Sulfonation of chloro- and dichloroanisoles with concentrated aqueous sulfuric acid and sulfur trioxide. Demethylation of chloroanisolesulfonic acids in sulfuric acid systems

Article abstract of DOI:10.1002/recl.19881070605

The nine chloro- and dichloroanisoles have been sulfonated with sulfuric acid.The observed sulfonic acid isomer distributions are determined mainly by the ortho- and para-directing effect of the methoxy substituent.In the reaction with sulfuric acid, the initially formed chloro- and dichloroanisolesulfonic acids are demethylated to give the corresponding phenolsulfonic acids.Demethylation occurs only in those cases where the methoxy substituent is sterically hindered by an o-chloro and/or o-sulfo substituent.Reaction of 2,3- and 3,5-dichloroanisole with fuming sulfuric acid yields initially the 4,6- and 2,4-disulfonic acids, respectively.The disulfonic acids are converted to the corresponding hydrogen sulfates either by direct sulfodemethylation or by protodemethylation followed by subsequent sulfation.The 2,3-dichloro-4,6-disulfophenyl hydrogen sulfate cyclizes to the 1,3,2,4-benzodioxadithiin 2,2,4,4-tetraoxide 4.The sulfonation of the chloro- and dichloroanisoles with SO3 in the solvents nitromethane or CCl3F leads only to sulfodeprotonation.