Preparation of Potassium Permanganate – KMnO4

The first discovery of KMnO4  production was in 1659 by Johann Glauber, a German-Dutch chemist. The water-soluble compound, Potassium Permanganate, is composed of two ions: Permanganate ion (MnO4–)   and Potassium ion (K+). The ions are put together by an ionic bond. In its physical state, it appears as a purple-coloured dark solid with no odour. KMnO4 comes under the inorganic compound category. This compound is well known for its exceptional oxidising properties and is therefore termed an oxidising agent. This is one of the most common chemical properties of Potassium Permanganate, and its first preparation was carried out to facilitate disinfection.

Preparation of Potassium Permanganate

Pyrolusite ore is combined with KOH (or K2CO3) in the presence of air or oxidising agents, like KNO3 or KClO3, to form potassium permanganate K2MnO4 also called green mass.

2MnO2 + O2 + 4KOH  →  2K2MnO4  + 2H2O

Potassium Manganate is used to form Potassium Permanganate in two methods, either by HCl or by H2SO4. 

• Preparation with HCl

There are mostly two equations to prepare KMnO4. The equation to prepare KMnO4 with the use of HCl is given below –

2K2MnO4 + 4HCl  →  2KMnO4  + H2O + MnO2 + 4KCl

• Preparation with H2SO4

The equation used in the preparation of KMnO4 with the use of H2SO4 is given below,

3K2MnO4 + 2H2SO4    →  2KMnO4  + 2H2O + MnO2 + 2K2SO4

• Laboratory preparation of Potassium Permanganate 

This is another method to prepare Potassium Permanganate. It includes oxidising manganese (II) ion salt by peroxodisulphate to get permanganate ions in the laboratory. The equation included is –

2Mn+2 + 5S2O8-2 + 8H2O →  2MnO4–  + 10 SO4-2+ 16H+ 

Chemical Properties of Potassium Permanganate 

Various well-known chemical properties of Potassium Permanganate are, 

1. The action of heat

On heating, potassium permanganate undergoes a decomposition reaction and decomposes to potassium manganate and manganese dioxide. The reaction is –

2KMnO4 → 2K2MnO4 + MnO2 + O2

2. The action of concentrated H2SO4

On treatment with cold and concentrated H2SO4, the potassium permanganate decomposes into Manganese heptoxide, which is known to explosively decompose subsequently. The reaction involved is –

2KMnO4 + 2H2SO4 (cold) → Mn2O7 + 2KHSO4 + H2O (cold)

Mn2O7 →Δ→ 2MnO2 + 3O2

On the other hand, when in reaction with hot concentrated H2SO4, potassium permanganate produces MnSO4 –

4KMnO4 + 6H2SO4(hot) → 4MnSO4 + 2K2SO4 + 6H2O + 5O2 (hot)

Acting as an Oxidising Agent 

Potassium permanganate is a strong oxidising agent involved in various oxidation reactions. The oxidation reactions in different mediums are given below – 

1. Oxidation in neutral medium

In a neutral medium, Potassium Permanganate gets reduced to MnO2.

MnO4− + 2H2O + 3e− → MnO2 + 4OH−

• Oxidising H2S to Sulphur

3H2S + 2MnO4−  → 2MnO2 + 2OH− + 3S + + 2H2O

• Oxidising thiosulphate into sulphate

8MnO4− + 3S2O32− + H2O → 6SO42− + 8MnO2 + 2OH−

2. Oxidation in alkaline medium 

Permanganate Ion converts into manganate ion when the alkali metal hydroxides are present.  

MnO4− + e− → MnO42−

There is a  further reduction of this Manganate ion by specific reducing agents. 

MnO42− + H2O → MnO2 + 2OH− + [O]

Therefore the summed up reaction will be –

MnO4− + 2H2O + 3e− → MnO2 + 4OH−

If looked at the equation, it resembles the one for neutral mediums.

Uses of Potassium Permanganate 

Potassium Permanganate, like any other compound, is used for different purposes. Among the various uses of Potassium Permanganate, mentioned below are some important ones, 

• The compound, Potassium Permanganate, is used to determine the value of permanganate in qualitative analysis.

• During the well water treatment, the chemical KMnO4 is used for regeneration as it helps in the removal of hydrogen sulphide and iron. 

• Potassium Permanganate also helps cure various skin conditions, including dermatitis, foot fungal infection, etc., thus acting as a disinfectant.  

• Potassium Permanganate also helps with the treatment of bacterial infections.

• It is helpful in the tanning of leather and fabric printing.  

• It is used as a bleaching agent, antiseptic, and pesticide.  

• Acts as an oxidising agent and helps synthesise various important compounds. 

Potassium Permanganate’s effects on health

Potassium Permanganate is known for its effects on health. The following points are the widely significant effects of Potassium Permanganate on health –

• Potassium Permanganate is often used in hospitals, but this does not disqualify them as not being an irritant for the human eye and skin in concentrated form.

• Potassium Permanganatecano reacts with organic materials and reducing agents, but it is also inflammable, which can be a health hazard.

• Being an oxidising agent, the antibacterial tendencies of potassium permanganate are completely reliant on oxidation, leading to the staining of tissues and skin. The antibacterial action potassium permanganate carries out is destructive and therefore is used for areas for external purposes only.

• Potassium permanganate is also known to be acting as an antidote for chloral hydrate or alkaloid poisoning and is mainly seen in barbiturates.

• Potassium Permanganate solution with 1:5000 concentration is brought into use as a gastric wash, and also helps oxidise poison and prevents its absorption. 

• The compound is usually stored in airtight containers because of its nature to initiate explosion when in contact with a substance easily oxidisable. 

Conclusion 

Potassium Permanganate is mostly found as purple-coloured solid crystals. It is a complex compound with tetrahedral geometry. The potassium permanganate compound can retain itself for a long time. One of the most important chemical properties of Potassium Permanganate is being an oxidising reagent. Potassium Permanganate is prepared using pyrolusite ore. Potassium Permanganate helps in the preparation of disinfectants. Potassium Permanganate is water soluble with two constituent ions, K+  and MnO4–. Being an oxidative reagent, KMnO4 is highly combustible.