1-Chloro-4-nitrobenzene is heated with aqueous sodium hydroxide at 443 K, and the solution is then acidified. What is the main organic product?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4-Nitrophenol
Aryl halides react with nucleophiles only with great difficulty: chlorobenzene gives phenol with aqueous NaOH only at 623 K and 300 atm.
An electron withdrawing –NO2 group at the ortho- or para-position makes the reaction much easier. It pulls electron density out of the ring, so OH− can attack the carbon bearing Cl, and it stabilises the negatively charged intermediate (carbanion) by resonance.
So OH− replaces Cl at 443 K, and acid then turns the sodium phenoxide into the phenol:
\( \displaystyle \ce{O2N-C6H4-Cl} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) NaOH, 443 K}} \ce{O2N-C6H4-OH} \)
Why the other options are incorrect
Option (1) 4-Chlorophenol — Incorrect. The group replaced is the halogen, not the nitro group. The –NO2 group stays on the ring and is the reason the reaction goes easily.
Option (2) Phenol — Incorrect. Only one group, the chlorine, is replaced by –OH. The nitro group is not removed, so the product still carries –NO2.
Option (4) No product is formed, because the reaction needs 623 K and 300 atm — Incorrect. Those drastic conditions are needed for chlorobenzene, which has no activating group. With the para-nitro group the reaction already takes place at 443 K.
NCERT (2026-27 edition):
6.7.2 Reactions of Haloarenes – “Replacement by hydroxyl group Chlorobenzene can be converted into phenol by heating in aqueous sodium hydroxide solution at a temperature of 623K and a pressure of 300 atmospheres.”
“The presence of an electron withdrawing group (-NO2) at ortho- and para-positions increases the reactivity of haloarenes.”
“…As shown, the presence of nitro group at ortho- and para-positions withdraws the electron density from the benzene ring and thus facilitates the attack of the nucleophile on haloarene. The carbanion thus formed is stabilised through resonance.”