Sulfoquinones in the Hydrolysis of Aryl Esters of o- and p-Hydroxyarenesulfonic Acids in Alkaline Aqueous Solutions of Dioxane

Article abstract of DOI:10.1021/jo00212a032

The alkaline hydrolysis of o- and p-hydroxyarenesulfonate esters of acidic phenols proceeds via an E1cB mechanism.Sulfoquinone (IUPAC name thioquinone dioxide) intermediates (e.g., 8) constitute the best hypothesis to account for the observed kinetic results which obey the rate law k_obsd (hydrolysis) = (k_a + k_b ->)/(1 + +>/K_a).There is negligible deuterium oxide solvent isotope effect on k_a and the entropy of activation is slightly positive.Apparent bimolecular rate constants for hydroxide ion attack on the un-ionized hydroxyl esters (k_aK_aK_w) are many orders of magnitude larger than the bimolecular rate constants for hydroxide ion attack on the corresponding methoxy esters which possess the BAc2 mechanism.Amines trap an intermediate to give more amide than is predicted from the second-order rate law for amine attack on the ionized hydroxy ester.The k_b term most likely arises from bimolecular attack of the hydroxide ion on the ionized hydroxy ester.The hydrolysis of o-hydroxyarenesulfonate esters undergoes strong competition from the "Smiles" rearrangement.