This produces the
dark green K2MnO4 which disproportionates in a neutral or acidic
solution to give permanganate 2MnO2 + 4KOH + O2 ® 2K2MnO4 + 2H2O
3MnO4
2– + 4H+ ® 2MnO4
– + MnO2 + 2H2O
Commercially it is prepared by the alkaline oxidative fusion of MnO2
followed by the electrolytic oxidation of manganate (Vl) F
used with KOH, oxidised
with air or KNO
2
3
2
4
MnO
MnO
;
manganate ion
−
→
42
4
Electrolytic oxidation in
alkaline solution
MnO
MnO
manganate
permanganate ion



Rationalised 2023-24
107
The d- and f- Block Elements
In the laboratory, a manganese (II) ion salt is oxidised by
peroxodisulphate to permanganate 2Mn
2+ + 5S2O8
2– + 8H2O ® 2MnO4
– + 10SO4
2– + 16H
+
Potassium permanganate forms dark purple (almost black) crystals which
are isostructural with those of KClO4