Kinetic, mechanistic and spectral investigation of ruthenium (III)-catalysed oxidation of atenolol by alkaline permanganate (stopped-flow technique)

Kinetics of ruthenium (III) catalyzed oxidation of atenolol by permanganate in alkaline medium at constant ionic strength of 0.30 mol dm³ has been studied spectrophotometrically using a rapid kinetic accessory. Reaction between permanganate and atenolol in alkaline medium exhibits 1 : 8 stoichiometry (atenolol : KMnO₄). The reaction shows first-order dependence on [permanganate] and [ruthenium (III)] and apparently less than unit order on both atenolol and alkali concentrations. Reaction rate decreases with increase in ionic strength and increases with decreasing dielectric constant of the medium. Initial addition of reaction products does not affect the rate significantly. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The active species of ruthenium (III) is understood as [Ru(H₂O)₅OH]₂₊. The reaction constants involved in the different steps of mechanism are calculated. Activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Kinetic and mechanistic studies of the iridium(III) catalyzed oxidation of sulphanilic acid by diperiodatocuprate(III) in aqueous alkaline medium

The effect of La₂O₃, K₂O and Li₂O on the properties and catalytic performance of silica-supported nickel catalysts for the hydrogenation of m-dinitrobenzene was investigated. The catalysts promoted with La₂O₃, Li₂O and K₂O showed better catalytic performance than the catalyst without promotion, especially the ones co-promoted with La₂O₃ and K₂O or Li₂O.     

Kinetics and mechanism of <Emphasis Type="Italic">L</Emphasis>-isoleucine oxidation by alkaline diperiodatoargentate(III)

The oxidation of L-isoleucine by alkaline diperiodatoargentate(III) (DPA) at 298 K and a constant ionic strength of 0.80 mol dm⁻³ was studied spectrophotometrically. The stoichiometry is [L-isoleucine]: [DPA] = 1:2. The reaction is first order in [DPA] and has less than unit order in both [L-isoleucine] and [alkali] and retarding effect in The oxidation reaction in alkaline medium has been shown to proceed via a L-isoleucine–DPA complex, which further reacts with one molecule of DPA in a rate determining step followed by other fast steps to give the products. Spot test and IR were used to identify the main products. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The probable active species of oxidant have been identified. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ruthenium(III) Catalyzed Oxidative Degradation of Amitriptyline-A Tricyclic Antidepressant Drug by Permanganate in Aqueous Acidic Medium

The oxidation of amitriptyline by potassium permanganate has been investigated spectrophotometrically in the presence of ruthenium(III) as catalyst in aqueous acidic medium at a constant ionic strength of 0.20 mol⋅dm⁻³. The stoichiometry was found to be 1:1 in terms of the mole ratio of amitriptyline and permanganate ions consumed. The order of the reaction with respect to manganese(VII) and ruthenium(III) concentration was unity while the order with respect to amitriptyline was less than unity over the concentration range studied. The rate increased with an increase in acid concentration. The reaction rates revealed that the Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. A tentative mechanism consistent with the kinetics has been proposed. The reaction constants involved in the different steps of the reaction mechanism were calculated. Kinetic experiments suggest that HMnO₄ is the reactive permanganate species and [Ru(H₂O)₆]³⁺ is the reactive Ru(III) species.     

Thermodynamic and kinetic behaviour of [Pt(2-methylthiomethylpyridine)(OH2)2]2+

The diaqua complex [Pt(2-methylthiomethylpyridine)(OH(2))(2)](2+), Pt(mtp), was synthesized and investigated thermodynamically as well as kinetically. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of the two coordinated water ligands. A low pK(a1) value of 3.15 was observed for the water molecule trans to the pyridine donor, whereas a pK(a2) value of 6.84 was found for the water molecule trans to the labilising sulphur donor. The substitution of coordinated water by a series of sterically hindered S-containing nucleophiles, viz. thiourea (tu), N,N'-dimethylthiourea (dmtu) and N,N,N',N'-tetramethylthiourea (tmtu), was studied under pseudo first-order conditions as a function of nucleophile concentration, pH (2, 4.75, 7.4), temperature and pressure, using stopped-flow techniques and UV-vis spectroscopy. In general the first substitution reaction takes place trans to the sulphur donor. At pH 2 the nucleophiles react in the order tu (634 ± 10) > dmtu (507 ± 5) ? tmtu (165 ± 3 M(-1) s(-1) at 25 °C), which is caused by steric hindrance. The second observed reaction involves two steps, viz. the displacement of the second water ligand and dechelation of the pyridine ring with the third-order rate constants 73.3 ± 0.8 (tu), 22.1 ± 0.1 (dmtu) and 6.8 ± 0.2 M(-2) s(-1) (tmtu) at 25 °C. At pH 4.75 the reactions are in general slower due to the presence of aqua-hydroxo species. The same order in reactivity was found, viz. tu (106 ± 1) > dmtu (72 ± 1) ? tmtu (14.1 ± 0.5 M(-1) s(-1) at 25 °C). No evidence for ring-dechelation could be observed under these conditions. At pH 7.4 the inert dihydroxo species is predominantly present in solution and consequently no substitution reaction was observed. Quantum chemical calculations were performed to support the interpretation and discussion of the experimental results.     

Mechanistic aspects of oxidation on L-tyrosine by diperiodatocuprate(III) complex in alkali media: a kinetic model

Oxidation of an amino acid, L-tyrosine (L-Tyr) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.1 mol dm⁻³ was studied spectrophotometrically at different temperatures (288.1–313.1 K). The reaction between DPC and L-Tyr in alkaline medium exhibits 1:4 stoichiometry (L-Tyr:DPC). Intervention of free radicals was observed in the reaction. Based on the observed orders and experimental evidence, a mechanism involving monoperiodatocuprate(III) (MPC) as the reactive oxidant species has been proposed. A suitable mechanism is proposed through the formation of a complex and free radical intermediate. The products were identified by spot test and characterized by spectral studies. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and are discussed. The thermodynamic quantities were determined for different equilibrium steps. Isokinetic temperature was also calculated and found to be 252.3 K.      

A kinetic and mechanistic study of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-lysine by the analytical reagent diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of oxidation of l-lysine by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm⁻³ was studied spectrophotometrically. The oxidation products are aldehyde, 5-aminopentanal and Ag(I). The main products were identified by spot test, IR and GC-MS. The stoichiometry is [l-lysine]:[DPA] = 1:1. The reaction is first order with respect to diperiodatoargentate(III) concentrations, whereas the order with respect to l-lysine and alkali concentrations changes from first order to zero order as the l-lysine and alkali concentrations are increased. The effects of added products, periodate, ionic strength, and dielectric constant of the reaction medium were investigated. Based on the experimental results, a mechanism involving complex formation between DPA species and l-lysine is proposed. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were determined and discussed.     

Kinetics and Mechanism of the Oxidation of 1,10-Phenanthroline by Diperiodatonickelate(IV)in Aqueous Alkaline Medium

Summary.  The title reaction was investigated in aqueous alkaline medium. A first order dependence on both [diperiodatonickelate(IV)] and [OH⁻] and an apparent fractional order in [1,10-Phenanthroline] was obtained. Addition of the reaction product has no effect on the reaction. The effects of dielectric constant, ionic strength, and temperature on the rate of the reaction were studied. A mechanism based on the experimental results is proposed, and the constants involved in the mechanism were evaluated. A good agreement between the observed and calculated rate constants at varying experimental conditions was obtained. Received May 26, 2000. Accepted (revised) July 27, 2000     

Kinetic study of ruthenium(III)-catalyzed oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-alanine by diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III)-catalyzed oxidation of l-alanine (Ala) by diperiodatoargentate(III) (DPA) in alkaline medium at 25 °C and a constant ionic strength of 0.90 mol dm⁻³ was studied spectrophotometrically. The products are acetaldehyde, Ag(I), ammonia and bicarbonate. The [Ala] to [DPA] stoichiometry is 1:1. The reaction is first order in both [Ru(III)] and [DPA] and has less than unit order in both [Ala] and [alkali]. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The reaction proceeds via a Ru(III)–Ala complex, which further reacts with one molecule of monoperiodatoargentate(III) in the rate-determining step. The reaction constants were calculated at different temperatures and the activation parameters have been evaluated.