Question

The reagent which is used to distinguish primary, secondary and tertiary amines from the mixture is

• A. Fehling's reagent
• B. Tollens reagent
• C. Lucas reagent
• D. Hinsberg's reagent

Hint:

Instead of working out the full mechanism first, recall that named reagent tests are each tied to one functional group: Fehling and Tollens reagents test for aldehydes, Lucas reagent tests for alcohols. That elimination alone narrows it down. Then confirm by checking how many hydrogens sit on the nitrogen of each amine type and whether the resulting product dissolves in alkali.

Answer 1

The Correct Option is D

Step 1: Identify the Reagent: Hinsberg's reagent is Benzenesulfonyl chloride (\( \text{C}_6\text{H}_5\text{SO}_2\text{Cl} \)). It reacts differently with amines:
Step 2: Reaction with Amines: - Primary Amine ($1^\circ$): Reacts to form N-alkylbenzenesulfonamide. The product has an acidic hydrogen attached to nitrogen, so it is soluble in alkali (NaOH). - Secondary Amine ($2^\circ$): Reacts to form N,N-dialkylbenzenesulfonamide. The product has no acidic hydrogen, so it is insoluble in alkali. - Tertiary Amine ($3^\circ$): Does not react with Hinsberg's reagent (no H on nitrogen). The amine remains insoluble (or soluble in acid).
Step 3: Conclusion: Because of these distinct observations (soluble product, insoluble product, no reaction), Hinsberg's reagent is the standard method to distinguish and separate the three classes of amines.