Ligand‐catalyzed metal ion reduction: Kinetics and analytical applications of nickel reduction catalyzed by nicotinamide

Abstract

AbstractThe catalytic reduction of Ni (II) in the presence of nicotihamide (NA) at pH < 7 was studied by direct‐current and differential‐pulse polarography (DPP). The prewave (with E1/2 around –0.78 V (versus saturated calomel electrode (SCE)) shows the typical behavior of an electrode process with regeneration of the reactant by a second‐order, rate‐determining chemical reaction. This reaction consists in the formation of the reducible nickel complex. The kinetics of the electrode process was studied by means of an adapted form of the equation derived by Koutecký for electrochemical reactions with a parallel chemical step. The rate constant for the formation of nickel‐nicotinamide complex is slightly dependent en pH and buffer composition and ranges between 4.5 and 6.7 × 103 mole−1 L s−1. This electrode process enables the selective determination of Ni (II) in presence of a large excess of cobalt. For example, nickel impurity in cobalt salts can be determined by DPP, in acetate buffer (pH 4.6) containing 0.01 M nicotinamide and about 0.1 M cobalt salt sample.