反应进度概念与化学反应体系

北京大学多年从事物理化学教学的教授们认为 :“以反应进度概念为基础建立相变和化学反应的学科体系和教学体系势在必行”[1]。本文介绍我们在学习将反应进度概念用于化学反应体系的过程中的一些粗浅体会。1　化学反应体系的热力学基本关系　　由热力学原理已导出多组分体系的基本方程 (以内能Ｕ和吉布斯函数Ｇ为例 ) :　　　ｄＵ =ＴｄＳ-ｐｄＶ+∑ＢμＢｄｎＢ ( 1ａ)　　　ｄＧ =-ＳｄＴ+Ｖｄｐ+∑ＢμＢｄｎＢ ( 1ｂ)　　对于有化学反应的体系 ,引入反应进度 ξ ,　　　ｄξ ｄｅｆ ｄｎＢνＢ可得 :　　　 ∑ＢμＢｄｎＢ =∑ＢνＢμ…     

1,4—二巯基苏糖醇与磷钼黄的反应机理及该反应的分析意义

在ＰＨ４的邻苯二甲酸氢钾缓冲溶液中，１，４－二巯基苏糖醇可较快地将磷钼黄还原成磷钼蓝。该反应对ＤＴＴ为准一级反应，反应中ＤＴＴ分子的两个巯基各失去一个电子，巯基失电子后相互结合成双硫链。该反应能定量进行，因此可用于ＤＴＴ的间接光度测定，应用此方法测定ＤＴＴ的适用范围为２．０×１０＾－６－１．０×１０＾－４ｍｏｌ／Ｌ。     

固相反应合成LiCoPO4中间体的反应动力学

以磷酸二氢铵、醋酸钴和氢氧化锂为原料, 用低温固相反应合成含Li⁺的NH₄CoPO₄前驱体, 再经过高温焙烧合成LiCoPO₄粉体. 应用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和热重-差热分析(TG-DTA)等技术对合成产物进行表征. 结果表明: 焙烧气氛影响中间体的生成, 含Li⁺的前驱体NH₄CoPO₄在210-500 °C的空气中发生脱水脱氨反应, 制备过程存在“酸碱共同体”的中间体(CoHPO₄·LiCoPO₄·Co₂(OH)PO₄·Li₃PO₄). 中间体生成反应遵循界面反应幂律机理, 表观活化能约50.0 kJ?mol^-1, 过程机理函数为g(x)=(1-α)^-1. 中间体继续脱水反应生成LiCoPO₄, 平均表观活化能约为54.2 kJ?mol^-1. 物系非晶化和晶化过程对中间体的存在没有直接的影响, 高温对中间体的分解产物LiCoPO₄和LiCoPO₄的晶体生长有利, 在550 °C以上温度中间体可分解得到完整的LiCoPO₄晶体.     

Nozaki-Hiyama-Kishi反应的研究进展

综述了Nozaki-Hiyama-Kishi反应的最新研究进展。参考文献33篇。     

有机合成反应中副反应的影响因素讨论

有机合成反应中副反应的产生和控制是反应成败的一个关键因素。对有机合成反应中常见副反应产生的过程进行了分析和总结,并讨论了传质、传热、加料方式、原料配比等合成工艺条件与这些副反应产生的相关性。可帮助学生更好地理解和分析有机合成反应工艺条件的选择和控制。     

硫脲氧化反应动力学研究进展

本文综述了硫脲氧化反应动力学的研究进展,根据氧化剂和氧化方式不同,将硫脲氧化体系分成含卤氧化体系和非卤氧化体系两大类,其中含卤氧化体系包括亚氯酸、碘酸、溴酸、卤素单质氧化硫脲的反应体系;非卤氧化体系包括双氧水、自由基、电化学和金属酸盐氧化硫脲的反应体系。总结了不同反应体系的动力学现象和反应机理研究状况,文中还介绍了在硫脲氧化反应动力学研究中光电磁及色谱方法的发展状况,提出硫脲氧化反应动力学机理研究突破可能途径。     

Influence of Reaction Conditions on Methanol Synthesis and WGS Reaction in the Syngas-to-DME Process

A series of CuO-ZnO catalysts (with different Cu/Zn molar ratios) were prepared, and evaluated under the reaction conditions of syngas-to-dimethyl ether (DME) with three sorts of feed gas and different space velocity. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The experiment results showed that the reaction conditions of syngas-to-DME process greatly affected the methanol synthesis and WGS reaction. The influence caused by Cu/Zn molar ratio was quite different on the two reactions; increasing of percentage of CO2 in feed gas was unfavorable for catalyst activity, and also inhibited both reactions: enhancement of reaction space velocity heavily influenced the performance of the catalyst, and the benefits were relatively less for methanol synthesis than for the WGS reaction.     

2-Phenacylbenzothiazole in the Biginelli Reaction

The cyclocondensation of 2-phenacylbenzothiazole with aromatic aldehydes and urea or thiourea in the Biginelli reaction gave previously unreported 4-aryl-5-(2-benzothiazolyl)-2-oxo-6-phenyl-1,2,3,4-tetrahydropyrimidines and their 2-thioxo analogs. An efficient procedure was developed for carrying out the three-component reaction at low temperatures. The structure peculiarities of the products were analyzed using IR, ¹H NMR, and X-ray diffraction data.     

2,2,4-Trimethylhydroquinolines in the Bischler-Melau Reaction

8-R-1-Aryl-4,4,6-trimethyl-4H-pyrrolo[3,2,1-ij]quinolines have been synthesized by the Bischler-Melau reaction in the series of 6-R-2,2,4-trimethylhydroquinolines.     

Reaction in the ketophosphonate-triethylphosphite-diethylchlorophosphite ternary system

Russian Journal of General Chemistry -     

水参与的电解反应体系中“电极反应式书写形式”再议

针对电解反应中关于电极反应式书写形式所引发的争议,从教科书的内容设计与编排、相关的化学术语、学生认知规律及电解反应理论等视角阐述了电解反应实质与电极反应式书写规则之间的差异是产生争议的根本原因,还讨论了如何认识和看待这种争议,以期为中学化学教学提供参考。     

Reaction of 2-Formyl Imidazole with Intermediates From the Baylis-Hillman Reaction

The reaction of formyl imidazole (in the presence and absence of DABCO, and with either THF or methanol as solvent) with α-hydroxylaryl derivatives of methyl acrylate affords novel synthetic intermediates. By controlling the reaction conditions, either allylic substitution products (THF, DABCO) or rearrangement (MeOH, no DABCO) products result.     

Pd-N-杂环卡宾化合物催化的Heck反应、Suzuki反应进展

Pd催化的C—C键偶联反应是形成碳—碳单键的重要反应之一.传统上,使用膦化合物为配体来调整催化活性及选择性.但大多数Pd-膦化合物对空气稳定性差,容易被氧化;在溶液中易于解离出膦配体而降低催化剂稳定性,通常需要给反应体系中加入较多的膦配体以保持催化剂的稳定性和活性.1991年发现的稳定N-杂环卡宾(NHC)类配体具有富含电子、给电子能力强,对金属配位能力强,结构易修饰等特点,使得金属-NHC化合物成为金属有机化学、催化等领域研究新的焦点.Pd-NHC化合物已经可催化多类有机反应,是继传统Pd-膦催化剂外的又一类高效催化剂.综述了近年来不同结构的NHC如单齿简单NHC、双齿NHC、含其它配位原子的NHC等配体与Pd的配合物在Heck反应、Suzuki反应等偶联反应中的应用.     

Reaction Kinetics of the Model Reaction of Benzoic Acid with Ethylene Carbonate

As a model for several polymer-related reactions, we have reexamined the reaction kinetics of benzoic acid with ethylene carbonate in which various quaternary ammonium salts were used as catalysts. The salt anion appeared to have little or no effect on the rate of reaction. At a 1:1 mole ratio of acid to carbonate, the reaction was zero-order to about 95% reaction. With tetraethyl-ammonium hydroxide catalyst at 0.4 mol% (based on carbonate moles), the activation energy was 20.8 kcal/mol with a preexponential factor of In A = 17.1 (activation entropy of -26 cal/deg). The activation energy for decomposition of the carbonate alone was 33.0 kcal/mol with a preexponential factor of In A = 27.3. This rules out previously suggested mechanisms that essentially involved decomposition of the carbonate prior to esterification. The proposed mechanism for the reaction involves the attack of the quaternary salt carboxylate on the methylene carbon of the carbonate. The attack causes ring opening and is followed by proton transfer and carbon dioxide loss from the carbonate half-ester intermediate. Ether linkages (such as diethylene glycol) are postulated to arise from the resultant alkoxide intermediate prior to protonation to give the hydroxyethyl ester rather than by separate postreaction of carbonate with the hydroxyethyl ester.     

New Photochemical Reaction in the Series of Diazofuranones

Russian Journal of Organic Chemistry -     

Crosslinking Reaction in the Formation of Porous Clays

Clay minerals are a class of hydrous layer aluminosilicates of the so-called phyllosilicate^[1] family made up of two basic types of layers, the SiO₄ tetrahedral sheet and the Al₂(OH)₆[or Mg₃(OH)₆] octahedral sheet, many of which posses interlayer cations capable of exchanging reaction with other cations. The preparation of porous clays are based on this reactivity of exchangeable interlayer cations by using the intercalation of polycations such as Al₁₃⁷⁺ oligomers^[2] into the galleries of clay minerals to form a microporous materials^[3] Here we reported a study on the interlayered crosslinking of a 2:1 type montmorillonites with a hydrolysed polycations Al in the formation of porous clays. Na-montmorillonite gel (Na-mont, particle size<2 μ) were purified by using sedimentation of Na-bentonite fines (400 mesh, Zhejiang, China) and subsequent extensively washing to remove any soluble Na⁺. Hydrolysed polycations Al was prepared by NaOH hydrolysis of AlCl₃ solutions in a condition^[2] of OH/Al=2.0 and then aging at 70-90℃ for 4 h by the following process^[3].