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.     

Reaction path synthesis methodology for waste minimization

Being the core of whole process, a chemical process is a key step for reducing waste generation. Therefore, to organize a reasonable reaction path is very important for reducing waste emission. Because of the large amount of the feasible reaction path and other factors in a chemical reaction system, the opti-mizing for reaction path is difficult. Since the reaction path synthesis problem has presented, lots of re-searchers focused on it. At the beginning, only chem-ists took the research work,…     

Implicit versus explicit solvent in free energy calculations of enzyme catalysis: Methyl transfer catalyzed by catechol O-methyltransferase

We compare free energy calculations for the methyl transfer reaction catalyzed by catechol O-methyltransferase using the quantum mechanical/molecular mechanical free energy method with implicit and explicit solvents. An analogous methylation reaction in a solution is also studied. For the explicit solvent model, we use the three-point transferable intermolecular potential model, and for the implicit model, we use the generalized Born molecular volume model as implemented in CHARMM. We find that activation and reaction free energies calculated with the two models are very similar, despite some structural differences that exist. A significant change in the polarization of the environment occurs as the reaction proceeds. This is more pronounced for the reaction in a solution than for the enzymatic reaction. For the enzymatic reaction, most of the changes take place in the protein rather than in the solvent, and, hence, the benefit of having an instantaneous relaxation of the solvent degrees of freedom is less pronounced for the enzymatic reaction than for the reaction in a solution. This is a likely reason why energies of the enzyme reaction are less sensitive to the choice of atomic radii than are energies of the reaction in a solution.     

Transition-metal-free Suzuki-type coupling reactions: scope and limitations of the methodology

The scope and limitations of the transition-metal-free Suzuki-type coupling of aryl halides and arylboronic acids to form biaryls are presented. Confirmation that the reaction is indeed metal-free is presented. The effects of changing base, solvent, reaction temperature, phase-transfer catalyst, and substrate are shown and the implications of these results discussed in terms of their impact on the synthetic versatility of the methodology. The main findings are that the reaction works well for aryl bromides, water is necessary as a solvent for the reaction, the optimum temperature for the reaction is 150 degrees C, the reaction is best performed by using microwave promotion with the exception of an electron-poor aryl bromide example where conventional heating may be used, only limited boronic acids can be used as coupling partners, sodium carbonate is the best base for the reaction, tetrabutylammonium bromide proves to be the best phase-transfer catalyst for the reaction, the reaction is limited to couplings between aryl halides and aryl boronic acids with sp(2)-sp(3) couplings proving ineffective, and NaBPh(4) can be used in the place of phenylboronic acid as a phenylating agent.     

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。     

Ab initio quantum mechanical/molecular mechanical molecular dynamics simulation of enzyme catalysis: the case of histone lysine methyltransferase SET7/9

To elucidate enzyme catalysis through computer simulation, a prerequisite is to reliably compute free energy barriers for both enzyme and solution reactions. By employing on-the-fly Born-Oppenheimer molecular dynamics simulations with the ab initio quantum mechanical/molecular mechanical approach and the umbrella sampling method, we have determined free energy profiles for the methyl-transfer reaction catalyzed by the histone lysine methyltransferase SET7/9 and its corresponding uncatalyzed reaction in aqueous solution, respectively. Our calculated activation free energy barrier for the enzyme catalyzed reaction is 22.5 kcal/mol, which agrees very well with the experimental value of 20.9 kcal/mol. The difference in potential of mean force between a corresponding prereaction state and the transition state for the solution reaction is computed to be 30.9 kcal/mol. Thus, our simulations indicate that the enzyme SET7/9 plays an essential catalytic role in significantly lowering the barrier for the methyl-transfer reaction step. For the reaction in solution, it is found that the hydrogen bond network near the reaction center undergoes a significant change, and there is a strong shift in electrostatic field from the prereaction state to the transition state, whereas for the enzyme reaction, such an effect is much smaller and the enzyme SET7/9 is found to provide a preorganized electrostatic environment to facilitate the methyl-transfer reaction. Meanwhile, we find that the transition state in the enzyme reaction is a little more dissociative than that in solution.     

硫碘循环制氢中Bunsen反应新方法的研究进展

热化学硫碘(S-I)循环分解水是目前有较高效率且可以在相对较低温度条件下进行的制氢方法之一。 其中的Bunsen反应作为循环的核心步骤尤为重要。 为了更方便有效地分离Bunsen反应的生成物硫酸与氢碘酸,许多学者研究了Bunsen反应的新方法。 本文对非水溶剂中的Bunsen反应和电化学Bunsen反应两种新方法进行了综述。 讨论了非水溶剂中实现反应生成物分离的方法,对比了各种非水溶剂的性质及其优缺点。 目前,所发现的溶剂在分离生成物方面已达到要求,可用于Bunsen反应,但溶剂的回收再利用比较困难。 概述了电化学Bunsen反应的研究现状,对目前在电化学Bunsen反应中有突破进展的两个团队的工作进行了对比。 现今对该方法的探讨主要集中在反应基础特性方面,未来可以加强电化学Bunsen反应机理、反应电池结构设计与优化、以及新型S-I循环系统构造的研究。     

甘氨酸螯合钙的合成与性能研究

以甘氨酸和金属钙盐为原料,采用水体系合成法制备甘氨酸钙螯合物,探讨不同反应温度、反应时问、反应体系pH等对产品产率的影响,从而确定反应的最佳条件,并对甘氨酸钙螯合物采用傅里叶红外光谱FT-IR进行表征。实验结果表明,合成甘氨酸钙螯合物的最适反应条件是,反应体系pH为5～6,反应时间为2～3h,反应温度为70～80℃。     

Theoretical study on the alkaline hydrolysis of methyl thioacetate in aqueous solution

A base-catalyzed hydrolysis reaction of thiolester has been studied in both gas and solution phases using two ab initio quantum mechanics calculations such as Gaussian09 and CPMD. The free-energy surface along the reaction path is also constructed using a configuration sampling technique, namely, the metadynamics method. While there are two different reaction paths obtained for the potential profile of the base-catalyzed hydrolysis reaction for thiolester in the gas phase, a triple-well reaction path is computed for the reaction in the solution phase by two quantum mechanics calculations. Unlike the S(N)2 mechanism (a concerted mechanism) found for the gas-phase reaction, a nucleophilic attack from the hydroxide ion on the carbonyl carbon to yield a tetrahedral intermediate (a stepwise mechanism) is observed for the solution-phase reaction. Moreover, the energy profiles computed by these two theoretical calculations are found to be very comparable with those determined experimentally.     

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.     

湿法脱硫中亚硫酸盐非催化氧化本征动力学

亚硫酸盐的氧化是湿法烟气脱硫工艺中的重要过程. 利用间歇式反应装置, 研究了亚硫酸盐非催化氧化的本征反应动力学. 结果表明, 该反应分为两个阶段进行, 即富氧区的快速反应和贫氧区的慢速反应. 在富氧区, 亚硫酸盐和溶解氧的分级数分别为1.0和1.0, 反应的表观活化能为49.3 kJ•mol^－1; 在贫氧区, 亚硫酸盐和溶解氧的分级数分别为2.0和0, 反应的表观活化能为122.6 kJ•mol^－1. 对反应的机理进行了预测, 结果与实验现象有较好的吻合.     

PRODUCTION OF LIGHT ALKENES FROM CO AND/OR CO_2 HYDROGENATION OVER K-Fe-MnO/SILICALITE-2 CATALYST

High selectivity to light alkenes can be achieved from CO and CO_2hydrogenation over K-Fe-MnO/Si-2 catalyst.The alkene selectivity isinsensitive to reaction temperature for CO hydrogenation,while apparentlyincreases for CO_2 hydrogenation with raising reaction temperature.An increasein alkene selectivity is observed for both CO and CO_2 hydrogenation with GHSVrising,While a decrease with the elevation of reaction pressure for both CO/H_2and CO_2/H_2 reaction.A two-step mechanism is suggested forCO_2 hydrogenation to form hydrocarbons,by which the variations incontributions of CO and HC as products of CO_2/H_2 reaction with change ofreaction temperature,GHSV and pressure are explained.Moreover,thecatalyst is favorable for selective production of light olefins,which can alsoconcern the slightly secondary reactions of light olefins to some extent.     

Synthesis of 2,3-anti-3,4-anti and 2,3-anti-3,4-syn propionate motifs: a diastereoselective tandem sequence of Mukaiyama and free-radical-based hydrogen transfer reactions

[reaction: see text] Reported herein is a strategy employing a Mukaiyama reaction in tandem with a hydrogen transfer reaction for the elaboration of 2,3-anti-3,4-anti and 2,3-anti-3,4-syn propionate motifs. The mode of complexation is controlled through monodentate or chelate pathways for the Mukaiyama reaction to give access to either syn or anti aldol products, precursors of the free-radical reduction reaction. Boron Lewis acid is used to control the free-radical reaction through the exocyclic pathway.     

The reduction ring-opening reaction of imidazoline

A new reduction ring-opening reaction of 2-imidazoline with sodium borohydride is reported, and the effect of reaction condition on the yield, reaction mechanism and the use of the new reaction in synthesis of ethylenediamine derivatives are discussed. A new method for the preparation of unsymmetrical substituted ethylenediamine via the reduction ring-opening reaction of imidazoline is provided.     

Investigation of reaction products of sulphuric acid with ilmenite

The reaction of sulphuric acid with titanium raw materials runs violently with simultaneous emission of gases. Such run of reaction creates danger of explosion. This process is very complicated from the reason of complexity of reactions and variety of compounds in reaction mixture. To determine safe conditions of reaction with high efficiency, it is necessary to investigate phase composition products of reaction. Products of reaction were investigated by using X-ray diffraction. However reaction products show high amorphy and this is the reason of difficulties to determine all phases. For this reason also was used additional method — ‘drop’ calorimeter. This method is used for determination of average specific heat of liquid or solid samples. In this case, this method was used for verification of phase composition of products of reaction. On the basis of investigation the phase composition of reaction product is following: titanyl sulfate, iron(III) sulfate, monohydrated iron(II) sulfate, magnesium sulfate and unreacted remainders of ilmenite and magnesium silicate.     

Assessing thermal hazards of reaction mixtures

A strategy for assessing thermal hazards of chemical manufacturing processes is presented with an emphasis on new developments in the areas of the desired and decomposition reaction research. In the case of the desired reaction, the application of a computer program, CAMEO, for assessing synthetic reaction pathways, and enthalpies, and for evaluating the chemistry of specific failure modes is demonstrated. For the decomposition reaction, an unexpected decomposition destabilization phenomenon in mixtures was observed, which clearly demonstrated the need for chemical/solvent mixture testing to provide reliable thermochemical data for reaction hazard assessment. An application of the reaction mixture hazard evaluation strategy to a chemical process is presented.The authors would like to thank P. R. Kingsley for carrying out the experimental work necessary to complete this project. The authors also wish to acknowledge the support of Eastman Kodak Company in the preparation of this study.     

Cholesterol study: Reaction plateau and kinetic determinations

A study has been described of a comparison between reaction plateaus and kinetic modes for measuring cholesterol. A similar investigation of bilirubin reactions under the same procedural conditions was also carried out because this compound is a major interference which is frequently encountered in abnormal serums. The findings indicate that bilirubin is a more sensitive reactant than cholesterol by LB reaction but that its effect as an interference can be lessened by a kinetic approach providing that the effect of H₂O on reaction velocity and molar absorptivity can be minimized. An iron reaction even though more sensitive proved less workable in the kinetic mode owing to reaction velocity and the presence of air bubbles. However, its reaction plateau characteristics were superior to the LB reaction because of a favorable ratio of colors generated for the two reacting constituents. Based on this study, it is predictable that a kinetic approach is quite workable for the LB reaction and could be made more workable for the iron reaction if, in the latter case, conditions perhaps such as temperature and reaction media, could be altered to slow the rate of color formation.     

用常温正丁烷异构化反应表征固体超强酸性

研究了室温下固体超强酸催化剂上正丁烷反应，发现转化率低于50％时，异构化选择性高于95％，正丁烷异构化反应动力学符合一级可逆反应规律，固体超强酸的酸强度与正丁烷异构化反应转化率和速率常数呈顺变关系，与反应表现活化能呈逆变关系．报出了一种新的表征固体超强酸性的实验方法．     

Theoretical Analysis of Structural Characteristics of Morin Rearrangement for Cephalosporins Prepared from Penicillin Sulfoxide

The structure of penicillin sulfoxide is rearranged to cephalosporins by the Morin rearrangement. It is a unit reaction for the preparation of various types of cephalosporins. In order to make better use of the reaction and in view of the shortage of the reaction theory, this study used m062x/6-311++G(d, p) to explore the possible ring-opening reaction of the penicillin sulfoxide. It is found that the isomer of(S)-sulfoxide is a necessary structure. At the same time, the intramolecular hydrogen bonding effect between the side-chain amide proton(-CONH-) and the sulfinyl oxygen(-SO) is the decisive structure factor for the formation of alkenyl in ring-opening reaction, and the best reaction path is S0- TS2- IN1 channel. The main effect of acid catalysis is to catalyze the dehydration reaction of sulfenic acid to form sulfur cations for subsequently ring closing reaction.     

Synthesis of 1,3-dialkylurea from ethylene carbonate and amine using calcium oxide

Several basic metal oxide catalysts were tested for the synthesis of 1,3-disubstituted urea from ethylene carbonate (EC) and amine. Among the catalysts used, CaO has been found to be an excellent recyclable catalyst for the reaction. It has been suggested that strongly basic property of CaO results in its high activity. Disubstituted ureas are obtained from propylamine and butylamine with high yields at 100 °C. Slightly higher reaction temperatures are necessary for obtaining good yields from amines having larger molecular weights and urea is not produced from dibutylamine as a secondary amine. Propylene carbonate can be used instead of EC for the reaction. A reaction mechanism was proposed, which involves reaction between EC and amine giving a carbamate followed by catalytic reaction between the carbamate and amine, yielding 1,3-disubstituted urea. It is suggested that the latter reaction is the rate-determining step. On the basis of this reaction mechanism, the synthesis of unsymmetric urea was also examined. 2-Hydroxyethyl butylcarbamate is selectively produced from EC with butylamine in the absence of the catalyst at a low temperature and reacts with benzylamine producing 1-butyl-3-benzylurea along with symmetric dialkyl ureas.