MolSynapsequestion bank
MolSynapse / Question bank / Reduction, Oxidation and Hydrolysis in Organic Chemistry / Dissolving metal reductions (Birch, Na/NH3)
JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ro184

Which of the following statements about the mechanism of the Birch reduction of benzene (Na, liquid , ethanol) are correct?

  1. AThe first step is transfer of a solvated electron to the ring, giving a radical anion.
  2. BThe radical anion is protonated by the alcohol.
  3. CLiquid ammonia alone is acidic enough to supply protons efficiently, so the alcohol is unnecessary.
  4. DOverall, two electrons and two protons are added per molecule of benzene.

Answer: A, B, D

The sequence is electron transfer, protonation of the radical anion by the alcohol, a second electron transfer and a second protonation, so two electrons and two protons are consumed. Ammonia is too weak an acid to protonate the radical anion efficiently, which is why an alcohol is added. Therefore options 1, 2 and 4 are correct.
Practice Reduction, Oxidation and Hydrolysis in Organic Chemistry More on Dissolving metal reductions (Birch, Na/NH3)
Previous questionNext question

More questions on Dissolving metal reductions (Birch, Na/NH3)