1,3—戊二烯／苯乙烯阳离子共聚合反应

本文研究了以甲苯为溶剂,ＡｌＣｌ３和ＢＦ３·ＯＥｔ２为引发剂,１,３－戊二烯（ＰＤ）与苯乙烯（Ｓｔ）的阳离子共聚合反应,并用红外光谱测定聚合物的微观结构。由共聚单体ＰＤ和Ｓｔ加入顺序的不同可生成无规共聚物Ｐ（ＰＤ－ｃｏ－Ｓｔ）和接枝共聚物Ｐ（ＰＤ－ｇ－Ｓｔ）和Ｐ（Ｓｔ－ｇ－ＰＤ）。无论是由ＡｌＣｌ３引发聚合反应,还是由ＢＦ３·ＯＥｔ２引发聚合反应,Ｓｔ上的碳阳离子的活性都高于ＰＤ上碳阳离子的活性。由ＡｌＣｌ３首先引发ＰＤ进行聚合反应,结束后再引入Ｓｔ时,聚合体系不能引发Ｓｔ聚合反应;相反ＡｌＣｌ３首先引发Ｓｔ聚合后的体系能继续引发ＰＤ的聚合反应。ＢＦ３·ＯＥｔ２无论先引发Ｓｔ或是ＰＤ,都能在聚合反应完成后接着引发另一单体而生成接枝共聚物Ｐ（ＰＤ－ｇ－Ｓｔ）和Ｐ（Ｓｔ－ｇ－ＰＤ）。二苯醚与烯丙基氯的加入,提高了碳阳离子的稳定性,增加了聚合物的分子量,但降低了碳阳离子的活性,使得聚合反应的产率降低,同时对Ｓｔ和ＰＤ碳阳离子的活性次序无明显影响     

1,3-戊二烯阳离子聚合过程中环化反应的研究

以ＡｌＣｌ３和（ＣＦ３ＳＯ３）３Ａｌ为引发剂，ＣＨ２Ｃｌ２为溶剂，在２０℃聚合了１，３ 戊二烯（ＰＤ）．对聚合物（ＰＰＤ）的结构分析表明，（ＣＦ３ＳＯ３）３Ａｌ生成的聚合物具有较高的环化度．聚合物的环化过程是通过两种机理，分子内链转移机理和阳离子引发机理，后者可以通过加入ＤｔＢＰ得到抑制．ＡｌＣｌ３引发的聚合反应中环化过程以前一种机理为主，而（ＣＦ３ＳＯ３）３Ａｌ则以后一种机理为主．通过阳离子引发的环化反应主要发生在ＰＰＤ１，２单元侧基双键上     

1,3戊二烯阳离子聚合体系交联反应的研究

研究了芳烃、卤代烃和醚对正己烷介质中AlCl3 引发的 1 ,3 戊二烯阳离子聚合反应的影响 ,讨论了这些组分对交联反应的抑制作用 .聚合体系引入芳烃后通过链转移机理抑制了凝胶的生成 ;卤代烃在聚合反应中可与AlCl3 形成复合引发体系参与引发过程 ,并可避免凝胶生成 ,也能作为链转移剂通过链转移机理抑制交联反应 ;醚类在聚合反应中的作用为 :与AlCl3 络合参与引发反应使得聚合物分子量升高 ,或与碳阳离子作用降低其活性并抑制交联反应 .     

四氢呋喃阳离子聚合向丁二酸酐链转移反应的研究

四氢呋喃阳离子聚合向丁二酸酐链转移反应的研究魏斌，赵庆香，栗方星（南开大学化学系天津３０００７１）关键词聚四氢呋喃，五氯化锑，表现链转移速率常数，表现聚合反应速率常数前言在用ＣＨ３ＣＯＳｂＣｌ５引发的四氢呋喃阳离子聚合［１］过程中，我们发现存在着活性...     

亲核性调节剂在异丁烯阳离子聚合中的作用机理

亲核性调节剂在异丁烯活性阳离子聚合中发挥着极其重要的作用 ,其作用机理主要包括 :(1)碳阳离子稳定化作用 ,即亲核性试剂或它们与Lewis酸生成的络合物与增长链的末端结合 ,来降低活性中心阳离子的“阳离子性” ,抑制副反应 ,使聚合反应呈现活性聚合特征 ;(2 )质子捕获作用 ,即亲核性试剂捕获质子 ,抑制质子的不可控引发和链转移反应 ;(3)增长链表观稳定作用 ,即亲核试剂降低了增长速率与引发速率之比 ,提高引发效率 ,降低增长速率 ,降低分子量分布 ;(4)抑制自由离子增长作用 ,即亲核试剂与质子源和Lewis酸反应 ,生成同阴离子 ,产生同离子效应 ,抑制自由离子活性中心的引发增长作用。     

乳液聚合反应中自由基的解吸

自由基的解吸是指在乳液聚合体系中,自由基从单体增溶的胶束或聚合物胶粒中解吸附的过程。这些自由基可以是单体自由基、齐聚物自由基、也可以是由于链转移反应生成的链转移自由基。自由基的解吸使乳液聚合反应速率下降、聚合物胶粒数目增加,并在聚合反应后期引起自加速现象。考虑到自由基解吸因素影响     

AlCl_3／SbCl_3引发α－蒎烯阳离子聚合反应──引发活性种本质研究

考察了复合催化剂ＡｌＣｌ_３／ＳｂＣｌ_３的不同配制方法和质子捕捉剂２，６－二异丁基－４－甲基吡啶（ＤＴＢＭＰ）对α－蒎烯阳离子聚合反应的影响。结果表明，ＡｌＣｌ_３和ＳｂＣｌ_３加热熔融复合比简单复合的引发聚合活性更高；ＤＴＢＭＰ对该复合催化剂的聚合反应速率及其产物分子量分布均无明显影响，证明该复合催化剂形成的活性种本质上与质子Ｈ活性种不同，是新型活性种。根据２７ＡｌＮＭＲ对该体系活性种分析结果，认为引发阳离子是［Ｓｂ（Ｖ）Ｃｌ_４］，抗衡阴离子是［Ａｌ_２Ｃｌ_７］     

对醇的消去反应规律的商榷

许多资料这样总结醇的消去反应规律:只有和醇羟基所在碳原子相邻的碳上有氢时,醇才能发生消去反应。笔者认为这种说法欠妥,值得商榷。1反应机理醇在酸的作用下,脱水成烯是经过E1反应机制而完成的,如下图所示:醇羟基接受质子,然后以水的形式离去,原羟基所在碳因而带1个正电荷成为碳正离子,碳正离子的邻碳失1个质子,1对电子转移过来中和碳正离子的正电荷从而形成碳碳双键。如果醇羟基接受质子失水后形成的碳正离子的邻碳上无氢而发生重排后形成的碳正离子的邻碳上有氢,则发生重排形成新的碳正离子,接着邻位碳失去质子而成烯。例如:此反应可表…     

AlEtCl_2／t－BuCl引发α－蒎烯阳离子聚合反应研究

考察了在ＡｌＥｔＣｌ２／ｔ－ＢｕＣｌ引发体系作用下的α－蒎烯阳离子聚合行为．结果表明，ｔ－ＢｕＣｌ与ＡｌＥｔＣｌ２复合后，由于生成（ＣＨ３）Ｃ正离子而使引发活性增大．但ｔ－ＢｕＣｌ的引人对产物分子量及其分布影响不大，产物主要由二、三聚体组成．聚合过程的动力学研究表明，α－蒎烯在进行阳离子聚合时容易发生链终止反应而导致单体转化率和产物分子量较低．α－蒎烯在聚合反应的同时伴随着异构化反应，用制备ＧＰＣ分离出异构化产物，然后经１ＨＮＭＲ测定其结构．     

顺－1，3－戊二烯的阳离子异构化聚合

顺－１，３－戊二烯的阳离子异构化聚合彭宇行，戴汉松，刘佳林，寸琳峰（中国科学院成都有机化学研究所，成都６１００４１）在阳离子聚合反应中，由于链增长过程中碳阳离子的不稳定性，可以导致异构化或重排反应￣［１］，这种异构化聚合（Ｉｓｏｍｅｒｉｚａｔｉｏｎｐ...     

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.     

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.     

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.     

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.     

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.     

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.