Potassium Permanganate: Structure, Preparation, Reactions, Uses and Effect

In the year 1659, German-Dutch chemist Johann Glauber was the first to discover the production of KMnO₄. Potassium Permanganate is water-soluble that consists of two ions: and Potassium ion (K⁺) and Permanganate ion (MnO–4) – which has an ionic bond between them. It is a dark purple odourless solid in its physical state. Potassium permanganate is an inorganic compound with the chemical formula is KMnO₄. It is famous as an oxidizing agent and a permanganate of potash. Potassium permanganate crystals when dissolved in water produces a purple solution. It is usually prepared from other minerals namely, manganese oxide. Commonly, it is a combination of manganese oxide and potassium hydroxide – first prepared as a disinfectant in 1857 

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Structure of potassium permanganate

The picture below showcases the structure of Potassium Permanganate The structure is that of an ionic bond between the potassium cation and the permanganate anion.

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Preparation of Potassium Permanganate

KMnO₄ is prepared by the fusion of MnO₂ with an alkali metal hydroxide and an oxidizing agent like KNO₃. This produces dark green K₂MnO₄ which is disproportionate in a neutral or acidic solution to give permanganate. 

2MnO₂ + 4KOH + O₂ → 2K₂MNO₄ + 2H₂O

3MnO₄^2-+ 4H⁺ → 2MnO₄^- + MnO₂ + 2H₂O

Commercially it is prepared by the alkaline oxidative fusion of MnO2 followed by the electrolytic oxidation of Manganate (VI) 

MnO₄^2- → MnO^4-

Electrolytic oxidation in alkaline solution 

Laboratory Preparation: in the laboratory a manganese (II) ion salt is oxidized by peroxodisulphate to permanganate:

2Mn2+ + 5S₂O₈^2- + 8H₂O → 2MnO₄^- + 10SO₄^2- + 16H⁺

Characteristics properties of Potassium Permanganate

• Potassium Permanganate is forms dark purple almost black crystals which are isostructural with those of KClO₄. The salt is not very soluble in water (6.4g/ 100g of water at 293 K)
• It has intense colour and weak temperature-dependent paramagnetism.
• Green manganate ion is paramagnetic while permanganate ion is diamagnetic.
• Π bonding takes place by the overlap of p orbital of oxygen with d orbital of manganese.
• KMnO₄ is a good oxidizing agent in acidic, basic and neutral mediums.
• The molecular weight of KMNO₄ =158.034 g/mol
• The density of potassium permanganate is 2.703 g/cc
• Room temperature is the storage temperature of potassium permanganate
• The boiling point of potassium permanganate is 100 degrees Celsius.
• The melting point of potassium permanganate is 240 degrees Celsius

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Potassium Permanganate: Reactions 

Oxidizing properties of Potassium permanganate:

Potassium permanganate acts as a very powerful oxidizing agent in acidic, neutral and alkaline medium.

Acidic medium

2KMnO₄ + H₂SO₄ → K₂SO₄ + 2MnSO₄ + 3H₂O + 5 [O] MnO₄^- + 8H⁺ + 5^e-

→Mn₂⁺ + 4H₂O

Neutral or alkaline medium

2KMnO₄ + H₂O → 2KOH + 2MnO₂ + 3 [O] MnO₄^- + 2H₂O + 3^e- → MnO₂ +4OH^- 

Effect of alkalies on potassium permanganate

Potassium permanganate changes into manganate, on heating with alkalies, and produces oxygen. 

4KMnO₄ + 4KOH → 4K₂MnO₄ + 2H₂O + O₂

Potassium permanganate: reaction with acid

Potassium permanganate reacts with concentrated hydrochloric acid to produce chlorine. Potassium permanganate is reduced by three electrons to produce manganese dioxide, in a neutral solution, where the oxidation state of manganese is (+4). Permanganate reduces in an alkaline solution and turns to green K2MnO4.

Thermal decomposition reaction of potassium permanganate:

Usually, solid potassium permanganate is heated and it undergoes a decomposition reaction:

2KMnO₄ → K₂MnO₄ + MnO₂ + O₂

Where MnO₂ is solid.

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Different Uses of Potassium Permanganate or KMnO4

• Potassium permanganate is used as a regeneration chemical in water treatment for the removal of iron and hydrogen sulphide
• Potassium permanganate is also used as a disinfectant to cure certain skin conditions such as foot fungal infections and eczema 
• Potassium permanganate is used for treating bacterial infections
• It is also used for tanning leathers, printing fabrics
• Potassium permanganate is also used as a bleaching agent, pesticide, and antiseptic
• Potassium permanganate finds significant industrial applications as an oxidizing agent in the chemical synthesis of many important compounds.
• Potassium permanganate is used for gargling sore throat, in hospitals, as well.
• Potassium permanganate is used to detect the presence of unsaturation in organic compounds, in the laboratory as Baeyer’s reagent (KMnO₄ + KOH).
• Potassium permanganate is used for making dry cells

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Potassium Permanganate: Effect on Health

• Although used in hospitals, potassium permanganate in a concentrated form is an irritant to human eyes and skin. 
• Potassium permanganate can react with many reducing agents and organic material; however, it is inflammable too.
• As a good oxidizing agent, the antibacterial action of potassium permanganate is dependent on the oxidation (of proteins of bacteria or tissues by this compound). It may lead to staining the skin or tissues. It is because potassium permanganate acts by destructive oxidation process on all organic matter, its use is restricted only to external purposes. 
• In barbiturates, chloral hydrate or alkaloidal poisoning potassium permanganate acts as an antidote. A solution of 1:5000 of potassium permanganate is used as a gastric wash, oxidizes poison and also prevents their absorption.
• Potassium permanganate should be handled with care since an explosion may occur when it comes in contact with readily oxidizable substances, which is why it is usually stored in tightly closed containers.

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Things to Remember

• Molecular formula for Potassium Permanganate is KMNO₄.
• Molecular Mass of KMNO₄ =158.04 g/mol.
• Found as Black crystals or bright purple in solution form.
• KMNO₄ is a good oxidizing agent.
• KMNO₄ is combustible and may explode in contact with readily oxidizable substances, hence should be handled with care.

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