Bromine Test for alkene and alkyne

Bromine Test:

Procedure:

In a hood, 0.1 g or 0.2 mL of the unknown is added to 2 mL of carbon tetrachloride, and a 5% solution of bromine in carbon tetrachloride is added drop by drop, with shaking, until the bromine color persists.



Positive Test:

Discharging of the bromine color without the evolution of hydrogen bromide gas is a positive test.



Complications:

1.Should be employed in conjunction with Baeyer test (dilute KMNO4).

2.Electron-withdrawing groups in the vinylic position can slow down bromine addition to the point that a negative test is erroneously produced.

3.Tertiary amines (like pyridine) form perbromides upon treatment with bromine and lead to false positive tests.

4.Aliphatic and aromatic amines discharge the bromine color without the evolution of HBr gas.