Benzene is treated with oleum to produce compound (X) which when further heated with molten sodium hydroxide followed by acidification produces compound (Y). The compound Y is treated with zinc metal to produce compound (Z). Identify the structure of compound (Z) from the following option.

Solution

Chemistry ma’am · 4 steps

Follow the OH group: it goes on in step two, and hot zinc dust takes it right back off.

1. Sulphonation gives X. Oleum (H₂SO₄ with extra SO₃) puts one -SO₃H group on the ring. So X is benzenesulphonic acid, C₆H₅SO₃H.
2. Alkali fusion gives Y. Heating with molten NaOH swaps -SO₃H for -ONa, giving sodium phenoxide. Acidification turns this into phenol, C₆H₅OH, which is Y.

   C₆H₆ →(oleum) C₆H₅SO₃H →((i) NaOH, fuse, (ii) H⁺) C₆H₅OH →(Zn dust, Δ) C₆H₆

3. Zinc removes OH. When phenol is heated with zinc dust, zinc pulls off the oxygen and becomes ZnO: C₆H₅OH + Zn → C₆H₆ + ZnO. The ring is left with only hydrogens.
4. So. Z is benzene, the plain ring shown in option (c). The sequence takes you from benzene back to benzene.

The idea to keep. Distilling phenol with zinc dust reduces it to benzene. Remember it as the reverse of the sulphonation and alkali-fusion route that turns benzene into phenol.

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