A kinetic study of the oxidation of the tetrakisoxalatouranate(IV) ion by the octacyanotungstate(V) and the octacyanomolybdate(V) ions in an acidic oxalate buffer medium

The oxidation of the tetrakisoxalatouranate(IV) ion by the octacyanometalate(V) ion of tungsten and molybdenum was studied in an oxalate buffer medium. The reaction was first order in both U IV (C 2 O 4 ) 4 4− and M(CN) 8 3− (M = W, Mo), and a second order rate constant of k 2 = 0.032 ± 0.002 M −1 s −1 at pH 4.27 and 24.8 °C was found for the W(CN) 8 3− reaction. For the Mo(CN) 8 3− reaction the second order rate constant is k 2 = 16.9 ± 0.1 M −1 s −1 at pH 4.77 and 25.3 °C. The reactions are inversely proportional to [H + ] and an equilibrium constant of K a ≈ 1.3 × 10 –6 M −1 (pK a ≈ 5.89) at 25 °C was found for the deprotonation of U IV (C 2 O 4 ) 3 (H 2 O) 2 2− . Activation parameters have been obtained by a least squares fit of temperature data directly to the Eyring equation. Graphical abstract