The oxidation of the uranium(IV)tetrachloride by the octacyanotungstate(V) and the octacyanomolybdate(V) ions in perchloric acid medium: A kinetic study

The oxidation of the uranium tetrachloride (UCl 4 ) by the octacyanometalate(V) ion of tungsten and molybdenum was studied in a perchloric acid medium at an ionic strength of 1.5 M (NaClO 4 ). The reaction was first order in both U IV (H 2 O) 8 4+ and M V (CN) 8 3– (M = W, Mo). A second order rate constant of k 2 = 0.111 ± 0.002 M −1 s −1 at [H + ] = 0.932 M and 15.0 °C was found for the W(CN) 8 3– reaction and for the Mo(CN) 8 3– reaction, k 2 = 32.9 ± 0.9 M −1 s −1 at [H + ] = 1.008 M and 29.7 °C. The reactions are proportional to [H + ] –2 and an equilibrium constant of K a2 ≈ 1.18 × 10 −3 M −1 (pK a ≈ 6.7) at µ = 1.5 M was found for the deprotonation of U IV (H 2 O) 8 4+ . Activation parameters have been obtained by a least squares fit of temperature data directly to the Eyring equation. Graphical abstract