Acylation of benzene in complete 4 steps which Lewis acid catalyst use in this reaction

The mechanism for Friedel Crafts alkylation and acylation reactions of benzene

Friedel Crafts alkylation and acylation reactions involve a three-step mechanism:

1. Generation of electrophile:

   Due to the presence of a Lewis acid, generation of electrophile takes place. As Lewis acid accepts the electron pair from the attacking reagent.

2. Formation of arenium ion:

   The electrophiles generated attacks on the benzene ring to form positively charged cyclohexadienyl cation better called arenium ion containing one sp3 hybridized carbon atom. The positive charge is effectively distributed over three carbon atoms due to resonance which makes it partially stable.

   As delocalization of electrons stops at  hybridized carbon atom, the arenium ion is not aromatic in nature.

3. Removal of positive charge from the carbocation intermediate:

   The arenium ion finally loses its proton from sp3 hybridized carbon to a Lewis base restoring the aromaticity.