Effektivität der photochemischen Co-C-Bindungsspaltung in σ-Alkyl-Co(III) (salen)- und -Co(III) (salphen)-Komplexen

Efficiency of the Photochemical Co-C-Bond Cleavage in σ-Alkyl-Co(III)(salen)-and-Co(III)(salphen)-Complexes. The photodealkylation rate of RCo^III(chel) X complexes (R = methyl, ethyl; chel = salen, salphen; X = H₂O, py, PPh₃) depends on the nature of ligands and solvents as well as on the concentration of oxygen and scavengers for alkyl radicals. The rapid recombination of the fragments R. and Co(chel)X is responsible for the low quantum yields of the anaerobic dealkylation. The quantum yields may reflect the H-donating ability of the solvents used. Lewis bases X in the trans position generally cause a decrease of quantum yields relative to the pentacoordinated species RCo (chel). The anaerobic photolysis can be accelerated by the addition of scavengers for alkyl radicals (e. g. Koelsch radical, nitrosodurene, styrene). The quantum yield also increases in the presence of oxygen, preventing the recombination of the fragments of the cobalt-carbon bond scission by forming alkyl-peroxocomplexes ROOCo(chel)X. α-Hydroxyalkylradicals arising from the decomposition of the ROOCo(chel)X complexes via secondary reactions probably react with the starting σ-alkyl complexes and cause the dependence of quantum yields on the light intensity.     

Photolyse von ternären Fe(III)-Komplexen mit Oxalat- und Phenolat-Liganden

Photolysis of Ternary Fe(III)-Complexes with Oxalate and Phenolate Ligands The overall iron(II) quantum yields of the photolysis of mixed ligand complexes [Fe(C₂O₄)_3−nL_n]³⁻ (L = salicylate, sulfosalicylate or the dianion of catechol, sodium 3,5-sulfocatechol, tetrachlorcatechol) in aqueous solution within the spectral region 436 nm ≤ ^λ_irr. ≤ 546 nm are much smaller than those of the complexes [Fe(C₂O₄)_3−n(H₂O)_2n]³⁻²ⁿ (n = 0; 1; 2). This means that the intramolecular photoredoxreaction between iron(III) and the oxalate ligand is not sensitized by the L→Fe(III) charge transfer excitation. Moreover, filter effects through photoinactive complexes [FeL₂(H₂O)₂]⁻ or [FeL(H₂O)₄]⁺ probably give rise to the strong decrease of the quantum yields.     

Analyse von Acrylnitril-Styrol-Copolymeren mit Hilfe der Pyrolyse-Gaschromatographie

Copolymers of acrylonitrile and styrene with various compositions and molecular weights have been pyrolysed at a temperature of 500°C. The degradation products have been separated by means of gaschromatography and 16 compounds were identified. The most important products are cyanic acid, acetonitrile, acrylonitrile, propionitrile, toluene, ethylbenzene and styrene. The formation of these products has been investigated quantitatively as a function of the composition of the copolymers. Plotting the quantitatively determined amount of the cyanic acid as a function of the copolymer composition a linear slope resulted. Thus a method was developed to analyse copolymers of acrylonitrile and styrene. The formed amounts of acetonitrile, acrylonitrile and propionitrile during pyrolysis are independent on the molecular weights of the copolymers.     

Die Untersuchung von Sterin-Gemischen mit Hilfe der Dünnschicht-Chromatographie

Investigation of Steroid Mixtures by Thin-Layer Chromatography A new method of thin-layer chromatography on MgO-Al₂O₃-CaSO₄-plates was developed for the separation of natural mixtures of steroids in the form of their acetates. By this method, the formation of critical pairs, which was observed till now, could be avoided and considerably better separation could be achieved. Application of this new method to various vegetable oils showed in all cases the occurence of a steroid with a Rf-value corresponding to that of cholesterol. This steroid, occuring in considerable amounts especially in palm oil, was isolated from the same in centigram amounts by preparative thin-layer chromatography and thoroughly investigated. Melting point, X-ray structural analysis, infrared- and mass-spectra, optical rotation and rotational dispersion of this substance were identical with the corresponding data of cholesterol obtained from gall-stones. Thus it was proved that cholesterol occurs in plants as well.     

Synthese von Cystinpeptiden mit Hilfe der Festkörpermethode von Merrifield

The problem of sulfur protection in peptide chemistry can be circumvented by synthesis of symmetrical cystine peptides. Such peptides are available also by the MERRIFIELD method as follows: Coupling of excessive bis-tert.-butyloxycarbonyl-cystine with an aminoacyl resin leads to the formation of resin bound symmetrical and mixed disulfides. After reduction with a large excess of thiophenol the unreacted cystine-halves are washed out and the disulfide bridges are regenerated by subsequent oxidation with air in the presence of iron (III)-sulfate in dimethylsulfoxide/methylene chloride, or with a small excess of 2,2′-dipyridyldisulfide forming the desired resin bound symmetrical cystine peptide. However, and elongation of this peptide without side reactions is only possible, if the cystine residue is separated from the binding site on the resin by more than one amino acid residue.     

Zur Kenntnis der katalytischen Dimerisation von Acrylsäurederivaten mit Hilfe von Palladium-Komplexen. III. Reaktionen von β-Palladioacrylestern und deren Beziehung zur Katalytischen Reaktion

On the Knowledge of the Catalytic Dimerization of Acrylic Acid Derivatives by Palladium Complexes. III Reactions of β-Palladio Acrylates and Their Relation to the Catalytic Reaction Complexes of the type L₂PdCl(CH  CHCOOCH₃) (L₂ = 2 PPh₃ or Ph₂PCH₂CH₂PPh₂) were decomposed to dimethyl muconate by pyrolysis or by substraction of the phosphine ligands with (CH₃CN)₂PdCl₂ in acetonitrile. The last mentioned reaction gave Δ³-dimethyl dihydromuconate in the presence of hydrochloric acid. Δ³-Dimethyl dihydromuconate was also formed by decomposition of (Ph₂PCH₂CH₂PPh₂) PdCl (CH  CHCOOCH₃) with HBF₄ in acetonitrile, but the analogous reaction in methyl acrylate as solvent gave Δ²-dimethyl dihydromuconate. Thus, we have simulated the formation of the two main products of the catalytic dimerization of methyl acrylate with palladium(II)chloride in a stoichiometric manner. Mechanisms with hydride and carbene intermediates are discussed.     

Quantitative Bestimmung von Phosphatidylcholin mit Hilfe der HPLC

Quantitative Determination of Phosphatidyl Choline by Means of HPLC A HPLC method for a fast quantitative determination of phosphatidyl choline in soya bean lecithine is described. The separation was carried out on Li Chrosorb SI 60. The detection took place at 206 nm. Comparing this method with the results of the up to now used choline determination by Reineckat precipitation and by statistical evaluation it could be significantly established that the HPLC method (variation coefficient 1.1) is superior to the Reineckat method (variation coefficient 2.6).     

Analyse von Wachsen und Wachsmischungen mit Hilfe der Dünnschicht-Chromatographie

Analysis of Waxes and Mixtures of Waxes by Thin-Layer Chromatography A few commercial waxes were investigated by thin-layer chromatography. The following mobile phases and temperatures were employed: benzene, benzene + 0.5% acetic acid and benzene + 2% methyl acetate at 45°C; tetrachloroethylene at 80°C and tetrachloroethylene + 0.5% acetic acid at 70°C. A few examples showing the possibility of analyzing wax mixtures with the help of the methods described here, are given.     

Die Bestimmung von Schwermetallspuren in organischen Waschrohstoffen mit Hilfe der Atomabsorptions-Spektralphotometrie (AAS)

Determination of Heavy Metal Traces in Organic Raw Materials for Washing Agents Using Atomic Absorption Spectrophotometry (AAS) In the past years AAS has been widely employed for the determination of traces of metals in the ppm range. After a short historic account, the author explains the principle of the method and describes a fusion process applicable to organic raw materials for washing agents. The actual determination of the elements Fe, Cu, Cr, Ni and Mn are referred to. Finally, the author deals with the sensitivity of the method, its reproducibility and accuracy.     

Weitergehende Reinigung von Abwässern der Chemischen Industrie mit Hilfe von Aktivkohle

Further treatment of waste water in the chemical industry by use of activated carbon . Biological treatment has proved to be no longer adequate for numerous waste water streams emitted by chemical plants. Some of the pollutants entrained by the waste water feature poor biodegradability, and certain compounds even have a detrimental effect on the microorganisms of the activate sludge. Adsorption by activated carbon is one of the potential methods for eliminating such substances. Explanations refer to the physical phenomena of the process. Adsorption may be performed prior to or after biological treatment. Commercial-scale plants use granular activated carbon and use an intermittent process (fixed bed) or a continuous process (countercurrent adsorber). Possibilities and aspects are exemplified by plants using this process. Operating results are presented. A recent development combines the biological and adsorptive treatment which is based on the continuous admission of powdered activated carbon into the activated-sludge basin. Results obtained in a demonstration plant will be discussed. Cost-effective application of this technology is, however, conditional upon reactivation of spent carbon.     

Eine Übersicht zur Berechnung von Phasengleichgewichten mit Hilfe der UNIFAC-Methode

Zur Auslegung von Trennanlagen und für viele andere praktische Zwecke benötigt man die quantitative Kenntnis des Phasengleichgewichts. Dieses Phasengleichgewicht kann mit Hilfe von neueren Ansätzen für die Gibbssche Exzeßenthalpie recht gut aus den binären Konstanten berechnet werden. Da jedoch die Anzahl der technisch interessanten Systeme sehr groß ist, wird man in vielen Fällen nicht für alle beteiligten binären Systeme Phasengleichgewichtsdaten in der Literatur finden. In diesen Fällen ist es notwendig, die benötigte Information mit Hilfe allgemein anwendbarer Methoden vorauszuberechnen. Zur Zeit liefern die Inkrementenmethoden (ASOG , UNIFAC ) die besten Resultate. Bei diesen Inkrementenmethoden wird die flüssige Phase wie eine Mischung von funktionellen Gruppen behandelt. Dies hat den Vorteil, daß eine große Zahl technisch interessanter Systeme mit einer relativ geringen Anzahl von Parametern, die die Wechselwirkung zwischen den Gruppen beschreiben, berechnet werden kann, da die Anzahl der verschiedenen Strukturgruppen viel kleiner ist als die Anzahl der möglichen unterschiedlichen Moleküle. In diesem Übersichtsartikel sollen die Möglichkeiten der UNIFAC -Methode zur Berechnung von Phasengleichgewichten demonstriert werden. Die UNIFAC -Methode heute für Nichtelektrolytsysteme im Temperaturbereich von 275 bis 425 K und Drücke bis 10 bar anwendbar. A survey of the calculation of phase equilibria with the aid of the UNIFAC -Methode. In the design of diffusional separation processes and for many other practical purposes one needs quantitative estimates of phase equilibrium compositions. These compositions can today be predicted with good results using modern, two-parameter models for the excess Gibbs energy. However, since the number of different multicomponent mixtures of interest in chemical technology is very large, it is in practise often not possible to find experimental data in the literature for all the possible binary combinations. In these cases it is necessary to use a predictive approach. Today, group-contribution methods such as ASOG and UNIFAC may be used with confidence to predict liquid phase excess Gibbs energies. In these methods, the mixture is assumed to consist not of molecules but of the functional groups which, when added form the parent molecules. This has the advantage that a large number of mixtures of interest in chemical technology can be described in terms of relatively few parameters characterizing the interactions between the groups. This review article demonstrates the application of the UNIFAC method to various practical problems within phase equilibria. The UNIFAC method applies to mixtures of nonelectrolytes in the temperature range of 275–425 K and at pressures up to 10 bar.