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Question #44019

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The Question

Consider the synthesis of the azo dye $\textbf{T}$ , 1-(4-hydroxy-3-(phenyldiazenyl)phenyl)propan-1-one, starting from 4-hydroxyacetophenone ( $\textbf{S}$ ). Which of the following reaction sequences will successfully yield $\textbf{T}$ as the major product?

Options

A.
1. \ce{MOM-Cl}, \ce{NaH} (1 eq), DMF; 2. LDA (1 eq), THF, $-78^\circ C$ , then \ce{CH3I} (1 eq); 3. Dil. \ce{HCl}, \ce{MeOH}, $\Delta$ ; 4. \ce{PhN2+Cl-}, aq. \ce{Na2CO3} (pH $\approx$ 9), $0^\circ C$
B.
1. \ce{PhN2+Cl-}, aq. \ce{Na2CO3} (pH $\approx$ 9), $0^\circ C$ ; 2. \ce{MOM-Cl}, \ce{NaH} (1 eq), DMF; 3. LDA (1 eq), THF, $-78^\circ C$ , then \ce{CH3I} (1 eq); 4. Dil. \ce{HCl}, \ce{MeOH}, $\Delta$
C.
1. \ce{NaH} (2 eq), THF, then \ce{CH3I} (2 eq); 2. \ce{PhN2+Cl-}, aq. \ce{Na2CO3} (pH $\approx$ 9), $0^\circ C$
D.
1. \ce{PhN2+Cl-}, aq. \ce{NaOH} (pH > 13), $0^\circ C$ ; 2. LDA (2 eq), THF, $-78^\circ C$ , then \ce{CH3I} (2 eq)

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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

Enolate Regioselectivity|Azo Coupling Regioselectivity

Why This Question Is Tricky

Common Mistakes

The question tests functional group compatibility and the precise conditions required for electrophilic aromatic substitution.

The hidden traps include: 1) The susceptibility of the azo linkage to strong bases/carbanions (invalidating early azo coupling), 2) The pH-dependent conversion of diazonium salts to unreactive diazotates in strong base, and 3) The insufficient activation of anisole derivatives for azo coupling when electron-withdrawing groups are present, necessitating a protection-deprotection strategy.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Enolate Regioselectivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free