A kinetic study of the oxidation of the tetrakisoxalatouranate(IV) ion by the hexacyanoferrate(III) ion in an oxalate buffer medium


The oxidation of the tetrakisoxalatouranate(IV) ion by the hexacyanoferrate(III) ion was studied in an oxalate buffer medium. The reaction was first order in both UIV(C2O4)44– and Fe(CN)63–, and a second order rate constant of k2av = (5.46 ± 0.04) × 10–2 M−1 s−1 at 34.9 °C was obtained. The reaction is inversely proportional to [H+] and a pKa of 5.99 was found for the deprotonation of UIV(C2O4)3(H2O)22−. Activation parameters have been obtained by application of the Eyring equation. Minimum excess concentrations of UIV(C2O4)44– over Fe(CN)63– for the kinetic study under pseudo-order conditions were evaluated following literature guidelines and also compared to results from a direct second order treatment of data. Contradictory to general beliefs, a fivefold excess of UIV(C2O4)44– was found to be sufficient for a pseudo-order kinetic treatment. The need to obtain results from traditional approximation methods, for example utilizing the linearized Eyring equation to obtain activation enthalpies (∆H#) and entropies (∆S#), was demonstrated not to be required anymore as modern computational capabilities utilizing least square fitting programs allows ∆H# and ∆S# to be obtained directly from temperature and rate constant data utilising the exponential Eyring equation easily and more accurately. A reaction mechanism for the reaction is proposed.

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The authors acknowledge the Central Research Fund of the University of the Free State, Bloemfontein, South Africa and the South African National Research Foundation Grant 105725 (EF) for funding.

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GJvZ: Investigation. EF: Investigation, writing, editing. CRD: Investigation, Writing, review, editing, project admin. SSB: Conceptualisation, methodology, review, editing, supervision. JCS: Conceptualization, methodology, review, editing, project admin supervision.

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Correspondence to C. Robert Dennis.

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Dennis, C.R., van Zyl, G.J., Fourie, E. et al. A kinetic study of the oxidation of the tetrakisoxalatouranate(IV) ion by the hexacyanoferrate(III) ion in an oxalate buffer medium. Reac Kinet Mech Cat (2021). https://doi.org/10.1007/s11144-021-01938-5

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  • Redox kinetics
  • Mechanism
  • Rate law
  • Activation parameters
  • Aqueous medium
  • Oxalate buffer
  • Tetrakisoxalatouranate(IV)
  • Transition metal cyano complex