Friedel Craft Alkylation/Acylation Reaction with supplement questions

In organic chemistry, Friedel Craft reaction holds its own importance for synthesizing alkyl-aryl or acyl-aryl compounds in the presence of Lewis acid. This reaction was first reported in 1887 by Charles Friedel and James Mason Craft for their isolation of amyl benzene under the action of Lewis acid.

However, the yield was found to be low due to the formation of other side products in the reaction. The reaction termed Friedel Craft alkylation. This reaction generally involves Lewis acids such as FeBr3, AlCl3, SnCl4, TiCl4, BF3, BeCl2, etc. The mechanism of the reaction shows the formation of carbocation which rearranges itself to direct the reaction in the forward reaction. Due to the formation of carbocations n-alkyl substituted product is difficult to form in this route.

Let us understand the mechanism of the reaction step by step.

The first point is the interaction of Lewis acid with the alkyl halide. The lone pair of halide interact with the vacant p-orbital of the Lewis acid and make an intermediate polar compound, which ultimately converts into an ionic salt and carbocation. This carbocation when formed gets rearranged themselves and acts as an electron-deficient species. The electron density of benzene then interact with the carbocation and forms the rearranged product.

Similarly in the acylation mechanism acyl ions formed with the interaction of lewis acid and acyl halide and the rest of the mechanism follows the same route.

Both these mechanism follows electrophilic substitution reaction.

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