The diazotization of aniline requires treating it with sodium nitrite () and a mineral acid (like ) — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

The reaction uses excess $HCl$ primarily to keep the unreacted aniline fully protonated as the anilinium ion ($Ph-NH_3^+$). The diazonium ion ($Ph-N_2^+$) is a weak electrophile that readily couples with highly activated rings like free aniline to form diazoamino compounds (yellow dyes). Protonation strongly deactivates the aniline ring, effectively preventing this unwanted side coupling reaction.