Iodine Test for alkene

Iodine Test:

Procedure:

Add 0.25 mL or 0.25 g of the unknown sample to 0.5 mL of the iodine in methylene chloride solution. If an ether is present, the purple solution becomes tan in color. Aromatic hydrocarbons, saturated hydrocarbons, fluorinated hydrocarbons, and chlorinated hydrocarbons do not react. Unsaturated hydrocarbons produce a light tan solid, while retaining the purple color of the iodine solution.
Iodine in Methylene Chloride Solution: Add a couple of crystals of iodine to 100 mL of methylene chloride. Stopper the flask tightly.

Positive Test:

alkene - the purple solution becoming tan in color is a positive test.


Complications:

1.Some alcohols and ketones give a positive test.

2.Some compounds with nonbonded electron pairs or -bonded electrons form charge transfer complexes with iodine yielding brown solutions.

3.ether - production of a light tan solid in the purple solution is a positive test.