In the above conversion of compound (X) to product (Y), the sequence of reagents to be used will be:

Solution

Chemistry ma’am · 4 steps

Use NH₂ to place both bromines where you want them, then remove it with diazotisation and H₃PO₂.

1. Read the target. In Y the two Br atoms are meta to CH₃ and there is no nitrogen left. CH₃ directs ortho/para, so it cannot put Br at those positions. You need a temporary group at C4 that sends Br to C3 and C5.
2. Reduce, then brominate. Fe/H⁺ reduces -NO₂ to -NH₂, giving p-toluidine. -NH₂ strongly activates the ring, so Br₂(aq) brominates both positions ortho to it, C3 and C5, with no catalyst. These are the positions meta to CH₃.
3. Remove the nitrogen. HNO₂ (from NaNO₂ + HCl, 273 to 278 K) turns -NH₂ into -N₂⁺. H₃PO₂ then replaces -N₂⁺ with H, and N₂ gas is released.

   ArNO₂ →(Fe/H⁺) ArNH₂ →(Br₂(aq)) Br₂ArNH₂ →(HNO₂) Br₂ArN₂⁺ →(H₃PO₂) Br₂ArH

4. So. The sequence Fe/H⁺, Br₂(aq), HNO₂, H₃PO₂ gives 3,5-dibromotoluene. The answer is option (c).

The idea to keep. Need substituents where no existing group can direct them? Bring in -NH₂ to direct, then diazotise and treat with H₃PO₂ to remove it without a trace.

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