Name: Electrophilic Aromatic Substitution: Friedel&amp;#8211;Crafts Alkylation of Benzene
Uploaded: 2023-04-30T10:32:05
Description: Learn by watching this video about Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene at JoVE.com

Friedel&#8211;Crafts alkylation of aromatic compounds was discovered by Charles Friedel and James Crafts.
It is a typical electrophilic aromatic substitution in which the hydrogen of an aromatic ring is replaced with an alkyl group.
For example, 2-chlorobutane reacts with benzene in the presence of aluminum chloride, a Lewis acid catalyst, to form 2-butylbenzene.
The alkylation starts with a Lewis acid&#8211;base reaction in which the alkyl halide reacts with aluminum chloride. The complex then dissociates to form a carbocation.
As an electrophile, the carbocation reacts with the &pi; electron cloud of benzene, forming a resonance-stabilized arenium ion.
Finally, deprotonation of the arenium ion restores aromaticity, giving 2-butylbenzene and regenerating the catalyst.
Notably, with secondary and tertiary halides, the carbocation is the reacting electrophile. 
With primary alkyl halides, the free primary carbocation is relatively unstable. Therefore, a complex of an alkyl halide with aluminum chloride serves as the electrophile.

electrophilic aromatic substitution: friedel&ndash;crafts alkylation of benzene

Friedel&#8211;Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel&#8211;Crafts alkylation refers to the replacement of an aromatic proton with an alkyl group via electrophilic aromatic substitution. A Lewis acid catalyst such as aluminum chloride reacts with an alkyl halide to form a carbocation. The resulting carbocation then reacts with the aromatic ring and undergoes a series of electron rearrangements before giving the final product. For instance, benzene reacts with 2-chlorobutane in the presence of aluminum chloride to form 2-butylbenzene.
<img alt="Figure1" src="/files/ftp_upload/12467/12467_PT_Figure_1v3.svg" style="text-align: center; height: 70px;" />
The alkylation starts with a Lewis-acid-base reaction in which the alkyl halide reacts with aluminum chloride, resulting in the formation of an electrophilic carbocation.
<img alt="Figure2" src="/files/ftp_upload/12467/12467_PT_Figure_2.svg" style="text-align: center; height: 90px;" />
The carbocation attacks the &#960; electron cloud of the aromatic ring, forming a resonance-stabilized arenium ion. The deprotonation of the arenium ion restores aromaticity, giving 2-butylbenzene and regenerating the catalyst.
<img alt="Figure3" src="/files/ftp_upload/12467/12467_PT_Figure_3v3.svg" style="text-align: center; height: 75px;" />
With secondary and tertiary halides, the carbocation is the reacting electrophile. In the case of primary alkyl halides, the free primary carbocation is unstable and difficult to generate. Instead, a complex of an alkyl halide with aluminum chloride acts as the electrophile.

Learn by watching this video about Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene at JoVE.com

Electrophilic Aromatic Substitution: Friedel&amp;#8211;Crafts Alkylation of Benzene

Electrophilic Aromatic Substitution: Friedel&ndash;Crafts Alkylation of Benzene

Friedel&#8211;Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel&#8211;Crafts ...