Friedel-Crafts reactions

In a nutshell

Benzene rings can be alkylated and acylated via Friedel-Crafts reactions. Friedel-Crafts reactions introduce a new $$C-C$$ bond. A halogen carrier is required for the reaction to happen. Friedel-Crafts reactions are an example of electrophilic substitution reactions.

Equations

These are general chemical equations. You will need to be able to use these when you write equations for specific substances.

​$$C_6H_6 \ + \ R-X \xrightarrow[reflux]{halogen \ carrier}C_6H_5R \ + \ HX \\ \ \\C_6H_6 \ + \ RCOCl \xrightarrow[dry \ ether, \ reflux]{AlCl_3}C_6H_5COR \ + \ HCl$$​​

Friedel-Crafts reactions

Benzene can be refluxed with a halogenoalkane or acyl chloride in the presence of a halogen carrier to form a new $$C-C$$ bond.​

Friedel-Crafts alkylation

Friedel-Crafts alkylation adds an alkyl group onto a benzene. A benzene is refluxed with a halogenoalkane in the presence of a halogen carrier.

$$C_6H_6 \ + \ R-X \xrightarrow[reflux]{halogen \ carrier}C_6H_5R \ + \ HX$$​​

General Mechanism

Electrophile formation

​$$R-X \ + \ AlCl_3 \rightarrow R^+ \ + \ AlCl_4^-$$​​

Electrophilic substitution

Electrophiles containing an $$OAlCl_3^-$$ group can be added to benzene rings to form alcohols.

Example

Friedel-Crafts acylation

​Friedel-Crafts acylation adds an acyl group onto a benzene. A benzene is refluxed with an acyl chloride in the presence of a halogen carrier. The reaction produces phenylketones or benzaldehydes, depending on the R group. The solvent used must be non-aqueous such as dry ether.

$$C_6H_6 \ + \ RCOCl \xrightarrow[dry \ ether, \ reflux]{AlCl_3}C_6H_5COR \ + \ HCl$$​​

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General Mechanism

Electrophile formation

$$R-COCl \ + \ AlCl_3 \rightarrow RCO^+ \ + \ AlCl_4^-$$​​

Electrophilic Substitution