Tuesday, April 10, 2012

Baeyer Test for Multiple Bonds (Potassium Permanganate Solution)

Cyclohexane, Cyclohexene and Bromobenzene.

Dissolve 1 drop or 0.02 grams of the unknown in 0.5 mL reagent grade acetone. Add a 1% aqueous solution of potassium permanganate dropwise with shaking. If more than one drop of reagent is required to give a purple color to the solution, unsaturation or an easily oxidized functional group is present. Run parallel tests on pure acetone and, as usual, the standards listed above.

Positive Test
The disappearance of the KMnO4's purple color and the appearance of a brown suspension of MnO2 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: a) Most aldehydes give a positive test. b) 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.
Carbonyl compounds which decolorize bromine/methylene chloride usually give a negative test.

Cleaning up
The solution should be diluted with water and flushed down the drain. Any solutions containing organic compound should be placed in the appropriate waste container.


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