FRIEDEL-CRAFTS ETHYLATION IN NONPOLAR SOLVENTS

Competitive Friedel-Crafts ethylations of benzene and toluene were carried out at 25° in homogeneous solutions of excess aromatics, nonpolar organic, or basic organic solvents. The rate of boron fluoride catalyzed ethylation with ethyl fluoride in n-hexane or chloroform was also measured under noncompetitive reaction conditions. Ethylation in nonpolar organic solvent shows an anomalous substrate selectivity. Benzene is more reactive than toluene. The isomer distributions of ethyltoluene formed in nonpolar organic solvents are not statistical. Aluminum bromide catalyzed ethylation of benzene with ethyl-2-14C iodide was carried out in n-hexane solution. Oxidation of the ethylbenzene obtained with nitric acid gave radioactive p-nitrobenzoic acid, indicating migration of radioactivity from the β- to the α-carbon atom of the ethyl group. It is suggested that the electro-phile in ethylation is either an ethyl carbonium ion in the nonpolar organic solvent or a nonionized ethyl halide-metallic halide complex in the basic organic solvent, and that the substrate and positional selectivities in all Friedel-Crafts alkylations are determined by an activation energy of the formation of ó complex. © 1969, American Chemical Society. All rights reserved.