Substituted Aromatic Carbon-carbon Bond Formation (OCR A Level Chemistry)

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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 

Hydrocarbons - Alkylation vs Acylation, downloadable AS & A Level Chemistry revision notes

Examples of Friedel-Crafts alkylation and acylation reactions

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.