Friedel–Crafts reaction

Friedel–Crafts Reaction

The Friedel–Crafts reaction is a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. These reactions are of two main types: Friedel–Crafts alkylation and Friedel–Crafts acylation.

Friedel–Crafts Alkylation

File:Friedel-Crafts Equation Overview.svg

Overview of Friedel–Crafts reactions

The Friedel–Crafts alkylation involves the alkylation of an aromatic ring with an alkyl halide using a strong Lewis acid catalyst such as aluminum chloride (AlCl₃). This reaction is used to introduce an alkyl group into an aromatic compound.

Ethylation of benzene

Mechanism

The mechanism of the Friedel–Crafts alkylation involves the formation of a carbocation intermediate. The Lewis acid catalyst helps to generate the carbocation from the alkyl halide, which then attacks the aromatic ring to form the alkylated product.

Reaction of propylene with benzene

Limitations

Friedel–Crafts alkylation has several limitations, including carbocation rearrangement, polyalkylation, and the deactivation of the aromatic ring by electron-withdrawing groups.

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Steric protection in Friedel–Crafts alkylation

Friedel–Crafts Acylation

The Friedel–Crafts acylation involves the acylation of an aromatic ring with an acyl chloride or acid anhydride in the presence of a Lewis acid catalyst. This reaction introduces an acyl group into the aromatic compound.

File:Friedel-Crafts-acylation-overview.png

Overview of Friedel–Crafts acylation

Mechanism

The mechanism of Friedel–Crafts acylation involves the formation of an acylium ion, which is a more stable electrophile than a carbocation. The acylium ion attacks the aromatic ring to form the acylated product.

Advantages

Friedel–Crafts acylation does not suffer from polyacylation because the acyl group is electron-withdrawing, which deactivates the aromatic ring towards further electrophilic substitution.

Applications

Friedel–Crafts reactions are widely used in the synthesis of aromatic ketones, alkylbenzenes, and other aromatic compounds. They are important in the production of pharmaceuticals, fragrances, and polymers.

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Synthesis of neophyl chloride

Related Reactions

Friedel–Crafts reactions are related to other electrophilic aromatic substitution reactions such as nitration, sulfonation, and halogenation.

Example of Friedel–Crafts alkylation

Related Pages

• Electrophilic aromatic substitution
• Aromaticity
• Lewis acid
• Carbocation

Synthesis of 1,3-diisopropylbenzene via transalkylation