The kinetics of formation of the nickel monooxalate complex in solution

Article abstract of DOI:10.1021/ic50013a012

The rate of formation of the monooxalate complex of nicklel(II) both in neutral and in acid solution has been studied by the use of a flow technique. The results are interpreted in terms of the reactions Ni²⁺ + A^2- ?_k1d^k1f NiA and Ni²⁺ + HA^- ?_k2d^k2f NiA + H⁺ where A^2- represents the oxalate ion. At 25.0° and ionic strength 0.10 M, k_1f = 7.5 × 10⁴ M^-1 sec.^-1, k_2f = 5 × 10³ M^-1 sec.^-1, k_1d = 3.6 sec.^-1, and k_2d = 1.5 × 10³ M^-1 sec.^-1. Studies at various temperatures between 5 and 35° give ΔH_1f* = 14 kcal, mole^-1, ΔH-_2f* = 14 kcal, mole^-1, ΔS_1f* = 12 cal. deg.^-1 mole^-1, and ΔS_2f* = 7 cal. deg. mole^-1. The results are consistent with a model in which the rate-determining step is the elimination of a water molecule from the inner hydration shell of the nickel ion.