 0.161 g) was added to freshly dia-
zonium silica sulfate (1 mmol) and the reaction mixture was
ground with a pestle in a mortar at room temperature for the time
specified in Table 1. The mixture was diluted with ethyl acetate
(12 mL) and, after stirring, was filtered. The residue was extracted
with ethyl acetate (3 ꢀ 10 mL) and the combined organic layers
were washed with 5% NaOH solution and then dried over anhy-
drous Na2SO4. The solvent was evaporated and the crude product
was purified by short column chromatography to afford the cor-
responding pure product.
(125 MHz, CDCl3)
d
¼ 147.60, 142.27, 134.86, 134.43, 125.48, 118.53,
34.94. Anal. Calcd for C7H7N3O4S2: C, 32.18; H, 2.70; N, 16.08; S,
24.54. Found: C, 32.15; H, 2.81; N, 16.05; S, 24.58.
2.3.7. 4-(2-(Methylthiosulfonyl)diazenyl) benzoic acid
(Table 1, entry 21)
Pale yellow solid; UV (lmax in acetone): 327 nm. Decomposed at
137 ꢁC; FTIR (KBr) cmꢂ1: 3100e2555, 1685, 1480, 1427, 1333, 1290,
1164, 1146, 966, 900, 871, 775. 1H NMR (500 MHz, CDCl3/DMSO-d6)
d
¼ 7.98 (2 H, d, J ¼ 8.80 Hz), 7.63 (2 H, d, J ¼ 8.80 Hz), 3.24 (3 H, s).
13C NMR (125 MHz, CDCl3/DMSO-d6)
d
¼ 166.28, 148.23, 136.22,
2.3. The spectral data of new compounds
130.56, 126.27, 35.30. Anal. Calcd for C8H8N2O4S2: C, 36.91; H, 3.10;
N, 10.76; S, 24.64. Found: C, 36.88; H, 3.15; N, 10.79; S, 24.56.
2.3.1. 4-Methylphenylazo methanethiosulfonate (Table 1, entry 15)
Pale yellow solid; UV (lmax in acetone): 325 nm. Mp 95e96 ꢁC;
FTIR (KBr) cmꢂ1: 3038, 3925, 1585, 1487, 1365, 1163, 970, 867, 762.
3. Results and discussion
1H NMR (500 MHz, CDCl3)
d
¼ 7.51 (2 H, d, J ¼ 8.10 Hz), 7.20 (2 H, d,
Aromatic diazonium salts have been prepared and studied for
years. These salts are important building blocks in classical and
modern organic synthesis. These salts, however, have a serious
drawback in their intrinsic instability. Therefore, these compounds
are usually synthesized at around 10 ꢁC, and to avoid their
decomposition, they are handled below 0 ꢁC. Moreover, because of
this instability, subsequent reactions with diazonium salts must
be carried out under similar conditions to which they are produced.
These problems restrict chemists for approaching potentially
important transformations of these salts. Thus, new diazonium
salts with high stability and versatility that can be easily made
and stored under solid state conditions with explosion proof
properties, are desired and necessary [29e33]. Recently, we have
reported an efficient, fast, and convenient method for the prepa-
ration of aryl diazonium salts supported on the surface of silica
sulfuric acid (aryl diazonium silica sulfates) [25e28]. We found that
these new aryl diazonium salts, ArN2þꢂOSO3-SiO2, were sufficiently
stable and could be kept at room temperature under anhydrous
conditions. In the present work, different kinds of aromatic amines
were rapidly converted to their corresponding arylazo sulfides in
good to high yields under mild conditions (Table 1, entries 1e14).
The crude products were extracted with ethyl acetate, and if
necessary, were purified by short column chromatography.
Aromatic amines with electron-withdrawing groups or elec-
tron-donating groups reacted effectively. The steric effects of ortho
substituents and electronic effects of functional groups on the aryl
amine rings had relatively little influence on the yields of the
products (Table 1). The corresponding disulfides and phenol
derivatives were formed in trace yields as the by-products. Unlike
the traditional methods, these reactions were carried out under
solvent-free conditions at room temperature. We also studied the
solvent effect on these reactions. Using water, methanol, or
dimethyl sulfoxide as the solvent, under the same conditions, led to
lower yields of the corresponding arylazo sulfides because the
J ¼ 8.10 Hz), 3.24 (3 H, s), 2.35 (3 H, s). 13C NMR (125 MHz, CDCl3)
d
¼ 147.30, 138.26, 128.28, 122.50, 35.28, 21.38. Anal. Calcd for
C8H10N2O2S2: C, 41.72; H, 4.38; N, 12.16; S, 27.85. Found: C, 41.65; H,
4.49; N, 12.05; S, 27.78.
2.3.2. 4-Chlorophenylazo methanethiosulfonate (Table 1, entry 16)
Yellow solid; UV (lmax in acetone): 330 nm. Decomposed at
111 ꢁC; FTIR (KBr) cmꢂ1: 3091, 3039, 2932, 1574, 1484, 1404, 1331,
1161, 1142, 1089, 953, 887, 844, 794. 1H NMR (500 MHz, CDCl3)
d
¼ 7.93 (2 H, d, J ¼ 8.65 Hz), 7.59 (2 H, d, J ¼ 8.65 Hz), 3.26 (3 H, s).
13C NMR (125 MHz, CDCl3)
d
¼ 147.78, 142.23, 130.28, 126.21, 35.31.
Anal. Calcd for C7H7ClN2O2S2: C, 33.53; H, 2.81; N, 11.17; S, 25.58.
Found: C, 33.49; H, 2.90; N, 11.25; S, 25.53.
2.3.3. 3-Chlorophenylazo methanethiosulfonate (Table 1, entry 17)
Pale yellow solid; UV (lmax in acetone): 325 nm. Mp 66e68 ꢁC;
FTIR (KBr) cmꢂ1: 3071, 3019, 2936, 1574, 1480, 1456, 1336, 1317,
1161, 1145, 1065, 960, 923, 817, 790. 1H NMR (500 MHz, CDCl3)
d
¼ 7.94 (1 H, s), 7.88 (1 H, d, J ¼ 8.00 Hz), 7.65 (1 H, d, J ¼ 8.00 Hz),
7.55 (1 H, t, J ¼ 8.00 Hz), 3.25 (3 H, s). 13C NMR (125 MHz, CDCl3)
d
¼ 149.70, 135.92, 134.88, 130.81, 123.63, 123.61, 34.90. Anal. Calcd
for C7H7ClN2O2S2: C, 33.53; H, 2.81; N, 11.17; S, 25.58. Found: C,
33.45; H, 2.88; N, 11.08; S, 25.49.
2.3.4. 4-Bromophenylazo methanethiosulfonate (Table 1, entry 18)
Orange solid; UV (lmax in acetone): 336 nm. Decomposed at
127 ꢁC; FTIR (KBr) cmꢂ1: 3086, 3038, 2930, 1582, 1571, 1481, 1400,
1328, 1160, 1141, 1060, 954, 893, 842, 831, 789, 724. 1H NMR
(500 MHz, CDCl3)
d
¼ 7.82 (2 H, d, J ¼ 8.65 Hz), 7.73 (2 H, d,
J ¼ 8.65 Hz), 3.23 (3 H, s). 13C NMR (125 MHz, CDCl3)
d
¼ 148.14,
133.60, 131.00, 126.26 35.32. Anal. Calcd for C7H7BrN2O2S2: C,
28.48; H, 2.39; N, 9.49; S, 21.73. Found: C, 28.52; H, 2.45; N, 9.41; S,
21.70.

46
A. Zarei et al. / Dyes and Pigments 91 (2011) 44e48
Table 1
Preparation of (E)-arylazo sulfides by using aryl diazonium silica sulfates and sodium thiolates at room temperature.a
Entry
Sodium thiolates
Aromatic amines
Products
Time (min)
Yield (%)
Mp (ꢁC)
Found
Reported
1
2
PhSNa
4-MePhN2þꢂOSO3-SiO2
2-MePhN2þꢂOSO3-SiO2
5
5
81
78
48e49
49e50 [24]
Me
N
N
S
Ph
N
N
N
N
S
Ph
Oil
19e20 [7]
31e33 [16]
46e47 [24]
44e45 [7]
59e60 [7]
46e47 [7]
110e111[11]
31e33 [16]
71e72 [12]
95e97 [11]
48e49 [11]
57e58 [11]
101 [21]
Me
S
Ph
3
2-MeOPhN2þꢂOSO3-SiO2
4-MeOPhN2þꢂOSO3-SiO2
2-BrPhN2þꢂOSO3-SiO2
4-ClPhN2þꢂOSO3-SiO2
2-ClPhN2þꢂOSO3-SiO2
4-NCPhN2þꢂOSO3-SiO2
4-MeCOPhN2þꢂOSO3-SiO2
4-PhCOPhN2þꢂOSO3-SiO2
4-NO2PhN2þꢂOSO3-SiO2
3-NO2PhN2þꢂOSO3-SiO2
2-NO2PhN2þꢂOSO3-SiO2
4-HOCOPhN2þꢂOSO3-SiO2
4-MePhN2þꢂOSO3-SiO2
4-ClPhN2þꢂOSO3-SiO2
5
5
75
78
79
87
82
82
85
83
84
86
81
82
80
81
33e34
47e48
OMe
4
MeO
N
S
N
S
Ph
N
N
Ph
5
5
45e46
Br
6
5
57e58
Cl
N
N
S
Ph
N
N
S
Ph
7
5
45e46
Cl
8
5
106e108
34e35
NC
N
N
S
Ph
O
9
5
H3C
C
N
N
S
Ph
O
C
10
11
12
13
14
15
16
5
70e71
Ph
N
N
S
Ph
5
94e95
O2N
N
N
S
Ph
N
N
N
S
Ph
5
47e48
O2N
N
S
Ph
5
56e57
NO2
O
5
98e100
95e96
HO
C
N
N
S
Ph
O
MeSO2Na
Me
N
N
S
S
CH3
10
10
e
O
O
S
111 Decomposed
e
Cl
N
N
S
CH3
O

A. Zarei et al. / Dyes and Pigments 91 (2011) 44e48
47
Table 1 (continued )
Entry
Sodium thiolates
Aromatic amines
Products
Time (min)
Yield (%)
Mp (ꢁC)
Found
Reported
O
S
N
N
N
S
CH3
17
18
19
3-ClPhN2þꢂOSO3-SiO2
4-BrPhN2þꢂOSO3-SiO2
3-NO2PhN2þꢂOSO3-SiO2
10
10
10
79
83
82
66e68
e
O
Cl
Br
O
127 Decomposed
121 Decomposed
e
e
N
S
S
CH3
O
O
N
N
N
S
S
S
CH3
O
O2N
O
S
N
CH3
20
2-NO2PhN2þꢂOSO3-SiO2
4-HOCOPhN2þꢂOSO3-SiO2
10
10
77
80
74e76
e
e
O
NO2
O
C
O
S
21
137 Decomposed
HO
N
N
S
CH3
O
a
The yields refer to isolated pure products which were characterized from their spectral data by comparison with authentic samples.
yields of the corresponding disulfides and phenol derivatives
increased as the by-products. It is known that replacement of aryl
diazonium groups with an appropriate nucleophile is usually
carried out by a SRN1 mechanism. It is a chain process involving the
coupling of an aryl radical with an anionic nucleophile [9,34]. Most
of these reactions are carried out in solvents that can undergo
electron transfer reactions. These electron transfer reactions can be
carried out between solvent/substrate and solvent/nucleophile
which lead to produce a number of by-products. In the present
work, by omitting the solvent, the formation of by-products was
reduced to trace yields. In contrast with the conventional methods,
the reaction rate increased because by supporting the aryl diazo-
nium salt on silica sulfuric acid, the surface area of the reaction
increased [25e28,35].
We also studied the synthesis of arylazo methanethiosulfonates
as a new derivation of arylazo sulfides (Table 1, entries 15e21). By
using the present method, different kinds of arylazo meth-
anethiosulfonates were easily synthesized in good yields and short
reaction times by treating aryl diazonium salts in the presence of
sodium methanethiosulfonate. Finally, after completion of the
reaction and isolation of the product, the solid support could be
recycled [25e28]. In addition, the present procedure for the prep-
aration of arylazo sulfides was shown to be safe and nonexplosive
because by supporting aryl diazonium salts on the surface of silica
sulfuric acid as a bulky support, the stability of these salts increased
[25,36].
Acknowledgements
We gratefully acknowledge the funding support received for this
project from the Islamic Azad University of Fasa and the Isfahan
University of Technology (IUT).
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