Functional Groups - The Iodoform Test
Shows positive test for:
acetaldehyde and methyl ketones
Reactions:
the methyl group of the ketone is removed from the molecule and produces iodoform (CHI3)
How to perform the test:
Three drops of the compound to be tested are added to 3 ml of water and 10 drops of KI/I2 solution (a dark purple-brown solution). 10% NaOH solution is added dropwise until the dark color of the solution fades to yellow. The solution is heated at 60oC. If the color of the solution becomes colorless, more KI/I2 solution is added.
Indications of a positive test:
The formation of a yellow precipitate or suspension of iodoform is a positive test.
a negative test (left) and a positive test (right)