Kalorimetrische Untersuchungen des Wassereinflusses auf den Lösungsvorgang von Aerosol OT in apolaren Lösungsmitteln

Calorimetric Investigations of the Effect of Water on the Solution Process of Aerosol OT in Apolar Media. Heats of solution of Aerosol OT in apolar solvents are influenced considerably by already small amounts of water. Calorimetric investigations of the solution process with differently dried surfactant and solvent samples showed the predominating effect on the heats of hydration with regard to the ionic and polar groups of the surfactant. Only if the hydration is finished prior to the process of solution, the latter is endothermic. An estimation of the various enthalpic contributions demonstrates that the destruction of the coherence of the built-in water within the surfactant is decisive in the latter case. Two models corresponding to definite structures of the liquid crystalline mesophase of the surfactant show very satisfactory agreement with the experimental ΔH-values.     

Elektronenspinresonanz freier Radikale bei photochemischen Reaktionen von Ketonen in Lösung

Transient alkyl and acyl radicals are detected and identified by electron spin resonance during UV.-Irradiation of dialkyl and alkyl aryl ketones in liquid solutions. They are formed by the primary processes of α-cleavage, intermolecular photoreduction or α-chloro elimination. For several ketones a temperature dependent competition between α-cleavage and photo-reduction is observed indicating a higher energy of activation for the cleavage than for the reduction process. The results are discussed with respect to the photochemical behaviour of the ketones. Electron spin resonance parameters are reported for a variety of radicals. In particular ¹³C coupling constants support a sigma type structure of acyl radicals and require a nearly planar radical center of t-butyl and isopropyl radicals.     

Übergangsmetall-Organoverbindungen in superkritischem Kohlendioxid: Löslichkeiten,Reaktionen, Katalysen

Organometallics of Transition Metals in Supercritical Carbon Dioxide: Solubilities, Reactions, Catalysis Monomeric compounds of the type Cp₂M (p. e. M = Fe, Co, Ni) are soluble in liquid or supercritical CO₂ (”︁scCO₂”︁”︁) without any reaction with the solvent. The polymeric compounds zincocene or manganocene form with CO₂ insoluble CO₂ insertion products. As well homoleptic metal carbonyls as a number of ligand-stabilized metal carbonyls are also soluble in scCO₂. Fe(CO)₅ reacts photochemically in this solvent to Fe₂(CO)₉ and thermically to Fe₃(CO)₁₂. The highly reactive (cdt)Ni(0) (cdt: cyclododeca-1,5,9-triene) is soluble in liquid CO₂. A reaction with the solvent could not been observed. Solved in scCO₂ (cdt)Ni reacts thermically to form Ni after a short time. CpCo(cod) catalyzes slowly the cyclo-cooligomerization of hex-3-yne with acetonitrile to form 2,3,4,5-Tetraethyl-6-methylpyridine. Propargylic alcohol reacts under formation of cyclotetrameres with a selectivity of 90% using (cod)₂Ni or (cdt)Ni as catalysts, hex-3-yne in and with carbon dioxide under selective formation of tetraethyl-2-pyrone when the catalyst system R₃P/(cod)₂Ni (R: Me, Et) is used. In situ IR measurements show that the catalytically active species will be desactivated by formation of nickel carbonyl complexes. The catalytic oxidation of cyclooctene to form cycloocteneoxid with t-BuOOH using Titan(IV)-isopropylate as soluble catalyst proceeds less selectively, however in the presence of Mo(CO)₆ the epoxid is formed in good yields and in a highly selective reaction.     

Anwendung von Klassifikationsverfahren zur Interpretation von Lösungsmitteleinflüssen auf EPR-Spektren

Use of Classification Methods to Interpret the Influence of Solvents on Parameters of EPR Spectra The influence of solvents on EPR spectra of Cu^II-Acetylacetonate (registered at room temperature) was investigated. The classification of mean values of the g-tensors and coupling constants using different clustering methods lead to groups of solvents which are related to the respective substance classes. The analysis of the relationship between EPR data and solvent parameters showed, that there exists a close relation between Lewis basicity of solvents and classification found by using clustering methods.     

Chemischer Transport fester Lösungen: Der chemische Transport von Mischkristallen im System Co3O4 /CoGa2O4

Chemical Transport of Solid Solutions: Transport Phenomena in the Co₃O₄ /CoGa₂O₄ System Chemical transport reactions are a suitable pathway to the preparation of mixed spinels Co(Ga, Co)₂O₄ in the Co₃O₄/CoGa₂O₄ system. Solid solutions with specific Co^III/Ga^III ratios are accessible via variation of the source material compositions, because Co₃O₄ and CoGa₂O₄ are completely miscible. Electron microprobe analyses indicate the beginning of a zoning process in the crystals deposited. Experiments are consistent with thermodynamic calculations.     

Der Einfluss der Temperaturführung auf die Kinetische Auswertung Nichtisothermer Reaktionen

Zusammenfassung Das Problem der rationellen Lösung des Zeitintegrals stand bei der kinetischen Auswertung nichtisothermer Prozesse häufig zur Diskussion. Nun werden für lineare und nichtlineare Aufheizung gemäß dT/dt=Q·T_b mitb von 4 bis –2 Auswerteverfahren vorgestellt, die in jedem Fall eine vollständige Korrektur derjenigen kinetischen Parameter gestatteten, die durch linearisierte Auswertung erhalten worden sind. Diese Methode der vollständigen Exponentialintegrale zeigt, daß eine klare Abstufung nach dem Typ der Aufheizung besteht. Die notwendigen Korrekturen fürb=1, 2 und 3 sind kleiner als fürb=0 d.h. für lineare Aufheizung. Die vier Korrekturtabellen sind für Verfahren der kinetischen Analyse anwendbar, denen ein Aktivierungsansatz nach Arrhenius bzw. Eyring zugrunde liegt. Die Realisierung nichtlinearer Aufheizprogramme wird empfohlen.

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The problems of rational solution of the time integral in kinetical evaluation of nonisothermal processes have often been discussed. Evaluation procedures are now presented for linear and nonlinear heating according to dT/dt=Q·T^b, withb between 4, and –2. In every case a complete correction of the kinetical parameters is possible if they are obtained by linearized plotting. This method of complete exponential integrals shows a clear graduation with the type of heating function. The corrections necessary forb=1, 2 and 3 are less than those forb=0, i.e. linear heating. Four tables of correction values are applicable to all procedures of kinetical analysis which are based on activation parameters from the Arrhenius or Eyring equations. Nonlinear heating programmes are recommended.

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Résumé On a souvent discuté les problèmes soulevés par la solution rationnelle de l'intégrale du temps dans l'évaluation cinétique des processus non-isothermes. On présente ici des méthodes d'évaluation dans le cas de chauffages linéaire et non-linéaire, selon dT/dt=Q·T^b avecb entre 4 et –2. Une correction complète des paramètres cinétiques est possible dans tous les cas, si ceux-ci ont été obtenus par des fonctions linéarisées. Cette méthode d'intégration complète des exponentielles montre une graduation nette selon le type de la fonction du chauffage. La correction nécessaire pourb=1, 2 et 3 est inférieure à celle pourb=0, c'est-à-dire pour le chauffage linéaire. Quatre tables de correction basées sur les paramètres d'activation des équations d'Arrhenius et respectivement d'Eyring peuvent être appliquées à tous les procédés de l'analyse cinétique. On recommande de réaliser des programmes de chauffage non-linéaires.

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