Sulfonation and sulfation on reaction of 1,2‐dihydroxybenzene and its methyl ethers in concentrated aqueous sulfuric acid

Abstract

AbstractThe homogeneous sulfonation of 1,2‐dihydroxybenzene (1), its monomethyl (2) and dimethyl ether (3) in concentrated aqueous sulfuric acid at 25°C has been studied and isomer distributions, as well as rate coefficients for the sulfonation of 1–3 and their monosulfonic acids, have been determined. In 73.5‐87.5% H2SO4, 1 yields the 3‐ and 4‐sulfonic acids in a ratio of 25:75, 2 yields the 4‐, 5‐ and 6‐sulfonic acids in a ratio of 46:36:18 in 73.5% H2SO4 and 50:39:11 in 87.5% H2SO4, whereas 3 yields only the 4‐sulfonic acid. The remarkable absence of the 3‐sulfonic acid (< 2%) with the 2‐methoxy substrates 2 and 3 is discussed in terms of conformer populations of the reactants. In sulfuric acid > 87.5% H2SO4, the 4‐sulfonic acid of 1 and the 5‐sulfonic acid of 2 are present in part in the form of their hydrogen sulfate. In that acid region, the 3‐ and 4‐sulforic acids of 1 both yield the 3,5‐disulfonic acid, the 4‐ and 6‐sulfonic acids of 2 both yield the 4,6‐disulfonic acid and the 4‐sulfonic acid of 3 mainly yields the 4,6‐ together with some 4,5‐disulfonic acid.