PAPER
939
A Novel Method. The Synthesis of Ketones and Azobenzenes Using Supported
Permanganate1
Nazih A. Noureldin,* Jody W. Bellegarde
Department of Chemistry, University of Regina, Regina, SK, Canada, S4S 0A2
Fax +1(306)5851289; E-mail: noureldn@meena.cc.uregina.ca
Received 3 December 1998
copper(II) sulfate pentahydrate is used as the oxidizing re-
Abstract: The heterogeneous use of potassium permanganate, sup-
agent.
ported on copper(II) sulfate pentahydrate, provides a simple and ef-
fective means for oxidizing amines. Primary aliphatic amines, such
as sec-butylamine, are oxidized to the corresponding carbonyl com-
pounds in good to excellent yields. Primary aromatic amines, such
as 4-chloroaniline, are converted quantitatively into the correspond-
ing azo compounds. Carbon–carbon bond cleavage, which usually
occurs when alkylbenzene side chains are oxidized by perman-
ganate under homogeneous conditions, does not occur. Under ap-
propriate reaction conditions carbon–hydrogen bond cleavage at the
benzylic position, known to occur under heterogeneous permanga-
nate conditions, is also eliminated. For example, a quantitative yield
of bis(2,4,6-trimethylphenyl)diazene is obtained from the oxidation
of 2,4,6-trimethylaniline using small amounts of permanganate and
copper(II) sulfate pentahydrate.
The products obtained from the heterogeneous oxidation
of primary aliphatic and aromatic amines by permangan-
ate are similar to those that have been reported for homo-
geneous permanganate oxidations. Rawalay and Shechter,
for example, have reported that cyclohexylamine is con-
verted into cyclohexanone in 75% yield when treated with
permanganate in an aqueous solution of tert-butyl alco-
hol.13 Similarly, Johnson and Hornstein undertook an in-
vestigation into the homogeneous ferrate oxidation of
aniline and its para-substituted analogues.14 Although the
focal point was exclusively of a kinetic nature, the report
revealed an important discovery; conversion of aryl-
amines either nitro- or azo compounds could be achieved
dependent upon the pH of the reaction medium. There-
fore, it is apparent that the use of heterogeneous condi-
tions does not result in the formation of new or
unexpected products when primary aliphatic and aromatic
amines are oxidized. In this respect, it is not similar to the
oxidation of other substrates, such as thiols, where differ-
ent products are obtained under heterogeneous7 and ho-
mogeneous conditions.15 The value of the heterogeneous
procedure is nevertheless very obvious; better yields,
milder conditions and the products are more easily isolat-
ed. In a typical procedure for the work that is represented
here, a solution of the amine in dichloromethane is added
to potassium permanganate, adsorbed onto hydrated cop-
per(II) sulfate, and the reaction takes place with stirring at
room temperature or under reflux. After a designated pe-
riod, typically 24 h, the isolation of products in quantita-
tive yields is easily achieved by filtration and flash
evaporation of solvent.
Key words: heterogeneous permanganate oxidation, amines, cop-
per(II) sulfate pentahydrate, ketones, azobenzenes
The last three decades have witnessed the development
and utilization of heterogeneous reactions in synthetic or-
ganic chemistry. For example, it has been documented
that permanganate can be used effectively as a selective
heterogeneous oxidant in organic solvents, such as dichlo-
romethane, if it is adsorbed onto a hydrated metal cation.2
To obtain high yields while employing a simple, straight-
forward experimental procedure, one may consider the
use of heterogeneous reactions. In fact, the literature con-
tains descriptions of the products that are obtained from
heterogeneous permanganate oxidations of numerous
classes of compounds such as alcohols,3–5 sulfides and se-
lenides,6 thiols,7 enamines8 and arenes.9,10
Previous reports have indicated that the heterogeneous
use of permanganate dramatically modifies its selectivity.
This is apparent, for example, from the comparative ox-
idations of arenes; in homogeneous solutions degradation
of the side chain occurs resulting in the formation of benz-
oic acid derivatives.11 However, under heterogeneous
conditions permanganate is a milder reagent that oxidizes
side chains at the benzylic positions without carbon–
carbon bond cleavage; ketones and alcohols are obtained
in good yields when the side chains are secondary or ter-
tiary, respectively.12
Similarly, it has been reported that dihaloazobenzenes
were obtained from the heterogeneous permanganate oxi-
dation of haloanilines; however, no yields were reported
and the oxidation of other aniline derivatives was not at-
tempted.16 Furthermore, in a somewhat similar reaction,
haloanilines are oxidatively coupled by bis(2,2-bipy-
ridyl)copper(II) permanganate to give the corresponding
azo compounds in moderate yields.17 Although both ex-
perimental methods are similar, the use of supported per-
manganate offers several practical advantages; better
yields, simpler experimental procedure, and the utiliza-
tion of commercially available oxidant that is safe to han-
dle. On the other hand, the bipyridyl reagent has to be
prepared and is extremely sensitive to sintered glass and
In this paper, we would like to describe a method for the
oxidation of primary aliphatic and aromatic amines while
emphasizing the remarkable advantage of using heteroge-
neous over homogeneous oxidation reactions in particu-
lar, when potassium permanganate adsorbed onto
Synthesis 1999, No. 6, 939–942 ISSN 0039-7881 © Thieme Stuttgart · New York