Preparation of Ketones from Acyl Chlorides (Friedel-Crafts Acylation)
Aromatic ketones are prepared by the Friedel-Crafts acylation of benzene or substituted benzenes with acyl chlorides in the presence of anhydrous aluminium chloride.
What is Preparation of Ketones from Acyl Chlorides (Friedel-Crafts Acylation)?
An electrophilic aromatic substitution reaction where an acyl group (R-CO-) is introduced onto an aromatic ring using an acyl halide or acid anhydride in the presence of a Lewis acid catalyst.
Key formula / rule: Acylium ion formation
Key points
- Describe the Friedel-Crafts acylation reaction.
- Identify the reactants, products, and catalyst for Friedel-Crafts acylation.
- Explain the mechanism of Friedel-Crafts acylation, including the generation of the acylium ion.
- Understand the advantages of acylation over alkylation (no polyalkylation, no rearrangements).
Common exam trap
Using hydrated AlCl₃ instead of anhydrous.
Definitions
- Term
Friedel-Crafts Acylation
- Meaning
An electrophilic aromatic substitution reaction where an acyl group (R-CO-) is introduced onto an aromatic ring using an acyl halide or acid anhydride in the presence of a Lewis acid catalyst.
- Term
Acylium ion
- Meaning
A resonance-stabilized carbocation with the general formula R-C⁺=O, which acts as the electrophile in Friedel-Crafts acylation.
- Term
Lewis Acid
- Meaning
A chemical species that can accept an electron pair to form a covalent bond; in Friedel-Crafts reactions, it activates the electrophile.
Learning objectives
Describe the Friedel-Crafts acylation reaction.
Identify the reactants, products, and catalyst for Friedel-Crafts acylation.
Explain the mechanism of Friedel-Crafts acylation, including the generation of the acylium ion.
Understand the advantages of acylation over alkylation (no polyalkylation, no rearrangements).
Predict the products of Friedel-Crafts acylation for simple aromatic compounds.
Formulae
- Name
Acylium ion formation
- Note
This shows the generation of the electrophile.
- Expression
R-COCl + AlCl₃ → R-C⁺=O + [AlCl₄]⁻
- Name
Friedel-Crafts Acylation (General Reaction)
- Note
Ar represents an aromatic ring, R represents an alkyl or aryl group.
- Expression
Ar-H + R-COCl --(Anhyd. AlCl₃)-→ Ar-CO-R + HCl
Prerequisites
Basic understanding of organic reaction mechanisms.
Knowledge of electrophilic aromatic substitution (EAS).
Understanding of Lewis acids and bases.
Concepts of resonance and carbocation stability.
Nomenclature of aromatic compounds, acyl chlorides, and ketones.
Common mistakes
Using hydrated AlCl₃ instead of anhydrous.
Forgetting the role of AlCl₃ as a Lewis acid catalyst.
Confusing acylation with alkylation (carbocation rearrangements, polyalkylation issues in alkylation).
Incorrectly identifying the electrophile.
Not understanding the deactivating effect of the acyl group on the ring.
Keywords
Friedel-Crafts
Acylation
Ketones
Acyl Chlorides
Aromatic
Electrophilic Aromatic Substitution
Lewis Acid
AlCl₃
Acylium Ion
Aromatic Ketones
Practice preview
What is the role of anhydrous aluminium chloride (AlCl3) in the Friedel-Crafts acylation of benzene with acetyl chloride?…
easy
When toluene is subjected to Friedel-Crafts acylation with acetyl chloride and anhydrous AlCl3, the major product formed is:…
medium
Which of the following acyl chlorides will yield acetophenone upon Friedel-Crafts acylation of benzene?…
medium