Crystal Structures of 1,5,9,18,22,26-Hexaaza[11.11]-p-cyclophane Adducts; Two-dimensional Supramolecular Networks

Two newly identified supramolecular structures arise from self-assembly of the macrocyclic 1,5,9,18,22,26- hexaaza[11.11]-p-cyclophane salts with o-nitrophenol (C₂₈H₅₀N₆)⁴⁺·4(C₆H₄NO₂O)⁻ (1) and with HCl (C₂₈H₅₂N₆)⁶⁺·6Cl^-·4H₂O (2). In both cases two-dimensional supramolecular sheets are formed.     

Thermal decomposition of Cr(III) dithiocarbamates

The thermal stability of chromium(III) complexes with dithiocarbamate acid derivatives was studied. The general formula of these complexes is (RCS₂)₃Cr where: The thermal stability of these complexes was found to depend on the kind ofR and the decomposition occur in several stages.The final product of the decomposition of the complexes in the 20–600 temperature range investigated is chromium sulphide, Cr₂S₃ or with incomplete combusted sulfur atoms.

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Zusammenfassung Die Thermostabilität von Chrom(III)-Komplexen mit sauren Derivaten von Dithiocarbamat wurde untersucht. Die allgemeine Formel dieser Komplexe ist (RCS₂)₃Cr. Es wurde festgestellt, da\ die Thermostabilität dieser Komplexe von der Art von R abhängt und die Zersetzung in mehreren Stufen verläuft.Das Endprodukt der Zersetzung der Komplexe im untersuchten Temperaturbereich von 20 bis 600 ist Chromsulfid, Cr₂S₃, oder solches mit überschüssigem Schwefel.

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Résumé On a étudié la stabilité thermique des complexes du chrome(III) avec les dérivés de l'acide dithiocarbamique. La formule générale de ces complexes est (RCS₂)₃Cr où: On a trouvé que la stabilité thermique de ces complexes dépendait de la nature du radical et que la décomposition se déroulait en plusieurs étapes.Dans l'intervalle de température étudié, de 20 à 600, le produit final de la décomposition des complexes est le sulfure de chrome, Cr₂S₃, éventuellement accompagné de soufre résultant d'une combustion incomplÊte.

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(III) - . — (RCS₂)₃ Cr, , R . 20–600 Cr₂S₃ .

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The autors would like to thank Doc. dr h. J. F. Biernat for valuable discussions.     

Demixing in athermal mixtures of colloids and excluded-volume polymers from density functional theory

We study the structure and interfacial properties of model athermal mixtures of colloids and excluded volume polymers. The colloid particles are modeled as hard spheres whereas the polymer coils are modeled as chains formed from tangentially bonded hard spheres. Within the framework of the nonlocal density functional theory we study the influence of the chain length on the surface tension and the interfacial width. We find that the interfacial tension of the colloid-interacting polymer mixtures increases with the chain length and is significantly smaller than that of the ideal polymers. For certain parameters we find oscillations on the colloid-rich parts of the density profiles of both colloids and polymers with the oscillation period of the order of the colloid diameter. The interfacial width is few colloid diameters wide and also increases with the chain length. We find the interfacial width for the end segments to be larger than that for the middle segments and this effect is more pronounced for longer chains.     

Investigation of eutectic transformation of Zn−Al alloy by DTA

The paper discusses the investigation of crystallization of metals and alloys by differential thermal analysis (DTA). It was assumed that this method allows determination of the mechanism and kinetics of volumetric crystallization underiso conditions (e.g. anisothermal) on the basis of the parameters of the equation expressing an integral form of the DTA curve. From DTA, a course of eutectic transformation was determined for a technical Zn?Al alloy containing 4wt% Al. Investigations were carried out under continuous cooling at various rates and the kinetics parameters were determined with the KEKAM equation:-ln(1-x)=kl _n     

The Effect of the Catalyst Used on the Kinetics of Di-2-Ethylhexyl Maleate Synthesis

Kinetics of the esterification of maleic anhydride with 2-ethylhexanol in the presence of sulfuric acid, amphoteric tetrabutyl titanate or in the absence of external catalyst has been studied. The kinetic equations and kinetic parameters have been determined.     

Effect of temperature and concentration on the structure of N-methylacetamide-water complexes: Near-infrared spectroscopic study

Generalized two-dimensional (2D) FT-NIR correlation spectroscopy and chemometric methods have been used to study temperature-dependent spectral changes in pure N-methylacetamide (NMA) and NMA-water mixtures. We also examined the effect of varying water content on the structure of the mixture. It has been found that the extent of self-association of NMA in CCl4 is very high; the association occurs even at concentration of 0.001 M. In the pure liquid NMA, the population of the monomers is negligible and the structure is dominated by the linear associates. An increase in temperature reduces the number of hydrogen bonds, but in contrast to alcohols their strength remains nearly the same. This reflects a difference in the mechanism of thermal breaking of the associates of NMA and alcohols. The present results reveal that the interaction between NMA and water in the NMA-rich region (X(H2O) < 0.1) does not have a significant effect on the intrinsic structure of NMA. The structure of NMA is dominant, and the molecules of water do not form separate clusters but are dispersed and incorporated into the structure of NMA. We did not observe the presence of the free OH groups in the mixture. This led to the suggestion that each molecule of water forms two hydrogen bonds to two different molecules of NMA. An analysis of the asynchronous spectra reveals that most of the peaks observed in the asynchronous spectra, constructed from the temperature-dependent data, simply result from the frequency shift. This assumption is supported by the simulation studies.     

Synthesis of new fluorinated 1,5-benzoxazepine derivatives

A simple approach to the fluorinated 1,5-benzoxazepine ring system is described. By reacting commercially accessible aminophenols 1 and the trifluoroacetylvinyl ether 2, high yields of enaminones 3 were obtained. Functionalization of methyl group of compounds 3 gave rise to dieneamines 4 that were cyclized in acidic environment to benzoxazepine derivatives 5.     

Sensitive spectrophotometric determination of tin with Pyrogallol Red and cetyldimethylbenzylammonium ions

Summary Tin(IV), in the presence of cetyldimethylbenzylammonium chloride (CDBA), forms with Pyrogallol Red (PR) a complex SnPR-CDBA. This complex floates at the interface between hexane and aqueous medium. It dissolves in acetone and can be advantageously used for the determination of tin. The molar absorptivity is 6.5×10⁴ l·mole^–1·cm^–1 at 480 nm. The method is selective when citric acid is used as masking agent. Phosphate, fluoride, EDTA, nitrite and sulphide interfere.

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Zusammenfassung Zinn(IV) bildet mit Pyrogallolrot (PR) in Gegenwart von Cetyldimethylbenzylammoniumchlorid (CDBA) einen Komplex. Dieser wird flotiert, in Aceton gelöst und zur Bestimmung von Zinn verwendet. Der molare Absorptionskoeffizient bei =480 nm beträgt =6,5·10⁴ l·mol^–1 cm^–1. Die Methode ist selektiv, wenn Zitrate zur Maskierung verwendet werden. Es stören Phosphat, Fluorid, ÄDTA, Nitrit und Sulfid.

     

Influence of perfluorinated carboxylic acids on ion-pair reversed-phase high-performance liquid chromatographic separation of betacyanins and 17-decarboxy-betacyanins

The ability of trifluoroacetic acid, pentafluoropropionic acid and heptafluorobutyric acid to act as ion-pairing agents for betacyanins and 17-decarboxy-betacyanins during HPLC analysis on a Luna C18(2) reversed-phase column is reported. While the perfluorinated carboxylic acids affect the retention of both groups of compounds by changing the pH of the mobile phase, the possibility of ion-pair chromatography for 17-decarboxy-betacyanins was noticed. In order to explain the accessibility of the positive charge for the counter-anion in decarboxy-betacyanins, the mesomeric structures of the polymethine system at low pH (around a value of 1.5), when the carboxylic group in the 2 position is protonated, should be taken into consideration.     

New phosphonic analogs of aspartic and glutamic acid by aminoalkylation of trivalent phosphorus chlorides with ethyl acetyloacetate or ethyl levulinate and benzyl carbamate

Preparation of the phosphonic analogs of -methylaspartic (4 a–d), glutamic (7 a–b) and -methylpyroglutamic (5 a–b) acids by aminoalkylation of trivalent phosphorus chlorides with ethyl esters of oxoalkyloacids and benzyl carbamate is described. The phosphonic analogs of pyroglutamic acid (8 a–b) was obtained by the cyclization of the corresponding esters (9 a–b). The stability of the phosphonic analogs of pyroglutamic acid in acidic and alkaline media was also studied.

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Die Herstellung von neuen Phosphonanalogen der Asparagin- und Glutaminsäure in der Reaktion von trivalenten Phosphorchloriden mit Ethyl-acetyloacetat oder Ethyl-lävulinat bzw. Benzylcarbaminat

Zusammenfassung Es wurde die Darstellung der Phosphonanalogen der -Methylasparaginsäure (4 a–d), Glutamin- (7 a–b) und -Methylpyroglutaminsäure (5 a–b) in der Reaktion der trivalenten Phosphorchloride und der Oxoalkansäureethylester sowie des Benzylcarbaminats beschrieben. In der Ringschlußreaktion der Ester (9 a–b) erhält man Phosphonanaloge der Pyroglutaminsäure. Die Stabilität der Analogen der Pyroglutaminsäure wurde in sauren und alkalischen Medien geprüft.