Potassium permanganate can be prepared from pyrolusite `(MnO_(2))`. The ore is fused with KOH in the presence of either atmospheric oxygen or an oxidising agent, such as `KNO_(3)` or `KClO_(4)`, to give `K_(2)MnO_(4)`.
`{:(2MnO_(2)+4KOH+O_(2) overset(heat)rarr 2K_(2)MnO_(4)+H_(2)O),(" "("Green")):}`
The green mass can be extracted with water and then oxidized either electrolytically or by passing chlorine/ozone into the solution.
Electrolytic oxidation
`K_(2)MnO_(4) harr 2K^(+)+MnO_(4)^(2-)`
`H_(2)O harr H^(+)+OH^(-)`
At anode, manganate ions are oxidized to permanganate ions.
`underset("Green"" ""Purple")(MnO_(4)^(-) harr MnO_(4)^(-)+e^(-))`
Oxidation by chlorine `2K_(2)MnO_(4)+Cl_(2)rarr 2KMnO_(4)+2KCl`
`2MnO_(4)^(2-)+Cl_(2)rarr 2MnO_(4)^(-)+2Cl^(-)`
Oxidation by ozone
`2K_(2)MnO_(4)+O_(3)+H_(2)O rarr 2KMnO_(4)+2KOH+O_(2)`
`2MnO_(4)^(-)+O_(3)+H_(2)O rarr 2MnO_(4)^(2-)+2OH^(-)+O_(2)`
(i) Acidified KMnO4 solution oxidizes Fe (II) ions to Fe (III) ions i.e., ferrous ions to ferric ions.
`(({:(MnO_(4)^(-)+8H^(+)+5e^(-) rarr Mn^(2+)+4H_(2)O),(" "Fe^(2+) rarr Fe^(3+)+e^(-)xx5):})/(MnO_(4)^(-)+5Fe^(2+)+8H^(+) rarr Mn^(2+)+5Fe^(3+)+4H_(2)O))/`
(ii) Acidified potassium permanganate oxidizes SO2 to sulphuric acid.
`{:(MnO_(4)^(-)+6H^(+)+5e^(-) rarrMn^(2+)+3H_(2)Oxx2),(2H_(2)O+2SO_(2)+O_(2) rarr 4H^(+)+2SO_(4)^(2)+2e^(-)xx5):}/(underline(2MnO_(4)^(-)+10SO_(2)+5O_(2)+4H_(2)O rarr 2Mn^(2+)+10SO_(4)^(2-)+8H^(+)))`
(iii) Acidified potassium permanganate oxidizes oxalic acid to carbon dioxide.
`(({:(MnO_(4)^(-)+8H^(+)+5e^(-) rarr Mn^(2+)+4H_(2)Oxx2),(" "C_(2)O_(4)^(2-) rarr 2CO_(2)+2e^(-)xx5):})/(2MnO_(4)^(-)+5C_(2)O_(4)^(2-)+16H^(+) rarr 2Mn^(2+)+10CO_(2)+8H_(2)O))/`
