Browsing by Author "Idris, S.O."

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    ELECTRON TRANSFER REACTIONS OF THIOSULFATE ION AND DIAQUOTETRAKIS (2,2’- BIPYRIDINE) - µ - OXODIRUTHENIUM(III) ION IN AQUEOUS PERCHLORIC ACID
    (Department of Chemistry, Nasarawa State University Keffi, 2015-01-05) Mohammed, Y.; Idris, S.O.; Iyun, J.F.
    Kinetics and mechanism of the electron transfer reactions of thiosulfate ions and diaquotetrakis (2,2’- bipyridine) - µ - oxodiruthenium(III) ion, [(H2O)2(bpy)4Ru2O]4+, has been studied in perchloric acid at a temperature, T = 31.0 ± 1°C, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The reaction showed a stoichiometry of 1:2 ([(H2O)2(bpy)4Ru2O]4+: S2O32–), first order dependence with respect to [(H2O)2(bpy)4Ru2O]4+] and [S2O32–], second order overall. Increase in [H+] affected the rate of reaction directly while increase of the ionic strength affected the rates of the reaction adversely. The rate equation for the reaction has been proposed as: –d[[(H2O)2Ru2O4+]/ dt = (a+b[H+])[[(H2O)2Ru2O4+][S2O32–].Added anions and cations altered the rates of the reaction. Based on the lack of evidence of the formation of intermediate complex (from absence of intercept in the Michaelis-Menten plot and lack of shift in λmax of the reaction mixture 1 minute after start of reaction from that of the dimer) and observable added ion catalysis, it is proposed that the reaction most probably proceeded through the outer sphere mechanism. A plausible mechanism is proposed.
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    INVESTIGATIONS INTO THE KINETICS AND MECHANISM OF THE ELECTRON TRANSFER REACTIONS OF N- METHYL THIOUREA AND DIAQUOTETRAKIS(2,2’- BIPYRIDINE) - μ - OXODIRUTHENIUM (III) ION, IN AQUEOUS ACIDIC MEDIUM
    (Department of Chemistry, Nasarawa State University Keffi, 2014-03-05) Mohammed, Y.; Idris, S.O.; Iyun, J.F.
    The kinetics of the oxidation of n- Methyl thiourea (MTU) by diaquotetrakis (2,2’- bipyridine) - μ - oxodiruthenium (III) ion, [(bipy)4(H2O)2Ru2O]4+, in an HClO4 medium has been studied spectrophotometrically at a temperature, T = 30 ± 1°C, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The stoichiometry of the reaction conformed to an overall equation [H2O(bipy)2RuORu(bipy)2H2O]4+ H+3CHN C NH2 + H2O 2[(H2O)2(bipy)2Ru]2+ + H3CHN C S S C NH2 NH S + 2 NH The reaction showed first order kinetics with respect to the dimer and [MTU], respectively, k2 = (3.14 ± 0.05) x 10–2 dm3 mol–1 s–1, and was inversely affected by changes in [H+]. Changes in ionic strength and dielectric constant of reaction medium and addition of ions to the reaction medium had no or little effect on the rate constants of the reaction. The reaction has been found to conform to the rate equation: –d[[(H2O)2Ru2O4+]/ dt = (a+b 1 [𝐻+] )[[(H2O)2Ru2O4+][MTU] The reaction is considered to proceed through the formation of ion – pairs which go on to decompose at the rate determining steps to give rise to free radicals which diamerise to form the reaction products. The reduction product was found to be disulfides and the reaction is considered to proceed through the outer sphere pathway. A plausible mechanism is proposed.
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    Kinetic approach to the mechanism of the redox reaction of malachite green and permanganate ion in aqueous acidic medium
    (Department of Chemistry, Nasarawa State University Keffi, 2009-11-09) Mohammed, Y.; Iyun, J.F.; Idris, S.O.
    The redox kinetic and mechanistic studies of the reactions of malachite green (MG+) and MnO4– were carried out in aqueous acidic medium, at a temperature of 32.5 ± 0.5°C; ionic strength, µµµµ = 0.50 mol dm–3 (Na2SO4), [H+] = 5.00 x 10–3 mol dm–3 (H2SO4). In the stoichiometry, one mole of malachite green was consumed by one mole of MnO4–. The reaction is first order in both [MG+] and the [MnO4–]. The rates of redox reaction showed dependence on acid concentrations (in the acid range used). Rate equation for the reaction has been proposed as: –d[MG+]/ dt = (a + b[H+])[MG+][MnO4–]. At [H+] = 5.00 x 10–3 mol dm– 3, the second order rate constant for the malachite green – MnO4– reaction was found to be (11.96 ± 0.13) x 10–3 dm3 mol–1 s–1. The rates of reaction displayed negative salt effect. Log k1 versus 1/D gave positive slope for the reaction. Added anions and cations catalysed the malachite green – MnO4– reaction. Results of the Michaelis- Menten analysis gave no evidence of intermediate complex formation. Based on the results obtained experimentally, the outer sphere mechanism is proposed for the malachite green – MnO4– reaction.
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    Kinetics and Mechanism of Malachite Green Oxidation by Hypochlorite Ion in Aqueous Acidic Medium
    (Deapartment of Chemistry, Nasarawa State University Keffi, 2014-11-11) Idris, S.O.; Tanimu, A.; Iyun, J.F.; Mohammed, Y.
    The kinetic investigations of the redox reaction between malachite green, MG+, and hypochlorite ion, ClO–, were carried out in aqueous HClO4 medium at [H+] = 1x10–3 mol dm–3, µ = 0.1 mol dm–3, T = 25±1°C. The reaction showed a stoichiometry of 1:2, which conforms to the equation: MG+ + 2ClO– Products Kinetic data revealed a first order dependence on both [MG+] and [ClO-] giving a second order overall. The second order rate law for the reaction conforms to the equation: −d[MG+]/dt = k2[MG+][ClO-] where k2 = 115.55± 1.21 dm3 mol-1 s–1 Reaction rate increased with increase in [H+]. Changes in ionic strength and dielectric constant of the reaction medium did not alter the reaction rate. Addition of anions at different concentrations also did not affect reaction rate. The absence of spectroscopic evidence of intermediate complex formation suggests that the reaction proceeds through the outersphere mechanism. This suggestion is further reinforced by kinetic evidence from the Michaelis-Menten plot. A plausible mechanism based on these observations is proposed.
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    Kinetics and Mechanism of Oxidation of L – Methionine by Potassium Bromate in Aqueous Hydrochloric Acid Medium
    (Department of Chemistry, Nasarawa State University Keffi, 2010-01-05) Idris, S.O.; Ibrahim, A.P.; Iyun, J.F.; Mohammed, Y.
    The kinetics of the oxidation of L - methionine by bromate ions in aqueous acidic medium at a constant ionic strength, µ , of 0.50 mol dm–3 were investigated spectrophotometrically at temperature of 30.0 ± 1ºC. The reaction shows a stoichiometry of 1:2 (Methionine/ bromate), first order kinetics in [methionine], first order in [bromate] and second order dependence in [H+]. An increase in ionic strength and a decrease in dielectric constant of the reaction medium increase the rate of reaction. The reaction is catalysed by anions. Polymerization test conducted suggests the absence of free radicals. The results obtained from this study supports the operation of outer – sphere mechanism. A plausible mechanism is proposed for the reaction.
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    Kinetics and Mechanism of the Periodate Oxidation of Malachite Green in Acidic Medium
    (Department of Chemistry, Nasarawa State University Keffi, 2014-01-06) Idris, S.O.; Hassan, H.; Iyun, J.F.; Mohammed, Y.
    The kinetics of the periodate (IO4 –) oxidation of malachite green (MG+) have been studied in aqueous acidic medium. The observed results at [H+] = 1 x 10–4 mol dm–3 (HCl), ionic strength of reaction medium, I = 0.5 mol dm–3 and T = 25.5±0.3°C are consistent with the rate law: d[MG+]/dt = k2[MG+][IO4 -] where k2 = (k7 + k6K5[H+]) The reaction was catalysed by increase in [H+] and added anions but displayed a negative BrØnsted–Debye salt effect. Spectrophotometric test showed the absence of intermediate complex formation. Based on these findings, a plausible mechanism is proposed.
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    Kinetics and Mechanism of the Reaction of Malachite Green and Dithionite Ion
    (Deparment of Chemistry, Nasarawa State University Keffi, 2014-11-11) Idris, S.O.; Tanimu, A.; Iyun, J.F.; Mohammed, Y.
    The kinetics of the oxidation of malachite green, MG+, by dithionite ions, S2O42- have been studied spectrophotometrically in an aqueous acid free medium. The investigation was carried out under pseudo- first order conditions of an excess of dithionite concentration. Reaction conditions were ionic strength of reaction medium, µ = 0.1 mol dm–3, λmax = 620nm and T = 25.5±0.5°C. The stoichiometry of the reaction, determined by spectrophotometric titration, was 1:1. Reaction rates increased with increase in µ and dielectric constant (D) of reaction medium. Added ions catalysis of the reaction and the result of the Michaelis - Menten analysis suggest that the reaction proceeded through the outersphere pathway. A plausible mechanism is proposed.
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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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    Mechanism of the Redox Reaction of Hydroxylamine and Bromate Ions in Aqueous Hydrochloric Acid Medium
    (Department of Chemistry, Nasarawa State University Keffi, 2010-03-03) Idris, S.O.; Sunday, E.; Iyun, J.F.; Mohammed, Y.
    Redox kinetics of the reaction of hydroxylamine hydrochloride (H2NOH.HCl) and BrO3– was carried out in aqueous acidic medium, at temperature of 29.5 ± 0.5ºC; ionic strength µ = 1.0 mol dm–3 (NaCl), [H+] = 1.0 x 10–2 mol dm–3 (HCl). The reaction showed a stoichiometry of 1:1.3, first order kinetics in both [NH3OH+] and [BrO3–], dependence on acid concentrations, positive salt effect, catalysis due to anions and absence of evidence of intermediate complex formation. Rate equation for the reaction has been proposed as: –d[NH3OH+]/ dt =(a[H+])[ NH3OH+][ BrO3–]. The second order rate constant for the NH3OH+– BrO3– reaction was found to be 0.233 dm3 mol–1 s–1. Based on the results obtained experimentally, the outer – sphere mechanism is suggested for the reaction
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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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    Redox Kinetics and Mechanism of the Oxidation of Thiourea by Diaquotetrakis(2,2’- Bipyridine) - µ - Oxodiruthenium (III) Ion, in Aqueous Perchloric Acid
    (Department of Chemistry Education, Nasarawa State University Keffi, 2014-08-08) Mohammed, Y.; Idris, S.O.; Iyun, J.F.
    The kinetics of the oxidation of thiocarbamide (thiourea) by diaquotetrakis(2,2’- bipyridine) - µ - oxodiruthenium (III) ion, [(bpy)2(H2O)RuORu(H2O)(bpy)2]4+, in perchloric acid has been investigated at a temperature, T = 30±1ºC, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The reaction showed a stoichiometry of 1:2 (oxidant/ thiourea), first order kinetics with respect to the thiourea (RSH), k2 = (7.39±0.05) dm3 mol–1 s–1, inverse [H+] dependence and zero salt effect. The rate equation for the reaction has been proposed – d[(bpy)2(H2O)RuORu(H2O)(bpy)2]4+]/dt=(a+b[ ])[(bpy)2(H2O)RuORu(H2O)(bpy)2]4+[RSH]. Outer sphere mechanism is implicated to operate in this reaction as evidenced by lack of the formation of a stable intermediate complex as suggested by absence of intercept in the Michaelis - Menten plot, lack of shift in λmax of the reaction mixture 1 minute after start of reaction and absence of observable anion catalysis. 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.