Kinetic study of the isotope exchange reactions of malonic acid and its derivatives in various acidic D2O media using H-1 NMR spectroscopy. Implication in the Belousov-Zhabotinsky reaction

The kinetics of the isotope exchange reactions of RCH(COOH)(2), (R=H, D, Me , Et, Bu, and Ph) in D2O solution were studied by using H-1 NMR spectroscop y. It was observed that the rate of isotope exchange reaction was inhibited by the presence of 1 M of DNO3, DCl, DBr or D2SO4 and catalyzed by the pre sence of 4 M of D2SO4. No inhibition effect was observed in the case of D3P O4. The effect of inorganic acids follows the order of D3PO4 > D2SO4 much g reater than (DNO3, DCl, DBr). The conjugated base (RCH(COOD)(COO-)) of RCH( COOD)(2) plays an important role in the isotope exchange reaction. The pres ence of deuterium ion suppresses the generation of RCH(COOD)(COO-) ion from RCH(COOD)(2) and inhibits the rate of isotope exchange. In general, the or der of reactivity of RCH(COOH), toward isotope exchange with deuterium atom is R=Ph > (H, Br) > Me > (Et, Bu). (C) 1999 John Wiley & Sons, Inc.