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): Reduction of nitriles.
Step 1: What happens. Nitriles \((R\text{-}C\equiv N)\) contain a carbon-nitrogen triple bond. On reduction (addition of hydrogen) this triple bond is converted to a single bond, giving a primary amine. Suitable reducing agents are H₂ with a Ni / Pt / Pd catalyst, or LiAlH₄, or sodium in alcohol (Mendius reduction).
Step 2: Equation.
\[R\text{-}C\equiv N + 2H_2 \xrightarrow{Ni} R\text{-}CH_2\text{-}NH_2\]
For example, methyl cyanide gives ethylamine:
\[CH_3CN + 2H_2 \xrightarrow{Ni} CH_3CH_2NH_2\]
The product is a primary amine having one more carbon than the parent alkyl group.
Part (ii): Carbylamine (isocyanide) reaction of aniline.
Step 3: Aniline, a primary amine, on heating with chloroform and alcoholic KOH gives foul-smelling phenyl isocyanide (carbylamine):
\[C_6H_5NH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} C_6H_5NC + 3KCl + 3H_2O\]