Dissociation Constants of α-d-Isosaccharinic Acid: “Composite” and “Intrinsic” Values

Abstract

The transformation of α-d-isosaccharinic acid into α-d-isosaccharino-1,4-lactone proceeds relatively slowly. Consequently, the transformation constant, KL, has been determined kinetically in 1.0 mol·dm−3 NaClO4 and at 23 °C. A previous determination in 0.1 mol·dm−3 NaClO4 and at 23 °C has been reinterpreted. The values obtained have been coupled with other data in the literature to demonstrate that the magnitude of the transformation constant is independent of ionic strength, and its value was determined to be log KL° = 0.80 ± 0.02. Data from the literature for the dissociation of α-d-isosaccharinic acid have been re-evaluated to determine both the “intrinsic” and “composite” dissociation constants at zero ionic strength, namely, log Ka° = −4.04 ± 0.06 and log Kc° = −4.90 ± 0.07, respectively. The present data permit a much more thorough understanding of the aqueous chemistry of α-d-isosaccharinic acid to be ascertained than has previously been possible.