Analytical applications of the reaction of thorium with benzenephosphonic acid

Benzenephosphonic acid quantitatively precipitates thorium as Th(C₆H₅PO₃)₂·3H₂O at pH values as low as 0.5. The compound may be dried at 140° to 180° C and weighed, as a gravimetric means of determining thorium. On ignition, Th (C₂H₅PO₃)₂ 3 H₂O undergoes decomposition at 240° to 300° C to form Th(C₆H₅PO₃)₂·2H₂O, at 450° to 650° C to form Th(HPO₄)₂·2H₂O and finally at 800° to 1000° C to form Th(HPO₄)₂. The latter compound is stable to 1200° C.Potentiometrically (pK₁' = 0.91, pK₂' = 6.41) and spectrophotometrically (pK₁' = 0.96, pK₂' = 6.51) determined pK' values are reported. Absorption spectra of C₆H₅PO₃H₂, C₆H₅PO₃H^- and C₆H₅PO₃^-2 are reported. The solubility of Th (C₆H₅PO₃)₂·3H₂O was studied as a function of pH and the average value of the solubility product (K_sp = 4s³) was found to be 3.24·10^-31.     

Synthesis of neutral and zwitterionic phosphinomethylpyrrolato complexes of nickel

Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R₂PCH₂C₄H₃N] (R = Ph, Cy) react with (η³-allyl)nickel bromide to give the chelate complexes (R₂PCH₂C₄H₃N)Ni(allyl), whereas the sterically hindered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (η³-allyl)nickel bromide afford a phosphine adduct (HNC₄H₂-5-Bu^t-2-CH₂PPh₂)Ni(allyl)Br which is stabilized by an intramolecular NHBr hydrogen bond. The addition of B(C₆F₅)₃ to (R₂PCH₂C₄H₃N)Ni(allyl) leads to an electrophilic attack in 5-position of the pyrrole ring, to give the thermally unstable zwitterions (η³-C₃H₅)Ni[NC₄H₃(2-CH₂PR₂)-5-B(C₆F₅)₃] which catalyse the isomerisation of 1-hexene. The addition of B(C₆F₅)₃ is reversible, and slow ligand rearrangement to Ni(N-P)₂ products appears to be the major catalyst deactivation pathway.     

不同结构的磷酸盐对凝胶体系中草酸钙晶体物相和相组成的影响

泌尿系结石的形成是一种病理性生物矿化过程，不同地区的结石发病率在3％～15％之间。且50％(美国)至80％(中国)的人会复发。结石中约70％以上为草酸钙(CaC2O4)结石。CaC2O4结石的形成与其热力学(过饱和度)和动力学(成核、生长和聚集)因素有关。由于结石患者尿液和正常人尿液中     

Electron spin resonance studies of the radiolysis of bi-π-cyclopentadienylalkyls of molybdenum and tungsten

Exposure of (C₅H₅)₂MO(CH₃)₂ and (C₅H₅)₂W(CH₃)₂, prepared from the corresponding dichlorides, to ²⁰Co γ-rays at 77 K gave H₂C.CML₃ carbene species characterised by their ESR spectra, together with a central feature possibly due to the parent cations. Dilute solutions in CD₃OD gave features assigned to the parent anions which were converted on bleaching with visible light into methyl radicals, and H₂C.ML₃ radicals. From the magnitude of the ¹H and ¹⁸³W hyperfine coupling constants, it is deduced that the SOMO for H₂C.WL₃ radicals is strongly localised on carbon.Dilute solutions in aqueous sulphuric acid also gave species with A(2H) = 20 G, identified as the carbene derivatives, H₂C.Ml₃. These were formed on annealing, as signals assigned to HSO₄ · radicals were lost.     

Derivatographic study of the thermal behaviour of 13 rare earth element oxides

The simultaneous TG-DTG-DTA thermoanalytical curves of 13 rare earth (4f) element oxides, namely, CeO₂, Dy₂O₃, Er₂O₃, Gd₂O₃, HfO₂, Ho₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃, Tb₄O₇, Tm₂O₃, Yb₂O₃ and Y₂O₃, were recorded with a MOM derivatograph under static air atmosphere over the temperature range from ambient to 1050°C. Only HfO₂, Nd₂O₃, Pr₆O₁₁, Sm₂O₃ and Tb₄O₇ showed appreciable weight losses due to the liberation of small amounts of oxygen. X-ray diffractometry was used to identify the thermal degradation products and their precursors.     

Unit cell dimensions of some oxofluorometallates of transition metals

Unit cell dimensions of seven oxofluorometallates of transition metals were investigated by powder X-ray diffraction method. The compounds K₃NbO₂F₄ and K₃TaO₂F₄ were found to be isomorphous with cubic (FCC) structure and having lattice parameters 8.885 and 8.942 Å respectively. Similarly, the compounds K₂NbOF₅ (a = 8.367 Å, c = 13.038 Å) and K₂TaOF₅ (a = 8.463 Å, c = 13.139 Å) were also found to be isomorphous with a tetragonal structure. The compound K₃Zr₂O₂F₇ (a = 9.367 Å) was found to possess a cubic (FCC) structure. Both K₂V₂O₅F₂ (a = 6.739 Å, c = 10.635 Å) and K₂VO₃F (a = 5.984 Å, c = 10.914 Å) have a hexagonal structure.     

Study of the stability of solid polyoxometalate Mo72Fe30 with a buckyball structure

Samples of polyoxometalate Mo₇₂Fe₃₀: [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂ {H₂Mo₂O₈(H₂O)}(H₂O)₉₁] · ??150H₂O with a buckyball structure, which can be both crystalline and amorphous, were synthesized. It was shown that such samples can be studied by neutron diffraction. The stability of Mo₇₂Fe₃₀ to heating and UV light exposure (in poly(vinyl alcohol) and polyvinylpyrrolidone films) was studied by IR, EPR, and electronic absorption spectroscopy; thermal analysis; and mass spectrometry. Mo₇₂Fe₃₀ was found to be less stable to heating and irradiation in a poly(vinyl alcohol) film as compared with the related polyoxometallate Mo₁₃₂ free of iron. The sorption properties of Mo₇₂Fe₃₀ to organic vapors and its stability under sorption conditions were studied. It was demonstrated that, in addition to sorption, organic substances cause the destruction of buckyballs.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

19F NMR analysis of the fluorides of perfluorocyclohexane-sulphonic acid and of 3-trifluoromethylperfluorocyclopentane-1-sulphonic acid

From the electrochemical fluorination of the chloride and the fluoride of benzenesulphonic acid, in addition to the main product C₆F₁₁SO₂F, the side products C₅F₈(CF₃)SO₂F, a structural isomer of the main product and C₆F₁₀Cl? SO₂F are also obtained. The NMR analysis of these products was performed. Chemical shift and coupling constant values were obtained for all the compounds. The NMR parameters of the main product are compared with those of perfluoromethylcyclohexane according to the data of Jolley, Sutcliffe and Walker. From the NMR parameters of C₅F₈(CF₃)SO₂F it was possible to demonstrate that substitution on the ring for —SO₂F and CF₃— is of the 1,3 and not the 1,2 type.     

Thermal chlorofluorination of propyne and propadiene II

Propyne and propadiene have been previously reported to readily undergo vapor phase catalyzed chlorofluorination at temperatures to 285 °C to form C₃F₄Cl₄ mixtures that are primarily CFCl₂-CF₂-CFCl₂. Continued fluorination at temperatures up to 485 °C produce the rearranged C₃F₆Cl₂ isomers CF₃-CCl₂-CF₃ and CF₂Cl-CFCl-CF₃.     

Thermal decomposition of managanese oxyhydroxide

Temperature-programmed thermal decomposition of γ- and α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen. Solid products at various temperatures have been analyzed by X-ray diffractometry. Under vacuum γ-MnOOH decomposed below 400°C to a mixture of Mn₅O₈, α-Mn₃O₄, and water according to the reaction scheme: 8MnOOH → Mn₅O₈ + Mn₃O₄ + 4H₂O. Above this temperature Mn₅O₈ was converted to α-Mn₃O₄ as a result of oxygen removal. The vacuum dehydration at 250°C of oxyhydroxide rich in α-MnOOH led to the formation of a new modification of Mn₂O₃ isostructural with corundum (α-Al₂O₃). In oxygen both oxyhydroxides decomposed to β-MnO₂. γ-MnOOH transformed directly to β-MnO₂ while α-MnOOH appeared to transform via corundum-phase Mn₂O₃ as an intermediate.     

Photodifluoramination of a series of hexafluoroacetone imines

Gas phase irradiation of N₂F₄ (NF₂) in the presence of hexafluoroacetone imine (I), N-chlorohexafluoroacetone imine (II), or N-bromohexafluoroacetone imine (III) resulted in the formation of products that correspond to either perhalogenation of the unsaturation or conversion of the substrate to a saturated halocarbon. The mechanism suggested involves the formation of an imino radical that reacts with N₂F₄(NF₂) to produce N,N-difluorohydrazone, (CF₃)₂CNNF₂. A bimolecular homolytic displacement (S_H2′) by Cl and F on the hydrazone forms an intermediate diazene which leads to the observed products. N-fluorohexafluoroacetone imine is inert to F atoms and NF₂ under the reaction conditions.     

An improved preparation of substituted phosphoryl difluorides. Synthesis of trifluoromethylthiodifluorophosphine and trifluoromethylthiophosphoryl difluoride

Difluorobromophosphine reacts readily with bis(trifluoromethylthio)- mercury to yield the fluorophosphine CF₃SPF₂ in excellent yields. The resulting new phosphine is readily oxidized under very moderate conditions by ClF, Cl₂ and O₂ to give new chlorofluorophosphorane and fluorophosphoryl compounds which contain the CF₃S moiety. CF₃SPF₂Cl₂ and CF₃SPF₂Cl were not characterized because of their tendency to disproportionate. CF₃SP(O)F₂ has, however, been isolated and characterized. All the new compounds are relatively unstable and decompose with a fluoride shift from the methyl group to the phosphorus atom. A new synthetic route to the known difluorophosphoryl compounds OPF₂Cl, OPF₂Br, OPF₂NCS and OPF₂(CH₃)₂, by the direct oxidation of the respective difluorophosphine with oxygen, has been found.     

Crystallographic analysis of the structure of a series of lozenge-like sulfides with Bi,In, Pb

Crystallographic analysis is used to study the structure of (Cd,Pb)Bi₂S₄ (kudriavite), Bi₃In₅S₁₂, Pb₄In₃Bi₇S₁₈, Pb_1.6In₈Bi₄S₁₉, Pb₄In₂Bi₄S₁₃, Bi₂In₄S₉ lozenge-like sulfides (with the m plane perpendicular to the translation ～4 Å). It is shown that the structure bases contain regular cation and anion sublattices whose conjugation within the common translation cell is determined by the cation/anion ratio. The independent collective ordering of cations results in complex variants of their occupation of separate crystallographic sites. Sometimes independent anionic ordering leads to unusual coordination environments.     

Pyrolysis of methyl chloride,a pathway in the chlorine-catalyzed polymerization of methane

The reaction of CH₄ + Cl₂ produces predominantly CH₃Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH₃Cl formed C₂H₄ and C₂H₂ in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH₄ C₂H₄ and C₂H₂ are formed by the recombination of ?H₃ and ?H₂Cl radicals. With added CH₄ recombination of ?H₃ forms C₂H₆, which dehydrogenates to C₂H₄ + H₂. C₂H₄ in turn dehydrogenates to C₂H₂ + H₂. While HCl, C, CH₄, and H₂ are the ultimate stable products, C₂H₄, C₂H₂, and C₆H₆ are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ?H₃ - initiated polymerization of ethylene is negligible relative to the ?₂H₃ formation through H abstraction by Cl. The fastest reaction of ?₂H₃ is its decomposition to C₂H₂. About 20% of the consumption of C₂H₂ can be accounted for by the addition of ?₂H₃ to it with formation of the butadienyl radical. The addition of the latter to C₂H₂ is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C₄H₄ leading to diacetylene has rates compatible with the experimental values. About 10% of ?₄H₅ abstracts H from HCl and forms butadiene. Successive additions of ?₂H₃ to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the ?₂H₃ radical (69 kcal/mol):      

Synthesis of Inorganic Structural Isomers By Diffusion‐Constrained Self‐Assembly of Designed Precursors: A Novel Type of Isomerism

The structure of precursors is used to control the formation of six possible structural isomers that contain four structural units of PbSe and four structural units of NbSe₂: [(PbSe)_1.14]₄[NbSe₂]₄, [(PbSe)_1.14]₃[NbSe₂]₃[(PbSe)_1.14]₁[NbSe₂]₁, [(PbSe)_1.14]₃[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₂, [(PbSe)_1.14]₂[NbSe₂]₃[(PbSe)_1.14]₂[NbSe₂]₁, [(PbSe)_1.14]₂[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₁[(PbSe)_1.14]₁[NbSe₂]₁, [(PbSe)_1.14]₂[NbSe₂]₁[(PbSe)_1.14]₁[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₁. The electrical properties of these compounds vary with the nanoarchitecture. For each pair of constituents, over 20 000 new compounds, each with a specific nanoarchitecture, are possible with the number of structural units equal to 10 or less. This provides opportunities to systematically correlate structure with properties and hence optimize performance.     

Reaction of carbonyl fluoride with fluorine in the presence of various fluorides as catalysts

The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF₂O + F₂→ CF₃OF. The list of catalysts for this process has now been enlarged to include NaF, MgF₂, CaF₂, SrF₂, BaF₂ and LaF₃. Lithium fluoride and thorium fluoride also give CF₃OF but are less active. Perhaps the substances CsF·HF, KAgF₄ and NiF₂ should be included in this list. Silver fluoride, usually as a mixture of AgF₂ with AgF, has been known to catalyze the reaction of CF₂O with F₂ to give both CF₃OF and CF₃OOCF₃. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF₃OOCF₃ is very high. It has now been shown that TIF₃ behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF₃OOCF₃ than of CF₃OF but require higher temperatures than AgF₂ (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed.     

Preparation of superacid of ruthenium-sulfated zirconia for reaction of butane to isobutane

A highly active superacid of 2–4 wt.% Ru-sulfated ZrO₂ for the isomerization of butane to isobutane was obtained by exposing RuO_x/ZrO₂ to 1 N H₂SO₄ followed by calcining in air at 550°C. The RuO_x/ZrO₂ was prepared by impregnating zirconium hydroxide with a solution of RuCl₃ followed by drying at 300°C. The catalyst was much more active than the superacid of sulfated zirconia, the temperature difference to show the same conversion between both catalysts being more than 145°C.     

Effect of Antioxidants on Stability of Aqueous Solutions of Selenurea and on Properties of Lead Selenide Films Obtained with These Antioxidants

Spectrophotometric method was used to study the kinetics of the process in which aqueous solutions of selenurea of various compositions are oxidized. Significant differences between the stabilities of selenurea solutions were revealed in relation to the selenurea concentration and also to the acidity, or alkalinity of a medium. It was shown that the stability of selenurea solutions is affected by additives of various antioxidants: sodium sulfite Na₂SO₃, ascorbic acid C₆H₈O₆, hydroxylamine chloride NH₂OH·HCl, hydrazine hydrate N₂H₄·H₂O, and tin chloride SnCl₂·2H₂O. It was found that using a 1 : 1 mixture of antioxidants Na₂SO₃ and C₆H₈O₆ substantially raises their antioxidant activity and stabilizes the aqueous solutions of selenurea during up to five days. A hydro-chemical precipitation in the acetate—ethylenediamine reaction system in the presence of the antioxidants under study was used to obtain lead selenide films of stoichiometric composition with thicknesses of 230?670 nm. With the Na₂SO₃ + C₆H₈O₆, Na₂SO₃, C₆H₈O₆, and SnCl₂ antioxidants used to stabilize selenurea solutions, a tendency is observed toward a decrease in the lattice constants of PbSe films from 6.1531 ± 0.0003 to 6.1367 ± 0.0002 Å, an increase in the share of nanosize particles, and rise in the PbSe energy gap width from 0.78 to 1.0 e V.

     

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C₂H₂, C₂H₄, C₂H₆) on the surface of a sorbent containing Ag⁰, Ag^δ+, and AgO sites. The dynamics of change in the structural characteristics of Ag _n (n ≤ 10) is analyzed and the adsorption of oxygen on Ag₈ and Ag₁₀ is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag₈, Ag₁₀, Ag ₁₀ ⁺ , Ag₁₀O, and Ag₁₀O₂ clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C₂H₂ increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Ag^δ+) but also to bind C₂H₂ and C₂H₄ directly to the sorbent’s surface.