1 Friedel-Crafts: Control Problems Multiple alkylations can occur because the first alkylation adds electron density and makes the ring more reactive:

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Presentation transcript:

1 Friedel-Crafts: Control Problems Multiple alkylations can occur because the first alkylation adds electron density and makes the ring more reactive:

2 Friedel-Crafts: Control Problems Carbocations may rearrange:

3 Friedel-Crafts Acylation Reaction of an acid chloride (RCOCl) and an aromatic ring in the presence of AlCl 3 i(Lewis acid catalyst) introduces an acyl group: -COR Benzene with acetyl chloride yields acetophenone:

4 Mechanism of Friedel-Crafts Acylation Similar to alkylation Reactive electrophile: resonance-stabilized acyl cation

5 Friedel-Crafts Acylation - Advantages An acyl cation does not rearrange The product has a carbonyl group on the ring, so the ring is deactivated. This means no over-alkylation with Friedel-Crafts Acylation. Example:

6 Reduction of Aryl Ketones Aromatic ring activates carbonyl toward reduction Ketone is converted into an alkylbenzene by catalytic hydrogenation over Pd catalyst Acylation Akylation

7 Friedel-Crafts Practice Give products for the following reactions, and list each as Friedel-Crafts alkylation or acylation.