Kinetic study of the isotope exchange reactions of malonic acid and malonate ion using H-1 NMR spectroscopy. Inhibition of acid and base

The isotope exchange reactions of malonic acid and a malonate ion were inve stigated in acidic and basic D2O solutions, respectively, using H-1 NMR spe ctroscopy. The isotope exchange reaction of malonic acid is inhibited by th e presence of DNO3 (0-3 M) and DSO4- ion (0-0.1 M), whereas it is catalyzed by the presence of DSO4- ion (greater than or equal to 0.2 M), D3PO4, D2PO 4- ion or DPO42- ion. The order of relative reactivity for catalyzing the i sotope reaction of malonic acid in D2O is DPO42- > D2PO4- > D3PO4 > DSO4- m uch greater than DNO3. The rate of the isotope exchange reaction of malonat e 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 aci dic D2O is different from the general acid-catalyzed mechanism generally ob served for organic acids like acetic and dichloroacetic acids. The bimalona te ion plays an important role in the isotope exchange reactions of this sy stem.