双语化学辞典Chem Lexicon
反应 · 有机化学 · 反应类型 Organic chemistry · Reaction types

卤化反应Halogenation

拼音Pinyin lǔ huà fǎn yìng　别名Also 卤代反应； halogenation reaction

定义Definition

卤化反应是向有机分子中引入卤素原子（F、Cl、Br、I）的反应，按机理可分为烷烃的自由基取代、烯烃炔烃的亲电加成、芳烃的亲电取代、羰基 α 位卤代以及醇羟基的亲核取代等。

Halogenation introduces halogen atoms (F, Cl, Br, I) into organic molecules: radical substitution of alkanes, electrophilic addition to alkenes and alkynes, electrophilic aromatic substitution, α-halogenation of carbonyls and nucleophilic substitution of alcohols.

主要类型Main types

①烷烃：光照自由基取代；②烯烃：Br₂ 反式加成（溴鎓离子中间体，溴水褪色可检验双键）；③芳烃：Br₂/FeBr₃ 或 Cl₂/AlCl₃ 亲电取代；④酮 α 位：酸催化经烯醇，碱性下全卤代（卤仿反应）；⑤醇 → 卤代烃：HX、SOCl₂、PBr₃。

(1) Alkanes: light-induced radical substitution; (2) alkenes: anti addition of Br₂ via a bromonium ion (bromine water decolourises, a test for C=C); (3) arenes: Br₂/FeBr₃ or Cl₂/AlCl₃; (4) ketone α-positions: acid via the enol, exhaustive in base (haloform); (5) alcohols to halides: HX, SOCl₂, PBr₃.

卤素活性Halogen reactivity

F₂ 反应极剧烈、难以控制（需稀释或改用 Selectfluor、DAST 等试剂）；Cl₂ 活性高；Br₂ 选择性好；I₂ 反应可逆、常需氧化剂辅助。

F₂ is violently reactive (diluted, or replaced by Selectfluor, DAST); Cl₂ is reactive; Br₂ selective; iodination is reversible and often needs an oxidant.

意义Significance

卤代烃是格氏试剂、偶联反应、亲核取代的起点；约 20% 的药物含氟。含氯、溴有机物（如 CFC、多溴联苯醚）也带来臭氧层破坏和持久性污染问题。

Organohalides start Grignard, coupling and substitution chemistry, and about 20 % of drugs contain fluorine. Chlorinated and brominated organics (CFCs, PBDEs) also cause ozone depletion and persistent pollution.

反应Reactions

R–H + X2 ⟶ R–X + HXC=C + X2 ⟶ X–C–C–X

视底物而定：光照、路易斯酸、酸或碱催化

Depends on substrate: light, Lewis acids, acid or base catalysis

  1. 确定底物类型与机理。

    Identify substrate and mechanism.

  2. 选择卤化试剂与条件。

    Choose halogenating reagent and conditions.

CH2=CH2 + Br2 ⟶ BrCH2CH2Br

乙烯使溴的四氯化碳溶液褪色。

Ethene decolourises bromine solution.

C6H6 + Br2 FeBr3⟶ C6H5Br + HBr

苯的溴代。

Bromination of benzene.

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.

1

π 键进攻 Br₂，Br–Br 异裂

The π bond attacks Br₂; Br–Br breaks heterolytically

2

环状溴鎓离子；Br⁻ 从背面开环

Cyclic bromonium ion; Br⁻ opens it from the back

3

反式加成产物

anti-addition product

年表Timeline

  • 1839

    杜马提出取代理论（氯取代氢）

    Dumas’s substitution theory (Cl replacing H)

  • 1937

    罗伯茨与金博尔提出溴鎓离子

    Roberts and Kimball propose the bromonium ion