Baeyers Test

The baeyers test is used to test for an unsaturated carbon carbon bond, such as an alkene or alkyne, but not an aromatic carbon carbon bond. Potassium permanganate (KMnO4) solution is a purple color. When potassium permanganate reacts with an alkene the solution changes from a purple color to a brown color, and a glycol is formed.

For example, potassium permanganate reacts with ethene to form ethylene glycol:

Materials

• Test tubes

• Test tube rack

• Potassium permanganate solution

• Sodium carbonate solution

• Acetone

• Compound to be tested

Safety

Sodium carbonate solution is an irritant. Potassium permanganate is oxidising and harmful. Acetone is flammable This test should be performed at room temperature.

Procedure

1. Dissolve 25-30 mg of organic compound in 2 mL of water or acetone (free of alcohol).

2. Add 1% potassium permanganate solution containing an equal volume of 1% sodium carbonate solution.

3. The potassium permanganate solution is purple. If the solution turns to a brown color when potassium permanganate is added an unsaturated carbon carbon bond is present. If the solution stays purple then no unsaturated carbon carbon bond is present. Carrying out the reaction under alkaline conditions removes the possibility of confusion due to substitution in aromatic compounds.

4. This test should be confirmed with the bromine test.

References:

• NCERT Lab Manual for Functional Group tests