Nitriles are hydrolysed to carboxylic acids in the presence of H+ or OH− as catalyst. Which class of compounds is formed at the intermediate stage, at which the reaction can be stopped by using mild conditions?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Amides
Hydrolysis of a nitrile takes place in two stages. Water first adds to the C≡N group to give an amide, and the amide is then hydrolysed to the carboxylic acid. Under mild conditions the reaction stops at the amide.
\( \displaystyle \ce{R-C#N} \xrightarrow[\ce{H2O}]{\ce{H+}\text{ or }\ce{OH-}} \ce{R-CONH2} \xrightarrow[\ce{H2O}]{\ce{H+}\text{ or }\ce{OH-}} \ce{R-COOH} \)
For example, ethanamide is hydrolysed to ethanoic acid, with ammonia set free:
\( \displaystyle \ce{CH3CONH2 + H2O} \xrightarrow[\Delta]{\ce{H3O+}} \ce{CH3COOH + NH3} \)
Why the other options are incorrect
Option (1) Primary amines — Incorrect. Primary amines are formed when nitriles are reduced, for example by LiAlH4, not hydrolysed.
Option (3) Aldehydes — Incorrect. An aldehyde is obtained from a nitrile only by a partial reduction (stannous chloride and HCl, or DIBAL-H) followed by hydrolysis; it does not lie on the hydrolysis route to the acid.
Option (4) Imines — Incorrect. The imine is the intermediate of that reduction of nitriles to aldehydes, not of their hydrolysis.
NCERT (2026-27 edition):
8.7 Methods of Preparation of Carboxylic Acids – “3. From nitriles and amides: Nitriles are hydrolysed to amides and then to acids in the presence of H+ or OH− as catalyst. Mild reaction conditions are used to stop the reaction at the amide stage.”