Question

Which of the following compounds can be detected by Molisch’s test?
A. Nitro compounds
B. Sugars
C. Amines
D. Primary alcohols

Answer 1

Molisch’s test is defined as a chemical test in which a Molisch reagent is added with addition of few drops of concentrated sulphuric acid to the mixture. A Molisch’s reagent is a solution of $\alpha -$naphthol in ethanol. A purple ring is formed when Molisch’s reagent is added in concentrated sulphuric acid.

Complete step-by-step answer: The basic principle of Molisch’s test is when the carbohydrate undergoes dehydration when concentrated sulphuric acid is added which results in the formation of aldehydes. After that, this aldehyde undergoes a condensation reaction with $\alpha -$naphthol. A purple coloured complex is formed.
Now let us see the procedure for Molisch test-
In a test tube, $2-3$ drops of molisch reagent are added in a small amount of the analyte. After that sulphuric acid is added drop wise along the walls of the test tube that results in the formation of a layer. If a purple ring is formed at the layer, this indicates the positive test and the given analyte contains sugar. If there is no colour arises that means the test is negative and the given analyte does not contain sugar.
We can detect sugar compounds using Molisch’s test.

Therefore the correct option is B.

Note: -The presence of red- purple layer between the acid and aqueous layer gives us the positive test.
-Molisch’s test is used to detect the presence of sugar present in the given analyte. It is also considered as a test for pentoses and hexoses.
-All the carbohydrates excluding tetroses and trioses gives a positive reaction for this test.