The influence of oxygen on the direct synthesis of methylchlorosilanes

The influence of oxygen on the direct synthesis of methylchlorosilanes in a fluidised bed with copper as a catalyst has been studied. At 320° C and a pressure of 1 atmosphere the oxygen content in the feed gas was varied from 1 to 5000 ppm. It was found that the oxygen sharply reduces the rate of reaction but hardly influences the product composition. The maximum degree of conversion of the silicon is about 70% if no oxygen is present; at an oxygen concentration of 2000 ppm the conversion decreases to 50 percent.     

The direct synthesis of methylchlorosilanes: New aspects concerning its mechanism

New results are given regarding the mechanism of the chemical process of copper alloyed silicon with methyl chloride (the `direct process'). As indicated by Photo-EMF measurements, carried out with doped silicon samples the reactivity of silicon significantly depends on the type of the doping with elements like phosphorus (n-type) tin, boron, indium (p-type). In-situ trapping experiments with 2,3-dimethylbutadiene are consistent with the creation of silylene intermediates SiMeCl and SiCl₂ . Theselectivity of their competitive insertion steps can be controlled by the doping type and concentrations of the doping elements, especially the phosphorus/tin ratio criterion. n-Type doping favors the silylene insertion into the C-Cl bond due to the electronic silylene stabilization on the silicon surface. In case of p-type doping silylene insertion into Si-Cl bond is favored more intensively leading to the formation of disilanes.     

Activation of CuSi and CuZnSnSi contact masses for the direct synthesis of methylchlorosilanes

The temperature-programmed-activation (TPA) of CuSi, CuSi(H) (prepared using CuCl and CuCl 2H2O, respectively), and CuSi copromoted with zinc and tin have been investigated. The main effect of promotion was to increase the activation temperature suggesting that zinc may inhibit the transfer of chlorine from CuCl to surface silicon atoms. The sample prepared using hydrated cuprous chloride initially exhibited reduced activity for the Direct Reaction relative to CuSi, apparently, due to oxidation of the contact mass surface inhibiting the formation of -Cu₃Si.     

Thermodynamic Insight into Protein Aggregation Using a Kinetic Ising Model

In this work, we present a kinetic analysis for protein aggregation using the kinetic Ising model, which serves as a new application of a previously proposed model [Liang et al., J. Chin. Chem. Soc.­ 2003 , 50, 335]. Considering protein as a single spin unit, we map two states of a unit to the aggregation‐prone (AP) and the fibril (F) states. This work shows that the model can successfully capture the nucleation‐growth features of protein aggregation from experiments, which offers thermodynamic interpretations of aggregation properties, such as lag‐time and fibril stability.     

有机膨润土结构对吡虫啉吸附热力学和动力学的影响机理

为深入了解有机膨润土结构对农药吸附性能的影响机理,论文制备十六烷基三甲基氯化铵(HTMA)载量系列变化的有机膨润土,通过吸附热力学和动力学研究了新烟碱杀虫剂吡虫啉与改性有机膨润土的相互作用和影响农药分子在有机膨润土层间扩散的结构因素。结果显示,季铵盐改性削弱了膨润土片层与吡虫啉的静电结合,但是增强与吡虫啉的疏水相互作用。吡虫啉吸附动力学与有机膨润土层间结构密切相关,低载量(<0.8′CEC)的HTMA对膨润土层间距的影响很小,但是层间堆积密度的增加导致吡虫啉吸附速率常数急剧下降。HTMA载量的进一步增加导致其层间排列方式由单层平铺向双层平铺的转变,层间距急剧增加使得吡虫啉吸附速率常数略有增大。     

量热法研究线粒体代谢的热力学和动力学行为

线粒体是细胞中极为重要的细胞器，是产生细胞所必需的“富能”物质ATP的重要场所，为细胞活动提供所需化学能．在生命体能量代谢过程中除一部分能量用于合成ATP外，其余则以热的形式释出．用精密热量计测出线粒体代谢过程中的热量输出对了解线粒体的功能和代谢机制具有十分重要的意义．用微量热法研究线粒体体外代谢已有一些报导［‘，’］．本工作用精密热量计和差式扫描量热仪侧定了水稻线粒体体外代谢热谱和DSC曲线，计算了水稻线粒体活性增长速率常数，比较了不同保藏时间的水稻线粒体体外代谢的差异，并初步探讨了水稻线粒体在变…     

Intermediacy of silylene and germylene in direct synthesis of organosilanes and organogermanes

In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane synthesis give new methods for the synthesis of organogermanes.     

Stereoselective synthesis of β-amino ketones via direct Mannich-type reaction catalyzed with silica sulfuric acid

At room temperature, the direct Mannich-type reaction of a variety of in situ generated aldimines using aldehydes and anilines with ketones in a three-component reaction was efficiently catalyzed by silica sulfuric acid (SSA) in EtOH. This rapid reaction afforded the corresponding β-amino ketones in good yields with excellent stereoselectivities and catalyst was recyclable.     

Functionalized ionic liquids catalyzed direct aldol reactions

A series of functionalized ionic liquids (FILs) incorporated with chiral-pyrrolidine unit have been synthesized and tested as reusable organocatalysts for direct aldol reactions. FIL 1b in combination with acetic acid and water as additives could effectively catalyze direct aldol reactions of various ketone donors in high yields and the FIL catalyst was easily recycled and reused for six times with slight reduction in activity. Based on experimental observations as well as previous reports, we proposed that the reactions occurred via syn-enamine intermediate and the ionic-liquid moiety in the FIL provides some space shielding for the participating aldehyde acceptors that accounts for the modest enantioselectivities observed in the reactions.     

MFI-type boroaluminosilicate: A comparative study between the direct synthesis and the templating method

Boroaluminosilicate with MFI zeotype (henceforth B-ZSM-5) was synthesized both via the direct synthesis where ZSM-5 was employed as crystal seed and the templating method by using TPABr as the structure-directing agent (SDA). Characterization based on its structure, bonding, surface acidity, and morphology was performed by powder X-ray diffraction (XRD), ¹¹B MAS NMR spectrometry, FT-IR spectrometry, pyridine-chemisorption IR spectrometry, and scanning electron microscopy (SEM). The composition of the prepared zeolites was determined by ICP-AES; the zeolite framework stability was investigated by steam treatment. The differences in the physicochemical properties of B-ZSM-5 prepared by the two methods were compared and discussed. In the direct synthesis, increasing initial boron-substitution ratio concomitantly brings about increasing difficulty to prepare pure B-ZSM-5 and, MFI-type borosilicate (free of aluminum) cannot be synthesized; the highest SiO₂/Al₂O₃ ratio=70.64 is received. B-ZSM-5 prepared by the templating method shows remarkable hydrothermal stability than its counterpart prepared by the direct synthesis.     

Sb对Pd基催化剂用于常压直接合成H2O2的促进效应

H2O2作为一种高效绿色氧化剂, 广泛应用于造纸、纺织、水处理等工业领域. 目前蒽醌法是工业上生产 H2O2的主要方法, 相比之下, 利用 H2和 O2直接合成 H2O2, 能耗低, 污染小, 适合与下游工艺技术进行耦合. 而缺乏高性能催化剂是制约直接法合成 H2O2工业化的主要原因. 本文通过浸渍法制备了一系列负载型 Pd-Sb/TiO2双金属催化剂, 并用于常压下H2O2直接催化合成反应. 利用透射电子显微镜 (TEM), X 射线光电子能谱 (XPS), H2/O2程序升温脱附 (H2/O2-TPD), X 射线衍射 (XRD), 原位 CO 吸附的傅里叶变换漫反射红外光谱 (CO-DRIFTS) 等手段对催化剂的电子和几何结构进行解析, 深入研究了助剂 Sb 对该体系的促进作用.结果显示, 与单金属 Pd 催化剂相比, 适量金属 Sb 的加入有效提高了催化性能, 抑制了副反应的发生. 当 Pd/Sb 摩尔比为 50/1(Pd50Sb) 时, H2O2的选择性高达 73%; 但是当 Pd/Sb 为 2 时, 催化剂对生成 H2O2几乎没有活性. TEM 和 XRD 证明, Sb 的加入显著促进了 Pd 颗粒在载体 TiO2上的分散. XPS 和 H2-TPD 实验, 发现, Sb 改变了催化剂表面 Pd2+/Pd0的比例, 抑制了金属 Pd 的氧化; 同时, Sb 主要以氧化态存在, 在催化剂表面形成 Sb2O3氧化层, 覆盖表面的 Pd 活性位, 从而抑制了反应中 H2在催化剂表面的活化以及 H2O2加氢副反应的发生. O2-TPD 结果表明, 随着 Sb 的加入, O2的脱附峰明显减弱, 表明 Pd-Sb/TiO2不利于 O2的解离吸附. 此外, 原位 CO-DRIFTS 实验结果表明, Sb 均匀分布在 Pd-Sb 催化剂表面, 致使有利于生成 H2O 的连续 Pd 活性位明显减少, 而有利于合成 H2O2的单个 Pd 原子活性位明显增加.总的来说, Sb 对 Pd 表面起到了显著的修饰作用, 提高了催化剂表面 O2的非解离活化, 从而促进了 H2O2的高选择性合成. 但是过量 Sb 的加入会抑制催化剂对 H2的活化作用, 致使催化剂活性下降, 因此优选 Pd/Sb 的比例对于提高催化剂性能具有重要作用.     

AgOTf catalyzed direct amination of benzyl alcohols with sulfonamides

AgOTf catalyzed direct amination of primary alcohols with sulfonamides is described. This effective catalyst requires no preactivation of the hydroxy group of alcohols and the reaction is environmentally benign with water as a by-product. Various primary alcohols on amination with sulfonamides gave the corresponding products in moderate to good yields.     

Amino acid catalyzed direct enantioselective formation of carbohydrates: one-step de novo synthesis of ketoses

The amino acid-catalyzed direct enantioselective one-step de novo synthesis of carbohydrates using dihydroxyacetone phosphate mimetics as donors and aldehydes or in situ generated imines as acceptors is presented. The addition of water significantly accelerates as well as improves the enantioselectivity of the biomimetic aldol and Mannich reactions. The C₃+C_n methodology presented herein is a direct entry to orthogonally protected C-5 and C-6 ketoses (e.g., ribulose, tagatose and piscose) and deoxy- and aminosugars such as 4-amino-4-deoxy-fructose.     

A Thermodynamic Frame for the Kinetics of Polymer Crystallization under Processing Conditions

Summary. A retrospective view is given on work, which has been carried out at the Johannes Kepler University during the last two decades on the structure formation in crystallizable polymers during their processing. Emphasis is laid on some useful principles lend from basic physical chemistry: use of the T,S-diagram and of the temperature dependent courses of (effective) surface tensions along coexistence lines of phases. These considerations should be helpful in creating an overview, where a deficiency of direct experimental crystallization kinetics data exists. For a series of industrially important, mostly fast crystallizing, polymers data are given in the present paper for the quiescent melt (temperature dependences of number densities of nuclei and of growth speeds). Critical minimum cooling speeds for bypassing crystallization are given on the basis of the given data. These critical cooling speeds vary by almost six decades from HDPE to i-PS. These results are also helpful in the formulation of a viable classification of materials in the light of their processing conditions. This classification includes metals and glass forming minerals as limiting cases for extremely fast and extremely slowly crystallizing materials.     

Facile synthesis of 7-amino anilinoquinazolines via direct amination of the quinazoline core

The facile preparation of 4-(3-chloro-4-fluoroanilino)-6-alkoxy-7-aminoquinazolines from their corresponding 7-triflate and 7-fluoro precursors are highlighted.     

Asymmetric multicomponent copper catalyzed synthesis of chiral propargylamines

A three-component stereoselective reaction between an aldehyde, an amine and phenylacetylene to afford optically active propargyl amines in good yields was developed. The reaction is catalysed by copper complexes of enantiomerically pure bis-imines. The best results were obtained with imines readily prepared in very high yields from the commercially available binaphtyl diamine.

A very simple experimental procedure at room temperature allowed to obtain optically active propargyl amines in very good yields and enantioselectivity up to 75%. The extremely simple methodology and the mild reaction conditions, as well as the possibility of a modular approach for developing new and more efficient bis-imine-based chiral ligands make the present methodology very attractive.     

Thermodynamic and kinetic characterization of a bridged-ethylene hybrid C18 stationary phase

In this study, a series of polycyclic aromatic hydrocarbons (PAHs) and nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) is separated on a hybrid stationary phase using methanol and acetonitrile mobile phases. Temperature is varied from 283 to 313 K in order to determine thermodynamic and kinetic parameters of the separation. Thermodynamic behavior is characterized by the retention factor and associated changes in molar enthalpy, whereas kinetic behavior is characterized by the rate constants and associated activation energies. In this study, the retention factors for the NPAHs are smaller than those for the parent PAHs in methanol, while they are more similar to the parent PAHs in acetonitrile. The changes in molar enthalpy are very similar for all solutes, yet are more negative in acetonitrile than in methanol. The rate constants for the NPAHs are smaller than those for their parent PAHs in both mobile phases. Moreover, the rate constants in acetonitrile are one to four orders of magnitude smaller than those in methanol. Based on these thermodynamic and kinetic results, the hybrid stationary phase is compared to traditional silica stationary phases. In addition, the relative contributions from the partition and adsorption mechanisms are discussed.     

Computational Study on Thermodynamic Properties of Fischer-Tropsch Synthesis Process

Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H₂/CO ratio. At low temperature, high pressure and high H₂/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H₂/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C₂-C₄ olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.     

Amino alcohol catalyzed direct asymmetric aldol reactions: enantioselective synthesis of anti-α-fluoro-β-hydroxy ketones

Prolinol but not proline-(a recently established catalyst of simple intermolecular aldol reactions) was found to be an efficient catalyst for fluoroaldol reactions providing anti-α-fluoro-β-hydroxy ketones with good regio-, diasterio-, and enantioselectivities.