Enantioselective Synthesis of Spiro Heterocyclic Compounds Using a Combination of Organocatalysis and Transition-Metal Catalysis

Over the last ten years, the combination of organocatalysis with transition metal (TM) catalysis has become one of the most important toolboxes used for synthesizing optically pure compounds containing chiral quaternary centers, including spiro heterocyclic molecules. The dominant method in the enantioselective synthesis of spiro heterocyclic compounds based on synergistic catalysis includes chiral aminocatalysis and NHC catalysis, as already established covalent organocatalytic strategies. Another area of organocatalysis widely combined with TM catalysis producing enantiomerically enriched spiro heterocyclic compounds is non-covalent catalysis, dominated by chiral phosphoric acids, thiourea, and squaramide derivatives. This review article aims to summarize enantioselective methods used for constructing spirocyclic heterocycles based on a combination of organocatalysis and transition metal catalysis.     

Treatment and Stability of Sodium Hyaluronate Films in Low Temperature Inductively Coupled Ammonia Plasma

Surface of sodium hyaluronate films was modified in the inductively coupled low temperature ammonia plasma. The amount of bonded nitrogen was measured by the XPS method. The optical emission and temperature of the sample surface were measured during sample processing. Increased processing time and increased discharge power caused a rise of nitrogen concentration on the surface of hyaluronan films, though this effect is limited due to surface saturation and sample destruction at elevated discharge power.     

Organic xerogels based on condensation of different m-substituted phenols with formaldehyde

Four samples of organic xerogels have been prepared by polycondensation of different m-substituted phenols (3-aminophenol, m-cresol, phenol and resorcinol) with formaldehyde and subsequent drying. From the set of tested solvents, n-butanol has been chosen as the most suitable one. The reactivity of the m-substituted phenols was ascertained in the order phenol < m-cresol < resorcinol < 3-aminophenol. Phenol and m-cresol did not completely react with formaldehyde during polycondensation reactions. The used type of m-substituted phenol strongly influenced the properties of the final material (the appearance of the organic xerogels, the values of densities and shrinkage after drying, the amount of humidity released during drying and the carbon yield after pyrolysis). The pyrolytic process has been evaluated by TG–MS as three-step process. The first step was characterised as volatile substances loss (n-butanol and water) and mostly CO₂ evolution, the second step as evolution of the rest volatiles and the beginning of the carbonisation processes, whilst during the third step merely carbonisation reactions occurred. On the basis of all considered results, 3-aminophenol has been evaluated as the most appropriate precursor for carbon xerogel preparation. It is cheap and the most reactive; it exhibited the lowest values of density, shrinkage and humidity content as well as relatively high carbon yield.     

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH₃, CO₂ and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH₃, CO₂, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H₂ and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.     

Nickel Poisoning of a Cracking Catalyst Unravelled by Single-Particle X-ray Fluorescence-Diffraction-Absorption Tomography

Ni contamination from crude oil in the fluid catalytic cracking (FCC) process is one of the primary sources of catalyst deactivation, thereby promoting dehydrogenation–hydrogenation and speeding up coke growth. Herein, single-particle X-ray fluorescence, diffraction and absorption (μXRF-μXRD-μXAS) tomography is used in combination with confocal fluorescence microscopy (CFM) after thiophene staining to spatially resolve Ni interaction with catalyst components and study zeolite degradation, including the processes of dealumination and Brønsted acid sites distribution changes. The comparison between a Ni-lean particle, exposed to hydrotreated feedstock, and a Ni-rich one, exposed to non-hydrotreated feedstock, reveals a preferential interaction of Ni, found in co-localization with Fe, with the γ-Al₂O₃ matrix, leading to the formation of spinel-type hotspots. Although both particles show similar surface zeolite degradation, the Ni-rich particle displays higher dealumination and a clear Brønsted acidity drop.     

The complex conductivity of the plasma of a d-c glow discharge in Ne

In paper [1] Fang derived an expression for the complex conductivity of plasma assuming that the distribution function of the electrons is Maxwellian and the collision frequency is directly proportional to their velocity. Since the assumptions are approximately satisfied in the positive column of a d-c glow discharge in Ne, the applicability of Fang's relation is investigated for this case.

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[1] , . , .

     

Bestimmung der Relaxationslänge der Elektronentemperatur in der positiven Säule der Glimmentladung

Zusammenfassung Die vorgenommenen Messungen und deren Vergleich mit den nach der Beziehung (2a) erwarteten Werten zeigen, daß die vorgelegte Methode zu einer verhältnismäßig genauen Messung der Relaxationslänge der Elektronentemperatur im Entladungsplasma dienen kann. Die Ergebnisse zeigen gleichzeitig, daß die theoretische Beherrschung der Schichtungserscheinung im Plasma der positiven Säule bereits jetzt schon neue Möglichkeiten in der Diagnostik des Plasmas eröffnet.

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A method of measuring the relaxation time of the temperature of electrons in the positive column of an electric discharge is described. The method uses measurements of the phase shift between the course of the electron temperature and that of the concentration of electrons in artificially excited moving striations of small amplitude. These data and the values measured for the electric field and temperature of the electrons in a homogeneous column are used to calculated the relaxation time of the electron temperature on the assumption that the diffusion of the electron temperature has no substantial influence on the time.

     

Microwave investigation of acoustic waves in low-pressure plasma

This paper deals with measurements of changes in electron concentration in acoustic waves excited mechanically in a low-pressure slightly ionized plasma by means of a microwave method. The measurements were performed by means of a rectangular resonator in the 3 GHz band. Periodic changes in the rhythm of the acoustic frequency of the electron concentration have been measured. A hypothesis of the origin of the changes in electron concentration has been suggested.Finally, the authors express their thanks to Prof. Dr. V. Kunzl and Prof. J. Kracík, Dr.Sc., for support and valuable suggestions during the preparation of this paper.     

Contributions to the basic problems of complexometry--XXII: determination of thorium and scandium in the presence of each other

A new method for the determination of thorium and scandium in the presence of each other is presented. Two aliquots of the solution are necessary. In one the sum of thorium and scandium is determined by direct titration with DCTA. In the second, thorium and scandium are treated with an excess of TTHA, phosphate is added, and zinc is used to titrate the excess of TTHA and to displace the scandium from its TTHA complex.     

1-Hydroxy-ethylidene-1,1-diphosphonic acid as a titrimetric agent

1-Hydroxy-ethylidene-1,1-diphosphonic acid (HEDPHA) has been proposed as a highly selective titrimetric reagent for thorium. In the presence of 1,2-diaminocyelohexanetetra-acetic acid (DCTA) a soluble binuclear ternary complex, Th(2)(DCTA)(2)(HEDPHA), is formed. The determination of thorium is carried out in a slightly acidic medium, buffered with urotropine, with 0.025M HEDPHA, and Xylenol Orange as indicator. DCTA masks all bivalent metals, rare earths, scandium, yttrium, bismuth, iron, gallium and indium. Only zirconium, titanium, aluminium and large amounts of thallium(III) interfere.