3024
A. Shaabani et al.
SHORT PAPER
KMnO4/MnO2
58–94%
Removal of the organic products by extraction leaves a
residue that consists primarily of manganese oxides con-
taining small amounts of potassium permanganate. Since
industrial processes for recycling and reoxidizing manga-
nese dioxide to permanganate are well established, the re-
actions are, in theory, infinitely sustainable.13 The
reactions, therefore, represent progress in the search for
methods that can be applied to make chemistry more en-
vironmentally friendly.
KMnO4
N
O
O
5–50%
KMnO4/Mn2+
49–90%
X
X = OH, NHCONH2, NHPh
Scheme 3
The yields from the reaction using finely powdered, but
unsupported, potassium permanganate are compared with
those obtained when activated manganese dioxide or
manganese(II) sulfate are added to the potassium perman-
ganate (in each case, 1.00 g of either MgSO4·H2O or
MnO2 was added to 1.00 g of KMnO4). Experimentation
also revealed that addition of a small amount of water to
the oxidant often improved yields and shortened reaction
times, as indicated by the data in Table 1.
Oxidation of Oximes and Semicarbazones; General Procedure
The five oxidants were prepared and used under identical condi-
tions. The first oxidant was prepared by grinding KMnO4 (1.00 g),
using a pestle and mortar, until a fine powder was obtained. A sec-
ond oxidant was prepared in exactly the same way with the excep-
tion that MnSO4·H2O (1.00 g) was added to the KMnO4 (1.00 g).
For the third oxidant, activated MnO2 (1.00 g) was added to finely
ground KMnO4 (1.00 g). The fourth and fifth oxidants were pre-
pared in the same way as the second and third oxidants, but with the
addition of a small amount of H2O (0.3 mg).
From consideration of these results (Table 1) and those
previously reported,10 it is apparent that finely powdered
potassium permanganate is not a satisfactory general pur-
pose oxidant for use under solvent-free conditions or in
dichloromethane. However, addition of either activated
manganese dioxide or manganese(II) sulfate markedly in-
creases the yields, especially if some moisture is present.
Although the difference is marginal for some reactions,
generally, the use of activated manganese dioxide gives
better yields.
These oxidants were placed in five separate round-bottom flasks
and to each flask was added the oxime or semicarbazone (1.0
mmol). The reactants were stirred continuously at r.t. using a mag-
netically controlled stirring bar; TLC was used to monitor the
progress of the reactions until the oxime or semicarbazone had com-
pletely reacted or until a reasonable amount of time had elapsed.
Then, CH2Cl2 (15 mL) was added to each flask and the mixtures
were filtered through a sintered glass funnel. The residues were
washed with additional CH2Cl2 (2 × 10 mL) and the solvent collect-
ed from each reaction was combined and evaporated on a flash
evaporator. The yields were determined by GC analysis or by
weight after preparation of 2,4-dinitrophenylhydrazone derivatives.
All products are known compounds and were characterized from
their well-defined 1H NMR spectra.
It was necessary to carry out the oxidative cleavage of
phenylhydrazones in dichloromethane because the reac-
tions under solvent-free conditions were so vigorous that
they often burst into flame.
Oxidation of Phenylhydrazones; General Procedure
The oxidations were completed similarly to those described above
using the first three oxidants, except that CH2Cl2 (15 mL) was added
to the oxidant before using it in the reaction with the phenylhydra-
zone.
It has been known for many years that manganese(II) ions
act as catalysts for the oxidation of certain organic com-
pounds with potassium permanganate in aqueous solu-
tions.16,17 Therefore, it is not surprising to observe that
addition of manganese(II) ions aids the oxidation of the
organic compounds described here. At this time, any sug-
gestion of the role manganese(II) plays would be highly
speculative; however, it is possible that the initial interac-
tion between potassium permanganate and manganese(II)
would be an electron transfer that results in the formation
of manganese(III) ions, which could act as a catalyst for
these reactions.18
Acknowledgment
Financial assistance from the Research Council of Shahid Beheshti
University of Iran is gratefully acknowledged.
References
(1) Green, T. W.; Wuts, P. G. Protective Groups in Organic
Synthesis, 3rd ed.; John Wiley and Sons: New York, 1991.
(2) Corsaro, A.; Chiacchio, U.; Pistara, V. Synthesis 2001, 1903.
(3) Barton, D. H. R.; Beaton, J. M. J. Am. Chem. Soc. 1961, 83,
4083.
(4) Kadzyauskas, P. P.; Zefirov, N. S. Russ. Chem. Rev. (Engl.
Transl.) 1968, 37, 543.
It is also known that manganese dioxide supported on sil-
ica gel can be used to cleave oximes.19 Hence, it is not sur-
prising that activated manganese dioxide is a good solid
support for solvent-free potassium permanganate oxida-
tions.
(5) Mukai, C.; Hanaoka, M. Synlett 1996, 11.
(6) Czekelius, C.; Carreira, E. M. Angew. Chem. Int. Ed. 2005,
44, 612.
(7) (a) Solid Supports and Catalysts in Organic Synthesis;
Smith, K., Ed.; Ellis Harwood and PTR Prentice Hall: New
York, 1992. (b) Laszlo, P. In Comprehensive Organic
Synthesis, Vol. 7; Trost, B. M., Ed.; Pergamon: New York,
1992, 893.
Potassium permanganate supported on manganese(II) sul-
fate or activated manganese dioxide can be used effective-
ly for the oxidative cleavage of oximes and
semicarbazones under solvent-free conditions and for the
cleavage of phenylhydrazones in dichloromethane. Addi-
tion of a small amount of water usually results in higher
yields and shorter reaction times.
Synthesis 2005, No. 18, 3023–3025 © Thieme Stuttgart · New York
Shaabani, Ahmad
