Not quite the last word on the Perkin reaction

Microwave irradiation does not accelerate the rate of the Perkin reaction carried out under normal atmospheric pressure. Water is an essential yet catalytic reactant for the Perkin reaction to occur. Containment of the Perkin reaction in a sealed vessel improves the yield. Two pressure increases are observed during a 4 h reaction time. An induction period is seen in the Perkin reaction when sodium acetate is used as a base. A re-appraisal of the reaction mechanism is proposed on the basis of these observations. The use of PFA^® reaction vessels enables the Perkin reaction to occur under aqueous conditions for around 80 reactions/vessel.     

低热固相反应的反应机理研究(Ⅰ)——冷融熔机理和冷溶熔机理的模型

本文提出了低热固相反应的冷融熔机理和冷溶熔机理,其中冷融熔机理主要针对于不含结晶水的反应体系,冷溶熔机理主要针对于含结晶水的反应体系,并对低热固相反应动力学提出冷融熔/冷溶熔、扩散、反应、成核、生长的五步机理。两种机理都避开了分子在固相晶格中的扩散,从而对低热固相反应的扩散问题进行了有效的解释,并给出了低热固相反应的热力学和动力学判据。     

烷基自由基β位裂解反应类反应势垒与速率常数的精确计算

提出反应类等键方法并用于高温燃烧机理中一类重要反应——烷基自由基β位裂解反应的反应势垒和速率常数的精确校正计算. 通过10种不同从头算水平对类反应中5个代表反应的反应势垒的计算发现, 用反应类等键反应方法和直接从头算方法获得的5 个代表反应的反应势垒最大绝对偏差的平均值分别为5.32 和16.16 kJ·mol^-1, 表明反应类等键反应方法计算的反应势垒对不同水平从头算方法的依赖性小, 可在较低从头算水平计算得到精确的反应势垒, 解决大分子体系反应势垒的精确计算问题. 此外应用反应类等键反应方法在BHandHLYP/cc-pVDZ 从头算水平计算了3 个代表反应的速率常数, 并与文献报道的实验值进行了比较, 其在500-2000 K温度区间内计算速率常数与实验速率常数中较大值与较小值的比值k_max/k_min的平均值为1.67, 最大值也仅有2.49. 表明应用反应类等键反应方法在较低从头算水平即可对同类反应的速率常数进行精确计算.最后在BHandHLYP/cc-pVDZ从头算水平用反应类等键反应方法计算了13个烷基自由基β位裂解反应的速率常数.     

Mechanistic Study on the Ozone‐Mercury Reaction and the Effect of Water and Water Dimer Molecules

The thermodynamics and mechanism of the reaction of elemental mercury with ozone has been studied computationally. The effect of water and water dimer molecules on the reaction has also been investigated. For dry reaction, we obtained two pathways and geometry optimization, atoms in molecules analysis and vibrational frequencies of all component of reaction have been used for confirming of reaction mechanism. Thermodynamic variable of reaction has been calculated. For the reaction in the presence of the water, our studies focus on ozone‐mercury complex reaction with water and water dimer and obtained the mechanism of reactions. Comparison of wet and dry reaction shows the energy profile of reaction decreases with water molecule correspond to experimental prediction. Calculated thermodynamic variable of all reaction shows the Gibbs free energy of reaction decreases with the number of water molecule.     

On the importance of steady-state isotopic techniques for the investigation of the mechanism of the reverse water-gas-shift reaction

The formation and reactivity of surface intermediates in the reverse water-gas-shift reaction on a Pt/CeO2 catalyst are critically dependent on the reaction conditions so that conclusions regarding the reaction mechanism cannot be inferred using ex operando conditions.     

On the complexity of kinetics and the mechanism of the thiosulfate-periodate reaction

The thiosulfate-periodate reaction has been studied spectrophotometrically in a slightly acidic medium at 25.0 ± 0.1 °C in an acetate/acetic acid buffer by monitoring the absorbance in the 250-600 nm wavelength range at a constant ionic strength adjusted by the buffer component sodium acetate. In agreement with a previous study, we found that the reaction cannot be described by a single stoichiometric equation, tetrathionate and sulfate are simultaneously formed, and its ratio strongly depends on the pH. As expected at certain initial concentration ratios of the reactants, the reaction behaves as a clock reaction, but after its appearance, iodine is slowly consumed mainly because of the moderate tetrathionate-iodine reaction. It is also enlightened that the initial rate of the reaction is completely independent of the pH, which apparently contradicts a previous study, which postulates a "supercatalytic" behavior of the hydrogen ion on the title reaction. Significant buffer assistance that may change the absorbance-time profiles was also observed. On the basis of the kinetic data, a robust 28-step kinetic model with 22 fitted parameters is proposed and discussed to explain adequately all of the important characteristics of the kinetic curves.     

Baylis-Hillman反应机理研究进展

介绍了一种形成碳—碳键的方法——Baylis-Hillman反应, 综述了单分子醛、双分子醛反应机理、TiCl₄催化机理、不对称诱导机理以及低温效应、溶剂效应、离子液体反应机理的研究进展.     

硝基烷基膦酸酯碳负离子烷基化反应区域选择性研究

α-或β-硝基烷基膦酸酯双负离子与卤代烷反应, 生成碳-烷基化产物, 反应区域选择性取决于硝基膦酸酯的结构, 讨论了可能的反应机理。     

关于反应分子数定义的讨论

There are two different views on the definition of reaction molecularity in physical chemistry textbooks and related literatures so far. We give a deep discussion about this conception herein. Starting with the development of chemical kinetics and the definition of elementary reaction and state-state reaction, we clarify that elementary reaction and state-state reaction are the conceptions belonging to macro-and micro-systems, respectively, and reaction molecularity is also belonging to micro-conception. Based on this conclusion, we think that the more reasonable definition of reaction molecularity should be "the number of chemical particles that take part in a state-state reaction (or an elementary chemi-physical reaction) as a reactant".     

有机磷化合物的研究 XXV: 溶剂性质对烯丙在膦酸酯碳阴离子和芳醛反应区域选择性的影响

本文研究烯丙基膦酸二乙酯碳阴离子和苯甲醛, 对甲基苯甲醛的反应, 考察了溶剂对反应区域选择性的影响.     

Interaction of dimethyl carbonate with anilines in the presence of potassium methylate: Kinetics and the role of the base

The kinetic patterns of the reaction between dimethyl carbonate and anilines in the presence of a potassium methylate as a catalyst were studied. The mechanism of aminolysis was clarified, which includes the detachment of the proton from the amino group of aniline and the subsequent attack of the resulting anion on the carbonyl group of dimethyl carbonate. It is shown that when the reaction occurs in the dimethyl carbonate-methanol 3:1 system, the process can be described as an irreversible first-order reaction in the aniline though the target reaction is complicated by side interaction between potassium methylate and dimethyl carbonate. The rate constants of the target reaction with substituted anilines and of the side reaction in the temperature range of 70-90°C were determined. It is shown that the influence of the substituent on the reaction rate is described by the Hammett equation, with the constant of the reaction series being positive and the best correlation being achieved for σ-scale. The results obtained are consistent with the proposed mechanism of the reaction and are explained by the facilitation of the aniline deprotonation with increasing acceptor properties of the substituent. Effective activation energies for the reaction of various anilines with dimethyl carbonate are found.     

N溴代丁二酰亚胺氧化醇反应的热动力学研究

氧化反应是有机化学中的一种重要反应类型,也是有机化学、化学工程和生物学家们研究的重点之一.但因其机理复杂,至今未见到用热动力学理论探索氧化反应体系的报道. N溴代丁二酰亚胺(NBS)是良好的溴化试剂,在不同反应条件下,它既可和不饱和键发生加成反应,也可在水溶液中作为次溴酸的来源,还可作为有效的氧化剂和脱氢剂.Reich和Reichstein首先报道了用N溴代乙酰亚胺将仲醇缓慢氧化为酮,Fieser等人报道了NBS的氧化作用.本文用RD-1型热导式自动量热计研究了35℃下NBS氧化异丙醇及环己醇2个反应体系,计算了反应速率常数,对反应的动力学及其机理提出了较合理的解释.     

Theoretical Studies on the Coordinate Exchange Reaction of the Dihydrogen Between Formic Acid and Water

The intermolecular hydrogen bond and coordinate exchange reaction of the dihydrogen between formic acid and water were studied by means of ab initio MO method at 6-31G basis set. The transition state of the reaction and the changes of some physical quantities of the reaction systems in the path of the intrinsic reaction coordinate(IRC) were obtained.. The results show that the exchange reaction of the dihydrogen between formic acid and water is coordinate and almost simultaneous.The frequency factor and activation energy of the reaction were also estimated.     

Stoichiometry of the reaction of diphenylchlorophosphine with dimethylformamide in the presence of NaI

Stoichiometric relations of initial compounds and reaction products in the synthesis of N,N-dialkyl-(diphenylphosphinomethylene)iminium are established; the second reaction product is diphenylphosphinic iodide. Bringing triphenylphosphine into the reaction increases the N,N-dialkyl(diphenylphosphinomethylene)-iminium yield approximately twice. One of the reaction intermediates is shown to be iododiphenylphosphine. The reaction can be regarded as disproportionation.     

金属参与的正电子放射性药物的合成进展

随着正电子发射断层显像技术的高速发展,正电子放射性药物的合成近年来已成为药物合成领域的热点之一.本文综述了金属参与的放射性同位素标记药物及中间体的合成方法,反应类型包括Stille偶联反应、Suzuki偶联反应、Heck偶联反应、Sonogashira偶联反应、羰基化反应、金属-卤素置换反应和点击反应等.     

Effect of the reaction temperature on the transglycosylation reactions catalyzed by the cyclodextrin glucanotransferase from Bacillus macerans for the synthesis of large-ring cyclodextrins

The synthesis of cyclodextrins with from 6 to more than 50 glucose units by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from Bacillus macerans was investigated. Analysis of the synthesized cyclic α-1,4-glucan products showed that a higher yield of large-ring cyclodextrins were obtained with a reaction temperature of 60 °C compared to 40 °C. The yield of large-ring cyclodextrins obtained at 60 °C represented about 50% of the total glucans employed in the reaction. Analysis of the cyclodextrin-forming cyclization reaction and of the coupling reaction of the CGTase resulting in the degradation of mainly the larger cyclic α-1,4-glucans indicated higher rates of the cyclization reaction at 60 °C compared to 40 °C while the opposite was found for the coupling reaction.     

Dramatic rate acceleration of the Baylis-Hillman reaction in homogeneous medium in the presence of water

[reaction: see text] In homogeneous H(2)O/solvent medium, the reaction rate of aromatic aldehydes and acrylonitrile or acrylate was greatly accelerated, which led to shorter reaction time, lower reaction temperature, and higher yield. In this reaction, Me(3)N, DMAP, DABCO, and urotropine were good catalysts. Except for low-carbon alcohols, tetrahydrofuran, 1,4-dioxane, and acetonitrile could be chosen as the solvent. Under this condition, the diastereoselective reaction of nitrobenzaldehyde and L-menthyl acrylate was realized with 88-99% de.     

Potential-Barrier Profile for the Adiabatic Electron Transfer Reaction in the Condon Approximation

An effective reaction coordinate is introduced and a self-consistent algorithm is proposed for the calculation of the potential barrier profile of the adiabatic electron transfer reaction in a polar solvent, taking into account electron wave functions of reagents with respect to the media polarization. A change in the functions when moving along the reaction coordinate reduces significantly the activation barrier and increases the reaction rate.     

三芳胺合成的研究进展

三芳胺化合物的合成方法主要有3种:(1)非金属催化的胺化反应;(2)铜催化的Ullnann反应,包括使用过量铜粉为催化剂的传统的Ullmann反应、使用相转移催化剂的Ullmann反应以及使用配体的post-Ullmann反应;(3)钯催化的Buchwald-Hartwig反应.该类反应活性的关键是配体的选择,根据配体结构的不同可分为双膦螯合型配体、单膦配体和非膦配体.对该类化合物的这几种合成方法的研究进展进行了总结.     

混合多卤甲烷与金属镁反应产生溴氯卡宾及其反应机理的研究

应用CHBr3/CHCl3或CHBr3/CCl4和金属镁在一般的Grignard反应条件下与烯烃反应, 制备偕溴氯环丙烷衍生物。该反应原料易得, 反应条件温和, 产率良好, 后处理方便, 是制备偕溴氯环丙烷衍生物的一种简便的新方法。文中研究了上述反应的单电子转移和自由基链循环的复杂反应机理。