Ahmed Fawzy

Further evidence for detection of short-lived transient hypomanganate(V) and manganate(VI) intermediates during oxidation of some sulfated polysaccharides by alkaline permanganate using conventional spectrophotometric techniques.

Spectrophotometric evidence for the formation of hypomanganate(V), [CAR-Mn(V)O43-], and manganate(VI), [CAR-Mn(VI)O42-], intermediate complexes has been confirmed during the oxidation of iota- and lambda-carrageenan-sulfated polysaccharides (CAR) by alkaline permanganate at pHs 12 using a conventional spectrophotometer. These short-lived intermediate complexes were identified and characterized. A reaction mechanism in good consistence with the experimental results is suggested.

Kinetic and mechanistic investigations on the oxidation of N’-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO4−]0 and [Azn-F]0, but with a fractional first-order dependence on [OH−]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.

Base-catalyzed oxidation of l -asparagine by alkaline permanganate and the effect of alkali metal ion catalysts: a kinetic and mechanistic approach

Kinetic investigations on the oxidation of l-asparagine (Asn) by alkaline permanganate have been carried out spectrophotometrically at a constant ionic strength and temperature. The reaction is first order with respect to [MnO4−] and less than unit order with respect to both [Asn] and [alkali]. The influence of pH indicated that the oxidation is base catalyzed. The reaction rate was found to increase with increasing ionic strength and temperature. The addition of alkali metal ion catalysts accelerates the oxidation rate. The proposed reaction mechanism involves the formation of a 1:1 intermediate complex between l-asparagine and an alkali-permanganate species in a pre-equilibrium step, which was confirmed by both spectral and kinetic evidence. The complex decomposes slowly in a rate determining step, resulting in the formation of a free radical. The latter reacts again with another alkali-permanganate species in a subsequent fast step to yield the final reaction products which were identified as aldehyde (α-formyl acetamide), ammonia, manganate(VI) and carbon dioxide. The appropriate rate laws are deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.

Oxidation of alginate and pectate biopolymers by cerium(IV) in perchloric and sulfuric acid solutions: A comparative kinetic and mechanistic study.

The kinetics of oxidation of alginate (Alg) and pectate (Pec) carbohydrate biopolymers was studied by spectrophotometry in aqueous perchloric and sulfuric acid solutions at fixed ionic strengths and temperature. In both acids, the reactions showed a first order dependence on [Ce(IV)], whereas the orders with respect to biopolymer concentrations are less than unity. In perchloric acid, the reactions exhibited less than unit orders with respect to [H(+)] whereas those proceeded in sulfuric acid showed negative fractional-first order dependences on [H(+)]. The effect of ionic strength and dielectric constant was studied. Probable mechanistic schemes for oxidation reactions were proposed. In both acids, the final oxidation products were characterized as mono-keto derivatives of both biopolymers. The activation parameters with respect to the slow step of the mechanisms were computed and discussed. The rate laws were derived and the reaction constants involved in the different steps of the mechanisms were calculated.

Kinetics and mechanism of permanganate oxidation of iota- and lambda-carrageenan polysaccharides as sulfated carbohydrates in acid perchlorate solutions.

The kinetics of oxidation of iota- and lambda-carrageenan as sulfated carbohydrates by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm(-3) have been investigated spectrophotometrically. The pseudo-first-order plots were found to be of inverted S-shape throughout the entire courses of reactions. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental observations showed first-order dependences in permanganate and fractional first-order kinetics with respect to both carrageenans concentration for both the induction and autoacceleration periods. The results obtained at various hydrogen ion concentrations showed that the oxidation processes in these redox systems are acid-catalyzed throughout the two stages of oxidation reactions. The added salts lead to the prediction that Mn(III) is the reactive species throughout the autoacceleration periods. Kinetic evidence for the formation of 1:1 intermediate complexes was revealed. The kinetic parameters have been evaluated and tentative reaction mechanisms in good agreement with the kinetic results are discussed.

Palladium(II)-catalyzed oxidation of l-tryptophan by hexacyanoferrate(III) in perchloric acid medium: a kinetic and mechanistic approach

AbstractThe catalytic effect of palladium(II) on the oxidation of l-tryptophan by potassium hexacyanoferrate(III) has been investigated spectrophotometrically in aqueous perchloric acid medium. A first order dependence in [hexacyanoferrate(III)] and fractional-first order dependences in both [l-tryptophan] and [palladium(II)] were obtained. The reaction exhibits fractional-second order kinetics with respect to [H +]. Reaction rate increased with increase in ionic strength and dielectric constant of the medium. The effect of temperature on the reaction rate has also been studied and activation parameters have been evaluated and discussed. Initial addition of the reaction product, hexacyanoferrate(II), does not affect the rate significantly. A plausible mechanistic scheme explaining all the observed kinetic results has been proposed. The final oxidation products are identified as indole-3-acetaldehyde, ammonium ion and carbon dioxide. The rate law associated with the reaction mechanism is derived. Graphical AbstractPalladium(II)-catalyzed oxidation of L-tryptophan by hexacyanoferrate(III) in aqueous perchloric acid medium has been investigated. The effect of temperature on the reaction rate has been studied and the activation parameters have been evaluated and discussed. The final oxidation products are identified as indole-3-acetaldehyde, ammonium ion and carbon dioxide.

Kinetics and Mechanistic Approach to Palladium (II)-Catalyzed OxidativeDeamination and Decarboxylation of Leucine and Isoleucine byAnticancer Platinum (IV) Complex in Perchlorate Solutions

Oxidations of two aliphatic α-amino acids (AA), namely, leucine and isoleucine by hexachloroplatinate (IV) as an anticancer platinum (IV) complex has been studied using a spectrophotometric technique in perchlorate solutions in the presence of palladium (II) catalyst at a constant ionic strength of 1.0 mol dm-3 and at 25°C. The reactions did not proceed in the absence of the catalyst. The reactions of both amino acids showed a first order dependence on both [PtIV] and [PdII], and less than unit order dependences with respect to both [AA] and [H+]. Increasing ionic strength and dielectric constant of the reactions medium increased the rates of the reactions. A probable oxidations mechanism has been suggested and the rate law expression has been derived. Both spectral and kinetic evidences revealed formation of 1:1 intermediate complexes between AA and PdII before the rate-controlling step. The oxidation products of the investigated amino acids were identified as the corresponding aldehyde, ammonium ion and carbon dioxide. The activation parameters of the second order rate constants were evaluated and discussed

Kinetics and Mechanism of Oxidation of Vanillin by Chromium(VI) inSulfuric Acid Medium

The kinetics of oxidation of vanillin (VAN) by chromium(VI) in sulfuric acid medium was studied by a spectrophotometric technique. The reaction exhibited a first order dependence with respect to [Cr(VI)] and fractionalfirst orders with respect to [VAN] and [H+]. Varying ionic strength or dielectric constant of the reaction medium had no significant effect on the oxidation rate. The proposed mechanism includes an intermediate complex formation between vanillin and chromium(VI) before the rate-determining step. The final oxidation product of vanillin was identified by both spectral and chemical analysis as vanillic acid. The suitable rate law has been deduced. The reaction constants included in the various steps of the suggested mechanism have been evaluated. The activation parameters of the rate constant of the rate-determining step of the mechanism and the thermodynamic quantities of the equilibrium constant have been evaluated and discussed.

Kinetics and mechanism of uncatalyzed and ruthenium(III)-catalyzed oxidation of formamidine derivative by hexacyanoferrate(III) in aqueous alkaline medium

AbstractThe catalytic effect of ruthenium(III) on the oxidation of N, N-dimethyl- N′-(4H-1,2,4-triazol- 3-yl) formamidine (ATF) by hexacyanoferrate(III) (HCF) was studied spectrophotometrically in aqueous alkaline medium. Both uncatalyzed and catalyzed reactions showed first order kinetics with respect to [HCF], whereas the reaction orders with respect to [ATF] and [OH −] were apparently less than unity over the concentration range studied. A first order dependence with respect to [RuIII] was obtained. Increasing ionic strength increased the rate of uncatalyzed reaction and decreased the rate of the catalyzed one Plausible mechanistic schemes of oxidation reactions have been proposed. In both cases, the final oxidation products are identified as aminotriazole, dimethyl amine and carbon dioxide. The rate laws associated with the reaction mechanisms are derived. The reaction constants involved in the different steps of the mechanisms were calculated. The activation and thermodynamic parameters have been computed and discussed. Graphical AbstractThe catalytic effect of ruthenium(III) on the oxidation of N,N-dimethyl-N’-(4H-1,2,4-triazol-3-yl) formamidine by alkaline hexacyanoferrate(III) has been studied. The final oxidation products are identified as aminotriazole, dimethyl amine and carbon dioxide.

A Study of the Kinetics and Mechanism of Oxidation of Fluorene by Alkaline Hexacyanoferrate(III)

Kinetics of hexacyanoferrate (III) (HCF) oxidation of fluorene (Fl) in organic alkaline medium has been studied by spectrophotometric technique at a constant ionic strength of 0.15 mol dm -3 and at a temperature of 25°C. The reaction showed a first order kinetics with respect to [HCF] and fractional-first order dependences on both [Fl] and [OH - ]. The oxidation rate was increased with the increase in the ionic strength of the reaction medium. The oxidation mechanism was suggested which involves formation of a 1:1 intermediate complex between fluorene and HCF species in a pre-equilibrium step. The final oxidation product of fluorene was identified by spectroscopic and chemical tools as 9H-fluorenone. The appropriate rate law expression was deduced and the reaction constants involved in the mechanism were evaluated. The activation parameters of the rate constant of the slow step along with the thermodynamic quantities of the equilibrium constants were evaluated and discussed.