杂多酸引发四氢呋喃聚合反应

八十年代中、后期发现，杂多酸（ＨＰＡ）是阳离子聚合反应的良好引发剂［１，２］．ＨＰＡ是一类酸强度比浓硫酸还高的质子酸［３］，不仅具有易于制备，结构稳定，腐蚀性低，易溶于大多数有机溶剂的特点，更为重要的是，ＨＰＡ可以回收和重复使用．因此，ＨＰＡ作为一类...     

杂多酸引发四氢呋喃开环聚合反应 Ⅳ.以环氧丙烷为促进剂

对杂多酸引发四氢呋喃开环聚合的研究从八十年代中期开始已有不少报道［１～４］,其引发聚合的活性低,当杂多酸浓度低时,聚合反应时间长,产物分子量高;而为制得工业通常使用的中等分子量四氢呋喃聚醚二醇,需要加大量的引发剂,且聚合收率低（最高仅为３５％）．针对以上问题,本实验室曾对以环氧乙烷（ＥＯ）促进低浓度十二磷钨杂多酸Ｈ３ＰＷ１２Ｏ４（ＰＷ１２）引发四氢呋喃开环聚合反应进行了系统的研究［５,６］,发现ＥＯ对ＴＨＦ聚合具有良好的促进效果,制得中等分子量聚醚二醇,转化率达到６０％以上．本文进一步研究了环氧…     

杂多酸引发四氢呋喃开环聚合反应Ⅵ.以环氧氯丙烷为促进剂

在以低浓度杂多酸(ＨＰＡ)催化四氢呋喃(ＴＨＦ)聚合反应中,我们曾采用环氧乙烷(ＥＯ)和环氧丙烷(ＰＯ)为促进剂,发现它们都具有很好的促进效果[1,2],并且活性相近.在以三氟化硼(ＢＦ3)为催化剂的四氢呋喃正离子开环聚合反应中,促进剂的活性次序为:ＥＣＨ(环氧氯丙烷)>ＰＯＥＯ[3].在ＨＰＡ催化ＴＨＦ聚合反应中,ＥＣＨ是否仍具有高的促进活性是本文研究的目的.1　原料及聚合操作ＴＨＦ的纯化见文献[4],ＥＣＨ的纯化见文献[5],十二磷钨杂多酸(ＰＷ12)的处理见文献[1],三氟醋酸酐的合成方法和聚合反应的操作均见前文[2].2　分析测试核磁共振…     

水合ZrO_2固载12-磷钨杂多酸催化四氢呋喃开环聚合

采用过量浸渍结合溶剂蒸发将12-磷钨杂多酸（TPA）分散于水合ZrO2干凝胶表面（以TPA质量分数表示的固载量为5～65 wt%）,再经120～500℃空气气氛焙烧得到水合ZrO2固载磷钨杂多酸催化剂.借助等离子体原子发射光谱（ICP-AES）、物理吸附、X射线衍射（XRD）、傅里叶变换红外（FTIR）光谱、吡啶吸附红...     

杂多酸引发四氢呋喃开环聚合反应Ⅶ.以氧杂环丁烷为促进剂

在以低浓度杂多酸(HPA)催化四氢呋喃(THF)聚合反应中,我们曾采用环氧乙烷(EO)、环氧丙烷(PO)和环氧氯丙烷(ECH)等三元环醚为促进剂,发现它们对聚合反应都具有很好的促进效果[1～3]. 本文进一步研究了具有四元环醚结构的氧杂环丁烷(OX)对THF聚合的促进效果.     

杂多酸引发四氢呋喃聚合反应 Ⅲ.环氧乙烷对聚合反应的影响

最近我们研究发现环氧乙烷（ＥＯ）可有效地促进低腐蚀性磷钨杂多酸（ＰＷ１２）引发的四氢呋喃（ＴＨＦ）聚合反应,产物分子量可通过体系中水或低分子二醇的含量进行控制［１,２］．而在没有ＥＯ存在时,相似条件下ＰＷ１２引发ＴＨＦ聚合反应２４ｈ,没有检出聚合物［...     

杂多酸引发四氢呋喃聚合反应 Ⅱ.水的反应行为

前报我们对低腐蚀性非均相的磷钨杂多酸Ｈ３ＰＷ１２Ｏ４０（ＰＷ１２）引发体系进行了研究［１］,发现环氧乙烷（ＥＯ）可有效地促进ＰＷ１２引发的四氢呋喃（ＴＨＦ）聚合反应,大幅度地降低了引发剂用量,聚合物收率显著提高,并发现聚合过程中不存在链终止反应．产物...     

多钨酸盐修饰ZrO2气凝胶催化四氢呋喃开环聚合

采用过量浸渍结合溶剂蒸发将磷钨杂多酸(TPA)分散于ZrO₂气凝胶表面(TPA的质量分数为5%-45%), 再经750 °C空气气氛焙烧得到多钨酸盐修饰ZrO₂固体酸催化剂. 借助N₂吸附、X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、氨程序升温脱附(NH₃-TPD)和吡啶吸附红外(Py-IR)光谱对催化剂的结构及酸性质进行表征, 针对四氢呋喃(THF)开环聚合反应考察其酸催化性能. 研究发现, TPA与ZrO₂之间较强的相互作用抑制了ZrO₂的晶化, 同时也在一定程度上稳定了TPA的Keggin(凯金)-阴离子结构. 高温焙烧的催化剂中, 活性组分以ZrO₂锚定的表面相(包括含有畸变或缺陷型Keggin单元的杂多酸盐及以Zr为杂原子的类杂多酸物种等)和TPA完全分解形成的氧化物体相存在, 各物种的相对量取决于TPA的负载量. 催化剂表面同时具有中等强度的布朗斯特德(Brönsted)酸与路易斯(Lewis)酸中心, 且初始TPA负载量为20%的催化剂实现了活性组分在载体表面的单层覆盖, 因而显示最大的总酸量, 对THF聚合反应也表现出最高的催化活性. 在反应温度为40 °C、时间为20 h条件下, 聚合物收率达30.9%±2%, 数均相对分子质量为2698±100; 在催化剂重复使用6次过程中, 活性未见明显降低.     

杂多酯引发四氢呋喃开环聚合反应Ⅶ.以氧杂环丁烷为促进剂

在以低浓度杂多酸(ＨＰＡ)催化四氢呋喃(ＴＨＦ)聚合反应中,我们曾采用环氧乙烷(ＥＯ)、环氧丙烷(ＰＯ)和环氧氯丙烷(ＥＣＨ)等三元环醚为促进剂,发现它们对聚合反应都具有很好的促进效果[1～3].本文进一步研究了具有四元环醚结构的氧杂环丁烷(ＯＸ)对ＴＨＦ聚合的促进效果.ＯＸ用作促进剂有以下优点,由ＯＸ促进ＴＨＦ聚合所得聚醚的端羟基为伯羟基,作为生产嵌段聚醚氨酯或嵌段聚酯弹性体的原料具有与四氢呋喃均聚醚相似的高反应活性;与ＥＯ相比,后者虽然促进ＴＨＦ聚合所得聚醚的端羟基也为伯羟基,但其沸点过低,不利于操作和贮存.1　原料及…     

稀土催化四氢呋喃开环聚合

1937年Meerwein首次发现Et_3O~(+BF)可催化四氢呋喃(THF)开环聚合。到目前为止,发现能使THF开环聚合的催化剂有质子酸、Lewis酸、洋离子、正碳离子等。1990年吴健等将(Acac)_3Nd-(i-Bu)_3Al-H_2O-环氧氯丙烷催化体系应用于THF聚合,发现它和(i-Bu)_3Al-H_2O-环氧氯丙烷体系具有相同的活性,这说明稀土配合物没有参与活性中心的形成。本工作发现(CF_3CO-2)3Ln(Ln=Y,La,Ce,     

Cyclodehydration of 1,4-butanediol to tetrahydro- furan catalyzed by supported silicotungstic acid

Summary Acid strength, acid density and the combination ability between silicotungstic acid and support were investigated when supported silicotungstic acid was used as a catalyst for cyclodehydration of 1,4-butanediol to tetrahydrofuran. The interaction between heteropoly acid and support influenced the catalytic activity. TiO2-supported silicotungstic acid catalyst exhibited higher activity than the other catalysts supported on kaolin, kieselguhr, and activated charcoal.     

Enantioselective ring-opening reaction of meso-epoxides with ArSeH catalyzed by heterometallic Ti-Ga-Salen system

The first example of enantioselective ring-opening reaction of meso-epoxides with aryl selenols to give optically active beta-arylseleno alcohol in up to 97% ee was realized, using a chiral Ti-Ga-Salen heterometallic catalyst. A strong synergistic effect of different Lewis acids in the system was exhibited in the catalytic process.     

Asymmetric ring-opening reaction of oxabicyclic alkenes with aryl boronic acids catalyzed by P-containing palladacycles

The chiral phosphine-containing palladacycle, synthesized easily from H-MOP, showed its high catalytic activity as well as asymmetric induction ability in ring-opening reaction of oxabicyclic alkenes with arylboronic acids, providing corresponding products in high yields and high ee.     

Enantioselective ring-opening reaction of meso-epoxides with ArSH catalyzed by heterobimetallic Ti-Ga-Salen system

The enantioselective ring-opening reaction of meso-epoxides with aryl thiols catalyzed by a chiral heterobimetallic Ti-Ga-Salen complex was realized, and the 1,2-mercapto alcohols were obtained in good yields and moderate to high enantioselectivities (up to 92% ee). A strong synergistic cooperation between different Lewis acids in the system was exhibited in the catalytic process.     

Cyclodehydration of 1,4-butanediol catalyzed by metal(IV) phosphates

Metal(IV) phosphates of tin, zirconium and titanium in different morphological forms, viz. amorphous, calcined and crystalline, have been used as catalysts for selective cyclodehydration of 1,4-butanediol to tetrahydrofuran. A comparative study of the three catalysts for the above reaction has been carried out to understand the effect of their composition and morphology on the catalytic activity.     

纳米钼钒砷杂多酸盐催化苯羟化合成苯酚的研究

过氧化氢作为一种清洁氧化剂,在苯的直接羟化的研究中受到重视。催化剂主要有含钛催化剂系列、含铁催化剂系列和含铜催化剂系列、含钒催化剂系列和其它杂原子催化剂。杂多化合物是一类酸性和氧化性较强的双功能催化剂,但由于受其低比表面积的限制,导致杂多化合物固有的高催化活性在苯的过氧化氢羟化反应中难以充分发挥。本文对所制得的4种过渡金属钼钒砷杂多酸盐纳米催化剂应用于苯的过氧化氢直接羟化合成苯酚的反应,取得了苯酚收率〉50％,选择性〉98％的结果。     

Enantioselective ring-opening reaction of meso-epoxides with ArSH catalyzed by a C2-symmetric chiral bipyridyldiol-titanium complex

This study describes a C₂-symmetric ligand comprising a central bipyridine-pinene-derived core and two functionalized diphenylmethanol subunits. [8′-(Hydroxy-diphenyl-methyl)-10,10,10′,10′-tetramethyl-[5,5′]bi[6-aza-tricyclo[7.1.1.0^2,7]undecyl]-2(7),3,5,2′(7′),3′,5′-hexaen-8-yl]-diphenyl-methanol 1 is an effective catalyst in the asymmetric ring opening (ARO) of meso-epoxides with PhSH and inductions of up to 69% ee. Importantly, there was a correlation between Hammett substituent constants and enantiomeric excesses; the electron-donating substituents at the meta- and para-positions of the substituted stilbene oxides had good enantioselectivity during the epoxide ring opening using PhSH.     

硅烷偶联剂改性SBA-15固载Keggin型杂多酸催化合成柠檬酸三丁酯

以3-(甲基丙烯酰氧)丙基三甲氧基硅烷(MEMO)表面改性的介孔分子筛SBA-15为载体,制备了一系列介孔分子筛/硅烷偶联剂@杂多酸复合催化剂SBA-15/MEMO@HnXW12O40(X=P⁵+,Si⁴⁺,B³⁺;n=3,4,5),并利用FTIR、P-XRD、TEM、N2吸附-脱附对其结构进行表征。以SBA-15/MEMO@HnXW12O40(X=P⁵⁺,Si⁴⁺,B³⁺;n=3,4,5)为负载型杂多酸催化剂对柠檬酸三丁酯的催化合成进行研究,分别考察了酸醇摩尔比、催化剂用量、反应温度、反应时间对催化合成柠檬酸三丁酯酯化率的影响,并获得合成柠檬酸三丁酯的最佳工艺条件。结果表明:当负载型硅钨酸催化剂的负载量为50%、催化剂用量为3.8%、酸醇摩尔比为1∶4、反应温度为140℃、反应时间为6 h、环己烷用量为5 mL时酯化率可达97.56%,重复使用7次后酯化率仍可达62.67%。     

磷的光化学分析新方法研究

在０．２ｍｏｌ／ＬＨ２ＳＯ４－１０％乙醇介质中及紫外光照射条件下磷钼杂多酸光还原为磷钼蓝（λｍａｘ＝７８０ｎｍ）。据此建立了一个测定０．０５～２．０μｇ／ｍＬ磷的光化学分析新方法，并用于试样分析。探讨了光化学反应机理。     

Dithiadiazolium salts as initiators for the cationic ring-opening polymerization of tetrahydrofuran

Mono-, bis- and tris-(1,3,2,4-dithiadiazolium) salts [R-(CNSNS ⁺)_n]_n+[AsF^-₆]_n (R = aryl, n = 1, 2, 3) were found to initiate the cationic ring-opening polymerization of tetrahydrofuran (THF) at room temperature to give clear gels from which the pure polymer was precipitated. 1,3,2,4-Dithiadiazolium cations associated with the hard [AsF₆]^- anion thus constitute a new class of cationic polymerization initiators. The poly(THF) formed by initiation with 1,3,2,4-dithiadiazolium cation was characterized by gel permeation chromatography, infrared spectrophotometry, and ¹³C-NMR spectroscopy. Number-average molecular weights of 198 700 g mol^-1 (polydispersity 1.96) and 190 000 g mol^-1 (polydispersity 1.61) were obtained using [PhCNSNS ] [AsF₆] and [C₆H₃-1,3,5-(CNSNS )₃][AsF₆]₃, respectively, as initiators. The use of multifunctional dithiadiazolium salts as initiators suggests that they may be useful in the preparation of starburst and dendritic polymers. © 1992 John Wiley & Sons, Inc.