定义Definition
硝化反应是向有机分子中引入硝基（–NO₂）的反应；最典型的是芳烃在浓硝酸与浓硫酸（混酸）作用下发生亲电取代生成硝基芳烃。
Nitration introduces a nitro group (–NO₂) into an organic molecule; typically an arene undergoes electrophilic substitution with a mixture of concentrated nitric and sulfuric acids (mixed acid) to give a nitroarene.
机理Mechanism
浓硫酸使硝酸质子化并失水，生成真正的亲电试剂硝酰正离子 NO₂⁺（HNO₃ + 2H₂SO₄ → NO₂⁺ + H₃O⁺ + 2HSO₄⁻，英戈尔德由动力学和光谱证实）。NO₂⁺ 进攻苯环生成σ络合物（惠兰德中间体），失去质子恢复芳香性。
Sulfuric acid protonates nitric acid, which loses water to give the nitronium ion NO₂⁺ (HNO₃ + 2 H₂SO₄ → NO₂⁺ + H₃O⁺ + 2 HSO₄⁻, established by Ingold’s kinetics and spectroscopy). NO₂⁺ attacks the ring to form the σ-complex (Wheland intermediate), which loses a proton.
定位效应Directing effects
硝基强吸电子，使产物钝化，所以一硝化可控制；进一步硝化需更强条件，且进入间位（1,3-二硝基苯）。甲苯硝化主要得邻、对位产物，逐级硝化最终得 TNT（2,4,6-三硝基甲苯）。
The nitro group strongly deactivates, so mononitration is controllable; further nitration needs harsher conditions and goes meta (1,3-dinitrobenzene). Toluene nitrates ortho/para, and exhaustive nitration gives TNT (2,4,6-trinitrotoluene).
应用与安全Uses and safety
硝基苯还原得苯胺（染料、聚氨酯原料 MDI）；炸药（TNT、硝化甘油、硝化纤维、RDX）都由硝化制备。硝化强放热，温度失控易爆炸，工业上严格控温并越来越多采用连续流微反应器。
Nitrobenzene is reduced to aniline (dyes, MDI for polyurethanes); explosives (TNT, nitroglycerin, nitrocellulose, RDX) are made by nitration. Nitrations are strongly exothermic and can run away, so temperature is tightly controlled and continuous-flow reactors are increasingly used.
反应Reactions
混酸（浓 HNO₃ + 浓 H₂SO₄），苯约 50–60 °C
Mixed acid (conc. HNO₃ + conc. H₂SO₄); for benzene about 50–60 °C
生成 NO₂⁺。
Generation of NO₂⁺.
亲电进攻生成 σ 络合物。
Electrophilic attack gives the σ-complex.
失去 H⁺ 恢复芳香性。
Loss of H⁺ restores aromaticity.
制备硝基苯。
Preparation of nitrobenzene.
反应机理图Mechanism
红色弯箭头表示一对电子的移动方向：从电子来源（孤对电子或化学键）指向电子去向。Red curly arrows show where an electron pair moves: from its source (lone pair or bond) to its destination.
苯环 π 电子进攻硝酰阳离子 NO₂⁺
The ring π electrons attack the nitronium ion NO₂⁺
σ 络合物（芳基正离子）失去质子，恢复芳香性
The σ-complex (arenium ion) loses H⁺ and regains aromaticity
硝基苯
Nitrobenzene
年表Timeline
- 1834
米切利希制得硝基苯
Mitscherlich prepares nitrobenzene
- 1847
索布雷罗合成硝化甘油
Sobrero synthesises nitroglycerin
- 1863
维尔布兰德合成 TNT
Wilbrand synthesises TNT
- 1950
英戈尔德等确证硝酰正离子机理
Ingold and co-workers establish the nitronium mechanism