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Question #44918

Difficulty: 8/10 | 🟢 Free

The Question

Benzenediazonium chloride ( $\ce{PhN2+Cl-}$ ) is synthesized at $273\text{ K}$ . It is then subjected to three distinct reaction conditions to test chemoselectivity and stability:

Condition I: The diazonium salt is added to an aqueous solution of phenol at $\text{pH} = 0.5$ and the mixture is allowed to warm to $298\text{ K}$ . The major organic product isolated is $\mathbf{X}$ .

Condition II: The diazonium salt is added to an equimolar mixture of phenol and aniline, strictly buffered at $\text{pH} = 9.5$ at $273\text{ K}$ . The major organic product isolated is $\mathbf{Y}$ .

Condition III: The diazonium salt is added to an equimolar mixture of phenol and aniline, strictly buffered at $\text{pH} = 4.5$ at $273\text{ K}$ . The major organic product isolated is $\mathbf{Z}$ .

Identify $\mathbf{X}$ , $\mathbf{Y}$ , and $\mathbf{Z}$ .

Options

A.
$\mathbf{X} = \text{Phenol}$ ; $\mathbf{Y} = \text{p-Hydroxyazobenzene}$ ; $\mathbf{Z} = \text{p-Aminoazobenzene}$
B.
$\mathbf{X} = \text{p-Hydroxyazobenzene}$ ; $\mathbf{Y} = \text{p-Hydroxyazobenzene}$ ; $\mathbf{Z} = \text{p-Aminoazobenzene}$
C.
$\mathbf{X} = \text{Phenol}$ ; $\mathbf{Y} = \text{p-Aminoazobenzene}$ ; $\mathbf{Z} = \text{p-Hydroxyazobenzene}$
D.
$\mathbf{X} = \text{Benzene}$ ; $\mathbf{Y} = \text{p-Hydroxyazobenzene}$ ; $\mathbf{Z} = \text{p-Aminoazobenzene}$

Check Your Answer

Correct Answer

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

Diazotization Temperature Sensitivity|Azo Coupling Regioselectivity|Sandmeyer vs Gattermann

Why This Question Is Tricky

Common Mistakes

This question tests the 'Hidden Variable' of pH-dependent chemoselectivity in azo coupling and the thermal instability of diazonium salts.

Students often memorize that diazonium salts couple with both phenol and aniline, failing to recognize that the reaction requires specific ionization states (phenoxide at pH 9-10, free amine at pH 4-5).

Furthermore, the trap in Condition I highlights that if coupling conditions (pH) are not met, the diazonium salt will simply undergo thermal decomposition to phenol upon warming, a common reason for failed syntheses in the laboratory.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Amines - Class 12
Concept	Diazotization Temperature Sensitivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free