A permanganate is the general name for a chemical compound containing the manganate(VII) ion, . Because manganese is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion has tetrahedral geometry. Permanganate solutions are purple in color and are stable in neutral or slightly alkaline media. The exact chemical reaction is dependent upon the organic contaminants present and the oxidant utilized. For example, trichloroethane (C2H3Cl3) is oxidized by permanganate ions to form carbon dioxide (CO2), manganese dioxide (MnO2), sodium ions (Na+), hydronium ions (H+), and chloride ions (Cl-).
8 + 3 -> 6 + 8 + + 4 + 9
In an acidic solution, permanganate(VII) is reduced to the pale pink +2 oxidation state of the manganese(II) (Mn2+) ion.
8 + + 5 e- -> Mn2+ + 4 H2O
In a strongly basic solution, permanganate(VII) is reduced to the green +6 oxidation state of the manganate ion, .
+ e- ->
In a neutral medium, however, it gets reduced to the brown +4 oxidation state of manganese dioxide MnO2.
They are produced commercially by electrolysis or air oxidation of alkaline solutions of manganate salts .
A series of potassium permanganate solutions with varying concentration, increasing to the right.
Absorption spectrum of an aqueous solution of potassium permanganate, showing a vibronic progression
Permanganates(VII) are salts of permanganic acid. They have a deep purple colour, due to a charge transfer transition. Permanganate(VII) is a strong oxidizer, and similar to perchlorate. It is therefore in common use in qualitative analysis that involves redox reactions (permanganometry). According to theory, permanganate is strong enough to oxidize water, but this does not actually happen to any extent. Besides this, it is stable.
It is a useful reagent, though with organic compounds, not very selective. Potassium permanganate is used as a disinfectant.