Potassium permanganate

Potassium permanganate is an inorganic compound with the chemical formula KMnO₄. It is a purplish-black crystalline salt, which dissolves in water as K⁺ and permanganate| ions to give an intensely pink to purple solution.

Potassium permanganate is widely used in the chemical industry and laboratories as a strong oxidizing agent, and also traditionally as a medication for dermatitis, for cleaning wounds, and general disinfection. It is on the World Health Organization's List of Essential Medicines. It has a great variety of niche uses such as biocide for water treatment purposes and for tanning and dyeing cloth.

It is also referred to as chameleon mineral, Condy's crystals, permanganate of potash, hypermangan, purple potion powder, permanganic acid (potassium salt), It is soluble in water, sulfuric acid, acetic anhydride, and benzonitrile, but dissolves best in methanol and acetone. In the solid (as in solution), each centre is tetrahedral. The Mn–O distances are 1.62 Å.

Color

The purplish-black color of solid potassium permanganate, and the intensely pink to purple color of its solutions, is caused by its permanganate anion, which gets its color from a strong charge-transfer absorption band caused by excitation of electrons from oxo ligand orbitals to empty orbitals of the manganese(VII) center. The crystal form can range from purple to black or gray, and has a blue metallic sheen. For treating eczema, it was recommended using for only a few days at a time due to irritating the skin.

The US Food and Drug Administration does not recommend its use in the crystal or tablet form. It should only be used in a diluted liquid form.

Historical use

Potassium permanganate was first made in the 1600s and came into common medical use at least as early as the 1800s. During World War I Canadian soldiers were given potassium permanganate (to be applied mixed with an ointment) in an effort to prevent sexually transmitted infections. Some have attempted to bring about an abortion by putting it in the vagina, though this is not effective. Other historical uses have included an effort to wash out the stomach in those with strychnine or picrotoxin poisoning.

Side effects

Side effects from topical use include irritation of the skin and discoloration of clothing. Therefore, in 2015 the British National Formulary recommended 100 mg be dissolved in a liter of water before use to form a 1:10,000 (0.01%) solution. Effects may include nausea, vomiting, and shortness of breath. If a sufficiently large amount (about 10 grams) is eaten death may occur. and therefore non medical grade potassium permanganate is sometimes used for medical purposes.

It is available under a number of brand names including Permasol, Koi Med Tricho-Ex, and Kalii permanganas RFF. It is occasionally called "Condy's crystals".

Veterinary medicine

Potassium permanganate may be used to prevent the spread of glanders among horses.

Industrial and other uses

Almost all applications of potassium permanganate exploit its oxidizing properties. though the EPA considers it a poor disinfectant. It can turn water a fuchsia or pink color.

Fisheries and aquatic management

Potassium permanganate is not FDA approved for use with food fish in the United States, however it is categorized under "regulatory action deferred" and is legal to use because the FDA considers it "low regulatory priority" and at low risk for adverse human health effects.

Potassium permanganate is a treatment for Ichthyophthirius multifiliis (commonly known as "ich") and protozoa (such as Trichodina), which infect and usually kill freshwater aquarium fish. A minimum dose of 2 ppm is required. Water with more organic load and a higher number of organisms including algae requires more permanganate. High concentrations and use more than once per week kill fish. Food fish require a 7-day period after treatment before they can be consumed.

===Synthesis of organic compounds===<!-- Baeyer's reagent redirects to this section -->

thumb|upright|KMnO₄ in water

KMnO₄ is a reagent for the synthesis of organic compounds. Significant amounts are used in the commercial synthesis of ascorbic acid, chloramphenicol, saccharin, isonicotinic acid, and pyrazinoic acid. The test is antiquated.

class=skin-invert-image|center|550px|Baeyer's reagent reaction

KMnO₄ solution is a common thin layer chromatography (TLC) stain for the detection of oxidizable functional groups, such as alcohols, aldehydes, alkenes, and ketones. Such compounds result in a white to orange spot on TLC plates.

Analytical use

Potassium permanganate can be used to quantitatively determine the total oxidizable organic material in an aqueous sample. The value determined is known as the permanganate value. In analytical chemistry, a standardized aqueous solution of KMnO₄ is sometimes used as an oxidizing titrant for redox titrations (permanganometry). As potassium permanganate is titrated, the solution becomes a light shade of purple, which darkens as excess of the titrant is added to the solution. In a related way, it is used as a reagent to determine the Kappa number of wood pulp. For the standardization of KMnO₄ solutions, reduction by oxalic acid is often used. In agricultural chemistry, it is used for estimation of active carbon<!-- not quite the meaning of the active carbon article --> in soil.

Aqueous, acidic solutions of KMnO₄ are used to collect gaseous mercury in flue gas during stationary source emissions testing.

In histology, potassium permanganate was used as a bleaching agent.

Fruit preservation

Ethylene absorbents extend storage time of bananas even at high temperatures. This effect can be exploited by packing bananas in polyethylene together with potassium permanganate. By removing ethylene by oxidation, the permanganate delays the ripening, increasing the fruit's shelf life up to 4 weeks without the need for refrigeration.

The chemical reaction, in which ethylene (C₂H₄) is oxidised by potassium permanganate (KMnO₄) to carbon dioxide (CO₂), manganese oxide (MnO₂) and potassium hydroxide (KOH), in the presence of water, is presented as follows:

3 C₂H₄ + 12 KMnO₄ + 2 H₂O → 6 CO₂ + 2 H₂O + 12 MnO₂ + 12 KOH

Survival kits

Potassium permanganate is sometimes included in survival kits: as a hypergolic fire starter (when mixed with glycerol antifreeze from a car radiator); as a water sterilizer; and for creating distress signals on snow. Modern hiking and survivalist guides advise against using potassium permanganate in the field because it is difficult to dose correctly. Both handheld helicopter- unmanned aircraft systems (UAS) or boat-mounted plastic sphere dispensers are used.

Other uses

Potassium permanganate is one of the principal chemicals used in the film and television industries to "age" props and set dressings. Its ready conversion to brown MnO₂ creates "hundred-year-old" or "ancient" looks on hessian cloth (burlap), ropes, timber and glass.

Potassium permanganate is used as an oxidizing agent in the synthesis of cocaine and methcathinone. It can purify cocaine paste with oxidization to increase its stability. This led to the Drug Enforcement Administration launching Operation Purple in 2000, with the goal of monitoring the world supply of potassium permanganate; however, potassium permanganate derivatives and substitutes were soon used thereafter to avoid the operation.

History

thumb|Treating a well with potassium permanganate in India (1949).In 1659, Johann Rudolf Glauber fused a mixture of the mineral pyrolusite (manganese dioxide, MnO₂) and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution (potassium manganate) which slowly shifted to violet and then finally red. The reaction that produced the color changes that Glauber observed in his solution of potassium permanganate and potassium manganate (K₂MnO₄) is now known as the "chemical chameleon".

The case of the chameleon mineral alludes to a broader reflection on how epistemological framework dictates what early modern scientists perceived as meaningful discoveries.  Little literature exists on Glauber's accidental discovery of potassium permanganate and the importance of both its dismissal and its conversion into a modern medical and hygienic staple.

The earliest description of the production of potassium permanganate is here. Just under 200 years later, London chemist Henry Bollmann Condy had an interest in disinfectants; he found that fusing pyrolusite with sodium hydroxide (NaOH) and dissolving it in water produced a solution with disinfectant properties. He patented this solution, and marketed it as 'Condy's Fluid'. Although effective, the solution was not very stable. This was overcome by using potassium hydroxide (KOH) rather than NaOH. This was more stable, and had the advantage of easy conversion to the equally effective potassium permanganate crystals. This crystalline material was known as 'Condy's crystals' or 'Condy's powder'. Potassium permanganate was comparatively easy to manufacture, so Condy was subsequently forced to spend considerable time in litigation to stop competitors from marketing similar products. According to Varlam Shalamov, potassium permanganate solution was used as a catch-all treatment for dysentery, frostbite and ulcers in the Gulag camps of Kolyma.

Early photographers used it as a component of flash powder. It is now replaced with other oxidizers, due to the instability of permanganate mixtures.

Preparation

Potassium permanganate is produced industrially from manganese dioxide, which also occurs as the mineral pyrolusite. In 2000, worldwide production was estimated at 30,000 tonnes. The MnO₂ is fused with potassium hydroxide and heated in air or with another source of oxygen, like potassium nitrate or potassium chlorate. The chlorine oxidation reaction is

:

and the acid-induced disproportionation reaction may be written as

:

A weak acid such as carbonic acid is sufficient for this reaction:

:

Permanganate salts may also be generated by treating a solution of Mn²⁺ ions with strong oxidants such as lead dioxide (PbO₂), sodium bismuthate (NaBiO₃), or peroxydisulfate. Tests for the presence of manganese exploit the vivid violet color of permanganate produced by these reagents.

Reactions

Organic chemistry

Dilute solutions of KMnO₄ convert alkenes into diols. This behaviour is also used as a qualitative test for the presence of double or triple bonds in a molecule, since the reaction decolorizes the initially purple permanganate solution and generates a brown precipitate (MnO₂). In this context, it is sometimes called Baeyer's reagent. However, bromine serves better in measuring unsaturation (double or triple bonds) quantitatively, since KMnO₄, being a very strong oxidizing agent, can react with a variety of groups.

Under acidic conditions, the alkene double bond is cleaved to give the appropriate carboxylic acid:

:

Potassium permanganate oxidizes aldehydes to carboxylic acids, illustrated by the conversion of n-heptanal to heptanoic acid:

:

Even an alkyl group (with a benzylic hydrogen) on an aromatic ring is oxidized, e.g. toluene to benzoic acid.

:

Glycols and polyols are highly reactive toward KMnO₄. For example, addition of potassium permanganate to an aqueous solution of sugar and sodium hydroxide produces the chemical chameleon reaction, which involves dramatic color changes associated with the various oxidation states of manganese. A related vigorous reaction is exploited as a fire starter in survival kits. For example, a mixture of potassium permanganate and glycerol or pulverized glucose ignites readily.

:

Similarly, addition of a crown ether also gives a lipophilic salt.

Reaction with acids and bases

Permanganate reacts with concentrated hydrochloric acid to give chlorine and manganese(II):

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In neutral solution, permanganate slowly reduces to manganese dioxide (MnO₂). This is the material that stains one's skin when handling KMnO₄.

KMnO₄ reduces in alkaline solution to give green K₂MnO₄:

:

This reaction illustrates the relatively rare role of hydroxide as a reducing agent.

Addition of concentrated sulfuric acid to potassium permanganate gives Mn₂O₇. Although no reaction may be apparent, the vapor over the mixture will ignite paper impregnated with alcohol. Potassium permanganate and sulfuric acid react to produce some ozone, which has a high oxidizing power and rapidly oxidizes the alcohol, causing it to combust. As the reaction also produces explosive Mn₂O₇, this should only be attempted with great caution.

Thermal decomposition

Solid potassium permanganate decomposes when heated: Contact with skin can cause skin irritation, skin and mucous membrane corrosion,

References

Bibliography

• Access this document via National Service Center for Environmental Publications (NSCEP), pubnumber 815R99014

Further reading

External links