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Reactions of the dihydroxybenzenes and their methyl ethers with sulfur trioxide. The effect of initial sulfation on the sulfonation product distribution

The sulfation and sulfonation resulting from the reaction of the dihydroxybenzenes and their mono- and dimethyl ethers with SO3 in nitromethane have been studied, and their product distributions are reported.As to the non-hydroxy-substituent-containing substrates, 1,2-dimethoxybenzene (3) yields the 4-sulfonic acid (3-4-S) which, upon further sulfonation, yields a 1:4 mixture of the 3,5- and 4,5-S2.The 1,3- (6) and 1,4-isomer (9) yield initially the 4- and 2-S, respectively, and subsequently exclusively 6-4,6- and 9-2,5-S2, respectively.With the substrates containing one hydroxy substituent, the sulfonation isomer distribution is dependent on the SO3 to substrate ratio if the OH and OMe substituents are in ortho or para orientation, due to increasing sulfonation of the corresponding methoxyphenyl hydrogen sulfate.Thus, 2-methoxy- (2) and 4-methoxyphenol (8) with one equiv of SO3 at 0 deg C yield a 3:1 mixture of 2-4-S and 2-5-S and a 9:1 mixture of 8-2-S and 8-3-S, respectively, but, with >/= 4 equiv of SO3, the former reactant yields only 2-5-S and the latter only 8-3-S. 3-Methoxyphenol (5) yields initially a 1:1 mixture of the 4- and 6-sulfonic acid.Further sulfonation yields only 5-O,4,6-S3 which slowly cyclizes to the 1,3,2,4-benzodioxadithiin 2,2,4,4-tetraoxide derivative 11.As to the dihydroxy-containing substrates, 1,2-dihydroxybenzene (1) with 1 equiv of SO3 first yields the hydrogen sulfate 1-O-S which rearranges to 1-4-S; on using an excess of SO3, the eventual product is 1-O(2),4-S2.Similarly, the 1,4-isomer (7) with 1 equiv of SO3 yields initially 7-O-S which isomerizes to 7-2-S.With 6 equiv of SO3, initially 7-O,O-S2 is formed and subsequently its 2-sulfonic acid, which eventually cyclizes slowly to the 1,3,2,4-benzodioxadithiin 2,2,4,4-tetraoxide derivative 12.The 1,3-isomer 4 with 1 equiv of SO3 yields the 4-sulfonic acid.With 4 equiv of SO3, initially 4-O,O-S2 is formed and subsequently 4-4,O,O-S3, which is converted into both 4-O,O,4,6-S4 and the cyclization product 10.Eventually, small amounts of 4-O,2,4,6-S4 and 14-2,6-S2 are formed by transsulfonation.

Sulfonation and sulfation of 1,3-dihydroxybenzene and its methyl ethers in concentrated sulfuric acid

The homogeneous sulfonations of 1,3-dihydroxybenzene (1), its monomethyl (2) and dimethyl ether (3) in concentrated aqueous sulfuric acid at 25 deg C have been studied and isomer distributions and rate coefficients for the sulfonation of 1-3 and their monosulfonic acids are reported.The initial process, upon dissolution of the reactants, is protonation at C(4) and C(6).The subsequent sulfonation of the symmetrical reactants 1 and 3 yields the 4-sulfonic acids and that of 2 the 4- and 6-sulfonic acids, the ratio of which is 0.8 +/- 0.1 at 73.5percent H2SO4.The sulfonation of the 4-sulfonic acid of 1 (1-4-S) yields a mixture of 2,4- and 4,6-disulfonic acids, that of 2-4-S and 3-4-S yields the 4,6-S2 and that of 2-6-S gives a mixture of 2,6- and 4,6-S2.The disulfonic acids 1-2,4-S2 and 2-2,6-S2 both slowly isomerize to yield the 4,6-disulfonic acid isomers.At acid concentrations >= 82.2percent H2SO4, the disulfonic acids of 1 slowly yield 1-2,4,6-S3, whereas those of 2 and 3 are not further sulfonated.The absence of 2-2,4-S2 from 2-4-S and of 2-2,4,6-S3 is discussed in terms of conformer populations of the precursory sulfonic acid substrates.