Preparing Aromatic Amines

Aromatic amines are made by reducing aromatic nitro compounds. The key example is making phenylamine from nitrobenzene.Step 1: reduction. Nitrobenzene is heated under reflux with tin and concentrated hydrochloric acid. The tin and acid act as the reducing agent. Because the mixture is strongly acidic, the amine formed is protonated, so the product at this stage is the salt phenylammonium chloride, C₆H₅NH₃⁺Cl⁻.Step 2: release the amine. Sodium hydroxide solution is added to remove the proton and release free phenylamine, which can then be separated (for example by steam distillation).The overall reduction, using [H] for the reducing agent, is:C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂OFrom benzene. Phenylamine is made from benzene in two steps: nitration (concentrated HNO₃ and H₂SO₄, about 50 °C) and then reduction (Sn and concentrated HCl, then NaOH). This is the usual way to put an NH₂ group on a benzene ring, because ammonia cannot substitute directly onto the ring.Worked example: what is the maximum mass of phenylamine from 12.3 g of nitrobenzene? Moles of nitrobenzene = 12.3 ÷ 123 = 0.10 mol. The ratio is 1 : 1, so 0.10 mol of phenylamine (M_r = 93) forms: 0.10 × 93 = 9.3 g.Aromatic amines are used to make dyes and pharmaceuticals.