Potassium permanganate is prepared from pyrolusite (MnO₂). Pyrolusite is fused with KOH in the presence of atmospheric oxygen or an oxidising agent like potassium nitrate or potassium chlorate to give potassium manganate, K₂MnO₄.
                                         
 

The green mass is taken out with water and oxidized to potassium permanganate, electrolytically or by passing chlorine or ozone into solution.

Electrolytic oxidation
                                                    
K₂MnO₄    2K⁺ + MnO₄^2-
                                                          
H₂O    H⁺ + OH^-

During electrolysis manganate ions are oxidized to permanganate at anode

 

At cathode hydrogen gas is liberated
                                              
2H₂O + 2e^-    H₂ + 2OH^-

Oxidation by chlorine
                                         
2K₂MnO₄ + Cl₂    2KMnO₄ + 2KCl
                                    
Or, 2MnO₄^2- + Cl₂    2MnO₄^- + 2Cl

Oxidation by ozone
                              
2K₂MnO₄ + O₃ + H₂O    2KMnO₄ + 2KOH + O₂
                         
Or, 2MnO₄^2- + O₃ + H₂O    2MnO₄^2- + 2OH^- + O₂

As a result of oxidation, the green colour of solution changes into purple. The purple solution containing KMnO₄ is concentrated by evaporation which on cooling gives crystals of KMnO₄.

The manganate (MnO₄^2-) and permanganate (MnO^2-) ions are tetrahedral in shape. The manganate is paramagnetic with one unpaired electron but the permanganate is diamagnetic.

The π-bonding takes place by overlie of p-orbitals of oxygen with d-orbitals of manganese. 

Properties 

Potassium permanganate is violet crystalline solid having m.p. 523 K. it is soluble in water and its aqueous solution is purple in colour.
    
Result of heat: on heating, potassium permanganate changes into manganate and oxygen gas is evolved.
                                              
2KMnO₄    K2MnO₄ + MnO₂ + O₂
    
Effect of alkalies: on heating with alkalies, potassium permanganate converts into manganate and oxygen gas is evolved.
                                
4KMnO₄ + 4KOH    4K₂MnO₄ + 2H₂O + O₂
    
Oxidising properties: KMnO₄ acts as a very powerful oxidising agent in acidic, neutral and alkaline media. The equations representing oxidation in these media are given below:

In acidic medium
                              
2KMnO₄ + 3H₂SO₄    K₂SO₄ + 2MnSO₄ + 3H₂O + 5[O]
                        
Or, MnO₄^- + 8H⁺ + 5e^-    Mn²⁺ + 4H₂O [   = + 1.52 V]

In neutral or alkaline medium
                                    
2KMnO₄ + H₂O    2KOH + 2MnO₂ + 3[O]
                      
Or, MnO₄^- + 2H₂O + 3e^-    MnO₂ + 4OH_- [   = + 1.23 V]