Aniline is highly reactive towards electrophilic aromatic substitution, often leading to poly-substi — Aromatic Hydrocarbons Chemistry Question
Question
Aniline is highly reactive towards electrophilic aromatic substitution, often leading to poly-substitution (e.g., tribromoaniline with bromine water). To strictly obtain a mono-substituted para-derivative (like p-bromoaniline or p-nitroaniline), which sequence of reactions must be employed?
💡 Solution & Explanation
The $-NH_2$ group is a powerful activator. To tame its reactivity, it is acetylated with acetic anhydride or acetyl chloride to form acetanilide. The $-NHCOCH_3$ group is still an ortho/para director but is only moderately activating because the nitrogen lone pair is cross-conjugated with the carbonyl group. This prevents poly-substitution and oxidation, allowing for clean mono-substitution (predominantly para due to sterics), after which the acetyl group is removed via hydrolysis.