Phenylamine, amides and azo dyes
Base strength depends on how available the N lone pair is: ethylamine > ammonia > phenylamine. Alkyl groups push electrons onto N; in phenylamine the lone pair delocalises into the ring, so it's a weaker base. Phenylamine is made by reducing nitrobenzene with Sn and conc. HCl (reflux), then NaOH. Its ring is activated: bromine water gives white 2,4,6-tribromophenylamine. Diazotisation: phenylamine + HNO₂ (NaNO₂ + HCl) below 10 °C gives benzenediazonium chloride, which couples with phenol in alkali to form an orange azo dye (–N=N–). Amides (RCONH₂) are neutral (lone pair delocalised onto C=O); they hydrolyse with acid or alkali and are reduced by LiAlH₄ to amines.
≈ 50 minAmines and nitriles
Amines contain N with a lone pair. Primary amines form when halogenoalkanes react with excess ammonia in ethanol, heated under pressure (excess limits further substitution to secondary and tertiary amines). Nitriles form from halogenoalkanes + KCN (ethanol) or carbonyls + HCN (hydroxynitriles); they can be hydrolysed (acid, reflux) to carboxylic acids or reduced (LiAlH₄, or H₂/Ni) to primary amines, giving an amine with one extra carbon and no mixture. Amines are bases: the N lone pair accepts H⁺, forming ammonium salts: .
≈ 40 min