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Grade: 12


friedel n crafts alkylation reaction

6 years ago

Answers : (2)

Rinkoo Gupta
askIITians Faculty
80 Points

Friedel-Crafts Alkylation

This Lewis acid-catalyzed electrophilic aromatic substitution allows the synthesis of alkylated products via the reaction of arenes with alkyl halides or alkenes. Since alkyl substituents activate the arene substrate, polyalkylation may occur. A valuable, two-step alternative is Friedel-Crafts Acylation followed by a carbonyl reduction.

Mechanism of the Friedel-Crafts Alkylation

Using alkenes :

Thanks & Regards
Rinkoo Gupta
AskIITians Faculty
6 years ago
47 Points
							1. Overall transformation :  Ar-H to Ar-R
2. Named after Friedel and Crafts who discovered the reaction in 1877.
3. Reagent : normally the alkyl halide (e.g. R-Br or R-Cl) with aluminum trichloride, AlCl3, a Lewis acid catalyst.
4. The AlCl3 enhances the electrophilicity of the alkyl halide by complexing with the halide.
5. Electrophilic species : the carbocation (i.e. R +) formed by the "removal" of the halide by the Lewis acid catalyst
6. The reactive electrophile, the carbocation is prone to rearrangement to a more stable carbocation which will then undergo the alkylation reaction.
alkylation with rearrangement1,2-hydride shift during a Friedel-Crafts reaction
7. Friedel-Crafts reactions are limited to arenes as or more reactive than mono-halobenzenes
8. Other Lewis acids such as BF3, FeCl3 or ZnCl2 can also be used
9. Other sources of carbocations can also be used:
a)-from loss of water from alcohols treated with acid such as H2SO4
b)-from the protonation of alkenes by acid such as H2SO4
10. Alkylation products can also be obtained by the reduction of Friedel-Crafts acylation products
6 years ago
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