Question

Phenyl isocyanide is prepared from aniline by

• A. Rosenmund's reaction
• B. Kolbe's reaction
• C. Reimer-Tiemann reaction
• D. Wurtz reaction
• E. Carbylamine reaction

Hint:

The Carbylamine reaction is often called the "foul smell test." Only primary amines give this reaction; secondary and tertiary amines do not!

Answer 1

Answer: (E)

Concept: The preparation of isocyanides (carbylamines) from primary amines is a classic diagnostic test for $1^\circ$ amines.
• Carbylamine Reaction: Primary amines (aliphatic or aromatic) react with chloroform ($CHCl_3$) and ethanolic potassium hydroxide ($KOH$) to produce foul-smelling isocyanides ($R-NC$).
• Intermediates: The reaction proceeds via the formation of a highly reactive dichlorocarbene ($:CCl_2$) intermediate.

Step 1: Match the starting material to the reaction. Aniline ($C_6H_5NH_2$) is a primary aromatic amine. When heated with $CHCl_3$ and $KOH$, it undergoes the following transformation: \[ C_6H_5NH_2 + CHCl_3 + 3KOH \rightarrow C_6H_5NC + 3KCl + 3H_2O \] The product $C_6H_5NC$ is Phenyl Isocyanide.

Step 2: Eliminate other named reactions. - Rosenmund's: Acid chloride to aldehyde. - Kolbe's: Phenol to salicylic acid. - Reimer-Tiemann: Phenol to salicylaldehyde. - Wurtz: Alkyl halides to alkanes.