Reactions of Alkyl Halides in Dimethyl Sulfoxide under Friedel-Crafts Conditions

When dimethyl sulfoxide, ethyl bromide, and 5 mole­-percent of ferric chloride are heated together, a yellow precipitate is formed. The product partially decomposes at 172 degrees, with evolution of gas. It is very soluble in water, but only slightly soluble in methanol. It contains 7.18% by weight of iron (III), suggesting a compound of high molecular weight or a mixture. It appears that a Friedel-Crafts alkylation of DMSO has taken place, perhaps giving an ethyldimethyloxosulfon­ium salt, however, the IR and NMR spectra do not substantiate this. The absence of alkoxydimethylsulfonium salts in the above reaction mixture has been demonstrated. An attempt to prepare ethyldimethyloxosulfonium iodide by reacting ethyl methyl sulfoxide with methyl iodide gave no precipitate. Addition of ferric chloride to this reaction mixture followed by heating gave a crystalline solid which showed only a singlet in the NMR