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Evaluation of equilibrium constants for deprotonation and lactonisation of $$alpha$$-D-isosaccharinic acid

Rai, D.*; Kitamura, Akira  

A great deal of disagreement exists in the literature regarding the intrinsic deprotonation and lactonisation constants of $$alpha$$-D-isosaccharinic acid (ISA). Based on a combination of nuclear magnetic resonance (NMR) and extensive experimental Ca(ISA)$$_{2}$$(cr) solubility data involving $$alpha$$-D-isosaccharinic acid, the reliable value of log K$$^{circ}$$ for [HISA(aq) $$leftrightarrow $$ ISA$$^{-}$$ + H$$^{+}$$] is -3.27 $$pm$$ 0.01 and for [HISA(aq) $$leftrightarrow $$ ISL($$alpha$$-D-isosaccharinate-1,4-lactone)(aq) + H$$_{2}$$O] is 0.49 $$pm$$ 0.09. These data also provide a composite log K$$^{circ}$$ of -3.76 $$pm$$ 0.09 for the reaction [ISL(aq) +H$$_{2}$$O $$leftrightarrow $$ ISA$$^{-}$$ + H$$^{+}$$]. Reinterpretation of extensive Ca(ISA)$$_{2}$$(cr) solubility data using the SIT activity coefficient model provides log K$$^{circ}$$ of -6.40 $$pm$$ 0.09 for [Ca(ISA)$$_{2}$$(cr) $$leftrightarrow $$ Ca$$^{2+}$$ + 2 (ISA)$$^{-}$$] and of 1.70 $$pm$$ 0.09 for [Ca$$^{2+}$$ + ISA$$^{-}$$ $$leftrightarrow $$ CaISA$$^{+}$$], based on the values that are consistent with the average of all of the available values.

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Category:Nuclear Science & Technology

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