Continuous enantioselective hydrogenation of activated ketones on a pt-cd chiral catalyst: use of h-cube reactor system

Summary The Pt-alumina-CD catalyzed enantioselective hydrogenations of ethylpyruvate (EP), ketopantolactone (KPL) and methyl benzoylformate (MBF) have been studied at first in an H-Cube flow hydrogenator in toluene and toluene + acetic acid. Based on the experience of previous studies carried out in batch-reactor and continuous flow systems, some parameters were kept constant (amount of catalyst, 380 mg; substrate concentration, 0.18 mol/L; temperature, 283 K), whereas others, namely chiral modifier (CD) concentration, hydrogen pressure and total liquid flow (TLF: substrate + modifier + solvent) were varied. In the course of enantioselective hydrogenation (R)-products were formed in excess: in the case of EP, KPL, MBF: 90, 60, 80 % enantioselectivities were obtained.     

Synthesis of 1-ethylpyrrolidone-2 by hydrogenation of 1-vinylpyrrolidone-2 over a Pd/C catalyst

A selective catalytic system for the hydrogenation of 1-vinylpyrrolidone-2 (VP) to 1-ethylpyrrolidone-2 (EP) is found. The factors responsible for the formation of by-products in the conversion of VP are studied. The presence of acid sites or radical species in a catalytic system results in the fast polymerization of VP. The resulting by-product, poly vinylpyrrolidone, may deactivate the hydrogenation catalyst by surface blocking. VP can be hydrogenated to EP under mild conditions and with a high selectivity using a palladium catalyst supported on a porous carbon material Sibunit. The kinetics of VP hydrogenation over the Pd/C catalyst is studied.     

Methylethers of cinchona alkaloids in Pt-catalyzed hydrogenation of ethyl pyruvate and ketopantolactone: Effect of stereochemical factors on the enantioselectivity

We studied the enantioselective hydrogenation of ethyl pyruvate (EP) and ketopantolactone (KPL) under mild experimental conditions (hydrogen pressure 1 bar, room temperature) on Pt-alumina catalyst modified with O-methyl derivatives of parent cinchona alkaloids (MeOCD, MeOCN, MeOQN, MeOQD) in two solvents with highly different polarities (AcOH, toluene). The best ee's were achieved (91–96%) using MeOCD and MeOQN modifiers in AcOH. Hydrogenation, especially in the presence of the chiral modifiers MeOCN and MeOQD in toluene proceeded with exceptionally low enantioselectivities (35–46% for EP and 2–4% for KPL) as compared to the already well-known Pt-MeOCD catalyst (ee%: 71–74 for EP, 38–48 for KPL). Results of the hydrogenations of the modifiers and studies on the hydrogenation of substrates using modifier mixtures suggested that the low ee are attributable to stereochemical reasons. Namely, it seems justified to suppose that the low ee observed is dependent on the various tilted adsorbed structures of the substrate and modifier 1:1 intermediate complex responsible for enantiodifferentiation.     

几种聚醚胺改性蒙脱土对环氧树脂固化过程的影响

首先制备了五种聚醚胺改性蒙脱土(MMT), 并将这五种聚醚胺改性蒙脱土加入到双酚A 型环氧树脂E51 和聚醚胺D400体系中, 采用差示扫描量热法(DSC)考察了五种聚醚胺改性MMT对环氧树脂升温固化进程的影响. 随后, 优选一种EP/MMT 混合体系即EP/D400-T500-MMT 混合体系, 系统地研究了该体系与纯环氧树脂体系在130, 140, 150 及160 ℃等几个温度下的等温固化过程, 考察了等温固化时间对固化度和固化度变化速率的影响以及固化度与固化度变化速率之间的关系, 并利用Kamal 模型进行拟合计算了固化动力学参数. 研究结果表明, 与纯环氧树脂相比, 几种聚醚胺改性MMT 的固化放热峰均向高温迁移, 同时聚醚胺D400 协同插层MMT 降低了高分子量聚醚胺插层MMT 所导致的环氧树脂DSC 曲线的畸变情况; EP/D400-T500-MMT 混合体系和纯环氧体系的等温固化反应过程符合Kamal 模型;在相同的固化温度下, EP/D400-T5000-MMT 混合体系的反应速率常数k₁ 和k₂ 值以及反应级数m 均比纯EP 体系小, 而反应级数n 以及总反应级数m+n 值比纯EP 体系大, 表明两种聚醚胺协同插层的改性蒙脱土D400-T5000-MMT 的加入降低了环氧体系固化反应速率. 另外, EP/D400-T5000-MMT 混合体系的活化能E_a1 和E_a2 与纯EP 体系的相比也略有升高.     

酸酐固化环氧树脂/蒙脱土复合材料的等温固化动力学

用等温差示扫描量热法(DSC)研究了酸酐固化环氧树脂/蒙脱土复合材料的等温固化过程，考察了未处理的蒙脱土(MMT)和有机蒙脱土(OMMT)对环氧树脂固化动力学的影响. 实验表明， 环氧树脂的固化过程包含自催化机理，加入蒙脱土没有改变固化反应机理. 用Kamal方程对该体系的固化过程进行拟合，得到反应级数m、n，反应速率常数k1、k2，总反应级数(m + n)在2.4～3.0之间. MMT的加入使环氧树脂体系的k1、k2有所降低，而OMMT的加入对体系的k1、k2影响较为复杂，加入蒙脱土对环氧树脂固化体系的活化能影响较小.     

Physico-chemical effects of the major quassinoids in a standardized Eurycoma longifolia extract (Fr 2) on the bioavailability and pharmacokinetic properties, and their implications for oral antimalarial activity

A simple validated LC-UV method for the phytochemical analysis of four bioactive quassinoids, 13alpha(21)-epoxyeurycomanone (EP), eurycomanone (EN), 13alpha,21-dihydroeurycomanone (ED) and eurycomanol (EL) in rat plasma following oral (200 mg/kg) and intravenous administration (10 mg/kg) of a standardized extract Fr 2 of Eurycoma longifolia Jack was developed for pharmacokinetic and bioavailability studies. The extract Fr 2 contained 4.0%, 18.5%, 0.7% and 9.5% of EP, EN, ED and EL, respectively. Following intravenous administration, EP displayed a relatively longer biological half-life (t1/2 = 0.75 +/- 0.25 h) due primarily to its lower elimination rate constant (k(e)) of 0.84 +/- 0.26 h(-1)) when compared with the t1/2 of 0.35 +/- 0.04 h and k(e) of 2.14 +/- 0.27 h(-1), respectively of EN. Following oral administration, EP showed a higher C(max) of 1.61 +/- 0.41 microg/mL over that of EN (C(max) = 0.53 +/- 0.10 microg/mL). The absolute bioavailability of EP was 9.5-fold higher than that of EN, not because of chemical degradation since both quassinoids were stable at the simulated gastric pH of 1. Instead, the higher log K(ow) value of EP (-0.43) contributed to greater membrane permeability over that of EN (log K(ow) = -1.46) at pH 1. In contrast, EL, being in higher concentration in the extract than EP, was not detected in the plasma after oral administration because of substantial degradation by the gastric juices after 2 h. Similarly, ED, being unstable at the acidic pH and together with its low concentration in Fr 2, was not detectable in the rat plasma. In conclusion, upon oral administration of the bioactive standardized extract Fr 2, EP and EN may be the only quassinoids contributing to the overall antimalarial activity; this is worthy of further investigation.     

Study on the optimum ratio and non-isothermal curing kinetics of EP2008/EP2008-S system

This paper systematically reports the optimum ratio and non-isothermal curing kinetics of EPOLAM 2008 RESIN (EP2008)/EPOLAM 2008-S HARDENER (EP2008-S) system studied using Differential Scanning Calorimetry (DSC). In view of the gel time, viscosity, and curing reaction heat, the optimum ratio of m (EP2008)/m (EP2008-S) can be confirmed as 100:20. Subsequently, non-isothermal curing kinetics of the composite system with the optimum ratio of m (EP2008)/m (EP2008-S) is investigated by dynamic DSC. The kinetics mechanism function is analyzed with the nth-order model and two-parameter (m and n) autocatalytic model (?esták–Berggren model). Results indicated that the Málek method discloses the autocatalytic behavior, and that the two-parameter autocatalytic model is able to well simulate the curing reaction. Through the analysis of chemical composition of EP2008/EP2008-S and the value of E _a , the possible curing reaction mechanism can be explained.     

Immobilization of DNA on carbon fiber microelectrodes by using overoxidized polypyrrole template for selective detection of dopamine and epinephrine in the presence of high concentrations of ascorbic acid and uric acid

The overoxidized polypyrrole (PPyox) film as a template for DNA immobilization has been demonstrated in this paper. The DNA molecules inserted into the micropores of the ultrathin PPyox matrix under the driving forces of an electric field and were firmly immobilized on the carbon fiber electrode (CFE). Such a DNA-PPyox biocomposite layer exhibited more effective rejection of anionic ascorbate (AA) and uric acid (UA) and more preferential collection of the cationic dopamine (DA) and epinephrine (EP) than pure PPyox and DNA coatings. The DPV peak currents increased linearly with increasing DA and EP concentrations in the range of 3.0 x 10(-7) to 1.0 x 10(-5) M and 5.0 x 10(-7) to 2.0 x 10(-5) M with the lowest detected concentrations of 8.0 x 10(-8) M and 6.0 x 10(-8) M, respectively. The electrochemical signal of AA could be totally suppressed under a concentration of 20 mM and beyond this concentration, the overlapped responses of AA, DA/EP and UA could be resolved into three well-defined voltammetric peaks. The selectivity factors k(DA/AA) and k(EP/AA) were about 5000 and 2000 for an equal concentration in the presence of 0.5 mM UA. The properties of the biocomposite film have been characterized by atomic force microscopy and electrochemical investigations.     

琥珀酸酐均相催化加氢生成γ-丁内酯的反应动力学研究

以RuCl3 /PPh3 为催化剂体系研究了琥珀酸酐均相催化加氢反应动力学 .结果表明当催化剂浓度小于1.0× 10 -2 mol /L ,n(PPh3 ) /n(Ru) =7,SA浓度小于 2 .2 5mol /L和反应氢压PH2 小于 2 .2 5MPa时 ,反应速率方程为R =k1[Ru][SA]PH2 ;当反应氢压PH2 大于 2 .77MPa时 ,反应速率方程为R =k2 [Ru][SA].琥珀酸酐加氢生成γ -丁内酯的活化能Ea为 85 .2kJ/mol,活化焓△H≠ 为 81.8kJ /mol     

Influence of samarium on the electrocatalytic activity of platinum electrodes for the hydrogenation of benzene

The hydrogenation of benzene on platinum electrodes in 0.5 M sulfuric acid as supporting electrolyte has been studied in the presence and the absence of samarium in solution. The hydrogenation overpotential of preadsorbed benzene was diminished to 90 mV with samarium in the solution and the hydrogenation current was significatively increased. These results are interpreted in terms of a synergic effect of samarium on hydrogen adsorption and, consequently, on the electrocatalytic activity of the platinum electrode for the hydrogenation of benzene.     

Stereoselective synthesis of two potential metabolites of cis-metconazole

The stereoselective synthesis of compounds 5 and 6, potential hydroxylated metabolites of the agricultural fungicide cis-metconazole, is reported. In a key step of the initially surveyed synthetic route, hydrodechlorination of 12 was competitive with hydrogenation of the trisubstituted olefin. Application of a Miyaura borylation/hydrogenation/boron-to-halogen exchange reaction sequence solved the chemoselectivity issue.     

Organic solvent‐free catalytic hydrogenation of diene‐based polymer nanoparticles in latex form. Part II. Kinetic analysis and mechanistic study

The central challenge that has limited the development of catalytic hydrogenation of diene‐based polymer latex (i.e., latex hydrogenation) in large‐scale production pertains to how to accomplish the optimal interplay of accelerating the hydrogenation rate, decreasing the required quantity of catalyst, and eliminating the need for an organic solvent. Here, we attempt to overcome this dilemma through decreasing the dimensions of the polymer substrate (such as below 20 nm) used in the hydrogenation process. Very small diene‐based polymer nanoparticles were synthesized and then used as the substrates for the subsequent latex hydrogenation. The effects of particle size, temperature, and catalyst concentration on the hydrogenation rate were fully investigated. An apparent first‐order kinetic model was proposed to describe the rate of hydrogen uptake with respect to the concentration of the olefinic substrate (C?C). Mass transfer of both the hydrogen and catalyst involved in this solid (polymer)–liquid (water)–gas (hydrogen) three‐phase latex system is discussed. The competitive coordination of the catalyst between the C?C and acrylonitrile units within the copolymer was elucidated. It was found that (1) using very small diene‐based polymer nanoparticles as the substrate, the hydrogenation rate of polymer latex can be increased vastly to achieve a high conversion of 95% while a quite low level of catalyst loading is required; (2) this latex hydrogenation process was completely free of organic solvent and no cross‐linking was found; (3) the mass transfer of hydrogen is not a rate‐determining step in the present hydrogenation reactions; (4) the catalyst was dispersed homogeneously within the polymer nanoparticles; (5) for the reaction that has reached about 95 mol % conversion, the kinetic study shows that the reaction is chemically controlled with an apparent activation energy of 100–110 kJ/mol; (6) the strong coordination of C[tbond]N to the catalytically active species RhH₂Cl(PPh₃)₂ imposed a negative effect on the hydrogenation activity. The present research provides a comprehensive study to appreciate the underlying chemistry of latex hydrogenation of diene‐based polymer nanoparticles and more importantly shows great promise toward the commercialization of a “green” catalytic hydrogenation operation of a diene‐based polymer latex in industry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Competitive Transfer Hydrogenation of Unsaturated Alcohol-Alkene-Diene Systems

The paper describes hydrogenation of unsaturated alcohols, alkenes and dienes in individual and binary systems of substrates by use of catalytic hydrogen transfer from ammonium formate in methanol on a palladium catalyst. A significant structural effect of hydrogenated alcohols upon their reactivity and adsorptivity was observed. Following comparison to the data acquired from typical hydrogenation by use of molecular hydrogen, it was inferred that the components of the CTH system increase the selectivity of competitive transfer hydrogenation to a significant extent in systems of unsaturated alcohol — unsaturated hydrocarbon with regard to the relative increase of reactivity of unsaturated alcohols. This occurs primarily due to affecting the relative adsorptivity.     

Differential Selectivity of Palladium–Phosphorus Catalysts in the Competitive Hydrogenation of Isomeric Chloronitrobenzenes

The competitive hydrogenation of сhloronitrobenzene isomers in the presence of different palladium- containing catalysts was studied. The nature of catalytic activity carriers for the Pd–P nanoparticles containing both Pd(0) clusters and palladium phosphides was determined by the method of phase trajectories. It was found that the hydrogenation of сhloronitrobenzene isomers under mild conditions occurred on the clusters of Pd(0), and the dependence of the differential selectivity of Pd–P clusters in the hydrogenation of o- and m-сhloronitrobenzene on the P/Pd ratio was related to the dispersity of the Pd(0) clusters.     

Synthesis of tunable bisphosphine ligands and their application in asymmetric hydrogenation of quinolines

A series of tunable axial chiral bisphosphine ligands have been synthesized from (S)-MeO-Biphep. The Ir complex of the MeO-PEG-supported ligand (S)-4k has been successfully applied in asymmetric hydrogenation of quinolines with up to 92% ee. The catalyst system is air-stable and recyclable.     

Preparation of 2,2′-octahydrodithienyl and its complexes with HgCl2 and CdCl2

Conclusions The ionic hydrogenation of 2,2-dithienyl with triethylsilane and trifluoroacetic acid gave 2,2-octahydrodithienyl, which was characterized by its complexes with HgCl₂ (II) and CdCl₂ (II).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1173–1174, May, 1976.     

Computer simulations of interactions between liquid crystal molecules and polymer surfaces II. Alignment of smectic C-forming mesogens

Computer simulations have been performed to examine the behaviour of the liquid crystalline molecule 4-n-heptyl-2-fluoro-phenyl 4-n-octyloxybiphenyl-4-carboxylate (MBF) when in contact with crystalline polymer surfaces. The simulations form part of a study of the alignment interactions that are found in liquid crystal displays. MBF forms several smectic phases including a chiral smectic C* phase when suitably doped. In this paper we examine the way that layers of MBF molecules interact with the structure of the crystalline polymer surface, with the aim of understanding how molecular level interactions give rise to macroscopic phenomena such as the cone angle in ferroelectric liquid crystal devices. Molecular dynamics simulations consisting of a fixed crystalline polymer surface in contact with either a single MBF molecule or up to two layers of them (48 molecules) have been performed. A variety of simple polymer surfaces have been examined and the simulations show that the cone angle is highly dependent on the geometry of both the liquid crystal molecule and the polymer substrate. For molecules of MBF on polyethylene substrates, a cone angle of 20 is predicted, in line with experimental findings.     

Transforming nonselective into chemoselective metal catalysts for the hydrogenation of substituted nitroaromatics

It is generally accepted that good hydrogenation noble and nonnoble metal catalysts such as Pt, Ru, or Ni are not chemoselective for hydrogenation of nitro groups in substituted aromatic molecules. We have found that it is possible to transform nonchemoselective into highly chemoselective metal catalysts by controlling the coordination of metal surface atoms while introducing a cooperative effect between the metal and a properly selected support. Thus, highly chemoselective and general hydrogenation Pt, Ru, and Ni catalysts can be prepared by generating nanosized crystals of the metals on the surface of a TiO 2 support and decorating the exposed (111) and (100) crystal faces by means of a simple catalyst activation procedure. By doing this, it has been possible to change the relative rate for hydrogenating competitive groups present in the molecule by almost 2 orders of magnitude, increasing the chemoselectivity from less than 1% to more than 95%.     

Homogeneous and heterogeneous asymmetric reactions. Part IX. Asymmetric transfer hydrogenation of 16-methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes

Chiral transfer hydrogenation of 16 methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes by hydrosilylation is described. During the preparation of the complex catalysts a wide variety of bidentate phosphines were used including chiral ligands, as well. The diastereoselectivity of the reduction depends strongly on the structure of the ligands. The method applied produces the hydroxy steroid products with excellent yield under very mild reaction conditions. Additionally, the procedure makes possible the preparation of 17α-OH isomers beside the easily synthesizable 17β-OH products. Part. VIII: B. T?r?k, K. Felf?ldi, G. Szakonyi, K. Balázsik and M. Bartók: Enantiodifferentiation in Asymmetric Sonochemical Hydrogenations, Catal. Letters (in press)     

A simple synthesis of acetyl and propionyl cyclododecanes

1-Formyl-4,8-cyclododecadiene, obtained by hydroformylation of 1,5,9-cyclododecatriene, reacts with MeMgHal or EtMgHal to give 1-(l-hydroxyethyl)-or 1-(l-hydroxypropyl)-4,8-cyclododecadiene, respectively. The hydrogenation of their double bonds and subsequent oxidation of the resulting alcohols afford, in high yields, acetyl- or propionylcyclododecane, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 418–419, February, 1993.