Friedel-Crafts Acylation

Chapter 12 : Reactions of Arenes. Electrophilic Aromatic Substitution

 

Friedel-Crafts Acylation of Benzene

acylation of arenes

Reaction type: Electrophilic Aromatic Substitution

Summary.

MECHANISM FOR THE FRIEDEL-CRAFTS ACYLATION OF BENZENE
Step 1:
The acyl halide reacts with the Lewis acid to form a more electrophilic C, an acylium ion
Friedel-Crafts acylation of benzene
Step 2:
The p electrons of the aromatic C=C act as a nucleophile, attacking the electrophilic C+. This step destroys the aromaticity giving the cyclohexadienyl cation intermediate.
Step 3:
Removal of the proton from the sp3 C bearing the acyl- group reforms the C=C and the aromatic system, generating HCl and regenerating the active catalyst.

Limitations of Friedel-Crafts reactions

There are two types of Friedel-Crafts reactions, alkylation and acylation:

alkylation
acylation

Reaction type: Electrophilic Aromatic Substitutions

However there are certain limitations:

Why aren't acylation reactions as prone to over acylation ? because the products are deactivated compared to the starting materials

Alkylation = Acylation then reduction

reduction of acylbenzenes

Clemmensen Reduction (acidic conditions)

Wolff-Kishner Reduction (basic conditions) Overview
example of acylation then reduction