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Question #44910

Difficulty: 8/10 | 🟢 Free

The Question

Separate samples of the following eight amines are subjected to the Hinsberg test using an excess of benzenesulfonyl chloride ( $\ce{PhSO2Cl}$ ) and 10% aqueous $\ce{KOH}$ at 298 K.

(I) $n$ -Dodecylamine (II) 2,2,2-Trifluoroethylamine (III) N-Phenylglycine (IV) N-Methylaniline (V) L-Proline (VI) Aniline (VII) N,N-Dimethylaniline (VIII) Diethylamine

How many of these amines yield a final product (or remain as a species) that is completely soluble in the aqueous alkaline layer?

Options

A.
3
B.
4
C.
5
D.
6

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Hinsberg Reagent Selectivity|Inductive Effect Trends|Basicity-Solvation Competition

Why This Question Is Tricky

Common Mistakes

This problem tests the boundaries of the Hinsberg test, disrupting rote memorization.

Students typically memorize that $1^\circ$ amines are soluble and $2^\circ$ amines are insoluble.

The trap introduces 'Solvation Energy Competition' where a long-chain $1^\circ$ amine ( $n$ -dodecylamine) forms an insoluble salt due to hydrophobic effects.

Conversely, it introduces $2^\circ$ amines with hidden acidic protons (N-phenylglycine and L-proline) which form soluble carboxylate salts in KOH.

Finally, it reinforces the inductive effect where the strong -I effect of the CF3 group in 2,2,2-trifluoroethylamine ensures high acidity and solubility, contrasting with standard aliphatic chains.

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