Formation of palladium nanoparticles in olefin oxidation with iron(III) aqua ions in the presence of the Pd/ZrO2/SO4 metallic catalyst

The reactions of the Pd/ZrO₂/SO₄-catalyzed oxidation of ethylene, propene, and but-1-ene in a 0.1–1.5 M solution of perchloric acid with iron(III) aqua ions to carbonyl compounds, viz., acetaldehyde, acetone, and methyl ethyl ketone, respectively, were studied. The formation of palladium nanoparticles (5 nm) in solution on contact of the initial heterogeneous Pd/ZrO₂/SO₄ catalyst with perchloric acid was proved by transmission electron microscopy. The palladium nanoparticles are assumed to play the key role in olefin oxidation with the iron(III) aqua ions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 627–632, April, 2006.     

Catalytic oxidation of Fe(II) aqua ions with atmospheric oxygen in the presence of Pd(II) tetraaqua complex and an aromatic compound

The effect of a series of aromatic compounds (toluene, benzyl alcohol, benzonitrile, phenylacetonitrile, and o-cyanotoluene) in a concentration of 0.01 M on the oxidation of Fe(II) aqua ions with oxygen in the presence of Pd(II) tetraaqua complex at 25–70°C was revealed. In the presence of an aromatic compound, palladium black is not formed, which results in an increased yield of Fe(III) in the Pd-catalyzed oxidation of Fe(II) with oxygen in a perchloric acid medium. A scheme involving the formation of a complex of palladium species in an intermediate oxidation state with arene and molecular oxygen was suggested.     

Role of Pd(0) particles in oxidation of lower olefins in the catalytic system Fe(III)_Pd/ZrO<Subscript>2</Subscript>

Oxidation of metallic Pd(0) particles applied onto an oxide support with Fe(III) ions in a concentration not exceeding 0.06 M at 70°C was studied. In contrast to palladium black, with the supported catalyst Pd/ZrO₂ Pd(II) is formed in the solution in the concentration corresponding to the thermodynamic equilibrium. With an increase in the initial Fe(III) concentration, the equilibrium yield of Pd(II) increases. The initial reaction rate grows with an increase in the weight of the initial Pd-containing catalyst and in the initial Fe(III) concentration. The revealed kinetic relationships of the dissolution of Pd(0) in the reaction with Fe(III) aqua ions allow a conclusion that, in oxidation of lower olefins C₂-C₄ in the catalytic system Fe(III)_Pd/ZrO₂ in aqueous solution, Pd(II) is regenerated in the catalytic cycle by oxidation of Pd(I) species, rather than of Pd(0), with Fe(III) aqua ions.     

Intramolecular hydroamination of unactived olefins with Ti(NMe2)4 as a precatalyst

Commercially available Ti(NMe(2))(4) has been used effectively as a precatalyst in a facile protocol for the intramolecular hydroamination of aminoalkenes to yield pyrrolidine and piperidine heterocyclic products with isolated yields up to 92%. Geminally substituted substrates display the highest reactivity. This precatalyst is also effective for the hydroamination of activated internal alkenes, providing access to more complex heterocyclic target molecules.     

Phosphoprotein electrophoresis in the presence of Fe(III) ions

Preparation of affinity polyacrylamide gels containing immobilized Fe(III) ions for the separation of proteins exhibiting metal ion binding properties is described. The presented method enables uniform distribution of immobilized metal ions in the affinity part of the polyacrylamide separating gel. Affinity gels prepared by this way are suitable to follow the effect of different concentrations of metal ions immobilized in polyacrylamide gel on a protein electrophoretic behavior. Polyacrylamide gels containing immobilized Fe(III) ions were used to study the electrophoretic behavior of two model proteins differing in their phosphate group content: chicken ovalbumin and bovine α‐casein. For the electrophoretic separation, both the native and the denaturating conditions were used.     

Investigation of the state of palladium in the Pd/SO4/ZrO2 system by diffuse-reflectance IR spectroscopy

The Pd/ZrO₂ and Pd/SO₄/ZrO₂ systems were investigated by diffuse-reflectance IR spectroscopy using CO as the probe molecule. For the Pd/ZrO₂ system, the behavior of the metal is characteristic of the weak metal-support interaction. Intense bands attibuted to the bridging CO species indicate the formation of large metal particles in the reduced systems. Modification of the ZrO₂ support with SO₄ ^2? anions leads to an increase in the metal—support interaction and makes the metal more resistant to reduction. On the surface promoted by SO₄ ^2? anions, metal particles with a positive charge (Pd⁺ and Pd^δ+) were observed. The smaller the size of the metal clusters and the higher degree of oxidation of sulfur, the stronger the influence of acidic protons and surface sulfur compounds on the metal.     

Catalysis by Ir(III), Rh(III) and Pd(II) metal ions in the oxidation of organic compounds with H2O2

Catalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H₂O₂. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetics of arylation of olefins by Pd(OAc)2 in benzene

. , -. Al₂O₃ .

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The adsorption of eugenol on Al₂O₃ in the isomerization process has been studied by the EPR method. As a result of eugenol adsorption on Lewis acid centers in the presence of molecular oxygen, an organic cation radical is formed. Eugenol isomerization on Al₂O₃ occurs via a radical mechanism.

     

CO oxidation to CO2 by Mo?V?P heteropolyacid in the presence of an aqua complex of Pd(II)

Kinetic oxidation of CO to CO₂ by Mo–V–P heteropolyacid in the presence of an aqua complex of Pd(II) has been studied. The reaction is suggested to involve the participation of carbonyl complexes of Pd(I). It has been established that VO ₂ ⁺ ions formed in HPA dissociation inhibits the reaction.

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CO CO₂ - Pd(II). Pd(I). , VO ₂ ⁺ , , .

     

Catalytic carbonylation of ethylene in the presence of the Pd(acac)2-m-Ph2PC6H4SO3Na(H)-AcOH system

Catalytic systems based on phosphine complexes of palladium have been developed for synthesizing propionic acid (monocarbonylation) and alternating (11) ethylene-carbon monoxide copolymers,i.e., polyketones (polycarbonylation).m-(Diphenylphosphino)benzenesulfonic acid or its sodium salt were used as ligands. Monocarbonylation proceeds at atmospheric pressure in dioxane or acetic acid solvents. Under high pressure, the reaction pathway can change from monocarbonylation, which occurs in the presense of the sodium salt of the ligand, to polycarbonylation when the sodium ion at the sulfo group is completely replaced by a proton. This change in reaction selectivity is observed when the process is performed in acetic acid. When the ligand is present both in the acid and the neutral form, products of di- and oligocarbonylation are formed along with propionic acid and the polyketone. These products were characterized by¹H and¹³C NMR spectra as alternating keto acids C₂H₅(COCH₂CH₂) _n COOH, wheren=1÷3. Kinetic equations were derived for the selective synthesis of propionic acid and polyketones.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 401–404, March, 1994.The authors are grateful to V. A. Zavel'skii who recorded the 1H NMR spectra on a Bruker CXP-200 spectrometer.     

Chemoselective aerobic oxidation of 4-allylanisol by Fe(III) porphyrins in an aqueous system

The allyl moiety of 4-allyl-anisol was oxidized in the presence of a Fe(III) porphyrin derivative to the corresponding α,β-unsaturated aldehyde in an initial oxidation step with perfect chemoselectivity. Molecular oxygen was employed as the sole environmental innocuous oxidant. The reaction was performed in an aqueous buffer/CH₂Cl₂ mixture using the detergent Tween 80 to homogenize the system.     

Kinetics and mechanism of the reaction of Cr(II) aqua ions with benzoylpyridine N-oxide

Aqueous chromium(II) ions, Cr(aq)(2+), react with benzoylpyridine oxide (BPO) much more rapidly than with other pyridine N-oxides previously explored. The kinetics were studied under pseudo-first order conditions with either reagent in excess. Under both sets of conditions, the major kinetic term exhibits first order dependence on limiting reagent, and second order dependence on excess reagent, i.e.k(Cr) = k2(Cr)[BPO][Cr(aq)(2+)]2 (excess Cr(aq)(2+)), and k(BPO) = k2(BPO)[Cr(aq)(2+)][BPO](2) (excess BPO), where k2(Cr) = (6.90 +/- 0.27) x 10(4) M(-2) s(-1) and k2(BPO) = (3.32 +/- 0.28) x 10(5) M(-2) s(-1) in 0.10 M HClO4. The rate constant k2(Cr) contains terms corresponding to [H+]-independent and [H+]-catalyzed paths. In the proposed mechanism, the initially formed Cr(aq)(BPO)(2+) engages in parallel oxidation of Cr(aq)(2+) and reduction of BPO. The latter reaction provides the basis for a convenient new preparative route for the BPO complex of Cr(III).     

The catalytic ozonization of model lignin compounds in the presence of Fe(III) ions

The ozonization of several model lignin compounds (guaiacol, 2,6-dimethoxyphenol, phenol, and vanillin) was studied in acid media in the presence of iron(III) ions. It was found that Fe³⁺ did not influence the initial rate of the reactions between model phenols and ozone but accelerated the oxidation of intermediate ozonolysis products. The metal concentration dependences of the total ozone consumption and effective rate constants of catalytic reaction stages were determined. Data on reactions in the presence of oxalic acid as a competing chelate ligand showed that complex formation with Fe³⁺ was the principal factor that accelerated the ozonolysis of model phenols at the stage of the oxidation of carboxylic dibasic acids and C₂ aldehydes formed as intermediate products.     

Spectrophotometric determination of Fe(II) with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine in the presence of large quantities of Fe(III) and complexing ions

A spectrophotometric method for the determination of Fe(II) in the presence of large amounts (up to 800 mg/l.) of Fe(III) is suggested. The Fe(III) is effectively masked by complexing with fluoride at pH 2.0-2.4 before development of the violet Fe(II) complex with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine. The absorbance is measured at 595 nm. Various commonly occurring ions which complex with Fe(II) and/or Fe(III) do not interfere.