Microwave induced synthesis of diphenylthiophenes from elemental sulfur and styrene [3]

Full text of DOI:10.1007/s10593-006-0268-y

Chemistry of Heterocyclic Compounds, Vol. 42, No. 11, 2006
MICROWAVE INDUCED SYNTHESIS
OF DIPHENYLTHIOPHENES FROM
ELEMENTAL SULFUR AND STYRENE
S. V. Yas'ko, N. A. Korchevin, N. K. Gusarova, T. I. Kazantseva,
N. A. Chernysheva, L. V. Klyba, and B. A. Trofimov
Keywords: 2,4- and 2,5-diphenylthiophenes, styrene, elemental sulphur, microwave irradiation.
Thiophene and its substituted derivatives (particularly diphenylthiophenes) find a wide practical use and
they continue to attract the attention of investigators as building blocks for organic synthesis [1-3]. One of the
routes to the synthesis of diphenylthiophenes is the reaction of elemental sulfur with styrene. Unfortunately this
is unselective and heating elemental sulfur with styrene (140-230°C) forms a complex mixture of acyclic and
cyclic (2,4-diphenylthiophene, 2,4-diphenylthiophane, 2,5-diphenyl-1,4-dithiane, 2,5-diphenyl-2,3-dehydrothiane)
products among which rubber like polysulfide oligomers and polymers predominate [4-6]. Increasing the
selectivity of the synthesis of diphenylthiophenes from styrene and elemental sulfur remains an unresolved problem.
We have found that styrene reacts with elemental sulfur in the strongly basic medium KOH-DMSO [7]
in the presence of hydroquinone under microwave irradiation (600 watts, 4 min) to form a 1: 12 mixture of 2,4-
and 2,5-diphenylthiophenes 1a,b in overall 30% yield (not optimized).
Ph
∆
+
S
8
Ph
+
KOH/DMSO
Ph
S
Ph
Ph
S
1
a
1b
The diphenylthiophenes are not formed when the elemental sulfur and styrene are heated (85-90°C, 6 h)
in the system KOH-DMSO-hydroquinone in the absence of the microwave irradiation and the unreacted styrene
is recovered.
In the absence of the hydroquinone the reaction is less selective. Along with the thiophenes 1a,b GC-MS
analysis of the reaction mixture shows the presence of bis(2-phenylethyl) sulfide, bis(2-phenylethyl) disulfide,
1
,4-diphenylbuta-1,3-diene, and 1,3,5-triphenylbenzene.
_
*
______
th
Dedicated to Academician M. G. Voronkov, Russian Academy of Sciences in his 85 year.
_
_________________________________________________________________________________________
A. E. Favorsky Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk 664033,
e mail: gusarova@irioch.irk.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1728-1729,
November, 2006. Original article submitted August 22, 2006.
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0009-3122/06/4210-1368©2006 Springer Science+Business Media, Inc.

Hence microwave irradiation in the reaction of styrene with elemental sulfur opens up a novel route to
the synthesis of 2,5-diphenylthiophene. The preparative possibilities of this reaction are under investigation.
1
3
H NMR spectra were recorded on a Bruker DPX 400 (400 MHz) instrument using CDCl and with
HMDS as internal standard. Mass spectra were taken on a Hewlett-Packard HP-5971A instrument (EI, 70 eV). A
domestic Samsung 181 DNR microwave oven was used for the microwave irradiation.
2
,4- and 2,5-Diphenylthiophenes. A mixture of styrene (2.08 g, 20 mmol), elemental sulfur (0.8 g,
5 mmol), hydroquinone (0.02 g, about 1% of the styrene), KOH (2.8 g, 50 mmol), water (0.5 ml), and DMSO
20 ml) was irradiated in the microwave oven (600 watts power, 4 min). The reaction mixture was cooled,
2
(
diluted with about 20 ml of water, and extracted with benzene (5 × 15 ml). The benzene extracts were washed
with water and dried with potassium carbonate. Benzene was removed at reduced pressure and the residue was
dried in vacuo to give the diphenylthiophenes 1a,b in the ratio 1: 12 (GC-MS) as yellow crystals soluble in
benzene dioxane, and ether. Found, %: C 80.98; H 5.27; S 13.60. C H S. Calculated, %: C 81.32; H 5.12;
1
6
12
S 13.57.
+
2
,4-Diphenylthiophene (1a). Mass spectrum, m/z (I , %): 236 [M] (100), 191 (14), 165 (5), 134 (5),
rel
1
21 (9), 105 (2), 89 (6), 77 (7), 63 (10), 51 (7), 39(7).
+
2
,5-Diphenylthiophene (1b). Mass spectrum, m/z (I , %): 236 [M] (100), 202 (10), 189 (5), 134 (7),
rel
1
1
21 (19), 115 (8), 101 (6), 89 (6), 77 (11), 63 (6), 51 (8), 39 (5). H NMR swpectrum, δ, ppm (J, Hz): 7.31 (2H,
s, H-3(4)); 7.33-7.38 (4H, m, m-C H ); 7.43-7.46 (4H, m, o-C H ), 7.65-7.69 (2H, m, p-C H ).
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5
6
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The work was carried out with state support for leading science schools (grant NSh-5444.2006.3) and
the Russian Fund for Basic Research (grant 05-03-32859).
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