电化学反应及其腐蚀

氧化―还原反应是普遍存在的一类重要的反应。冶金、锈蚀及许多化工生产都涉及到氧化―还原反应。氧化―还原反应的本质是电子得失或偏移,如何通过化学能转变为电能,使氧化―还原反应获得或失去电子等,是化学教学中的重点和难点。文章介绍了氧化―还原反应中电化学的概念和原电池的原理,利用电化学的知识来解释一些电化学腐蚀现象。     

2,6-二氯吡啶的定向合成及结构测定

研究了以吡啶为原料,通过光氯化反应定向合成2,6-二氯吡啶。并对光氯化反应的工艺进行了研究。当吡啶与氯气配比为1:2.3,反应温度为200℃,反应5h时,光氯化反应的转化率可达95.7%。反应的进程和产品的纯度通过GC-MS进行控制。并用元素分析、红外光谱、质谱对产物的结构进行了表征。     

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.     

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.     

土卫六大气中H2和N+反应的动力学研究

依据Titan大气的压强和温度条件计算了N++H2→NH++H反应的热化学函数. 结果发现, 该反应是一个吸热反应, 在Titan的低温环境中不具有反应自发性. 运用量子化学理论计算研究了反应的动力学性质, 发现该反应在300 K温度下的反应速率k=4.16×10−10 cm3•mol−1•s−1, 在实验室温度下(298.15 K)的反应势垒是109.847 kJ•mol−1. 依据Titan电离层气压温度条件计算了90 Pa压强条件下1 K到5000 K温度范围内(极低温度和极高温度)的 反应活化能和反应速率, 研究发现低温下该反应的反应速率非常低, 而且, 随着温度的降低, 反应速率急剧降低. 理论计算值和文献中的实验值也符合得较好, 理论计算数据可以为星际分子的模拟实验提供一定的参考.     

浅析有机化学反应机理的教与学

有机化学的基本理论和反应机理是有机化学的核心内容。反应机理的教与学是有机化学教学过程中的难点,一直困扰着教师和学生。笔者采用了"教师引导–学生练习–学生综合讲解"三段式的反应机理教学方式。首先是教师引导:教师结合国内外教材和文献,先讲授基本理论,再详细讲解反应机理;接着是学生练习:教师根据教学进度布置习题让学生练习,然后结合前后相关的反应机理,组装成比较复杂的多步反应,要求学生根据机理推导反应产物;最后是学生综合讲解:给每个学生分配一个反应,要求围绕该反应,通过查阅文献和资料,整理好素材,在课堂上讲解展示反馈,教师据此进行补充和修改。经过实践证明,该方式便于学生理解有机化学反应机理,从而达到事半功倍的教学效果。     

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.     

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.     

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.     

Synthetic and structural chemistry of groups 11 and 12 metal complexes of the zwitterionic ammonium thiolate ligands

The chemistry of metal complexes of the zwitterionic ammonium thiolates has expanded dramatically in the recent years. This review is intended to summarize the synthesis and crystal structures of groups 11 and 12 metal zwitterionic ammonium thiolate complexes. Seven methods for the synthesis of these metal complexes of the zwitterionic ammonium thiolates are outlined: proton transfer reaction, precursor reaction, ligand exchange reaction, oxidation–reduction reaction, solid-state reaction, electrochemical reaction and hydro(solvo)thermal reaction. These metal complexes of the zwitterionic ammonium thiolates are classified according to the number of metal atoms; their specific structures are briefly discussed.     

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。     

The Combined Role of Catalysis and Solvent Effects on the Biginelli Reaction: Improving Efficiency and Sustainability

The traditional Biginelli reaction is a three‐component condensation between urea, benzaldehyde and an acetoacetate ester to give a dihydropyrimidinone. An investigation into catalytic and solvent effects has returned the conclusion that the diketo–enol tautomerisation equilibrium of the dicarbonyl reactant dictates the yield of the reaction. Whereas the solvent is responsible for the tautomerisation equilibrium position, the catalyst only serves to eliminate kinetic control from the reaction. Generally, to preserve reaction efficiency and improve sustainability, bio‐derivable p‐cymene was found to be a useful solvent. The metal–enolate intermediate that results from the application of a Lewis acidic catalyst often cited as promoting the reaction appears to hinder the reaction. In this instance, a Brønsted acidic solvent can be used to return greater reactivity to the dicarbonyl reagent.     

Acid-base-catalysed condensation reaction in water: isoxazolines and isoxazoles from nitroacetates and dipolarophiles

Base‐catalysed condensation reactions of nitroacetic esters with dipolarophiles to give isoxazole derivatives proceed faster, and often with higher yields, in the presence of water than in organic solvents such as chloroform. Kinetic profiles show that induction times are greatly reduced when the reaction is performed “in water” or “on water”. Any specificity of the base related to H‐bonding ability observed in chloroform is lost in water: all bases either organic or inorganic give the same result that is simply depending on concentration. A 0.1 molar ratio of base to nucleophile gives the best conversion, whereas addition of one equivalent of base or strong acid prevents the reaction from occurring. These results fit into a reaction sequence in which reversible addition to a dipolarophile is followed by acid‐catalysed irreversible dehydration of the cycloadduct. This is a remarkable example of a condensation reaction occurring in water because of irreversible acid‐catalysed water elimination. The reaction has been successfully applied to dipolarophiles containing a wide variety of functional groups, including carboxylic acids and ammonium salts, under mild conditions. This new click‐style reaction is expected to be compatible with biological environments.     

苯甲醛肟偶极互变反应的理论研究

研究了苯甲醛肟Z构型和E构型两种异构体与相应偶极体的3条互变反应途径:(1)单分子内质子转移反应,质子由肟羟基转移至邻位的氮上,过渡态为三角形结构,反应能垒较高;(2)二聚体内的质子互换反应,质子分别从一个肟羟基转移到另一个肟的氮上,过渡态为六元环结构,能垒较低,理论反应速度较大,但平衡常数较小;(3)肟羟基与甲醇的质子互换反应,过渡态具有五元环结构,能垒和反应速度介于上述两者之间.结果表明,在3条反应途径上,Z构型和E构型均有类似的过渡态,Z构型有利于偶极体存在.在室温下主要通过二聚体内质子交换进行互变反应,实际体系中由于偶极体不断被消耗,反应可以持续进行.     

Synthesis and characterization of graft copolymers from lignin and 2-propenamide

Free radical polymerization of 2-propenamide in the presence of lignin, anhydrous calcium chloride, and cericion in photolyzed dioxane solvent produces a reaction product containing lignin-(1-amidoethylene) graft copolymer. Up to 49 weight percent of the product is poly(1-amidoethylene) homopolymer. Photolysis products of dioxane and the presence of anhydrous calcium chloride are critical to the reaction. A maximum yield of polymer is obtained when the dioxane solvent is irradiated for 3 h in a Pyrex vessel and the reaction mixture contains 2.0 weight percent calcium chloride. Aqueous size exclusion chromatography of reaction products shows that the molecular size of the lignin-(2-propenamide) reaction product is significantly greater than that of unreacted lignin, that the side chain and the lignin backbone migrate as one unit through the column, and that mixtures of lignin and poly(1-amidoethylene) are easily separated by the chromatographic column.     

Studies on the reaction of p-hydroxybenzyl alcohol and hydroxyl radicals

The reaction of p-hydroxybenzyl alcohol and hydroxyl radicals generated by the Fenton reaction is studied. The products of the reaction are separated and identified by high-performance liquid chromatography (HPLC)-diode-array detection and HPLC-mass spectrometry. According to the structures of the products, a mechanism of the reaction is proposed.     

丁醇醛和丁醇酸热解形成CO和CO2机理的密度泛函理论研究

采用密度泛函理论方法B3LYP/cc-pVTZ,对模型化合物2,3,4-羟基丁醛的脱羰基和2,3,4-羟基丁酸的脱羧基反应机理进行了量子化学理论研究。对两种模型化合物分别设计了三种热解反应途径,计算了不同温度下各热解反应途径的标准热力学及动力学参数。计算结果表明,纤维素热解过程中CO₂和CO的逸出分别与脱羧基和脱羰基反应相对应,脱羧基和脱羰基反应均为分子内氢原子转移的协同过程。脱羰基反应是吸热反应,而脱羧基反应是放热反应。饱和丁醇醛的脱羰基反应反应能垒为288.8 kJ/mol,脱水后的不饱和烯醇醛的脱羰基反应能垒增大;饱和丁醇酸的脱羧基反应能垒较高,为303.4 kJ/mol,脱水后的不饱和烯醇酸的脱羧基反应能垒明显减小,这说明脱水有利于CO₂的生成。     

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.     

Linear free energy relationship in reactions between diphenyl amine and benzyl bromides

Rate of reaction between benzyl bromide and diphenyl amine is retarded by electron-donating groups and enhanced by electron-withdrawing groups present on the benzene ring of the substrate. Hammett’s reaction constant p of the reaction decreases with increase in temperature according to the equation, ρ =-11.92+ 3.54/T. Minimal structural effects observed are attributed to the fact that the isokinetic temperature of the reaction is close to the reaction temperature.     

Simple and efficient protocol for the synthesis of functionalized styrenes from 1,2-dibromoethane and arylboronic acids

[reaction: see text] A simple and efficient protocol for the preparation of functionalized styrenes is disclosed that employs the palladium-catalyzed cross-coupling reaction of arylboronic acids with vinyl bromide, generated in situ from 1,2-dibromoethane. The reaction is carried out under mild reaction conditions. Compared with the cross-coupling reactions usually employed to obtain vinylarenes, this protocol is very simple, overcomes the inconvenience of using of ethylene under pressure, and uses air-stable and widely available arylboronic acids instead of vinyl organometallic reagents.