MOLISCH’S REACTION – GENERAL REACTIONS OF CARBOHYDRATES

MOLISCH’S REACTION general reaction for the detection of carbohydrates.

PRINCIPLE:

Sugars on reaction with dehydrating agents like strongly concentrated acids (Concentrated H2SO4) yield furfural and furfural derivatives such as hydroxymethyl furfural, which condense With α-naphthol and give a reddish Violet ring.

REAGENTS:

1.Molisch’s Reagent:

i- α-naphthol,

ii- Ethyl alcohol

2. Concentrated H2SO4

3. Original solution (O.S)- containing a carbohydrate.

PROCEDURE:

• To 2ml of sugar solution (original solution) add 2 to 3 drops of Molisch’s reagent.
• Mix thoroughly.
• Carefully pour 5 ml concentrated H2SO4 along the side of the test tube.
• Acid being heavier will form a layer beneath the sugar solution.

INDICATION:

The formation of a reddish violet ring at the junction of the two liquids indicates the presence of carbohydrates.

RESULT:

Carbohydrates are present.

NOTE:

This test is very sensitive and is given by all the carbohydrates

Precautions:

• Wash the apparatus before and after the experiment.
• Carefully pour the acids along the side of the test tube.

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