Remarkable substituent effects on the oxidizing ability of triarylbismuth dichlorides in alcohol oxidation

Substituent effects on the oxidizing ability of triarylbismuth dichlorides were examined by intermolecular and intramolecular competition experiments on geraniol oxidation in the presence of DBU. It was found that the oxidizing ability of the dichlorides increases with increasing electron-withdrawing ability of the para substituents, and by introduction of a methyl group at the ortho position of the aryl ligands attached to the bismuth. The intermolecular and intramolecular H/D kinetic isotope effects observed for the competitive oxidation of p-bromobenzyl alcohols indicate that the rate-determining step involves C-H bond cleavage. Several primary and secondary alcohols were oxidized efficiently under mild conditions by the combined use of newly developed organobismuth(V) oxidants and DBU.     

Unique gold chemoselectivity for the aerobic oxidation of allylic alcohols

Gold nanoparticles supported on nanocrystalline ceria has been found to be more active and chemoselective than palladium and gold(core)-palladium(shell) nanoparticles for the aerobic oxidation of allylic alcohols.     

Improvement of the resistance to oxidation of the ecological greases by the additives

This article presents the results of research aimed at improving the oxidation stability of the ecological greases addressed toward application in machines working in the food industry. In order to improve the functional properties of grease, additives that modify the thermal stability have been added. Then, the influence of the additive on the grease resistance to the oxidation was examined. The results of tests of lubricants containing different types of additives are presented. The thermal examinations of the greases were carried out with the use of scanning differential calorimetry techniques. The lubricated properties of greases were investigated with the use of a four-ball tribotester. Based on the results, the relationships between the kind of additive, the resistance to oxidation and the lubricated properties of the grease were analysed, and the relationships between thermal and antiwear properties of grease were identified. Based on the results of this research, a new formulation of grease was proposed, which meets both the ecological needs and the working conditions in the food industry.     

Synthesis of sulfoxides by the hydrogen peroxide induced oxidation of sulfides catalyzed by iron tetrakis(pentafluorophenyl)porphyrin: scope and chemoselectivity

The oxidation of sulfides with H(2)O(2) catalyzed by iron tetrakis(pentafluorophenyl)porphyrin in EtOH is an efficient and chemoselective process. With a catalyst concentration 0.03-0.09% of that of the substrate, sulfoxides are obtained with yields generally around 90-95% of isolated product. With vinyl and allyl sulfides, no epoxidation is observed. With a catalyst concentration between 0.09% and 0.25% of that of the substrate, sulfones are obtained in almost quantitative yield and with the same high chemoselectivity observed in the synthesis of sulfoxides.     

Solubility of additives in polyethylene and aliphatic polyamides. The effect of oxidation

The solubility of diphenylamine, phenyl benzoate and diphenyl methane in high-density polyethylene and various polyamides has been studied as a function of oxidation and of sample annealing.

Oxidative destruction of topological structures forming the non-polar sorption centers and accumulation of new-formed polar groups, participating in sorption of polar compounds, result in complicated dependencies of solubility upon oxidation, in some cases showing minima.     

Remarkable CO-catalyst effect of gold nanoclusters on olefin oxidation catalyzed by a manganese-porphyrin complex

The effect of dodecanethiolate-protected metallic nanoclusters of gold (Au:SC12, 1), silver (Ag:SC12), palladium (Pd:SC12), and platinum (Pt:SC12) on the catalytic activity of Mn(TPP)Cl (TPP = tetraphenylporphinato) was investigated in styrene oxidation with iodosylbenzene. Among the four metal clusters, only Au:SC12 led to appreciable acceleration of the catalytic reaction. The major role of the Au cluster was to regenerate the active catalytic path involving Mn(III) and Mn(V) from the deactivated Mn(IV) species. The binary 1/Mn(TPP)Cl catalyst system showed an absorption spectrum characteristic of Mn(III)-porphyrin after reaction, whereas a catalytically ineffective Mn(IV) species was observed as the sole porphyrin species in the absence of the Au cluster or in the presence of Pd, Ag, and Pt clusters. Accordingly, the slow oxidation reaction with Mn(TPP)Cl was accelerated by the addition of Au:SC12, and complete conversion of Mn(IV) into Mn(III) was observed in the absorption spectrum. 1H NMR inspection of the reaction of Au:SC12 and iodosylbenzene revealed that the surface dodecyl groups were partially oxidized into dodecanal and eliminated from the cluster surface, thereby producing unprotected gold sites on the surface. A reactivation mechanism involving the reaction of the Mn-porphyrin and the oxidant activated on the gold surface is proposed.     

Protection of a protein against irradiation-induced degradation by additives in the solid state

The impact of ionizing radiation on a globular protein (porcine somatotropin, pST) in the solid state was studied using rate of dissolution, high-performance liquid chromatography, and Electron spin resonance (ESR) in the presence of different additives. o-Vanillin stabilized pST against irradiation-induced degradation whereas effects of trolox and isopropyl alcohol were less significant. Stabilization effect of o-vanillin has been related to the energy transfer from pST molecules to the additive which was facilitated by formation of covalent bonds between o-vanillin and pST molecules. Anticorrelation between the level of free radicals and chemical degradation (i.e. degradation increased with decrease in a free radical level) was observed in the presence of o-vanillin.     

Kinetic salt effects in the bromide oxidation by bromate

The kinetic salt effect on the oxidation of bromide ion by bromate have been studied. It is concluded that the salt effects are the result of ion-solvent interactions and seem to be connected not only to the strength of these interactions, as measured by the lowering of solvent activity, but also by the structural characteristics of ion-solvent interactions. This conclusion is based on the use of Pitzer's treatment to estimate the activity coefficients.     

Diselenides and allyl selenides as glutathione peroxidase mimetics. Remarkable activity of cyclic seleninates produced in situ by the oxidation of allyl omega-hydroxyalkyl selenides

A series of aliphatic diselenides and selenides containing coordinating substituents was tested for glutathione peroxidase (GPx)-like catalytic activity in a model system in which the reduction of tert-butyl hydroperoxide with benzyl thiol to afford dibenzyl disulfide and tert-butyl alcohol was performed under standard conditions and monitored by HPLC. Although the diselenides showed generally poor catalytic activity, allyl selenides proved more effective. In particular, allyl 3-hydroxypropyl selenide (25) rapidly generated 1,2-oxaselenolane Se-oxide (31) in situ by a series of oxidation and [2,3]sigmatropic rearrangement steps. The remarkably active cyclic seleninate 31 proved to be the true catalyst, reacting with the thiol via a postulated mechanism in which the thioseleninate 32 is first produced, followed by further thiolysis to selenenic acid 33 and oxidation-dehydration to regenerate 31. In contrast to catalysis with GPx, formation of the corresponding selenenyl sulfide 34 comprises a competing deactivation pathway in the catalytic cycle of 31, as a separate experiment revealed that authentic 34 was a much less effective catalyst than 31. 1,2-Oxaselenane Se-oxide (37), the six-membered homologue of 31, was formed similarly from allyl 4-hydroxybutyl selenide (26), but proved a less effective catalyst than 31. Compounds 31 and 37 are the first examples of unsubstituted monocyclic seleninate esters.     

Remarkable effect of nitrogen dioxide for N-hydroxyphthalimide-catalyzed aerobic oxidation of methylquinolines

Aerobic oxidation of methylquinolines was successfully achieved by the use of N-hydroxyphthalimide/Co(OAc)2/Mn(OAc)2 as catalyst in the presence of a small amount of nitrogen dioxide as an initiator.     

The origin of chemoselectivity in the hydrocarbonylation of alkenes catalysed by trialkylphosphine complexes of rhodium

The formation of monophosphine acyl intermediates explains why PPr(i)(3) and PBu(i)(3) generate aldehydes in alkene hydrocarbonylation reactions carried out in protic solvents, whilst PEt(3), for which the acyl complex contains two phosphines, produces alcohols.     

Cooperative effects in the oxidation of CO by palladium oxide cations

Cooperative reactivity plays an important role in the oxidation of CO to CO(2) by palladium oxide cations and offers insight into factors which influence catalysis. Comprehensive studies including guided-ion-beam mass spectrometry and theoretical investigations reveal the reaction products and profiles of PdO(2)(+) and PdO(3)(+) with CO through oxygen radical centers and dioxygen complexes bound to the Pd atom. O radical centers are more reactive than the dioxygen complexes, and experimental evidence of both direct and cooperative CO oxidation with the adsorption of two CO molecules are observed. The binding of multiple electron withdrawing CO molecules is found to increase the barrier heights for reactivity due to decreased binding of the secondary CO molecule, however, reactivity is enhanced by the increase in kinetic energy available to hurdle the barrier. We examine the effect of oxygen sites, cooperative ligands, and spin including two-state reactivity.     

Characterization of oxidation progress by chemiluminescence: A study of polyethylene with pro-oxidant additives

Non-isothermal chemiluminescence measurements in nitrogen and isothermal measurements in oxygen were used for the evaluation of degradation in pre-oxidized polyethylene either pure or containing Mn-based pro-oxidant additives. The results were compared with infrared spectroscopy data. Chemiluminescence measurements of pure polyethylene and polyethylene with additive made it possible to calculate the set of rate constants, based on the Bolland-Gee oxidation scheme. The oxidation rate constants of polyethylene with additive were significantly higher, while the activation energy of the process appeared lower (65 kJ mol⁻¹), than those of pure polyethylene. The method provides an access to study oxidation processes during the induction period of oxidation when infrared spectroscopy cannot provide sufficient information.     

Exploration of relative chemoselectivity in the hydrodechlorination of 2-chloropyridines

The chemoselectivity of hydrodechlorination in 2-chloropyridine derivatives possessing reduction-sensitive functionalities is examined. The reaction conditions employed tolerate a variety of functionalities illustrating highly chemoselective hydrodechlorination in the presence of nitrile, allyl, terminal olefin, and nitroamine functionalities in excellent yield. Chemoselective deprotection of carboxybenzyl ethers is illustrated in moderate yield.     

Remarkable nanosize effect of zirconia in Au/ZrO2 catalyst for CO oxidation

Nanosize effect of ZrO2 in Au/ZrO2 catalyst was studied by deposition-precipitation of Au nanoparticles in similar sizes (4-5 nm) on ZrO2 nanoparticles of varying sizes. The catalysts were characterized with XRD, TEM, XPS, and nitrogen adsorption to understand the effect of ZrO2 particle size on the catalytic nanostructures. Nanocomposite Au/ZrO2 catalysts consisting of comparably sized Au-metal (4-5 nm) and ZrO2 (5-15 nm) nanoparticles are found advantageous over those containing similarly sized Au-metal but larger ZrO2 (40-200 nm) particles for CO oxidation. This finding may have important implications on the designed preparation of advanced nanostructured catalysts and other chemical materials.     

Torsional effects in the baeyer-villiger oxidation

The regioselectivity in the Baeyer-Villiger oxidation of tetracyclic ketones 1A–C have been interpreted in terms of torsional effects.     

Synthesis of chiral tripeptides by asymmetric hydrogenation of dehydrotripeptides. Remarkable effects of N-protecting groups on stereoselectivity and reactivity

Dehydrotripeptides, X-$\text{C}\text{*}$CH(Rⁱ)-ΔPhe-$\text{C}\text{*}$CH(R^k)COOMe ($\text{3}$: X = ^tBOC-NH,CBZ-NH, CF₃CONH and N₃), were employed for the asymmetric hydrogenation catalyzed by chiral rhodium complexes and it was found that ^tBOC-$\text{3}$ brought about by far the best results. Stereoselective dideuteration of a ^tBOC-$\text{3}$ was successfully performed.