Abstract:
Octahedral MnO2 molecular sieve (OMS) was prepared
using a hydrothermal synthesis route in the absence and the presence of
urea. OMS was also prepared by a solvent-free method. Catalysts were
characterized by the complementary combination of X-ray diffraction, N2
adsorption, scanning electron microscopy, UV−visible spectroscopy,
thermogravimetric analysis, and NH3 and CO2 temperature-programmed
desorption techniques. Catalysts were investigated in the oxidation of benzyl
alcohols, hydration of aromatic/heterocyclic nitrile, and condensation
reactions (Knoevenagel and Aldol). Furthermore, applicability of the
catalyst was extended in one-pot tandem conversion of benzyl alcohol to 2-
benzylidene-malononitrile, (E)-chalcone, and 2,3-dihydro-1,5-benzothiazepine.
2-Benzylidene-malononitrile and (E)-chalcone were prepared by a
two-step tandem reaction from benzyl alcohol, whereas 2,3-dihydro-1,5-
benzothiazepine was prepared by a three-step tandem reaction from benzyl alcohol. Recycling study showed that no significant
decrease in the catalytic activity was observed even after five recycles. To the best of our knowledge, this is the first report that
shows that OMS materials obtained using different synthesis methods exhibited significant differences in their catalytic activity in
the above-mentioned reactions
