Here’s a explanation of the Friedel-Crafts alkylation reaction:
What It Is
- Friedel-Crafts alkylation is a reaction where an alkyl group (a carbon chain) is introduced into a benzene ring.
- It is a type of electrophilic aromatic substitution, meaning the benzene ring substitutes a hydrogen atom with an alkyl group.
Step 1: Formation of the Electrophile
- The alkyl group is usually provided by an alkyl halide (like methyl chloride or ethyl chloride).
- A Lewis acid catalyst (like AlCl₃) is used to generate a positively charged alkyl species (carbocation), which acts as the electrophile.
Step 2: Attack on the Benzene Ring
- The electron-rich benzene ring attacks the alkyl carbocation.
- This forms a temporary sigma complex (arenium ion) where the ring loses its aromaticity temporarily.
Step 3: Restoration of Aromaticity
- A hydrogen atom is removed from the carbon that bonded to the alkyl group.
- This restores the aromatic character of the benzene ring.
- The final product is an alkyl-substituted benzene.
Key Points
- Alkyl groups activate the ring, making it more reactive for further substitutions.
- The reaction requires a Lewis acid catalyst to generate the carbocation.
- Rearrangement of the carbocation can occur, sometimes leading to unexpected products.