Identify A in the following reaction.

Solution

Chemistry ma’am · 3 steps

Dichromate does not stop at the nitrogen. It attacks the electron-rich ring and turns it into a quinone.

1. Electron-rich ring. The -NH₂ group pushes electron density into the benzene ring, most strongly at the ortho and para positions. That makes aniline very easy to oxidise, and the ring itself is attacked.
2. What dichromate does. With acidified K₂Cr₂O₇, the carbon carrying -NH₂ and the carbon para to it both become C=O groups. The nitrogen leaves as ammonia, which ends up as NH₄⁺ in the acid.

   C₆H₅NH₂ →(K₂Cr₂O₇/H⁺) O=C₆H₄=O (p-benzoquinone)

3. So. A is p-benzoquinone, the six-membered ring with two C=O groups opposite each other and two ring C=C bonds. That is option (a).

The idea to keep. Strong oxidants like acidified dichromate attack the activated ring of aniline and give p-benzoquinone. To turn -NH₂ into -NO₂ you need a peroxy acid instead.

Answer from the NTA final answer key. Solution by PrepWiser.