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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 on reaction of 1,4-dihydroxybenzene and its methyl ethers in concentrated sulfuric acid

The homogeneous reactions of 1,4-dihydroxybenzene (1), its monomethyl (2) and dimethyl ether (3) and 2-3-sulfonic acid in 68-105percent H2SO4 at 25 deg C have been studied and isomer distributions and rate coefficients for the various subsequent sulfonations, as well as the equilibrium data for the sulfation (-OH -OSO3H), are reported.For 2, the ratio of 2- to 3-sulfonation decreases upon increasing the sulfuric acid concentration from 68-98.5percent H2SO4, due to a gradual change-over in the effective sulfonating entity from H3SO4(1+) to H2S2O7.For 1-2-sulfonic acid (1-2-S), 2-2-S and 2-3-S, the ratios of 5- to 6-sulfonation are all ca. 25:75, whereas 3-2-S only yields the 5-sulfonic acid.Demethylation of the sulfonic acids of 2 and 3 in = 98.5percent H2SO4 is of minor importance, but plays a major role in 105,0 percent H2SO4, the eventual products being the bis(hydrogen sulfate)s 10 and 15, the tricyclic bis(sulfate sulfonate anhydride) 11 and the bicyclic hydrogen sulfate 16.Mechanisms for the sulfodemethylation and for the cyclization of the 2-sulfophenyl hydrogen sulfate moiety to the 1,3,2,4-benzodioxadithiin 2,2,4,4-tetraoxide system are proposed.