Zn(II)-, Al(III)-, and Cu(II)-Catalyzed Decarboxylation of 2-Oxalopropionic Acid

Article abstract of DOI:10.1021/ja00388a021

Distributions of species formed by the coordination of 2-oxalopropionic acid by Zn(II), Al(III), and Cu(II) ions are presented, and kinetics of decarboxylation are discussed in terms of the species present in solution.Studies of initial rates of metal ion catalyzed decarboxylation of 2-oxalopropionic acid (H2L) show dependence on the degree of formation of the metal chelate (ML).Rate constants (k_ML) for the decarboxylation of ZnL, CuL, and AlL⁺ were found to be 18.2 x 10^-3 s^-1, 21.0 x 10^-3 s^-1, and 9.51 x 10^-3 s^-1, respectively.The equilibrium constants for ML(keto) <-/-> ML(enol) were evaluated for the Zn(II) and Al(III) systems and rate constants (k^K_ML) for the decarboxylation of the active keto forms of the Zn(II) and Al(III) chelates were found to be 31 x 10^-3 s^-1 and 79 x 10^-3 s^-1, respectively.The decarboxylation rate constant for the 2:1 Al(III) chelate, AlL2^-, was determined to be 33.5 x 10^-3 s^-1.The keto-enol equilibrium constant -(enol)>/-(keto)> was evaluated, and the decarboxylation rate constant of AlL2^-(keto) was calculated as 43 x 10^-3 s^-1.