Which of the following reactions can be used to prepare carboxylic acids?
I. Oxidation of an aldehyde
II. Hydrolysis of an acid anhydride
III. Hydrolysis of a ketone
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → I and II only
I. Oxidation of an aldehyde — True. An aldehyde is oxidised to the carboxylic acid with the same number of carbon atoms, even by mild oxidising agents.
\( \displaystyle \ce{RCHO} \xrightarrow{[\ce{O}]} \ce{RCOOH} \)
II. Hydrolysis of an acid anhydride — True. Water splits an acid anhydride into the corresponding acid(s); for example, ethanoic anhydride gives ethanoic acid:
\( \displaystyle \ce{(CH3CO)2O + H2O -> 2CH3COOH} \)
III. Hydrolysis of a ketone — False. A ketone has no group that water can split off, so it is not hydrolysed to an acid. A ketone gives carboxylic acids only by oxidation under vigorous conditions, with cleavage of a carbon-carbon bond.
NCERT (2026-27 edition):
8.7 Methods of Preparation of Carboxylic Acids – “Carboxylic acids are also prepared from aldehydes by the use of mild oxidising agents (Section 8.4).”
“… Anhydrides on the other hand are hydrolysed to corresponding acid(s) with water.”
8.4 Chemical Reactions – “Ketones are generally oxidised under vigorous conditions, i.e., strong oxidising agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.”