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A permanganate is the general name for a chemical compound containing the manganate(VII) ion, (MnO−
4). 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, trichloroethene (C2HCl3) is oxidized by sodium permanganate to form carbon dioxide (CO2), manganese dioxide (MnO2), sodium ions (Na+), hydronium ions (H+), and chloride ions (Cl−).
Contents
- Elephant toothpaste potassium permanganate hydrogen peroxide foamy chemical reaction
- Production
- Properties
- Compounds
- References
In an acidic solution, permanganate(VII) is reduced to the colourless +2 oxidation state of the manganese(II) (Mn2+) ion.
8 H++ MnO−
4 + 5 e− → Mn2+ + 4 H2O
In a strongly basic solution, permanganate(VII) is reduced to the green +6 oxidation state of the manganate ion, MnO2−
4.
4 + e− → MnO2−
4
In a neutral medium, however, it gets reduced to the brown +4 oxidation state of manganese dioxide MnO2.
2 H2O + MnO−4 + 3 e− → MnO2 + 4 OH−
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Production
Permanganates can be produced by oxidation of manganese compounds such as manganese chloride or manganese sulfate by strong oxidizing agents, for instance, sodium hypochlorite or lead dioxide:
It may also be produced by the disproportionation of manganates, with manganese dioxide as a side-product:
3 Na2MnO4 + 2 H2O → 2 NaMnO4 + MnO2 + 4 NaOHThey are produced commercially by electrolysis or air oxidation of alkaline solutions of manganate salts (MnO2−
4).
Properties
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 doesn't actually happen to any extent. Besides this, it is stable.
It is a useful reagent, though with organic compounds, not very selective.
Manganates(VII) are not very stable thermally. For instance, potassium permanganate decomposes at 230 °C to potassium manganate and manganese dioxide, releasing oxygen gas:
2 KMnO4 → K2MnO4 + MnO2 + O2A permanganate can oxidize an amine to a nitro compound, an alcohol to a ketone, an aldehyde to a carboxylic acid, a terminal alkene to a carboxylic acid, oxalic acid to carbon dioxide, and an alkene to a diol. This list is not exhaustive.
In alkene oxidations one intermediate is a cyclic Mn(V) species: