Sulfonation of anisole, phenol, toluene and related alkyl and alkoxy derivatives with SO3. The influence of the solvent system on the reactivity and the sulfonic acid product distribution

Abstract

The reactions of anisole (1), phenol (2), the alkoxy- and alkylphenyl ethers 3–11, toluene (12) and the o-dialkylbenzenes 13–15 with sulfur trioxide in dichloromethane or trichlorofluoromethane have been studied. Our results have been compared with those obtained with the same substrates upon reaction with SO3 in nitromethane and dioxane. We show that ortho substitution is enhanced for sterically unhindered phenyl ethers and phenols due to complex formation between SO3 and the C(sp2)-bonded oxygen when dichloromethane is used as solvent instead of nitromethane or dioxane. This is mainly as a result of intramolecular SO3, transfer from the oxygen to the ortho carbon and subsequent conversion of the resulting σ-complex into the ortho sulfonic acid.