An acyl group is an alkyl group attached to a carbonyl carbon:
R-C=O
Acylation involves the generation of the acyl group as an electrophile and substituting it upon a Benzene ring.(Fig 1)
The reaction mechanism is shown in Fig 2 below:
Friedel-Crafts Acylation is an alternative to the alkylation reaction because the acyl group deactivates the ring toward further substitution and the acylium cation is not a carbocation and therefore does not undergo molecular rearrangement. However, if the original goal was to produce an alkyl Benzene, then the acyl group must be converted to an alkyl group. This can be done by reacting the acyl Benzene with a Zinc-Mercury amalgam and HCl at elevated temperature for an extended period of time.(Fig 3)
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R. H. Logan, Instructor of Chemistry, Dallas County Community College District, North Lake College.
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Revised: 5/20/97
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