Functional Groups - The KMnO4 Test
Shows positive test for:
aldehydes, alkenes and phenols
Reactions:
aldehydes are oxidized to carboxylic acids
alkenes are oxidized to glycols
monohydroxy phenols do not yield stable products but dihydroxyl phenols can be oxidized to quinones
How to perform the test:
Three drops of the compound to be tested are dissolved in 2 ml of water or aqueous ethanol. 2% KMnO4 solution (a purple solution) is added dropwise and the solution is shaken.
Indications of a positive test:
The purple color of the KMnO4 solution disappears and a precipitate of MnO2 is formed.
a negative test (left) and a positive test (right)