Baeyer Test for alkene and alkyne

Baeyer Test:

Procedure;

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.

Positive Test:

The disappearance of the purple color and the appearance of a brown suspension is a positive test.

Complications:

1.Water insoluble compounds should be dissolved in ethanol, methanol, or acetone.

2.Often, the brown precipitate fails to form and the solution turns reddish-brown.

3.Easily oxidized compounds give a positive test:
• most aldehydes give a positive test
• formic acid and its esters give a positive test
• alcohols with trace impurities give a positive test
• phenols and aryl amines give a positive test
• mercaptans and thioethers give a positive test
• carbonyl compounds which decolorize bromine/carbon tetrachloride usually give a negative test