Ruthenium(III) Catalyzed Oxidation Of Ethylenediaminetetraacetic Acid By N-Bromosuccinimide In Aqueous Alkaline Medium – A Kinetic And Mechanistic Study

The formation mechanism of microheterogeneous hydrogenation catalysts based on phosphinepalladium (II) complexes has been considered. According to elemental analysis, X-ray diffraction, electron microscopy, NMR, and IR spectroscopy, the catalyst is a nanoscale palladium organophosphorus matrix and (or) palladium phosphide with immobilized palladium clusters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Europium(III) Catalysis for Reduction of Thionine Dye by Selenous Acid in Aqueous Sulfuric Acid Solutions: A Kinetic and Mechanistic Approach

The catalytic effect of europium(III) on the reduction of thionine dye (Th) by selenous acid has been studied by spectrophotometry in aqueous sulfuric acid solutions at a constant ionic strength of 3.0 mol dm^?3 and at different temperatures (283–313 K). A first‐order dependence with respect to both [Th] and [Eu^III] was obtained, whereas the orders with respect to [Se^IV] and [H⁺] were less than unity. Variation of ionic strength and dielectric constant of the reaction media did not affect the reaction rates. Probable mechanistic schemes for thionine reductions in both the absence and presence of europium(III) catalyst were proposed. The rate laws associated with the reaction mechanisms were derived, and the reaction constants were calculated. The activation parameters of the rate constants of the slow steps of both uncatalyzed and catalyzed reactions along with thermodynamic quantities of the equilibrium constants are computed and discussed.     

Kinetics and Mechanism of Oxidation of l‐Histidine by Permanganate Ions in Sulfuric Acid Medium

The reaction kinetics for the oxidation of l ‐histidine by permanganate ions have been investigated spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The order with respect to permanganate ions was found to be unity and second in acid concentration, whereas a fractional order is observed with respect to histidine. The reaction was observed to proceed through formation of a 1:1 intermediate complex between oxidant and substrate. The effect of the acid concentration suggests that the reaction is acid catalyzed. Increasing the ionic strength has no significant effect on the rate. The influence of temperature on the rate of reaction was studied. The presence of metal ion catalysts was found to accelerate the oxidation rate, and the order of effectiveness of the ions was Cu²⁺ > Ni²⁺ > Zn²⁺. The final oxidation products were identified as aldehyde (2‐imidazole acetaldehyde), ammonium ion, manganese(II), and carbon dioxide. Based on the kinetic results, a plausible reaction mechanism is proposed. The activation parameters were determined and discussed with respect to a slow reaction step.     

Mechanistic Study of Oxidation of Palladium(II) by Cerium(IV) in Aqueous Acid

The kinetics of oxidation of Pd^II by Ce^IV have been studied spectrophotometrically in HClO₄ media at 40 °C. The reaction is first order each in [Ce^IV] and [Pd^II] at constant [H⁺]. Increasing [H⁺] accelerates the reaction rate with fractional order in [H⁺]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At constant acidity, increasing the added chloride concentration enhances the rate of reaction. H₃Ce(SO₄)₄⁻ and PdCl₄²⁻ are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants involved have been determined.     

Kinetics and Mechanism of the Autocatalytic Oxidation of L-Asparagine in a Moderately Concentrated Sulfuric Acid Medium

The reaction kinetics of the Autocatalytic Oxidation of L-asparagine by permanganate ions has been investigated in moderately strong acid medium using the spectrophotometric technique. In all cases studied, an autocatalytic effect due to Mn²⁺ ions formed as a reaction product was observed. Both catalytic and noncatalytic processes were determined to be first order with respect to the permanganate ions while a first and a fractional order with respect to the amino acid for noncatalytic and catalytic reactions were obtained, respectively. The overall rate equation for this process may be written asd[MO₄ ^–]/dt= k´₁[MnO₄ ^–]+k´₂[MnO₄ ^–][Mn⁺²],where k´₁ and k´₂ are rate pseudoconstants for noncatalytic and catalytic reactions, respectively. The influence of some factors such as temperature and reactant concentration on the rate constants has been studied, and the activation parameters have been calculated. Reaction mechanisms satisfying observations for both catalytic and noncatalytic routes have been presented.     

Kinetics and Mechanism of the Autocatalyzed Oxidation of Theophylline by Permanganate in Aqueous Perchloric Acid Medium

The reaction kinetics for the oxidation of theophylline by permanganate ions have been investigated in perchloric acid medium using spectrophotometric techniques at 25?^°C, and at constant ionic strength 1.60 mol?dm^?3, under pseudo first order conditions. An autocatalyzed reaction is observed due to one of the products formed is Mn(II). The orders with respect to theophylline and Mn(VII) were both found to be unity, whereas fractional order is observed with respect to the autocatalyst, Mn(II). The rate of the reaction increases as the concentration of acid increases, but the order with respect to acid concentration is less than unity. The influence of temperature on the rate of reaction was studied. Based on the experimental results a suitable mechanism is proposed. The activation and thermodynamic parameters were determined with respect to slow reaction step.     

Oxidation of Carbamazepine by Lipopathic Mn(VII), Cetyltrimethylammonium Permanganate: A Mechanistic Study

In this contribution, we report the oxidation of an established anticonvulsant and antiepileptic drug, carbamazepine, by a lipopathic oxidant, cetyltrimethylammonium permanganate (CTAP), in a nonpolar medium. 1H‐Dibenzo[b,f]azepine‐4,5‐dione is found to be the major product of the oxidation reaction. The kinetics of the reaction is studied in organic media spectrophotometrically by monitoring the disappearance of Mn(VII) at 530 nm. The reaction is found to be fractional order with respect to carbamazepine and first order with respect to CTAP. Based on the experimental findings, a suitable ionic mechanism is proposed where carbamazepine reacts with CTAP in a slow rate‐determining step to form a hypomanganate ester intermediate through a nonpolar cyclic transition state. Subsequently, the intermediate decomposes and hydrolyzes in fast steps to the dicarbonyl product. The proposed reaction mechanism is also supported by the effect of solvent and temperature on the rate of the reaction. The addition of ionic surfactants increases the rate of reaction, and the catalyzing effect is explained through the possible formation of mixed reverse micellar aggregates where carbamazepine is partitioned more to the interfacial region in the vicinity of the permanganate anion.     

Oxidation of Acyclovir by a Cuprate(III) Periodate Complex in Aqueous Alkaline Media: A Kinetic and Mechanistic Approach

The oxidation of acyclovir by diperiodatocuprate(III) in aqueous alkaline media, at a constant ionic strength of 0.01 mol?dm^?3, was studied spectrophotometrically at 25?°C. The reaction between acyclovir and DPC in alkaline media exhibits 1:4 stoichiometry (acyclovir:diperiodatocuprate(III)). The main oxidation products were identified by a spot test, along with infrared and liquid chromatography mass spectral studies. The oxidation reaction is first order with regard to the diperiodatocuprate(III) concentration, but has less than unit order in the acyclovir concentration and negative fractional orders in the periodate and alkali concentrations. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline media was shown to proceed via a diperiodatocuprate(III)?Cacyclovir complex, which decomposes slowly in a rate determining step followed by subsequent fast steps to give the products. A suitable mechanism is proposed for these observations. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism, along with the thermodynamic quantities, were determined and discussed.     

Kinetic Stability of Indium(III) Complexes with Azaporphyrins in Aqueous Sulfuric Acid

Stability of chloro(octaphenyltetraazaporphinato)indium(III) and chloro(2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-diazaporphinato)indium(III) in 90-98 % aqueous sulfuric acid was studied. Kinetic parameters of solvoprotolytic dissociation of the complexes were determined, and a mechanism of the reaction was proposed. Diaza substitution results in more stable complexes than tetraaza substitution. The state of chloro(2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-diazaporphinato)indium(III) in a proton-donor medium was studied to show that the acid-base interaction involves one by one two meso-nitrogen atoms. Dissociation constants of the resulting acid forms were determined.     

Thermodynamic and Kinetic Studies of Oxidation of L-histidine by Manganese(VII) in Concentrated Sulfuric Acid Medium in the Absence and Presence of Silver(I)

Abstract

Thermodynamic and kinetic studies and mechanism of manganese(VII) oxidation of L-histidine has been studied both in the absence and presence of silver(I) in aqueous sulfuric acid medium. Various hypotheses for the mechanism of acid catalysis have been tested and it has been found that rate is related to the activity of water in accord with Bunnett's hypothesis. The energy and entropy of activation and frequency factor have been calculated using the Arrhenius and Eyring plots. Mechanisms in agreement with the observations are reported. The experimental rate law for the both uncatalyzed reaction and in the presence of silver was found. The applicability of Burnett's theory has been tested.     

Silver(I) and Copper(II) Catalysis for Oxidation of Histidine by Cerium(IV) in Acid Medium: A Comparative Kinetic Study

The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm⁻³ and at 25°C. In both uncatalyzed and metal ions‐catalyzed paths, the reactions exhibited first‐order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first‐order dependences with respect to [His] and [H⁺]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2‐imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second‐order rate constants were evaluated.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

 The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism.     

Substitution Reaction of the Hydroxopentaaquarhodium(III) Ion with l-Glutamine,Glycine and l-Histidine in Aqueous Medium: A Kinetic and Mechanistic Approach

The title reactions have been studied spectrophotometrically. A two step consecutive mechanism for the amino acids was found which differs from that of the dipeptides, which follow two parallel paths under identical reaction conditions. In the case of amino acids the first step is ligand dependent, but the second step is a ligand independent chelation step, whereas for dipeptides two parallel ligand dependent paths are observed. A comparison between these closely related systems and the unique findings in their mechanistic behavior is discussed in detail.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000     

硫酸溶液中胶束催化Ce(IV)氧化D-甘露糖

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40℃ both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and in cerium(Ⅳ), which decreased with increasing [H2SO4]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (Ⅳ) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was reactive form of cerium (Ⅳ). From the kinetic data, micelle-cerium (Ⅳ) binding and rate constants in micellar medium were evaluated.The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression --d[Ce(Ⅳ)]= k1Kcl[D-mannose] [Ce(Ⅳ)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.