Nitrogen kinetic isotope effects on the decarboxylation of 4-pyridylacetic acid.

Nitrogen kinetic isotope effects on the decarboxylation of 4-pyridylacetic acid have been measured in solvents of different polarity and have been found to vary from the inverse value of 0.994 to the normal value of 1.002 upon increase of water content of the binary dioxane--water solvent from 25% to 75% (v/v), respectively. These changes were successfully modeled theoretically and shown to originate from the large inverse nitrogen isotope effect on the equilibrium between acidic and zwitterionic forms.