Thiation of heterocycles using silica gel supported P2S5 under microwave irradiation in solventless system

Article abstract of DOI:10.1081/SCC-100104819

The efficient and environmentally friendly thiation of heterocycles using P₂S₅ under microwave irradiation in solvent free condition is described.

Full text of DOI:10.1081/SCC-100104819

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THIATION OF HETEROCYCLES USING SILICA GEL
SUPPORTED P2S5 UNDER MICROWAVE IRRADIATION IN
SOLVENTLESS SYSTEM
Majid M. Heravi a , Ghadir Rajabzadeh b , Mohammad Rahimizadeh b , Mehdi Bakavoli b
Mitra Ghassemzadeh c
&
a Department of Chemistry , School of Sciences, Azzahra University , Vanak, Tehran, Iran
b Department of Chemistry , School of Sciences, Ferdowsi University of Mashad , Iran
c Chemistry & Chemical Engineering Research Center of Iran , P.O. Box 14335-186,
Tehran, Iran
Published online: 09 Nov 2006.
To cite this article: Majid M. Heravi , Ghadir Rajabzadeh , Mohammad Rahimizadeh , Mehdi Bakavoli & Mitra
Ghassemzadeh (2001) THIATION OF HETEROCYCLES USING SILICA GEL SUPPORTED P2S5 UNDER MICROWAVE IRRADIATION IN
SOLVENTLESS SYSTEM, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 31:15, 2231-2234, DOI: 10.1081/SCC-100104819
To link to this article: http://dx.doi.org/10.1081/SCC-100104819
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SYNTHETIC COMMUNICATIONS, 31(15), 2231–2234 (2001)
THIATION OF HETEROCYCLES
USING SILICA GEL SUPPORTED P2S5
UNDER MICROWAVE IRRADIATION
IN SOLVENTLESS SYSTEM
Majid M. Heravi,1, Ghadir Rajabzadeh,1
*
Mohammad Rahimizadeh,1 Mehdi Bakavoli,1
and Mitra Ghassemzadeh2
1Department of Chemistry, School of Sciences,
Ferdowsi University of Mashad, Iran
2Chemistry & Chemical Engineering Research Center of Iran,
P.O. Box 14335-186, Tehran, Iran
ABSTRACT
The efficient and environmentally friendly thiation of hetero-
cycles usingP S5 under microwave irradiation in solvent free
condition is described.
2
Carbonyl compounds have been generally been converted into thiones
1
by treatment with P2S5 in a refluxingnonpolar solvent. Scheeren and his
co-workers reported that the reaction proceeds more readily in polar sol-
vents such as acetonitrile, THF or diglyme.2 The reaction is accelerated still
further by addition of 2–6 molar equiv. of sodium bicarbonate. The reaction
* Correspondingauthor. Current address: Department of Chemistry, School of
Sciences, Azzahra University, Vanak, Tehran, Iran. E-mail: mmheravi@azzahra.
ac.ir
2231
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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HERAVI ET AL.
under these conditions proceeds at 300ꢀC and requires 3–6 hrs and the yields
of thiones are generally in the range of 50–85%.2
Thiation of heterocycles for the conversion of oxo group to thio group
provides precursors for fused heterocyclic systems.3 In these conversions
usually use of large amounts of P2S5 in toxic pyridine is required,4 the
time of reaction is longand the yields are moderate to low especially
in an scale up.5 Faced with this dilemma we explored more effective and
much faster routes for the implementation of this thiation.
Reagents impregnated on mineral supports have gained popularity
in organic synthesis because of their selectivity and ease of manipulation.6,7
Table. Thiation of Various Heterocycles UsingP 2S5 Under Microwave Irradiation
in Solventless System
*All products were known and identified by comparison with authentic samples.

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THIATION OF HETEROCYCLES
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Recently there has been a growing interest in the use of microwave
irradiation in chemical reaction enhancement.8 The solvent free reactions
under microwave irradiation can provide an opportunity to work with open
vessels, thus avoidingthe risk of hihg-pressure development and with
a possibility of carryingout the reaction on a preparative scale. 9 In connec-
tion with our interest in usingmicrowaves to increase the rates of reactions 10
we have investigated the above thiation under microwave irradiation.
Phosphorus pentasulphide (P2S5) and a weight equivalent of silica
gel (silica gel 60, particle size 0.2–0.6 mm for column chromatography)
were crushed together so as to form an intimate mixture. In a typical
reaction 2–3 equivalent of supported P2S5 was mixed with the appropriate
heterocycles with oxo group in a beaker. The beaker was exposed to micro-
wave irradiation (900 W) for the indicated time (Table). The residue was
extracted with boilingethanol, the solvent was evaporated to dryness and
the crude product was crystallized from an appropriate solvent to afford
the correspondingthio heterocycles (Table).
It is noteworthy to mention that this method is not selective for
monothiation of dicarbonyl heterocycles such as uracil and thymine.
Thiation of these heterocyclic systems under above condition gave dithio
compounds (Table).
Caution. Although we did not have accident using P2S5 in microwave
oven, for safety reasons it is advisable to perform the experiments in an
efficient hood in order to avoid contact with vapors. It is also advised to
use a tall beaker and irradiation sequence is interrupted with a 5 minutes
cooling.
REFERENCES
1. Kekule, A. LiebigAnnal. Chem. 1854, 90, 311.
2. Scheeren, J.W.; Oomas, P.H. and Nivard, R.J.F. Synthesis 1973, 149.
3. Chyi Tzang, Ch.; Motola, N.C. and Panzica, R.P. J. Org. Chem. 1983,
48, 1271 and references cited therein.
4. Mizuno, Y.; Ikehara, M. and Watanahe, K.A. Chem. Pharm. Bull.
1962, 10, 647.
5. Taylor, E.C. and Garcia, E.E. J. Org. Chem. 1964, 29, 2121.
6. McKillop, A. and Young, D.W. Synthesis 1979, 401 and 481.
7. Balogh, M. and Laszlo, P. ‘‘Organic Chemistry using Clays’’, Springer
Verlag, Berlin, 1993.
8. For recent reviews on microwave assisted chemical reactions see
a) Abramovich, R.A. Org. Prep. Proced. Int. 1991, 23, 683;
b) Caddick, S. Tetrahedron 1995, 51, 10403.

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HERAVI ET AL.
9. Varma, R.S.; Dahija, R. and Saini, R.K. Tetrahedron Lett. 1997,
38(51), 8819.
10. a) Heravi, M.M.; Kiakojoori, R. and Tabar-Hydar, K. J. Chem
Res. 1998, 656, b) Heravi, M.M.; Ajami, D. and Tabar-Hydar, K.
Synth. Commun. 1999, 21, 163, c) Heravi, M.M.; Ajami, D.;
Mojtahedi, M.M. and Ghassemzadeh, M. Tetrahedron Lett. 1999, 40,
561, d) Heravi, M.M.; Ajami, D.; Aghapoor, K. and Ghassemzadeh,
M. J. Chem. Soc., Chem. Commun. 1999, 833.
Received in Japan June 20, 2000

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