乙酰乙酸乙酯制备实验的改进

乙酰乙酸乙酯的制备,实验教材上是以乙酸乙酯为原料,钠作缩合试剂,通过Claisen缩合反应制备。其实验存在着安全性差、耗时长、产品纯度差和收率低等不足。依据实验的目的、原理、内容不变的原则,采用钠与乙酸乙酯物质的量比为0.52,回流下加入细砂搅拌制备钠珠,缩合反应过程加入环己烷,分馏提纯产品等措施进行改进实验。改进后的实验操作的安全性和产品的质量提高,产品收率可达70%以上。     

对乙酸乙酯制备实验中饱和碳酸钠溶液作用的定量研究

乙酸乙酯的制备实验,是中学化学教材中的一个比较重要的实验,收集乙酸乙酯时使用了饱和碳酸钠溶液。对于该实验,有几个问题困扰着我们:(1)饱和碳酸钠溶液起何作用?(2)可否用饱和碳酸氢钠溶液     

乙酸乙酯制备实验的绿色化改进

基于绿色化学的理念,对传统学生有机基础实验乙酸乙酯制备进行改进,运用超声波辅助技术合成了离子液体[EMIm]BF4,利用合成的[EMIm]BF4催化合成乙酸乙酯。从学生实验结果来看,该实验提高了学生的创新能力。     

利用知识误区培养学生观察和分析问题的能力──兼谈低级酯的水溶性

不少资料明确指出：乙酸乙酯不溶于水。现行教材也提到,酯一般“难溶于水”。正是这个知识误区,影响到高中化学中“乙酸乙酯的制备”实验的成败。     

乙酸乙酯的可视化制备

在基础教学实验中引入可视化实验理念以强化酯化反应操作,对乙酸乙酯的制备实验进行了综合改进。以乙酸和乙醇为原料,硫酸氢钠为催化剂、变色硅胶为吸水剂、甲基紫为可视化试剂,实现了乙酸乙酯可视化制备,解决了试剂限购和碳化等问题。气相色谱分析结果表明乙酸几乎完全转化,并通过氢核磁共振(1H NMR)证实了乙酸乙酯产物结构。利用颜色明显变化进行化学反应过程可视化教学,让学生在视觉上感知酯化反应的动态过程,从而增强学生学习有机化学的兴趣,活跃学生的思维以及提高学生学习效率。     

微型化学实验与常规实验的比较研究

通过对2个有机化学实验的常规实验与微型实验加以比较,说明研究和推广微型实验的必要性. 1实验部分 (1)实验内容:乙酸乙酯的制备和苯甲酸的制备. (2)实验方法:常量法,实验方法见文献[1];微量法,实验方法见文献[2].     

医学化学设计实验的探索——以乙酸乙酯的制备为例

以“乙酸乙酯的制备”为例, 针对原实验教学中存在的诸多弊端, 从实验性质、教学模式、组织模式、考核评价方面进行了改革,探讨了开展设计实验的必要性及实施的方法。     

制备过氧化钠演示实验的探究

从钠在空气中燃烧的化学原理及过氧化钠的性质入手,探究制备过氧化钠的实验条件、实验装置设计,根据所设计的实验装置制备过氧化钠取得了满意的效果。     

乙酸乙酯制备实验教学中的问题探究

3个版本化学教材中对于乙酸乙酯制备实验的阐述有所不同,化学教师在教学实践中对该实验会产生一些疑问。通过定量研究的方法探究该实验能否用水浴加热法、能否改变加药品的顺序、是否一定要加沸石等,以得出最佳实验条件。     

多功能微型气体制备实验装置的设计研究

传统的气体制备实验装置是由一套玻璃器材组合而成,而这些玻璃装置的体积较大且易破,而且在实验前的准备与实验中的操作皆有不便之处,做实验时若一不小心便会弄破。由于延续等的制备与其性质的检验不易,实验过程较费时间,耗用药品也较多,并且也较易产生更多废液而造成污染。本文中所设计改进而成的实验装置“多功能微型气体制备装置”。其实验装置器材简单、制作容易、操作方便、效果显著又正确,此外又可减少很多药品,使用过的药品也可回收再重复使用,降低污染,真可谓是具有减量减废环保理念的绿色实验,实值得推广。     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.