Bromine test
The bromine test is used to test for an unsaturated carbon carbon bond, such as an alkene or alkyne. The test uses a type of chemical reaction called addition, where a reactant, here bromine, is added to an organic compound to break a double or triple bond.
For example the addition of bromine to but-2-ene:
Bromine has an orange-brownish color when in solution, so the color of the solution is lost when an alkene or alkyne is present for bromine to react with. Bromine will also react with aromatic compounds, such as phenol, but it can't react with alkanes as they contain only single bonds, and therefore there is no color change when these are mixed. Benzene can react with bromine in the presence of a catalyst, but not without a catalyst since it is not reactive enough. Phenol is more reactive than benzene so can react with bromine without a catalyst. This is because the alcohol group donates electron density into the delocalized benzene ring.
Materials
- Test tubes
- Test tube rack
- Carbon tetrachloride
- Chloroform
- Bromine water
- Compound to be tested
Safety information
Bromine is corrosive, toxic, and an environmental hazard. Bromine causes eye and skin burns, as well as digestive and respiratory tract burns. It may be fatal if inhaled and is a strong oxidizer. Contact with other material may cause a fire. Corrosive to metal. Carbon tetrachloride is toxic. Chloroform is harmful. This test should be performed at room temperature.
Procedure
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Dissolve 0.1 g or 5 drops of organic compound in 2 mL of carbon tetrachloride. If you do not have carbon tetrachloride, a solvent such as chloroform or water can be used to dissolve the organic compound.
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Add 2% solution of bromine water drop by drop with continuous shaking.
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If the bromine solution becomes colorless then there is an unsaturated carbon carbon bond in the organic compound. This test should be confirmed with the baeyers test.
References:
- NCERT Lab Manual for Functional Group tests