AUTOCATALYTIC REDUCTION OF PYRIDINECOBALOXIME(III) BY MOLECULAR HYDROGEN

Abstract

In the presence of added cobaloxime(II), hydroxopyridinecobaloxime(III) is autocatalytically reduced by molecular hydrogen in methanol at 20°C. The sigma-shaped volumetric curves were evaluated by computer simulation of the system of differential equations corresponding to a 4-step mechanism. The key reduction step is presumably H-atom transfer from hydridocobaloxime(III) to cobaloxime(III). The lower limit of its rate constant is k₄=(5.0 ± 0.5) × 10⁴ M⁻¹ sec⁻¹ at 20°C. Hydridopyridinecobaloxime(III) is thermodynamically unstable, its estimated formation equilibrium constant being (3.9 ± 0.6) × 10⁻⁴ M⁻¹. The possible role of cobaloxime(I) species is discussed.