There is an increasing need as well as interest in developing some processes that
minimize production of toxic waste due to environmental
concerns. In this context,
the combination of supported reagents and microwave irradiation without solvent
has proved to be of prime importance in synthetic organic chemistry with a wide
range of reactions in short times, high conversion and selectivity. However, some of
these reagents and catalysts have limitations like availability of the reagent, difficult
work-up, longer reaction time, toxicity and high cost of the reagents. Thus, Hashemi
et al. (2005) used iodic acid as an oxidant, which is milder and more selective
with moderate oxidizing power in aqueous acidic medium and has lower toxicity to
humans.
where R and R' = H, Aryl, Heteroaryl.
They carried out oxidation of benzyl alcohol successfully by using montmorillonite
K10 and silica gel supported
iodic acid under microwave irradiation without
solvent and that too with simplicity of performance and with high yield (92%).
Rajabi et al. (2013) also used supported iron oxide nanoparticles on aluminosilicate
catalyst as efficient and easily recoverable material in the aqueous selective
oxidation of alcohols to their corresponding carbonyl compounds using hydrogen
peroxide under both; conventional and microwave heating. This procedure also has
an easy work-up, simplicity and the utilization of mild reaction conditions as well
as high selectivity toward aldehydes. In addition, the supported iron oxide nanoparticles
could be easily recovered from the reaction mixture and reused several times
without any loss in activity.
A remarkable decrease in reaction time from 4 h to 15 min with 98% yield in
presence of microwave irradiation has been reported without any significant loss of
activity and metal leaching.
The solvent-free potassium permanganate promoted oxidation of alcohols into
the corresponding carbonyl derivatives has been examined by Luu et al. (2008).
Secondary alcohols were oxidized very efficiently to the corresponding ketones at
ambient temperature by KMnO4 absorbed on a fourfold molar amount of copper (II)
sulfate pentahydrate. The reaction rate was enhanced considerably by ultrasonic irradiation
also, but drastically in the presence of microwave irradiation, may be due