Synthesis and Catalytic Asymmetric Reaction of Chiral Pyridine Prolinol Derivatives

The enantioselective reduction of prochiral ketones with borane in the presence of a chiral ligand leading to enantiomerically pure secondary alcohols has received considerable attention in recent years. [1] Enantiomerically pure secondary alcohols are important intermediates for the synthesis of various other organic compounds such as halides, esters, ethers, ketones and amines. To the best of our knowledge, the use of pyridine prolinol derivatives in the reduction of ketones has not been reported so far. Thus, it should be of interest to investigate the catalytic a bility of such ligands. We have an ongoing project in the synthesis and application of chiral pyridine derivatives in chiral molecular recognition[2] and we want to evaluate the effect resulting from the introduction of a pyridinyl moiety onto the catalysts. We expect that the cooperation of pyridine unit and chiral prolinol unit in new ligands may result in unique properties for catalytic reaction.     

New synthesis routes to 2-halopyridines. I. 2-chloropyridine

In contrast to the wide variety of products previously reported from the non-photolytic liquid or vapor phase chlorination of pyridine (I), it has been demonstrated that the corresponding photochemical chlorination of I in carbon tetrachloride under reflux conditions gave 2-chloropyridine (IV) in 62–78 percent yield.     

TiO2‐nanoparticles as efficient catalysts for the synthesis of pyridine dicarbonitriles

The catalytic effects of two forms of nano‐TiO₂, which are prepared via an ordinary or a magnetized process, are investigated in the synthesis of pyridine dicarbonitriles by one‐pot multicomponent reaction of 4‐methyl thiophenol, malononitrile, and aryl aldehydes. The results have shown that both prepared nano‐TiO₂ exhibited high catalytic activities toward the synthesis of pyridine dicarbonitrile derivatives but the nano‐TiO₂, which is prepared via a magnetized process, has shown better catalytic activity. Furthermore, this new catalytic method for the synthesis of pyridine dicarbonitriles provides rapid access to the desired compounds in high yields and so a simple work‐up procedure in the presence of water at room temperature. Therefore, this method represents a significant improvement incompatible of the other methods that are available for the synthesis of pyridine dicarbonitriles.     

晶化时间对ZSM-5分子筛物化性质及催化性能的影响

 考察了ZSM－5分子筛在晶化过程中的变化规律及其在苯与乙烯气相烷基化制乙苯反应中的催化性能．结果表明,当晶化时间为70h时,分子筛晶体开始出现;晶化90h时无定形物相基本消失．晶化时间从90h再延长至150h,ZSM－5分子筛晶粒的大小、形貌和体相硅铝比都基本不变,但分子筛表面的硅铝比逐渐降低．以晶化时间为90h的ZSM－5分子筛原粉为活性组元制备的催化剂,对苯与乙烯气相烷基化制乙苯反应表现出最佳的催化性能．     

氧化铝负载催化剂作用下以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚(英文)

苯甲醚作为重要的化学品和医药中间体而广泛应用于香料、调味剂及有机合成.液相法是传统的苯甲醚制备工艺,例如在碱性环境下,通过酚钠与硫酸二甲酯反应,溴苯与甲醇反应,酚钠与氯代甲烷反应均可制得苯甲醚.然而,这些方法具有环境处理负担较重和所用原料毒性较强等不足而备受限制.因此,环境友好的绿色苯甲醚合成工艺的开发成为必然,苯酚的气相烷基化工艺由此提出.其中,以碳酸二甲酯(DMC)为烷基化试剂的苯酚气相转化苯甲醚制备方法最受关注.DMC是常用的绿色高效烷基化试剂,但其价格相对较高,在一定程度上增加了苯甲醚制备工艺的复杂性和产品成本.鉴于DMC可由甲醇经氧化羰基化制得,因此以甲醇为烷基化试剂的苯酚气相烷基化转化制备苯甲醚方法成为另一研究热点.然而,与DMC的烷基化性能相比,以甲醇为烷基化试剂的反应产物分布较为复杂,作为苯酚O-烷基化(在苯酚的羟基氧原子上发生的烷基化)产物的苯甲醚相对较难获得,而苯酚的C-烷基化(在苯酚的芳环上发生的烷基化)产物甲基酚产率更易提高.总体而言,与DMC烷基化方法相比,以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚方法有待改善,相关反应机理也更欠明晰,因此具有重要的研究价值.本文研究了γ-Al_2O_3(AA)负载型催化剂上以甲醇为烷基化试剂的苯酚气相转化制备苯甲醚方法,考察了反应温度、气体空速、苯酚与甲醇配比以及催化剂中K负载量和焙烧温度等对反应性能的影响,并分析了该体系中的反应机理.研究表明,在AA上负载的8种化合物(NaCl,MgCl_2,Fe_2(SO_4)_3,Co(NO_3)_2,ZnCl_2,La(NO_3)_3,Ce(NO_3)_3和KH_2PO_4)的催化剂中,KH_2PO_4/AA的催化性能最佳,相应催化剂中K离子负载量为7.53 wt%,于700 oC焙烧8 h.苯酚与甲醇气相反应过程中,苯甲醚最大收率出现在400–450 oC,且随甲醇与苯酚的摩尔比升高而增加,但随空速的提高而降低.另外,在KH_2PO_4/AA催化剂的高K含量,以及低温、高空速、低甲醇含量的物料配比的条件下,对苯酚的O-烷基化过程有利.产物除主产物苯甲醚以外,还有少量甲基苯酚、甲基苯甲醚以及二甲基苯酚等副产物.在K含量为7.53 wt%的KH_2PO_4/AA催化剂作用下,苯甲醚收率最高时反应条件为400–450 oC,空速小于0.18 h儃1,甲醇与苯酚摩尔配比为5.本文所开发的催化剂制备方法简单,反应条件温和,产物收率较高,因此具有较好的应用前景.X射线衍射结果显示,经高温焙烧及固相反应后,KH_2PO_4/AA催化剂中产生了K_3Al_2(PO_4)_3新物相.推测该反应机理是酸性氧化铝促进甲醇脱羟基负离子以及K离子促进酚羟基脱氢质子,所形成的甲基正离子进一步与苯氧基负离子结合得到苯甲醚的"钾离子-酸"双功能催化作用过程     

Process optimization of vapor phase pyridine synthesis using response surface methodology

The vapor phase pyridine synthesis from acetaldehyde, formaldehyde and ammonia over HZSM-5 catalyst was studied. The process parameters like temperature, aldehyde ratio, and Si/Al ratio in HZSM-5 was investigated and the process conditions were optimized using surface response methodology (RSM) based on Box-Behnken design. The influence of process parameters investigated using analysis of variance (ANOVA), to identify the significant parameters. The optimum conditions for high yield of pyridine were identified to be a reaction temperature 400°C, aldehyde ratio 1: 1 and Si/Al ratio 106.7. A maximum of 55% yield of pyridine formed under the optimum experimental conditions. The proposed model equation using RSM has shown good agreement with the experimental data, with a correlation coefficient R ² = 0.99.     

4-Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]

The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 10⁴ times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs.     

The photochemistry of 3,4,5-trideuteriopyridine

Irradiation of 3,4,5-trideuteriopyridine at 254 nm in the vapor phase results in the formation of a mixture of 2,3,4-trideuteriopyridine and 2,3,6-trideuteriopyridine. The formation of these products is consistent with a photoisomerization mechanism involving equilibrating azaprefulvene intermediates. This is the first direct evidence that pyridine vapor undergoes photoisomerization resulting in transposition of the pyridine ring atoms.     

Preparation of Carbon Nanotubes by the Catalysis of Polymer Metal Complex on Porous Al203 Matrix

At present, synthesis of carbon nanotubes (CNTs) is normally conducted on a vapor-to-solid interface at ca. 500-3500℃ via various vapor phase methods, such as are discharge, laser ablation, catalytic pyrolysis and chemical vapor deposition, etc.1-2 Recently, channel materials (such as channels of alumina and of AlPO4-5 zeolite) 3 have been utilized as solid-state templates to grow CNTs inside the channel. Here we described a novel method to prepare the carbon nanotubes based on the decomposition of C2H2 gas on the Co-Ni catalyst anchored by polymer complex on the porous A12O3 matrix. The degree of graphitization of synthesized CNTs and catalysts are of great interest.     

Bis(oxazoline) Lewis acid catalyzed aldol reactions of pyridine N-oxide aldehydes--synthesis of optically active 2-(1-hydroxyalkyl)pyridine derivatives: development, scope, and total synthesis of an indolizine alkaloid

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.     

Sinter‐Resistant Platinum Catalyst Supported by Metal–Organic Framework

Single atoms and few‐atom clusters of platinum are uniformly installed on the zirconia nodes of a metal‐organic framework (MOF) NU‐1000 via targeted vapor‐phase synthesis. The catalytic Pt clusters, site‐isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few‐atom clusters that depend upon synthesis conditions. Operando X‐ray absorption spectroscopy and X‐ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size‐selected clusters, including noble metals, on a high surface area support.     

Synthesis of pyridine bases: general methods and recent advances in gas phase synthesis over ZSM-5 zeolite

Pyridine bases are widely used in pharmaceuticals, insecticides, and herbicides due to their high bioactivity. In this paper, in addition to the conventional synthesis methods for pyridine bases, recent advances in the gas phase synthesis of pyridine bases over the shape selective catalysts (ZSM-5) are described.     

Pyridine and related ligands in transition metal homogeneous catalysis

This review provides a broad overview of the literature related to the importance of pyridine and related ligands in homogeneous catalysis. In particular, it describes the various ways by which this ligand can stabilised the metal within a complex for homogeneous catalysis. We surveyed the important transition metal homogenous catalysts containing pyridine and related ligand acting as backbone for other ligands in homogeneous catalytic reactions explicitly from 2011 up to early 2014 and summarized their comparative catalytic activities.     

手性双噁唑啉配体的合成进展

总结了近年来用于不对称催化的各种双噁唑啉配体的合成方法,包括丙二酸酯类、酒石酸类、吡啶类、联苯、联萘及二茂铁类等多种双噁唑啉配体的合成.另外,还讨论了苯甲醚类、二联苯噁二唑类、联苯胺类与氮杂类等新型双噁唑啉配体的合成.     

One-pot three-component reaction for the synthesis of pyran annulated heterocyclic compounds using DMAP as a catalyst

The one-pot three-component reaction for the synthesis of pyran annulated heterocycles is reported by condensing aromatic aldehydes, ethyl cyanoacetate, or malononitrile and C-H activated acidic compounds in the presence of catalytic amount of 4-(dimethylamino)pyridine (DMAP) in ethanol under reflux conditions. The significant features of the present protocol are simple, environmentally benign, high yields, non-aqueous work-up procedure, no chromatographic separation and recyclability of the catalyst.     

绘画资料中所见的宋代建筑避风与遮阳装修*

甲硫醇(CH_3SH)是医药、农药、饲料和合成材料等领域的重要有机合成中间体,以硫化氢合成气(CO/H_2/H_2S)一步催化合成CH_3SH具有广泛的应用前景.目前,钾改性的二硫化钼材料是一步法合成CH_3SH最高效和广泛的催化剂,但是对催化剂活性相以及K和MoS_2之间物理化学行为认知的不足严重限制了其催化性能.我们主要综述了钾钼基催化剂上3类活性相(MoS_2相、 K-MoS_2相和K_xMoS_2相)在一步法合成CH_3SH过程的研究现状,简要介绍了可控合成3类活性相的关键因素,重点关注了K对MoS_2相的调控作用及其对合成CH_3SH反应机理的影响,并对钾钼基催化剂一步法合成CH_3SH的未来发展进行了展望.     

硅烷化对Ti/HMS分子筛催化性能的影响

分别用水热法和气相沉积法制备了Ti/HMS分子筛,采用三甲基氯硅烷(TMCS)和六甲基二硅氮烷(HMDSZ)对Ti/HMS样品进行了气相硅烷化,并用X射线衍射、N2吸附、红外光谱、29Si核磁共振和紫外-可见光谱对样品进行了表征.丙烯环氧化反应的测定结果表明,硅烷化可显著提高环氧化催化活性.水热法制备的Ti/HMS经HMDSZ硅烷化后的催化活性比经TMCS硅烷化后的稍高;气相沉积法制备的Ti/HMS经HMDSZ硅烷化后的催化活性远高于经TMCS硅烷化后的催化活性.这是由于TMCS不但能与分子筛表面的硅羟基反应,而且能破坏分子筛骨架中的Si-O-Ti甚至Si-O-Si键,形成新的羟基,导致样品的亲水性较强,同时还能对气相沉积法制备的Ti/HMS中的四配位骨架钛产生破坏作用.     

Vapor phase synthesis of tungsten nanowires

A concept is presented for synthesizing metal nanowires directly from the vapor phase using chemical vapor transport to temperatures higher than the corresponding metal oxide decomposition temperature. Specifically, this concept is demonstrated with the synthesis of tungsten metal nanowires with sizes ranging from 70 to 40 nm by increasing the condensation temperature. The simultaneous condensation and decomposition of the tungsten oxide species during nucleation and growth is suggested for 1-D growth of metallic tungsten nanowires. This synthesis concept could potentially be extended to the vapor phase synthesis of metal nanowires of several other nonvolatile and refractory metals. The tungsten nanowires could find potential applications in gas sensors and as electron sources in electron microscopes.     

Theoretical investigation of formation mechanism of bipyridyl molecule on Ni(111) surface: implication for synthesis of N-doped graphene from pyridine

The formation mechanism of bipyridyl molecule catalyzed by nickel catalyst with pyridine precursor has been studied using density functional theory calculations. The formation of bipyridyl on Ni(111) surface from two pyridine molecules is considered as the initial process of N-doped graphene growth, and the minimum energy pathway for the formation has been investigated in detail. The whole formation processes mainly includes three steps, i.e., the dehydrogenation of the first pyridine, adsorption and dehydrogenation of the second pyridine, and formation of the bipyridyl molecule. It is found that the C-H bond of pyridine could be selectively dissociated while the C-C and C-N bond connections are retained during the catalytic processes. The N-doped graphene formed by pyridine only contains pyridine-like nitrogen atoms, suggesting a possible way to produce N-doped graphene with pure pyridine-like nitrogen atoms. The comparison of formation mechanisms between bipyridyl and biphenyl molecules was carried out, and the results imply a lower temperature process for synthesis of N-doped graphene from pyridine than that for graphene from benzene.     

La和KF改性Y型分子筛催化丙烯醛二乙缩醛/氨合成吡啶和3-甲基吡啶

在连续流动固定床反应中,以丙烯醛二乙缩醛、水和氨为原料,合成了吡啶和3-甲基吡啶。 比较了La-和KF-改性Y型分子筛的活性大小,考察了La负载量和改性方式、KF负载量及KF/Y的焙烧温度的影响。 研究结果表明,与纯Y型分子筛相比,La和KF改性Y型分子筛均能增强催化活性。 采用浸渍法和La负载量为1%(质量分数)时,吡啶和3-甲基吡啶总收率达到最高值;与浸渍法相比,采用离子交换法制备La-Y的活性更好。 采用浸渍法、KF负载量为1%(质量分数)和KF/Y的焙烧温度为700 ℃时,吡啶和3-甲基吡啶总收率达到最大值。