Friedel-Crafts alkylations with silicon compounds

Abstract

Publisher Summary This chapter discusses the reactivities of organo-silicon compounds for the Frieda–Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions. The reactivities of alkenylsilanes in the presence of a Lewis acid vary depending upon the nature of substituents on silicon. The substituent effect of vinylsilanes is similar to that of allylsilanes. The reactivity of vinylsilanes increased as the number of chlorine atom on the silicon increased, but decreased as the number of methyl groups increased. The rearrangement of alkylating agent under Friedel–Crafts reaction conditions and chloride exchange between aluminum chloride and alkyl chloride are well known. These indicate that the alkylation proceeds via the transitory existence of carbocations resulting from complexation between the alkylating agent and Lewis acid catalyst. The alkylation of mono-substituted benzenes gives an isomeric mixture of ortho, meta, and para-products. The ratio of isomeric products varies depending upon the electronic nature and steric bulk of the substituents on the benzene.