Friedel-Crafts Alkylation
When an alkyl halide is treated with a Lewis acid (i.e. AlX3, FeX3 and BX3 etc. where, X = Cl, Br and F) in the presence of an aromatic ring, an alkyl group is introduced in the aromatic ring. This electrophilic aromatic substitution reaction is known as the Friedel-Crafts alkylation reaction. Friedel-Crafts alkylation usually involves treating benzene with a secondary or tertiary alkyl halide, and the Lewis acid AlCl3. Generally, no reaction occurs in the absence of Lewis acid.
In substituted benzene, the alkyl group introduced according to the substituted group attached to the benzene ring. If the substituted group is ortho or para directing (i.e. EDG) then alkyl group introduced at ortho and para postion in the ring and if the substituted group is meta directing (i.e. EWG) the alkyl group introduced at meta position in the ring. Generally, para product predominates.
Friedel crafts alkylation reaction is an electrophilic substitution reaction. So, the benzene ring with strong electron withdrawing group does not undergo Friedel crafts alkylation reaction. Therefore, C6H5NO2, C6H5COOH, C6H5COR , C6H5N+( CH3)3 compounds does not exhibit Friedel crafts alkylation reaction.
In substituted benzene, the alkyl group introduced according to the substituted group attached to the benzene ring. If the substituted group is ortho or para directing (i.e. EDG) then alkyl group introduced at ortho and para postion in the ring and if the substituted group is meta directing (i.e. EWG) the alkyl group introduced at meta position in the ring. Generally, para product predominates.
Friedel crafts alkylation reaction is an electrophilic substitution reaction. So, the benzene ring with strong electron withdrawing group does not undergo Friedel crafts alkylation reaction. Therefore, C6H5NO2, C6H5COOH, C6H5COR , C6H5N+( CH3)3 compounds does not exhibit Friedel crafts alkylation reaction.
