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Permanganate

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"MnO4" redirects here. For the manganate ion MnO42−, see Manganate.
Permanganate
Lewis structure of the manganate(VII) anion
Names
Systematic IUPAC name
Permanganate
Identifiers
Properties
MnO−
4
Molar mass 118.934 g mol-1
Except where otherwise noted, 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.[1] 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 ion (H+), and chloride ions (Cl-)[2]

In an acidic solution, permanganate(VII) is reduced to the colourless +2 oxidation state of the manganese(II) (Mn2+) ion.

8 H+
 + MnO4− + 5 e− → Mn2+ + 4 H2O

In a strongly basic solution, permanganate(VII) is reduced to the green +6 oxidation state of the manganate ion, MnO42−.

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−

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:

2 MnCl2 + 5 NaClO + 6 NaOH → 2 NaMnO4 + 9 NaCl+ 3 H2O
2 MnSO4 + 5 PbO2+ 3 H2SO4 → 2 HMnO4 + 5 PbSO4 + 2 H2O

It may also be produced by the dismutation of manganates, with manganese dioxide as a side-product:

3 Na2MnO4 + 2 H2O → 2 NaMnO4 + MnO2 + 4 NaOH

They are produced commercially by electrolysis or air oxidation of alkaline solutions of manganate salts (MnO4-2).[3]

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 stable thermally. For instance, potassium permanganate decomposes at 230 °C to potassium manganate and manganese dioxide, releasing oxygen gas:

2 KMnO4 → K2MnO4 + MnO2 + O2

A permanganate can oxidize an amine to a nitro compound,[4][5] an alcohol to a ketone,[6] an aldehyde to a carboxylic acid,[7][8] a terminal alkene to a carboxylic acid,[9] oxalic acid to carbon dioxide,[10] and an alkene to a diol.[11] This list is not exhaustive.

In alkene oxidations one intermediate is a cyclic Mn(V) species:

Permanganate oxidation mechanism

Compounds

See also

  • Perchlorate, a similar ion with a chlorine(VII) center
  • Chromate, which is isoelectronic with permanganate

References

  1. ^ Sukalyan Dash, Sabita Patel and Bijay K. Mishra (2009). "Oxidation by permanganate: synthetic and mechanistic aspects". Tetrahedron. 65 (4): 707–739. doi:10.1016/j.tet.2008.10.038.
  2. ^ http://geocleanse.com/permanaganate.asp
  3. ^ Cotton, F. Albert; Wilkinson, Geoffrey (1999). Advanced Inorganic Chemistry (6th ed.). New York: John Wiley & Sons, Inc. p. 770. ISBN 978-0471199571. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ A. Calder, A. R. Forrester1, and S. P. Hepburn (1972). "2-methyl-2-nitrosopropane and its dimer". Organic Syntheses. 6: 803{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link); Collected Volumes, vol. 52, p. 77.
  5. ^ Nathan Kornblum and Willard J. Jones (1963). "4-nitro-2,2,4-trimethylpentane". Organic Syntheses. 5: 845; Collected Volumes, vol. 43, p. 87.
  6. ^ J. W. Cornforth (1951). "Ethyl pyruvate". Organic Syntheses. 4: 467; Collected Volumes, vol. 31, p. 59.
  7. ^ R. L. Shriner and E. C. Kleiderer (1930). "Piperonylic acid". Organic Syntheses. 2: 538; Collected Volumes, vol. 10, p. 82.
  8. ^ John R. Ruhoff (1936). "n-heptanoic acid". Organic Syntheses. 2: 315; Collected Volumes, vol. 16, p. 39.
  9. ^ Donald G. Lee, Shannon E. Lamb, and Victor S. Chang (1981). "Carboxylic acids from the oxidation of terminal alkenes by permanganate: nonadecanoic acid". Organic Syntheses. 7: 397{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 60, p. 11.
  10. ^ Kovacs KA, Grof P, Burai L, Riedel M (2004). "Revising the Mechanism of the Permanganate/Oxalate Reaction". J. Phys. Chem. A. 108 (50): 11026. doi:10.1021/jp047061u.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ E. J. Witzemann, Wm. Lloyd Evans, Henry Hass, and E. F. Schroeder (1931). "dl-glyceraldehyde ethyl acetal". Organic Syntheses. 2: 307{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 11, p. 52.
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