Potassium permanganate

  • Kaliumtetraoxomanganat (VII)
  • Potassium manganate (VII )
  • About Manga of potash ( to )
  • D08AX06
  • V03AB18

Purple solid

Fixed

2.70 g · cm -3

Decomposition above 240 ° C.

1 Pa (at 20 ° C)

Moderately in water ( 64 g · l-1 at 20 ° C)

Risk

0.5 mg · m-3

Template: Infobox chemical / molecular formula search is not possible

Potassium permanganate ( KMnO4 ) is the potassium salt of the free state unknown permanganic, HMnO4. It is a deep red- purple, shiny metallic, crystalline solid and a strong oxidizing agent. Only the permanganate anion is responsible for the intense color of the salt. The color is attributed to charge-transfer transition. Permanganates in the manganese is present in its highest oxidation state VII.

Properties

Potassium permanganate forms dark red-purple shiny crystals, which are soluble in water and result in a moderately intense violet solution even in low concentrations. On heating, the crystals do not melt but decompose above about 240 ° C with a clear crackle under release of oxygen. Crystalline potassium permanganate is stable at room temperature, but its aqueous solutions decompose over time to manganese ( IV) oxide and oxygen

Since in the permanganate anion is present, the manganese in its highest oxidation state, in redox reactions, it acts as a very strong oxidant. Thus, potassium permanganate oxidizes eg hydrochloric acid to chlorine gas (laboratory method for the preparation of chlorine):

Furthermore, it is oxidized, for example, sulfites to sulfates, Fe (II) - and Fe (III ) ions, alcohols to carboxylic acids. It can also cause the decomposition of organic substances. Potassium permanganate is oxidizing.

Potassium permanganate decomposes above 240 ° C. Potassium permanganate ( potassium manganate (VI ), K2MnO4 ), pyrolusite ( MnO2), potassium oxide ( K2O) and oxygen ( O2):

At still higher temperatures is also destroyed by the potassium manganate:

Scheme of the redox reaction of sulfite with permanganate:

Complexed with crown ethers, potassium permanganate can be dissolved in non-polar organic solvents such as benzene or toluene, which is used in the organic synthetic chemistry.

Production

The industrial production is based on manganese dioxide MnO2, which with potassium hydroxide and oxygen from the air to the green colored potassium manganate (VI ) K2MnO4 responding. This is electrochemically processed potassium permanganate ( anodic oxidation) and is crystalline in the trade.

In the laboratory, a selective two-step synthesis is possible to first oxidized at the MnO2 in strongly basic medium ( eg by KClO3 ) to K2MnO4 and is subsequently transferred MnO44 - after Disproportionierungsgleichgewicht in KMnO4 and which decays OH followed by hydrolysis in MnO2 and and injection of CO2 or the addition of dilute sulfuric acid is neutralized.

Disproportionation:

Use

Because of the strong oxidizing action of potassium permanganate is used among other things as a disinfectant, deodorant and algaecide. In the quantitative chemical analysis ( Oxidimetrie, Manganometry, a redox titration ) it is used to determine a variety of substances (eg, iron, nitrite, oxalate, reducing sugars and, indirectly, calcium) used; Here, the end point of the determination is indicated by a permanent purple color. In the laboratory, alkaline potassium permanganate is also used for cleaning glassware. In photography it is used for the detection of hypo ( sodium thiosulfate ) and as attenuators of overexposed images; Here, the silver is oxidized. It is also used for the bleaching of natural sponges to get the typical white -yellow color. As a fungicide and bactericide potassium permanganate is approved for the treatment of fruit trees, olive trees and vines according to EEC regulation for organic farming.

When dropping of glycerol to a surplus of salt, the mixture ignites after a few seconds to minutes and burns with a characteristic violet flame. This delayed reaction occurring was used because of the intense heat at the start of thermite. Mixtures with magnesium or aluminum powder react explosively bright flash of light. With glycerol, ethylene glycol, mannitol, acetaldehyde, and numerous other substances takes place auto-ignition. A quantitatively important application of potassium permanganate is carried out in the production of saccharin.

Medicine

In medicine, potassium permanganate is used as an astringent and disinfectant for external treatment of the skin, including diaper rash or athlete's foot when used ( ATC code D08AX06 ). In the emergency toxicology burgundy colored potassium permanganate solution (about 0.1%) for gastric lavage in poisoning after ingestion of oxidizable pollutants. Likewise, it is used in the treatment of parasitic diseases of fish. Potassium permanganate destroys odors and acts bactericidal.

Historical

The photographers earlier times used potassium permanganate as a component of flash powder. Potassium permanganate was used as a gargle for sore throats and in the butcher business to take rotten meat smell and make it re-appear edible. Furthermore, the skin turns brown after contact with potassium permanganate solution; therefore, such solutions have also been targeted as a tanning agent.

Safety

Potassium permanganate has the Water hazard class 3 (highly hazardous), what should be considered in addition to its oxidizing effect in the disposal of Permanganatresten. Potassium permanganate is of only low acute toxicity (LD50 (rat, oral) = 750 mg / kg), however, has its strong oxidizing effect a pronounced irritant effect on living tissue, making it easily comes to burns. Any contact beyond the medical application or even oral intake is therefore to prevent. Permanganatstäube cause the eye clouding of the cornea.

The discoloration of the skin itself, which occurs in contact, however, is harmless and is caused by resulting in the reduction of the permanganate manganese. Larger discolored areas can discolor again by solutions of sulfites.

Because of its strong oxidizing effect of potassium permanganate reacts with many reducing action or combustible materials sometimes very violently; it can enter self-ignition. Mixtures containing such substances that do not lead to spontaneous reaction, are extremely flammable and then react explosively under certain circumstances.

KMnO4 in aqueous solution

461256
de