Phenol reacts with a compound (X) in the presence of aqueous NaOH to give phenyl benzoate. Identify (X).
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Benzoyl chloride
Phenyl benzoate, \( \ce{C6H5COOC6H5} \), is an ester: a benzoyl group (\( \ce{C6H5CO-} \)) joined to the oxygen of phenol. Phenols form esters with acid chlorides, so (X) must supply the benzoyl group: (X) is benzoyl chloride, \( \ce{C6H5COCl} \).
\( \displaystyle \ce{C6H5OH + C6H5COCl + NaOH -> C6H5COOC6H5 + NaCl + H2O} \)
The H of the phenolic –OH and the Cl of benzoyl chloride leave as HCl, which the base neutralises; this drives the reaction forward. This is benzoylation of phenol.
Why the other options are incorrect
Option (1) Benzyl chloride — Incorrect. \( \ce{C6H5CH2Cl} \) has no C=O group. The phenoxide ion replaces its Cl to give an ether, benzyl phenyl ether \( \ce{C6H5OCH2C6H5} \), not an ester.
Option (3) Acetyl chloride — Incorrect. \( \ce{CH3COCl} \) introduces an acetyl group and gives phenyl acetate, \( \ce{CH3COOC6H5} \), not phenyl benzoate.
Option (4) Benzophenone — Incorrect. \( \ce{C6H5COC6H5} \) is a ketone with no leaving group on the carbonyl carbon, so it cannot transfer a benzoyl group to phenol.
NCERT (2026-27 edition):
2. Esterification – “Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.
\( \displaystyle \ce{R/ArOH + R'COCl} \xrightarrow{\text{Pyridine}} \ce{R/ArOCOR' + HCl} \)
… The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralise HCl which is formed during the reaction.”