J.-D. Lou et al.
almost all of the described procedures are performed under heterogeneous condi-
tions, or are assisted by microwave irradiation.
Recently, considerable attention has been paid to solvent-free reactions [5]. They
are not only of interest from ecological point of view, but in many cases also offer
considerable synthetic advantages in terms of yield, selectivity, and simplicity of
the procedure. These factors are especially important in industry. Therefore, some
of the traditional organic synthesis methods, which have long been carried out in
solvents, may be modified to more modern, elegant, and safe versions.
Results and Discussion
We have described a new reagent, potassium permanganate supported on alumi-
num silicate, for the heterogeneous selective oxidation of alcohols [6]. In connec-
tion with this recent work [6] we now report here a novel and selective oxidation of
primary and secondary alcohols to the corresponding aldehydes and ketones using
this supported reagent under solvent-free conditions and shaking at room tempera-
ture without microwave irradiation (Scheme 1). A shaking machine is employed
for this reaction. We find that shaking is much more effective than using a stirrer
for this kind of solvent-free reactions. Some previous methods needed heat, but in
the present work heating is unnecessary and the reaction times are quite reduced.
The present method has manipulative advantages over previous heterogeneous
oxidations [6], e.g., the yields of the products are higher, the reaction conditions are
milder, and the work-up is easier. In addition, for selective oxidation testing, some
more sensitive functionalised substrates were investigated without causing any
problems (see Table 1). Furthermore, the important benefit of the present method
is that it needs no microwave irradiation, an extra energy. On the other hand, owing
to the reaction under solvent-free conditions, combustion, toxicity, and environ-
mental pollution of the solvents are reduced.
In the present procedure, the oxidant is first carefully added to the substrate and
then the mixture is shaken mechanically at room temperature. The progress of the
reaction is monitored by TLC. In general, the oxidations are completed within
60 min. The residue is then washed with dichloromethane or diethyl ether. Purifi-
cation of the residue gives a product that is of acceptable purity for most pur-
poses. As can be seen in Table 1, this method is generally applicable to a range
of alcohols, and gives the corresponding aldehydes and ketones in good yields.
Therefore, it compares favourably with some traditional KMnO -based oxidation
4
methods [2].
In conclusion, solvent free oxidation of primary and secondary alcohols using
KMnO supported on aluminum silicate at room temperature by shaking is a new
4
and efficient method for the preparation of the corresponding aldehydes and
ketones.
Scheme 1