Bondline / Reactions

Friedel–Crafts acylation

AlCl₃ turns an acyl chloride into an acylium ion, which the benzene ring attacks. Loss of H⁺ restores the ring. The product ketone deactivates the ring, so only one acyl group adds.

Aromatic substitution · 2 steps

Conditions

RCOCl with AlCl₃, then aqueous workup.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

HO+HOClAl−ClClCl++
Step 1The ring attacks the acylium ion carbon.
HOClAl−ClClClOHClClAlClClAlCl₄⁻+++
Step 2An Al–Cl bond delivers chloride to the proton; the C–H electrons restore the aromatic ring. HCl and AlCl₃ are released.

About aromatic substitution reactions

Benzene keeps its stable aromatic ring by substituting rather than adding. An electrophile attacks, then a proton is lost to restore aromaticity.

Practise this mechanismDraw the curly arrows yourself and Bondline checks each one. Or add it to your notes and watch it in 3D.

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