Heterogeneous asymmetric reactions. 23. Enantioselective hydrogenation of ethyl pyruvate over cinchonine- and α-isocinchonine-modified platinum catalysts

The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over cinchonine- and gif" alt="agr" align="BASELINE" BORDER="0">-isocinchonine-modified Pt/Al₂O₃ catalysts was studied as a function of modifier concentration and reaction temperature. The maximum enantioselectivities obtained under the applied mild conditions were 89% ee using cinchonine (0.014 mmolgif" alt="thinsp" align="MIDDLE" BORDER="0">dm^–3, 1 bar H₂, 23gif" alt="thinsp" align="MIDDLE" BORDER="0">°C, 6% AcOH in toluene), and 76% ee in the case of gif" alt="agr" align="BASELINE" BORDER="0">-isocinchonine (0.14 mmolgif" alt="thinsp" align="MIDDLE" BORDER="0">dm^–3, 1 bar H₂, –10gif" alt="thinsp" align="MIDDLE" BORDER="0">°C, 6% AcOH in toluene). Since gif" alt="agr" align="BASELINE" BORDER="0">-isocinchonine of rigid structure exists only in gif" alt="ldquo" align="MIDDLE" BORDER="0">anti-opengif" alt="rdquo" align="MIDDLE" BORDER="0"> conformation these data provide additional experimental evidence to support the former suggestion concerning the dominating role of gif" alt="ldquo" align="MIDDLE" BORDER="0">anti-opengif" alt="rdquo" align="MIDDLE" BORDER="0"> conformation in these cinchona-modified enantioselective hydrogenations.     

Fluorinated γ-alumina aerogels and xerogels: characterisation and catalytic behaviour

The porosity of gif" alt="gamma" align="MIDDLE" BORDER="0">-alumina-based materials is an important parameter affecting the extent of fluorination (aerogels > commercial gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ > xerogels) and, consequently, also the textural, acidic and catalytic properties of the final fluorinated materials. Only the highly fiuorinated aluminas having strong Lewis acidic sites catalyse the isomerisation of CHF₂CHF₂ to CF₃CH₂F.     

Simple and economic syntheses of some (Z)-7- and (Z)-9-alkenyl acetates,and of (E,Z)-7,9-dodecadien-1-yl acetate,the sex pheromone of the European grapevine moth,using aleuritic acid as a common starting material

Short syntheses of (Z)-7-dodecen-1-yl acetate, (Z)-7-tetradecen-1-yl acetate, (Z)-9-dodecen-1-yl acetate, and (Z)-9-tetradecen-1-yl acetate from 7-hydroxyheptanal and 9-oxononanoic acid precursors obtained by oxidative cleavage of easily available aleuritic acid are reported. The key step in these syntheses is a stereoselective Wittig reaction between aldehyde and alkyl-phosphonium salt. Wittig-Horner type reaction of 7-hydroxyheptanal and diethyl cyanomethylphosphonate gave the gif" alt="agr" align="BASELINE" BORDER="0">,gif" alt="beta" align="MIDDLE" BORDER="0">-unsaturated nitrile derivative which after protection of the hydroxyl group was reduced to the corresponding aldehyde. Wittig reaction of the latter, followed by acetylation, completed the synthesis of (E,Z)-7,9-dodecadien-1-yl acetate, the sex pheromone of the European grapevine mothLobesia botrana Schiff.     

Oligomer-Rich Fraction from Polydisperse Sample of Poly(bis(β-phenoxyethoxy)phosphazene)

Poly[bis(gif" alt="beta" align="MIDDLE" BORDER="0">-phenoxyethoxy)phosphazene] [PBPEP] had been shown in our previous paper to be a very useful polymer for investigating the crystallization mechanism of polymers, as the crystallization rate of PBPEP is extraordinarily small when isothermally crystallized from the melt. The crystallization of the low molecular weight oligomers of PBPEP was first studied in comparison to the high molecular weight polymers. The oligomer-rich fraction was obtained by fractionation of the as-polymerized sample, which had a broad molecular weight distribution. The fractions thus obtained were characterized by solution viscometry and size exclusion chromatography. The melting temperature and the growth rate of the spherulite from the melt were investigated by differential scanning calorimetry and optical microscopy. The growth rate was one or two orders of magnitude smaller in the oligomer-rich fraction than in the other high molecular weight fractions. A collapsed spherulite appeared in the oligomer-rich fraction at high crystallization temperatures. It is speculated that in the oligomer-rich fraction there is an excess free energy due to defects in the crystal phase. This defect is considerably larger in the oligomer-rich fraction than in the other fractions because a large quantity of short length chains is present.     

The study on the conductivity of styrene-maleic anhydride copolymer electrolytes based on poly(ethylene glycol)400 and LiClO4

Polyelectrolytes, in this study were synthesized from styrene-maleic anhydride (SMA) copolymer, poly(ethylene glycol)400 (PEG400), and lithium perchlorate (LiClO₄). Fourier transform infrared spectroscopy (FTIR), and gif"> magic angle spinning (MAS) solid-state NMR were used to monitor the interaction between Li⁺ ions and polymer. The results of FTIR and gif"> MAS solid-state NMR indicate the Li⁺ ions are preferentially coordinated to the ether oxygen of PEG. The T_g of the PEG segments in polyelectrolyte increases with LiClO₄ concentration, as determined by differential scanning calorimetry (DSC), indicating that solubility of the Li⁺ ions in the host polymer increases with the PEG content. Impedance spectroscopy (IS) shows that the bulk conductivity of polyelectrolytes and the conductivity behavior obeys the Vogel-Tamman-Fulcher (VTF) equation.     

Suppression of the α → β-nickel hydroxide transformation in concentrated alkali: Role of dissolved cations

The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the gif" alt="agr" align="BASELINE" BORDER="0"> gif" alt="rarr" align="BASELINE" BORDER="0"> gif" alt="beta" align="MIDDLE" BORDER="0">-nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the gif" alt="agr" align="BASELINE" BORDER="0">-phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases.     

α-Tocopherol alteration of soybean antiherbivory toTrichoplusia ni larvae

The antioxidant vitamin E, gif" alt="agr" align="BASELINE" BORDER="0">-tocopherol, was tested as a candidate elicitor of alterable antiherbivory in soybean plants against cabbage looper larvae. Although a nonspecific antioxidant, vitamin E proved elicitory to the involved sulfhydryl-dependent receptor-energy transducer protein in soybean plasma membrane. Effects of gif" alt="agr" align="BASELINE" BORDER="0">-tocopherol were dependent on dosage, time, and space in the plant. The observed elicited effects were all decreases in herbivory. The best negative phytochemical correlate of looper feeding was the percentage of increased total HPLC peak area of extractables from elicited as compared to nonelicited leaves. Some specific compounds, e.g., glyceollins, were quantitatively major components of the total profile of secondary metabolites.     

The influence of an intermediate MoO3 layer on the solid state reaction of cobalt oxide withγ-Al2O3

In view of the importance for Co_xO_y,-MoO₃/gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ hydrodesulphurization (HDS) catalysts, the reactivity of cobalt oxide layers towards cobalt aluminate formation was investigated on both MoO₃-covered and bare gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ substrates. Co₃O₄/MoO₃/gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ and Co₃O₄/gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ systems were prepared by vapour-deposition of MoO₃ (12 × 10¹⁵ Mo atoms/cm²) and Co (400 × 10¹⁵ Co atoms/cm²) layers onto a gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ substrate, followed by oxidation of the Co layer to Co₃O₄. After annealing at 800°C for 40 h, the interfacial reaction to cobalt aluminate was assessed using Rutherford backscattering spectrometry. The presence of molybdenum oxide appeared to enhance cobalt aluminate formation. The Mo atoms, which spread out over the entire cobalt-containing layer, presumably caused a high defect density, which explains the observed higher reaction rate. The amount of MoO₃ was much too low to stabilize all cobalt atoms by cobalt molybdate formation.     

The ring transformations of 1,2,3,4-diepoxybutane (2,2′-bioxirane) catalysed by various aluminosilicates

The transformations of a molecule containing two adjacent epoxide rings, 2,2gif" alt="prime" align="BASELINE" BORDER="0">-bioxirane that is, were studied over various acidic aluminosilicates (HZSM-5, HY-FAU, AlMCM-41), for the first time, In the 373–473 K temperature range, in a pulse reactor, a ring-opening–ring-enlargment reaction producing furan only occured over the zeolites and it was the predominant reaction on AlMCM-41 as well. The driving force of this transformation route is water formation via elimination from 2,2gif" alt="prime" align="BASELINE" BORDER="0">-bioxirane. Suprising is the lack of the mono- or dialdehyde, the would-be products of the cleavage of the sterically more hindered C–O bonds – an acid-catalysed reaction typical for alkyl-substituted oxiranes.     

Preparation of rechargeable lithium batteries with poly(methyl methacrylate) based gel polymer electrolyte by <Emphasis Type="Italic">in situ</Emphasis>γ-ray irradiation-induced polymerization

An admixture of commercial liquid electrolyte (LB302, 1 M solution of LiPF₆ in 1:1 EC/DEC) and methyl methacrylate (MMA) was enclosed in CR2032 cells. The assembled cells were then gif" alt="gamma" align="MIDDLE" BORDER="0">-ray-irradiated using configurations of half cells and full cells. Through this in situ irradiation polymerization process, we obtained rechargeable lithium ion cells with poly(methyl methacrylate) (PMMA) based gel polymer electrolytes (GPE). Galvanostatic cycling, AC impedance spectroscopy, and cyclic voltammetry were employed to investigate the electrochemical properties of the cells and the gel polymer electrolyte. This PMMA-based gel polymer electrolyte was found to exhibit a high ionic conductivity (at least 10^–3 S cm^–1) at room temperature. Due to a significant increase in the charge transfer resistance between the GPE and the cathode, the cell impedance of a PMMA-based lithium ion cell is greater than that of a liquid-electrolyte-based cell. The discharge capacity of a LiNi_0.8Co_0.2O₂/GPE/graphite is approximately 145 mAh g^–1 for the first cycle and decreases to123 mAh g^–1 after 20 cycles. In addition, a large initial cell impedance (LICI) was observed in the irradiated positive half cell. In this paper, we propose a possible mechanism related to the detachment of the PMMA layer from the lithium electrode. This detachment of the PMMA layer from the lithium electrode has not been explicitly discussed previously.