Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 6255–6257
A new, efficient and simple method for the thionation of ketones to
thioketones using P4S10/Al2O3
Vivek Polshettiwar and M. P. Kaushik*
Process Technology Development Division, Defence R&D Establishment, Jhansi Road, Gwalior 474002 (MP), India
Received 27 May 2004; revised 17 June 2004; accepted 22 June 2004
Abstract—A simple, efficient and new method has been developed for the synthesis of thioketones by thionation of ketones using
P4S10/Al2O3 in acetonitrile. It has been found that the P4S10/Al2O3 combination provides a simple and convenient method for the
synthesis of thioketones.
Ó 2004 Elsevier Ltd. All rights reserved.
Organosulfur compounds are valued not only for their
rich and varied chemistry, but also for many important
biological properties.1 Since organosulfur compounds
have become increasingly useful and important in
organic synthesis, the development of convenient and
practical methods for the preparation of thioketones is
desirable. Thioketones have been used in the pharma-
ceutical, polymer, pesticide and herbicide industries.2
Thionation, the conversion of a carbonyl group to a
thiocarbonyl group, is a commonly used procedure for
the synthesis of thioketones. Several methods are re-
ported in the literature for this transformation, which
makes use of elemental sulfur,3 P4S10,4 LawessonÕs rea-
gent5,6 and P4S10/HMDO (hexamethyldisiloxane).7–10
Thionation of ketones to thioketones can be effected
by P4S10, but typically in rather low yield.4,11 In recent
years LawessonÕs reagent (LR) and a combination of
P4S10/HMDO has replaced P4S10 as the reagent of
choice for many thionations. However, besides its high
cost, LR results in the formation of by-products derived
from the reagent itself, which cannot be easily removed
by an extractive procedure and require chromatography,
making the method more expensive. The combination of
P4S10/HMDO is good in terms of reactivity but the use
of HMDO makes the method expensive and the by-
products formed need to be removed by column chro-
matography. Despite this wide range of synthetic
methods for the conversion of ketones to thioketones,
no attempt has been made to use the readily accessi-
ble P4S10 on a solid support for the thionation of
ketones. In recent years, the use of reagents and
catalysts supported on solid supports has received
much attention. Such reagents not only simplify purifi-
cation processes but also help prevent release of reac-
tion residues into the environment. This has led to
growth in the field of solid supported reagents on
alumina.12
Herein we report a new procedure for the conversion of
ketones into thioketones using phosphorus pentasulfide
supported on alumina in acetonitrile (Scheme 1).
The reaction was carried out by refluxing a mixture of
the ketone and P4S10/Al2O3 in acetonitrile as solvent.
A series of experiments established that 0.34 mol of
P4S10/Al2O3 per mole of ketone were required to obtain
maximum yield of the thioketone. Using standard con-
ditions, the thionation of a series of ketones was exam-
ined. The carbonyl substrates were chosen to reflect a
variety of structural types. Alkyl and aryl ketones re-
acted smoothly with P4S10/Al2O3 under these reaction
conditions to produce the corresponding thioketones
in good to excellent yields. The results are summarized
in Table 1.
The catalytic role of Al2O3 was also studied by carrying
out the reaction in the absence of Al2O3 using P4S10
alone. It was found that the yield of the thioketones
using the combination of P4S10/Al2O3 were greater
than those with P4S10 alone. The beneficial effect of
Keywords: P4S10/Al2O3; Thionation; Thioketones.
*
Corresponding author. Tel.: +91-751-2343972; fax: +91-751-
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.06.091