Kinetics and mechanism of ninhydrin reaction with copper(II) complexes of glycine and α-alanine. Elucidation of the template mechanism

Ninhydrin has been found to react with Cu(glycine)+ and Cu(alanine)+ in the ratio of 1:1. The kinetic studies of the reaction were carried out at different concentrations of the reactants at 80°C (pH = 5.0). The reaction proceeds through the formation of a ternary labile complex of ninhydrin with Cu(II) complexes of glycine and alanine. The kinetics were found to follow pseudo‐first‐order reaction path with respect to Cu(II)‐complex in presence of excess [Ninhydrin]. Formation of a ternary labile complex indicates a template reaction mechanism based on the reactions with coordinated ligands. The variation of pseudo‐first‐order rate constants with [ninhydrin] was found to be in good agreement with equation \documentclass{article}\pagestyle{empty}\begin{document}$$ 1/k_{obs} = \frac{{B1}}{{[{\rm Ninhydrin}]}} + B_2 $$\end{document} where B1 and B2 are the unknown empirical parameters. The [acetate ion] has no significant effect on the rate constants. On the basis of observed data a probable mechanism has been proposed. © 1993 John Wiley & Sons, Inc.