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.     

Regioselective palladium-catalyzed electrophilic allylic substitution in the presence of hexamethylditin

[reaction: see text]. Palladium-catalyzed electrophilic allylic substitution of functionalized allyl chlorides and allyl acetates can be achieved in the presence of hexamethylditin under mild reaction conditions. The substitution reaction occurs with very high regioselectivity at the branched allylic terminus. Regioselective tandem bisallylation reaction could be performed by employing benzylidenemalonitrile as substrate. The reaction mechanism can be explained by involvement of a bisallylpalladium intermediate. A particularly interesting mechanistic feature of this reaction is that palladium catalyzes up to three different transformations in the same catalytic cycle. DFT calculations indicate that the regioselectivity is determined by the location of the allylic substituent in the eta1-allyl moiety of the reaction intermediate.     

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.     

Dawson结构钼钒磷杂多化合物催化乙苯选择氧化的活性研究

合成了系列Ｄａｗｓｏｎ结构钼钒杂多化合物，并将其用于 苯的过氧化氢选择氧化研究，实验发现，对于该类反应，其最佳的工艺条件为：乙苯２．５ｍｍｏｌ，催化剂０．０２ｍｍｏｌ，溶剂１０ｍＬ、３０％Ｈ２Ｏ２２．５ｍｍｏｌ，乙酸为该类最佳溶剂，而在与之性质相近的甲酸中则活性极低，即该反应过程与过氧酸的存在无关，讨论了反应过程中催化剂的状态及活性中间体，并运用ＵＶ－Ｖｉｓ、ＥＳＲ等手段进行了表征，实验结果有最佳     

Feedback Kinetics in Mechanochemistry: The Importance of Cohesive States

Although mechanochemical synthesis is becoming more widely applied and even commercialised, greater basic understanding is needed if the field is to progress on less of a trial‐and‐error basis. We report that a mechanochemical reaction in a ball mill exhibits unusual sigmoidal feedback kinetics that differ dramatically from the simple first‐order kinetics for the same reaction in solution. An induction period is followed by a rapid increase in reaction rate before the rate decreases again as the reaction goes to completion. The origin of these unusual kinetics is found to be a feedback cycle involving both chemical and mechanical factors. During the reaction the physical form of the reaction mixture changes from a powder to a cohesive rubber‐like state, and this results in the observed reaction rate increase. The study reveals that non‐obvious and dynamic rheological changes in the reaction mixture must be appreciated to understand how mechanochemical reactions progress.     

Thermolysis of polyethylene hydroperoxides in the melt, Part 12: Mechanisms and kinetics of thermolysis

The thermolysis of polyethylene hydroperoxides is attributed to the reaction of two hydroperoxide groups. This bimolecular reaction appears as a first-order reaction with the mean values of the hydroperoxide concentrations that can be used for the experimental verification of the kinetics. In low molecular mass liquids and solutions these findings would be irreconcilable. However, in polymer melts, this contradiction is more apparent than real. It is a consequence of the heterogeneous kinetics valid in polymer melts. The bimolecular reaction involves the decomposition of pairs of hydroperoxide groups that are relatively close in the elementary oxidation volumes. By diffusion these hydroperoxide groups can come close enough for reaction. From the chemical point of view the decomposition is a bimolecular reaction. However, from the kinetic point of view it is a first-order reaction of the hydroperoxide pairs. The dependency of the first-order rate on the initial hydroperoxide concentration is explained by the heterogeneous kinetics. The activation energy of the overall process can be related to the sum of the activation energies pertaining to the chemical reaction and to the diffusion process.     

馏分油浆态床加氢处理研究: II FCC柴油加氢工艺条件及动力学研究

对FCC柴油在浆态床柴油加氢催化剂SP25上的加氢工艺条件进行了优化,并考察了加氢脱硫（HDS）和加氢脱氮（HDN）动力学。结果表明,提高反应温度、提高反应压力、增加催化剂的加入量、延长反应时间都能提高催化剂的加氢精制活性,最佳的FCC柴油浆态床加氢工艺条件为,温度350℃、压力6MPa、催化剂加入量6%、反应时间2h。催化剂循环使用性能的考察结果表明,SP25催化剂具有良好的活性稳定性。动力学研究结果表明,FCC柴油的加氢脱硫反应过程可以分为两个阶段。第一阶段为较易脱除的苯并噻吩类（BTs）硫化物的加氢脱硫反应,反应活化能为70.00kJ/mol;第二阶段为较难脱除的二苯并噻吩类（DBTs）硫化物的加氢脱硫反应,反应活化能为85.65kJ/mol。FCC柴油HDN反应的活化能为79.91kJ/mol。烷基取代的二苯并噻吩类硫化物（特别是DMDBTs）是加氢精制反应中最难脱除的含杂原子（S或N）烃类化合物。     

Pressure effects on Friedel-Crafts alkylation reactions in supercritical difluoromethane.

Dielectrometry is used as a novel technique for following the rate of a Friedel-Crafts alkylation reaction in supercritical (sc) difluoromethane. Although the process was not optimized, good product yields were obtained and reaction rates were found to be larger than in CO2 at comparable conditions. The reaction order is determined using the initial rate method and the reaction is shown to be first-order with respect to both anisole and t-butyl chloride. The reaction rate constant is unaffected by pressures above 120 bar but close to the critical pressure the value decreases with increasing pressure. It is also shown that the product distribution for the alkylation of anisole shows significant pressure dependence with substitution at the ortho-position being favored at lower pressures, which is ascribed to hydrogen bonding. This pressure dependency is not observed in sc CO2 or using toluene as a substrate, which supports the idea that hydrogen bonding may be important in the reaction mechanism. The effect of the different reagents and temperature on the rate of the alkylation reaction was also determined.     

Kinetics of polycondensation in an industrial environment

The influence of industrial reaction conditions on the kinetics of the polycondensation of polyamides is discussed. For analysis reasons the overall process was subdivided into individual kinetic phases. It will be shown that the basic features of the reaction rate in the final reaction stage can be explained assuming second order kinetics combined with a superposed reaction equilibrium. The influence of non-stoechiometry on the reaction rate is also demonstrated.     

丙烯酸气相热解机理的理论探讨

用自洽场分子轨道法(半经验AM1法及从头算HF/3-21G法)研究了基态丙烯酸脱羧的反应途径. 计算结果表明, 除前人从理论上已经得到的一步反应途径外, 尚有一个与之竟争的二步反应途径, 且两步反应的总速率大于一步反应的. 计算所得的反应速率常数很小, 与实验结果(丙烯酸在827 K仅有25%左右发生脱羧, 脱水等反应)是一致的. 研究表明, 有较稳定的中间体存在, 有可能在实验中被检测到, 但有待于进一步验证.     

An efficient protocol of iridium-catalyzed allylic substitution reaction and its application to polymer synthesis: complementary regio- and stereoselective allylation polycondensation via Ir and Pd catalyses

An efficient protocol of the Ir-catalyzed allylic substitution reaction is reported using N,O-bis(trimethylsilyl)acetamide as a base in the presence of nBu4NF as a cocatalyst. The reaction completely proceeded under very mild conditions, and a branched allylated compound that is not easy to access via the Tsuji-Trost reaction can be synthesized. The reaction system is practical enough to be applicable for polymer syntheses. The Ir- and Pd-catalyzed allylation polycondensations generally show complementary regio- and stereoselectivities. The Ir-catalyzed reaction is versatile, and a mixed dual regioselectivity such as a branched-linear selectivity on each electrophile can also be achieved.     

Impact of water on the OH + HOCl reaction

The effect of a single water molecule on the OH + HOCl reaction has been investigated. The naked reaction, the reaction without water, has two elementary reaction paths, depending on how the hydroxyl radical approaches the HOCl molecule. In both cases, the reaction begins with the formation of prereactive hydrogen bond complexes before the abstraction of the hydrogen by the hydroxyl radical. When water is added, the products of the reaction do not change, and the reaction becomes quite complex yielding six different reaction paths. Interestingly, a geometrical rearrangement occurs in the prereactive hydrogen bonded region, which prepares the HOCl moiety to react with the hydroxyl radical. The rate constant for the reaction without water is computed to be 2.2 × 10(-13) cm(3) molecule(-1) s(-1) at room temperature, which is in good agreement with experimental values. The reaction between ClOH···H(2)O and OH is estimated to be slower than the naked reaction by 4-5 orders of magnitude. Although, the reaction between ClOH and the H(2)O···HO complex is also predicted to be slower, it is up to 2.2 times faster than the naked reaction at altitudes below 6 km. Another intriguing finding of this work is an interesting three-body interchange reaction that can occur, that is HOCl + HO···H(2)O → HOCl···H(2)O + OH.     

Pd(PPh3)2Cl2-CuCl体系催化有机高价碘杂环化合物与末端炔烃的化学选择性交叉偶联反应

以有机高价碘杂环化合物1,2为底物,在Pd(PPh3)2Cl2-CuCl催化剂存在下与末端炔烃进行交叉偶联反应,实验发现该反应为--化学选择性反应,控制反应体系的物料比、温度及反应时间可以分别得到单偶联或双偶联产物,从而证实了有机高价碘杂环化合物的碘盐在进行交叉偶联反应时的反应活性比sp2的碘化物高.     

An Introduction to the Combustion of Carbon Materials

Combustion is arguably as old as homo sapiens ability to observe and use fire. Despite the long tradition of using carbon combustion for energy production, this reaction is still not fully understood. This can be related to several facts that are intertwined and complicate the investigation, such as the large variety of possible carbon structures, the actual surface structure, porosity, the solid-gas nature of this reaction, diffusion limitation and fundamental reaction steps. In this review, a brief history of carbon combustion science is given, followed by a detailed discussion of the most important aspects of carbon combustion. Special attention is given to limitations for example diffusion. In carbon combustion, kinetic control can rarely be observed. The literature of the fundamental reaction steps actually occurring on the carbon framework is reviewed and it becomes apparent that the reaction is occurring primarily on defects on the basal plane. Thus, the reaction between oxygen and carbon may be used as an analytical tool to provide further insights into novel materials, for example synthetic carbon materials, fibres and graphene type materials. Mastering the combustion reaction in all its complexity may prove to be very valuable in the future.     

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".     

铂电极BZ反应体系的系统动力学分析

在一定的条件下,将铂电极BZ化学反应的六变量高维动力学系约化为三变量体系,同时对该体系进行了全面的系统动力学分析.研究结果表明,通过改变耦合体系的外控参数条件,在将体相保持在均一稳定定态的参数范围内,电极反应相可能进入振荡区,而呈现出电极反应相与体相的动力学行为不一致性.进一步计算出体相处于非振荡状态时,电极反应相产生电化学振荡的外控参数区域.     

IRC analysis of methanol carbonylation reaction catalyzed by rhodium complex

In the reaction cycle for methanol carbonylation catalyzed by Rh complex, the structure geometries of the reactant, intermediates, transition states and product of each elemental reaction have been studied by using the energy gradient method at HF/LANL2DZ level, and the changes of their potential profiles have also been calculated. Through IRC analyses of the transition states for each elemental reaction, it is confirmed that the various structure geometries obtained are stationary points on the cycle reaction pathway of methanol carbonylation catalyzed by Rh complex, and the changes are given in energies and structure geometries of the reactant molecules along the reaction pathway of lowest energy. It has been proposed that the geometrical conversions of intermediates play an important role during the cycle reaction. Through analyses of structure geometries, it has been suggested that, in addition to cis- and trans-structure exchange linkage of catalysis reactive species, the two pathways, cis- and tra     

Effect of temperature on the determination of aromatic nitro-compounds by coulometrically generated chromium(II)

The analytical utility of the reaction between aromatic nitro-compounds and electrogenerated chromium(II) can be extended to several previously undeterminable compounds by increasing the temperature of the reaction solution. For some substances the stoichiometry of the reduction is changed; for others the rate of reaction, along with precision and accuracy, is appreciably increased; in at least one instance the reaction becomes less satisfactory as an analytical method. Temperature is thus shown to be an important variable that may explain differences in previously reported stoichiometries.     

Reaction mechanism of carbon gasification in CO<Subscript>2</Subscript> under non-isothermal conditions

Experiments of carbon (graphite) gasification in CO₂ have been carried out by thermal analysis techniques (TG-DTG-DSC) under non-isothermal conditions. The results indicate that the entire carbon gasification process can be divided into an exothermic slow gasification stage during the initial period and an endothermic fast gasification later. The analyses of energy conservation and non-isothermal kinetics arrive at the following conclusions; (1) The exotherm of the initial stage is caused by the combined effect of the exothermic chemisorption and the endothermic chemical reaction. The gasification reaction may be expressed by the series of chemisorption and chemical reaction and the overall process is controlled by interface reaction via chemisorption. (2) The endothermic effect of fast gasification stage is almost equal to the reaction heat of carbon gasification, which implies that the chemisorption step disappears. The gasification process can be expressed by a simple interface reaction.     

Shift of the rate-determining step in a consecutive chemical reaction with variation of the reaction affinity

A consecutive single-route reaction is considered. When two (groups of) steps compete in controlling the overall reaction rate, there exists a general rule that the earlier step in the flow of the overall reaction tends to be rate-determining with the increase of the reaction affinity. The latter may, however, be distributed more or less evenly to both steps.