Alkylation & Acylation
Friedel-Crafts Reactions
- Friedel-Crafts reactions are also electrophilic substitution reactions
- Due to the aromatic stabilisation in arenes, they are often unreactive
- To use arenes as starting materials for the synthesis of other organic compounds, their structure, therefore, needs to be changed to turn them into more reactive compounds
- Friedel-Crafts reactions can be used to substitute a hydrogen atom in the benzene ring for an alkyl group (Friedel-Crafts alkylation) or an acyl group (Friedel-Crafts acylation)
- Like any other electrophilic substitution reaction, the Friedel-Crafts reactions consist of three steps:
- Generating the electrophile
- Electrophilic attack on the benzene ring
- Regenerating aromaticity of the benzene ring
Friedel-Crafts Alkylation
- In the Friedel-Crafts alkylation, an alkyl group is substituted into the benzene ring
- The benzene ring is reacted with a chloroalkane (e.g. chloroethane) in the presence of an AlCl3 catalyst
- An example of alkylation is the reaction of benzene with chloroprpane to form propylbenzene
- The Friedel-Crafts alkylation reaction is a method of generating alkylbenzenes by using alkyl halides as reactants
Friedel-Crafts Acylation
- In the Friedel-Crafts acylation reaction, an acyl group is substituted into the benzene ring
- An acyl group is an alkyl group containing a carbonyl, C=O group
- The benzene ring is reacted with an acyl chloride in the presence of an AlCl3 catalyst
- An example of an acylation reaction is the reaction of benzene with propanoyl chloride to form phenylpropanone
- The Friedel-Crafts alcylation reaction is a method of generating ketones
Examples of Friedel-Crafts alkylation and acylation reactions