Kinetic Studies of Fast Equilibrium by Means of High-performance Liquid Chromatography. II. Ligand Exchange of N,N-Disubstituted Dithiocarbamate Chelates of Ni(II)

Abstract

Abstract The equilibrium of the ligand exchange of labile Ni(II) dialkyldithiocarbamate chelates (MA2+B\ightleftharpoonsMAB+A, MAB+B\ightleftharpoonsMB2+A, K1=[MAB][A]/[MA2][B], K2=[MB2][A]/[MAB][B]) has been investigated by means of high-perfromance liquid chromatography, two solutions of MA2 and B being mixed and then equilibrated. The equilibrium constants, K1 and K2, have been determined by measuring the concentrations of each complex, including the kinetically unstable ternary complex in the equilibrium state. The ratio of the stability constants of the two Ni(II) chelates, which is equal to K1K2, has been calculated. The following series of increasing stability constants has been found for the alkyl substituents in chloroform; tetramethylene<dimethyl<pentamethylene<diethyl<hexamethylene<dipropyl<dibutyl. The rate of ligand exchange has been investigated by mixing very dilute MA2 and B and by injecting the mixture into HPLC after the lapse of a certain time. The rate of ligand exchange is slow when low initial concentrations of MA2 and B are chosen. The rate of ligand exchange is more than ten times faster than that of ternary complex formation.