Tollens试剂与银镜反应探讨

Tollens 试剂即硝酸银的氨水溶液,是一种比较弱的氧化剂,能与醛发生银镜反应,而不能与酮反应,因此常用于醛和酮的鉴别。目前国内通用的有机化学实验教材中关于 Tollens 试剂的配制多是采用加入氢氧化钠溶液的方法,但是按照此法配制的 Tollens 试剂进行银镜反应,有时实验效果并不理想,除了醛能发生反应以外,酮以及很多其它化合物也呈正性反应,不能用于区别醛和酮。针对这一问题,我们进行了一些实验与探讨,发现加碱的 Tollens 试剂进行空     

乙醛2个特征反应实验应注意的问题

做银镜反应实验常常遇到一些问题,如镜面发暗,不够光亮,不产生银镜等。而乙醛与氢氧化铜反应常遇到产生黄褐色混浊、暗褐色沉淀或红褐色沉淀等问题。针对以上可能出现的现象,提出了这2个实验在试剂配制和操作过程中应注意的问题,从而为教师提高这2个实验成功率提供借鉴与参考。     

常温下快速银镜反应条件探究

银镜反应作为高中化学教学中醛基的一个重要性质演示实验,在演示时通常需要水浴加热,且形成银镜所需时间较长。在一系列实验探究的基础上,发现在银氨溶液中加入一定量碳酸钠溶液后再加入乙醛,常温下能够在较短时间内生成银镜。该反应操作简单,银镜形成较快。     

探究不同银配合物对银镜反应的影响

为探究配体与银形成不同银配合物对银镜反应的影响,以氨水、乙二胺、硫氰化钾和甲胺为配体,通过利用不同银配合物的稳定常数研究不同温度条件下银镜反应的情况,对银镜形成时间和质量做比较。结果表明,在这4种配体中,以乙二胺为配体形成的银配合物稳定常数较高,且碱性较强,室温条件下能快速形成高质量的银镜,利于课堂上开展银镜反应实验演示教学。     

银镜反应实验条件优化的研究性学习活动及行为分析

选择银镜反应实验优化条件为研究性学习活动,阐述了活动目标、实施步骤、银镜反应的正交设计、实验过程及结论。利用NVivo 10.0质性分析工具,对上述活动进行质性分析,阐述了研究过程以及利用NVivo 10.0质性分析工具获得的结论。     

2012年高考理综北京卷对银镜反应考查的研究和思考

2012年高考理综北京卷第27题以实验为载体,以银镜反应的条件和试剂改变为研究对象,让学生经历了问题的提出、资料检索、提出假设、设计实验、预测现象、观察实验、分析结果、得到结论、实验收尾处理的实验探究全过程,是北京市高中新课程改革第3年高考全面提高对化学实验和探究能力考查力度的体现。笔者走进实验室,对试题所涉及的实验条件进行研究,对银镜反应及其操作有了更加明确的认识,并对实验题的命制提出了建议。     

浅议甲酸的银镜反应

甲酸的结构既具有羧基,又具有醛基,因而兼有羧酸和醛的性质,能够象醛一样发生银镜反应。但由于甲酸结构上的特点,其银镜反应条件与醛又有所不同,若条件控制不当,反应结果往往得不到银镜,而是白色混浊或金属银的黑色沉淀。一些资料上建议甲酸的银镜反应最好在强碱性条件下进行。如《甲酸的银镜反应》一文中介绍,应先用固体KOH中和甲酸,使其pH=12,才可使甲酸生成银镜。     

不加热不振荡情况下葡萄糖银镜反应的最佳实验条件探究*

对不加热不振荡情况下的葡萄糖银镜反应进行正交实验设计,以硝酸银浓度、氢氧化钠浓度、葡萄糖浓度3个因素为变量,设计成三因素四水平实验,利用SPSS25.0软件对实验结果进行统计学分析,分别得出考虑银镜镜面效果、银镜反应时长和综合考虑2者时的主要影响因素及最佳实验条件,并结合反应机理对影响因素、最佳条件进行进一步分析。     

用正交试验法选择乙醛发生银镜反应的最优条件

本文用正交试验法设计并进行了乙醛与银氨溶液反应的实验,以求找出最优实验条件,尽可能得到更好的银镜,增进实验的效果。     

长期放置的乙醛实验前需预处理

在高中化学实验教学中,经常做乙醛性质实验。乙醛在常温下会自动聚合成三聚乙醛。若用这种乙醛做银镜反应实验,将得不到正确的实验结果。     

Neutral diterpenoids of oleoresins of five species of conifers of Transcarpathia

The compositions of the neutral diterpenoids of the oleoresins of five species of conifers growing in the Transcarpathia have been studied. It has been found that the oleoresins ofAbies alba M.,Larix decidua M., andPicea excelsa L. contain more than 50% of neutral diterpenoids. The group and qualitative compositions of the oxygen-containing diterpenoids have been determined. In the oleoresins ofAbies alba,Picea excelsa, andPicea abies tertiary alcohols — cis-abienol and isocembrol — predominate, while inLarix decidua the main component is the hydroxy ester larixyl acetate. Primary alcohols related to the resin acids have been found in all the oleoresins investigated. Features of the distribution of diterpenoids according to the species of conifers have been revealed. The results obtained are necessary for the chemotaxonomy of conifers of the family Pinceae.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 812–816, November–December, 1988.     

利用手持技术改进测定乙醇分子结构实验

利用压强传感器代替排水集气法,改进测定乙醇分子结构实验的仪器装置,并探索最佳反应条件。另外,设计两个空白实验,结合压强变化曲线对实验误差进行相关讨论。     

光谱仪测试范围的扩展

由于石化行业的生产需要，其材质的使用具有多样性和广泛性，经常会出现顾客委托的测试样品的一个或几个元素跨越光谱仪现有测试程序测量范围的情况。本法通过对光谱仪测试原理的认识，根据光谱仪的测试能力及标样的采集，实现了一个或几个元素测量范围的扩展，并对其测量的影响因素进行了研究。     

Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

Influence of viscosity of medium on processes of oxygen quenching of excited states of mesoporphyrin

The oxygen quenching rate constants for singlet and triplet excited states of the dimethyl ester of mesoporphyrin IX increase with decreasing viscosity of the medium and reach a maximum at a viscosity of approximately 0.4 mPa·sec, after which the rate constants begin to decrease. The drop in rate constant with increasing fluidity of the medium may be related to a nonequilibrium character of the elementary act in the interaction of the reactants in the solvent cage. In viscous media such as isopropyl alcohol, isobutyl alcohol, and isoamyl alcohol, the reaction radius is greater than the sum of the radii of the reacting particles. The long-range character of these processes is due to the relatively weak dependence of the quenching probability on distance.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 161–167, March–April, 1989.     

Effect of the Method of Modification of Zeolite X on Selectivity of Catalytic Methylation of Toluene

Theoretical and Experimental Chemistry - The effect of the method of modification of catalysts based on zeolite X by cesium and magnesium cations (ion exchange and impregnation) on the selectivity...     

Synthesis of tetrabenzoporphins of the basis of isoindoline

Chemistry of Heterocyclic Compounds -