Preparation of Phenylamine

Phenylamine, C₆H₅NH₂, is made in two stages from benzene. First benzene is nitrated with concentrated nitric and sulfuric acids to give nitrobenzene. The nitro group is then reduced to an amine group.Nitrobenzene is heated under reflux with tin and concentrated hydrochloric acid. The tin and acid act as the reducing agent, written as [H] in equations:C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂OBecause the mixture is strongly acidic, the basic phenylamine is protonated as it forms, and it is present as the phenylammonium ion, C₆H₅NH₃⁺. Excess sodium hydroxide solution is added to remove the proton and release free phenylamine:C₆H₅NH₃⁺ + OH⁻ → C₆H₅NH₂ + H₂OThe phenylamine is then separated from the mixture, usually by steam distillation, and purified.Worked example: 12.3 g of nitrobenzene (M_r = 123) is reduced. Amount = 12.3 ÷ 123 = 0.100 mol. The ratio is 1 : 1, so the theoretical yield of phenylamine (M_r = 93.0) is 0.100 × 93.0 = 9.30 g. If 6.51 g is collected, the percentage yield is 6.51 ÷ 9.30 × 100 = 70.0%.