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:

Summarize the Hinsberg Test: - 1° Amine: Reacts, product is soluble in alkali. - 2° Amine: Reacts, product is insoluble in alkali. - 3° Amine: Does not react. This clear difference in reactivity and solubility is the basis of the test.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The question asks for a chemical test that can differentiate between primary (1°), secondary (2°), and tertiary (3°) amines. This requires a reagent that reacts differently with each class of amine based on the number of hydrogen atoms attached to the nitrogen.
Step 2: Analyzing the Reagents:
- (A) Fehling's reagent and (B) Tollens' reagent: These are mild oxidizing agents used to distinguish aldehydes from ketones. They do not react with amines in a way that allows for their differentiation.
- (C) Lucas reagent (Anhydrous ZnCl₂ + Conc. HCl): This reagent is used to distinguish between primary, secondary, and tertiary alcohols based on the rate of formation of alkyl chlorides. It does not distinguish between amines.
- (D) Hinsberg's reagent (Benzenesulfonyl chloride, C₆H₅SO₂Cl): This is the classic reagent used for the distinction of primary, secondary, and tertiary amines. The test is based on the formation of sulfonamides. - Primary amines (R-NH₂): Have two H-atoms on N. They react with Hinsberg's reagent to form an N-alkylbenzenesulfonamide. This product has an acidic hydrogen on the nitrogen, making it soluble in aqueous alkali (like KOH or NaOH). - Secondary amines (R₂NH): Have one H-atom on N. They react with Hinsberg's reagent to form an N,N-dialkylbenzenesulfonamide. This product has no acidic hydrogen on the nitrogen, so it is insoluble in alkali. - Tertiary amines (R₃N): Have no H-atoms on N. They do not react with Hinsberg's reagent at all (under these conditions).
Thus, by observing the reaction with Hinsberg's reagent and the subsequent solubility in alkali, one can distinguish between the three classes of amines.
Step 3: Final Answer:
Hinsberg's reagent is used to distinguish primary, secondary, and tertiary amines. Therefore, option (D) is correct.