To 2 mL of water or ethanol add 0.1 g or 0.2 mL of the unknown. Then add a 2% aqueous potassium permanganate solution drop by drop with shaking until the purple color of the permanganate persists.
The disappearance of the purple color and the appearance of a brown suspension is a positive test.
Water insoluble compounds should be dissolved in ethanol, methanol, or acetone.
Often, the brown precipitate fails to form and the solution turns reddish-brown.
Easily oxidized compounds give a positive test: