What Is The Mechanism Of The Friedel-Crafts Reaction Catalyzed By Aluminium Bromide?

The Friedel-Crafts reaction is a type of electrophilic aromatic substitution reaction that involves the reaction of an arene (or other electron-rich aromatic compound) with an alkyl halide or acyl halide in the presence of a Lewis acid catalyst. Aluminum bromide (AlBr3) is a commonly used Lewis acid catalyst for this reaction.

The mechanism of the Friedel-Crafts reaction catalyzed by AlBr3 can be divided into three main steps:

1. Activation of the catalyst: AlBr3 reacts with a molecule of the alkyl halide or acyl halide to form an intermediate complex, which activates the catalyst for the subsequent reaction. This activation occurs through coordination of the halogen atom in the reagent with the aluminum ion in the catalyst, leading to the formation of a highly electrophilic species.

2. Formation of the carbocation intermediate: The activated catalyst then interacts with the arene molecule to form a new intermediate species. This interaction leads to the transfer of the highly electrophilic species from the catalyst to the arene ring, generating a carbocation intermediate.

3. Reaction with nucleophilic species: The final step involves the reaction of the carbocation intermediate with a nucleophilic species, such as a chloride ion or an alcohol molecule. This results in the formation of a new substituted arene molecule and regenerates the catalyst for further reaction.

Overall, the Friedel-Crafts reaction catalyzed by AlBr3 proceeds through an electrophilic aromatic substitution mechanism, where the aluminum ion acts as a Lewis acid catalyst to activate the electrophile and facilitate the reaction.