Preparation of Potassium permanganate (KMnO4)

Pottassium Permanganate (KMnO4) is prepared from Pyrolusite ore (MnO2). The finely powdered Pyrolusite ore (MnO2) is fused with an alkali metal hydroxide like KOH in the presence of air or an oxidizing agent like KNO3 to give the dark green potassium Manganate (K2MnO4). Potassium manganate disproportionate in a neutral or acidic solution to give potassium permanganate.

2 MnO2 + 4 KOH + O2 ----------> 2K2MnO4 + 2H2O

3 MnO42- + 4H+ ------------> 2MnO4- + MnO2 + 2H2O

Commercially potassium permanganate is prepared by the alkaline oxidative fusion of Pyrolusite ore (MnO2) followed by the electrolytic oxidation of manganate (4) ion.

2 MnO2 + 4KOH + O2 -----------> 2K2MnO4 + 2H2O

MnO42- ------(electrolytic oxidation)----> MnO4- + e-


Potassium permanganate forms dark purple (almost black) crystals, which are iso structural with those of KCLO4. It has weak temperature dependent paramagnetism. the manganate and permanganate ions are tetrahedral. The green manganate is paramagnetic with one unpaired electron but the permanganate is diamagnetic. The pie-bonding takes place by overlaping of P orbitals of oxygen with d orbitals of manganese.

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