组合氧化法测空气中的氧气含量

“空气中氧气体积含量的测定”是人教版初三《化学》上册和浙教版《科学》八年级下册的一个重要的定量实验,课本中的设计方案有明显缺陷,测定结果不够准确。用烧杯和水槽组装成水封,消除了反应容器内外气体交换的可能性;烧杯上的体积刻度可以直观地反映出反应前后的气体体积变化;活性铁粉缓慢氧化提供热量,使白磷达到着火点燃烧,用组合氧化(白磷燃烧+活性铁粉缓慢氧化)耗尽烧杯中的氧气,该设计方案更为周密、完善。测定过程中现象明显,结果更准确。     

白磷和红磷燃烧条件探究及空气中氧气含量测定的组合实验

用白磷和红磷在探究燃烧的条件,同时测定空气中氧气的含量,将这两个实验有机地结合在一起进行,既避免了产生的P2O5白烟污染空气,又简化了实验操作,而且实验现象明显,成功率高,特别适合用作在教师指导下的学生探究实验。     

利用试管控制白磷在水中燃烧

对白磷在水中燃烧的实验作了进一步改进:将白磷放入盛热水的试管,通过玻璃导管鼓入空气或通过胶头滴管注入过氧化氢溶液产生氧气,即可出现明显的燃烧现象。     

铁丝在氧气中燃烧的实验改进

“铁丝在氧气中燃烧”是初中化学教材中证明氧气化学性质的一个演示实验,该实验证明了氧气比较活泼,在一定条件下可以和金属发生剧烈反应。但是与木炭在氧气中燃烧、硫在氧气中燃烧、蜡烛在氧气中燃烧的演示实验相比,铁丝在氧气中燃烧的实验存在着一些不足的地方,针对这些不足,对铁丝在氧气中燃烧的实验进行了改进。1实验存在的问题按照教材要求,铁丝在氧气中燃烧的实验,须将铁丝绕成螺旋状,并在铁丝的末端绑上一根火柴杆,实验时先将火柴杆点燃,待火柴杆将燃尽时,迅速伸入盛满氧气的集气瓶中。这样的操作存在2个问题:第一,火柴燃烧的程度不…     

简便、准确测定空气中含氧量的方法

空气中氧气体积分数的测定是义务教育阶段一个重要的化学实验.传统实验是用红磷的燃烧来测定,实验安全性和准确性不高,不能满足实验教学之所需.前人对此已经有很多改进研究[1,2],但不能让学生直观地观察到空气中氧气的体积分数为21%.笔者对该实验重新设计,改用白磷在注射器内燃烧来测定,使实验达到满意的效果.     

燃烧实验的改进

燃烧是可燃物踉空气中的氧气发生的一种发光放热的剧烈氧化反应。我们用水浴的方法做白磷自燃实验,省时间、效果好。一、改进装置如图所示二、实验步骤1．在250mL的烧杯中,注入约200mL的开水,同时投进一小块白磷;然后取2支试管分别放进少量的白磷和红磷后把试管分别放进烧杯中,并在盛白磷的试管口塞入带导管的单孔胶塞,在导管上再绑一个小气球作为尾气袋。2．请同学们注意观察现象,学生则会发现在试管中的白磷立即燃烧,而水中的白磷和另一支试管中的红磷则无变化。3．弓I导学生对以上3种现象进行分析。根据分析,应得出两个结论：…     

“燃烧条件的实验”改进

阐述了教材中“燃烧条件的实验”存在的问题,说明了具体的改进方法和实验效果,解决了没有白磷的问题。改进后的实验现象明显,操作简单,安全环保,具有很好的借鉴作用。     

白磷水下燃烧实验的改进

有些书中,介绍这一实验时,往往是将白磷放入盛水的烧杯中,倒入热水,来演示这个实验.当通入氧气时,气流往往将白磷吹得乱跑,使白磷很难与氧气接触,至使这一实验不好实现.若改用试管代替烧杯,效果就会好一些,若改用大号离心式试管代替,演示效果就会更好.     

初中化学“碳、燃烧”的教学法(下)

第四课什么是燃烧燃烧的条件一、本课目的:使学生知道燃烧的意义,并使学生了解温度和空气中的氧在可燃性物质燃烧时所起的作用。二、检查学生知识:(1)在自然界分布最广的是哪种碳酸盐?(2)一氧化碳有什么主要用途?(3)哪类反应叫化合反应?那类反应叫分解反应?(4)碳和硫各在氧中燃烧有什么相似现象(生光和热)?生成什么物质(氧化物)? 三、讲新课: 1.教师结合上面的提高,叫学生回想氧气性     

白磷水下燃烧演示实验的再研究

“白磷水下燃烧实验”由于其在教学中的重要性以及所涉及物质的剧毒性、易燃性使实验充满了危险。该实验一直是中学教师探讨的热点,虽然相关的实验改进方法很多,但笔者通过对各类文献中介绍的改进方法的试验比较和研究发现,这些方案依然有改进的余地。     

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%.     

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.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

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.     

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.     

Microwave-assisted copper-catalyzed stereoselective ring expansion of three-membered heterocycles with α-diazo-β-dicarbonyl compounds

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes through an intramolecular S_N2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis-3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis-oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively.     

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.     

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%).