Abstract
The kinetics of substitution reactions of nickel(II) complexes of diethylenetriamine and ethylenediaminemonoacetic acid with diethylenetriaminepentaacetic acid and those of diethylenetriamine and ethylenediamine with cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetic acid were studied systematically by using the polarographic technique. All the reactions studied were found to be first-order with respect to the attacking group and also first-order with respect to the nickel(II) complex of diethylenetriamine, ethylenediamine, or ethylenediaminemonoacetic acid with a 1-to-1 composition. From a comparison of the relative rate constants determined experimentally with those calculated on the basis of a postulated reaction intermediate, the reaction mechanism was described in detail. All the reactions were concluded to proceed through the mixed ligand complex reaction intermediates which are characterized as having two nitrogen (amino) groups of displaced ethylenediamine, diethylenetriamine, or ethylenediaminemonoacetate ions bonded to the nickel(II) ion. This finding is contrary to the observation obtained by Rorabacher and Margerum from their kinetic study of the exchange reaction of the ethylenediaminetetraacetate anion with nickel(II) complexes of triethylenetetramine and tetraethylenepentamine.
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