Ionization constants of some hydroxypyrones in water and in 80%(w/w) dimethyl sulphoxide–water at 25 °C

Abstract

The ionization constants of some hydroxypyrones have been measured spectrophotometrically at 25 °C in water and in 80%(w/w) dimethyl sulphoxide–water. A few of them are exceptionally strongly acidic. The pKa values of these compounds are discussed in relation to their molecular structures. A plot of the pKa in water against the corresponding pKa in 80%(w/w) dimethyl sulphoxide–water is linear, although ΔpKa varies from negative values for the weaker acids to positive values for the stronger acids. Possible solvent effects have been suggested.