Reactions of a series of methyl ethers of the trihydroxybenzenes and three dimethoxyphenyl methanesulfonates with sulfur trioxide. The effect of initial sulfation on the sulfonation product distribution

The sulfation and sulfonation of a series of mono‐, di‐ and trimethyl ethers of the trihydroxybenzenes with SO3 have been studied and the product distributions are reported. As for the trimethoxybenzenes, 1,2,3‐trimethoxybenzene (4) yields the 4‐sulfonic acid (4‐4‐S) and, upon further sulfonation, 4‐4,6‐S2. 1, 2, 4‐Trimethoxybenzene (7) yields a mixture of the 5‐sulfonic acid and its anhydride. 1, 3, 5‐Trimethoxybenzene (11) yields the 2‐sulfonic acid and, upon further sulfonation, 11‐2,4‐S2. 1, 2‐Dihydroxy‐3‐methoxybenzene (1) with up to 2.0 equiv of SO3 yields the 6‐sulfonic acid. For 2, 6‐dimethoxyphenol (2), the ratio of 3‐ to 4‐sulfonation increases from 1.04 to 7.1 on using 4.0 instead of 0.9 equiv of SO3, due to initial formation of the hydrogen sulfate derivative and subsequent ring sulfonation of that species. 3,4‐Dimethoxyphenol (5), upon sulfonation with both 1.0 and 4.0 equiv of SO3, only yields the 6‐sulfonic acid. 1,3‐Dihydroxy‐5‐methoxybenzene (8), upon sulfonation with 1.0 equiv of SO3, yields 8‐2‐S and 8‐4‐S in a 1:1 ratio in addition to 20% of the hydrogen sulfate of 8. Upon further reaction, a mixture of 8‐2,4(= 2,6)‐S2 and 8‐4,6‐S2 is formed. 3,5‐Dimethoxyphenol (9), upon reaction with 1.0 equiv of SO3, yields 9‐2‐S, whereas with 4.0 equiv of SO3, a 32:68 mixture of 9‐2‐S, 9‐4‐S is obtained. The reactions with SO3 of three dimethoxyphenyl methanesulfonates, as model compounds for the corresponding hydrogen sulfates, which are the initial products formed by sulfation of the corresponding phenols, have also been studied. The observed sulfonic acid product distributions are discussed on the basis of the Curtin‐Hammett principle.