Kinetic and Mechanism of Oxidation of Methylaminopyrazole Formamidine by Alkaline Hexacyanoferrate(III) and the Effect of Divalent Transition Metal Ions

摘要

In aqueous alkaline medium, the kinetics of oxidation of methylaminopyrazole formamidine (MAPF) by hexacyanoferrate(III) (HCF)has been studied spectrophotometrically under the conditions, MAPF HCF at a constant ionic strength of 0.1 mol dmsup-3/sup and at 25°C. The reaction showed first order dependence on [HCF] while it exhibited fractional-first order kinetics with respect to [MAPF] and [OHsup-/sup]. The oxidation rate increased with increasing ionic strength and dielectric constant of the reaction medium. Addition of small amounts of some divalent transition metal ions accelerates the oxidation rate and the order of catalytic efficiency was: Cu(II) Ni(II) Zn(II) Co(II) Cd(II). The suggested mechanism involves formation of a 1: 1 intermediate complex between HCF and the deprotonated MAPF species in a pre-equilibrium step. The final oxidation products were identified as methylaminopyrazole, dimethylamine and carbon dioxide. The appropriate rate law was deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.