Sulfonation of a series of naphthalenes containing two different oxy substituents

Article abstract of DOI:10.1002/recl.19931120303

The reactions of a series of α,α- and β,β-disubstituted naphthalenes containing two different substituents OR¹ (R¹ = H, SO2CH3) and OR² (R² =CH3, SO2CH3) with sulfur trioxide in CD3NO2 has been studied.The electronic directing effect of the hydroxy group was found to be dominant over that of the methoxy group, which in turn dominates that of the mesyloxy group.Upon reaction with an excess of sulfur trioxide, the hydroxy group is, at least in part, sulfated.For the β-hydroxy-β-methoxynaphthalenes 3a-5a and for 3-mesyloxy-2-naphthol (3c) especially, hydrogen sulfate formation strongly influences the product mixture composition.Thus, upon reaction with 1.0 equiv of SO3, 7-methoxy-2-naphthol (5a) yields its 1-sulfonic acid (1-S), whereas upon reaction with 2.0 equiv, it is the 8-S that is mainly formed due to initial hydrogen sulfate formation.Furthermore, sulfonic acid isomerizations due to steric hindrance are observed.Upon using >2.0 equiv of SO3, formation of di- and trisulfonic acids, as well as sulfo derivatives of both 8,1-naphthalenesultone and the cyclic naphthalene-1-sulfonate-2-sulfate anhydride is observed.