Wet Silica -Su p p or ted P er m a n ga n a te for
th e Clea va ge of Sem ica r ba zon es a n d
P h en ylh yd r a zon es u n d er Solven t-F r ee
Con d ition s
changes the selectivity and reactivity in various reac-
tions.11 We previously reported potassium permanganate
supported on alumina for the oxidation of urazoles to
1
2a
triazolinediones, oxidation of alcohols to aldehydes and
ketones under solvent-free conditions,1 oxidation of
2b
1
2c
sulfides and thiols to sulfoxides and disulfides,
the
Abdol R. Hajipour,*,†,‡ Hadi Adibi, and
†
Arnold E. Ruoho‡
oxidative deprotection of trimethylsilyl and tetrahydro-
pyranyl ethers and of ethylene acetals to the correspond-
Pharmaceutical Research Laboratory, College of Chemistry,
Isfahan University of Technology, Isfahan 84156, Iran, and
Department of Pharmacology, University of Wisconsin,
Medical School, 1300 University Avenue, Madison,
Wisconsin 53706-1532
12d
ing carbonyl compounds, and conversion of oximes to
12e
carbonyl compounds under solid-state conditions. There
has also been increasing interest in reactions that
proceed in the absence of solvent.1
3,14
We now report
potassium permanganate supported on wet silica gel as
an inexpensive, selective, and efficient reagent for the
oxidative cleavage of semicarbazones 1a -q and phenyl-
hydrazones 1r -y to the corresponding carbonyl com-
pounds 2a -y under solvent-free conditions.
Received February 19, 2003
Abstr a ct: Wet silica-supported potassium permanganate
was used as an inexpensive and efficient reagent for conver-
sion of semicarbazones and phenylhydrazones to the corre-
sponding carbonyl compounds under solid-state conditions.
The oxidative cleavage of 3-methoxybenzaldehyde semi-
carbazone 1d as a model compound with potassium
permanganate failed in the absence of the supporting
agent, even upon grinding for a prolonged period of time.
The reaction carried out in the presence of dry alumina
and silica gel indicated that wet silica gel is the most
effective. Dry silica gel required longer time and gave
lower yield (60%) whereas the yield of 2d increased to
91% in the presence of premoistened reagent. The
optimum molar ratio of substrate to oxidant (1:3) was
determined for complete conversion of semicarbazones
1a -q and phenylhydrazones 1r -y to the corresponding
carbonyl compounds 2a -y while the reaction was incom-
plete with lesser amounts of reagent (i.e., 1:1, 1:2, and
1:2.5). The mechanism of the reaction and the role of wet
silica gel are not clear for us at this stage.
Hydrazine derivatives of carbonyl compounds are
highly crystalline and are used for the characterization
and purification of carbonyl compounds.1 Since, the
regeneration of carbonyl compounds under mild condi-
tions is important, extensive studies on the cleavage of
these derivatives to the parent carbonyl compounds have
2
-8
been carried out.
Over the last 2 decades, the use of solid supports has
become popular due to their characteristic properties
such as enhanced selectivity and reactivity, straightfor-
ward workup procedure, milder reaction conditions, and
9
associated ease of manipulation. Adsorption of potas-
In this method, oxidative cleavage is achieved by
grinding a mixture of semicarbazones 1a -q or phenyl-
hydrazones 1r -y (1 mmol) and potassium permanganate
sium permanganate10 on the surface of solid supports
*
To whom correspondence should be addressed. Fax: +98(0311)-
(3 mmol) supported on wet silica gel (3 g) in a mortar
3
912350.
†
with a pestle under solvent-free conditions at room
temperature. The reaction time is usually short (15-45
min) and isolation of product is straightforward (Table
Isfahan University of Technology.
University of Wisconsin, Medical School.
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(
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(
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1
(
(
1
0.1021/jo034217y CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/02/2003
J . Org. Chem. 2003, 68, 4553-4555
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