Oxidation of tantalum metal by lead chromate

Differential thermal analysis and gravimetry techniques have been used in the investigation of the tantalum/lead chromate pyrotechnic composition for a range of fuel/oxidant mixtures. Studies include investigation of tantalum and lead chromate individually as well as co-precipitated mixtures, when heated up to approximately 900°C in air and in nitrogen. The kinetics of oxidation of metallic fuels by metal oxides is one of the most important parameters in determining the utility of any metal oxide system in pyrotechnic applications. Infrared spectroscopy has been utilised in an attempt to characterise the reaction products in air and in nitrogen atmosphere.     

Oxidation of perfluoronaphthols by lead tetraacetate and lead dioxide

Depending on the reaction conditions, oxidation of perfluoronaphthols by Pb(OAc)₄ proceeds by two routes. Under mild conditions (20°C) oxidation leads to the products of dimerisation of perfluoronaphthoxy radicals. At a higher temperature (80°C) the reaction leads to acetoxydienones. The mechanistic aspects of oxidation of perfluoronaphthols by Pb(OAc)₄ are discussed.     

Oxidation with metal oxides—VIII: Oxidation of bisphenylhydrazones of 1,2-diketones with nickel peroxide

The nickel peroxide oxidation of bisphenylhydrazones of 1,2-diketones gives rise to a variety of products such as bisphenylazoolefins, phenylazopyrazoles and triazoles, depending on the reaction conditions. Thus, glyoxal bisphenylhydrazone in benzene at room temperature gave bisphenylazoethylene5a, whereas methylglyoxal bisphenylhydrazone gave a mixture of bisphenylazoolefin10a and phenylazopyrazole14a. The oxidation of phenylglyoxal bisphenylhydrazone, on the other hand, gave a mixture of the triazole33 and a tetraazapentalene derivative40. Reasonable mechanisms for the formation of the various oxidation products have been suggested.     

Oxidation of a PPy-modified tantalum electrode

A tantalum electrode on which polypyrrole (PPy) had been previously formed by electropolymerization was galvanostatically electrolyzed in an aqueous solution of 0.01 wt% phosphoric acid. This process contains the irreversible oxidation of a PPy film, the decomposition of solvent, and the formation of Ta₂O₅ by the reaction of OH^? coming through the PPy film, with Ta electrodes. A three layer-structure (PPy/Ta₂O₅/Ta) was confirmed by electron spectroscopy for chemical analysis (ESCA). A PPy film containing CIO₄^? as dopant [PPy(CIO₄^?)] was significantly deteriorated in comparison with PPy(TsO^?) at the electrolysis. Therefore, the (PPy(TsO^?)/Ta₂O₅/Ta) system showed better electrical characteristics as a capacitor than the (PPy(CIO₄^?)/Ta₂O₅/Ta) system showed better electrical characteristics as a capacitor than the (PPy(ClO₄^?)/Ta₂O₅/Ta) system.     

Oxidation with metal oxides—VI : Oxidation of benzoylhydrazones of aldehydes,ketones and 1,2-diketones with nickel peroxide

Benzaldehyde benzoylhydrazone on oxidation with nickel peroxide gives a mixture of 2,5-diphenyl-1,3,4-oxadiazole and nickel-bis-benzaldehyde benzoylhydrazone. Similarly, p-tolualdehyde benzoylhydrazone, o-methoxybenzaldehyde benzoylhydrazone and anisaldehyde benzoylhydrazone give the corresponding 1,3,4-oxadiazole derivatives and nickel complexes. Acetophenone benzoylhydrazone on the other hand, gives a mixture of acetophenone and methylbenzylidene-∞-dibenzoyl-amino-∞-methylbenzylamine. Similarly, propiophenone benzoylhydrazone and benzophenone benzoylhydrazone give the corresponding ketones and Schiff's bases. Biacetyl bisbenzoylhydrazone and benzil bisbenzoylhydrazone on oxidation with nickel peroxide in chloroform give the corresponding enol-benzoates and nickel complexes. In contrast, phenylmethylglyoxal bisbenzoylhydrazone gives only the enolbenzoate under analogous conditions. Phenylglyoxal bisbenzoylhydrazone on oxidation with nickel peroxide gives a mixture of products consisting of 1-dibenzoylamino-4-phenyl-1,2,3-triazole, 1-benzoylamino-4-phenyl-1,2,3-triazole and nickel-bis-phenyl-2-(5-phenyl-1,3,4-oxadiazolyl)-ketone benzoylhydrazone. Similarly, 4-methoxyphenylglyoxal bisbenzoylhydrazone gives a mixture of triazoles and the corresponding nickel complex.     

Determination of metal traces in tantalum by proton activation analysis

Procedures for determining traces of calcium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum and tungsten in tantalum are described utilizing 11 MeV proton activation. The instrumental method of analysis with the use of a Ge(Li) detector and the radiochemical separation of the corresponding fractions are described. The formula for the calculation of the concentration of traces with the use of thick target yields is given. Experimental data on the thick target yields of radioisotopes⁴⁴Sc,⁵²Mn,⁵⁶Co,⁶⁵Zn,^93mMo,⁹⁶Tc are presented. Based on the experimental data, the detection limits are estimated at 1–10 ppb for the above mentioned metal traces in tantalum. The successful solution of the task of the simultaneous determination of nine elements in tantalum confirms the wide applicability of proton activation analysis.     

Oxidation of caffeine with hydrogen peroxide catalyzed by metalloporphyrins

The biomimetic oxidation of caffeine with hydrogen peroxide using metalloporphyrins as catalysts, which are known to be good biomimetic models of cytochrome P450 enzymes, is investigated. The two manganese porphyrins tested, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III), [Mn(TDCPP)Cl], and chloro [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III), [Mn(TPFPP)Cl], afford high conversions of caffeine for all substrate/catalyst molar ratios. Selectivity was found to be dependent on the catalyst employed, and a new spiro racemic compound is described and fully characterized in the solid state from X-ray diffraction studies.     

Spectrophotometric determination of niobium in tantalum metal

A new method for the determination of traces of niobium in tantalum metal has been developed. The niobium is separated from tantalum by solvent extraction with hexone from hydrofluoric acid-hydrochloric acid solution, and from molybdenum and tungsten by solvent extraction with oxine-chloroform solution from ammoniacal citrate solution. The niobium is then determined by the spectrophotometric thiocyanate method.     

Oxidation of γ-stannyl sulfides by monochloramine CB and hydrogen peroxide

The first γ-trimethylstannyl sulfimide, Me³Sn(CH₂)₃S(=NSO₂Ar)C₅H₁₁-n, was synthesized by oxidative imination of Me₃Sn(CH₂)₃SC₅H₁₁-n with ArSO₂(Na)Cl (Ar=C₆H₄Cl-4). Oxidation of γ-trimethylstannyl sulfimide by an alkaline solution of H₂O₂ gave γ-trimethylstannyl sulfoximide, Me₃Sn(CH₂)₃S(O)(=NSO₂Ar)C₅H₁₁-n, and γ-trimethylstannyl sulfone, Me₃Sn(CH₂)₃SO₂C₅H₁₁-n, the latter compound resulting from hydrolysis of the arylsulfimide group. Oxidation of stannyl sulfide by hydrogen peroxide yielded γ-trimethylstannyl sulfoxide, Me₃Sn(CH₂)₃S(O)C₅H₁₁-n (under mild conditions) or γ-trimethylstannyl sulfone (under more severe conditions). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 371–374, February, 1997.     

Determination of traces of copper and silver in tantalum metal by anodic stripping voltammetry

Summary Nanogram quantities of copper and silver are electrodeposited on a glassy carbon electrode from a hydrofluoric-nitric acid solution containing 0.5–1 g of tantalum. The deposit is then anodically removed in 0.1M hydrochloric acid, a current-voltage curve being recorded. The impurities at the parts per billion level in high-purity tantalum metal powder are determined within 3 hours.

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Zusammenfassung Nanogrammengen Kupfer und Silber werden aus flußsaurer, salpetersaurer Lösung von 0,5–1 g Tantal elektrolytisch an einer Elektrode aus glasartigem Kohlenstoff abgeschieden. Während der anodischen Auflösung in Salzsäure wird eine Stromspannungskurve geschrieben. Verunreinigungen in der ppb-Größenordnung in hochreinem Tantalpulver lassen sich so innerhalb 3 Stunden bestimmen.

     

Oxidation of organic compounds by hydrogen peroxide using polymer-anchored azo-metal catalysts

Polymer-anchored azo complexes of Cu(II) and Ni(II) were synthesized by the reaction of chloromethylated polystyrene, 3-aminophenol, and 1-nitroso-2-naphthol with the metal chlorides. The catalytic activities of these complexes were studied in the oxidation of various organic substrates including alkenes, alcohols, alkanes, and sulfides with 30 % aqueous hydrogen peroxide. The structures of both catalysts have been investigated by physiochemical methods. Both catalysts proved to be very stable and could be reused more than five times without significant loss of activity. Furthermore, these catalysts require very mild reaction conditions.     

Oxidation of aliphatic alcohols with the lead tetraacetate—metal halide system under mechanical activation

The mechanochemical oxidation ofn-pentanol,n-hexanol, andn-octanol with the Pb(OAc)₄-MHal system (M=Li, K; Hal=Cl, Br) in the absence of a solvent affords esters. and secondary alcohols with the composition C₈H₁₇OH and C₉H₁₉OH give ketones. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1870–1873, November, 2000.     

Oxidation of the methyl ester of O-amino-p-tert-butylphenol by lead dioxide

Conclusions As a result of the oxidation of the methyl ester of O-amino-p-tert-butyl-phenol with lead dioxide, two products were isolated and characterized -2,2-dimethoxy-5,5-di-tert-butylazobenzene and 2,6-di-tertbutylphenazine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 1851–1854, October, 1966.     

Oxidation of sulfoxides by hydrogen peroxide,catalyzed by methyltrioxorhenium(VII)

Dialkyl and diaryl sulfoxides are oxidized to sulfones by hydrogen peroxide using methyltrioxorhenium as the catalyst. The reaction rate is negligible without a catalyst. The kinetics study was performed in CH3CN-H2O (4:1 v/v) at 298 K with [H+] at 0.1 M, conditions which make the equilibration between MTO and its peroxo complexes more rapid than the oxygen-transfer step. The values for the rate constant for the oxygen-transfer step lie in the range 0.1-3 L mol-1 s-1. The rate constants were significantly smaller than for the oxidation of sulfides to sulfoxides. A study of ring-substituted diaryl sulfoxides yielded kinetics results that are consistent with nucleophilic attack of the sulfur atom on the peroxide oxygen group since rho = -0.65. The results cited refer to the reactions of the diperoxo from the catalyst, MeRe(O)(eta 2-O2)2H2O. The monoperoxo complex showed no measurable reactivity toward sulfoxides, in contrast with the situation for nearly every other substrate. That unusual finding suggests a hydrogen-bonded interaction between the substrate and the diperoxorhenium compound which cannot exist with the monoperoxo compound.