Question

Ethylbenzene is generally prepared by acetylation of benzene followed by reduction and not by direct alkylation. Think of a possible reason.

Answer 1

Preparation of ethylbenzene by the acetylation of benzene and reduction can be shown as:

• The direct alkylation cannot be performed because a poly-substituted product is also formed. After the monoalkylation, the benzene ring is activated and can undergo further alkylation.
• However, after acetylation, the benzene ring is deactivated due to −R effect of the acetyl group. This decreases the tendency of the aromatic ring to undergo further electrophilic substitution.
• Due to the disadvantage of poly-substitution, Friedel−Craft’s alkylation reaction is not preferred for the preparation of alkylbenzenes. Instead, Friedel-Craft’s acylation is used.