反应类等键反应方法及类反应热动力学参数计算

本文提出了反应类等键反应方法,将通常用于热力学性质计算的等键反应方法推广用于类反应中反应势垒和反应焓变的计算. 对碳氢燃料低温燃烧反应机理中的一类重要反应类：?烷基自由基过氧化氢裂解生成烯烃和HO2自由基的反应势垒和反应焓变进行了计算. 通过对该类16个反应中的5个代表反应分别在不同计算水平HF、DFT、MP2、CCSD(T)的比较计算发现,采用等键反应方法可在较低从头算级别计算得到类反应较高精度的反应势垒,提高了计算的效率和精度. 本文采用反应类等键反应方法在B3LYP/6-311G(d,p)计算水平对该类16个反应进行了反应势垒和反应焓变的计算,并建立了反应势垒和反应能的线性自由能关系：delta V=71.02+0.41?delta E.     

Study on the reaction kinetics between PBT and epoxy by a novel rheological method

In the present study, the reaction kinetics of polybutylene terephthalate (PBT) and epoxy system was studied by a novel rheological method. The reaction process was determined by rheological test and the results showed that there were three stages in the reaction between PBT and epoxy, which were reaction-controlling stage (stage I), reaction-stagnation stage (stage II) and diffusion-controlling stage (stage III). In addition, the stage I was selected to study the reaction kinetics by the rheological method. The results showed that the reaction between PBT and epoxy could be classified as a pseudo-first-order reaction due to the excessive amount of epoxy group. Furthermore, the reaction apparent activation energy of the stage I determined by the rheological method was 143 kJ/mol. To confirm these results, the reaction kinetics was also evaluated by the endgroup determination method, and the results showed that the reaction could also be classified as a pseudo-first-order reaction. Moreover, the apparent activation energy of the reaction was 116 kJ/mol, which was similar to that of the value obtained by the rheological method.     

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.     

固相合成胸腺五肽(TP5)

采用Fmoc固相多肽合成中的活化酯方法和2,6-二氯苯甲酰氯(DCB)混合酸酐法, 对Fmoc-Tyr(t-Bu)-OH与Wang树脂反应中的反应级数和表观活化能进行了研究, 并采用常规方法和微波强化方法分别进行了胸腺五肽的合成. 实验结果表明, 活化酯方法的反应级数为1.855, 表观活化能15.24 kJ/mol, 混合酸酐法的表观活化能为35.14 kJ/mol. 与传统方法相比, 微波将缩合反应速率提高了30倍以上, 氨基酸过量倍数也从传统的三倍降低到两倍.     

建立反应速率方程的新方法

对于有一定级数的反应,不论反应级数是几,建立反应速率方程时都可以用非线性拟合法来完成。该方法分为两步。第一步,初次对实验数据进行非线性拟合,从而得到反应级数;第二步,借助已得到的反应级数再次对实验数据进行非线性拟合,从而得到反应速率常数。与传统建立反应速率方程的方法相比较,非线性拟合法不仅简单易操作,而且处理结果准确、图线美观大方。     

烷烃与氢过氧自由基氢提取反应类反应能垒与速率常数的精确计算

氢过氧自由基从烷烃分子中提取氢的反应是碳氢燃料中低温燃烧化学中非常重要的一类反应。本文用等键反应方法计算了这一类反应的动力学参数。所有反应物、过渡态、产物的几何结构均在HF/6-31+G(d)水平下优化得到。以反应中的过渡态反应中心的几何结构守恒为判据,该反应类可用等键反应处理。本文选取了乙烷和氢过氧自由基的氢提取反应为参考反应,其它反应作为目标反应,用等键反应方法对目标反应在HF/6-31+G(d)水平的近似能垒和反应速率常数进行了校正。为了验证方法的可靠性,选取C5以下的烷烃分子体系,对等键反应方法校正结果和高精度CCSD(T)/CBS直接计算结果进行了比较,最大绝对误差为5.58k J?mol~(-1),因此,采用等键反应方法只需用低水平HF从头算方法就可以再现高精度CCSD(T)/CBS计算结果,从而解决了该反应类中大分子体系的能垒的精确计算。本文的研究为碳氢化合物中低温燃烧模拟中重要的烷烃与氢过氧自由基氢提取反应提供了准确的动力学参数。     

Rapid Optimization of Reaction Conditions Based on Comprehensive Reaction Analysis Using a Continuous Flow Microwave Reactor

Generally, the flow method has the advantage of a precise control over the reaction parameters and a facile modification of the reaction conditions, while a continuous flow microwave reactor allows for the quick optimization of reaction conditions owing to the rapid uniform heating. In this study, we developed a “9+4+1 method” to optimize reaction conditions based on comprehensive reaction analysis using a flow microwave reactor. The proposed method is expected to contribute to the synthesis of various fine and bulk chemicals by reducing cost and wastage, and by conserving time.     

Kinetic investigation of redox reaction between vitamin C and ferric chloride hexahydrate in acidic medium

The kinetics of the reaction between vitamin C (l-ascorbic acid) and ferric chloride hexahydrate was investigated in acidic medium at pH 3 spectrophotometrically. The order of the reaction was established by applying different methods, such as initial rate method, integration method and half-life method. The results obtained from each method were correlated with each other and consistency in all methods was observed. The order of the reaction with respect to each reactant was found first and the overall second order was recommended for the reaction.     

An initial-rate potentiometric method for the determination of uric acid using a fluoride ion-selective electrode

The principle of a general potentiometric method based on Emerson-Trinder reaction for the assay of various hydrogen peroxide generating systems is reported. Emerson-Trinder reaction, habitually employed as a spectrophotometric indicator reaction, is exploited in this method as a potentiometric indicator reaction. This method is based on the detection of F⁻ ions, liberated from the oxidation of a fluorophenol compound used as hydrogen-donor in Emerson-Trinder reaction, by a fluoride ion-selective electrode. The ability and usefulness of this method are illustrated by an initial-rate potentiometric determination of uric acid in aqueous and human serum samples, for which, initial-rate reaction progress curves, linear calibration curve, within-day precisions, upper and lower detection limits, and also its analytical recovery were reported.     

Multistructural microiteration technique for geometry optimization and reaction path calculation in large systems

We propose a multistructural microiteration (MSM) method for geometry optimization and reaction path calculation in large systems. MSM is a simple extension of the geometrical microiteration technique. In conventional microiteration, the structure of the non‐reaction‐center (surrounding) part is optimized by fixing atoms in the reaction‐center part before displacements of the reaction‐center atoms. In this method, the surrounding part is described as the weighted sum of multiple surrounding structures that are independently optimized. Then, geometric displacements of the reaction‐center atoms are performed in the mean field generated by the weighted sum of the surrounding parts. MSM was combined with the QM/MM‐ONIOM method and applied to chemical reactions in aqueous solution or enzyme. In all three cases, MSM gave lower reaction energy profiles than the QM/MM‐ONIOM‐microiteration method over the entire reaction paths with comparable computational costs. © 2017 Wiley Periodicals, Inc.     

热动力学特征对比参量法及其应用研究

基于简单级数反应的积分和微分热动力学方程，建立了热动力学特征对比参量 法的数学模型，提出了一种由特征时间参量计算特征对比参量的方法，通过几种不 同级数模型反应的热动力学研究证明了方法的正确性，并利用该法研究了过氧化氢 在磷酸盐缓冲液中氧化对苯醌反应的动力学特征，实验结果表明该反应动力学方程 可以表示为：dC(醌)/dt=kC(醌)C(H_2O_2)~0.5C(H~+)~(-0.5)     

蔗糖酯的合成研究进展

综述了蔗糖酯的合成方法及工艺的研究进展,并对其反应机理进行了阐述.蔗糖酯的合成方法主要有四种:溶剂法、微乳化法、无溶剂法以及酶催化法.溶剂法采用DMF或DMSO为溶剂,但是这两种溶剂均有毒,限制了蔗糖酯在食品等行业的应用.微乳化法采用丙二醇或水代替溶剂法所使用的有毒溶剂,并加入乳化剂,使反应体系近似为均相体系.无溶剂法则是通过在反应体系中加入乳化剂或表面活性剂等使熔融相成均一相,反应平稳.但是一般无溶剂法反应温度较高,反应不易进行,产率低,且产品质量得不到保证.酶催化合成法是一种新的生物合成方法,采用生物酶代替传统的催化剂合成蔗糖酯,该法催化活性高、反应条件温和、选择性强、产物易分离等优点.文中还对蔗糖酯粗品的纯化工艺进行了介绍.     

室温固-固反应初期动力学的粉末紫外-可见漫反射光谱研究

以丁二酮肟和水合醋酸镍及无水醋酸镍的反应为模板, 利用反应物与产物之间的颜色差异, 通过粉末紫外-可见漫反射光谱对反应初期产物生成量的变化进行测定, 从而研究其反应动力学. 由于光谱性质与产物的晶型无关, 并且如果反应物与某一产物之间的光谱性质(如颜色)差异较大, 即使在微量产物的情况下也很容易跟踪到产物量的变化. 因此, 该方法对于固-固反应初期的动力学响应非常灵敏, 但当反应进行到一定程度后则不适用.     

固相反应法制备Pt-Ru/C催化剂对乙醇氧化的电催化活性研究

0引言近年来,直接甲醇燃料电池(DMFC)由于其燃料来源丰富、价格低廉、甲醇携带和储存安全方便等独特的优越性而越来越受到重视[1]。但是甲醇具有一定的毒性,因此要想实现DMFC在诸如手机、笔记本电脑以及电动车等可移动电源领域的应用,必须探索新的液体燃料以替代有毒性的甲醇。     

Preparation of Pt／C Catalyst with Solid Phase Reaction Method

The Pt/C catalyst was prepared with solid phase reaction method (Pt/C(S)) for the first time.Its Performances were compared with that prepared by the traditional liquid phase reaction method. The results demonstrate that the electrocatalytic activity of Pt/C catalyst with solid phase reaction method for methanol oxidation is higher than that with liquid phase reaction method. XRD and TEM measurements indicate that the Pt/C(S) possesses low crystalline extent and small particle size.     

Efficient NaOH-Catalyzed Reaction of Aromatic Aldehyde,Cyclic Ketones,and Malononitrile Under Solvent-Free Conditions Using a Grinding Method

An efficient and facile synthesis of 2,6-dicyanoanilines via a one-pot reaction of aromatic aldehydes, malononitrile, and cyclic ketones in the presence of NaOH under solvent-free conditions using a grinding method has been developed. Compared with the classical reaction conditions, the new synthetic method has the advantages of excellent yields, shorter reaction times, and mild reaction conditions.     

The efficient synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthenes catalyzed by bismuth(Ⅲ)chloride under solvent-free conditions

An efficient method for the synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthene derivatives by the reaction of β-naphthol,and aldehydes in the presence of a catalytic amount of bismuth（Ⅲ） chloride（BiCl₃） under solvent-free conditions at 110℃is described.Aliphatic and aromatic aldehydes were used in the reaction and in all cases the desired products were synthesized successfully.This reaction was studied under different temperatures;the maximum yield was obtained in a short reaction period at 110℃.The method offers the advantages of high yields,short reaction times,simplicity and easy workup compared to the conventional method of syntheses.     

超声波辐射制备羧甲基壳聚糖

应用超声波辐射方法制备水溶性的羧甲基壳聚糖,利用胶体滴定法测定产物中羧基含量,探讨超声波作用下,反应时间、反应温度及反应物投料比对羧甲基化程度的影响。结果表明,在其它反应条件相同时,使用超声波辐射比使用机械搅拌提高羧甲基取代程度,反应时间缩短５ｈ。     

Toward De Novo Catalyst Discovery: Fast Identification of New Catalyst Candidates for Alcohol-Mediated Morita–Baylis–Hillman Reactions**

Recently we have demonstrated how a genetic algorithm (GA) starting from random tertiary amines can be used to discover a new and efficient catalyst for the alcohol-mediated Morita–Baylis–Hillman (MBH) reaction. In particular, the discovered catalyst was shown experimentally to be eight times more active than DABCO, commonly used to catalyze the MBH reaction. This represents a breakthrough in using generative models for catalyst optimization. However, the GA procedure, and hence discovery, relied on two important pieces of information; 1) the knowledge that tertiary amines catalyze the reaction and 2) the mechanism and reaction profile for the catalyzed reaction, in particular the transition state structure of the rate-determining step. Thus, truly de novo catalyst discovery must include these steps. Here we present such a method for discovering catalyst candidates for a specific reaction while simultaneously proposing a mechanism for the catalyzed reaction. We show that tertiary amines and phosphines are potential catalysts for the MBH reaction by screening 11 molecular templates representing common functional groups. The method relies on an automated reaction discovery workflow using meta-dynamics calculations. Combining this method for catalyst candidate discovery with our GA-based catalyst optimization method results in an algorithm for truly de novo catalyst discovery.     

Quantification of anhydride groups in anhydride‐based epoxy hardeners by reaction headspace gas chromatography

We demonstrate a reaction headspace gas chromatographic method for quantifying anhydride groups in anhydride‐based epoxy hardeners. In this method, the conversion process of anhydride groups can be realized by two steps. In the first step, anhydride groups in anhydride‐based epoxy hardeners completely reacted with water to form carboxyl groups. In the second step, the carboxyl groups reacted with sodium bicarbonate solution in a closed sample vial. After the complete reaction between the carboxyl groups and sodium bicarbonate, the CO₂ formed from this reaction was then measured by headspace gas chromatography. The data showed that the reaction in the closed headspace vial can be completed in 15 min at 55°C, the relative standard deviation of the reaction headspace gas chromatography method in the precision test was less than 3.94%, the relative differences between the new method and a reference method were no more than 9.38%. The present reaction method is automated, efficient and can be a reliable tool for quantifying the anhydride groups in anhydride‐based epoxy hardeners and related research.