In which of the following, nitro chlorobenzene derivative can easily be converted into its corresponding phenolic compound by heating with water.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 2,4,6-Trinitrochlorobenzene
Chlorobenzene itself is converted to phenol only on heating with aqueous NaOH at 623 K and 300 atm. An electron withdrawing –\( \ce{NO2} \) group at the ortho or para position stabilises the carbanion intermediate by resonance and makes the replacement of Cl by OH much easier; the more such groups, the milder the conditions:
4-Nitrochlorobenzene — aqueous NaOH at 443 K
2,4-Dinitrochlorobenzene — aqueous NaOH at 368 K
2,4,6-Trinitrochlorobenzene — warm water alone
2,4,6-\( \ce{(NO2)3C6H2Cl} \) + \( \ce{H2O} \) \( \xrightarrow{\text{warm}} \) 2,4,6-\( \ce{(NO2)3C6H2OH} \) (picric acid) + HCl