How will you distinguish between primary, secondary and tertiary amines by Hinsberg’s Test?

Hinsberg's Test is a chemical test used to distinguish primary, secondary, and tertiary amines based on their reaction with benzene sulfonyl chloride (Hinsberg's reagent).

Here's how the test works:

Primary Amines: Primary amines react with benzene sulfonyl chloride to form N-alkylbenzenesulfonamide, which is soluble in alkali. This is because the primary amine group is more nucleophilic and can easily displace the chlorine atom from the sulfonyl chloride group. The reaction can be represented as:

R-NH₂ + C₆H₅SO₂Cl ⟶ R-NHSO₂C₆H₅ + HCl

This sulfonamide product is soluble in alkali and can be separated from the unreacted amine.

Secondary Amines: Secondary amines react with benzene sulfonyl chloride to form N,N-dialkylbenzenesulfonamide, which is also soluble in alkali. The reaction involves the displacement of two chlorine atoms by the amine groups:

R₂NH + C₆H₅SO₂Cl ⟶ R₂NHSO₂C₆H₅ + HCl

Like primary amines, the sulfonamide product is soluble in alkali and can be separated.

Tertiary Amines: Tertiary amines do not react with benzene sulfonyl chloride under normal conditions. This is because they lack a hydrogen atom attached to the nitrogen atom, which is necessary for the nucleophilic attack on the sulfonyl chloride. Therefore, no reaction occurs, and the tertiary amine remains unchanged.

By observing the solubility of the products formed after reacting with benzene sulfonyl chloride in alkali, you can distinguish between primary, secondary, and tertiary amines. Primary and secondary amine sulfonamide products are soluble, while tertiary amine remains insoluble since it does not react.