PCBs的超(亚)临界水催化氧化及还原裂解

简要分析了多氯联苯(PCBs)的来源及其对环境构成的危害,介绍了PCBs在超（亚）临界水中的反应及其处理效果。分别从超临界水氧化、超临界水裂解及亚临界水还原三个方面阐明了超临界反应过程中PCBs降解的反应路径和降解效率,解释了共溶剂（甲醇、苯）、碱催化剂（Na₂CO₃、NaOH）、氧化剂（NaNO₃、NaNO₂）等对PCBs脱氯和分解的增效作用机理。发现在超临界水氧化与超临界水裂解条件下CH3OH对PCBs降解反应的促进机制有所不同,碱催化剂通过中和反应过程中产生的HCl生成NaCl沉淀导致体系中Cl的含量降低,从而促进脱氯反应的进行。对反应器防腐、处理的经济性方面略作讨论,在总结上述研究工作的基础上提出了PCBs的超临界反应处理技术未来发展的若干研究方向。     

超临界二氧化碳中聚合体系的发展与新型功能高分子材料的制备

因拥有诸多特性,超临界二氧化碳作为聚合反应介质受到了学术界和工业界的广泛关注。近十余年来,超临界二氧化碳中聚合体系的研究有了新的进展,反应介质由单一二氧化碳发展为二氧化碳/水或二氧化碳/有机溶剂复合物,得益于连续搅拌反应装置的出现,聚合方式由间歇式发展为连续式。同时,在超临界二氧化碳中制备得到了多种新型功能高分子材料,例如含氟塑料、含氟弹性体、核壳复合材料、多孔材料以及膜材料,显示出传统溶剂无法比拟的优越性。本文对以上两方面作一介绍和评述。     

钒基催化剂在双氧水存在下对甲、乙苯液相选择氧化的研究

研究了若干钒基催化剂在双氧水存在下对甲、乙苯的液相选择性氧化催化性能.结果表明:在乙腈为溶剂的反应体系中,所研究的钒基催化剂包括VPO,VOPO₄,V₂O₅,VO(acac)₂和NH₄VO₃等均表现出以苯甲醛为甲苯选择性氧化主产物和以苯乙酮为乙苯选择氧化主产物的反应结果;从反应活性和主产物选择性来看,按以下顺序递减:VPO＞V₂O₅＞VOPO₄＞VO(acac)₂＞NH₄VO₃.对于具有(VO)₂P₂O₇晶相的VPO催化剂,在双氧水存在下对甲苯选择性氧化主产物苯甲醛的最高选择性为58.8%,乙苯选择性氧化主产物苯乙酮的最高选择性为67.8%;其催化性能与P/V比、焙烧条件、双氧水的使用量、反应溶剂等有关.从已有的实验结果推测,钒基催化剂在双氧水存在下的甲、乙苯选择氧化反应与V⁵⁺/V⁴⁺的"氧化-还原"作用密切相关.     

铁锑氧化物表面氧的性质及氨的吸附特性

研究了Fe₂O₃和Sb₂O₄及Sb/Fe比由1/9至9/1五种复合氧化物表面氧的TPD行为。Fe₂O₃在200～450℃间有少量氧脱出,Sb₂O₄在700℃以后出现脱氧峰,而Sb/Fe复合氧化物则出现所谓α和β脱氧峰。随Sb/Fe比增加α氧的脱附活化能也增高,Sb/Fe比为3/7、5/5和7/3时分别为33、36、51kcal/mol。Fe-Sb氧化物中α氧比β氧对烯烃氧化具有更高的活性。在50—275℃范围内NH₃在Fe-Sb氧化物上的吸附等温线符合Freundlich式,同时由NH₃的TPD可明显看出Fe-Sb氧化物具有不同强度的吸附中心,它们与所含表面氧有关,但表面氧对NH₃的氧化是很弱的。讨论了烯烃选择氧化反应与表面氧强度之间的联系。     

超临界二氧化碳中羰基钴催化的端基炔烃环三聚反应研究

原子经济性良好的炔烃[2+2+2]环加成反应与绿色溶剂超临界二氧化碳相结合,是一个符合绿色化学原则的环境友好反应过程.建立了一个纯超临界二氧化碳介质中八羰基二钴催化的端基炔烃环三聚反应体系,在优化的反应条件下,以较高产率选择性地制备1,2,4-三取代苯衍生物.优化了催化剂用量、二氧化碳压力、反应温度及时间等反应条件,讨论了反应物料及催化剂在超临界二氧化碳介质中的溶解性和相行为,提出了端基炔烃环三聚反应机理,并将反应底物从C≡C键拓展至C≡N键,对超临界二氧化碳介质中炔-腈环加成反应进行了初步探索.优化出的炔烃环三聚催化反应体系无需使用有机助溶剂和各类助剂,底物适应性好,产物选择性高,为合成1,2,4-三取代苯衍生物提供了一种绿色合成方法.     

超临界二氧化碳介质中钯催化伯胺羰基化反应的研究

以正丁胺为模板 ,比较了超临界二氧化碳介质和常规有机溶剂中钯催化伯胺羰基化反应的规律。研究结果表明 ,在超临界二氧化碳中钯催化伯胺羰基化反应的化学选择性发生了改变 ,而且助溶剂对反应的化学选择性和产率也有较大的影响     

New Polymerization Systems in Supercriticai Carbon Dioxide and Related Functional Polymer Materials

因拥有诸多特性,超临界二氧化碳作为聚合反应介质受到了学术界和工业界的广泛关注。近十余年来,超临界二氧化碳中聚合体系的研究有了新的进展,反应介质由单一二氧化碳发展为二氧化碳／水或二氧化碳／有机溶剂复合物,得益于连续搅拌反应装置的出现,聚合方式由间歇式发展为连续式。同时,在超临界二氧化碳中制备得到了多种新型功能高分子材料,例如含氟塑料、含氟弹性体、核壳复合材料、多孔材料以及膜材料,显示出传统溶剂无法比拟的优越性。本文对以上两方面作一介绍和评述。     

铁系催化剂对丁烯的氧化脱氢催化作用特征

x光衍射分析表明,所制备的五种丁烯氧化脱氢用铁系催化剂样品分别具有α-Fe₂O₃、γ-Fe₂O₃、ZnFe₂O₄、ZnFe₂O₄•20%α-Fe₂O₃和ZnFe₂O₄20%γFe₂O₃物相结构。在五种样品上分别进行了氧和丁烯的吸附及其程序升温脱附,初步结果表明:α-Fe₂O₃、γ-Fe₂O₃和ZnFe₂O₄都是丁烯氧化脱氢反应的活性相,但它们吸附氧和吸附丁烯的能力不同,对丁烯的异构化、氧化脱氢和燃烧反应的作用也有所不同。结合样品作为供氧体的试验结果,对丁烯在混合双相样品上的氧化脱氢过程作了初步讨论。     

超临界二氧化碳中PdCl2-CuCl2体系催化末端炔烃氧化偶联反应

研究了在超临界二氧化碳中实现PdCl₂-CuCl₂体系催化末端炔烃的氧化偶联反应, 研究结果表明: 催化剂、超临界二氧化碳及其共溶剂对反应结果有着重要的影响, 炔烃的取代基会影响末端炔烃在氧化偶联反应中的反应活性.     

超临界二氧化碳中的聚合反应*

本文对超临界二氧化碳(ScCO₂)中进行的聚合反应进行了综述。评述了ScCO₂作为聚合反应介质的优点,以及在ScCO₂中可进行的聚合反应类型,包括均相聚合、沉淀聚合、分散聚合、乳液及反相乳液聚合、阳离子聚合、开环聚合、熔融态缩聚、溶液-凝胶聚合、聚合物混合合成、链催化转移聚合、氧化-偶合反应聚合、氮氧自由基可控活性聚合、原子转移自由基聚合、可逆加成-断裂链转移、电化学聚合、原子转移聚合与酶催化开环聚合两种活性聚合在ScCO₂中同时聚合、二氧化碳作为原料共聚合等。     

超临界二氧化碳体系中PVDF微孔膜的表面接枝改性

超临界二氧化碳（SCCO2）是一种T〉31．1℃,P〉7．38MPa的二氧化碳流体,不仅具有类似于气体的粘度和类似于液体的密度,而且可以通过改变温度或压力控制SCCO2的密度及溶解性．SCCO2对有机小分子具有优良的溶解、扩散和渗透性能,化学惰性,无污染,易于分离,作为一种聚合反应介质,受到学术界日益增多重视．SCCO2极低的粘度使其具有良好的流动性和扩散渗透性能,零表面张力使其对聚合物具有良好的润湿和增塑性,这将促进引发剂和聚合单体向微孔膜的外表面及内表面扩散．利用温度和压力改变SCCO2的溶解性能调整单体在聚合物相和SCCO2相之间的分布,进而控制微孔膜内外表面的接枝程度．所以SCCO2接枝聚合反应对于聚合物膜的表面改性具有极其重要的意义．     

Metal(salen)-catalyzed oxidation of limonene in supercritical CO2

Summary The Mn(Salen)Cl and Ni(Salen)-catalyzed oxidation of limonene has been carried out. The catalytic cycle involved PhIO via a rebound mechanism. In all cases the use of organic solvents resulted in reasonable selectivities of oxidized products. The use of supercritical carbon dioxide (SCCO₂) led at least to comparable results in terms of conversions, but showed different selectivities. In ordinary solvents epoxidation appears to predominate over allylic oxidation. This tendency, in SCCO₂, appears only after 4 h of reaction. Shorter reaction times (2 h) appear to lead to opposite selectivity. These results showed the advantages of using SCCO₂ as solvent in these reactions. SCCO₂ is much more compatible with green technology than are organic solvents.     

超临界二氧化碳中过渡金属催化有机反应研究进展

主要综述了近年来超临界二氧化碳作为反应介质过渡金属催化有机反应的最新进展.通过与常规有机溶剂中有机反应的对比,着重介绍了超临界二氧化碳作为反应介质在有机反应中所显示出的优越性,例如调控反应的选择性,提高反应速度和增加催化剂催化效率等.     

Selective oxidation of alkanes with molecular oxygen and acetaldehyde in compressed (supercritical) carbon dioxide as reaction medium

The oxidation of cycloalkanes or alkylarenes with molecular oxygen and acetaldehyde as sacrificial co-reductant occurs efficiently in compressed (supercritical) carbon dioxide (scCO2) under mild multiphase conditions. No catalyst is required and high-pressure ATR-FTIR online measurements show that a radical reaction pathway is heterogeneously initiated by the stainless steel of the reactor walls. For secondary carbon atoms, high ketone to alcohol ratios are observed (3.5-7.9), most probably due to fast consecutive oxidation of alcoholic intermediates. Since C--C scission reactions are detected only to a very small extent, tertiary carbon atoms are transformed into the corresponding alcohols with high selectivity. Detailed analysis of the product distributions and other mechanistic evidence suggest that acetaldehyde acts not only as the sacrificial oxygen acceptor, but also as an efficient H-atom donor for peroxo and oxo radicals and as a crucial reductant for hydroperoxo intermediates. In comparison to other inert gases such as compressed N2 or Ar, the use of carbon dioxide was shown to increase the yields of alkane oxygenates under identical reaction conditions.     

CO2/离子液体体系热力学性质的分子动力学模拟

超临界CO2和离子液体(ILs)是两种绿色溶剂. 离子液体可以溶解超临界CO2, 而超临界CO2不能溶解离子液体. 由此设计构成的CO2/IL二元系统, 同时具备了超临界CO2和离子液体的许多优点: 既可以降低离子液体的粘度, 还便于相分离, 是新型的耦合绿色溶剂. 其物理化学性质对于设计反应、分离等过程非常重要. 因此, 本文以CO2/IL二元系统为研究对象, 通过选择合适的分子力场和系综, 运用分子动力学(MD)模拟方法研究了CO2/[bmim][PF6]、CO2/[bmim][NO3]等体系的热力学性质. 结果表明, CO2对ILs膨胀度的影响非常小, 当CO2摩尔分数为0.5时, ILs膨胀仅为15%. CO2/ILs的扩散系数远小于CO2膨胀甲醇、乙醇溶液的扩散系数. 随着CO2含量的增加, ILs的扩散系数提高, 粘度显著下降, 表明CO2能有效地改善ILs扩散性, 减小其粘度. 因此CO2可用以改善离子液体溶剂体系的传递特性, 增强反应分离过程在其中的进行.     

Diels–Alder Cycloaddition Reactions in Sustainable Media

Diels–Alder cycloaddition reaction is one of the most powerful strategies for the construction of six-membered carbocyclic and heterocyclic systems, in most cases with high regio- and stereoselectivity. In this review, an insight into the most relevant advances on sustainable Diels–Alder reactions since 2010 is provided. Various environmentally benign solvent systems are discussed, namely bio-based derived solvents (such as glycerol and gluconic acid), polyethylene glycol, deep eutectic solvents, supercritical carbon dioxide, water and water-based aqueous systems. Issues such as method’s scope, efficiency, selectivity and reaction mechanism, as well as sustainability, advantages and limitations of these reaction media, are addressed.     

Some Organic Reactions in Supercritical Carbon Dioxide

Organic reactions in supercritical carbon dioxide (scCO2) have facilitated great progress in recent years . ScCO2, as an environmentally friendly reaction medium, may be a substitute for 1 volatile and toxic organic solvents and show some special advantages. Firstly, CO2 is inexpensive, nonflammable, nontoxic and chemical inert under many conditions. Secondly, scCO2 possesses hybrid properties of both liquid and gas, to the advantage of some reactions involving gaseous reagents. Control o…     

Platinum/Carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells

Carbon nanotube (CNT)-supported Pt nanoparticle catalysts have been synthesized in supercritical carbon dioxide (scCO(2)) using platinum(II) acetylacetonate as metal precursor. The structure of the catalysts has been characterized with transmission electron micrograph (TEM) and X-ray photoelectron spectroscopy (XPS). TEM images show that the platinum particles' size is in the range of 5-10 nm. XPS analysis indicates the presence of zero-valence platinum. The Pt-CNT exhibited high catalytic activity both for methanol oxidation and oxygen reduction reaction. The higher catalytic activity has been attributed to the large surface area of carbon nanotubes and the decrease in the overpotential for methanol oxidation and oxygen reduction reaction. Cyclic voltammetric measurements at different scan rates showed that the oxygen reduction reaction at the Pt-CNT electrode is a diffusion-controlled process. Analysis of the electrode kinetics using Tafel plot suggests that Pt-CNT from scCO(2) provides a strong electrocatalytic activity for oxygen reduction reaction. For the methanol oxidation reaction, a high ratio of forward anodic peak current to reverse anodic peak current was observed at room temperature, which implies good oxidation of methanol to carbon dioxide on the Pt-CNT electrode. This work demonstrates that Pt-CNT nanocomposites synthesized in supercritical carbon dioxide are effective electrocatalysts for low-temperature fuel cells.     

离子液体/超临界二氧化碳两相体系在有机合成中的应用

介绍了近年来在离子液体/超临界二氧化碳两相体系中进行有机合成的最新进展, 包括烯烃氢甲酰化反应、酶催化反应、二氧化碳和环氧化物的环加成反应、烯烃环氧化反应、烯烃不对称二羟化反应、氢化反应、Heck反应、醇氧化反应、烯烃氢乙烯化反应、烯烃二聚反应等.     

Supercritical fluid solvents in organic chemistry

The solubility of complex organic molecules in supercritical solvents is well-established. Under isothermal conditions, slightly above the critical temperature, this phenomenon, as well as most other physical properties of the solvent, exhibits a substantial pressure dependence. This behavior makes supercritical solvents attractive as media for organic reactions, both from a synthetic and a physical organic perspective.

An apparatus has been constructed and techniques have been developed to investigate the effects of supercritical solvent interactions on organic reaction rates and equilibria. The construction and operation of a supercritical reactor is described. Finally the reactor is used to investigate the photoisomerization of trans-stilbene in supercritical carbon dioxide.