镁铝复合氧化物制备及其 丙酮缩聚制异佛尔酮反应研究

采用共沉淀法制备了一系列不同镁铝比的镁铝复合氧化物催化剂,通过XRD、BET和Py-IR等分析手段对催化剂进行了分析,并在连续流动常压固定床微反装置上研究了镁铝复合氧化物催化剂对丙酮气相缩聚制异佛尔酮反应的催化性能。结果表明,共沉淀法制得的镁铝复合氧化物催化剂具有较高的比表面积、较大的平均孔径和孔容,其中MA35催化剂是性能最好的镁铝复合氧化物催化剂,在反应温度为250 ℃、空速为1 h-1、压力为0.1 MPa的条件下,催化剂对丙酮气相缩聚反应的单程转化率为18.8%,异佛尔酮选择性为46.5%。     

An efficient catalyst system for the carbonylation to esters of α-arylpropionic acids

The polymer-supported bimetallic catalyst system PVP–PdCl₂–CuCl₂/PPh₃ has good conversion and regioselectivity to carbonylation of α-(6′-methoxy-2′-naphthyl)ethanol under mild conditions. The effects of temperature, CO pressure, reaction time and P/Pd ratio have been studied to obtain optimum reaction conditions. The carbonylation of various α-arylethanols and styrene derivatives are also investigated with the same catalyst. X-ray photoelectron spectroscopy (XPS) and transmission electron micrograph (TEM) show that the polymer would protect palladium particles against aggregation and serve as a ligand.     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

Polyaniline-supported acid as an efficient and reusable catalyst for a one-pot synthesis of β-acetamido ketones via a four-component condensation reaction

Polyaniline-supported acid salts such as polyaniline-hydrochloride, polyaniline-sulfate and polyaniline-nitrate were prepared by oxidation of aniline using ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalyst for the preparation of β-acetamido ketones. Polyaniline-sulfate salt was found to be the best catalyst for the preparation of β-acetamido ketones. Present methodology offers several advantages, such as cheaper process, easy synthesis of stable catalyst, simple work-up procedure, and excellent activity with less amount of catalyst and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity.     

Catalytic Asymmetric Hydrogenation of α‐Arylcyclohexanones and Total Synthesis of (−)‐α‐Lycorane

An efficient catalytic asymmetric hydrogenation of racemic α‐arylcyclohexanones with an ethylene ketal group at the 5‐position of the cyclohexane ring via dynamic kinetic resolution has been developed, giving chiral α‐arylcyclohexanols with two contiguous stereocenters with up to 99% ee and >99:1 cis/trans‐selectivity. Using this highly efficient asymmetric hydrogenation reaction as a key step, (−)‐α‐lycorane was synthesized in 19.6% overall yield over 13 steps from commercially available starting material.     

Calculation of the energy profile for the fluorination of dichloromethane over an α-alumina catalyst

We present a periodic density functional theory study of the energetic profile of the fluorination of dichloromethane over the {0 0 0 1} surface of α-alumina. This is a model system for the industrially important fluorination process used in synthesis of fluorohydrocarbon replacements of the environmentally detrimental chlorofluorcarbons. The results indicate that HF is readily, and strongly, chemisorbed to the alumina surface producing a surface fluorine ion and a hydroxyl group. Using this model of the fluorinated surface we calculate the adsorption energy of dichloromethane and estimate the barrier to its reaction to CH₂ClF through an S_N2 scheme with the surface fluorine acting as a nucleophile. From the energy profile generated we propose a kinetic scheme and estimate the expected experimentally observed barrier for the overall process. To test the calculation results we have also carried out experimental studies of dichloromethane fluorination over α-alumina and show that the calculated and measured activation energies are in good agreement.     

Preparation of novel MgCl2‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization

In this article, preparation of novel MgCl₂‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization is reported. The factors affecting the particle size (PS) and particle size distribution (PSD) of the prepared support were investigated. In this method, the internal donor added while preparing MgCl₂‐adduct support was supposed to act as a crosslinking agent. Therefore it provided a reasonable way to enhance the morphology and control the PS of the resultant polymer particles. The possible mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 945–948, 2006     

Synthesis of acrylamide end‐functionalised poly(1‐hexene) using an α‐diimine nickel catalyst

The nickel precursor [bis(N,N′‐dimesitylimino)acenaphthene]dibromonickel and methylaluminoxane were used to catalyse the functionalisation of 1‐hexene with acrylamide by passivation of acrylamide with tri‐isobutylaluminium. The polymer obtained was characterised by GPC/SEC and NMR. The NMR experiments performed, COSY, DEPT, long‐range selective INEPT, HSQC and TOCSY 1D, showed that a 2,1 insertion of a single molecule of acrylamide per macromolecule had occurred at the end of the polyhexene chain. Copyright © 2004 Society of Chemical Industry     

Ring-opening homo- and copolymerization of lactones. Part 1. Homo- and copolymerization of racemic β-butyrolactone with ε-caprolactone and δ-valerolactone by tetraisobutyldialuminoxane (TIBAO) catalyst

Copolymers of racemic β-butyrolactone (β-BL) with ε-caprolactone (ε-CL) (P(BL-co-CL)) and δ-valerolactone (δ-VL) (P(BL-co-VL)) were prepared by ring-opening polymerization reactions using the commercial aluminoxane catalyst tetraisobutyldialuminoxane (TIBAO). The yields, molecular weights, compositions and crystallinities were determined for both copolymers by gel permeation chromatography (GPC), nuclear magnetic resonance (¹H NMR) spectroscopy and differential scanning calorimetry (DSC). A detailed study by ¹³C NMR spectroscopy has been made to determine monomer diad sequence distributions. These results and those of reactivity ratios indicate that the co-polymers may consist of compatible blocks of BL units and VL units of variable size. © 1998 SCI.     

Gold(I)‐Catalysed Cyclisation of Alkynoic Acids: Towards an Efficient and Eco‐Friendly Synthesis of γ‐, δ‐ and ϵ‐Lactones

The improved synthesis of γ‐, δ‐ and ϵ‐lactones using a dinuclear N‐heterocyclic carbene (NHC)‐gold(I) catalyst is reported. This solvent‐free process provides access to γ‐ and δ‐lactones in high regio‐ and stereoselectivity. Reactions were performed at low catalyst loadings and without the need for any additives. The use of a digold pre‐catalyst provides a new synthetic route to functionalised ϵ‐lactones, poorly accessible using previous methodologies.

     

An Efficient and Simple Procedure for the Preparation of α‐Keto‐β‐lactams

The methods for the preparation of α‐keto‐β‐lactams described in the literature are generally specific for a particular target molecule and lack generality. A short route to several of these compounds has been developed and is described in this communication. The protocol based on an efficient cyclization procedure followed by hydrolysis and oxidation allows preparation of α‐keto‐β‐lactams 5a—g with sensitive substituents.     

Synthesis of polar vinyl monomer–olefin copolymers by α‐diimine nickel catalyst

Vinyl acetate, methyl methacrylate, acrylonitrile and methyl vinyl ketone were investigated for co‐ and terpolymerization with ethylene and ethylene–propylene. Precursor [bis(N,N ′‐dimesitylimino)acenaphthene]dibromonickel, activated by methylaluminoxane was used as a catalyst system and trialkylaluminium was employed to block the polar groups for these polymerizations. Polymerization activities of the order of magnitude of 10⁶ in the case of vinyl acetate and methyl methacrylate, and 10⁵ in the case of acrylonitrile were achieved. Microanalysis and GPC of acrylonitrile copolymers found about 17 units of acrylonitrile per polymer chain. Copolymers with very different properties from the parent homopolymers were obtained in all cases except that of methyl vinyl ketone. © 2001 Society of Chemical Industry     

Highly Regio‐ and Diastereoselective Addition of Organolithium Reagents to Chiral Fluoroalkyl α,β‐Unsaturated N‐tert‐Butanesulfinyl Ketimines: A General and Efficient Access to α‐Tertiary Fluoroalkyl Allylic Amines and α‐Fluoroalkyl α‐Amino Acids

Highly regio‐ and diastereoselective 1,2‐addition of organolithium reagents to chiral fluoroalkyl α,β‐unsaturated N‐tert‐butanesulfinyl ketimines was developed, providing a general and efficient method for the asymmetric synthesis of structurally diverse α‐tertiary fluoroalkyl allylic amines in high yields and with excellent diastereoselectivities (dr up to>99:1). The synthetic application of the method was demonstrated by the rapid and convenient preparation of challenging α‐fluoroalkyl α‐amino acids with α‐tetrasubstituted carbon.

     

Efficient Synthesis of β,γ‐Alkynyl α‐Amino Acid Derivatives by Ag(I)‐Catalyzed Alkynylation of α‐Imino Esters

The first catalytic synthesis of β,γ‐alkynyl α‐amino acid derivatives was achieved by direct addition of terminal alkynes to α‐imino esters in the presence of an Ag(I) salt under mild reaction conditions.     

Zheda‐Phos for General α‐Monoarylation of Acetone with Aryl Chlorides

A new, readily available, and air‐stable monophosphine ligand, i.e., Zheda‐Phos , has been developed for the general and highly effective palladium‐catalyzed monoarylation of acetone with aryl chlorides. The reaction rate is of first‐order dependence with the aryl chloride.     

Efficient Photochemical Synthesis of Peptide‐α‐Phenylthioesters

Low yields and substantial epimerization of peptide‐α‐thioesters often compromise the overall efficiency of native chemical ligation (NCL). Peptide arylthioesters are more reactive than peptide alkylthioesters in NCL, but are also more difficult to handle due to their propensity to hydrolyze, and are therefore often generated in situ. However, pre‐prepared peptide arylthioesters are required for some NCL applications. Here we present a 7‐nitroindoline‐based photochemical method that generates protected peptide phenylthioesters under neutral reaction conditions via their activated esters from photoreactive peptide precursors in high isolated yields, and with low levels of epimerization. This method is fully compatible with Fmoc‐strategy solid‐phase peptide synthesis. Global deprotection with trifluoroacetic acid furnishes peptide phenylthioesters for NCL. Photoreactive peptide precursors can also be converted into their hydrazides in two steps by this method.     

Hydrogenation of (—)-α-pinene over nickel—phosphorus/aluminum oxide catalysts prepared by electroless deposition

Liquid-phase hydrogenation of (—)-α-pinene was investigated using a new type of amorphous nickel-phosphorus catalyst supported on aluminum oxide. The catalyst was prepared by the electroless deposition of nickel on the solid support at atmospheric pressure and moderate temperature from an aqueous solution. Two types of supports, aluminum oxide powder and pellet, were used. Electron probe micro-analysis (EPMA) indicated that the nickel profile on the aluminum oxide powder was uniform throughout the whole particle of the powdery support; however, the nickel deposition on the catalyst supported by pellet aluminum oxide exhibited an eggshell-type profile with a thickness about 8 μm. The amorphous structure of the nickel was confirmed by X-ray diffraction (XRD). The procedure by which the catalysts were prepared involved four steps: etching, sensitization, activation and deposition. The conditions employed for the sensitization, activation and deposition steps significantly affected the composition, structure, metal profile and activities of the catalysts. Etching, however, had a negligible effect on the properties of the catalysts. Very high selectivity was found for hydrogenation of (—)-α-pinene to cis-pinane.     

Pd-Ag/α-Al2O3催化剂在乙烷裂解配套制乙烯工艺中的选择加氢性能研究

在乙烷裂解配套制乙烯选择加氢的工艺条件下,考察载体焙烧温度、助剂Ag含量、溶液pH值、CO含量及空速对等体积浸渍法制备的Pd-Ag/α-Al₂O₃催化剂性能的影响。结果表明,载体焙烧温度的增加,有助于提高催化剂活性;催化剂Ag含量增加,反应温度变化不大,选择性及抗结焦性能增加;不同溶液pH制备催化剂,选择加氢性能差异不大,但溶液的酸性过高会降低催化剂的抗结焦性能;随着CO的升高,乙炔转化率降低,乙烯选择性先增高后降低,为保证催化剂选择性,原料中的CO最好保持在(700~1 600) μL·L^-1;随着空速的升高,乙炔转化率降低,乙烯选择性增加。