也谈氧化还原滴定等当点电位的计算

在讨论氧化还原滴定曲线的过程中,常常涉及到氧化还原反应达到等当点时体系电报电位(即等当点电位)的计算。在这方面,国内外许多学者均做了大量工作。例如,对于反应物与对应的生成物的系数为1:1的氧化还原滴定:     

高中化学项目教学案例——探寻柠檬水中的维生素C

选取“维生素C”这一生活中常见的还原性物质,面向已经学习“氧化还原反应”基础知识的高一年级学生开展项目教学活动。通过提出项目问题、师生共同拆解项目问题设计研究方案和子任务、学生实施子任务研究等项目教学环节,在形成相应子任务成果的同时,进一步帮助学生巩固从氧化性和还原性视角认识化学物质性质的认识角度,建立基于物质性质定量分析目标物质含量的实验思路和思维框架,提升学生对于氧化还原反应功能和价值的认识。     

高中化学“氧化还原反应的应用”项目式教学——设计过氧化氢使用注意事项标签

以“设计过氧化氢使用注意事项标签”为项目主题,开展高中化学“氧化还原反应的应用”教学。学生通过说明书对比发现问题,完成“探究过氧化氢能否与氧化性物质混用”“探究过氧化氢为何不能与还原性物质混用”“探究过氧化氢起消毒作用原理”等3个主项目任务及“寻找日常生活中常见消毒剂”的拓展任务,完成过氧化氢性质的预测及验证,在探究过程中建构并应用价性模型,形成从化合价角度认识物质氧化性或还原性的思路方法,认识氧化还原反应的重要意义。本教学设计为单课时微项目,学生思维的开放度稍弱,可以适当延长课时。     

大学无机化学中“原电池”的启发探究式教学实践*

介绍了大学无机化学课堂中“原电池”部分的教学实践。通过启发-探究式教学模式,启发学生把常见的氧化还原反应,经过不断的设问和探究,最终设计成原电池,实现了通过原电池装置来证实氧化还原反应发生了电子传递的教学目的。学生在教师的启发下探究、分析、推导、创新和修正,使学生清晰地认识到知识的前后逻辑关系,对氧化还原反应概念、原电池装置有更深刻的理解,培养了学生的科学辩证思维能力。     

化学实验中的几个差异问题

化学实验中,不同反应物参加反应,会得到不同的生成物,这是人所共知的。然而实验中也常常出现这样的现象,即所加试剂（反应物）相同,但所得结果（生成物）却不同。     

逆向配平法

逆向配平法是从给生成物配系数开始配平氧化还原反应方程式的一种方法。此方法根据氧化还原反应中氧化数的增减总数相等的原则,配平氧化还原反应方程式的步骤如下。(1)写出反应式,标出发生氧化和还原的元素原子在反应前后的氧化数,例如:Cu2S 1-2 HN 5O3Cu 2(NO3)2 H2S 6O4 N 2O H2O(2)分别确定氧化剂、还原产物、还原剂和氧化产物的代表,通常它们的代表是化学式中标明氧化数的原子和标明氧化数的同种原子部分(如Cu 12S-2中的Cu 12)。例如在上面反应式中,氧化剂HN 5O3的代表是N 5,还原产物N 2O的代表是N 2,还原剂Cu 12S-2的代表是…     

中德高中化学教材比较研究*——以“氧化还原反应”为例

基于闫春更等建立的“二维度四指标”教材难度微观评价模型,选取德国巴登符腾堡州(Baden-Württemberg)《今日化学Ⅰ》和中国人教版《化学1》为研究对象,就“氧化还原反应”主题的教材难度进行了测评和比较,为我国教材编写提供建议。     

增加一种反应物浓度对反应物转化率影响的研究

通过建构模型探讨了多反应物平衡体系中增加反应物浓度对转化率的影响,并用曲线进行表征。模型表明,转化率的变化与反应物和生成物化学计量数相对大小关联紧密。文中结论澄清了某些错误认知,对中学化学教学有一定的指导意义。     

求活化能时速率常数中可以用压力单位

求活化能时速率常数中可以用压力单位崔晓丽（河北师范大学化学系石家庄０５００１６）恒温恒容理想气体的反应中，反应速率可用反应物（或生成物）的浓度随时间的变化率表示；由于压力比浓度容易测定，也可用反应物（或生成物）的分压随时间的变化率表示。对ｎ级反应，若...     

“蓝瓶子”实验再探究*

利用SPSS 25.0统计软件对“蓝瓶子”实验进行正交实验设计,通过统计学分析得出最佳实验条件。利用氧化还原传感器(ORP)对“蓝瓶子”振荡体系的电极电势变化曲线进行分析,并针对蓝色的产生和消失过程设计3组对比实验深入探究,阐明其反应原理,意在引导学生深刻理解趣味实验现象背后的微观反应本质。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.