Study of the pyrolysis of H2O2 in the presence of H2and CO by use of UV absorption of HO2

In dissociation experiments of H₂O₂ under shock wave conditions, the spectra of H₂O₂ and HO₂ have been observed in the UV at 2200 ≤ 2800 Å. By the use of these spectra the H₂O₂ decomposition in the presence of H₂ and CO at 870 ≤ T ≤ 1000°K has been analyzed. It was found that in this temperature range, in contrast to low temperature behavior, reactions of H atoms with H₂O₂ and with HO₂ are equally important. The rate of the reaction H + H₂O₂ ← HO₂ + H₂ was estimated in comparison with the rate of the reaction between H and HO₂. Good agreement between calculated and measured concentration profiles of HO₂ and H₂O₂ was obtained.     

Synthesis and Application of New Salan Titanium Complexes in the Catalytic Reduction of Aldehydes

Complexes of formula [(H₂N₂O₂)TiCl₂] and [(H₂N₂O₂)Ti(OⁱPr)₂] (H₂N₂O₂H₂ = HOPh’CH₂NH(CH₂)₂NHCH₂Ph’OH, where Ph’ = 2,4-(CMe₂Ph)C₆H₂) were synthesized by the reaction of the salan ligand precursor H₂N₂O₂H₂ with TiCl₄ and Ti(OⁱPr)₄, respectively, in high yields. The dichlorido complex [(H₂N₂O₂)TiCl₂] revealed to be an efficient catalyst for the reduction of benzaldehyde in toluene. Full conversion was observed after 24 h at 55 °C in THF. The same catalyst also converted phenylacetaldehyde and hydrocinnamaldehyde into the corresponding alkanes quantitatively.     

Computational study of reaction pathways in the course of interaction of deactivated silylenes with buta-1,3-diene

The PESs of systems including deactivated silylenes (SiHHal, SiHal₂, Hal = F, Cl, and 2-silaimidazol-2-ylidene, SiN₂H₂C₂H₂) and buta-1,3-diene have been studied using G3(MP2)//B3LYP method. Two major reaction channels, (2 + 1) and (4 + 1) cycloaddition reactions, leading to 2-vinylsiliranes and silacyclopent-3-enes, respectively, as well as [1,3]-sigmatropic rearrangements between 2-vinylsiliranes and the corresponding silacyclopent-3-enes, have been considered in detail. Reactivity of silylenes toward buta-1,3-diene decreases in the following series: SiHHal > SiHal₂ > SiN₂H₂C₂H₂, which is reflected in increase of the reaction barriers for both cycloaddition reactions and in decrease of exothermicity of the formation of the corresponding products. The (4 + 1) cycloaddition is preferable for SiHal₂ and SiN₂H₂C₂H₂ and can compete with (2 + 1) cycloaddition for SiHHal. [1,3]-Sigmatropic rearrangement is important for isomerization of 2-vinylsiliranes to the corresponding silacyclopent-3-enes for all systems studied, except the SiCl₂ system.     

A study of the selenites of cerium

The solubilities of the systems CeO₂-SeO₂-H₂O and Ce₂O₃-SeO₂-H₂O were studied at 100°C. The field of crystallization of Ce(SeO₃)₂ was established in the system CeO₂-SeO₂-H₂O, and fields of crystallization of Ce₂(SeO₃)₃ and Ce₂(SeO₃)₃H₂SeO₃ were established in the system Ce₂O₃-SeO₂-H₂O. The compound obtained were identified by means of chemical, X-ray and derivatograph analysis. The mechanism of thermal dissociation of Ce(SeO₃)₂, Ce₂(SeO₃)₃ and Ce₂(SeO₃)₃·H₂SeO₃ was studied. This revised version was published online in August 2006 with corrections to the Cover Date.     

钛硅分子筛催化环己酮液相氨肟化固定床工艺

采用固定床模式,研究了钛硅分子筛催化环己酮制环己酮肟液相氨肟化反应.结果表明,该工艺模式具有可行性与普适性.优化的反应条件为:温度333K,体系氨浓度>2%,酮/H₂O₂摩尔比=5,H₂O₂空速0.083h^-1.此时环己酮转化率、环己酮肟选择性、H₂O₂转化率及其有效利用率分别达18.7%,99.5%,94.7%和98.7%.进一步研究了H₂O₂在该过程中的反应行为,发现固定床工艺模式能有效提高H₂O₂的有效利用率,其主要原因是该模式有利于羟胺的生成及其进一步与酮反应生成肟.适当的空速与氨和酮的浓度是实现H₂O₂高效利用的关键因素.     

Structural Diversity of Silver Clusters in Double and Triple Salts of Silver Acetylide with Silver Perfluoro-Dicarboxylates

The reactions of Ag₂C₂ and the corresponding silver perfluoro-dicarboxylates result in the formation of three new double and triple salts, Ag₂C₂·3AgO₂CCF₂CF₂CO₂Ag·7H₂O (1), 2Ag₂C₂·6AgO₂CCF₂CF₂CO₂Ag·AgNO₃·12H₂O (2) and Ag₂C₂·4AgO₂CCF₂CF₂CF₂CO₂Ag·17.5H₂O (3), which have been structurally characterized by single crystal X-ray analysis. Their structures contain silver cages of various shapes: crown in 1, pentagonal bipyramid together with monocapped pentagonal bipyramid in 2, and square antiprism in 3, each containing an encapsulated acetylide dianion. Except for the pentagonal bipyramid, the other three silver cages are unprecedented. Compound 2 provides a unique example in which two kinds of silver polyhedra with different numbers of vertices (C₂@Ag₇ and C₂@Ag₈) co-exist in the crystal structure.     

Regularities of formation of nanocrystalline particles in titanium subgroup dioxides

Trends in formation and evolution of nanocrystalline phases in TiO₂, ZrO₂, and HfO₂ powders were studied. The stability of metastable phases increases in the order of HfO₂ > ZrO₂ > TiO₂, and the probability of formation of thermodynamically stable phases increases in the order of TiO₂ > ZrO₂ > HfO₂. The enthalpies of formation were determined for TiO₂, ZrO₂, and HfO₂ nanocrystallites, as well as the activation energies of their subsequent growth. For TiO₂ and ZrO₂, a phenomenological model was advanced to describe nanocrystallite formation and subsequent polymorphic transformations.     

Solid solubility of the oxisulfides of Y, La, and Gd

The solid solubility in the systems Y₂O₂S---La₂O₂S, Y₂O₂S---Gd₂O₂S, and Gd₂O₂S---La₂O₂S has been investigated. Solid solutions of all compounds, throughout the whole composition range, were readily obtained, using coprecipitated oxalates and a polysulfide flux.     

Electrochemical Studies on Effects of Psychostimulants,Opioids and Alcohol Intake Towards Level of Hydrogen Peroxide in the Brain Striatum

Hydrogen peroxide (H₂O₂) was the main types of many peroxides produced in living mammalian cells that consumed oxygen. In the brain, the main source of H₂O₂ was the superoxide dismutase (SOD)‐catalyzed reaction in mitochondria. However, the level of H₂O₂ would be elevated through administration of control drugs and alcohol by dopamine metabolism of monoamine oxidase. In this study, a H₂O₂ microsensor was used to investigate the level of H₂O₂ in the brain striatum after administration of methamphetamine (MAP), morphine (MrP) or ethanol (Eth). The placement of microsensor in the brain was done at coordinates A/P 1.1 from bregma, M/L+2.6 and D/V‐1.5. A working potential of +0.05 V vs. Ag/AgCl was applied. The H₂O₂ concentration was measured direct from the current generated by its catalytic reaction at the electro active surface of the electrode. A significant increase of H₂O₂ level was observed after 7 successive injections of the controlled drugs or alcohol. The initial measurement of H₂O₂ is essential as excess dosage of H₂O₂ during treatment will contribute to the formation of neurotoxin oxygenated radicals. The H₂O₂ was the precursor of O_2? and OH radicals. Thus, this study provided a mean to monitor H₂O₂ level in the brain.     

Acetylenic derivatives of metal carbonyls of the triad Fe,Ru, Os—XI Mass spectra of some binuclear complexes

The mass spectra of the following acetylenic derivatives of iron, ruthenium and osmium carbonyls are reported: the iron compounds Fe₂(CO)₆[C₂(C₆H₅)s₂]₂, Fe₂(CO)₆[C₂(CH₃)₂]₂ and Fe₂(CO)₆[C₂(C₂H₅)₂]₂, the ruthenium compounds Ru₂(CO)₆[C₂(C₆H₅)₂]₂, and Ru₂(CO)₆[C₂(CH₃)₂]₂ and the osmium compounds Os₂(CO)₆[C₂(C₆H₅)₂]₂, Os₂(CO)₆[C₂HC₆H₅]₂ and Os₂(CO)₆[C₂(CH₃)₂]₂. Iron compounds exhibit breakdown schemes where binuclear, mononuclear and hydrocarbon ions are present. On the other hand, ruthenium and osmium compounds fragment in a similar way and give rise to singly and doubly charged binuclear ions. Phenylic derivatives of ruthenium and osmium also give weak triply charged ions. The results are discussed in terms of relative strengths of the metal-metal and metal-carbon bonds.     

Kinetics of decomposition of alkylammonium salts

The thermogravimetric curves of di-n-propylammonium, di-iso-propylammonium, di-n-butylammonium and di-iso-butylammonium chlorides showed similar profiles, characterized by mass loss in only one stage, corresponding to decomposition of compounds. The following thermal stability order was obtained: [Bu₂ ⁿNH₂]Cl>[Pr₂ ⁿNH₂]Cl>[Pr₂ ⁱNH₂]Cl>[Bu₂ ⁱNH₂]Cl. The values of activation energy for non-isothermal data obtained by Ozawa and Coats-Redfern integral methods were in agreement and stability order obtained by thermogravimetry were reproduced in both methods. The decomposition reactions of [Pr₂ ⁿNH₂]Cl, [Pr₂ ⁱNH₂]Cl and [Bu₂ ⁱNH₂]Cl were better described by A3 model and [Bu₂ ⁿNH₂]Cl by A2 model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic Analysis of the Decomposition of Chelates of Di-alkyldithiocarbamate of Cd(II)

The thermal decomposition kinetics of the solid complexes Cd(S₂ CNR₂ )₂ , where R =C₂ H₅ , n -C₃ H₇ , n -C₄ H₉ or iso -C₄ H₉ , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R₁ . The thermal analysis data suggested the thermal stability sequence Cd(S₂ CNBuⁿ ₂ )₂ >Cd(S₂ CNPrⁿ ₂ )₂ >Cd(S₂ CNBuⁱ ₂ )₂ >Cd(S₂ CNEt₂ )₂ , which accords with the sequence of stability of the apparent activation energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

An ab initio and density functional study of microsolvation of carbon dioxide in water clusters and formation of carbonic acid

Geometry of the CO₂–H₂O complex and reaction barriers leading to the formation of H₂CO₃were studied at the RHF/6-311++G**, MP2/6-311++G**, B3LYP/AUG-cc-pVDZ, B3LYP/AUG-cc-pVTZ, MP2/AUG-cc-pVDZ and CCD/AUG-cc-pVDZ levels of theory. The rotational barrier of the CO₂–H₂O complex and the reaction barrier leading to the formation of H₂CO₃–H₂O from CO₂–(H₂O)₂ were studied using the first three of the above-mentioned methods. Microsolvation of CO₂ in water clusters having upto eight water molecules was studied using the B3LYP/AUG-cc-pVDZ method. Various methods except MP2/AUG-cc-pVDZ predict the equilibrium structure of the CO₂–H₂O complex to be symmetric while the MP2/AUG-cc-pVDZ method predicts it to be unsymmetric. Formation of H₂CO₃ from CO₂–H₂O is strongly catalyzed by the presence of a second water molecule. Atomic orbitals are strongly rehybridized in going from the equilibrium structures of the CO₂–H₂O and CO₂–(H₂O)₂ complexes to the transition states involved in the formation of H₂CO₃ and H₂CO₃–H₂O, respectively, as shown by hybridization displacement charges.     

Mass spectrometric study of SF6-N2 plasma during etching of silicon and tungsten

The reaction products in the SF₆-N₂ mixture rf plasma during reactive ion etching of Si and W have been measured by a mass spectrometric method. Two kinds of cathode materials were used in this work; they were stainless steel for the Si etching, and SiO₂ for the W etching. The main products detected in the etching experiments of Si and W included SF₄, SF₂, SO₂, SOF₂, SOF₄, SO₂F₂, NSF, NF₃, N₂F₄, N_xS_y, NO₂, and SiF₄. In the W etching with the SiO₂ cathode, additional S₂F₂, N₂O, and WF₆ molecules were also obtained. The formation reactions about the novel NSF compound and the sulfur oxyfuorides were discussed.     

New cyclic phosphonium salts derived from the reaction of phosphine-aldehydes with acid

Various cyclic phosphonium structures are formed in high yield by the deprotection of unstable phosphine-aldehydes in acidic solution. When there is a methylene spacer between the phosphine and the aldehyde, a phosphonium ion [PHR₂CH₂CH(OEt)₂]Br₂, R=iPrOH, Et is obtained. Reaction of these phosphonium salts with water produces the dimers [-PR₂CH₂CH(OH)-]₂[Br]₂ R = iPr, Et. When there is an ethylene spacer as in PPh₂CH₂CH₂CH(OCH₂CH₂O), a remarkable tetramer with a 16-membered ring [-PPh₂CH₂CH₂CH (OH)-]₄[Cl]₄ forms as one diastereomer in hydrochloric acid solution. Reaction of HCl with the protected phosphine-aldehyde with a propylene spacer (PPh₂CH₂CH₂CH₂CH(OCH₂CH₂O)) results in the formation of the monomeric phosphonium salt [-PPh₂ CH₂CH₂CH₂CH(OH)-]Cl with a 5-membered ring. Solid state structures of different ring types were determined using X-ray diffraction experiment.     

Synthesis of CeO2 by thermal decomposition of oxalate and kinetics of thermal decomposition of precursor

CeO₂ was synthesized by calcining Ce₂(C₂O₄)₃·8H₂O above 673 K in air. The precursor and its calcined products were characterized using thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectra, X-ray powder diffraction, scanning electron microscopy, and UV–Vis absorption spectroscopy. The result showed that cubic CeO₂ was obtained when the precursor was calcined above 673 K in air for 2 h. The UV–Vis absorption spectroscopy studies showed that superfine CeO₂ behaved as an excellent UV-shielding material. The thermal decomposition of the precursor in air experienced two steps, which are: first, the dehydration of eight crystal water molecules, then the decomposition of Ce₂(C₂O₄)₃ into cubic CeO₂. The values of the activation energies associated with the thermal decomposition of Ce₂(C₂O₄)₃·8H₂O were determined based on the Starink equation.     

Experimental and computational studies of the thermal decomposition of halon 1211

Thermal pyrolysis of halon 1211 (CBrClF₂), diluted in nitrogen, in a tubular alumina reactor, has been studied over the temperature range of 773–1073 K at residence times from 0.3 to 2 s. At temperatures below 973 K, the major products were CCl₂F₂, CBr₂F₂, C₂Cl₂F₄, C₂BrClF₄, C₂F₄, and C₂Br₂F₄. Further increasing temperature resulted in the formation of CBrF₃, CClF₃, and many other species whose formation necessitated the rupture of C? F bonds. Coke formation was also observed on the surface of the reactor at high temperatures. A kinetic reaction scheme involving 16 species and 25 reaction steps was developed and applied to model the thermal pyrolysis of halon 1211 over the temperature range of 773–973 K. Sensitivity analysis suggests that the reaction CBrClF₂ + CClF₂→CCl₂F₂ + CBrF₂ constitutes the major pathway for the decomposition of halon 1211 under the conditions investigated. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 134–146, 2005     

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.     

Preparation of nanocrystalline BiFeO3 and kinetics of thermal process of precursor

The Bi₂Fe₂(C₂O₄)₅·5H₂O was synthesized by solid-state reaction at low heat using Bi(NO₃)₃·5H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. The nanocrystalline BiFeO₃ was obtained by calcining Bi₂Fe₂(C₂O₄)₅·5H₂O at 600 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, FT-IR, X-ray powder diffraction, and vibrating sample magnetometer. The data showed that highly crystallized BiFeO₃ with hexagonal structure [space group R3c(161)] was obtained when the precursor was calcined at 600 °C in air for 1.5 h. The thermal process of the precursor in air experienced five steps which involved, at first, the dehydration of an adsorption water molecule, then dehydration of four crystal water molecules, decomposition of FeC₂O₄ into Fe₂O₃, decomposition of Bi₂(C₂O₄)₃ into Bi₂O₃, and at last, reaction of Bi₂O₃ and Fe₂O₃ into hexagonal BiFeO₃. Based on Starink equation, the values of the activation energies associated with the thermal process of Bi₂Fe₂(C₂O₄)₅·5H₂O were determined. Besides, the most probable mechanism functions and thermodynamic functions (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of thermal processes of Bi₂Fe₂(C₂O₄)₅·5H₂O were also determined.     

Organotin and tin(IV) derivatives of dimethyldithioarsinic acid

Organotin derivatives of dimethyldithioarsinic (dithocacodylic) acid have been obtained from the appropriate organotin chloride and the sodium salt of the latter. Tin(IV) chloride and NaS₂AsMe₂ · 2 H₂O yielded only two products, namely Cl₂Sn(S₂AsMe₂)₂ and Sn (S₂AsMe₂)₄, regardless of the reagent ratio. Spectroscopic characterization of the compounds (infrared and¹H NMR) provides structural information suggesting that the dimethyldithioarsinato group behaves as monodentate (or anisobidentate) ligand in Me₂Sn(S₂AsMe₂)₂, Bu₂Sn-(S₂AsMe₂)₂ and Cy₃Sn(S₂AsMe₂), as bidentate in Ph₂Sn(S₂AsMe₂)₂, Ph₃Sn(S₂AsMe₂) and Cl₂As(S₂AsMe₂)₂, whereas Sn(S₂AsMe₂)₄ contains both mono- and bidentate ligands, presumably in a six-coordinate structure.