# How can you identify alkenes?

Jul 14, 2016

Permanganate Oxidation (Von Baeyer test) and the addition of bromine are useful test to identify unsaturation.

#### Explanation:

Permanganate Oxidation (Von Baeyer test)

Under neutral conditions

$3 \text{Alkene"+ 2 KMnO_4 + 4 H_2O -> 3 "Glycol} + 2 M n {O}_{2} \downarrow + 2 K O H$

Note that in the course of this reaction under alkaline conditions, the purple color of the aqueous potassium permanganate is changed first to green as a result of the formation of manganate(VI) ions . . . Then the color changes to brown due to the formation of a brown solid which is manganese (IV) oxide ($M n {O}_{2}$).

The color change is a positive test for the presence of a double bond (or triple bond). Although this test has limitations, it is a good test to differentiate alkanes and aromatics from alkenes.