Kinetic Studies of Fast Equilibrium by High-performance Liquid Chromatography I. Ternary Complex Formation of N,N-Disubstituted Dithiocarbamate Chelates of Ni(II) and Cu(II)

The equilibrium of labile ternary complex formation of metal dialkyldithiocarbamate chelates (MA2+MB2− 2MAB, K=[MAB]2/[MA2][MB2]) has been investigated by high-performance liquid chromatography, the separation process of which is so fast that kinetically unstable ternary complexes can be eluted with no disproportionation during the course of chromatography. High-performance liquid chromatography makes it possible to halt the progress of considerably fast reactions at the moment when the solution of reaction system is injected into the column. Thus, chromatograms obtained indicate the concentration of each species before chromatography, facilitating the determination of equilibrium constant K of Ni(II) and Cu(II) chelates. The equilibrium constants obtained are always 4.0, suggesting that ternary complex formation is controlled by a statistical factor. Disproportionation takes place by collision of two ternary metal chelates, the rate constants being of the order 101–102 M−1 s−1 (Ni(II) chelates) and 103 M−1 s−1 (Cu(II) chelates). The activation parameters of ternary complex formation have been obtained.