|Molar mass||118.934 g mol-1|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
A permanganate is the general name for a chemical compound containing the manganate(VII) ion, (MnO4−). 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-)
- 8 H+
+ MnO4− + 5 e− → Mn2+ + 4 H2O
- MnO4− + e− → MnO42−
In a neutral medium however, it gets reduced to the brown +4 oxidation state of manganese dioxide MnO2.
- 2 H2O + MnO4− + 3 e− → MnO2 + 4 OH−
- 2 MnCl2 + 5 NaClO + 6 NaOH → 2 NaMnO4 + 9 NaCl+ 3 H2O
- 2 MnSO4 + 5 PbO2+ 3 H2SO4 → 2 HMnO4 + 5 PbSO4 + 2 H2O
- 3 Na2MnO4 + 2 H2O → 2 NaMnO4 + MnO2 + 4 NaOH
They are produced commercially by electrolysis or air oxidation of alkaline solutions of manganate salts (MnO42-).
Permanganates(VII) are salts of permanganic acid. 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.
- 2 KMnO4 → K2MnO4 + MnO2 + O2
A 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:
- Ammonium permanganate, NH4MnO4
- Calcium permanganate, Ca(MnO4)2
- Potassium permanganate, KMnO4
- Sodium permanganate, NaMnO4
- Silver permanganate, AgMnO4
- Perchlorate, a similar ion with a chlorine(VII) center
- Chromate, which is isoelectronic with permanganate
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- Cotton, F. Albert; Wilkinson, Geoffrey; Carlos A. Murillo and Manfred Bochmann (1999). Advanced Inorganic Chemistry (6th ed.). New York: John Wiley & Sons, Inc. p. 770. ISBN 978-0471199571.
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