Potassium permanganate

Structural formula
__ K +      __ O 2−      __ Mn 7+
Crystal system	orthorhombic
Space group	Pnma (No. 62)
Lattice parameters	a  = 9.128  Å , b  = 5.728 Å, c  = 7.436 Å
General
Surname	Potassium permanganate
other names	Potassium tetraoxomanganate (VII) Potassium manganate (VII) Hyper manganese Super-manganese acid potash (um)
Molecular formula	KMnO 4
Brief description	purple odorless solid
External identifiers / databases
CAS number 7722-64-7 EC number 231-760-3 ECHA InfoCard 100,028,874 PubChem 516875 ChemSpider 22810 DrugBank DB13831 Wikidata Q190865
Drug information
ATC code	D08 AX06 V03 AB18
properties
Molar mass	158.03 g mol −1
Physical state	firmly
density	2.70 g cm −3
Melting point	Decomposition above 240 ° C
solubility	moderate in water (64 g l −1 at 20 ° C)
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 272-302-314-361d-373-410 P: 210-220-280-301 + 330 + 331-303 + 361 + 353-305 + 351 + 338-310
MAK	0.5 mg m −3
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium permanganate (KMnO ₄ ) is the potassium salt of the permanganic acid HMnO _{4, which} does not occur in the free state . Potassium permanganate is a metallic, shiny, almost black crystalline solid and a strong oxidizing agent . The dry, not too fine powder, made up of acute-angled crystals, has a more greenish than purple shimmer. The finest dust, abrasion - the line , traces stuck to rough surfaces or penetrated into porous materials appear dark purple, like parts loosened by traces of water. The permanganate as a crystal lattice building block or anion is solely responsible for the intense color of the salt and its solution . The color is due to charge-transfer transitions . In permanganates, manganese is in its highest oxidation state + VII.

properties

Potassium permanganate forms dark, red-violet, shiny crystals that are moderately soluble in water and give an intensely violet solution even in low concentrations . Crystalline potassium permanganate is stable at room temperature, but its aqueous solution decomposes over time to manganese (IV) oxide and oxygen. It crystallizes orthorhombically , space group Pnma (space group no. 62) , with the lattice parameters a = 9.128 Å , b = 5.728 Å, c = 7.436 Å.

Play media file

Crystallization of the aqueous KMnO ₄ solution due to evaporation, recorded in real time at 200x magnification

Since manganese is in its highest oxidation state in the permanganate anion, it appears as a very strong oxidizing agent in redox reactions . Thus, potassium permanganate oxidizes z. B. hydrochloric acid to chlorine gas and thus represents a laboratory method for the representation of chlorine:

${\displaystyle {\ce {2MnO4^- + 10Cl- + 16H3O+ -> 2Mn^{2}+ + 5Cl2 ^ + 24H2O}}}$

It also oxidizes, for example, sulfites and sulfides to sulfates , Fe (II) to Fe (III) ions, and alcohols to aldehydes . It can also cause organic matter to decompose .

Potassium permanganate shows no melting point. From 240 ° C it decomposes to form potassium manganate (potassium manganate (VI), K ₂ MnO ₄ ), manganese dioxide (MnO ₂ ), potassium oxide (K ₂ O) and oxygen (O ₂ ): This makes potassium permanganate a fire-promoting agent.

${\displaystyle {\ce {10KMnO4 -> 3K2MnO4 + 7MnO2 + 2K2O + 6O2 ^}}}$

At even higher temperatures, the potassium manganate also breaks down:

${\displaystyle {\ce {2K2MnO4 -> 2MnO2 + 2K2O + O2 ^}}}$

Scheme of the redox reaction of sulfite with permanganate:

${\displaystyle {\ce {Oxidation:}}}$	${\displaystyle \mathrm {{\overset {\underset {+IV}{}}{\ S}}O_{3}^{2-}+3\ H_{2}O} }$	${\displaystyle {\ce {->}}}$	${\displaystyle \mathrm {{\overset {\underset {+VI}{}}{\ S}}O_{4}^{2-}+2\ e^{-}+2\ H_{3}O^{+}} }$	${\displaystyle \mathrm {|\cdot 5} }$
${\displaystyle {\ce {Reduktion:}}}$	${\displaystyle \mathrm {{\overset {\underset {+VII}{}}{Mn}}O_{4}^{-}+5\ e^{-}+8\ H_{3}O^{+}} }$	${\displaystyle {\ce {->}}}$	${\displaystyle \mathrm {\ {\overset {\underset {+II}{}}{Mn}}{}^{2+}+12\ H_{2}O} }$	${\displaystyle \mathrm {|\cdot 2} }$
${\displaystyle {\ce {Redox:}}}$	${\displaystyle {\ce {5SO3^{2}- + 2MnO4^- + 6H3O+}}}$	${\displaystyle {\ce {->}}}$	${\displaystyle {\ce {5SO4^{2}- + 2Mn^{2}+ + 9H2O}}}$

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

Manufacturing

The technical production is based on manganese dioxide MnO ₂ , which reacts with highly concentrated potassium hydroxide and atmospheric oxygen at 250 ° C to form the green colored potassium manganate (VI) K ₂ MnO ₄ . This is processed electrochemically to form potassium permanganate (anodic oxidation) and is marketed in crystalline form.

A targeted two-step synthesis is possible in the laboratory, in which MnO _{2 is} first oxidized to K ₂ MnO ₄ in a strongly basic medium (e.g. by KClO ₃ ) and then, after the disproportionation equilibrium , is converted into KMnO ₄ and MnO ₄ ⁴⁻ , which decomposed by subsequent hydrolysis into MnO ₂ and OH ^- and neutralized by introducing CO ₂ or adding dilute sulfuric acid .

${\displaystyle {\ce {3MnO2 + KClO3 + 6KOH -> 3K2MnO4 + KCl + 3H2O}}}$

Disproportionation:

${\displaystyle {\ce {3MnO4^{2-}<=> 2MnO4- + MnO4^{4-}( + 2H2O -> 2MnO4- + MnO2 + 4OH^{-})}}}$

The neutralization shifts the equilibrium to the right, since the manganese (IV) oxide which precipitates can no longer dissolve in the basic medium, which increases the yield of potassium permanganate.

${\displaystyle {\ce {3K2MnO4 + 2CO2 + 2H2O -> 2KMnO4 + MnO2 + 2K2CO3 + 2H2O}}}$

Instead of the carbonic acid resulting from the introduction of the CO ₂ , the equivalent amount of dilute sulfuric acid can also be used.

use

Detection of glucose through the reduction of permanganate ions using the example of gummy bears

Because of its strong oxidizing effect, potassium permanganate is used in a variety of applications:

• It is widely used as a disinfectant , deodorant and algicide .
• In quantitative chemical analysis ( oxidimetry , manganometry , a redox titration ) it is used to determine a large number of substances (for example iron , nitrite , oxalate , reducing sugars and, indirectly, calcium ); the end point of the determination is indicated by a permanent violet color. In the laboratory, alkaline potassium permanganate solution is also used to clean glass appliances.
• In analog photography it is used to detect fixing salt ( sodium thiosulphate ) and as a reducer of overexposed images; the silver is oxidized in the process.
• It is used to bleach natural sponges to get their typical white-yellow color. As a fungicide and bactericide, potassium permanganate for the treatment of fruit trees, olive trees and vines is also approved for organic farming according to the EEC regulation.
• When glycerine is dripped onto an excess of the salt, the mixture ignites after a few seconds to minutes and burns with a characteristic violet flame. This delayed reaction was used to start thermite reactions because of the intense heat . Mixtures with magnesium or aluminum powder react explosively under a bright flash of light. With glycerine, ethylene glycol, mannitol, acetaldehyde and numerous other substances, self-ignition occurs.
• In terms of quantity, potassium permanganate is used in the manufacture of saccharin .
• In organic chemistry, potassium permanganate can be used for the dihydroxylation of alkenes . Since it tends to further oxidize the 1,2-diols formed, the yields are usually poorer than, for example, in the case of dihydroxylation with osmium (VIII) oxide . However, potassium permanganate is significantly cheaper and significantly less harmful to health, so that it is still used in simple syntheses.
• To remove cinnamoyl cocaine and other impurities from coca paste, potassium permanganate is also used in the manufacture of cocaine . It is therefore listed in category 2 in the Basic Materials Monitoring Act in Germany ; production, import, export and trade are therefore subject to registration from a quantity of 100 kg.
• Another use is in staining wood.
• Large amounts are used in bleaching (oxidizing) denim dye to create a vintage look.
• In medicine, potassium permanganate solution is used as an astringent and disinfectant for the external treatment of the skin , u. a. for athlete's foot or diaper rash , used ( ATC code D08AX06). In emergency toxicology, a burgundy-colored potassium permanganate solution (approx. 0.1%) is used for gastric lavage in the event of poisoning after oral ingestion of oxidizable poisons.
• It is also used in the therapy of parasitic fish diseases.
• Potassium permanganate destroys odorous substances and has a bactericidal effect.
• In the production of fatty acids through paraffin oxidation , potassium permanganate was used as an oxidizing agent.

Historical

Potassium permanganate was first described in 1659 by Johann Rudolf Glauber . Potassium permanganate solution was previously marketed as Condy's Fluid by Henry Bollmann Condy (1826–1907) and was used for disinfecting and bleaching. Earlier photographers used potassium permanganate as an ingredient in flash powder . Potassium permanganate was used to gargle for sore throats and in the butcher industry to take the smell out of spoiled meat and make it palatable again. Furthermore, the skin turns brown after contact with potassium permanganate solution due to the deposition of manganese dioxide; therefore, such solutions were also used specifically as tanning agents.

• 

  KMnO ₄ crystals

• 

  KMnO ₄ in aqueous solution

safety instructions

Potassium permanganate has water hazard class 3 (highly hazardous to water), which, in addition to its oxidizing effect, must be taken into account when disposing of permanganate residues. Potassium permanganate has only a low acute toxicity ( LD ₅₀ (rat, oral) = 750 mg / kg), but has a pronounced irritant effect on living tissue due to its strong oxidizing effect, so that chemical burns can easily occur. Any contact beyond medical application or even oral intake must therefore be prevented. Permanganate dusts cause the cornea to become cloudy .

The discoloration of the skin itself, which occurs on contact, however, is harmless and is in the reduction resulting permanganate Braunstein caused. Larger discolored areas can be discolored again with solutions of sulfites .

As a result of its strong oxidizing effect, potassium permanganate sometimes reacts very violently with many reducing or flammable substances; spontaneous combustion can occur. Mixtures with substances that do not lead to spontaneous reactions are extremely flammable and may then react explosively.

At the suggestion of the French chemicals authority, the chemical classification of potassium permanganate was revised in 2016. The French authorities applied for repr 1B to be classified as toxic to reproduction. The Committee for Risk Assessment (RAC) of the European Chemicals Agency (ECHA) only partially followed the application and added the following to the classification for potassium permanganate on December 9, 2016: Potassium permanganate is classified as repr 2 toxic for reproduction. The additional warning has been set to H361d. This classification of the RAC has yet to be implemented by the EU Commission into applicable law, but with the publication it represents the state of knowledge that must be taken into account by companies and authorities.

Potassium permanganate was included by the EU in 2017 in accordance with Regulation (EC) No. 1907/2006 (REACH) in the context of substance evaluation in the Community's rolling action plan ( CoRAP ). The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The reasons for the uptake of potassium permanganate were concerns about consumer use and exposure of sensitive population groups as well as the possible danger from reproductive toxicity . The reassessment took place from 2017 and was carried out by France . A final report was then published.

Web links

Commons : Potassium Permanganate  - Collection of pictures, videos and audio files

Individual evidence

1. ↑ ^{a b c d e f g} Entry on potassium permanganate in the GESTIS substance database of the IFA , accessed on November 18, 2019(JavaScript required) .
2. ↑ Entry on potassium permanganate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on November 18, 2019. Manufacturers or distributors can expand the harmonized classification and labeling .
3. ^ R. Hoppe, D. Fischer, J. Schneider: On the knowledge of oxides A [MO ₄ ]: About LiMnO ₄ , KMnO ₄ , RbMnO ₄ , CsMnO ₄ as well as RbIO ₄ and CsIO ₄ . (- What does “the crystal structure of ...” actually mean? -). In: Journal of Inorganic and General Chemistry . 625 (7), 1999, pp. 1125-1142, doi : 10.1002 / (SICI) 1521-3749 (199907) 625: 7 <1135 :: AID-ZAAC1135> 3.0.CO; 2-L .
4. ↑ Eberhard Schweda: Jander / Blasius Inorganische Chemie 1 . 17th edition. Hirzel Verlag, Stuttgart 2012, ISBN 978-3-7776-2134-0 , p. 324 .
5. ↑ Entry on potassium permanganate. In: Römpp Online . Georg Thieme Verlag, accessed on June 15, 2014.
6. ^ Arnold Willmes, Pocket Book Chemical Substances , Harri Deutsch, Frankfurt (M.), 2007.
7. ↑ Regulation (EC) No. 889/2008 Annex II: Pesticides .
8. ↑ FR Kreißl, O. Krätz, fire and flame, sound and smoke. , Wiley-VCH Weinheim, 2nd edition 2008, ISBN 978-3-527-32276-3 , p. 123 ( limited preview in Google book search).
9. ↑ Cocaine and Crack on the EMCDDA website , accessed May 24, 2014.
10. ↑ Bernhard Schultz: Farbwarenkunde . Vieweg + Teubner Verlag, Wiesbaden 1953, ISBN 3-322-97907-5 , p. 46 , doi : 10.1007 / 978-3-322-98438-8_4 .
11. ↑ Kathrin Werner: Now a robot is laser cutting the used look into jeans . In: Tages-Anzeiger, Tages-Anzeiger . ( tagesanzeiger.ch [accessed on February 28, 2018]).
12. ↑ Lutz Roth, Max Daunderer, Kurt Kormann: Toxic Plants-Plant Poisons. Occurrence, effect, therapy . 2nd Edition. Ecomed, Landsberg 1988, ISBN 3-609-64810-4 , pp. 810 ff .
13. ↑ G. Wietzel: Production of synthetic fatty acids by oxidation of paraffinic hydrocarbons with molecular oxygen . In: Chemical Engineering Science . tape 3 , 1954, pp. 17 – IN4 , doi : 10.1016 / S0009-2509 (54) 80003-0 .
14. ↑ Derek Lowe, Das Chemiebuch, Librero 2017
15. ^ RAC decision of December 9, 2016
16. ↑ European Chemicals Agency (ECHA): Substance Evaluation Conclusion and Evaluation Report .
17. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Potassium permanganate , accessed on March 26, 2019.