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Dihydroxylation of Alkenes

Cis-dihydroxylation of Alkenes: Laboratory Application

Baeyer test:

The Baeyer test checks for double bonds. In this test, a cold solution of potassium permanganate is added to the liquid to be tested. A color change from purple to colorless is indicative of the presence of double bonds.

Movie of double bond test

Fig.
Test for C=C double bonds

Example

Preparation of cis-cyclohexan-1,2-diol with potassium permanganate:

An ethanol solution of cyclohexene, potassium permanganate and magnesium sulfate is placed in a three-neck flask fitted with a thermometer, dropping funnel and stirrer and cooled in an ice-salt mixture. Water is added at such a rate not allowing the temperature to rise above 5°C. After two hours, manganese dioxide is removed by filtration and the filtrate is evaporated to give the desired product.

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