Johnson Femi Iyun

Electron transfer at tetrahedral cobalt(II), Part III: kinetics of copper(II) ion catalysed reduction of periodate

SummaryThe stoichiometry, kinetics and mechanisms of copper(II)-catalysed reduction of periodate ion by the dodecatung-stocobaltate(II) anion in aqueous HClO4 has been investigated. The reaction follows the empirical rate law: d[Reductant]/dt=2(a+b [H+]) [Cu11] [oxidant] [Reductant] wherea=1.47±0.07×10−4 M−2 s−1b=1.90±0.05×10−4 M−3 s−1 at 24.5±0.1°C [H+]=0.02–0.20 M and I=0.50 M (NaClO4). This is, to our knowledge, the first example of an outer-sphere reduction of periodate by a metal complex in aqueous solution.

Electron transfer at tetrahedral cobalt(II). Part II : Kinetics of silver(I) ion catalysed reduction of peroxodisulphate

SummaryThe kinetics of the silver(I) ion catalysed reduction of peroxodisulphate by 12-tungstocobaltate(II) anion in aqueous HC1O4 has been studied. Although the reaction in the range [H+ ] = 0.1−1.0 M was acid-independent, it was first-order each in AgI, the oxidant and the reductant. We propose that reaction proceeds by univalent changes with the production of free radical intermediates. The reduction is rationalised in terms of the outer-sphere mechanism.

Electron transfer at tetrahedral cobalt(II). Part 1. Kinetics of bromate ion reduction

SummaryThe bromate ion reduction by 12-tungstocobaltate(II) anion has been investigated. The reaction obeys the empirical rate law:-d[reductant]/dt=5(a+b[H+]2)[BrO3−][reductant]: where a=(2.49±0.18)×10−4M−1 s−1, b=(4.65±0.20)×10−5M−3s−1 at 24.5±0.1°C [H+]=0.05–1.50M and I=2.0M (NaClO4). This rate law is interpreted in terms of parallel reactions of BrO3− and H2BrO3+. On the basis of the observed anion catalysis, substitution intertness of the reductant and Marcus type linear free energy relations, the outer sphere mechanism is proposed for both pathways.

The kinetics and mechanism of the oxidation of diaquotetrakis(2,2′-bipyridine)-μ-oxodiruthenium(III) ion by bromate in aqueous perchloric acid

Abstract At I = 1.0 M (NaClO 4 ), T = 25.0±0.1°C, 0.01 ⩽ [H + ] ⩽ 0.20 M, the oxidation of diaquotetrakis-(2,2′-bipyridine)-μ-oxo-diruthenium(III) ion (hereafter referred to as RuORu 4+ ) by bromate obeys the rate law −d[RuORu 4+ ]/d t = 5[ k + k H [H + ] 2 ][BrO 3 − ] T [RuORu 4+ ], with k = (6.50±0.10) × 10 −2 M −1 s −1 and k H = 2.67±0.28 M −3 s 1 , respectively. The reaction occurs by parallel acid-independent and acid-dependent pathways suggesting H 2 BrO 3 + and BrO 3 − as the principal reactant bromate species. The reaction was mildly catalysed by anions in the order CH 3 COO − > NO 3 −

Oxidation of glutathione by diaquatetrakis(2,2′-bipyridine)-μ-oxo diruthenium(III) ion in aqueous acidic solutions

HCOO − . The activation parameters were determined at [H + ] = 0.01 M as Δ H ‡ = −9.6±0.3 kJ mol −1 and ΔS ‡ = 112.9 ± 5.1 J mol −1 K −1 respectively. The observed anion catalysis, the Michaelis-Menten plot and the result of the spectroscopic investigation do not support a mechanism involving pre-electron-transfer precursor complex formation between the reactant species. The outer-sphere mechanism is therefore suggested for both the acid-independent pathway. Using the Marcus theory the E ° for the RuORu 4+ /RuORu 5+ couple is estimated as −0.74±0.08 V.

Kinetics and mechanism of the oxidation of iodide by diaquote- trakis(2,2′-bipyridine)-μ-oxodiruthenium(III) ion in acid medium

SummaryThe kinetics of the oxidation of glutathione by diaquatetrakis(2,2′-bipyridine)-μ-oxo diruthenium(III) ion in aqueous HClO4 have been investigated. The reaction obeys the empirical rate law:-2d[oxidant]/dt = k[oxidant][reductant]/[H+] where k = 7.42 ± 0.40 × 10-3 s-1 at 25.5 °C, [H+] = 0.005–0.05 M and I = 1.0 M (LiClO4). Free radicals are important in the reaction and a mechanism consistent with the experimental results has been postulated.

Electron transfer at tetrahedral cobalt(II), part IV: kinetics of silver(I) catalysed chlorate reduction

SummaryThe kinetics of the oxidation of iodide by diaquotetrakis-(2,2-bipyridine)-μ-oxodiruthenium(III), [Ru2O]4+, were studied in aqueous perchloric acid at 25.0±0.1°C, I = 1.0 M (NaClO4). The reaction conforms to the overall equation:

Kinetics and Mechanism of the Reaction of Malachite Green and Dithionite Ion

{⤪ [Ru_{2}O]^{4+}+I^{-}⌝ghtarrow [Ru_{2}O]^{3+}+{1⩈er 2}I_{2}}