Micellar catalysis in the oxidation of lipids

The features of the catalytic effects of surfactants (S) in the oxidation of hydrocarbons and lipids are considered. It is shown that the primary amphiphilic products of the oxidation of hydroperoxides (ROOH) and lipids and the known cationic surfactants form mixed micelles {nS-mROOH} in which the accelerated decomposition of ROOH occurs and other polar components, such as metal-containing compounds, inhibitors, etc., can be concentrated, thus producing a large effect on the oxidation rate and mechanism.     

Kinetics of oxidation of certain pyrimidines by Ce(IV)

The kinetics of the oxidation of certain biologically important pyrimidine bases (Uracil, Thymine, and 6-Methyluracil) by Ce(IV) in aqueous H₂SO₄ has been investigated. A first-order dependence of rate each on [Ce(IV)], [pyrimidine], and an inverse first-order dependence on [H₂SO₄] has been observed. Rate and activation parameters for the oxidation of these pyrimidines have been computed. A suitable rate law and a mechanism consistent with the kinetic observations and product analysis have been proposed. © 1996 John Wiley & Sons, Inc.     

Micellar catalysis of oxidation of glycolic acid by N-bromophthalimide

Catalysis of oxidation of glycolic acid by N-bromophthalimide by micelles of cetyltrimethylammonium bromide (CTAB) at 318 K was investigated. The observed value of critical micelle concentration of CTAB in the presence of other components was lower than those reported in the literature. The oxidation reaction was strongly catalyzed by cationic micelles of CTAB. The reaction rate increased with CTAB concentration until the steady state was achieved. The reaction kinetics corresponded to first, fractional and inverse fiactional orders with respect to changes of concentration of reaction components. Effects of solvent, phthalimide, mercuric acetate, and potassium chloride on the reaction kinetics were also studied. The micelle-catalyzed oxidation reaction was shown to fit Arrhenius equation. The experimental data were rationalized in terms of Menger-Portnoy model considering a distribution of the reactants between the micellar and aqueous phases.     

Effect of Cetylpyridinium chloride on the electron transfer reactions of acetophenones with Ce(IV)

The kinetics of electron transfer reactions between acetophenones with Ce(IV) have been studied in aqueous acetic acid medium in the presence of cationic micelle Cetylpyridinium chloride (CPyCl) at different temperatures. Kinetic data reveal first-order dependence with respect to each of Ce(IV) and acetophenones. The cationic micelle, Cetylpyridinium chloride enhances the oxidation reactions. The catalysis fits to a model developed by Menger and Portnoy as well as Berezin's phase separation model. The binding and partition constants and the transfer free energy from water to micelle have been estimated and discussed, suggesting that the solubilization of both the reactants in the micellar phase, facilitates the oxidation. © 1993 John Wiley & Sons, Inc.     

Zirconium(IV) catalysis in perborate oxidation of iodide

Zirconium(IV) catalyzes perborate oxidation of iodide ion. In acidic solution the oxidation is zero order with respect to perborate, first order with respect to Zr(IV), independent of [H⁺] and exhibits Michaelis-Menten dependence on [I⁻]. Mechanistic pathway of the catalysis is discussed and a rate equation is derived.     

Mechanistic investigation of substrate oxidation by Ce(IV) reagents in acetonitrile

Rates and activation parameters for the Ce(4+)-mediated oxidation of a beta-keto ester, a beta-diketone, and a beta-keto silyl enol ether were determined in acetonitrile. In the case of the dicarbonyls, the enol content of the substrate impacts the rate of oxidation by Ce(4+), predominantly through contributions from DeltaH(). For the silyl enol ether, the transition state for oxidation by Ce(4+) is substantially more ordered than it is for the beta-keto ester or the beta-diketone.     

Kinetics and mechanism of oxidation of S-phenylthioacetic acids by Ce(IV)

The kinetics of oxidation of several S-phenylthioacetic acids by ceric ammonium nitrate (CAN) in presence of perchloric acid has been studied spectrophoto- metrically in 50 %(v/v) aqueous acetic acid. The order with respect to Ce(IV) is one and the order with respect to S-phenylthioacetic acid is found to be 0.8. A linear plot of k_obs⁻¹ vs [substrate]⁻¹ with an intercept on the rate of axis suggests the formation of an equilibrium complex between the reactants prior to the rate determining step. The added acrylonitrile retards the reaction rate considerably suggesting that the oxidation process may involve a free radical mechanism. Electron-releasing substituents generally accelerate the rate, while electron-withdrawing groups retard the rate. A good correlation is found to exist between log k_1.8 and Hammett σ constants.     

Kinetics of ruthenium(III)-catalyzed oxidation of arylthioacetic acids by Ce(IV)

The kinetics of ruthenium(III)-catalyzed oxidation of several arylthioacetic acids by Ce(IV) have been studied. The proposed mechanism involves the formation of a 1∶1 complex between Ru(III) and arylthioacetic acid, which then reacts with Ce(IV).     

Micellar catalysis by perfluorooctanoic acid

Rates of acidic hydrolysis of hexano-, octano-, and decanohydroxamic acids and of 4-bromophenylaceto- and phenylacetohydroxamic acids have been determined in aqueous perfluorooctanoic acid—a reactive counterion surfactant system. Typical micellar catalysis was observed for the hydrolyses of the n-alkyl hydroxamic acids but not for the arylacetohydroxamic acids. The Arrhenius activation energy for hydrolysis of octano-hydroxamic acid is smaller above the cmc of the surfactant than it is below the cmc.     

Facile formation of a homoleptic Ce(IV) amide via aerobic oxidation

Oxidation of [Ce(NCy2)3(thf)] or [Ce(NCy2)4Li(thf)] with dry air produced the first homoleptic Ce(IV) amide [Ce(NCy2)4].     

Micellar catalysis on 1,10-phenanthroline promoted hexavalent chromium oxidation of ethanol

The kinetics and mechanism of Cr(VI) oxidation of ethanol in the presence and absence of 1,10-phenanthroline in aqueous acid media have been carried out. Monomeric species of Cr(VI) are kinetically active in the absence of phen, while in the phen catalyzed path, the Cr(VI)-phen complex has been suggested as the active oxidant. In the catalyzed path, the Cr(VI)-phen complex participates in the oxidation of ethanol and ultimately is converted into the Cr(III)-phen complex. In the uncatalyzed path, the Cr(VI)-substrate ester experiences an acid catalyzed redox decomposition in the rate-determining step. The uncatalyzed path shows a second-order dependence on [H⁺], while the phen catalyzed path shows a first-order dependence on [H⁺]. Both the uncatalyzed and phen-catalyzed paths show first-order dependence on [ethanol]_T and [Cr(VI)]_T. The phen-catalyzed path is first order in [phen]_T. These observations remain unaltered in the presence of externally added surfactants. CPC inhibits the reactions while SDS catalyzes the reactions. The observed miceller effects have been explained by considering partitioning of the reactants between the miceller and aqueous phase.     

Micellar catalysis on picolinic acid promoted hexavalent chromium oxidation of glycerol

Under pseudo-first-order conditions, monomeric Cr(VI) was found to be kinetically active in the absence of picolinic acid (PA), whereas in the PA-promoted path, the Cr(VI)–PA complex undergoes nucleophilic attack by the substrate to form a ternary complex which subsequently experiences redox decomposition, leading to glyceraldehydes and Cr(IV)–PA complex. The uncatalyzed path shows a second-order dependence on [H⁺], whereas the PA-catalyzed path shows zero-order dependence on [H⁺]. Both the uncatalyzed and PA-catalyzed path show a first-order dependence on [glycerol]_T and [Cr(VI)]_T. The PA-catalyzed path is first order in [PA]_T. All these observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant cetyl pyridinium chloride (CPC) and anionic surfactant sodium dodecyl sulfate (SDS) on the PA-catalyzed path have been studied. CPC inhibits, whereas SDS accelerates the reaction. Here, SDS is a catalyst for glyceraldehydes production and at the same time reduction of carcinogenic hexavalent chromium to nontoxic trivalent chromium. The reaction proceeds simultaneously in both aqueous and micellar phase. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase. The Menger–Portnoy model, Piszkiewicz cooperative model, and pseudo-phase ion exchange model have been tested to explain the observed micellar effect.     

Chemiluminescent Emitter Based on the Reactions by Ce(IV)

Abstract

The chemiluminescence spectra of Ce(IV) with pyrogallol and sulfite were measured using an automatic luminescence spectrum analyzer. The presented chemiluminescence spectra were similar to that reported for sulfite. Ce(III) as a chemiluminescent emitter is proposed.     

Cr(III) or Ce(IV) impregnated perfluorinated resin-sulfonic acid catalyst for the oxidation of alcohols

Several polymer supported catalysts are prepared by treatment of Nafion® 511 (abbreviated as NAFK below) with metal salts and found to be effective in promoting the dehydrogenative oxidation of alcohols with ^tBuOOH.     

Adduct formation in Ce(IV) thenolytrifluoroacetonate

Russian Chemical Bulletin -     

Oxidation of ethanol by Ce(IV) in acid nitrate medium

The oxidation kinetics of ethanol by Ce(IV) has been studied as a function of pH, nitrate and water concentration. Even at high concentration of H⁺ and NO ₃ ^– several species appear to exist. The oxidation is fastest in strongly acidic medium without added nitrate ions.

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Ce(IV) pH, . H⁺ NO ₃ ^– , Ce(IV). .

     

Osmium(VIII)/palladium(II) catalysis of cerium(IV) oxidation of allyl alcohol in aqueous acid

Summary Catalysis of the Ce^IV-allyl alcohol (AA) reaction in acid solution depends both on the of rate enhancement and product distribution on the catalyst used: Os^VIII results mainly in acrolein, whereas Pd^II gives acrylic acid. The rate laws in the two cases also differ:viz., Equations 1 and 2K₁ is the equilibrium constant of formation of the Os^VIII-allyl alcohol complex and k₁ is the rate constant of its oxidation by Ce^IV; K₂ is the equilibrium constant for the formation of the Ce^IV-Pd^II-allyl alcohol complex and k₂ is its rate constant of decomposition. Rate = K₁k₁[Ce^IV][AA][Os^VIII]/(1+K₁[AA]) (1) Rate = K₁k₁[Ce^IV][Pd^II]/(1+K₂[Ce^IV]) (2)While Os^VIII is effective in H₂SO₄ solution, aqueous HClO₄ is needed for Pd^II. Both reactions proceed through formation of catalyst-allyl alcohol complexes with participation of free radicals. The details of these observations are discussed.