Permanganate
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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 manganate(VII) ion is a strong oxidizing agent. The ion has a tetrahedral geometry [1] Permanganate solutions are purple in color and are stable in neutral or slightly alkaline media.
In an acidic solution, manganate(VII) is reduced to the colourless +2 oxidation state of the Manganese(II) (Mn2+) ion.
In a strongly basic solution, manganate(VII) is either reduced to the brown +4 oxidation state of manganese dioxide MnO2 or to the green +6 oxidation state of the manganate MnO42−.
- 2 H2O + MnO4− + 3 e− → MnO2 + 4 OH−
- MnO4− + e− → MnO42−
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[edit] Production
Permanganates may be produced by oxidation of manganese compounds by strong oxidizing agents, for instance, sodium hypochlorite or lead dioxide.
- 2 MnCl2 + 5 NaClO + 6 NaOH → 2 NaMnO4 + 9 NaCl+ 3 H2O
- 2 MnSO4 + 5 PbO2+ 3 H2SO4 → 2 HMnO4+ 5 PbSO4 + 2 H2O
Or by dismutation of manganates:
[edit] Properties
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).Besides this, it is stable.
It is a useful reagent, though with organic compounds, not very selective.
Manganates(VII) are not very thermally stable. For instance, potassium permanganate decomposes at 230 °C:
A permanganate can oxidize an amine to a nitro compound [2][3], an alcohol to a ketone [4], an aldehyde to a carboxylic acid [5][6], a terminal alkene to a carboxylic acid [7], oxalic acid to carbon dioxide [8] or an alkene to a diol [9] (list not exhaustive)
In alkene oxidations one intermediate is a cyclic Mn(V) species:
[edit] Compounds
- Ammonium permanganate
- Calcium permanganate, Ca(MnO4)2
- Potassium permanganate, KMnO4
- Sodium permanganate, NaMnO4
[edit] References
- ^ Oxidation by permanganate: synthetic and mechanistic aspects Sukalyan Dash, Sabita Patel and Bijay K. Mishra Tetrahedron Volume 65, 2009, Pages 707-739 doi:10.1016/j.tet.2008.10.038
- ^ OS 52:77 http://www.orgsynth.org/orgsyn/pdfs/CV6P0803.pdf
- ^ OS 43:87 http://www.orgsynth.org/orgsyn/pdfs/CV5P0845.pdf
- ^ OS 39:51 http://www.orgsynth.org/orgsyn/pdfs/CV4P0467.pdf
- ^ OS 10:82 http://www.orgsynth.org/orgsyn/pdfs/CV2P0538.pdf
- ^ OS 16:39 http://www.orgsynth.org/orgsyn/pdfs/CV2P0315.pdf
- ^ OS 60:11 http://www.orgsynth.org/orgsyn/pdfs/CV7P0397.pdf
- ^ Kovacs KA, Grof P, Burai L, Riedel M (2004). "Revising the Mechanism of the Permanganate/Oxalate Reaction". J. Phys. Chem. A 108: 11026. doi:.
- ^ OS 11:52 http://www.orgsynth.org/orgsyn/pdfs/CV2P0307.pdf
