Abstract
The monoβ and disulfonations of the two methoxynaphthalenes (MON's), nine dimethoxynaphthalenes (DMON's) and 2,3β(ethylenedioxy)naphthalene (EDN) with sulfur trioxide in mainly nitromethane have been studied. Both the monosulfonations and the disulfonations of the MON's and DMON's in nitromethane lead to one or two products. Steric hindrance caused by the preferred conformation of the methoxy substituent(s) appears to have a strong influence on the substitution pattern. Provided that allowance is made for this specific steric hindrance, the substitution patterns are in agreement with the localization energies, obtained by simple HΓΌckel MO calculations. The positional reactivity orders for the sulfonation of the (D)MONβmonosulfonic acids have been analyzed in terms of (i) the localization energies of the parent compounds, (ii) the (electronic) directing effect of the sulfonic acid substituent and (iii) the difference in steric hindrance for the introduction of the second sulfonic acid group. This analysis suggests that the electronic directing effect of the sulfonic acid group is at most quite small, and is overruled by both the electronic and steric requirements of the methoxy group.