Base-catalysed mutarotation of glucose in dimethylformamide and dimethyl sulphoxide

Abstract

The rate of mutarotation of glucose has been measured in pure dimethylformamide and dimethyl sulphoxide with substituted benzoate ions as catalysts, and in 80 vol % dimethyl sulphoxide-water with acetate and chloroacetate as catalysts. Unlike many other base–catalysed reactions in these solvents, the rates show no subtantial increase over those observed in water. This is interpreted in terms of a strong involvement of water with the transition state in aqueous media, in accordance with earlier suggestions concerning the mechanism of related reactions such as the addition of water and alcohols to carbonyl compounds. In combination with previously reported pK values in the appropriate solvents, the results show that there is a good correlation of the catalytic effect of the anion bases with their basic strengths. The observed Brönsted coefficients are slightly higher (β= 0.6 in dimethylformamide and dimethyl sulphoxide) than in water (β= 0.4).