Aromatic sulfonation. Part 120. Reaction of dihydroxy- and dimesyloxy-naphthalenes with sulfur trioxide in nitromethane. Directing effects and the influence of initial sulfation on the product distributions

Abstract

The reaction of nine dihydroxynaphthalenes (DHNs) and eight dimesyloxynaphthalenes (DMSNs) with sulfur trioxide in C²H₃NO₂ as solvent has been studied by ¹H NMR spectroscopy. The monosulfonation of the DHNs leads to one or two carbon sulfonated products; only 2,3-DHN yields all the three possible sulfonic acids. The disulfonations of the DHNs yield one or two disulfonic acids which are usually also mono- or di-sulfated. Furthermore, derivatives of two cyclic naphthalene-sulfonate sulfate anhydrides and of 8,1-naphthalenesultone are formed. The DMSNs initially yield one or two monosulfonic acids, and, in some cases, subsequently (in part) the corresponding sulfonic anhydrides.

The substitution patterns of the DHNs are generally in agreement with the cation localization energies, obtained by simple Hückel MO calculations. The results of the disulfonations of the DHNs suggest that: (i) sulfonation does not (exclusively) occur via the corresponding di(hydrogen sulfates); and (ii) hydrogen sulfate formation is more pronounced for the β- than the α-hydroxy group.