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The behaviour of electrogenerated hydrogen peroxide in the presence of chemical acceptors I. Uranyl tricarbonate aqueous solutions

par Žutić, Vera;Poty, C.;Gierst, Lucien
Référence Journal of electroanalytical chemistry, 56, 2, page (269-283)
Publication Publié, 1974-10

Article révisé par les pairs

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Résumé :

The kinetics of the fast homogeneous chemical reaction between the uranyl tricarbonate ion and hydrogen peroxide has been studied by following the rate of de-activation of H2O2, generated electrochemically from dissolved oxygen at a mercury electrode. The combined use of the polarographic and chronocoulometric techniques allows the determination of the reaction orders, the kinetic parameters and the energy of activation. It has been found that the presence of uranyl tricarbonate catalyses the oxygen reduction by shifting the redox potential toward more positive values, and by increasing the total number of electrons involved. Reduction of indanone (I), tetralone (II) and benzosuberone (III) was studied by d. c. and pulse polarography, cyclic voltammetry and controlled potential electrolysis with a dropping mercury electrode in aqueous solutions containing 2% ehtnaol at various pH values. In acidic media the protonated form, at higher pH values the free carbonyl form is reduced. The reduction of the unprotonated form is accompanied by protonation of the radical anion formed. The behavior of all three ketones I-III in this pH region is similar and differs only in the half-wave potential values and the rates of protonation of the radical anion. The reduction of the protonated form is affected both by differences in potentials of the ketones I-III and by differences in the rates of protonation, but most significantly by the half-wave potential of the radical formed in the first electron uptake. For indanone (I) this reduction is so positive that only one two-electron step is observed. For benzosuberone (III) the half-wave potential of this reduction is sufficiently more negative than the first electron uptake and two one-electron separated waves result. For tetralone (II) the reduction of the radical occurs at so negative a potential that it is overlapped by the hydrogen evolution current. Only one one-electron wave is thus observed. The effect of ring size on potentials and protonation reactions is discussed from the point of view of ring strain, adsorbability and radical stability. © 1974.