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NTA Abhyas JEE Main2020ChemistryAldehydes and KetonesPractice

Imine formation using an aldehyde/ketone and primary amine is acid-catalyzed, yet the rate drops below pH 4.5. Why does the rate drop below this pH?

Options

  1. AThe carbinolamine intermediate is stable at low pH
  2. BThe imine product is hydrolyzed at low pH
  3. CProtonation of the amine decreases its nucleophilicity
  4. DThe amine is hydrolyzed at low pH

Correct answer

C. Protonation of the amine decreases its nucleophilicity

Step-by-step solution

Imine formation: The reaction is possible pH 4 to 5 only. Hence, the reaction is pH dependent. At very low pH (high conc. of H + ): ammonia derivative will form their respective salts due to their basic nature and at the same time will lose their nucleophilic nature. At very high pH (high conc. of O H - ): carbonyl group will not be able to undergo sufficient protonation.

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