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Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part 7. Role of trace metal ions, and catalysis by ethylenediaminetetra-acetatocopper(II) in the oxidation of hexacyanoferrate(II) in acid perchlorate media

1980; Royal Society of Chemistry; Issue: 9 Linguagem: Inglês

10.1039/dt9800001526

2050-5671

Lalit M. Bharadwaj, Devendra Nath Sharma, Y. K. GUPTA,

Chemical Synthesis and Characterization

Oxidation of [Fe(CN)]64– by peroxodiphosphate [equation (i)] is influenced by trace iron(II) and copper(II) ions 2[Fe(CN)6]4–+ H2P2O82–→ 2[Fe(CN)6]3–+ 2HPO42–(i) present in the distilled water and the reagents used. A detailed study has shown that Fe2+(aq), Fe3+(aq), and [Cu(edta)]2– catalyse the reaction, [Fe(edta)]2– and [Fe(edta)]–(edta = ethylenediaminetetra-acetate) are not reactive, and Cu2+(aq) inhibits the reaction. The increase in hexacyanoferrate(III) concentration has been followed colorimetrically and rate of reaction in the presence of edta and added CuII is given by (ii), where [FeII], d[Fe(CN)63–]//dt=k1′[Cu(edta)2–][FeII][peroxodiphosphate]//k2′[FeIII]+k3′[peroxodiphosphate](ii)[FeIII], and [peroxodiphosphate] are the total concentrations of the iron(II), iron(III), and peroxodiphosphate species respectively. The hydrogen-ion dependent values of k1′/k2′ and k3′/k′2 are 5.9 ± 1.1 and (1.09 ± 0.24)× 10–1 respectively at 35 °C and [H+]= 0.05 mol dm–3. The reactive species and the mechanism are as in equations (iii) and (iv). [Cu(edta)]2–+[HFe(CN)6]3– [graphic omitted] [Cu(edta)]3–+[HFe(CN)6]2–(iii), [Cu(edta)]3–+ H4P2O8 [graphic omitted] [Cu(edta)]2–+ products (iv)