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Kinetics and Mechanism of trans-[Cr(cyca)(OH)F]+Complex Oxidation by [Fe(CN)6]3- Ion in Strongly Alkaline Aqueous Solutions

Katafias A., Impert O., Kita P., Wrzeszcz G., Dominiak D.

Polish Journal of Chemistry

2006

Vol. 80, nr 6

931-941

Oxidation of the trans-[Cr(cyca)(OH)F]+ complex, where cyca = meso-5,5,7,12,14- hexamethyl-1,4,8,11-tetraazacyclotetradecane, by [Fe(CN)6]3- ion in strongly alkaline media has been studied. A long-lived intermediate chromium(V) species was detected basing on the EPR signal at giso = 1.986. The hyperfine structure of the main EPR signal is consistent with the d1-electron interactions with four equivalent or nearly equivalent nitrogen nuclei and [CrV=O(cycaox)]3+ formula, where cycaox = oxidized cyca, can be postulated for the intermediate CrV complex. Kinetics of the rate limiting stage - electron transfer from the chromium(III) complex - has been studied in details applying an excess of the reductant and [OH-] at ionic strength equal 2.0 M. The rate law: -d[FeIII] dt = d[CrIV] dt = 0,5k cb K[OH-] 1+ 0,5(K-1)[OH-] [CrIII][FeIII] is consistent with an outer-sphere electron transfer from the conjugate base (cb) of the reductant formed in a preequilibrium (K) step. Reactivity of the deprotonated chromium(III) complex is characterized by kcb 298 = 9.7,deltaH#= (44.1š 0.5) kJ_mol-1, deltaS# = (-78.0 š 2.0) JxK-1xmol-1 and the preequilibrium step -by K298 = 0.237, delta H0 = (11.5 š 1.8) kJ_mol-1, delta S0 = (26.6 š 5.8) JxK-1xmol-1.

Platinum(IV) Inhibition during Hexacyanoferrate(III) Oxidation of Reducing Sugars

Pandey E., Kambo N., Upadhyay S.

Polish Journal of Chemistry

2005

Vol. 79 / nr 10

1689-1698

The kinetics of oxidation of reducing sugars viz glucose, fructose, lactose and maltose by alkaline hexacyanoferrate(III) in the presence of platinum(IV) has been studied. The kinetic data support the formation of {platinum(IV)-sugar} complexes and their resistance to react with hexacynoferrate(III). A spectrophotometric evidence for the formation of 1:1 and 1:2 complexes between platinum(IV) and reducing sugar has also been obtained