双语化学辞典Chem Lexicon
反应 · 有机化学 · 亲电芳香取代 Organic chemistry · Electrophilic aromatic substitution

傅-克烷基化反应Friedel–Crafts alkylation

拼音Pinyin fù kè wán jī huà fǎn yìng　别名Also 弗里德尔-克拉夫茨烷基化； Friedel–Crafts alkylation reaction

定义Definition

傅-克烷基化是芳烃在路易斯酸（AlCl₃、FeCl₃ 等）催化下与卤代烷、烯烃或醇反应，在芳环上引入烷基的亲电取代反应。

Friedel–Crafts alkylation installs an alkyl group on an arene by electrophilic substitution with an alkyl halide, alkene or alcohol under Lewis-acid catalysis (AlCl₃, FeCl₃, etc.).

机理Mechanism

AlCl₃ 与卤代烷络合，生成碳正离子（或高度极化的 R⁺···AlCl₄⁻ 络合物）作为亲电试剂；芳环进攻生成 σ 络合物，AlCl₄⁻ 夺取质子恢复芳香性并再生催化剂。

AlCl₃ complexes the halide to give a carbocation (or polarised R⁺···AlCl₄⁻) as the electrophile; the ring attacks to give a σ-complex, and AlCl₄⁻ removes the proton, regenerating the catalyst.

三个局限Three limitations

①碳正离子重排：正丙基氯与苯反应主要得异丙苯；②多烷基化：烷基使环活化，产物比原料更易反应；③强吸电子基（–NO₂、–COR）钝化的芳环和含 –NH₂ 的芳胺（与 AlCl₃ 络合）不反应。为得直链烷基，常改用傅–克酰基化再还原。

(1) Carbocation rearrangement: n-propyl chloride gives mainly cumene; (2) polyalkylation, since alkyl groups activate the ring; (3) no reaction with strongly deactivated rings or anilines (which complex AlCl₃). For straight chains, acylate then reduce.

由来与工业Origin and industry

法国的夏尔·傅里德尔和美国的詹姆斯·克拉夫茨于 1877 年报道。工业上苯与乙烯、丙烯在沸石或固体酸上反应生产乙苯和异丙苯（年产数千万吨），取代了污染较大的 AlCl₃ 工艺。

Reported in 1877 by Charles Friedel and James Crafts. Industrially, benzene is alkylated with ethylene and propylene over zeolites or solid acids to make ethylbenzene and cumene (tens of millions of tonnes per year), replacing AlCl₃ processes.

反应Reactions

ArH + R–Cl AlCl3⟶ Ar–R + HCl

无水 AlCl₃ 或 FeCl₃，0 °C 至室温；烯烃作烷基化剂时用质子酸或沸石

Anhydrous AlCl₃ or FeCl₃ at 0 °C to room temperature; with alkenes, protic acids or zeolites

  1. 路易斯酸活化卤代烷生成碳正离子。

    Lewis acid activates the halide to a carbocation.

  2. 芳环进攻得 σ 络合物。

    Ring attack gives a σ-complex.

  3. 失去质子，再生催化剂。

    Deprotonation regenerates the catalyst.

C6H6 + (CH3)3CCl AlCl3⟶ C6H5C(CH3)3

叔丁基苯（叔碳正离子不重排）。

tert-Butylbenzene (the tertiary cation does not rearrange).

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

AlCl₃ 夺取氯，生成仲碳正离子

AlCl₃ abstracts chloride, giving a secondary carbocation

2

苯环 π 电子进攻碳正离子

The ring π electrons attack the carbocation

3

失去质子，恢复芳香性

Loss of H⁺ restores aromaticity

4

异丙苯；产物比原料更活泼，易多烷基化

Cumene; the product is more reactive, so polyalkylation is common

年表Timeline

  • 1877

    傅里德尔与克拉夫茨报道

    Friedel and Crafts report the reaction

  • 1980s

    沸石催化乙苯工艺工业化（美孚–巴杰尔）

    Zeolite ethylbenzene process commercialised (Mobil–Badger)