Kinetic Study of the Isotope Exchange Reactions of Malonic Acid and Malonate Ion Using ~1H NMR Spectroscopy. Inhibition of Acid and Base

摘要

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D_2O solutions, respectively, using ~H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO_3 (0-3 M) and DSO_4-ion (0-0.1 M), whereas it is catalyzed by the presence of DSO_4-ion (>=0.2M), D_3PO_4, D_2PO_4-ior or DPO_4~(2-) ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D_2O is DPO_4~(2-)>D_2PO_4->D_3PO_4>DSO_4-DNO_3. The rate of the isotope exchange reaction of malonate ion in D_2O decreases to a minimum and then increases with increased [NaOD]_0. The mechanism of the isotope exchange reaction of malonic acid in acidic D_2O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic aicds. The bimalonate ion plays an important role in the isotope exchange reactios of this system.