January 20, 2024 | UR Gate
Friedel-Crafts Acylation
Explore the Friedel-Crafts acylation reaction, mechanism, a key electrophilic aromatic substitution where an acyl group replaces a hydrogen atom in benzene, forming aromatic ketones.
Friedel-Crafts Acylation Reaction
The Friedel-Crafts acylation reaction is a type of reaction within the Friedel-Crafts reactions, named after its discoverers Friedel and Crafts. It involves the substitution of a hydrogen atom in the benzene ring with an acyl group. [1]
This reaction begins with a benzene molecule to which acetyl chloride is added. The catalyst used in this reaction is aluminum chloride (AlCl3). It is noteworthy that the outcome of the reaction is the replacement of the positively charged hydrogen proton or ion attached to the aromatic ring with an acetyl group, resulting in the formation of methyl phenyl ketone and hydrochloric acid. [2]
Note:
Friedel-Crafts acylation is an electron-loving reaction.
Example
The acylation reaction can be succinctly defined through this example as the introduction of the acetyl group in place of the hydrogen atom in the benzene molecule [3], as per the following equation:
It is observed that the acetyl group replaces the hydrogen atom in the benzene molecule, resulting in the formation of methyl phenyl ketone and hydrochloric acid.
Mechanism of Friedel-Crafts Acylation Reaction
The Friedel-Crafts acylation reaction occurs in three stages :[4]
First Stage:
Acetyl chloride reacts with aluminum chloride, resulting in the formation of the electrophilic catalyst and the negative ion AlCl-4.
Second Stage:
The electrophilic catalyst attacks benzene, leading to the generation of the arenium ion.
Third Stage:
The arenium ion reacts with the negative ion AlCl-4, resulting in the formation of methyl phenyl ketone, hydrochloric acid, and aluminum chloride.