320 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
Regeneration of Ketones from Semicarbazones in
the Solid State on Wet Silica Supported Sodium
Bismuthate under Microwave Irradiationy
Alok Kumar Mitra,* Aparna De and Nilay Karchaudhuri
1
999, 320^321y
Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road,
Calcutta^700 009, India
Microwave irradiation of ketosemicarbazones on wet silica supported sodium bismuthate under environmentally
benign solvent-free condition provides a fast, efficient and simple method for regeneration of ketones in good yields.
Protection of carbonyl compounds as semicarbazones is of
great interest to organic chemists as they are readily prepared
and highly stable compounds. Semicarbazones are exten-
support. The dry reagent decomposes under microwave
irradiation. Using conventional heating (oil bath) at 110 8C,
the reaction is incomplete even after 24 h.
1
sively used for puri¢cation and characterisation of carbonyl
compounds. Although a number of methods for the regen-
eration of carbonyl compounds from semicarbazones have
2
R1
R1
Wet NaBiO3-silica
microwave
C
R2
NNHCONH2
C
R2
O
3
a
been reported, viz. sodium nitrite/glacial acetic acid,
3
b
pyruvic acid,
lead(iv) acetate,
tetrakis(pyridine)silver
mercury(ii) acetate, thallium(iii) acetate,
3c
3d
3e
3f
Scheme 1
clayfen,
dichromate/benzene,
3-carboxypyridinium chlorochromate/MeCN
nitrous acid,
Dowex-50,
3g
copper
The reagent has wide applicability for regeneration of
ketones from aliphatic and aromatic ketosemicarbazones
and disemicarbazones of diketones. However, semicarbazones
of aldehydes under similar reaction conditions gave a
complex mixture of products.
3h
3i
chloride,
3j
and zirconium sulfophenyl phosphonate, the discovery of
new e¤cient and fast methods is the goal of the organic
chemists. Very recently a number of other reagents, viz.
4
a
4b
ammonium persulphate^Al2O3,
bismuth trichloride,
4
c
4d
sodium periodate^SiO2 and hypervalent iodine have been
successfully utilised for deprotection of semicarbazones,
phenylhydrazones, hydrazones, tosylhydrazones and oximes.
Currently, the growing interest in the application of
Experimental
IR spectra were run on Perkin-Elmer 782 spectrometer. 1H NMR
spectra were recorded in CDCl3 solution on a Bruker AM 300L
NMR spectrometer operating at 300 MHz using tetramethylsilane
as the internal standard. The reactions were carried out in a domestic
microwave oven (BPL-SANYO, BMO-700T, 1200 W).
5
microwave irradiation in chemical reaction enhancement
is due to high reaction rates and formation of cleaner pro-
6
ducts. The solvent-free reaction condition is especially
General Procedure.öThe reagent was prepared by adding silica gel
(20 g, 230^400 mesh, SRL) to a stirred solution of NaBiO3 (6.5 g,
3.2 mmol) in water (30 ml). After removal of water under reduced
pressure, the dry reagent (2.28 g, 2 mmol) was moistened with water
0.5 ml) and was mixed with the neat ketosemicarbazone (1mmol)
in a 25 ml Erlenmeyer £ask. It was then placed in an alumina bath
heat sink) inside a domestic microwave oven operating at medium
appealing for providing an environmentally benign system.
Herein we report a solid state method for regeneration of
ketones from semicarbazones using sodium bismuthate
supported on wet silica under microwave irradiation (Scheme
2
(
7
1). The reaction proceeds e¤ciently in good yields at ambient
(
pressure within a few minutes (Table 1). To the best of our
knowledge, this is the ¢rst report of the regeneration of
ketones from semicarbazones using sodium bismuthate.
Among several mineral supports examined, silica was found
to give best results. The optimum molar ratio of the substrate
to the reagent is found to be 1: 2. The reaction remains
incomplete when lower amounts of the reagent are used
or if the reaction was performed in the absence of silica
power (600 W) for a speci¢ed time (Table 1). After completion of
the reaction (monitored by TLC), the product was extracted with dic-
hloromethane (3 Â 10ml). All the products obtained were character-
1
ised by H NMR spectroscopy and by comparison with IR
spectra of authentic samples.
In conclusion, we have developed a solvent-free method for
the facile cleavage of a variety of ketosemicarbazones in the
solid state on wet silica supported sodium bismuthate.
Ta b l e 1 Microwave-assisted regeneration of ketones from semicarbazones using wet silica supported sodium bismuthate
a
Entry
Semicarbazone
Product
t/min
Yield (%)
1
2
3
4
5
6
7
8
9
Isobutyl methyl ketone semicarbazone
Cyclohexanone semicarbazone
Acetophenone semicarbazone
4-Methylacetophenone semicarbazone
4-Methoxyacetophenone semicarbazone
4-Nitroacetophenone semicarbazone
2-Hydroxyacetophenone semicarbazone
6-Methoxytetralone semicarbazone
2-Acetylnaphthalene semicarbazone
Benzil disemicarbazone
Isobutyl methyl ketone
Cyclohexanone
Acetophenone
4-Methylacetophenone
4-Methoxyacetophenone
4-Nitroacetophenone
2-Hydroxyacetophenone
6-Methoxytetralone
2-Acetylnaphthalene
Benzil
6
8
6
6
4
2
4
8
5
5
73
72
76
74
83
84
76
73
79
85
1
0
a
Yields refer to pure isolated products.
*
To receive any correspondence ( e-mail: akmitra@cucc.ernet.in).
We are grateful to the CSIR, the UGC, New Delhi and the
University of Calcutta for providing ¢nancial support for this
work.
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
Mitra, Alok Kumar
