Heck arylation of acrolein acetals using the 9-bromoanthracene: A case of study

The influence of several parameters on the selectivity of the palladium catalysed Heck coupling of 9-bromoanthracene with acrolein acetals was studied. While the ester is the quasi exclusive product when only a base (i.e. NaOAc, K₂CO₃, etc.) is added in the medium, the presence of halide abstracting agent such as thallium or silver salts decreases noticeably the selectivity towards the ester. On the other hand, the addition of n-Bu₄NOAc yields to the formation of the aldehyde with up to 74% selectivity. The presence of water was found to play a significant role not only on the rate but also on the selectivity of the reaction. A comprehensive mechanism is proposed outlining the influence of each additive, particularly on the selectivity of the reaction.     

低温高活性熔铁催化剂上的超临界相费托合成反应

在固定床反应器中超临界相条件下研究了熔铁催化剂上的费托合成反应,发现在超临界介质中反应物和产物更容易扩散,较好地抑制了催化剂表面非活性碳的沉积,从而提高了费托合成反应中的CO转化率和烯烃选择性,增加了链增长因子,降低了甲烷选择性.同时,考察了超临界介质、反应温度、压力、H2/CO比和空速等条件对费托合成反应的影响.结果表明,C5-8正构烷烃在催化剂活性温度下都是适宜的超临界介质.当温度和压力都在介质的临界点以上时,介质表现出较好的传质与传热性能,可改善费托合成反应性能.     

硅胶负载钯: 一种新型有效而可循环的Heck反应的催化剂

本文报道了一种新型硅胶负载钯催化剂在Heck 反应中的应用。在硅胶负载钯催化剂,碳酸钾为碱,DMF为溶剂的反应条件下（无膦和无游离胺的存在）,碘代芳烃、溴代芳烃和活泼的氯代芳烃与烯烃发生偶联反应生成高产率相应的偶联产物。而且硅胶负载的钯催化剂经简单处理,可循环使用6次不降低活性。     

硝基苯在离子液体EMimBF4中的选择性电还原

采用循环伏安法和恒电位电解法研究了离子液体EMimBF4中硝基苯在微铂电极上的选择性电还原特性. 研究结果表明, 硝基苯在铂电极上的电还原反应为双分子八电子三步骤电化学过程: 第一步反应为准可逆单电子转移步骤, 产生阴离子自由基; 第二步为二电子转移步骤, 并伴有随后的双分子不可逆自由基偶合反应和快速质子化及脱水反应, 主要产物为氧化偶氮苯; 第三步是二电子转移产生偶氮苯的过程. 通过控制电位, 可以选择性地合成氧化偶氮苯和偶氮苯; 在EMimBF4中, 硝基苯和水的浓度变化对电化学行为产生较大影响.     

Oxidation of Styrene with Molecular Oxygen in Supercritical CO2

The oxidation of styrene with molecular oxygen catalyzed by PdCl2 CuCl2 has been investigated in supercritical CO2 with a batch reactor. The oxidative system of styrene contains four components at the beginning and seven components during the reaction. The critical temperature, critical pressure, and critical density at different conversions are determined by using a high-pressure view cell. The effect of phase behavior on the conversion and selectivity were studied. Experimental results showed that the critical parameters of the reaction mixture at fixed initial molar ratio changed with the conversion of reactant. The conversion of styrene reached maximum near the critical density of the reaction mixture. Product selectivity also varied with density of reaction mixture and could be tuned to some degree.     

Sodium 2-(2-pyridin-3-ylethylamino)sulfonate: an efficient ligand and base for palladium-catalyzed Heck reaction in aqueous media

The first successful Pd(OAc)₂, N-donor ligand and base mediated Heck coupling reaction of aryl halides and alkenes in water is described. The corresponding Heck products were obtained in good to excellent yields.     

Nickel‐Catalyzed Mizoroki–Heck Reaction of Aryl Sulfonates and Chlorides with Electronically Unbiased Terminal Olefins: High Selectivity for Branched Products

Achieving high selectivity in the Heck reaction of electronically unbiased alkenes has been a longstanding challenge. Using a nickel‐catalyzed cationic Heck reaction, we were able to achieve excellent selectivity for branched products (≥19:1 in all cases) over a wide range of aryl electrophiles and aliphatic olefins. A bidentate ligand with a suitable bite angle and steric profile was key to obtaining high branched/linear selectivity, whereas the appropriate base suppressed alkene isomerization of the product. Although aryl triflates are traditionally used to access the cationic Heck pathway, we have shown that, by using triethylsilyl trifluoromethanesulfonate, we can effect a counterion exchange of the catalytic nickel complex, such that cheaper and more stable aryl chlorides, mesylates, tosylates, and sulfamates can be used to yield the same branched products with high selectivity.     

In situ formation of dispersed palladium nanoparticles in microemulsion: efficient reaction system for ligand-free Heck reaction

The ligand-free Heck reaction catalyzed by Pd(OAc)2 performed well in a TX10 oil-in-water microemulsion. TEM proved in situ formation distributed palladium nanoparticles in the microemulsion. The role of TX10 in the reaction system is the palladium nanoparticles reducing agent and stabilizer. The effect of reaction parameters on the Heck reaction conversion were discussed. The results indicated that the aqueous phase concentration, the base concentration, and the temperature played key roles in the conversion of the reaction. Iodobenzene was converted to the corresponding trans-stilbene quantitatively within 90-150 min. Therefore, the heptane/TX 10/butanol/water/propylene glycol microemulsion containing in situ formed palladium nanoparticles was a very efficient catalyst system for the ligand-free Heck reaction.     

纤维素超临界水预处理与水解研究

利用超临界水解工艺进行生物质废弃物(秸秆)能源转化, 使其主要成分纤维素在超临界水中快速水解为低聚糖, 为其进一步葡萄糖转化和乙醇发酵解决技术瓶颈. 其中纤维素在超临界水中的溶解是预处理与水解过程的限速步骤. 研究表明, 反应温度达到380 ℃及以上时, 纤维素可迅速溶解并进行水解, 液化比例可达100%; 在374～386 ℃范围内反应温度对纤维素的转化率有明显作用, 低聚糖和六碳糖的总产率在临界点附近出现最大值. 超临界条件下, 低聚糖和六碳糖转化率在较短反应时间内出现峰值, 而后随反应时间的延长快速下降, 固液比对于纤维素的低聚糖和六碳糖转化也有显著影响. 最优水解条件研究显示, 在380 ℃, 40 mg纤维素/2.5 mL水条件下反应16 s可获得最大的低聚糖产率, 为29.3%, 在380 ℃, 80 mg纤维素/2.5 mL水条件下反应18 s可获得最大的六碳糖产率, 为39.2%.     

Dilute Methane Treatment by Atmospheric Pressure Dielectric Barrier Discharge: Effects of Water Vapor

Oxidation of dilute methane in oxygen containing mixtures by atmospheric pressure dielectric barrier discharge at moderate temperature (below 150°C) has been studied with regard to the effect of water vapor. First, the impact of water vapor on methane conversion was studied in nitrogen. In dry nitrogen, methane was converted into hydrogen cyanide and hydrogen in the absence of oxidant. When water was added, it both acted as a scavenger in competition with methane for reactive nitrogen species and changed the reaction product speciation from HCN to carbon monoxide and carbon dioxide. The addition of water also led to the formation of hydrogen and nitrogen oxides. In the presence of oxygen, the addition of 1% water vapor enhanced methane conversion. Increasing water vapor content above 1% had a slight positive effect on methane conversion, and was found to enhance selectivity of the reaction products toward carbon dioxide over carbon monoxide.     

Heck reaction catalyzed by PD-modified zeolites.

[Pd]-exchanged NaY zeolites have been prepared, characterized, and applied for the first time for catalytic carbon-carbon coupling reactions. The catalysts exhibit a high activity and selectivity toward the Heck reaction of aryl bromides with olefins for small palladium concentrations (< or =0.1 mol % of Pd). The catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity. No limitation to the diffusion of adducts in the zeolite cages was observed (for linear alkenes). The electronic nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The heterogeneous catalysts quantitatively convert all types of all aryl bromide (complete conversion of bromobenzene within 30 min) and activated aryl chlorides under standard reaction conditions. Product form selectivity is observed in the Heck reaction with cyclic olefins.     

Cu-Mn-Si催化剂在环己醇脱氢和糠醛加氢耦合反应中的研究:沉淀pH值和焙烧温度的影响

采用共沉淀法制备了Cu-Mn-Si催化剂,并将其应用于常压气相环己醇脱氢和糠醛加氢耦合反应中,考察了沉淀pH值和焙烧温度对耦合反应的影响。沉淀pH值对糠醛加氢制2 甲基呋喃反应影响不大,但对环己酮的选择性影响较大。pH值在7.5~10.0制备的催化剂具有优良的反应性能。焙烧温度的提高,导致催化剂的比表面积减小,孔径变大,铜的比表面积下降,还原温度提高。在耦合一体化反应中,环己醇脱氢制备环己酮反应受焙烧温度影响不大,但糠醛转化率和2 甲基呋喃选择性随着焙烧温度的提高而减小。     

超临界和近临界条件下Fischer Tropsch合成研究：溶剂的影响

研究了超临界和近临界条件下费托合成过程中溶剂对反应行为的影响。反应在固定床反应器中进行，催化剂为Co/SiO2，所选择的溶剂有两类：纯溶剂（正戊烷和正己烷）和混和溶剂（由正己烷和少量的C5~10烃组成）。结果表明,正己烷分压对CO转化率影响很小，但是产物中1 烯烃含量随正己烷分压增加而增加，超临界条件下1 烯烃含量明显高于非临界条件下。溶剂的种类对CO转化率、CH4和CO2选择性以及产物炭分布影响不大。这一结果表明为了减少溶剂用量，对含有适量轻组分（C5~10）的正己烷溶剂进行循环使用是可行的。结果同时表明与正己烷相比，混和溶剂（25%正己烷和75%正葵烷）具有较高的1 烯烃选择性。     

n-Butane isomerization in the gas phase and under supercritical conditions

The aromatization of n-butane under supercritical conditions on gallium-, zinc-, and platinum-modified high-silica zeolites with a modulus of 30–70 was first studied, and the experimental data were compared to the results of a study of this process in the gas phase. It was found that the operational efficiency of catalysts for n-butane conversion under supercritical conditions was much higher than that for the gas-phase reaction in terms of activity, productivity, and resistance to poisoning by condensation products. The aromatization of gaseous n-butane at 530°C and 1 atm was characterized by rapid catalyst deactivation. The selectivity for the benzene-toluene-xylene (BTX) fraction was higher than 50%. Under supercritical conditions at 430–560°C and 100–200 atm, the selectivity of formation of aromatic compounds decreased by a factor of 2, whereas the yield of C₁-C₃ cracking products increased by the above factor. On the other hand, it was found that an increase in the productivity of catalysts by a factor of 20–50 with the retention of almost 100% activity for several days of operation is an advantage of the process performed under supercritical conditions. The almost complete conversion of butane under supercritical conditions was found on promoted HZSM-5 zeolite samples. The thermogravimetric analysis of spent samples suggested a higher degree of catalyst carbonization under supercritical conditions, as compared with that in the reaction performed in the gas phase. However, the deposition of 20–30 wt % condensation products on the catalysts had no detectable effect on the high activity of the catalysts in the reaction performed under supercritical conditions.     

CaO对褐煤在超临界水中制取富氢气体的影响

以褐煤在超临界水中制取富氢气体为目的,利用小型高压间歇反应装置,在Ca/C 摩尔比为0～0.60、温度450℃～680℃、压力23MPa～38MPa和停留1min～30min下,考察了小龙潭褐煤的反应特性。研究表明,CaO不仅可以固定气相中的CO2,提高H2的体积分数,而且可以提高碳转化率和气体产率。600℃、28MPa,Ca/C摩尔比为0.42时,气相产物中的CO2趋于完全固定,H2产率比无添加剂时提高2.5倍,H2体积分数为48％,其余为CH4和烃类气体。升高反应温度使CaO的催化作用更为显著, 碳转化率和气体产率（H2、CH4、烃类气体）随着反应温度的升高而逐渐增加,液相收率减少。增大反应压力可以促使煤转化率和气体产率升高,停留时间对反应的影响相对较小。以900℃热解焦为反应原料进行了气化实验,结果表明,在600℃和650℃反应5min后,碳转化率分别为8.6％和12.5％,CaO对气化反应和甲烷化反应起不同程度的催化作用。     

Heck reactions of iodobenzene and methyl acrylate with conventional supported palladium catalysts in the presence of organic and/or inorganic bases without ligands

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.     

Conversion of polymers and biomass to chemical intermediates with supercritical water

Recent results are described on conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent. Reactions of cellulose in supercritical water are rapid (<50 ms) and proceed to 100% conversion with no char formation. They show a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. Further, there is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system. For polyethylene, higher yields of short-chain hydrocarbons, higher alkene/alkane ratios and higher conversions were obtained in supercritical water than those obtained by pyrolysis.     

Low temperature recyclable catalyst for Heck reactions using ultrasound

The Heck reaction of iodobenzene with methyl acrylate in NMP as a solvent has been studied using Pd/C as a catalyst in the presence of ultrasound at room temperature. The ultrasound increased the rate of the reaction. The effect of base, solvent and recyclability of catalyst were studied in the presence of ultrasound and without ultrasound. The reaction only takes place in the presence of ultrasound. The catalyst could be recycled using HCOONa-ultrasound.     

Anti-selective and regioselective aldol addition of ketones with aldehydes using MgI2 as promoter

The first example of a direct aldehyde-ketone coupling using the secondary amine piperidine as base in the presence of MgI₂ to generate high selectivity of anti-aldol products from unmodified ethyl ketones in high yield is reported. The coupling reactions were carried out in a one-pot reaction by mixing four reaction components at room temperature. In the case of unsymmetrical ketones, addition was made to the less hindered α-side.     

Palladium supported on diaminoglyoxime‐functionalized Fe3O4 nanoparticles as a magnetically separable nanocatalyst in Heck coupling reaction

A hybrid material of palladium supported on diaminoglyoxime‐functionalized Fe₃O₄ was used as an effective and recyclable catalyst in Mizoroki–Heck coupling reactions. The catalyst was very effective for the Mizoroki–Heck reaction of aryl halides with styrene and conversion was in most cases excellent. The yields of the products were in the range 75–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without significant leaching and loss its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.