Water-catalysed mutarotation of glucose and tetramethylglucose in dioxan, acetonitrile, and dimethyl sulphoxide

Abstract

We have studied the mutarotation of glucose and 2,3,4,6-tetra-O-methylglucose in mixtures of water and the organic solvents 1,4-dioxan, acetonitrile, and dimethyl sulphoxide at 303.2 K. At high water concentration the reaction orders with respect to water are about two for all the solvents. For low (≲11M) water concentration this reaction order decreases to about one for dioxan and acetonitrile, whereas it increases to about 3.7 for dimethyl sulphoxide. This behaviour parallels a decrease and an increase, respectively, in both the activation energy and the activation entropy for the two groups of solvents. On the basis of information about the properties of the mixed solvents and predictions of modern quantum theories of proton transfer reactions in polar media the data are shown to be compatible with concerted proton transfer via the water catalyst molecules.