A Novel Oxidation of Valine by N-Bromophthalimide in the Presence of Ruthenium(III) Chloride as a Homogeneous Catalyst

Kinetics of Ruthenium(III) [Ru(III)] chloride catalyzed oxidation of valine (Val) has been studied by N-bromophthalimide (NBP) in the acidic medium at 35 °C. The reaction rate follows first-order and zero-order dependence with respect to [NBP] and [Val]. First-order kinetics was observed for Ru(III) chloride at low range of concentrations and tending towards zero-order at higher concentrations. A negative effect was observed for [H⁺] and [phthalimide], while a positive effect was observed for [Cl^?] on the reaction rate. Hg(OAc)₂, ionic strength (I), and dielectric constant (D) of the medium did not change significantly the reaction rate. The rate constants as a function of temperature (298–318 K) were used to calculate activation parameters of the oxidation of Val by NBP. A plausible mechanism was proposed to explain the results of kinetic studies, reaction stoichiometry and product analysis.     

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of L-phenylalanine (L-Pal) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 27 °C and a constant ionic strength of 0.25 mol dm^?3 was studied spectrophotometrically. The involvement of free radicals was observed in the reactions. The reaction between DPA and L-Pal in alkaline medium exhibits stoichiometry as [L-Pal]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)] and [DPA] and has negative fractional order in [IO₄ ^?]. It has less than unit order in [L-Pal] and [OH^?]. However, the order in [L-Pal] and [OH^?] changes from first order to zero order as their concentrations increase. The main oxidation products were identified by spot test and spectral studies. The probable mechanisms were proposed and discussed. The catalytic constant (K _c) was also calculated for Os(VIII) and Ru(III) catalysis at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified.     

Investigation of electron-transfer reaction between alkaline hexacyanoferrate(III) and ranitidine hydrochloride – a histamine H2 receptor antagonist,in the presence of homogenous ruthenium(III) catalyst

The ruthenium(III)-catalyzed electron-transfer reaction between hexacyanoferrate(III) and ranitidine hydrochloride is studied in alkaline medium at 25°C and at an ionic strength of 1.10?mol/dm³. The reaction stoichiometry is established and is found to be 1:4, that is, for the oxidation of one mole of ranitidine, four moles of hexacyanoferrate(III) are consumed. The reaction products were characterized by spectral studies such as IR, GC-MS, ¹H-NMR and ¹³C-NMR. The reaction rate shows a less than unit order in substrate and alkali and a first-order dependence in oxidant, [Fe(CN)₆]^3? and the catalyst, ruthenium(III) concentrations. The active species of ruthenium(III), [Ru(H₂O)₅OH]²⁺, forms an intermediate complex with the substrate. The attack of complex by hexacyanoferrate(III) in the rate determining step produces a radical cation, which is further oxidized in the subsequent step to form the oxidation product. The effect of the reaction environment on the rate constant upon adding varying concentrations of KNO₃ and t-butanol was studied. The initially added products did not have any significant effect on the reaction rate. A plausible mechanism is proposed based on the experimental results. The effect of varying temperature on the reaction rate was also studied. The activation parameters for the slow step and the thermodynamic quantities for the equilibrium steps were evaluated.

The mechanism of title reaction has been studied and one mole of ranitidine consumes four moles of [Fe(CN)₆]^3?, as shown in the following equation:     

Kinetic,Mechanistic and Spectral Investigation of Ruthenium(III) Catalysed Oxidation of Atenolol by Alkaline Diperiodatonickelate(IV) (Stopped Flow Technique)

The kinetics of ruthenium(III) catalysed oxidation of atenolol by diperiodatonickelate(IV) (DPN) in alkaline medium at a constant ionic strength of 1.0 mol dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:1 stoichiometry (DPN:atenolol). The reaction shows first order dependence on [DPN] and [Ruthenium(III)] and apparent less than unit order dependence each in atenolol and alkali concentrations. Addition of periodate has no effect on the rate of reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by IR, NMR, fluorimetry and mass spectral studies. The results suggest the formation of a complex between the atenolol and ruthenium(III) species which reacts with one mole of diperiodatonickelate(IV) species in a rate determining step, resulting in the formation of a free radical, which in a subsequent fast step yields the products. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism and discussed.     

Ru(III)-catalyzed oxidation of N-acetyl-L-cysteine by methylene blue in absence and in presence of Cu(II) in acidic medium: influence of solvent and morphology

N-acetyl l-cysteine (NAC), the substrate used presently has got diverse medicinal applications and is widely used as a mucolytic agent. The oxidation of bioactive molecules, in general, involves metal ion catalysis facilitated by the participation of metal nanoparticles. In view of this, the oxidation of NAC by a phenothiazine dye methylene blue (MB), a model electron receptor, catalyzed by Ru(III) in the absence and in the presence of Cu(II) has been investigated in acidic medium. The concentration order in MB is zero, while the order in NAC is one and two in Ru(III)-catalyzed and Ru(III)-Cu(II)-catalyzed reactions, respectively. Hydrogen ions retard the rate in Ru(III)-Cu(II)-catalyzed reaction, whereas the rate increases linearly with increasing [Ru(III)] in both the systems. The rate increases with increasing [Cu(II)] and attains a limiting value. The addition of the reaction products does not affect the rate of reaction. The reaction is characterized by a large negative entropy of activation. The kinetic deviations of the reaction, explained by presuming the participation of a reactive form of the NAC molecule or its new conformational polymorph reported recently, indicate the regulatory influence of the morphology of nanoparticles.     

Ru(III)/Os(VIII) Catalysed Oxidation of Gabapentin (Neurotin) Drug by Diperiodatoargentate(III) in Aqueous Alkaline Medium (Stopped Flow Technique): A Comparative Study

The kinetics of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of neuroleptic drug, gabapentin (GBP) by diperiodatoargentate(III) (DPA) in alkaline medium at 27 °C and a constant ionic strength of 0.60 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases are 1-(hydroxymethyl) cyclohexane acetic acid and Ag(I). The stoichiometry is the same in both the catalysed reactions i.e. [gabapentin]:[DPA] = 1:1. The reaction is of first order in Os(VIII)/Ru(III) and [DPA] and has less than unit order in both [GBP] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)/Ru(III)-gabapentin complex, which further reacts with one mole of monoperiodatoargentate(III) (MPA) species in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K _c) was also calculated for both catalysed reactions at different temperatures. From the plots of log K _c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII)>Ru(III). The probable active species of catalyst and oxidant have been identified.     

Kinetics of glycine oxidation by N-bromophthalimide in the presence of sodium dodecyl sulfate

The kinetics of oxidation of glycine by N-bromophthalimide (NBP) were studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP] and fractional-order dependence on [glycine] and [H⁺]. The addition of reduced product of the oxidant had no significant effect on the rate of reaction. Increasing [Hg(OAc)₂] and [Br⁻] increased the rate of reaction, whereas a change in ionic strength (μ) of the medium had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. HCN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The index of cooperativity and the micelle binding constant have been calculated.     

Os(VIII)/Ru(III) Catalysed Oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-Valine by Ag(III) Periodate Complex in Aqueous Alkaline Medium: A Comparative Kinetic Study

Abstract  

The kinetics of osmium(VIII) (Os(VIII)) and ruthenium(III) (Ru(III)) catalysed oxidation of l-valine (l-val) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 25 °C and a constant ionic strength of 0.006 mol dm⁻³ was studied spectrophotometrically. The stoichiometry is the same in both the catalysed reactions, i.e., [l-val]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)], and [DPA] and has less than unit order in [l-val] and negative fractional order in [OH⁻]. Added periodate had no effect on rate of reaction. The products were identified by spot test and characterized by spectral studies. The catalytic constant (K _C) was also calculated for both catalysed reactions at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The probable active species of catalyst and oxidant have been identified.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

Spectral and Mechanistic Study of the Ruthenium(III) Catalysed Oxidation of Gabapentin (Neurontin) by Heptavalent Manganese: A Free Radical Intervention

The kinetics of ruthenium(III) catalysed oxidation of Gabapentin by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and gabapentin in alkaline medium exhibits 2:1 stoichiometry (KMnO₄: gabapentin). The reaction shows first order dependence on [permanganate] and [ruthenium(III)] and apparent less than unit order dependence each in gabapentin and alkali concentrations. Reaction rate decreases with increase in ionic strength and decrease in solvent polarity of the medium. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The activation parameters were computed with respect to the slow step of the mechanism and discussed.     

Osmium(VIII)/Ruthenium(III) Catalysed Oxidation of l-lysine by Diperiodatocuprate(III) in Aqueous Alkaline Medium: A Comparative Mechanistic Approach by Stopped Flow Technique

Abstract The kinetics of osmium(VIII) and ruthenium(III) catalysed oxidation of l-lysine (l-lys) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.15 mol dm⁻³ was studied spectrophotometrically. The reaction between l-lys and DPC in alkaline medium exhibits 1:2 stoichiometry in both catalysed reaction (l-lys: DPC). The reaction is first order in [DPC] and has less than unit order both in [l-lys] and [alkali]. Increase in periodate concentration decreases the rate. Intervention of free radicals was observed in the reaction. The main products were identified by spot test, IR and GC-MS studies. Probable mechanisms are proposed and discussed. 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. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified. Graphical Abstract The kinetic and mechanistic investigations of the reaction between DPC and l-lysine has been studied in presence of microamounts of ruthenium(III) and osmium(VIII) in alkaline medium. The monoperiodatoargentate(III), [Ru(H₂O)₅OH]²⁺ and [OsO₄(OH)₂]²⁻ are considered as the active species of oxidant, DPC, ruthenium(III) and osmium(VIII) respectively.      

Oxidative conversion of thiourea and N-substituted thioureas into formamidine disulfides with acidified chloramine-T: a kinetic and mechanistic approach

The kinetics of oxidation of thiourea and N-substituted thioureas namely: N-methylthiourea, N-allylthiourea N-phenylthiourea and N-tolylthiourea to the corresponding formamidine disulfides by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in the presence of HClO₄ has been investigated at 278 K. The reactions follow identical kinetics for all thioureas, being first order each with respect to [CAT]_o, [Thiourea]_o and [H⁺]. Ionic strength of the medium and addition of p-toluenesulfonamide or halide ions have negligible influence on the rate. The solvent isotope effect has been studied using D₂O in the case of the oxidation of thiourea. Decrease in the dielectric constant of the medium by adding methanol decreases the rate. The reactions were studied at different temperatures, and the composite activation parameters have been computed. An isokinetic relationship was observed with β=314 K, indicating that enthalpy factors control the reaction rate. Under comparable experimental conditions, the rate of oxidation of thioureas increases in the order: N-allylthiourea>N-phenylthiourea>N-methylthiourea>thiourea>N-tolylthiourea. A mechanism involving the interaction of conjugate acid (CH₃C₆H₄SO₂NHCl) and substrate giving an intermediate complex, in a slow step, has been suggested. The derived rate law is in agreement with the observed kinetics.     

Oxidative decolorisation of Eriochrome Black T with Chloramine‐T: kinetic,mechanistic, and spectrophotometric approaches

The kinetics and mechanism of oxidative decolorisation of Eriochrome Black T (EBT) with sodium N‐chloro‐p‐toluenesulfonamide or Chloramine‐T (CAT), catalysed by osmium tetroxide [Os(VIII)] in alkaline medium and uncatalysed in acid medium, have been spectrophotometrically investigated at 303 K. The reaction exhibited a first‐order dependence of rate on [CAT]₀ and [EBT]₀ in both media, and also with respect to [H⁺]. The order with respect to [OH^‐] and [Os(VIII)] was fractional. Activation parameters were deduced. It was observed that the uncatalysed decolorisation reaction was ca. eightfold faster in acid medium in comparison with alkaline medium, while the Os(VIII)‐catalysed reaction was ca. sevenfold faster than the uncatalysed reaction. Mechanisms and rate laws were determined. The chemical oxygen demand of Eriochrome Black T dye was also determined. Importantly, the developed oxidative decolorisation method is simple, efficient, inexpensive, requires less time, and is environmentally benign. Hence, it can be adapted for treating Eriochrome Black T present in industrial and laboratory wastewater.     

Selective and an efficient oxidative conversion of glutathione to glutathione disulfide with N-bromosuccinimide in aqueous acidic solution: kinetic and mechanistic chemistry

Oxidative conversion of thiols to disulfides is an important chemical transformation in organic synthesis. A tripeptide, glutathione (GSH), composed of glutamate, cysteine and glycine, has been found to be the most abundant low molecular weight thiol in most biological systems. Its importance in mammal systems is believed to be related to its functions in oxidative metabolism and detoxification. It is noted that despite the importance of this substrate, less information is available in the literature on the oxidation of this substrate viewed from its kinetic and mechanistic studies. N-Bromosuccinimide (NBS) is a mild and selective oxidant for many organic compounds, and hence, it has been used as an oxidant for the present redox system. Consequently, the kinetics of oxidation of GSH with NBS in aqueous HClO₄ medium has been investigated at 283 K. The reaction rate exhibits first-order dependence on [NBS]_o and fractional-order dependence each on [GSH]_o and [H⁺]. The effect of added succinimide, ionic strength and dielectric constant of the medium on the rate of the reaction has been studied. The solvent isotope effect was studied using D₂O. The reaction was studied at different temperatures and thermodynamic parameters have been computed. Glutathione disulfide is characterized as the oxidation product of GSH. The protonated species RN⁺HBr (here R = (CH₂O)₂?) of the NBS is assumed to be the reactive oxidizing species. The reaction constants involved in the mechanism were evaluated. The observed results have been explained by a plausible mechanism, and the related rate law has been deduced.     

Mechanistic studies of ruthenium(III)-catalyzed oxidation of DL-methionine by hexacyanoferrate(III) in an alkaline medium

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of dl-methionine by alkaline hexacyanoferrate(III) (HCF(III)) in an alkaline medium were studied spectrophotometrically at 30±0.1°C. The reaction was first-order-dependent each on [HCF(III)] and [ruthenium(III)] and fractional-order-dependent on [alkali]. The rate of the reaction was found to be decreased with the increase in [methionine]. The main product of oxidation was methionine sulfone nitrile (3-(methylsulfonyl)propanenitrile) and it was identified and confirmed by FT-IR and mass spectral studies. Further, no effect of added reaction product was observed. A plausible mechanism was proposed involving complexation between methionine and ruthenium(III) species, [Ru(H₂O)₅OH]²⁺. Thermodynamic parameters for the reaction, E _a and Δ S ^#, were computed using linear least squares method and are found to be 65.83±1.03 kJ/mol and?249.58±3.35 J/K mol, respectively.

     

Kinetics of Ag(I) catalyzed oxidation of amino acids by peroxomonosulphate

Silver(I) catalyzed oxidation of amino acids such as glycine and α-alanine by peroxomonosulphate (PMS) in aqueous perchloric acid medium was found to be first order in [peroxomonosulphate] and fractional order in [amino acid] and [Ag(I)]. The rate equation was derived by assuming equilibrium formation of adduct between amino acids and Ag(I). This adduct was presumed to react with PMS in a slow step to yield (adduct)²⁺, which was self-oxidized in a fast step to give the products. The kinetic results revealed that silver catalyzed reaction occurred approximately 10⁴ times faster than the uncatalyzed reaction and this is attributed to the formation of (adduct)²⁺. The bimolecular rate constant (k) for the slow step and the activation parameters were calculated and the results are discussed.     

Aqueous polymerization of acrylonitrile by Ce(IV)-diacetone alcohol redox system

The kinetics of oxidation of DAA by Ce(IV) in dilute sulphuric acid medium has been studied and the reaction was found to obey a second order rate law. This DAA — Ce(IV) redox system has been used for the polymerization of acrylonitrile and the rate of polymerization was found to be proportional to[Ce(IV)]^0.5, [DAA]^0.5 and [M]^1.5. Based on these results a probable mechanism for initiation and termination has been proposed. The chain lengths of the polymers were found to increase with [M] and decrease with both [Ce(IV)] and [DAA].     

Hydrazine oxidation catalyzed by ruthenium hexacyanoferrate-modified glassy carbon electrode

A ruthenium (III) hexacyanoferrate (Ru(HCF)) film coated on a glassy carbon electrode was explored as an electrocatalyst for hydrazine oxidation. Surface cyclic voltammograms of Ru(HCF) film showed four reversible one-electron redox waves. Two, which corresponded to the redox processes of Ru(III)/Ru(IV) and Fe(II)/Fe(III), were identified to be responsible for the catalytic activity of hydrazine oxidation. Kinetic studies using potential scan rate dependency, Tafel plots, and rotating disk electrode technique found that this catalyzed hydrazine oxidation was a complete four-electron/four-proton process producing N₂, with the rate determining step possibly a one-electron process with a transfer coefficient (α) of ~0.31–0.36. In addition, based on kinetic analysis and findings in the literature, we propose a possible reaction mechanism for catalyzed hydrazine oxidation in order to facilitate further understanding.     

Study of the kinetics of oxidation of amines by potassium ferricyanide in the presence of <Emphasis Type="Italic">N,N</Emphasis>-dimethyldodecylamine <Emphasis Type="Italic">N</Emphasis>-oxide

This research reports on the oxidation of different amines such as dibutylamine, diethylamine, dipropylamine, ethylamine, ethylmethylamine, propylamine, triethylamine, and trimethylamine by 0.001 M potassium ferricyanide in the presence of 0.03 M NaOH at 25°C in aqueous medium and/or in 0.03 M N,N-dimethyldodecylamine N-oxide (DDAO). Oxidation rates were studied with a spectrophotometer at 420 nm. The experimental data showed that the reaction was first-order with respect to [amine] _T and [Fe(CN)₆]³⁻. Also, the rate constant (k _obs) had values within the concentration range of 0.015–0.05 M of NaOH and increased above the critical micelle concentration values of DDAO. The dependence of the reaction rate on the nature of the salt was also investigated, and the thermodynamic parameters ΔG ^*, ΔH ^*, and ΔS ^* were calculated. A pseudo-phase model was applied to the system, and the binding constant of the amine to DDAO micelles was calculated.