The replacement of a hydrogen atom in benzene with an alkyl group using an alkyl halide and AlCl₃ is called:

Friedel–Crafts alkylation is an important electrophilic substitution reaction in organic chemistry. In this reaction, a hydrogen atom on the benzene ring is replaced by an alkyl group. The reaction requires an alkyl halide (R–X) and a Lewis acid catalyst, typically aluminum chloride (AlCl₃). The Lewis acid activates the alkyl halide by forming a complex, generating a carbocation or an equivalent electrophilic species. This electrophile then reacts with the benzene ring, substituting a hydrogen atom.

The reaction introduces alkyl groups into the aromatic ring, forming substituted benzene derivatives. For example, using methyl chloride (CH₃Cl) with AlCl₃ on benzene produces toluene. Similarly, ethyl chloride can produce ethylbenzene. The process is widely used in the synthesis of aromatic compounds for pharmaceuticals, dyes, and fragrances.

Friedel–Crafts alkylation differs from Friedel–Crafts acylation, where an acyl group (R–CO) is introduced instead of an alkyl group. Acylation uses acid chlorides and AlCl₃, and it avoids issues like carbocation rearrangement that can occur in alkylation reactions.

Other options, such as Dow’s process or Clemmensen reduction, involve different chemical transformations. Dow’s process is related to chlorination and industrial chemical preparation, while Clemmensen reduction reduces carbonyl compounds to hydrocarbons using zinc amalgam and hydrochloric acid.

Friedel–Crafts alkylation is therefore the standard method for introducing alkyl groups onto benzene. It demonstrates the reactivity of aromatic compounds toward electrophilic substitution, the role of Lewis acids, and the formation of substituted aromatic molecules.