Tuesday, April 10, 2012

Bromine (in Methylene Chloride) Test for Multiple Bonds

Cyclohexane, Cyclohexene, and Bromobenzene

In a hood, 0.02 g or 1 drop of the unknown is added to 0.5 mL of methylene chloride. Add a dilute solution of bromine in methylene chloride dropwise, with shaking, until the bromine color persists. The bromine solution must be fresh.

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


Should be employed in conjunction with Baeyer test (dilute KMnO4).
Electron-withdrawing groups in the vinylic position can slow down bromine addition to the point that a negative test is erroneously produced.
Tertiary amines (like pyridine) form perbromides upon treatment with bromine and lead to false positive tests.
Aliphatic and aromatic amines can discharge the bromine color without the evolution of HBr gas.

Cleaning up
The solution should be placed in the appropriate waste container.


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