Browsing by Author "Onu, A.D."

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    Kinetics and mechanism of the reduction of diaquotetrakis (2,20-bipyridine)-l-oxodiruthenium(III) ion by hypophosphorous acid in acidic medium
    (Department of Chemistry, Nasarawa State University Keffi, 2017-03-13) Mohammed, Y.; Idris, S.O.; Onu, A.D.
    The kinetics and mechanism of the reduction of diaquotetrakis(2,20-bipyridine)-l-oxodiruthenium(III), [(H2O)2(bipy)4Ru2O]4?, by H3PO2 has been studied in aqueous acid at ionic strength = 0.5 mol dm-3 (NaClO4), [H?] = 5.0 9 10-2 mol dm-3 and temperature = 31 ± 1 �C. Measurement of the stoichiometry showed that 1 mole of [(H2O)2(bipy)4Ru2O]4? was reduced by 1 mole of H3PO2. The reaction was found to be first order with respect to both [(H2O)2(bipy)4Ru2O4?] and [H3PO2], hence second order overall. Variations in the ionic strength and dielectric constant of the reaction medium had no effect on the rate. Also, addition of various ions to the reaction medium did not significantly alter the rate. Free radicals were identified during the course of the reaction by a polymerisation test. Spectroscopic information and Michaelis–Menten plots suggested the absence of an intermediate complex prior to electron transfer. [(H2O)2 (bipy)2Ru]2?, the reduction product of [(H2O)2(bipy)4 Ru2O]4?, plus H3PO3, the oxidation product of H3PO2, were identified in the product solutions. It is suggested that the reaction proceeds through the outer sphere pathway. A mechanism for the reaction is proposed.
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    Oxidation Of N, N-Dimethylthiourea By Diaquotetrakis(2,2’- BIPYRIDINE) - µ - Oxodiruthenium (III) Ion In Aqueous Acid Medium: A Kinetic Approach To Mechanism Of Reaction
    (Department of Chemistry Education, Nasarawa State University Keffi, 2020-07-29) Mohammed, Y.; Idris, S.O.; Onu, A.D.; Opaluwa, O.D.
    Background: Electron transfer (redox) reactions play very important roles in many biological processes including collagen synthesis, steroid metabolism, the immune response, drug activation, neurotransmitter metabolism, nitrogen fixation, respiration and photosynthesis. Ruthenium complexes with polypyridyl ligands have received much attention owing to their interesting spectroscopic, photophysical, photochemical and electrochemical properties, which are responsible for their potential uses in diverse areas such as photosensitizers for photochemical conversion of solar energy. Thiourea and its derivatives, of which DMTU is one, can be oxidised by a wide variety of oxidising agents and the reaction pathways and final products of the oxidation reaction depend on the reagents used and condition of the reaction mixtures. Materials and Methods: Kinetic and mechanistic studies of the oxidation of N,N-dimethyl thiourea (DMTU) by diaquotetrakis(2,2’-bipyridine) - μ - oxodiruthenium (III) ion, hitherto referred to as Ru2O4+, has been carried out in hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3 (HClO4), ionic strength, I = 0.5 mol dm-3 (NaClO4) and at a temperature, T = 30±1ºC. Results: The reaction revealed that a stoichiometry of 2:1 (DMTU/ Ru2O4+, first order dependence with respect to [DMTU], an acid – independent and inverse acid dependent pathways. The reaction rates were not affected by changes in ionic strength and dielectric constant of the reaction medium. Addition of ions to the reaction medium had little or no effect on the reaction rates. There was evidence of the participation of free radicals in the reaction. There was no shift in λmax of the reaction mixture 1 minute after start of reaction. Michaelis Menten plot revealed no appreciable intercept. Conclusion: Based on the findings, an outersphere mechanism is implicated to operate in the reaction and a plausible mechanism is proposed
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    STUDIES OF THE KINETICS AND MECHANISM OF THE ELEC TRON TRANSFER REACTIONS OF DIAQUOTETRAKIS(2,2’-BIPYRIDINE)-µ- OXODIRUTH ENIUM(III) ION AND DITHIONITE IN AQ UEOUS MEDIUM
    (Department of Chemistry, Nasarawa State University Keffi, 2016-02-05) Mohammed, Y.; Idris, S.O.; Onu, A.D.; Iyun, J.F.
    he kinetics and mechanism of the electron transfer reaction of diaquotetrakis(2,2’ -bipyridine)-µ- oxodiruthenium(III) ion (hereafter denoted as Ru2O4+ or [(H2O)2Ru2O]4+) and dithionite ions (S2O 42 ) has been studied in aqueous medium at ionic strength, I, = 0.5 mol dm-3 and temperature, T = 31±1 ºC. The stoichiometry of the reaction was found to be 1:1. The rate of reaction showed first order kinetics with respect to [Ru2O4+] and [S2O 24 ] respectively, second order overall. Rate equation for the reaction has been proposed as; d[((H2O)2Ru2O4+]/dt = kobs[((H2O)2Ru24+] = k2 [((H2O)2Ru2O4+][S2O42-] . Varying I and dielectric constant, D, of the reaction medium had no effect on the reaction rates, while free radicals were not detected in the course of the reaction. Product analysis revealed [(H2O)2(bpy)2Ru]2+as the reduction product of [(bpy)2(H2O)RuORu(H2O)(bpy)2]4+. Spectroscopic evidence of formation of stable intermediate complex was lacking which, in addition to absence of intercept in the Michaelis – Mentenplot and catalysis/ inhibition of the reaction due to added ions, suggest the implication of outer sphere mechanism operating in the reaction. A plausible mechanism was proposed.