The Effect of Phthalate Ion and Acetate Ion on the Rate of the Reaction between Nickel(II) and Cobalt(II)-Nitrilotriacetate Complexes

Abstract

Abstract A kinetic study of the substitution reactions of nickel(II) ions and cobalt(II)-nitrilotriacetate complexes in phthalate and in acetate buffer has been carried out using a procedure previously reported. The reaction was made to proceed through both hydrated nickel(II) ions and monophthalatonickel(II) complexes or monoacetatonickel(II) complexes. The rate constants for eight elementary reaction paths, four of which involve the hydrated nickel(II) ions, while the others involve the monophthalatonickel(II) complexes (the monoacetatonickel(II) complexes in the case of the measurements in acetate media), were determined at an ionic strength of 0.2 at 25°C. The values obtained indicate that all the reactions proceeding through the monophthalatonickel(II) complexes are slower than the corresponding reactions proceeding through hydrated nickel(II) ions; however, all the reactions proceeding through monoacetatonickel(II) complexes are faster than the corresponding reactions proceeding through hydrated nickel(II) ions. Thus, the kinetic reactivity is in the order of: NiOAc+>Ni2+>NiPh, where Ph2− indicates a bivalent phthalate anion.