What other reaction is commonly used as a functional group test for alkenes?

1 Answer
Feb 8, 2015

There are two common tests for alkenes.

Bromine in CCl₄

Add a few drops of the Br₂/CCl₄ solution to the unknownd.

If your unknown is an alkene, the reddish-brown colour of the bromine will disappear quickly.

CH₂=CH₂ + Br₂ → BrCH₂-CH₂Br

The video below shows the colour change.

The Baeyer Test

Shake a few drops of a dilute solution of aqueous potassium permanganate with a small amount of the unknown.

If your compound is an alkene, the purple colour of the permanganate ion will disappear and a brown precipitate of MnO₂ will form:

3CH₂=CH₂ + 2KMnO₄ + 4H₂O → 3HOCH₂-CH₂OH + 2MnO₂(s) +2KOH

The video below shows the colour changes for a positive test.