Solvent free oxidation of alcohols with manganese dioxide

Article abstract of DOI:10.1016/S0040-4039(02)01345-X

The oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones by manganese dioxide under solvent free conditions are described. This new oxidation procedure is very simple and affords good yields.

Full text of DOI:10.1016/S0040-4039(02)01345-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 6149–6150
Solvent free oxidation of alcohols with manganese dioxide
Ji-Dong Loua,* and Zhi-Nan Xub
aInstitute of Chemical and Biological Technology, New University of Lisbon, 2780 Oeiras, Portugal
bDepartment of Chemical Engineering and Bioengineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
Received 10 June 2002; accepted 2 July 2002
Abstract—The oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones by manganese dioxide
under solvent free conditions are described. This new oxidation procedure is very simple and affords good yields. © 2002 Elsevier
Science Ltd. All rights reserved.
The oxidation of primary and secondary alcohols to the
corresponding aldehydes and ketones is a fundamental
reaction that is encountered at all levels of organic
synthesis. Manganese dioxide (MnO2) is a useful selective
oxidising reagent that is available for carrying out this
transformation. For instance, the corresponding alde-
hydes or ketones can be obtained with MnO2 by oxidation
of allylic alcohols in petroleum ether, hexane, acetone or
chloroform,1–4 of propargylic alcohols in dichloro-
methane,5–7 of benzylic or heterocyclic alcohols in chlo-
roform, dioxane or acetone,8–10 of saturated alcohols in
petroleum ether or acetonitrile,11 and by oxidative cleav-
age of 1,2-diols in dichloromethane.12
As a part of our program related to developing new
oxidation methods15–22 we wish to report here a new,
simple, and general procedure that can be used for the
oxidative transformation of primary and secondary alco-
hols into the corresponding aldehydes and ketones using
an inexpensive and environmentally friendly oxidant,
MnO2, under solvent free conditions. Solvent free reac-
tions are of general interest because of their potential
applications in combinatorial chemistry.
Active MnO2 is prepared from potassium permanganate
(KMnO4) under basic conditions according to the liter-
ature.23 The amount of active MnO2 required to perform
the oxidation of an alcohol substrate depends on the type
of MnO2 and on the substrate. In our cases, the ratio of
MnO2 to substrate is 10 to 1 by weight. The oxidation
is very simple: the oxidant is added to the substrate in
a flask in one portion and the mixture is stirred magnet-
ically at room temperature until TLC analysis indicates
a completed reaction. The residue is then washed with a
minimum amount of solvent such as dichloromethane or
diethyl ether. Distillation of the solvent gives a product
that is of acceptable purity for most purposes. The results,
which are shown in Table 1, show that the method is
generally applicable to a range of alcohols, and gives the
corresponding aldehydes and ketones in good yields.
Meantime, we have observed that unactivated alcohols
such as 1-hexanol or 1-octyl alcohol are not efficiently
oxidised under these conditions.
It is well known that the oxidation of organic compounds
with MnO2 has been performed in many solvents. The
choice of the solvents is important. Thus primary or
secondary alcohols (or water) are unsatisfactory since
they can compete with the substrate being adsorbed on
the MnO2 surface and they have a strong deactivating
effect.13 A similar but less pronounced influence has also
beenobservedwithvariouspolarsolventssuchasacetone,
ethyl acetate, DMF, and DMSO. However, these polar
solvents, including water,14 acetic acid, and pyridine,
should be used at higher temperatures. This deactivating
influence due to the polarity of the solvent can be used
to control the reactivity of active MnO2 and sometimes
to avoid side reactions or to improve the selectivity. In
general, most of the reactions described in the literature
are carried out in aliphatic or aromatic hydrocarbons,
chlorinated hydrocarbons, diethyl ether, THF, ethyl
acetate, acetone, and acetonitrile.
In summary, solvent free oxidation using MnO2 as an
oxidant is a new and efficient method for the oxidation
of primary and secondary alcohols.24
Acknowledgements
Keywords: oxidation; alcohols; aldehydes; ketones; manganese diox-
ide; solvent free.
We thank Professor Christopher D. Maycock for helpful
suggestions and carefully reading the manuscript.
* Corresponding author. Fax: +351-21-44-03-609; e-mail: lou@
itqb.unl.pt
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01345-X

6150
J.-D. Lou, Z.-N. Xu / Tetrahedron Letters 43 (2002) 6149–6150
Table 1. Solvent free manganese dioxide oxidations
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