The Friedel-Crafts acylation and alkylation reactions are both electrophilic aromatic substitution reactions that involve the formation of a new carbon-carbon bond between an aromatic ring and an electrophile. However, they differ in the type of electrophile used and the products formed.Friedel-Crafts Acylation:In the Friedel-Crafts acylation reaction, an acyl halide RCOCl or an acid anhydride RCOOCOR' is used as the electrophile. The reaction is typically carried out in the presence of a Lewis acid catalyst, such as aluminum chloride AlCl3 or ferric chloride FeCl3 . The mechanism of the reaction involves the following steps:1. Formation of the acylium ion: The Lewis acid catalyst coordinates to the carbonyl group of the acyl halide, making the carbonyl carbon more electrophilic. The halide then leaves, generating an acylium ion RCO+ .2. Electrophilic attack: The aromatic ring acts as a nucleophile and attacks the electrophilic acylium ion, forming a resonance-stabilized carbocation intermediate.3. Deprotonation: A base usually the halide ion that was formed in step 1 deprotonates the carbocation intermediate, restoring the aromaticity of the ring and forming the final acylated product.Example: Acylation of benzene with acetyl chloride CH3COCl in the presence of AlCl3 forms acetophenone C6H5COCH3 .Friedel-Crafts Alkylation:In the Friedel-Crafts alkylation reaction, an alkyl halide R-X is used as the electrophile. The reaction is also carried out in the presence of a Lewis acid catalyst, such as AlCl3 or FeCl3. The mechanism of the reaction involves the following steps:1. Formation of the carbocation: The Lewis acid catalyst coordinates to the halide, making the alkyl group more electrophilic. The halide then leaves, generating a carbocation R+ .2. Electrophilic attack: The aromatic ring acts as a nucleophile and attacks the electrophilic carbocation, forming a resonance-stabilized carbocation intermediate.3. Deprotonation: A base usually the halide ion that was formed in step 1 deprotonates the carbocation intermediate, restoring the aromaticity of the ring and forming the final alkylated product.Example: Alkylation of benzene with ethyl chloride CH3CH2Cl in the presence of AlCl3 forms ethylbenzene C6H5C2H5 .Selectivities:The Friedel-Crafts acylation reaction is more selective than the alkylation reaction. In the acylation reaction, the product is less prone to further substitution due to the electron-withdrawing effect of the carbonyl group, which deactivates the aromatic ring. In contrast, the alkylation reaction can lead to multiple substitutions and over-alkylation, as the alkyl group is an electron-donating group, activating the aromatic ring for further substitution. Additionally, the alkylation reaction can be subject to carbocation rearrangements, leading to unexpected products. The acylation reaction does not have this issue, as the acylium ion is stabilized by resonance and does not undergo rearrangement.