硝酸生成的演示实验

高一化学讲授硝酸生成时如能设置下述实验,可以使学生加深理解以下三方面的概念:(1)NO2溶于水生成硝酸并放出1/3体积的NO。(2)NO极易被空气中氧气氧化。(3)NO和NO2是经过多次的氧化和吸收,才能比较完全地被水吸收。     

用长铜丝代替小铜片跟硝酸反应

在高中化学课本中,有铜与硝酸反应的实验,书中讲的是用小铜片与硝酸反应。我们从实践中发现,尽管所用铜片很小,反应后铜片仍有剩余,现在我们只用一根比试管长些的铜丝,头上略加弯曲一下（防止戳穿试管底）。先在试管中加入半毫升稀硝酸,随即把此长铜丝插入硝酸中,当看到反应已明显发生,溶液已变成蓝绿色,试管下部已充满 NO2但还未从试管口逸出时,就把铜丝从浓硝酸中取出洗净,反应也就停止了。     

应当正视教材练习题上的2处硬伤

指出了人教版《化学1》教材上的2处硬伤,常温常压下硫酸铜溶液浓度不可能达到2 mol/L,实验时更不可能给学生1试管NO2。实验发现,通常情况下,将1试管NO2倒扣在水中,待液面基本稳定时,水位上升远远不止2/3试管。     

中学化学教学中的学理分析

学理,简单说就是反映客观规律的原理。与学理分析相比,中学化学中更倾向于用事实来分析、解释事实。例如,充满氨气的试管倒立在水槽中,水将会充满试管。解释是:氨气极易溶解于水。这就是用事实解释事实。而用学理解释,则是试管内形成了较强的负压。这就是说,如果没有形成负压,氨气易溶于水也不会导致水充满试管;试管内形成了负压,即使氨气不溶于水,水也会充满试管。学理分析的缺失,致使学生认知结构中的知识与知识之间缺乏实质性的联系。     

恒容吸收系统中水和稀硝酸对NO2的吸收过程研究

采用恒容吸收系统研究了水和稀硝酸对二氧化氮气体的吸收行为,通过测量吸收液的组成和气相压力来考察吸收剂浓度、吸收剂的量和吸收压力对NO2吸收效率和产物的影响。增加水的质量,则吸收效率增加,而所得硝酸的浓度先增加后减小。随着NO2初始压强的增加,水对NO2的吸收效率和所得硝酸浓度均增加。结果表明二氧化氮在稀硝酸中的吸收速度比在水中快,较高的气相初始压力(>90 kPa)或较高的硝酸浓度(>7wt%)都有利于吸收效率的提高。从反应关系分析计算,可获得气相组成、N2O4的转化率和HNO2的分解率等参数,发现随着水的量的增加,N2O4的转化率逐渐增大,而HNO2的分解率先增大后减小,在NO2和水的物质的量的比为0.024时达到最大值。     

NO,NO_2性质的演示装置

NO,NO_2性质的演示装置必须显示出: ①NO不溶于水, ②NO遇氧很易生成红棕色的NO_2, ③NO_2很易溶于水。④NO_2溶于水后显酸性。根据这些要求设计了上图的演示装置。甲为圆底烧瓶带有三孔橡皮塞,其中一孔插长玻璃管,玻管一端直至瓶底,另一端伸入乙瓶,也伸至瓶底;另二孔插入两根短的弯玻管,再套以橡皮管与启普发生器丙、丁相连。乙瓶为与甲瓶同容积的平底烧瓶,带有二孔橡皮塞,其中一孔即插由甲瓶来的玻管如前所述,另一孔插一短的弯玻管3。丙、丁均为启普发生器,在此处用作储气瓶。(收集气体时可先将整个发生器充满了水,然后将气体从发生器出气嘴处压入,水即进入顶上漏斗中。)     

浓硫酸不能干燥NO2的实验探究

二氧化氮为红棕色、有强烈刺激性气味、有毒性的气体.易溶于水,且能与水反应的一种酸性氧化物.在实验室制取NO2时,能否用浓H2SO4来干燥NO2气体,一般化学参考资料都没有明确指出,大学教材[1]中的有关内容也是如此.但是目前在一些权威性著作[2]中出现"浓硫酸可以用来干燥NO2气体".在一些高中化学复习资料中,用浓硫酸来干燥NO2的练习和测试题频频出现.然而,这是一个十分明显的科学性错误.下面笔者就先用2个实验的客观现象来说明浓硫酸不能用于干燥二氧化氮气体.     

二氧化氮溶于水的定量实验

本实验说明以下四点:1.二氧化氮溶于水生成硝酸,并生成1/3体积的无色一氧化氮气体。2.生成的硝酸具有酸性。     

挥发性液体可否形成雾的探究

利用实验、文献对挥发性液体形成雾的条件进行了探究。结果显示,挥发性液体形成雾需要的条件为湿空气环境,溶液浓度大,挥发性强,挥发出的气体易溶于水,溶于水后的生成物易电离,形成的水合物能与水分子作用凝结成的粒子线性大小在10-3~10-7cm。     

对铝表面氧化膜性质的探究

铝表面生成的氧化膜是致密坚硬的。该氧化膜可溶于盐酸,不溶于硫酸、硝酸等酸。在硫酸、硝酸溶液中加入NaCl,铝表面氧化膜可溶解其中。CuCl2溶液可破坏铝表面的氧化膜,CuSO4、Cu(NO3)2的溶液不能破坏铝表面的氧化膜。     

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%.     

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.     

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.     

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.     

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.     

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.