Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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Kinetics and mechanism of ruthenium (III) catalyzed oxidation of ethanol by cerium (IV) in aqueous sulfuric acid media

The kinetics of oxidation of ethanol by cerium(IV) in presence of ruthenium(III) (in the order of 10^?7 mol dm^?3) in aqueous sulfuric acid media have been followed at different temperatures (25–40°C). The rate of disappearance of cerium(IV) in the title reaction increases sharply with increasing [C₂H₅OH] to a value independent of [C₂H₅OH] over a large range (0.2–1.0 mol dm^?3) in which the rate law conforms to: where [Ru]_T gives the total ruthenium (III) concentration. The values of 10^?3k_c and 10^?3k_d are 3.6 ± 0.1 dm³ mol^?1 s^?1 and 3.9 ± 0.2 s^?1, respectively, at 40°C, I = 3.0 mol dm^?3. The proposed mechanism involves the formation of ruthenium(III)^? substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)^? substrate complex followed by the rapid red-ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(IV) rapidly. The mechanism is consistent with the existence of the complexes Ru^III · (C₂H₅OH) and Ru^III · (C₂H₅O^?) and both are kinetically active. The overall bisulphate dependence conforms to: k_obsd = A[Ru]_T/{1 + C[HSO₄^?]} where A = 2.2 × 10⁴ dm³ mol^?1 s^?1, C = 1.3 at 40°C, [H⁺] = 0.5 mol dm^?3, and I = 3.0 mol dm^?3. The observations are consistent with the Ce(SO₄)₂ as the kinetically active species. © 1995 John Wiley & Sons, Inc.     

Kinetics and mechanism of oxidation of 4-oxoacids by N-bromosuccinimide in aqueous acetic acid medium

Kinetics and mechanism of oxidation of substituted and unsubstituted 4-oxoacids (S) by N-bromosuccinimide (NBS) in aqueous acetic acid medium have been studied potentiometrically. The reaction follows first-order kinetics, each in 4-oxoacids, NBS and H⁺. The effect of changes in the electronic nature of the substrate reveals that there is a development of positive charge in the transition state. Based on the kinetic results and the product analysis, a suitable mechanism has been proposed for the reaction of NBS with 4-oxoacids.     

Kinetics and mechanism of the oxidation of nitrous acid by bromine in aqueous sulfuric acid

The kinetics and mechanism of the reaction between nitrous acid and bromine are studied in dilute sulfuric acid medium, using both the stopped‐flow method and conventional spectrophotometry. The partial reaction order with respect to Br₂ moderately differs from 1, showing a saturation at a higher concentration of bromine. The second order of the reaction towards nitrous acid has been observed. Hydrogen and bromide ions significantly suppress the rate of reaction. Despite the apparent simplicity, the mechanism is rather complex, with two reaction pathways proposed. The first one is represented by the reaction of bromine with the intermediate dinitrogen trioxide. A direct nucleophilic attack of NO₂⁻ ion towards the bromine molecule is suggested as the second pathway. The proposed mechanism accounts for the observed behavior; in almost all cases a satisfactory quantitative agreement with the experiments is obtained. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 279–285, 2000     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol by cerium(IV) in sulfuric acid media

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol (THFA) by cerium(IV) in sulfuric acid media have been investigated spectrophotometrically in the temperature range 298–313 K. It is found that the reaction is first-order with respect to Ce^IV, and exhibits a positive fractional order with respect to THFA and Ru^III. The pseudo first-order ([THFA]≫[Ce^IV]≫[Ru^III]) rate constant k _obs decreases with the increase of [HSO ₄ ⁻ ]. Under the protection of nitrogen, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed and the rate equations derived from the mechanism can explain all the experimental results. From the dependence of k _obs on the concentration of HSO ₄ ⁻ , has been found as the kinetically active species. Furthermore, the rate constants of the rate determining step together with the activation parameters were evaluated.     

Kinetics and mechanism of oxidation of aniline and substituted anilines by isoquinolinium bromochromate in aqueous acetic acid

Oxidation of anilines by isoquinolinium bromochromate (IQBC) in aqueous acetic acid leads to the formation of corresponding azobenzenes. The reaction is first order with respect to both aniline and IQBC and is catalyzed by hydrogen ion. The rate of oxidation decreases with increasing dielectric constant of solvent, indicating the presence of an ion-dipole interaction. The rate of oxidation decreases with increase in concentration of KCl, possibly due to the formation of less reactive species by interaction of Cl^- and protonated IQBC. The specific rate of oxidizing species anilines reaction correlates with substituents constant affording a negative reaction constant. Hammett plot is found to be valid and the correlation between enthalpies and free energies of activation is reasonably linear with an isokinetic temperature of 401 K.     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Kinetics and mechanism of Ru(III)-catalyzed oxidation of aliphatic alcohols by trichloroisocyanuric acid in HClO4 medium

The kinetics and mechanism of Ru(III)-catalyzed oxidation of some aliphatic alcohols by trichloroisocyanuric acid (TCICA) has been studied in aqueous HOAc-HClO₄ medium. The reaction is zero order in [TCICA], fractional order in [alcohol] and first order in [Ru(III)]. The reaction is insensitive towards changes in acid concentration. The rate is not affected by an increase in [Cl⁻]. The polar reaction constant (ρ*) was found to be −1.27 at 308 K. A mechanism involving complex formation between the substrate and catalyst in the fast equilibrium step followed by its decomposition in a slow step is proposed.     

Kinetics and mechanism of Ru(III) catalyzed iodination of anisole and substituted anisoles by iodine monochloride in aqueous acetic acid

The order with respect to ICl and Ru(III) is unity and fractional with respect to [substrate]. The effect of varying [acid] is negligible at lower [HClO₄] but at higher [acid] (>0.01 M) there is first order dependence on [H⁺]. The Hammett plot gives a value of –1.6. A plausible mechanism has been postulated.

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ICl Ru(III) . [HClO₄], (>0,01 M) [H⁺]. -1,6. .

     

Kinetics of oxidation of isopropanol by IO4? catalyzed by metal ions

The kinetics of oxidation of isopropanol (IPA) by IO ₄ ^– in the presence of Os(VIII), Ru(III) and mixture of Os(VIII) and Ru(III) has been studied. The catalytic effect was found to be in the order Os(VIII)

IO ₄ ^– Os(VIII), Ru(III) Os(VIII) Ru(III), . : Os(VIII)     

Manganese(III) oxidation of L‐serine in aqueous sulfuric acid medium: Kinetics and mechanism

Kinetics and mechanism of oxidation of L‐serine by manganese(III) ions have been studied in aqueous sulfuric acid medium at 323 K. Manganese(III) sulfate was prepared by an electrolytic oxidation of manganous sulfate in aqueous sulfuric acid. The dependencies of the reaction rate are: an unusual one and a half‐order on [Mn(III)], first‐order on [ser], an inverse first‐order on [H⁺], and an inverse fractional‐order on [Mn(II)]. Effects of complexing agents and varying solvent composition were studied. Solvent isotope studies in D₂O medium were made. The dependence of the reaction rate on temperature was studied and activation parameters were computed from Arrhenius‐Eyring plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 525–530, 1999     

Preparation and Structure of Cerium Titanates Ce2TiO5, Ce2TiO7, and Ce4Ti9O24

Compounds Ce₂TiO₅, Ce₂Ti₂O₇, and Ce₄Ti₉O₂₄ were prepared by heating appropriate mixtures of solids containing Ce⁴⁺ and Ti³⁺ or Ti which were placed in a platinum-silica-ampoule combination at T = 1250°C (3d) under vacuum. The new compounds were characterized by powder patterns. We obtained Ce₂TiO₅ which is isotypic to La₂TiO₅ and crystallizes in the Y₂TiO₅-type (space group Pnma) with a = 10.877(6) Å, b = 3.893(1) Å, c = 11.389(8) Å, Z = 4. Ce₂Ti₂O₇ is isotypic to La₂Ti₂O₇ and crystallizes in the monoclinic Ca₂Nb₂O₇ type (space group P 2₁) with a = 7.776(6) Å, b = 5.515(4) Å, c = 12.999(6) Å, β = 98.36(5), Z = 4. The compound Ce₄Ti₉O₂₄ crystallizes orthorhombic with a = 14.082(4) Å, b = 35.419(8) Å, c = 14.516(4) Å, Z = 16. The new cerium titanate Ce₄Ti₉O₂₄ is isotypic to Nd₄Ti₉O₂₄ (space group Fddd (No. 70)) which represents a novel type of structure.     

The OsO4-mediated oxidative cleavage of olefins catalyzed by alternative osmium sources

The OsO₄-mediated oxidative cleavage of olefins is compatible with alternative, easier-to-handle osmium sources. Four different osmium sources were employed with favorable results.     

Kinetics and mechanism of hydrogen peroxide oxidation of chromone-3-carboxaldehydes in aqueous acid and micellar media

Oxidation of chromone-3-carboxaldehyde (CCA) and substituted analogues by H₂O₂ has been carried out in aqueous acid (HCl and H₂SO₄) and micellar media. Reaction kinetics indicated order in [CCA] as well as [H₂O₂] to be unity while it is a fraction (1 > n > O) in [acid]. Reaction rates were found to be faster in the solvents of low-dielectric constant (D). Added salt (KCl or (NH₄)₂SO₄) increased the rate of oxidation marginally. On the basis of observed linearity of Amis plot and marginal positive salt effect, protonated CCA (enol form of CCA, a cation) and H₂O₂ (neutral molecule) were considered as reactive species in the rate limiting step. Reaction rates were found to be enhanced significantly in anionic and nonionic micellar (sodium dodecylsulfate (SDS) and Triton X-100 (Tx), respectively) media. However, cationic micelles [cetyl trimethyl ammonium bromide (CTAB)] indicated marginal retardation effect. Effect of anionic and cationic micelles has been interpreted in terms of electrostatic interactions, while that of nonionic micelles in terms of hydrophobic interactions. Structure-reactivity correlations have been interpreted by Hammett's equation. Negative “ρ” (reaction constant) values indicated cationic transition state. © 1996 John Wiley & Sons, Inc.     

The He(I) photoelectron spectra of OsO4, and RuO4

The photoelectron spectra of ruthenium tetroxide and osmium tetroxide excited by He(I) radiation are reported. From their interpretation it follows that the first two strong low energy transitions in the electronic absorption spectra of OsO₄, RuO₄, TcO^?₄, ReO^?₄, MoO^2?₄ and WO^2?₄ can be assigned to t₁ → 2e and 3t₂ → 2e respectively.     

Kinetics and mechanism of osmium(VIII) mediated cerium(IV) oxidation of dimethylsulfoxide in aqueous sulfuric acid

Under the experimental conditions [DMSO]T [CeIV]T [Os]T the kinetics of oxidation of dimethylsulfoxide (DMSO) to dimethylsulfone (DMSO2) have been followed at different temperatures (40–55°C) in 1.0 mol dm–3 sulfuric acid media. The rate of disappearance of [CeIV] shows a first-order dependence on both [Os]T and [DMSO]T and zeroth-order kinetics with respect to [CeIV]. The suggested mechanism involves oxidation of DMSO by OsVIII in a rate-determining step through an outer-sphere mechanism, followed by rapid regeneration of OsVIII by CeIV from OsVI. The rate law conforms to: –d[CeIV]/dt=k0=k[Os]T[DMSO]T. The values of k and the activation parameters are: 102k=(4.9 ± 0.10) mol–1 dm3 s–1 at 40°C, [H2SO4] =1.0 mol dm–3;H=58±3kJmol–1, S= –88 ±5JK–1mol–1.     

Kinetics and mechanism of oxidation of sulfanilic acid by periodate ion in aqueous medium

Results of kinetic studies of the sodium metaperiodate oxidation of sulfanilic acid in aqueous medium are discussed. A mechanism for the formation of azobenzene-4,4-disulfonic acid, isolated and characterized as its S-benzylisothiuronium derivative, is proposed.

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. -4,4- , S- .

     

H3PW12O40催化水相介质中苯并恶嗪和喹唑啉合成（英文）简

A heteropolyacid efficiently catalyzed the cyclocondensation reaction of 2-aminobenzamide and salicylamide with aldehydes and ketones to afford good yields of benzoxazine and quinazoline ring systems in an aqueous medium. The method gives clean reactions, has simple workup procedure, and uses environment friendly conditions.