Question

(i) Explain reduction of nitriles, with chemical reaction.
(ii) Write only the chemical equation for the reaction that occurs when aniline is heated with chloroform in the presence of alcoholic KOH.

Hint:

Nitriles are reduced (H₂/Ni or LiAlH₄) to primary amines; aniline with CHCl₃ and alcoholic KOH is the carbylamine reaction that gives phenyl isocyanide.

Answer 1

Part (i):
Step 1: Concept. Reduction means adding hydrogen. A nitrile has the group \(-C\equiv N\); adding four hydrogen atoms (two H₂ molecules) across the triple bond converts it, through an imine, into a primary amine \(-CH_2-NH_2\).
Step 2: Reagents and equation. Catalytic hydrogenation (H₂/Ni) or LiAlH₄ is used:
\[R\text{-}CN \xrightarrow{H_2/Ni} R\text{-}CH_2\text{-}NH_2\]
This route is useful because it increases the carbon chain by one carbon and always gives a primary amine.
Part (ii):
Step 3: Carbylamine test. This reaction is a test for primary amines. Aniline reacts with chloroform and alcoholic potassium hydroxide on heating to form phenyl isocyanide, which has an extremely unpleasant smell:
\[C_6H_5NH_2 + CHCl_3 + 3KOH\,(alc.) \xrightarrow{heat} C_6H_5NC + 3KCl + 3H_2O\]
The bad odour confirms that aniline is a primary amine.