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

Article abstract of DOI:10.1002/recl.19881070905

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.