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Question #44944

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of 4-methylbenzenediazonium chloride (0.10 M0.10\text{ M}) is prepared at 273 K273\text{ K} in dilute \ceHCl\ce{HCl}. The thermal decomposition of this diazonium salt to 4-methylphenol and \ceN2(g)\ce{N2(g)} proceeds via an SN1\text{S}_\text{N}1 mechanism. The first-order rate constant for this decomposition is k=6.93×10−2 min−1k = 6.93 \times 10^{-2}\text{ min}^{-1} at 298 K298\text{ K}.

During a synthesis protocol, the cooling bath fails, and the acidic reaction mixture is inadvertently exposed to 298 K298\text{ K} for exactly 20 minutes. The mixture is then rapidly quenched to 273 K273\text{ K}, and an excess of alkaline naphthalen-2-ol (β\beta-naphthol) is immediately added to achieve complete electrophilic aromatic substitution.

Assuming no volume change and quantitative coupling of the surviving diazonium ions, identify the major organic products in the final mixture (excluding unreacted naphthalen-2-ol) and their exact molar ratio. (Given: ln⁡2=0.693\ln 2 = 0.693)

Options

  • A.

    1-(p-tolylazo)naphthalen-2-ol and 4-methylphenol in a 1:31:3 molar ratio

  • B.

    1-(p-tolylazo)naphthalen-2-ol and 4-methylphenol in a 3:13:1 molar ratio

  • C.

    4-(p-tolylazo)naphthalen-2-ol and 4-methylphenol in a 1:31:3 molar ratio

  • D.

    1-(p-tolylazo)naphthalen-2-ol and 4-methylphenol in a 1:41:4 molar ratio

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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

Coupling Reactivity|Diazotization Temperature Sensitivity|Sandmeyer vs Gattermann

Why This Question Is Tricky

Common Mistakes

This question tests the thermodynamic and kinetic instability of diazonium salts, a frequently overlooked concept.

Students often assume diazonium salts are indefinitely stable and ready for coupling regardless of temperature.

The trap introduces a thermal threshold conflict: at 298 K298\text{ K}, the diazonium salt undergoes competitive SN1\text{S}_\text{N}1 decomposition to a phenol faster than it can be preserved.

The problem requires integrating first-order chemical kinetics with organic synthesis, recognizing that coupling with the formed phenol is suppressed in acidic media, and correctly identifying the C-1 regioselectivity of β\beta-naphthol coupling.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterAmines - Class 12
ConceptCoupling Reactivity
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree