Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Oxidation of α-ketoglutaric acid with Ce(IV) ions in a solution of sulphuric acid is a reaction of the first order with respect to both Ce(IV) ions and substrate, is acid catalysed, and its rate is proportional to the reciprocal square of the equilibrium HSO₄^- concentration. From the temperature dependence of the rate constant in 1.5M-H₂SO₄, the activation parameters were determined as ΔH^##f = 57 kJ/mol and ΔS^##f = -45 J mol^-1 K^-1. The redox reaction proper consists apparently of two steps: in the first one, the enol form of α-ketoglutaric acid reacts with Ce(IV) ions with the formation of the corresponding radical; in the second one, the latter is oxidized further with Ce(IV) to give malonic and succinic acids. Conditions are indicated under which α-ketoglutaric acid serves as substrate for the Belousov-Zhabotinskii oscillation reaction in the presence of Ce(IV)-Ce(III) redox catalyst. Oscillations of Ce(IV) and Br₂ concentrations, shifted in phase, can be recorded polarographically with a rotating platinum electrode.