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

Abstract

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D2O solutions, respectively, using 1H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO3 (0–3 M) and DSO4− ion (0–0.1 M), whereas it is catalyzed by the presence of DSO4− ion (> 0.2 M), D3PO4, D2PO4− ion or DPO42– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D2O is DPO42– > D2PO4− > D3PO4 > DSO4− > DNO3. The rate of the isotope exchange reaction of malonate ion in D2O decreases to a minimum and then increases with increased [NaOD]0. The mechanism of the isotope exchange reaction of malonic acid in acidic D2O is different from the general acid‐catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system.