The Kinetics of the Complex-forming Reaction between Nickel(II) and Ethylenediaminetetraacetate

The complex-forming reaction of nickel (II) with ethylenediaminetetraacetate (EDTA) was found to proceed in acetate buffers of pH 3.8 to 5.2 through four different reaction paths, Ni2++HY3− 1a NiHY− NiOAc++HY3− 1b NiHY−+OAc− NiHY− NiY2−+H+ Ni2++H2Y2− 2a NiH2Y NiOAc++H2Y2− 2a NiH2Y+OAc− NiH2Y NiHY−+H+ NiY2−+2H+ The change in the polarographic diffusion current of nickel(II) at the rotated dropping mercury electrode was utilized to follow the decrease of the nickel(II) concentration in the reaction mixture after the initiation of the reaction. The rate constants of the reaction paths were determined at 0°C and ionic strength 0.2, with the results: k 1a=1.06×104 mol−1 liter sec−1 k 1b=2.25×104 ” k 2a=2.04×102 ” k 2b=6.04×102 ” These constants are much smaller than those of the corresponding reactions between copper(II) and EDTA.