OXIDATION OF GLYCEROL WITH POTASSIUM PERMANGANATE: A CHEMICAL VOLCANO




       
            The structure of glycerol. Picture courtesy Google.



You may have heard of glycerin, or glycerol, which is an essential component in many cosmetics and soap cakes. It is used as a laxative, a moisturizer, and an antibacterial drug. This experiment, depicting the oxidation of glycerol by potassium permanganate, is extremely dangerous, and should not be attempted by inexperienced personnel.

The IUPAC name for glycerol is propane-1,2,3-triol. Glycerol is a polyhydric alcohol, where three hydroxyl groups are attached to adjacent atoms in a propane chain. Due to this, it is highly viscous, and miscible in water. It has a sweet taste.

Potassium permanganate is an extremely powerful oxidizing agent, which in an acidic medium, normally converts 1° alcohols to carboxylic acids, and 2° alcohols to ketones (they can be oxidized further to carboxylic acids under drastic conditions). However, in the case of glycerol, a spectacular reaction is seen.

REAGENTS:

• Anhydrous glycerol (5-10 mL)

• Some dry potassium permanganate crystals, finely ground. (The crystals have to be finely ground, for the oxidation to be faster.)

• Adequate water (The water is essential to minimize the risks of an accident.)

PROCEDURE:

• Make a small heap of potassium permanganate in a porcelain dish, and make a small, fairly deep cavity at the top.

• Take up some glycerol in a dropper, and add 7-8 drops into the cavity. Be extremely careful while doing this; the moment you see smoke, move away from the dish, and remove all flammable items nearby as well.

• If smoke doesn't start evolving immediately, very carefully, add some more potassium permanganate crystals, and move away immediately.

• The mixture bursts into lilac flames without any heating. This is because the potassium permanganate oxidizes the glycerol to carbon dioxide and water, creating a lot of heat in the process, which ignites the glycerol remaining in the mixture. The lilac flames are observed due to the presence of the potassium cation.

• Extinguish the fire with water so as to prevent its spread.


The oxidation of glycerol by potassium permanganate produces lilac flames.


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