Ethanoyl chloride gives ethanoic acid on hydrolysis. Under which of the following conditions is the hydrolysis faster, and what is formed in it before any acidification?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → With aqueous base; the ethanoate ion, which gives ethanoic acid on acidification
Acid chlorides are hydrolysed by water to carboxylic acids, but they are hydrolysed more readily by aqueous base. In the base, the acid formed is at once turned into its anion, so the product is the carboxylate ion; adding acid then gives the carboxylic acid:
\( \displaystyle \ce{CH3COCl + 2OH- -> CH3COO- + Cl- + H2O} \)
\( \displaystyle \ce{CH3COO- + H3O+ -> CH3COOH + H2O} \)
Why the other options are incorrect
Option (2) With water alone; ethanoic acid directly — Incorrect. Water does give the acid directly, \( \ce{CH3COCl + H2O -> CH3COOH + HCl} \), but this hydrolysis is slower than the one with aqueous base.
Option (3) With aqueous base; ethanoic acid directly, with no need of acidification — Incorrect. The base is the faster condition, but in a basic solution the acid cannot stay as such; it is present as the ethanoate ion until the solution is acidified.
Option (4) With water alone; the ethanoate ion, which gives ethanoic acid on acidification — Incorrect. Water alone is the slower condition, and it gives ethanoic acid itself, with HCl; no base is present to form the carboxylate ion.
NCERT (2026-27 edition):
8.7 Methods of Preparation of Carboxylic Acids – “5. From acyl halides and anhydrides
Acid chlorides when hydrolysed with water give carboxylic acids or more readily hydrolysed with aqueous base to give carboxylate ions which on acidification provide corresponding carboxylic acids.…”