Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system

Abstract

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mertrispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H 2 O 2 at constant pH. The initial rate method gives a rate expression of the form: Àd½RuðIIÞ=dt ¼ k II ½H 2 O 2 ½RuðIIÞ but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H 2 O 2 and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H 2 O 2 than ruthenium(II)-ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mertrispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.

Kinetics and Mechanism of the Reduction of mer‐Tris‐picolinatoruthenium(III) by L‐Ascorbic Acid

“…The values of ΔG were calculated from the overall redox potential of the studied reactions by using the data in Figure 1 (a) at pH 1.5, 5.0 and 12 for AscH 2 , AscHand Asc 2-, respectively, combined with the measured redox potential of 0.330 V (vs. NHE) for the [Ru(pic) 3 ]/[Ru(pic) 3 ]system. [24] Both plots in Figure 5 show an excellent correlation for the three protolytic forms of ascorbic acid.…”

“…[24,25] The reduction of the sparingly soluble mer-[Ru(pic) 3 ] in water to the very soluble anionic Ru II species by ascorbic acid was evidenced spectrophotometrically by the characteristic changes of the electronic spectrum in the visible region ( Figure 2). [24,25] The reduction of the sparingly soluble mer-[Ru(pic) 3 ] in water to the very soluble anionic Ru II species by ascorbic acid was evidenced spectrophotometrically by the characteristic changes of the electronic spectrum in the visible region ( Figure 2).…”

“…[24,25] The reduction of the sparingly soluble mer-[Ru(pic) 3 ] in water to the very soluble anionic Ru II species by ascorbic acid was evidenced spectrophotometrically by the characteristic changes of the electronic spectrum in the visible region ( Figure 2). [24] Preliminary spectral measurements confirmed the almost complete conversion of Ru III into Ru II under a large excess of ascorbic acid. [24] Almost identical spectral changes accompany the reduction of the mer-[Ru(pic) 3 ] by one-electron donors as for the aqua complexes of Cr II and Eu II .…”

Kinetics and Stoichiometry of the Reduction of Hydrogen Peroxide by an Aminocarboxylactocobaltate(II) Complex in Aqueous Medium

“…The kinetics and mechanisms of its decomposition by transition metal complexes, which demonstrates the importance and role of specific free radical species [8], have received considerable attention [3] [9]- [11]. The reactions have been studied under acidic [9] [10] and basic [11] media and the mechanisms for the decomposition reaction established in addition to other kinetic parameters which are calculated. Furthermore, Schmitz and Furrow [12] used iodate reduction by hydrogen peroxide to demonstrate Bray-Liebhafsky and Briggs-Rauscher oscillatory reactions and Yong, et al [13] studied the reduction of the latter at Au (100) electrode.…”