添加气对非平衡等离子体转化低碳烷烃的影响

在常压下, 研究了添加气的种类(N₂, He, Ar, H₂, NH₃, CO和CO₂)对介质阻挡放电低碳烷烃(甲烷、 乙烷和丙烷)转化制低碳烯烃的影响. 结果表明, 以甲烷或乙烷为原料时, N₂, He, Ar和CO的引入有利于提高原料的转化率和总烯烃的选择性; 而CO₂, H₂和NH₃的引入对甲烷、 乙烷的转化率无明显影响, 但H₂和NH₃的引入会使总烯烃的选择性显著降低. 以丙烷为原料时, 所研究的添加气均可提高丙烷的转化率, 而只有CO的引入可提高总烯烃选择性. 综上所述, 80%(摩尔分数) CO添加量最有利于低碳烷烃转化成低碳烯烃, 对应的甲烷、 乙烷和丙烷的转化率分别提高了14.4%, 17.6%和42.8%, 总烯烃的选择性分别提高了19.9%, 25.0%和11.9%. 以CH₄为例, 通过对放电电流波形和等离子体区物种的发射光谱(OES)研究发现, 引入CO能显著增加等离子体的电子密度, 并且体系中出现激发态O^*物种(777.5和844.7 nm), 这种O^*物种能够促进C-H键的断裂, 有利于烯烃的生成. 因此, 等离子体区电子密度的增加和激发态O^*物种的出现可能是CH₄-CO体系中CH₄有效转化的主要原因.     

Selective oxidation of alkenes catalysed by ruthenium(II) complexes containing coordinated perchlorate

Ruthenium(II) perchlorate complexes, [Ru(dppm)₃(ClO₄)]ClO₄ 1, [Ru(dppe)₃(ClO₄)]ClO₄ 2, and [Ru(dpae)₃(ClO₄)]ClO₄ 3, catalyse the selective homogeneous oxidation of alkenes with TBHP and H₂O₂ as oxidizing agents. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-ol, 2-cyclohexenone and 1-(tert-butylperoxy)-2-cyclohexene. The homogeneous liquid phase oxidation of cyclohexene with TBHP shows appreciable solvent effect. Styrene on oxidation with TBHP gave benzaldehyde as the major product and styrene oxide as the minor product. Oxidation with H₂O₂ is radical-initiated and gives low conversion to products. TBHP and H₂O₂ are compared for their oxidizing ability and TBHP is more effective than H₂O₂ as an oxidizing agent. Linear and long chain alkenes are not efficiently oxidized. Cyclooctene and trans-stilbene are oxidized to the corresponding epoxides.     

Study of the responses of a gas chromatography—reduction gas detector system to gaseous hydrocarbons under different conditions

The response of a reduction gas detector (RGD) to C₂-C₆ alkenes, C₂-C₆ alkanes, isoprene and benzene has been investigated using gas chromatography (GC) with a packed column. The RGD is considerably more sensitive to alkenes than is the flame ionization detector. The detection limit of this present GC/RGD system for alkenes is about 0.01 ng. It has much greater sensitivity to alkenes than to alkanes. Its sensitivity increases with increasing HgO bed temperature, but its selectivity towards alkenes decreases at the same time. The selectivity of the RGD may not be significant for much heavier molecules. The sensitivity of the RGD is inversely proportional to the carrier gas flow rate through the HgO bed. The baseline of the system increases significantly with increasing oven temperature.     

The mechanism of the addition of haloalkanes to alkenes in the presence of dichlorotris(triphenylphosphine)ruthenium(II), [RuCl2(PPh3)3]

The addition of haloalkanes to alkenes in the presence of [RuCl₂(PPh₃)₃] has been subjected to a detailed kinetic study. The results of this study, together with an examination of reaction intermediates, suggest a mechanism inolving a non-chain sequence in which [RuCl₂(PPh₃)₃] acts as a catalyst, but which involves free radical intermediates.     

Nickel-promoted coupling of orthomanganated aryl ketones with alkenes as a route to indanols

Orthomanganated aryl ketones undergo NiBr₂(PPh₃)₂-promoted reactions with activated alkenes to give indanol products with higher specificity than similar Pd(II)- or Me₃NO-promoted reactions.     

Hydroformylation of alkyl alkenes catalyzed by rhodium supported on MCM-41: The effect of H3PW12O40 on the catalytic activity and recycling

Heteropolyacids impregnated with rhodium(I) or (III) complexes were prepared and used as supported catalysts in the hydroformylation of alkyl alkenes. Two general types of catalysts were prepared and tested: rhodium(I) or (III) in the presence and in the absence of the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (adopted as HPW₁₂) supported on MCM-41 (30 Å). 1-Octene was chosen as a model substrate. Different types of supported catalysts were tested in the hydroformylation of 1-octene and other alkyl alkenes. The effects of the temperature and the type of solvent on the reaction were studied. The results showed that the supported catalysts containing the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (HPW₁₂) along with rhodium(I) or (III) gave higher catalytic activity. In addition, the recycling of the supported catalysts was studied and the results showed again the important effect of the presence of HPW₁₂ on the recycling of the rhodium catalysts.     

Bu3P-CS2加合物与含不饱和键化合物的环化反应

Bu₃P-CS₂加合物与含不饱和键化合物(富电子炔类、磷酰基炔类、磷酸基烯类)以及醛进行一锅反应以较好的收率得到1,3-二硫环戊烯或1,3-二硫环戊烷衍生物.Bu₃P-CS₂加合物与偶氮化合杨和醛类进行类似反应却得到四氢噻二唑硫酮衍生物.对反应机理进行了讨论.     

Polymer chemistry. Part V. γ-Ray induced telomerisation reactions involving 1,1-difluoroethene and hexafluoropropene

Telomerisation reactions have been investigated for the alkenes 1,1-difluoroethene (5) and hexafluoropropene (3) with the telogens CF₂Br₂ (1), CF₃CFBr₂ (8) and CF₃CBr₃ (9), as a means of preparing telomers and co-telomers. The efficiency of chain transfer increases as 18<9. Surprisingly, co-telomerisations of 5 with 3 occurred more efficiently than the corresponding telomerisations with 5 alone. The effects of solvent are described.     

A new route for isoquinolines catalyzed by palladium

3-Bromopyridine-4-carbaldehyde is tethered with suitably electron withdrawing group substituted alkenes via Heck coupling followed by aldol reaction in dioxane at 150 °C under a catalytic system of Pd(OAc)₂/PPh₃/NaOAc to afford the corresponding isoquinolines in good yields.     

Gas chromatographic determination of volatile alkenes with on-column bromination and electron-capture detection

A method is described for the gas chromatographic-electron-capture detection determination of alkenes via on-column bromination reactions. Pyridinium bromide perbromide (PBPB) was used as the Br₂ source, and a cholesterol-glass beads mixture, treated with methanol, was used to remove excess Br₂. The optimum ratio of cholesterol to glass beads was found to be 1:10, at which 93% of the bromine released from PBPB can be removed, without removal of the derivitized analytes. The conversion efficiency of alkene to the brominated derivative is extremely low (less than 2%) for ethene, whereas for propene and 1-butene it is 41 and 79%, respectively. For C₃---C₅ alkenes, this method is 200–300 times more sensitive than analysis of the underivitized analytes by using conventional flame ionization detection.     

Synthesis and H-NMR complexation studies of alkalimetal bithioxanthylidene crown ether complexes

Two synthetic routes to a novel class of sterically overcrowded alkenes, bithioxanthylidene crown ethers 1, are described. The ¹H spin-lattice relaxation times (T₁) of the crown ethers as well as those of the corresponding complexes with Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ in CDCl₃ were measured and the results were interpreted in terms of complexation affinities.     

Ir2S3/ZnIn2S4催化下可见光诱导发生的烯烃/炔烃的高效硫氢化反应:Ir2S3的作用

C–S键的构建在化学中具有非常重要的意义.利用硫醇和烯烃/炔烃的硫氢化反应来构建C?S键是一种绿色、可持续和低成本的方法.本文以ZnCl2,InCl3,硫代乙酰胺为前驱体,在微量IrCl3存在条件下,通过一步溶剂热法制备得到了含有不同Ir摩尔比(0.5 mol％,1 mol％和2 mol％)的Ir2S3/ZnIn2S4...     

Structural, electrical and electron spin resonance properties of CoCl2-filled polyvinylidene fluoride films

Polyvinylidene fluoride (PVDF) films, filled with mass fractions w≤15% of CoCl₂, were prepared. The X-ray diffraction (XRD) scans evidenced semicrystalline structures containing - and/or β-PVDF phases. IR spectra confirmed these findings, and revealed some structural defects such as mono- and di-fluorinated alkenes and head-to-head segments. The optical absorption spectra suggested the presence of: (a) two optical gaps (one of them, Eg₂, depends on W); (b) tetrahedral Co(II) coordination for all of the filling levels (FL); and (c) octahedral Co(II) forms at 15% FL. The electrical resistivity results are discussed on the basis of the modified interpolaron hopping model of Kuivalainen et al., Phys Rev 1985;B31:7900. The temperature and FL dependences of the calculated hopping distance (R_o) are discussed. It is implied that the difluorinated alkenes exert a significant influence on Eg₂ and R_o. The electron spin resonance (ESR) spectra confirmed the optical absorption implications.     

Hydrogenation of non-activated alkenes catalysed by water-soluble ruthenium carbonyl clusters using a biphasic protocol

The use of the water soluble ruthenium clusters Ru₃(CO)_12−x(TPPTN)_x (x=1 1, 2 2 or 3 3) and H₄Ru₄(CO)₁₁(TPPTN) 4 (TPPTN=P{m-C₆H₄SO₃Na)₃) as catalyst precursors in the hydrogenation of non-activated alkenes under biphasic conditions is described. Each cluster displays activity under moderate conditions, ca. 60 atm. H₂ at 60°C, with catalytic turnovers up to ca. 500. The trinuclear clusters undergo transformation during reaction but can be reused repeatedly without loss of activity. Other methodologies such as ionic liquid–organic and the use of silica supports have been attempted with these clusters but they are less effective than the aqueous–organic regime.     

由有机硼烷立体选择合成(Z)、(E)链烯-1-醇乙酸酯类昆虫性信息素

等摩尔的甲硼烷甲硫醚(H₃B·SMe₂)与四溴化碳在60℃下反应20h,定量得到一溴硼烷甲硫醚。从链端烯烃、一卤硼烷甲硫醚和2-[7-辛炔-1-氧基]四氢吡喃及其8-溴代衍生物出发,经硼氢化反应和Zweifel的顺-,反-烯烃合成法,立体选择地合成了鳞翅目昆虫性信息素:(Z)-7-十四烯-1-醇乙酸酯9a、(Z)-7-十六烯-1-醇乙酸酯9b、(E)-7-十四烯-1-醇乙酸酯12及其相应的醇13。产物经GC分析和MS、¹H及¹³C NMR数据证实了它们的纯度和几何构型。     

Bi(OTf)3-catalyzed 5-exo-trig cyclization via halide activation

Lewis acid activation of allyl halides utilizing Bi(OTf)₃ resulted in cationic cyclization of alkenes with high efficiency. While other Lewis acids could catalyze this process with highly substituted alkenes, bismuth salts demonstrated unique reactivity in come cases. This suggested that bismuth triflate possesses interesting halophilic properties.     

Azobridges from azines, XVII. Intra- and intermolecular [3+2] cycloaddition between nonstabilized azomethineimines and alkenes

Azo compounds 1 and 3 containing a CC-double bond in a parallel but distant position are quatemized by Me₃OBF₄ to 1,MeBF₄ and 3,MeBF₄, whereas MeI produces the cage compounds 2,HX and 4,HX. These [3+2] cycloadducts also are quantitatively formed from 1,MeBF₄ and 3,MeBF₄ with catalytic amounts of azo compounds. Intermolecular [3+2] cycloadditions occur with a mixture of DBH (5) or DBO (8), MeI and a variety of alkenes (→ HI) salts of (6, 7, 9 — 12). The intermediate azomethineimines, if stabilized by a fluorenylidene group, can be isolated (20, 22,24), but not, however, in the presence of a close parallel CC-bond (25 → 26).     

Convenient method for the preparation of catecholborane and promotion of the formation of alkenyl catecholborane using BH3 complexes

Catecholborane is prepared in benzene by passing B₂H₆, generated from I₂/NaBH₄, through a suspension of catechol at 25°C. The reagent prepared in this way is used for hydroboration-oxidation of representative alkenes and alkynes at 80°C. Hydroboration of 1-alkynes followed by iodination with I₂/NaOH gives the corresponding trans-1-alkenyl iodides in 70–72% yield. The alkenyl catecholboranes can be prepared at 25°C by performing the reaction in the presence of 10 mole% of H₃B:N(C₂H₅)₂Ph or H₃B:THF. The reaction is believed to go through hydroboration of the alkynes by borane followed by exchange with catecholborane. Studies of the preparation of dialkylphenoxyboranes and alkenyldiphenoxyboranes through hydroboration of 1-decene and 1-decyne by use of H₃B:N(C₂H₅)₂Ph and phenol are also reported.     

过渡金属催化CO2/H2参与的羰基化研究进展

Ever-increasing energy demands due to rapid industrialization and urban population growth have drastically reduced petroleum reserves and increased greenhouse-gas production, and the latter has consequently contributed to climate change and environmental damage. Therefore, it is highly desirable to produce fuels and chemicals from non-petroleum feedstocks and to reduce the atmospheric concentrations of greenhouse gases. One solution has involved using carbon dioxide (CO₂), a main greenhouse gas, as a C1 feedstock for producing industrial fuels and chemicals. However, this requires high energy input from reductants or reactants with relatively high free energy (e.g., H₂ gas) because CO₂ is a highly oxidized, thermodynamically stable form of carbon. H₂ can be generated through water photolysis, making it an ideal reductant for hydrogenating CO₂ to CO. In situ generation of CO such as this has been developed for various carbonylation reactions that produce high value-added chemicals and avoid deriving CO from fossil fuels. This is beneficial because CO is toxic, and when extracted from fossil fuels it requires tedious separation and transportation. This combination of CO₂ and H₂ allows for functional molecules to be synthesized as entries into the chemical industry value chain and would generate a carbon footprint much lower than that of conventional petrochemical pathways. Based on this, CO₂/H₂ carbonylations using homogeneous transition metal-based catalysts have attracted increasing attention. Through this process, alkenes have been converted to alcohols, carboxylic acids, amines, and aldehydes. Heterogeneous catalysis has also provided an innovative approach for the carbonylation of alkenes with CO₂/H₂. Based on these alkene carbonylations, the scope of CO₂/H₂ carbonylations has been expanded to include aryl halides, methanol, and methanol derivatives, which give the corresponding aryl aldehyde, acetic acid, and ethanol products. These carbonylations revealed indirect CO₂-HCOOH-CO pathways and direct CO₂ insertion pathways. The use of this process is ever-increasing and has expanded the scope of CO₂ utilization to produce novel, high value-added or bulk chemicals, and has promoted sustainable chemistry. This review summarizes the recent advances in transition-metal-catalyzed carbonylations with CO₂/H₂ and discusses the perspectives and challenges of further research.     

Variable catalytic behavior of Nb, Mo, Ta, W, and Re halide clusters: Isomerization of alkynes to conjugated dienes under nitrogen and hydrogenation to alkenes under hydrogen

When a tantalum chloride cluster [(Ta₆Cl₁₂)Cl₂(H₂O)₄]·4H₂O (1) was treated in a nitrogen stream at temperatures above 300 °C, a catalytic activity developed for the isomerization of pentynes and hexynes to the corresponding conjugated dienes with smaller amounts of allenes. Niobium and tungsten clusters with the same metal framework also catalyzed the reactions. In a hydrogen stream, niobium, molybdenum, and tungsten clusters, and a trinuclear rhenium cluster catalyzed the partial hydrogenation of alkynes to the corresponding alkenes. The isomerization activity was ascribed to the Brønsted acidity of hydroxo species of the activated cluster complexes, and the hydrogenation activity was attributed to the nature of the metal atoms incorporated in the cluster.