“Vapor–liquid” equilibrium measurements and modeling for the cyclohexane + cyclohexanol binary system

To simulate cyclohexane oxidation reactors using a dynamic model linking kinetics, thermodynamics and hydrodynamics, the acquisition and modeling of vapor–liquid equilibria of the key components, under the process conditions, are essential. In this work, the vapor–liquid equilibria of the cyclohexane + cyclohexanol system were determined at temperatures 424, 444, 464 and 484 K. The measurements were carried out using an apparatus based on the “static-analytic” method, with two ROLSI™ pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng–Robinson (PR) and the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT). A comparison of model performances reveals the former being better in data representation, while the latter has a broader applicability over larger range of temperatures.     

Catalytic asymmetric allylation of aldehydes using the chiral (salen)chromium(III) complexes

The enantioselective addition of allylstannanes to glyoxylates and glyoxals, as well as simple aromatic and aliphatic aldehydes, catalyzed by chiral (salen)Cr(III) complexes, has been studied. The reaction proceeded smoothly for the reactive 2-oxoaldehydes and allyltributyltin in the presence of small amounts (1-2 mol %) of (salen)Cr(III)BF₄ (1b) under mild, undemanding conditions. However, in the case of other simple aldehydes, the use of high-pressure conditions is required to obtain good yields. Classic chromium catalyst 1b, easily prepared from the commercially available chloride complex 1a, affords homoallylic alcohols usually in good yield and with enantiomeric purity of 50-79% ee. The stereochemical results are rationalized on the basis of the proposed model.     

A new structure type of RE4B4O11F2: High-pressure synthesis and crystal structure of La4B4O11F2

The first lanthanum fluoride borate La₄B₄O₁₁F₂ was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La₄B₄O₁₁F₂ crystallizes in the monoclinic space group P2₁/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE₄B₄O₁₁F₂. The crystal structure contains BO₄-tetrahedra interconnected with two BO₃-groups via common vertices, B₂O₅-pyroborate units, and isolated BO₃-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La₄B₄O₁₁F₂ are discussed and compared to Gd₄B₄O₁₁F₂.     

Structural and physical properties evolution of BaIr1−xMnxO3 solid solutions synthesized by high-pressure sintering

The BaIr_1−xMn_xO₃ (0.0≤x≤1.0) solid solutions were synthesized by using the solid-state chemical method and high pressure sintering in the pressure range 0-5 GPa. According to the pressure-composition “phase diagram” at 1000 °C, the 9M BaIr_1−xMn_xO₃ transforms to the 6M form at 5 GPa and x≤1/6. In the x range 0.5-1.0, it transforms to the 9R form in a large pressure range. For the 9M BaIrO₃, the Mn ions substitution for Ir ions enhances the semiconducting property, and reduces the weak ferromagnetism. When x is larger than 1/3, the 9M/9R BaIr_1−xMn_xO₃ behave spin-glass-like state at low temperature, with the glass transition temperature T_g about 60 K. For the 6M BaIrO₃, the Mn ions doping results in that it transforms to insulator and spin-glass-like magnetism from the initial paramagnetic metal.     

Soxhlet extraction: Past and present panacea

An overview of Soxhlet extraction, the advantages and shortcomings of this centenary technique as well as the attempts to improve its performance and achievements reached is here presented. Assistance of high pressure, ultrasound or microwaves has decreased or minimized the negative characteristics of the conventional extractor. Automation of Soxhlet performance opened the door to commercialization of a number of different approaches. The evolution of Soxhlet extractor is here critically discussed, and the conclusion from this overview is that the adoption of new technologies to improve its performance converts Soxhlet extraction in almost a “panacea” in this field.     

High-pressure structural integrity and structural transformations of glass-derived nanocomposites: A review

A review of our recent and ongoing extensive high-pressure synchrotron X-ray diffraction and high-pressure optical spectroscopy studies of nanocrystalline composites is presented. These heterophased, nano-architectured composites consist of amorphous matrices with dispersed nanocrystals or quantum dots. We show how besides compositional variations, additional tuning of these glass-derived nanocomposites can be done by exploiting elevated pressure. We examine stability and pressure-driven phase transitions occurring in nanocrystals as well as structural changes occurring in the glass matrix. Finally, we discuss the influence of the glass matrix of a composite on the structural transformations occurring in the embedded nanocrystals.     

Das erste gemischte Erdalkalimetall-Oxomercurat: Ba0.75Sr0.25HgO2

Summary Ba_0.75Sr_0.25HgO₂ was prepared for the first time by an oxygen high-pressure technique. Single cystal X-ray investigations lead to hexagonal symmetry, space group D ₆ ⁶ -P6₃22;a=6.897;c=11.986 Å;Z=6. Hg²⁺-ions show a dumbbell-like coordination by two O^2–-ions. The alkaline earth ions Ba²⁺ and Sr²⁺ are surrounded by deformed trigonal O^2–-prisms. Only one of the two Ba²⁺ point positions of the BaHgO₂-type can be substituted by Sr²⁺. Polyhedra size and deformation are discussed in respect to the exchange of Ba²⁺ by Sr²⁺.

     

Eich- und Standardisierungsprobleme in der HPLC

Zusammenfassung In der Praxis der Hochdruck-Flüssigkeits-Chromatographie muß der Analytiker möglichst genaue Resultate erhalten unter der Bedingung, daß der Zeit- und Arbeitsaufwand für die Eichung möglichst gering ist. Häufig sind die Komponenten einer Analyse nicht in einer Form erhältlich, die für Eichzwecke rein genug ist. Hier wird gezeigt, wie man unter gewissen Voraussetzungen dennoch die Eichfaktoren der reinen Komponenten bestimmen kann. Durch Sammeln und Auswerten von Faktorverhältnissen über einen längeren Zeitraum läßt sich der für die Eichung erforderliche Zeitaufwand wesentlich herabsetzen, wobei die Genauigkeit erhalten bleibt oder sogar verbessert wird. Dadurch, daß durchflußbereinigte Faktoren benutzt werden, kann dies noch weiter verbessert werden.

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On the problem of calibration and standardization in HPLC

Summary In practical high-pressure liquid chromatography the analyst must get results as accurate as possible under the condition that the amount of time and labour spent for calibration should be as low as possible. Often the components of the analysis are not available sufficiently pure for calibration purposes. It is shown here as under certain conditions the calibration factors of the pure components could be determined even with impure standard substances. By collecting and evaluating calibration factor ratios for a longer time, the time necessary for calibration could be reduced remarkably while maintaining or even improving the accuracy. This could be improved further by using factors which are flow-corrected.

     

High-pressure synthesis and crystal structure of silicon phosphate hydroxide, SiPO4(OH)

A new high-pressure phase, silicon phosphate hydroxide, was prepared at and 1000 °C in >98% purity. From X-ray diffraction on a pseudo-merohedrally twinned crystal, it was found that SiPO₄(OH) crystallizes in a monoclinic cell with space group P2₁/n (No. 14), , and Z=4. The refinement gave a conventional R_obs of 0.0320 and wR_obs of 0.0864 for the overlapped data from both twin components. In the structure, SiO₆ octahedra form chains along [101], with PO₄ tetrahedra alternating along the chain in the b-direction. The parallel chains link up with tetrahedral corners from other chains to form a 3-dimensional network. SiPO₄(OH) belongs to a structural family that includes HgSeO₄·H₂O. It is also related to the SbOPO₄ structure by a small distortion that lowers the symmetry from C2/c in SbOPO₄ to in SiPO₄(OH).     

High-pressure synthesis, crystal structure and magnetic properties of a new cuprate (Nd,Ce)2+xCaCu2O6+y

New phase (Nd,Ce)_2+xCaCu₂O_6+y was prepared at a high-pressure/high-temperature condition of 6 GPa and 1300°C. It had a nonstoichiometric composition close to Nd_2.16Ce_0.225CaCu₂O_6+y. According to X-ray diffraction pattern, the Nd_2.16Ce_0.225CaCu₂O_6+y phase has a tetragonal lattice with a = 3.845(1) Å, c = 19.349(5) Å. However, electron microscopic observations revealed a complicated shear structure for this phase. Magnetic susceptibility and magnetic hysteresis measurements were performed for the Nd_2.16Ce_0.225CaCu₂O_6+y sample and it was found that the phase undergoes a weak ferromagnetic transition at 150 K. Below ≈40 K, complicated magnetic behavior was observed suggesting the presence of second weak ferromagnetic transition near 40 K.