Friedel-Crafts Alkylation Reaction with Organosilicon Compounds

FRIEDEL-CRAFTS ALKYLATION REACTION WITH ORGANOSILICON COMPOUNDS 

Allylchlorosilanes undergo Friedel-Crafts alkylation with aromatic compounds such as benzene derivatives and ferrocene to give [p-(chlorosilyl)alkyl]arene compounds in the presence of Lewis acid catalyst. Allylsilanes containing two or more chlorine atoms on silicon react smoothly with benzene under mild conditions to give alkylation products in good yields [Eq. (15)]. In alkylations of benzene, the reactivity of the allylsilanes increases as the number of chlorine atoms on the silicon increases, but decreases as the number of methyl groups increases. Because the reactivity of allylsilanes is sensitive to the electronic nature of the substituents on the silicon atom, allylsilane selection is an important factor for alkylation reactions. 

The effects of ring constituents in the alkylation of benzene derivatives (Ph-R) with la are summarized in Table I. 

Relative Alkylation Rates and Substituent Constants (s) for Substituted Benzenes (Ph-R) 

Definitions ctr, resonance constant cti, field constant a = or + ai. Reaction mole ratio of Ib/Ph-R/aluminum chloride = 1 20 0.1. 

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IV. Friedel-Crafts Alkylation Reaction with Organosilicon Compounds. 50... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

Substitution by Alkyls of Zinc, Mercury, and Aluminum. The reaction of alkyls of zinc with ethyl silicate or silicon tetrachloride was the first to be used for the preparation of organosilicon compounds. During the period 1863 to 1880 Friedel and Crafts and later Ladenburg employed zinc dimethyl and zinc diethyl to prepare the corresponding alkyls of silicon and many of the intermediate substitution products as well. The reactions were conducted in sealed tubes heated to about 160° and were of a straightforward metathetical type ... 

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