Polyacylations Friedel-Crafts reaction

Polyacylations are not a problem in Friedel—Crafts acylations. The acyl group (RCO —) by itself is an electron-withdrawing group, and when it forms a complex with AICI3 in the last step of the reaction (Section 15.7), it is made even more electron withdrawing. This strongly inhibits further substitution and makes monoacylation easy. 

Before explaining the previous data, it is important to understand why 54 is formed in the Friedel-Crafts alkylation reaction. This means that the reactivity of benzene derivatives must be addressed. If 54 is formed by a reaction of 53, then 53 must react with the intermediate carbocation more quickly than benzene. Why does 53 react more quickly than benzene In addition, this discussion must address the question of why polyalkylation is a problem but polyacylation is not. The answers to these questions will also explain the regioselectivity of the reaction. 

Friedel-Crafts acylation does not suffer from polyacylation reactions. In the light of the discussion in Section 21.4.1, the initially formed ketone product must be less reactive than the benzene starting material. The product 50 from the reaction of butanoyl chloride and benzene is a ketone, and the carbonyl unit attached to benzene is an electron-withdrawing group. Electron-withdrawing... 

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