Colloidal catalysts based on iron(III) oxides. 1. Decomposition of hydrogen peroxide

The catalytic activity of a colloidal catalyst based on iron(III) oxides in decomposition of H₂O₂ is studied. The catalyst is obtained by hydrolysis followed by peptization of FeCl₃ · 6H₂O salt in water in the presence of 1% ethanol. The structure, composition, and size of colloidal particles of the catalyst are studied by the methods of Mössbauer spectroscopy, X-ray fluorescence, X-ray diffraction, and transmission electron microscopy. The obtained catalyst is based on α-Fe₂O₃ crystals with an admixture of other crystalline structures of iron oxides and carbon-containing compounds. The activity of the catalyst with respect to H₂O₂ decomposition undergoes nonlinear and nonmonotonic variations and its particle size enlarges beginning from 1 to 3 nm with increasing initial concentration of FeCl₃ · 6H₂O. The catalyst obtained under optimal conditions exhibits high activity corresponding to the most efficient agents of H₂O₂ decomposition.     

Efficient solvent-free iron (III) catalyzed oxidation of alcohols by hydrogen peroxide

Selective oxidation of secondary and benzylic alcohols was efficiently accomplished by H₂O₂ under solvent-free condition catalyzed by FeBr₃. Secondary alcohols are selectively oxidized even in the presence of primary ones. This method is high yielding, safe and operationally simple.     

Cement-containing catalysts of ozone decomposition based on iron oxides

Cement-containing catalysts of ozone decomposition were synthesized on the basis of iron oxides obtained by ozonation of iron-containing aqueous solutions. X-ray diffraction analysis and Mössbauer spectroscopy showed that α-Fe₂O₃ occurs in the catalyst as highly dispersed nanoparticles. The catalysts obtained are efficient in the reaction of ozone decomposition and are as active as the best representatives of cement-containing catalysts of the GTT type.     

Some reactions of iron (III) and chromium (III) fluorides with oxides

Reactions of FeF₃ with several oxides at elevated temperatures are described. Reaction products were usually Fe₂O₃ and the fluoride of the other element. With higher valency elements complete fluorine exchange did not always occur and oxyfluorides were formed. Intermediates in the reactions include oxyfluorides and mixed oxides, again only found with higher valency elements. Some shorter studies on the reaction of CrF₃ with oxides are included for comparisons, the reactions observed being generally similar.     

Organic iodine(V) compounds as terminal oxidants in iron(III) phthalocyanine catalyzed oxidation of alcohols

The pseudocyclic iodine(V) oxidants, such as esters of iodoxybenzoic acid (IBX-esters) and 2-iodylphenol ethers, can serve as stable and efficient sources of oxygen in catalytic oxidations, and their reactivity is similar to the commonly used thermally unstable and potentially explosive iodosylbenzene. In a specific example, primary or secondary benzylic alcohols are selectively oxidized by isopropyl IBX-ester in the presence of μ-oxo-(tetra-tert-butylphthalocyaninato)iron(III) (0.1 mol equiv) in dichloromethane at room temperature in 0.5-2 h to afford the respective carbonyl compounds in 100% conversion and preparative yields 91-95% after column chromatography.     

Rhodium(III) catalyzed oxidation of cyclic ketones by alkaline hexacyanoferrate(III)

The kinetics of the oxidation of 2-methyl cyclohexanone and cycloheptanone with Fe(CN)₆ ³⁻ catalyzed by RhCl₃ in alkaline medium was investigated at four temperatures. The rate follows direct proportionality with respect to lower concentrations of hexacyanoferrate(III) ion, but tends to become zero order at higher concentrations of the oxidant, while the reaction shows first-order kinetics with respect to hydroxide ion and cyclic ketone concentrations. The rate shows a peculiar nature with respect to RhCl₃ concentrations in that it increases with increase in catalyst at low catalyst concentrations but after reaching a maximum, further increase in concentration retards the rate. An increase in the ionic strength of the medium increases the rate, while increase in the Fe(CN)₆ ⁴⁻ concentration decreases the rate.     

Regularities of formation of iron(III) nanocrystalline oxides and oxyhydroxides during oxidation of iron(II) compounds in an alkaline medium

Regularities of formation of nanocrystalline iron(III) oxides and oxyhydroxides via oxidation of iron(II) compounds in an alkaline pH range (pH ≥ 12) were studied using pH and E _h measurements, chemical analysis, electron microscopy, and X-ray diffraction. When the molar ratio [OH⁻]/[Fe^II] ∼ 2 (pH ∼ 12–12.5), the oxidation process yields cube-shaped magnetite Fe₃O₄ particles. An excess of an alkaline agent with an overstoichiometric concentration equal to or higher than 0.5 mol/L (pH ≥ 13.5) induces the formation of anisotropic particles of nanocrystalline goethite α-FeOOH over the entire range of the synthesis parameters studied. Reaction products (Fe₃O₄ and/or α-FeOOH) are formed immediately as the initial Fe(OH)₂ starts oxidizing by the dissolution-oxidation-precipitation mechanism near the surface of Fe(OH)₂ precursor particles. Carbonate ions considerably change the structure and shape of newly formed α-FeOOH particles.     

Chiral Mn(III) salen catalyzed oxidation of hydrocarbons

Four chiral manganese(III)-salen complexes (1–4) were employed as catalysts in the oxidation of hydrocarbons at room temperature using pentafluoroiodosylbenzene as terminal oxidant. The reactions were carried out in acetonitrile and dichloromethane. Norbornene has been selectively oxidized to exo-epoxynorborane in 85% yield. At room temperature, oxygenation of cyclohexane up to 14% in acetonitrile medium has also been achieved.     

Spinels as heterogeneous catalysts for oxidation of water to dioxygen by tris-bipyridyl complexes of iron(III) and ruthenium(III)

Cobaltites, ferrites and chromites of some metals were found to be catalytically active in oxidation of water to dioxygen by trisbipyridyl complexes of Fe(III) and Ru(III). The possible catalytic action of surface compounds of hydroxide type is discussed.

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Aerobic oxidation of benzylic aldehydes to acids catalyzed by iron （Ⅲ） meso-tetraphenylporphyrin chloride under ambient conditions

Highly efficient aerobic oxidation of benzylic aldehydes to the corresponding acids catalyzed by iron (Ⅲ) meso-tetraphe- nylporphyrin chloride (Fe(TPP)Cl) under ambient conditions was developed.The catalyst has been proved to be an excellent catalyst for the system in the presence of molecular oxygen and isobutryaldehyde at room temperature.     

Oxygen catalyzed mobilization of iron from ferritin by iron(III) chelate ligands

Tridentate chelate ligands of 2,6-bis[hydroxy(methyl)amino]-1,3,5-triazine family rapidly release iron from human recombinant ferritin in the presence of oxygen. The reaction is inhibited by superoxide dismutase, catalase, mannitol and urea. Suggested reaction mechanism involves reduction of the ferritin iron core by superoxide anion, diffusion of iron(II) cations outside the ferritin shell, and regeneration of superoxide anions through oxidation of iron(II) chelate complexes with molecular oxygen.     

Iridium(III) catalyzed oxidation of cyclic ketones by cerium(IV)

IrCl₃which is considered to be a sluggish catalyst in alkaline media, was found to surpass the catalytic efficiency of even osmium and ruthenium in acidic media in the oxidation of cyclopentanone and 2-methylcyclohexanone by cerium(IV) sulphate in aqueous sulphuric acid medium. It was observed that the order of the reaction shows direct proportionality with respect to low concentrations of the oxidant and alcohols, but tends to become independent of concentration at higher concentrations. On increasing the concentrations of externally added Cl^-, H⁺ and Ce^IIIions, the rate of the reaction decreases sharply initially but the decrease in rate becomes less prominent as their concentration is increased. The rate of reaction is directly proportional with respect to IrCl₃concentrations. Kinetic data suggest that the production of Ce^III ion occurs before the rate-determining step. Parameters such as the energy of activation, free energy of activation and entropy data collected at five different temperatures suggest that cyclopentanone forms the activated complex more easily.     

Methane oxidation catalysts based on the perovskite-like complex oxides of cobalt and nickel

Russian Chemical Bulletin - The results of the last 20 year research on the development of rare earth cobaltate- and nickelate-based catalysts of the partial oxidation of methane (POM) are...     

Benzylic oxidation catalyzed by dirhodium(II,III) caprolactamate

[reaction: see text] Dirhodium caprolactamate [Rh2(cap)4] is an effective catalyst for benzylic oxidation with tert-butyl hydroperoxide (TBHP) under mild conditions. Sodium bicarbonate is the optimal base additive for substrate conversion. Benzylic carbonyl compounds are readily obtained, and a formal synthesis of palmarumycin CP2 using this methodology is described.     

Preparation of iron molybdate catalysts for methanol to formaldehyde oxidation based on ammonium molybdoferrate(II) precursor

It was demonstrated that iron molybdate catalysts for methanol oxidation can be prepared using Fe(II) as a precursor instead of Fe(III). This would allow for reduction of acidity of preparation solutions as well as elimination of Fe(III) oxide impurities which are detrimental for the process selectivity. The system containing Fe(II) and Mo(VI) species in aqueous solution was investigated using UV–Vis spectroscopy. It was demonstrated that three types of chemical reactions occur in the Fe(II)–Mo(VI) system: (i) formation of complexes between Fe(II) and molybdate(VI) ions, (ii) inner sphere oxidation of coordinated Fe(II) by Mo(VI) and (iii) decomposition of the Fe–Mo complexes to form scarcely soluble Fe(III) molybdate, Mo(VI) hydrous trioxide and molybdenum blue. Solid molybdoferrate(II) prepared by interaction of Fe(II) and Mo(VI) in solution was characterized by EDXA, TGA, DTA and XRD and a scheme of its thermal evolution proposed. The iron molybdate catalyst prepared from Fe(II) precursor was tested in methanol-to-formaldehyde oxidation in a continuous flow fixed-bed reactor to show similar activity and selectivity to the conventional catalyst prepared with the use of Fe(III).     

Determination of hexacyanoferrate based on its catalytic influence on the oxidation of p-phenylenediamines by iron(III)

Summary Both hexacyanoferrate(III) and hexacyanoferrate(II) catalyze the oxidation of p-phenylenediamines by iron(III)_aq. The rate of this reaction in the presence of a sample with an unknown amount of hexacyanoferrate is compared with the reaction rate of solutions containing well defined concentrations of this substance. In this way, hexacyanoferrate can be determined photometrically down to <10^–9 mol/l. Although this procedure is very sensitive, the analysis can be performed with a simple photometer. Absorbance changes >0.2 can easily be obtained in 1 cm cuvettes, even at extremely small concentrations of hexacyanoferrate, because it is not an absorbance proportional to the concentration of hexacyanoferrate but rather the formation rate of p-semiquinonediimine which enables the quantitative determination of hexacyanoferrate.     

Recent advances in iron(III) chloride catalyzed synthesis of heterocycles

Heterocyclic compounds particularly five, six and seven membered ring containing heterocycles are the most abundant which constitute a staggeringly diverse and important class of molecules that occur ubiquitously in a variety of synthetic drugs, bioactive natural products, pharmaceuticals and agrochemicals. Owing to the glorious past and impressive present of the biologically active heterocyclic scaffolds, these skeletons have long been a subject of immense interest. Hence, substantial efforts have been made to the development of new and innovative synthetic strategies for the synthesis of these heterocycles involving use of different metal catalysts, organic and inorganic reagents etc. Among the different types of metal catalysts used, iron catalysts are one of the cheap and easily available. In recent time, several new and innovative iron(III) chloride catalyzed synthesis of heterocycles with structural diversity are coming in the forefront of the literature by the scientific community. This review highlights the advancements made so far by iron(III) chloride for the synthesis of different assemblies of small heterocycles covering the year 2014–2018.     

Kinetics of the Ru(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The rate of oxidation of formaldehyde is directly proportional to [Fe(CN) _3– ⁶ ] while that of acetaldehyde is proportional tok[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]}, wherek, k andk are rate constants. The order of reaction in acetylaldehyde is unity while that in formaldehyde falls from 1 to 0. The rate of reaction is proportional to [Ru(III)] _T in each case. A suitable mechanism is proposed and discussed.

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Die Kinetik der Ru(III)-katalysierten Oxidation von Formaldehyd und Acetaldehyd mittels alkalischem Hexacyanoferrat(III)

Zusammenfassung Die Untersuchung der Kinetik erfolgte spektrophotometrisch. Die Geschwindigkeitskonstante der Oxidation von Formaldehyd ist direkt proportional zu [Fe(CN) _3– ⁶ ], währenddessen die entsprechende Konstante für Acetaldehyd proportional zuk[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]} ist, wobeik,k undk Geschwindigkeitskonstanten sind. Die Reaktionsordnung für Acetaldehyd ist eine erste, die für Formaldehyd fällt von erster bis zu nullter Ordnung. Die Geschwindigkeitskonstante ist in jedem Fall proportional zu [Ru(III)] _T . Es wird ein passender Mechanismus vorgeschlagen.

     

Composition catalysts of ethylbenzene oxidation based on bis(acetylacetonato)nickel(ii) and phase transfer catalysts as ligands 2. Quaternary ammonium salts

New composition catalysts based on bis(acetylacetonato)nickel(II) and ammonium salts, R₄NBr (Me_4NBr,n-C₁₆H₃₃Me₃NBr) for selective oxidation of aromatic hydrocarbons to the appropriate hydroperoxides have been introduced. It is demonstrated that the rate, selectivity, and degree of conversion of ethylbenzene to -ethylphenylhydroperoxide in this case are significantly higher than those observed for monodentate and macrocyclic ligands used as activating additives. The data obtained are in good agreement with the suggestion that the selective catalyst is formed in the course of ethylbenzene oxidation as a result of regioselective interaction of dioxygen with the -carbon atom of the acetylacetonate ligand controlled by R₄NBr.For communication 1 see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1412–1417, August, 1994.