Organic chemistryLesson 4 of 5 in the course Aromatic compounds

Friedel–Crafts Alkylation and Acylation: Mechanisms and Limitations

5 flashcards · 5 quiz questions · 5 match pairs · 3 fill-in sentences · English

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Summary

Friedel–Crafts alkylation attaches an alkyl group to an aromatic ring through electrophilic aromatic substitution. It is important both in large-scale chemical manufacturing and as a way to understand how electrophiles react with aromatic compounds.

In a Friedel–Crafts alkylation, an aromatic ring gains an alkyl substituent. The ring acts as a nucleophile and reacts with an electrophile; loss of a proton restores aromaticity. This is a type of electrophilic aromatic substitution.

All flashcards

What is Friedel–Crafts alkylation?
An electrophilic aromatic substitution that attaches an alkyl group to an aromatic ring.
What is an acylium ion?
A resonance-stabilized electrophile generated from an acylating agent in Friedel–Crafts acylation.
What is overalkylation?
Further alkyl substitution promoted by the increased reactivity of an alkyl-substituted aromatic ring.
Why is stoichiometric AlCl₃ commonly needed in Friedel–Crafts acylation?
The ketone product binds strongly to AlCl₃, limiting its availability for further reaction.
How can an acyl group be converted into an alkyl group?
Reduce the ketone carbonyl using Clemmensen or Wolff–Kishner conditions.

Quiz questions

  1. What product class is typically formed when an aromatic ring undergoes Friedel–Crafts acylation?Answer: An aromatic ketone
  2. Why are carbocation rearrangements not typical in Friedel–Crafts acylation?Answer: The acylium ion is resonance-stabilized.
  3. Why is a stoichiometric amount of AlCl₃ commonly used in Friedel–Crafts acylation?Answer: The ketone product forms a strong complex with AlCl₃.
  4. Which pair of reactions can reduce the carbonyl group of an acylation product to an alkyl substituent?Answer: Clemmensen and Wolff–Kishner reductions
  5. Which reagents and conditions are used in the Gattermann–Koch preparation of benzaldehyde from benzene?Answer: Carbon monoxide and hydrogen chloride under high pressure, with AlCl₃ and CuCl catalysts

Based on the Wikipedia article Friedel–Crafts reaction, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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