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Abstract
The reactions of 3,5-dimethoxyphenol (1) and its methanesulfonate ester (3) with sulfur trioxide have been studied. On reaction with 0.9 equiv of SO3 in nitromethane, 1 gives a 65:35 mixture of its 2sulfonic acid (1-2-S) and 1-4-S, whereas with 4.0 equiv of SO3, exclusively 1-2,6-S2 is formed. 1-2,6-S2 is subsequently converted into its hydrogen sulfate (2-2,6-S2), which in turn rearranges to give the intramolecular anhydride 5,7-dimethoxy-8-sulfobenzo-1,3,2,4-dioxadithiin 2,2,4,4-tetraoxide (4). Reaction of 3 with SO, in nitromethane leads to a 85:15 mixture of 3-2-S and 3-4-S which, upon further reaction, yields initially 3-2,6-S2 and eventually 4. Temperature dependent 1H NMR evidence suggests that there exist for both 1 and 3 equilibria between the two monosulfonic acids and the substrate.