Nitration of Benzene

Nitration puts a nitro group, NO₂, onto a benzene ring. It is an electrophilic substitution.Reagents and conditions: benzene is warmed with a mixture of concentrated nitric acid and concentrated sulfuric acid (the nitrating mixture) at about 50 °C. The temperature must be kept at or below this: at higher temperatures more than one nitro group is substituted, giving 1,3-dinitrobenzene.Forming the electrophile. The sulfuric acid reacts with the nitric acid to form the electrophile NO₂⁺, the nitronium ion:HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂OAt the end of the reaction the H⁺ released from the ring reacts with HSO₄⁻ to regenerate H₂SO₄, so sulfuric acid acts as a catalyst.Overall equation:C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂OThe product, nitrobenzene, is a pale yellow oily liquid.Worked example: what is the maximum mass of nitrobenzene from 7.8 g of benzene? Moles of benzene = 7.8 ÷ 78 = 0.10 mol. The ratio is 1 : 1, so 0.10 mol of nitrobenzene (M_r = 123) forms: 0.10 × 123 = 12.3 g.The step-by-step mechanism is covered in the next lesson.