“水上”(“on water”)有机反应

"水上"有机反应的发展是水相绿色合成反应研究领域中的一个突破。体系的非均相性质是"水上"反应的基本特征。水不仅是重要的绿色反应介质,在大多数"水上"有机反应中都能观察到水对反应的速度和选择性有明显的提升作用。采用"水上"反应的条件,可以使反应的规模扩大,有利于产物的分离、纯化。本文以反应的类型分类综述了近年来有关"水上"有机反应研究的进展,以及在绿色有机合成中的应用。     

Gas-phase Boudouard disproportionation reaction between highly vibrationally excited CO molecules

The gas-phase Boudouard disproportionation reaction between two highly vibrationally excited CO molecules in the ground electronic state has been studied in optically pumped CO. The gas temperature and the CO vibrational level populations in the reaction region, as well as the CO₂ concentration in the reaction products have been measured using FTIR emission and absorption spectroscopy. The results demonstrate that CO₂ formation in the optically pumped reactor is controlled by the high CO vibrational level populations, rather than by CO partial pressure or by flow temperature. The disproportionation reaction rate constant has been determined from the measured CO₂ and CO concentrations using the perfectly stirred reactor (PSR) approximation. The reaction activation energy, 11.6 ± 0.3 eV (close to the CO dissociation energy of 11.09 eV), was evaluated using the statistical transition state theory, by comparing the dependence of the measured CO₂ concentration and of the calculated reaction rate constant on helium partial pressure. The disproportionation reaction rate constant measured at the present conditions is k_f = (9 ± 4) × 10⁻¹⁸ cm³/s. The reaction rate constants obtained from the experimental measurements and from the transition state theory are in good agreement.     

Eco-friendly synthesis of jasminaldehyde by condensation of 1-heptanal with benzaldehyde using hydrotalcite as a solid base catalyst

The catalytic activity of hydrotalcite ([M(II)_1−xM(III)_x(OH₂)]^x+(CO₃²⁻)_x/n·mH₂O; where M(II) = Mg, Ni, Zn and M(III) = Al) was evaluated for the synthesis of jasminaldehyde by solvent free condensation of 1-heptanal with benzaldehyde. The effect of activation of as-synthesized Mg-Al hydrotalcite samples of varied Mg/Al molar ratio on its catalytic activity was studied and correlated with their basicity as determined from the model test reaction. The effect of reaction parameters such as, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and reaction temperature on conversion of 1-heptanal and selectivity of jasminaldehyde was studied in detail. Maximum selectivity of jasminaldehyde (86%) with 98% conversion of 1-heptanal was observed using as-synthesized Mg-Al hydrotalcite of Mg/Al molar ratio of 3.5 as a catalyst. The kinetics of the reaction was measured and reaction rate and order of reaction were determined under optimum reaction conditions. The catalyst was re-used upto three cycles without significant loss in its activity. The base catalyzed reaction mechanism for condensation of 1-heptanal with benzaldehyde is proposed.     

Reaction force constant and projected force constants of vibrational modes along the path of an intramolecular proton transfer reaction

We have explored the relationships between the reaction force F(ξ), the reaction force constant κ(ξ) and the projected force constants of the intramolecular proton transfer HO−NS → ON−SH along the intrinsic reaction coordinate ξ. The structural changes and energetics associated with the reaction are analyzed in terms of the three regions defined by F(ξ): reactant, transition and product. The significance of the similarity between κ(ξ) and the variation of the force constant associated to the reaction coordinate mode, k_ξ(ξ), is discussed in detail.     

碳纳米管的聚合物功能化与结构控制:聚合物接枝碳纳米管

碳纳米管高分子化是发展高性能的聚合物基纳米功能材料的重要研究方向,本文从"grafting-to"和"grafting-from"两种方式对聚合物接枝碳纳米管的最新进展进行了系统综述。"Grafting-to"方法主要包括羧基衍生反应(酰化、酯化)、加成反应(大分子自由基加成、叠氮环加成)和硫醇偶联反应。"Grafting-from"方法包括普通自由基聚合、可控/活性自由基聚合、离子聚合、开环聚合和逐步聚合反应,其中碳纳米管表面引发活性自由基聚合进一步分为原子转移自由基聚合、氮氧稳定自由基聚合和可逆加成-断链转移聚合。此外,本文还简述了碳纳米管自身的聚合反应,并探讨了目前聚合物修饰碳纳米管所面临的问题和今后的发展方向。     

氧化反应对胜利褐煤水蒸气气化反应的促进作用Ⅰ:宏观反应特性研究

在φ80×3 000mm耐高温不锈钢管气流床反应器中,以150-180μm胜利褐煤为气化原料,考察了800和900℃时添加氧气前后褐煤转化率的变化,研究了氧化反应对水蒸气气化反应影响的宏观特征。结果表明,添加氧气后褐煤转化率明显大于O_2和H_2O气氛下褐煤转化率之和,即向水蒸气气氛添加氧气后褐煤转化率的增幅大于氧气氧化作用导致的褐煤转化率的增幅,随着H_2O含量增大以及温度的升高此现象愈加明显。该协同作用主要是氧化反应对水蒸气气化反应的促进作用造成的。利用φ40×200 mm石英圆筒流化床反应器进行了类似的实验,也发现了该协同作用。同时,借鉴收缩核模型并结合气流床气化实验条件推导了水蒸气气化宏观动力学方程,得到的速率方程(Z-(1-x))~(1/3)=(tβk_(H_2O)/Rρ_C)φ_(H_2O)=K_(H_2Oφ_(H_2O))与实验值吻合较好,添加氧气后水蒸气气化反应速率和水蒸气气化反应表观速率常数K_(H_2O)明显增大,这是氧气对水蒸气气化反应促进作用的动力学特征。     

过渡金属催化[2 + 2 + 2]环加成反应合成吡啶衍生物

环加成反应可以一步同时构建多个化学键,是目前国内外研究最为活跃的领域之一。相比于传统方法,过渡金属催化的[2+2+2]环加成反应是合成吡啶衍生物的有效手段。本文从反应机理、非手性吡啶化合物合成和手性吡啶化合物合成三个方面阐述了近年来吡啶衍生物的研究情况,涉及Co、Rh、Ru、Fe、Ni、Ti等金属催化体系。     

Kinetics of the gas‐phase reactions of hydroxyl radicals with C1–C6 aliphatic alcohols in the presence of ammonium sulfate aerosols

The effects of ammonium sulfate aerosols on the kinetics of the hydroxyl radical reactions with C₁–C₆ aliphatic alcohols have been investigated using the relative rate technique. P‐xylene was used as a reference compound for the C₂–C₆ aliphatic alcohols study, and ethanol was used as a reference compound for the methanol study. Two different aerosol concentrations that are typical of polluted urban conditions were tested. The total surface areas of aerosols were 1400 μm² cm^?3 (condition I) and 3400 μm² cm^?3 (condition II). Results indicate that ammonium sulfate aerosols promote the ethanol/OH radical and 1‐propanol/OH radical reactions as compared to the p‐xylene/OH radical reaction. The relative rate of the ethanol/·OH reaction versus the p‐xylene/·OH reaction increased from 0.19 ± 0.01 in the absence of aerosols to 0.24 ± 0.01 and 0.26 ± 0.02 under aerosol conditions I and II, respectively. The relative rate of the 1‐propanol/·OH reaction versus the p‐xylene/·OH reaction increased from 0.45 ± 0.03 in the absence aerosols to 0.56 ± 0.02 and 0.55 ± 0.03 under aerosol conditions I and II, respectively. However, significant changes in the relative rates of the 1‐butanol/·OH, 1‐pentanol/·OH, and 1‐hexanol/·OH reactions versus the p‐xylene/·OH reaction were not observed for either aerosol concentration. The relative rates of the methanol/·OH reaction versus the ethanol/·OH reaction were identical in the absence and presence of aerosols. These results indicate that ammonium sulfate aerosols promote the methanol/·OH reaction as much as the ethanol/·OH reaction (as compared to the p‐xylene/·OH reaction). © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 422–430, 2001     

化学修饰方法对聚乙二醇功能化碳纳米管的影响

通过酰氯化法与碳二亚胺缩合法(EDC/NHS)制备氨基化聚乙二醇(PEG1500N)修饰的多壁碳纳米管(MWNTs)并采用FTIR、Raman、TEM、原子力显微镜(AFM)、TGA-DTA-DSC、UV-Vis进行表征与分析。实验结果发现：两种方法PEG1500N都能很好地修饰MWNTs,但EDC/NHS缩合法采用更短的反应时间(反应1 d),达到了更好的接枝效果。EDC/NHS缩合法提高了碳管上羧基的利用率,接枝率大大提高。TGA-DTA分析表明缩合法接枝率为30%,而酰氯化法(反应4 d)为15%。UV-Vis分析表明EDC/NHS缩合法得到的产物溶解性也更好,溶解度由1.19 mg·mL^-1(酰氯化法得到的产物的溶解度)提高到2 mg·mL^-1以上。     

Microwave Assisted Radical Grafting of Maleic Anhydride onto Polyethylene in Solution

The reaction of maleic anhydride (MAH) grafted onto low density polyethylene (LDPE) in nylene solvents in the presence of benzoyl peroxide (BPO) as an initiator by microwave irradiation has been investigated. The influence of reaction conditions such as initiator content, monomer content and irradiation time have been examined. In the weight composition of xylene/LDPE/MAH/BPO=10/1/1/0.07, the grafting degree reaches 56.5 mmol MAH/100 g PE within only 8 min of microwave irradiation. The grafting reaction time of microwave irradiation shortens over 40 times than in the conventional grafting reaction.     

Can chlorine anion catalyze the reaction of HOCl with HCl?

The reaction of HOCl + HCl → Cl₂ + H₂O in the presence of chlorine anion Cl⁻ has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol⁻¹ and this reaction has been shown to have a high activation barrier of 46.5 kcal mol⁻¹. Cl⁻ is found to catalyze the reaction via the formation of HOCl·Cl⁻, ClH·HOCl·Cl⁻ and Cl⁻·H₂) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl.     

Photochemical reaction kinetics in optically dense media: The influence of thermal reactions

The kinetics of photochemical reactions in optically dense media essentially free from diffusion was considered. The photochromic isomerization A ↔ B was studied as an example. If thermal isomerization is possible, a stationary state is achieved in time determined by rate constants for the thermal reactions. The concentration wave profile is changed during the photochemical reaction propagation. Low values of thermal reaction constants and decrease in sample optical density during photochemical isomerization were found to be essential for maximal wave penetration into the sample. Sharp concentration gradients of A and B can be observed when both the optical density is increased during photochemical isomerization and the quantum yield of the direct photochemical reaction A → B is higher than that of the reverse photochemical reaction B → A.     

A Novel Process for CO2 Capture by Using Sodium Metaborate,Part II: Carbonation Reaction and Kinetic Studies

In Part II of this two‐part series of papers, optimization of carbonation reaction with sodium metaborate and kinetics of the reaction are studied and compared to the structural properties, which were reported in Part I. This paper presents a comprehensive study on the optimization of reaction conditions and determination of reaction parameters of sodium metaborate (NaBO₂) and carbon dioxide (CO₂). Both hydrated and dehydrated forms of NaBO₂ have high sorption capacities of CO₂ up to 400°C. Decomposition of the products starts beyond 400°C and completes at 600°C. The shrinking core model is used to explain the kinetics of the noncatalytic heterogeneous reaction. The reaction progresses in two stages: one is surface reaction controlled and the other is diffusion controlled. The apparent activation energy and preexponential factor for reaction‐controlled and diffusion‐controlled regions are calculated as 11.8 kJ/mol and 3.5 × 10⁶ cm²/min and 18.2 kJ/mol and 6.5 × 10⁻⁵ cm²/min, respectively.     

Pyrolysis mechanism of carbon matrix precursor cyclohexane(III)—pyrolysis process of intermediate 1-hexene

The pyrolysis mechanism of important intermediate 1-hexene of carbon matrix precursor cyclohexane was studied theoretically. Possible reaction paths were designed based on the potential surface scan and electron structure of the initial C–C bond breaking reactions. Thermodynamic and kinetic parameters of the possible reaction paths were computed by UB3LYP/6-31+G* at different temperature ranges. The results show that 1-hexene pyrolyzes at 873 K. When below 1273 K, the major reaction paths are those that produce C₃H₄, and above 1273 K, the major reaction paths are those that produce C₃H₃ from the viewpoint of thermodynamics. From the viewpoint of kinetics, the major product is C₃H₃, it results from the pyrolysis reaction of 1-hexene cracking bond C₃–C₄ and generating C₃H₅ and C₃H₇ with the activation energy ΔE₀^≠θ=296.32 kJ/mol. Kinetic results also show that product C₃H₄ accompany simultaneously, which is the side reaction starting from the pyrolysis of 1-hexene forming C₄H₇ and C₂H₅ with the activation energy of 356.73 kJ/mol. When reaching 1473 K, the rate constant of the rate-determining steps of these two reaction paths do not show much difference, which means both the reaction paths exist in the pyrolysis process at the high temperature. The above results are basically in accordance with mass spectrum analysis and far more specific.     

微量热法研究过氧化氢酶反应

利用微量热法和热动力学方程研究了过氢化氢酶反应.该反应遵循Michaelis-Menten动力学,298.15K和pH7.0时,其米氏常数、酶转换数以及摩尔反应焓分别为2.36×10^-2mol/L、1.20×10⁴s^-1和-83.67kJ·mol^-1.过氧化氢酶反应后期对底物是一级反应,其总反应速度常数和一级速度常数分别为k_o=6.31×10⁵L·mol^-1·s^-1和k₁=6.31×10⁵/[E_o]s^-1.该反应服从Ogura机理,其酶-底物三元复合物的分解速度常数为6.00×10³s^-1.     

手性三齿席夫碱金属络合物催化的不对称反应*

各种手性三齿席夫碱与金属（钛, 铬, 钒, 铁, 铜, 铝）形成的络合物,在催化醛的硅腈化、Diels-Alder、Aldol、杂ene、硫化物的氧化等不对称反应中具有良好的催化活性和对映选择性;其中一些催化体系已成功的应用于天然产物的全合成中,该研究取得了系统性的研究成果。本文综述了手性三齿席夫碱金属络合物在不对称催化反应中的研究进展,同时,探讨了催化剂结构和反应条件对其催化活性和对映选择性的影响。     

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

The title reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C-H oscillator /2000>- or in a local mode containing one quantum each in two C-H oscillators /1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH2D2/2000>- reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH2D2/1100> reaction yields methyl radical products that are C-H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH2D2/2000>- reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH2D2/1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH2D2/2000>- reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH2D2/1100> reaction. The results can be explained by a simple spectator model and by noting that the /2000>- mode leads to a wider cone of acceptance for the reaction than the /1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction.     

Determination of Optimal Reaction Conditions and Influence of Metal Ions on Cellulose Degradation by Cellulase in the Dioctyl Sulfosuccinate Sodium Salt (AOT)/n-Hexanol/Cyclohexane Reversed Micelle System

The power-time curves of the cellulose degradation by cellulase were determined under the different conditions with the existence of metal ions or not in the dioctyl sulfosuccinate sodium salt (AOT)/n-hexanol/cyclohexane reverse micelle system by the microcalorimeter method. From these curves, the Michaelis constant and the maximum reaction rate of this reaction were obtained. The optimum T, pH and W_o were determined as W_o = 3.011, pH = 5.015, and T = 315.43 K. Under these optimum reaction conditions, the power-time curves of the cellulose degradation by the cellulase with the metal ions were also obtained. The apparent Michaelis constant and the maximum reaction velocity were gained. The relationship between the apparent Michaelis constant and the concentration of the metal ions was established, and the influence of metal ions was discussed as well. The results indicate that some metal ions have promotion roles on the reaction. However, others could inhibit the reaction. These results are significant for the theoretical and application in the field of reverse micelles enzyme catalysis system.     

A novel electrogenerated chemiluminescence sensor for pyrogallol with core-shell luminol-doped silica nanoparticles modified electrode by the self-assembled technique

The core-shell luminol-doped SiO₂ nanoparticles were synthesized and immobilized on the surface of chitosan film coating graphite electrode by the self-assembled technique. Then, a novel electrogenerated chemiluminescence (ECL) sensor for pyrogallol was developed based on its ECL enhancing effect for the core-shell luminol-doped silica nanoparticles. The ECL analytical performances and the sensing mechanism of this ECL sensor for pyrogallol were investigated in detail. The corresponding results showed that: compared with the conventional ECL reaction procedures by luminol ECL reaction system, the electrochemical (EC) reaction of pyrogallol and its subsequent chemiluminescence (CL) reaction occurred in the different spatial region whilst offering a high efficiency to couple the EC with the CL reaction to form the ECL procedures. In this case, this new sensing scheme offered more potential to improve the analytical performances of the ECL reaction. Under the optimum experimental conditions, this ECL sensor showed less than 5% decrease in continuums over 100 times ECL measurements, the detection limit was 1.0 × 1.0⁻⁹ mol/L for pyrogallol. The linear range extended from 3.0 × 10⁻⁹ mol/L to 2.0 × 10⁻⁵ mol/L for pyrogallol.     

氧化反应对胜利褐煤水蒸气气化反应的促进作用Ⅱ.作用机理研究

在φ80×3 000 mm耐高温不锈钢管反应器中,进行了N2/N2+O2/N2+H2O/N2+O2+H2O气氛下800和900℃的胜利褐煤气化实验,采用红外光谱、X射线光电子能谱、拉曼光谱和烟气在线分析等研究了添加氧气前后半焦的物理结构、官能团及煤气组成的变化,旨在探讨氧化反应促进水蒸气气化反应的作用机理。结果表明,氧化反应对水蒸气气化反应的促进作用可用半焦的微观结构变化和水蒸气气化解离吸附机理解释。氧化反应的开孔和扩孔作用使碳颗粒微孔数量、比表面积、孔容、吸附量明显增加,更多的碳表面活性位暴露出来,也促进了半焦中甲基、亚甲基、C=O键、C-O键的断裂和高活性的羧基COO-和大量氢自由基的生成,这些都有利于水蒸气气化反应的进行,尤其在高温和水蒸气含量较高时。同时,氧气的加入改变了反应气氛中CO2、CO、H2相对含量和水蒸气分子/活性炭原子内能,也有利于水蒸气气化反应的进行,这与水蒸气气化解离吸附机理相吻合。