The Friedel-Crafts alkylation reaction proceeds via a three-step mechanism.
Step 1
The Lewis acid catalyst (AlCl3) undergoes reaction with the alkyl halide, resulting in the formation of an electrophilic carbocation.
Step 2
The carbocation proceeds to attack the aromatic ring, forming a cyclohexadienyl cation as an intermediate. The aromaticity of the arene is temporarily lost due to the breakage of the carbon-carbon double bond.
Step 3
The deprotonation of the intermediate leads to the reformation of the carbon-carbon double bond, restoring aromaticity to the compound. This proton goes on to form hydrochloric acid, regenerating the AlCl3 catalyst.
An illustration describing the mechanism of the Friedel-Crafts alkylation reaction is provided above.