It is worthy of note that the percentage water content strongly influences both the oxidizing power and the selectivity (oxidation of multifunctional
molecules) of active MnO2.
Thus it is well known that the wet material (40â60% H2O) obtained after filtration must be activated by drying (heating to 100â130 âŚC
for 12â24 hours or, better at 125 C for 52 hours ).
Indeed, an excess of water decreases the oxidation power since, according tthe triphasic mechanism generally postulated it would prevent the
adsorption of the substrate to the oxidatively active polar site on the surface of MnO2.
On the other hand, it is very important not to go past the point of complete activation since the presence of hydrated MnO2 species is essential to
obtain an active reagent. For this reason, the drying conditions must be carefully controlled. Alternatively, the wet material can be activated by
azeotropic distillation since this mild procedure preserves the active hydrated species. Thus azeotropic distillation has been used to remove the
water produced during the oxidation reaction to follow the rate of MnO2 oxidations.
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