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Question #44909

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The Question

Compound $\mathbf{X}$ has the molecular formula $C_{19}H_{17}N$ . Its IR spectrum exhibits two distinct, sharp absorption bands in the $3300-3500\ \text{cm}^{-1}$ region. When $\mathbf{X}$ is subjected to the Hinsberg test using benzenesulfonyl chloride ( $\ce{PhSO2Cl}$ ) in excess aqueous $\ce{NaOH}$ at 298 K, a biphasic mixture is observed with an insoluble organic layer. Separation of this organic layer followed by treatment with dilute aqueous $\ce{HCl}$ results in its complete dissolution, yielding a clear solution. Which of the following correctly identifies $\mathbf{X}$ and the primary reason for its anomalous Hinsberg behavior?

Options

A.
$\mathbf{X}$ is tritylamine ( $\ce{Ph3C-NH2}$ ); extreme steric hindrance prevents nucleophilic attack on $\ce{PhSO2Cl}$ , leaving unreacted amine that dissolves in $\ce{HCl}$ .
B.
$\mathbf{X}$ is $N,N$ -diphenylbenzylamine ( $\ce{Ph2N-CH2Ph}$ ); as a 3° amine, it inherently lacks an acidic proton to form a soluble sulfonamide salt, and the free base dissolves in $\ce{HCl}$ .
C.
$\mathbf{X}$ is tritylamine ( $\ce{Ph3C-NH2}$ ); it reacts to form a highly lipophilic sodium sulfonamide salt that is insoluble in $\ce{NaOH}$ but undergoes protonation to dissolve in $\ce{HCl}$ .
D.
$\mathbf{X}$ is $N$ -benzhydrylaniline ( $\ce{Ph2CH-NH-Ph}$ ); it forms an insoluble sulfonamide in base that undergoes rapid acid-catalyzed hydrolysis to dissolve in $\ce{HCl}$ .

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Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Hinsberg Reagent Selectivity|Ammonolysis Complexity

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of spectroscopic identification and mechanistic anomalies in standard qualitative tests.

Students often rely on rote memorization of the Hinsberg test (1° = soluble in base, 3° = insoluble in base/soluble in acid).

The trap introduces a sterically hindered 1° amine (tritylamine) that kinetically fails to react with the Hinsberg reagent, perfectly mimicking a 3° amine's macroscopic behavior.

Distractor B is a 3° amine isomer that fits the physical observations but contradicts the IR data.

Distractor C tests the misconception that sulfonamides can act as bases and dissolve in aqueous acid.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Amines - Class 12
Concept	Hinsberg Reagent Selectivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free