New chiral phosphine-phosphite ligands in the enantioselective palladium-catalyzed allylic alkylation

A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities.     

Intercalation of Benzamide into Kaolinite

Well-crystallized kaolinite (K) was initially reacted at 60 degrees C with a water/dimethylsulfoxide (DMSO) mixture and the resulting intercalation derivative (K-DMSO) was characterized by powder X-ray diffractometry (PXRD), thermal analysis (simultaneous TG and DSC), and Fourier-transformed infrared spectroscopy (FTIR). Benzamide crystals were then melted with the K-DMSO derivative at 140 degrees C for 4 days, when a gradual displacement of DMSO by benzamide was observed within the interlayer spacing of the modified kaolinite. The resulting material, after extensive washing with acetone, was characterized and compared to the results obtained previously for the K-DMSO composite. Benzamide intercalation proceeded by gradual displacement of DMSO molecules until completion. The structural stabilization of the K-BZ derivative was explained through the establishment of hydrogen bonds between the carbonyl oxygen atoms of the intercalated benzamide and aluminol groups present at the surface of the kaolinite layer. The interlamellar spacing of K-BZ was shown to be possibly occupied by benzamide molecules that were located at a 68 degrees orientation in relation to the layer surface. Unlike most intercalation molecules such as DMSO, variations in the interplanar spacing of kaolinite were consistent with the nonkeying of any other part of the molecule between the aluminosilicate interlayers. Copyright 2000 Academic Press.     

Relevance of chemistry to white biotechnology

White biotechnology is a fast emerging area that concerns itself with the use of biotechnological approaches in the production of bulk and fine chemicals, biofuels, and agricultural products. It is a truly multidisciplinary area and further progress depends critically on the role of chemists. This article outlines the emerging contours of white biotechnology and encourages chemists to take up some of the challenges that this area has thrown up.     

Zirconyl-alizarin blue s complex a spectrophotometric study

Alizarin blue S in 0.5N hydrochloric acid and 10% acetone gives a coloured complex with zirconium salts, which is used for the estimation of zirconium. Measurements were made at 625 mμ and the interference of several cations and anions was studied     

Biaxial bulge testing of polymeric sheets

The through thickness total strains of hydrostatically bulged domes of materials are usually determined indirectly. The in-plane circumferential strains are readily measured, and then constancy of volume is invoked to determine the “missing” or unknown strain. Some of our recent work with polymers has shown that volume constancy in large-scale deformation does not hold so that the usual computations of stress and strain during bulging of sheet may be in error. We describe an electrical device that reduces such errors by directly measuring the through thickness (and, thus, the thickness “strain”) for nonmetallic materials.     

Trifluoroethanol as a Metal-Free,Homogeneous, and Recyclable Medium for the Efficient One-Pot Synthesis of Dihydropyrimidones

Trifluoroethanol is an efficient and recyclable medium in promoting one-pot, three-component condensation reactions of β-ketoesters, aldehydes, and urea (or thiourea) to afford the corresponding dihydropyrimidones in good yields. This protocol does not require the use of an acid or base catalyst.     

Amorphous structure heat: Heats of solution versus temperature for polysulfone in o-dichlorobenzene

The data presented for polysulfone in o-dichlorobenzene support previous observations on other systems in which the heats of solution decrease linearly with increasing temperature of measurement. Consistent with similar measurements on polycarbonate and polyphenylene oxide, a dramatic slope change from 0.078 cal/g-C° below 120°C to 0.019 cal/g-C° above 120°C occur for the data on polysulfone. The source of these heats is due primarily to the enthalpy difference between the solid polymer and its corresponding liquid amorphous state at the measurement temperature since the heats of mixing are rationalized to be small.     

Synthesis of MWCNTs‐core/thiophene polymer‐sheath composite nanocables by a cationic surfactant‐assisted chemical oxidative polymerization and their structural properties

Multi‐walled carbon nanotubes (MWCNTs)‐core/thiophene polymer‐sheath composite nanocables were synthesized by chemical oxidative polymerization of 3,4‐ethylenedioxythiophene (EDOT) with oxidant (FeCl₃) in the presence of cationic surfactant, deceyltrimethyl ammonium bromide (DTAB). In the polymerization process, DTAB surfactant molecules were adsorbed on the surface of MWCNTs and forms MWCNTs‐DTAB soft template. Upon the addition of EDOT and oxidant, the polymerization take place on the surface of MWCNTs and PEDOT is gradually deposited on the surface of MWCNTs. The resulting MWCNTs‐PEDOT nanocomposites have the nanocable structure. Nanocomposites were characterized by HRTEM, FE‐SEM, XRD, XPS, TGA, FTIR and PL, respectively. The π‐π interactions between PEDOT and MWCNTs enhancing the thermal and electrical properties of the nanocomposites with loading of MWCNTs. The temperature dependence conductivity measurements show that the conductivity of the nanocomposite decrease with a decrease of temperature, and conductivity‐temperature relationship is well fit by the quasi‐one dimensional variable range hopping mode. The mechanism for the formation of composite nanocables was explained on the basis of self‐ assembly of micelles. The reported self‐assembly strategy for the synthesis of PEDOT‐coated MWCNTs in micellar medium is a rapid, versatile, potentially scalable, stable, and making it useful for further exploitation in a varies types of applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1477–1484, 2010     

Theoretical and experimental vibration analysis of an oblique space frame

This paper has the general objectives of relating analytical and experimental techniques for analysis of indeterminate spatial frames under dynamic loading. The model used has been made as general as possible to explore validity for nonstereotyped configurations. A highly redundant oblique four-bar space frame was selected having a lowest natural frequency of 42.1 cps. Recent success of the finite-element-matrix method and progress in the field of nonlinear optimization provides a rational basis for the synthesis of space frames; however, the validity of the discretization, both for strength-stiffness analysis and dynamic analysis, has not been explored for this type of configuration. The flexibility influence coefficients, the natural frequencies and the steady-state vibration amplitudes were experimentally determined and compared with theoretical values. Influence coefficients had an “error” of between four and 10 percent; the six lowest natural frequencies were in agreement within 15 percent when rotary inertia was considered. Steady-state amplitudes were in good agreement at frequencies not too close to resonance.