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JEE Main levelSingle correct optionDifficulty 2 of 3nc269

Why is the coupling of the diazonium salt shown with phenol carried out at pH about 9-10 rather than in strongly acidic solution?

  1. AIn mild alkali phenol is partly present as the phenoxide ion, a much stronger nucleophile, while the diazonium ion is still present
  2. BIn acid the diazonium ion is destroyed to phenol
  3. CAlkali removes the nitrogen from the diazonium ion to make it electrophilic
  4. DPhenol itself is non-aromatic unless it is deprotonated

Answer: A

The compound shown is phenol. The weak diazonium electrophile needs a strongly activated partner, so phenoxide (formed at pH 9-10) is used. At pH above about 11 the diazonium ion is converted to the unreactive diazotate, and in acid phenol is too poorly nucleophilic, so the optimum is mildly alkaline.
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