Study of the Acid-Base Properties of sio2-Supported Nimoo4 Catalysts by Temperature-Programmeddesorption. Effect of the Active Phase Content

The acid-base properties of a series of SiO₂-supported NiMoO₄ catalysts were investigated by temperature-programmed desorption of NH₃ and CO₂. Results show that supported catalysts with ca. one monolayer of the active phase are less acidic than the unsupported stoichiometric NiMoO₄.     

Synthesis and Reactions of 4-Oxiranylmethylfuro[3,2-b]pyrroles and Their Benzo Derivatives

Methyl 4-oxiranylmethyl-4H-furo[3,2-b]pyrrole-5-carboxylates 2a-c and methyl 1-oxiranylmethyl-1H-benzo[4,5]furo[3,2-b]pyrrole-2-carboxylate (2d) were prepared by reaction of the appropriate starting compounds 1a-d with excess chloromethyloxirane. The compounds 2a-d undergo oxirane ring opening by heterocyclic amines (morpholine, pyrrolidine, piperidine or 4-methylpiperazine) giving N-2-hydroxy-3-heteroaminopropyl-substituted compounds 3a-f or substituted 4,5-dihydrofuro[2',3':4,5]pyrrolo[2,1-c][1,4]oxazin-8-ones 4a-e.     

Investigations of Imidazoles. 101. Synthesis of 2,3-Dihydroimidazo[1,2-a]pyrimidine from 2-Aminopyrimidine

Two novel preparative methods have been developed for the synthesis of 2,3-dihydroimidazo[1,2-a]pyrimidine from 2-aminopyrimidine. These are the reaction with 1,2-dibromoethane and also the reaction with ethylene chloro(bromo)hydrin, subsequent treatment of 1--hydroxyethyl-2-imino-1,2-dihydropyrimidine with thionyl chloride, and cyclization of the intermediate 1--chloroethyl-2-imino-1,2-dihydropyrimidine in the presence of sodium hydroxide.     

Quantitative determination of gas mixture composition by gas chromatography—New approach

Summary A new method has been developed for the quantitative determination of gas mixture composition where air penetration during gas sample collection would lead to erroneous results. It requires the use of a stationary phase that separates gas sample components and the air and involves 4–5 analyses of samples of equal volumes containing different amounts of air. By graphical extrapolation of the air peak area (S _air ) as a function of the peak areas of the individual components (S _comp ) the areas for these components in the absence of air can be obtained forS _air =0. Using calibration curves for the pure gas components the true quantitative composition of the gas mixture is estimated.     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

稀土偶联剂对Mg(OH)_2的改性作用及其在PP/Mg(OH)_2体系中的应用

研究了稀土偶联剂 (ReC)对Mg(OH) 2 的表面改性作用及PP/Mg(OH) 2 体系的燃烧性能、流动性能、力学性能及老化性能。稀土偶联剂可显著改善Mg(OH) 2 在非极性介质中的分散性 ;PP/Mg(OH) 2 体系当Mg(OH) 2 填充量超过 5 0 %时 ,氧指数 (OI)≥ 2 8.5 ,但这时冲击强度不足纯PP的 30 % ,熔体流动速率 (MFR)低于 0 .6g/1 0min ;而填料用 2 .5 % (质量 )ReC处理后 ,填充量为 5 0 %的体系冲击强度接近纯PP ,MFR达 2 .8g/1 0min ;Mg(OH) 2对体系光氧老化过程有加速作用 ,而对热氧老化过程有阻滞作用 ;稀土偶联剂对体系光氧老化过程有轻微的促进作用 ,而对热氧老化过程无明显影响     

Influence of the Native Oxide Layer on the Silicon Surface During Initial Stages of Nitridation

 Thin SiO₂ layers were produced by thermal oxidation of Si wafer material. To study the effect of nitridation on the oxide layers, the specimens were nitrided in a furnace at high temperature. Non-destructive ion beam analysis was performed to determine changes in the elemental concentrations and depth profiles of the major components. In particular, N and O concentrations were measured using the non-resonant nuclear reactions ¹⁴N(d, α)¹²C and ¹⁶O(d, p)¹⁷O, respectively. To obtain depth profiles of the as-prepared and nitrided specimens, the samples were measured with RBS and heavy ion elastic recoil detection analysis. The ion beam analyses revealed an increase in thickness of the SiO₂ layers with temperature. The specimens nitrided at 1200 °C were almost free of N. Surface topology investigations with scanning electron microscopy revealed concentric annular artificial patterns at the surfaces. In the centre of the pattern, only silicon was measured. Additionally, a band consisting of Si, O, and N surrounding the pattern was discovered. The findings are in agreement with specimens prepared at higher temperatures. Received June 19, 2000. Revision December 9, 2000.     

Efficient Synthesis of Functionalized 2H-Thiopyrans via Hetero-Diels-Alder Reactions of an Enaminothione with Electrophilic Olefins

Summary.  The hetero-Diels-Alder reaction of 3-dimethylamino-1-(2-thienyl)-2-propene-1-thione (diene) with substituted β-nitrostyrenes, as well as maleic and fumaric acids (dienophiles) yielded 3,4-dihydro-2H-thiopyran derivatives. The treatment of some of those cycloadducts with acetic acid caused elimination of dimethylamine, affording stable 2H-thiopyrans. A reaction of the diene with maleic anhydride furnished a cycloadduct which underwent spontaneous rearrangement to form an N,N-dimethylamide derivative. Cycloadditions of the diene to maleimide, N-phenylmaleimide, maleic acid monoanilide, diethyl maleate, fumarate, and butenolide carried out in the presence of acetic anhydride were followed by elimination of dimethylamine under formation of stable 2H-thiopyran derivatives. Received February 19, 2001. Accepted (revised) March 12, 2001     

Spectroscopic analysis of asymmetric top free radicals

Several key problems involved in the analyses of spectra of asymmetric top molecules, i.e., the effective Hamiltonian, the representation and basis vector, identification of energy levels, the selection rules, the relative intensity, and Zeeman tuning rate, were elucidated systematically. Introducing the high-order centrifugal distortion terms into the effective Hamiltonian, the precision for calculation has been improved substantially, which allows us to analyze the high-lying rotational transitions. A global analysis of all available spectra of¹⁴N¹⁶O₂ in the ground vibronic state has been made to obtain a set of molecular constants of¹⁴N¹⁶O₂ in the ground vibronic state which is the most precise and extensive so far. Using the improved parameters, some FIR LMR lines left unassigned hitherto have been identified successfully.     

Preconcentration and Separation of Trace Amounts of Strontium Ions from Alkali and Alkaline Earth Metal Ions Using Octadecyl Silica Membrane Disks Modified with Decyl-18-Crown-6 and Its Determination by Flame Atomic Absorption Spectrometry

 A simple and reliable method for rapid and selective separation of trace amounts of Sr²⁺ ions from alkali and alkaline earth metal ions by using octadecyl silica membrane disks modified with decyl- 18-crown-6 in the presence of 1.0 × 10⁻³ M picric acid is presented. The influence of picric acid concentration, flow rates and nature and amount of the stripping acid have been investigated. Maximum capacity of the membrane disks modified with 10 mg of the macrocycle was found to be 484 μg of Sr²⁺ ions. The proposed method permitted enrichment factors of about 80 and higher. The limit of detection of the proposed method is 1.5 μg per 1000 ml. The method was successfully applied to the recovery of Sr²⁺ ions from different synthetic and water samples. Received August 10, 2000. Revision April 17, 2001.