Toluene disproportionation and coking on zeolites Y modified with Lewis-connected InO acid sites

The effect of introduction of Lewis acid sites on the reactions of toluene transformation and catalysts coking has been studied over parent (Si/Al = 2.5) and dealuminated (Si/Al = 3.7) Y zeolites modified with Lewis connected InO⁺ cationic acid sites. The catalysts with prevalent amount of Brönsted acid sites (less than 40% of protons exchanged by InO⁺) possess the typical for the proton directed reaction of methyl transfer upon toluene disproportionation long period of activation, the longer the higher the concentration of bridging protons. In contrast, at predominant Lewis sites concentration, the activation period disappear, an enhanced initial activity is observed, followed by deactivation on the expense of a rapid process of accumulation of strongly held reaction products and intermediates. Their further condensation leads to catalysts aging, the faster the higher the concentration of electron acceptor Lewis acid sites. A relation has been found between the initially accelerated processes of alkyl transfer and the reinforced formation of carbonaceous deposits over the In-modified catalysts.     

Reaction of dodecanol-1 with H2S on acid catalysts

The reaction of dodecanol-1 with H₂S has been studied at 275°C and 0.1 MPa on acid catalysts. Catalysts having only strong proton sites accelerate alcohol dehydration, whereas catalysts with Lewis acid sites support dodecanethiol-1 formation as well. The catalytic activity per one Lewis acid site rises with the increase of the site strength.     

金/钯双金属纳米颗粒协同催化酰胺和醇间氢自转移反应中路易斯酸驱动反应路径

金属纳米颗粒,特别是金和它的双金属纳米颗粒作为强大的绿色催化剂广泛用于有机合成反应中。在一个反应体系中使用2个不同催化剂(如协同催化),在均相催化中是一个很好的策略。然而,这种方法仍在发展中。最近我们发现,金/钯双金属纳米颗粒与路易斯酸的协同催化体系可用于伯胺的N-烷基化：即酰胺与醇之间的氢自转移反应。我们详细报道了路易斯酸对该氢自转移反应的影响。结果表明,所选的路易斯酸不仅影响生成目标产物的反应路径,而且影响生成多个中间体和副产物的反应路径。弱的路易斯酸,如三氟甲磺酸碱土金属盐,非常适合酰胺的N-烷基化反应。     

全氟辛基磺酰亚胺稀土(Ⅲ)催化氟两相Friedel-Crafts烷基化反应

制备了全氟辛基磺酰亚胺盐(M[N(SO2C8F17)2]n,n:3,4),并用于催化氟两相烷基化反应。考察了催化剂种类、反应时间、反应温度和催化剂用量对烷基化反应的影响,同时探讨了Yb[N(SO2C8F17)2]3对烷基化试剂摩尔比为0.2%时,催化烷基化试剂与不同芳烃的反应,表明Yb[N(SO2C8F17)2]3是一种有效的烷基化催化剂。含有催化剂的氟相通过简单的相分离后,可回收利用。氟相重复使用5次,其催化活性降低不大。     

Friedländer反应中催化体系的研究进展

综述了近几年来国内外Friedländer反应中催化体系的研究进展, 其中涉及质子酸碱/Lewis酸碱催化、有机金属催化以及离子液体催化等, 并讨论了部分反应机理.     

A new carbon—phosphorous bond forming reaction and synthesis of aminoalkylphosphonic acid derivatives

A new carbon—phosphorous bond forming reaction, that is, the reaction of α-methoxyurethanes with trialkyl phosphites in the presence of Lewis acid catalysts was studied on twelve examples.     

Development of bifunctional salen catalysts: rapid,chemoselective alkylations of alpha-ketoesters

Lewis acid-Lewis base salen complexes have been identified as highly efficient catalysts for the addition of dialkylzincs to alpha-ketoesters. In contrast to aldehydes or ketones, the reaction between diethylzinc and alpha-ketoesters is significant in the absence of catalyst. In the presence of catalyst, the reaction rate is increased over 100-fold relative to the background. Furthermore, the reduction product, which is a major coproduct with other catalysts, is not observed with these bifunctional salens. As a result, high yields of the addition products can be obtained (57-99%). Both the Lewis acid and Lewis base portions of the catalyst are critical to the reactivity and selectivity. The two separate portions of the catalyst have been shown to function in a cooperative manner.     

Enantioselective Diels-Alder reactions of 3-(acyloxy)acrylates

Diels-Alder reactions with 3-(acyloxy)acrylates using chiral Lewis acid catalysts have been successfully carried out. These reactions proceed with high enantioselectivity when a chiral Lewis acid derived from Cu(OTf)₂ and a bisoxazoline is used. The facility of the reaction is dependent on the nature of the acyloxy group in the dienophile.     

Lewis碱协助的 Lewis酸催化醇脱水合成烯烃及二氢吡喃开环合成2-肉桂基取代1,3-二羰基化合物

醇脱水是合成烯烃的重要方法之一。全球每年约有15%的苯乙烯是通过1-苯乙醇在酸性条件下脱水反应生产。虽然人们对该反应进行了较为深入的研究,但是当使用活性较高的1-苯乙醇衍生物为底物时,由于得到的取代苯乙烯产物具有较高的反应性,在脱水过程中会发生聚合而导致反应选择性降低,因此有必要探索适宜在高活性1-苯基乙醇脱水反应中应用的催化剂体系。
　　本文借助酸碱协同催化方法考察了1-(4-甲氧基苯基)乙醇制备4-甲氧基苯乙烯的反应。发现三苯基磷与 AlCl3构建的 Lewis碱/Lewis酸协同催化体系在硝基甲烷中可以接近定量的收率得到4-甲氧基苯乙烯。 Lewis碱/Lewis酸协同催化体系有效避免了4-甲氧基苯乙烯的二聚现象。底物拓展研究显示该方法具有很好的底物普适性,对多种取代苯乙烯的收率均超过80%。机理研究表明,1-(4-甲氧基苯基)乙醇在酸作用下先生成碳正离子,三苯基磷作为偶极性的电子给体不但能在一定程度上稳定该苄基碳正离子,而且抑制了其与4-甲氧基苯乙烯之间的亲电反应,进而最大化了脱质子生成4-甲氧基苯乙烯的选择性。
　　将Lewis碱协助的 Lewis酸催化提高反应选择性策略用于2-苯基-3,4-二氢吡喃衍生物合成2-肉桂基-1,3-二羰基化合物的开环反应。该类取代二氢吡喃在酸催化剂作用下也可生成苄基碳正离子,但是该中间体易受分子间和分子内亲电反应影响,反应选择性不高。而当使用单质碘/三苯基磷协同催化体系时,2-苯基-3,4-二氢吡喃衍生物能高选择性地实现开环反应,得到反式2-肉桂基-1,3-二羰基化合物。该类1,3-二羰基化合物具有丰富的反应性,是一类重要的合成子。     

Fluorous reverse-phase silica gel-supported Lewis acids as recyclable catalysts in water

Fluorous reverse-phase silica gel (FRPSG)-supported Lewis acids which have fluorous ligands acted as effective catalysts of Baeyer-Villiger and Diels-Alder reactions in water. Direct esterification of carboxylic acid with alcohol in organic media was also catalyzed. The FRPSG-supported Lewis acids could be recycled by simple filtration after the reaction.     

Electron-Deficient Borinic Acid Polymers: Synthesis,Supramolecular Assembly,and Examination as Catalysts in Amide Bond Formation

The Lewis acidic character of borinic-acid-functionalized polymers suggests broad potential applications in supramolecular materials, chemo- and biosensors, as well as supported catalysts. Two highly electron-deficient borinic acid copolymers ( 3 a and 3 b ) with variable steric hindrance at the boron center were prepared by reaction of aryldibromoboranes ArBBr₂ ( 2 , Ar=2,4-Cl₂Ph, 3,5-Cl₂Ph) with a 10 % stannylated polystyrene random copolymer, followed by conversion to the desired PS-B(Ar)OH functionalities. The supramolecular assembly of these polymers through Lewis acid–Lewis base interactions and reversible covalent B−O−B bond formation was investigated. Exposure of a polymer solution of 3 a to pyridine triggered spontaneous gelation, whereas 3 b only gelled upon addition of molecular sieves to favor formation of boroxane crosslinks. The crosslinking process was readily reversed by addition of small amounts of water or wet solvent. The dynamic processes were studied in detail by variable-temperature (VT) NMR by using molecular model compounds. The polymers and their corresponding model compounds were also examined as catalysts in the amide bond formation reaction between phenylacetic acid and benzylamine. The 3,5-dichlorophenyl borinic acid derivatives proved to be the more effective catalysts. Mechanistic studies suggested that the borane Lewis acid-catalyzed coupling involves initial acid-induced protodeboronation to release the dichlorophenyl boronic acid as the active catalyst.     

Synergistic role of Brønsted and Lewis acidity in alkali metal-exchanged heteropolyacid catalysts for esterification of acetic acid at room temperature

A series of Cs exchanged phosphotungstic acid (PTA) catalysts were synthesized by the ion exchanged method and were characterized by X-ray diffraction, FT-IR spectroscopy, pyridine adsorbed FT-IR spectroscopy, SEM, BF-TEM, ICP-OES and BET surface area analysis. For comparison purposes, K exchanged PTA, Cs and K exchanged phosphomolybdic acid (PMA) catalysts were also prepared. XRD diffractograms showed that the crystallites of the Keggin ion are maintained, while FT-IR spectra also revealed the characteristic bands of the Keggin ion at all metal loadings of all the catalysts. From pyridine adsorbed FT-IR spectroscopy, it was observed that the Brønsted and Lewis acidity were significantly maintained at lower metal loadings, whereas STEM analysis showed a uniform distribution of the elements which correlated well with the theoretical atomic values of the loaded metals for all the catalysts, which were verified by ICP results. The efficiency of various metal-exchanged heteropolyacid catalysts was assessed for the esterification reaction using various substrates, and the Cs exchanged phosphotungstic acid catalysts showed superior activity compared to the other catalysts. In particular, the Cs exchanged phosphotungstic acid with a 1 wt% loading showed the highest activity and was most tolerant to the presence of water that was produced in the reaction. The catalytic activity correlates well with the Brønsted and Lewis acidity, as well as Keggin ion density of the catalysts.     

Sn-Al-β分子筛酸性在葡萄糖转化反应中作用的固体NMR研究

制备了一系列具有不同酸性质的β分子筛催化剂, 通过固体核磁共振(NMR)探针分子技术对其酸性质进行了表征, 并考察了其催化葡萄糖转化为乙酰丙酸甲酯的性能. 吸附三甲基磷的³¹P NMR实验结果表明, 含有骨架Sn以及Al原子的Sn-Al-β催化剂同时具有Br?nsted与Lewis酸性. 通过2-¹³C-丙酮探针分子区分出 3种酸强度的Br?nsted酸位, 其中一种酸强度接近“超强酸”, 可能是由于空间邻近的Br?nsted酸位和Lewis酸位发生协同作用产生的. 葡萄糖转化为乙酰丙酸甲酯的催化反应结果表明, 相比于分别只含有Lewis酸位和Br?nsted酸位的Sn-β和Al-β样品以及两者的物理混合样品, Sn-Al-β分子筛催化剂具有高催化活性与产物选择性, 这主要是由于Br?nsted酸位和Lewis酸位的协同作用产生了强Br?nsted酸位, 这种强Br?nsted酸位进一步导致了更高的催化活性.     

Activity of catalysts in the synthesis of dimethyl sulfide from dimethyl disulfide

Dimethyl disulfide conversion at T = 190–350°C over catalysts containing acid and basic sites is reported. The products of this reaction are dimethyl sulfide, methanethiol, hydrogen sulfide, carbon disulfide, methane, and ethylene. At 190°C, these products form via parallel reactions. At higher temperature of up to 350°C, dimethyl sulfide can form by the condensation of the resulting methanethiol. The strong basic sites of the catalysts are uninvolved in dimethyl sulfide formation. Over catalysts whose surface has only strong protonic or strong Lewis acid sites, dimethyl sulfide formation does take place, but slowly and nonselectively. The highest dimethyl sulfide formation activity and selectivity are shown by catalysts having medium-strength basic sites along with strong protonic and strong Lewis acid sites.     

Carbocations as Lewis Acid Catalysts in Diels–Alder and Michael Addition Reactions

In general, Lewis acid catalysts are metal‐based compounds that owe their reactivity to a low‐lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels–Alder reaction for a range of substrates. Catalyst loadings as low as 500 ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction.     

The study of industrializable ionic liquid catalysts for long-chain alkenes Friedel–Crafts alkylation

Catalysts based on different halo-alkanes structures with durable catalytic performance were synthesized and applied to the Friedel–Crafts alkylation of long-chain alkenes (mixed C_16–24 olefins) with toluene. Surprisingly, compared with the usual industrial catalysts (~10 runs), the cyclic times of the ionic liquid (IL) catalysts reached up to 24 runs, which greatly promotes the industrialization process. Then, Lewis acids of catalysts with different precursor/AlCl₃ molar ratios were investigated and a close relation was discovered between the Lewis acid and catalytic activity. In addition, a comparison of the different halo-alkanes structures about those catalysts was made. The results showed that the [C₆Et₃N]Cl–AlCl₃ had the strongest Lewis acid, corresponding to the highest catalytic performance. Also, the structures of precursors and the specific gravity and active site species of catalysts were investigated by Fourier transform infrared and Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). Meanwhile, the various parameters (catalyst dosage, toluene/olefin molar ratio, reaction temperature and reaction time) of long-chain alkenes alkylation with toluene were studied. Finally, under the optimized reaction conditions, the conversion and selectivity of long-chain alkenes alkylation reached 99.92 and 32.99%, respectively.     

Towards perfect catalytic asymmetric synthesis: dual activation of the electrophile and the nucleophile

The design and development of new high-performance catalysts for applications in asymmetric catalytic reactions is of ongoing interest in organic chemistry. The combination of a Lewis acid and a Lewis base working in concert is now considered state of the art in stereoselective syntheses. The synergistic activation by two or more reactive centers allows high reaction rates and excellent transfer of stereochemical information. Despite the self-quenching reaction between Lewis acids and Lewis bases that might lead to an inactive catalyst, considerable effort has been directed towards the development of the dual-activation concept. The ultimate goal is to mimic nature by the discovery of catalytic systems analogous to enzymatic processes that involve metal-ion cocatalysts. With this aim, the dual activation concept greatly broadens the range of artificial catalysts. The most efficient catalytic systems are reviewed, and the mechanisms of action are discussed.     

Investigation of the mechanism of catalytic recyclization of furan to thiophene

Investigation of the formation of thiophene from furan and hydrogen sulfide at various catalysts showed that the activity of the catalysts increases with increase in the strength and concentration of Lewis acid centers. It was found by IR spectroscopy that if the degree of coverage of the aluminum oxide surface with hydrogen sulfide is higher than monolayer its dissociative chemisorption does not occur. Mechanism was postulated wich assume that the reaction takes place through stage with the formation of a surface intermediate, including coordination of the α-carbon atoms of the furan ring with the Lewis acid center and with the sulfur atom of molecular hydrogen sulfide.     

Mechanism and scope of salen bifunctional catalysts in asymmetric aldehyde and α-ketoester alkylation

Metal complexes of C₂-symmetric Lewis acid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewis acid and Lewis base components of the catalyst and established that both moieties are essential for asymmetric catalysis. These catalysts are also effective in the asymmetric addition of diethylzinc to α-ketoesters. This finding is significant because α-ketoesters alone serve as their own ligands to accelerate racemic 1,2-carbonyl addition of Et₂Zn and racemic carbonyl reduction. The latter proceeds via a metalloene pathway, and often accounts for the predominant product. Singular Lewis acid catalysts do not accelerate enantioselective 1,2-addition over these two competing paths. The bifunctional amino salen catalysts, however, rapidly provide enantioenriched 1,2-addition products in excellent yield, complete chemoselectivity, and good enantioselectivity (up to 88% ee). A library of the bifunctional amino salens was synthesized and evaluated in this reaction. The utility of the α-ketoester method has been demonstrated in the synthesis of an opiate antagonist.     

Effect of butterfly-shaped sulfur-bridged ligand and counter anions on the catalytic activity and diastereoselectivity of organobismuth complexes

In the direct Mannich reaction and synthesis of α,β-unsaturated ketones, the use of organobismuth complexes as catalysts leads to high diastereoselectivity and products of single trans conformation. In this paper, we illustrate the relationship between structure and catalytic activity as well as diastereoselectivity of organobismuth complexes having a 5,6,7,12-tetrahydrodibenz [c,f][1,5]thiobismocine framework as well as bearing a butterfly-shaped sulfur-bridged ligand and tunable anions. With the exposed bismuth center acting as a Lewis acid site and the uncoordinated lone pair electrons of sulfur as a Lewis base site, the cationic organobismuth complexes work as bifunctional Lewis acid/base catalysts. Due to the steric influence of the butterfly-shaped structure and synergistic effect of Lewis acid and Lewis base centers, the complexes can direct substrate attack in organic synthesis. By adjusting the electron-withdrawing ability of the counter anions, the S-Bi bond strength can be regulated, leading to a significant change in Lewis acidity and Lewis basicity as well as catalytic activity. Through synergistic modulation of the above effects, one can control the diastereoselectivity of the organobismuth complexes for the generation of a single diastereoisomer.