Aromatic Compounds
7.0 Friedel-Crafts Acylation
7.0 Friedel-Crafts Acylation
The group is called an acyl group and a reaction whereby an acyl group is introduced into a compound is called an acylation reaction.
The Friedel-Crafts acylation reaction is an effective means of introducing an acyl group into an aromatic ring. The reaction is often carried out by treating the aromatic compound with an acyl halide.
Acyl chlorides (also called acid chlorides) are early prepared by treating carboxylic acids with thionyl chloride ( $SOC{l_2}$) or phosphorous pentachloride ($PC{l_5}$).
Friedel-Crafts acylations can also be carried cut using carboxylic acid anhydrides. eg.
Mechanism
In most Friedel-Crafts acylation reactions the electrophile appears to be an acylium ion formed from an acyl halide in the following way.
Step I
Step II
Step III
Step –IV
Step-V
In the last step, $AlC{l_3}$ (a Lewis acid) forms a complex with the ketone (a Lewis base). After the reaction is over, treating the complex with water liberates the ketone.
