Alkyation

Reaction

Alkyation Reaction

Mechanism

Generation of Electrophile

Alkyation Mechanism

Friedel Crafts Alkylation

Alkyation Mechanism

Notes

In Friedel Crafts Alkylation of benzene, benzene will react with a haloalkane in the presence of a Lewis acid (eg aluminium chloride). Alkylation is also possible with alkenes. Ethylbenzene is synthesised by alkyation using 90C and HCl/AlCl3, this reaction is useful due to the fact that it is cheaper than the reaction with corresponding haloalkane. There are however two major problems when using Friedel Crafts Alkylation, the first of these is polyalkation and the second is skeletal rearrangement. Alkyation results in polyalkation since the reaction cannot be stopped, monoalkylbenzene is more electron rich than benzene due to the alkyl group and is therefore more reactive with electrophiles and substitutes more easily. Skeletal rearrangement occurs because the final product will be produced using the most stable of the carbocation imtermediates.

Uses

Two alkylbenzenes (ethylbenzene and 1-methylethylbenzene) are produced on a large scale. Ethylbenzene is the monomer which is used to produce phenyethene (styrene). Styrene can be converted into polystyrene which is used for thermoplastics, elastomers , and thermosetting resins.

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Copyright 2002 Nick Barwell.