Über Chrom(II)-carboxylate und Halogenochromate(II)

Highly pure chromium(II) acetate, was obtained from chromium powder and anhydrous acetic acid in the presence of a small amount of acetylhalide. Cr^II acetate reacts with acetyl halide in anhydrous acetic acid to sesquisolvates like CrCl₂ · 3/2 CH₃COOH. If one equivalent of alkali acetate or an organic nitrogen base is added to solutions of Cr^II acetate in acetyl halide/acetic acid mixtures, trihalochromates(II) are precipitated which are hexagonal in structure, except the ammonium and the potassium salt. With two equivalents of alkali or ammonium acetate tetrachlorochromates(II) of cesium, rubidium and ammonium are precipitated. They are tetragonal in structure (K₂NiF₄ type). Using pyridinium acetate with various mixtures of acetyl bromide and acetic acid, only the solvates (PyH)₃(CrBr₅) · 2CH₃COOH is formed.     

L?sungsmitteleinflu? auf das Redoxverhalten des Hexakismethylisonitrilmangan (I) ions

The redox behaviour of hexakismethylisonitrilmanganese(I) [MnL ₆ ⁺] has been studied in acetic acid, dichloromethane, 1,2-dichloroethane, propylenecarbonate, butyrolactone, methanol, ethanol, nitromethane, acetonitrile, N-methyl-2-pyrrolidinone, dimethylformamide, dimethyl sulfoxide and water. The reversible diffusion-controlled oxidation MnL ₆ ⁺/MnL ₆ ²⁺ could be observed in all solvents studied, on both the dropping mercury electrode and the stationary platinum electrode. Employing tetrabutylammonium perchlorate as supporting electrolyte, the oxidation MnL ₆ ²⁺/MnL ₆ ³⁺ was observable only in acetic acid, nitromethane, 1,2-dichloroethane, dichloromethane, propylenecarbonate, butyrolactone and acetonitrile. In all other solvents oxidation of the solvent preceded the oxidation MnL ₆ ²⁺/MnL ₆ ³⁺. Poorly defined polarographic waves attributable to the one electron reduction of the MnL ₆ ⁺ were observed in butyrolactone, propylenecarbonate, acetonitrile, dimethylformamide, N-methyl-2-pyrrolidinone and dimethyl sulfoxide. All potential values were recorded versus bisbiphenylchromium(I)-iodide [BBCr(I)J], the problems of measuring against external aqueous reference electrodes are discussed. The redox potential of the process MnL ₆ ⁺/MnL ₆ ²⁺ was found to be a function of the donor properties of the solvents used; the effects of outer sphere coordination on the redox behaviour of this couple are discussed. No effect of the supporting electrolytes tetrabutylammonium perchlorate, tetraethylammonium nitrate and tetraethylammonium perchlorate on the redox behaviour of MnL ₆ ⁺ was found. The UV-spectrum of MnL ₆(PF₆)₂ has been recorded.     

Die Fehlordnung des Natriumazides und deren Einfluß auf die thermische Zersetzung, 2. Mitt.: Berechnung der Polarisationsenergie für den Ausbau eines Ionenpaares aus Natriumazid

Zusammenfassung Zur Berechnung der Polarisationsenergie nach dem Konzept eines starren Gitters wird zuerst die Polarisierbarkeit des N₃ ^– in NaN₃ berechnet. Mit den bekannten Daten für die Brechungsindizes in den Hauptachsen kann nach einer Methode vonMott der erforderliche Polarisierbarkeitstensor aufgestellt werden. Um Argumente für die Berechtigung des Verfahrens zu erhalten, wird die Polarisierbarkeit des Chlorions in NaCl analog berechnet. Unter Zugrundelegung der vonPauling gegebenen Strukturdaten des NaN₃ wird dann die Polarisationsenergie mit Hilfe verallgemeinerter Grundlagen für den Ausbau eines Ionenpaares aus NaN₃ und NaCl berechnet, während Dipol—Dipol-Wechselwirkungen abgeschätzt werden. Vernachlässigt man den Beitrag der Verschiebungspolarisation, so erhält man für die gesamte Polarisationsenergie bei NaN₃ 3,4 eV und bei NaCl 4,2 eV, wasSchottky-Fehlordnung vermuten läßt. Der Zusammenhang mit der Fehlerbildungsenergie wird im Anschluß daran diskutiert.

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For the determination of the polarization energy based upon the model of a rigid lattice, the polarizability of the azide ion in sodium azide is calculated. WithMott's method and the known data for the refractive indices along the main directions the polarizability tensor can be constructed. An analogous calculation is performed for the polarizability of the chlorine ion in NaCl in order to test arguments of our method. WithPauling's data of the NaN₃ structure, the polarization energy for the removal of an ion pair from both NaN₃ and NaCl is calculated by means of a generalized basis estimating dipole—dipole interactions. Neglecting the displacement polarization, one obtains for the total polarization energy a value of 3,4 eV for NaN₃, and 4,2 eV for NaCl, resp., pointing atSchottky-disorder. The connection with the energy of defect formation is discussed hereupon.

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A simple cobalt catalyst system for the efficient and regioselective cyclotrimerisation of alkynes

The intermolecular cyclotrimerisation of terminal and internal alkynes can be catalysed by simple cobalt complexes such as a CoBr2(diimine) under mild reaction conditions when treated with zinc and zinc iodide with high regioselectivity in excellent yields.     

Furancarbonsäuren aus Rinderharn

Furancarboxylic Acids in Cattle Urine The urine of cattle contains large amounts of furancarboxylic acids. The same acids were isolated from rats after feeding with methyl esters of the so-called F-acids. Since the F-acids were not detected in cattle-food, they must be produced somewhere in the body of cattle.     

Formation and reactions of metal-metal bonded heterobimetallic (C5H4PR2)-bridged (Zr-Ir) and (Zr-Rh) complexes: evidence for the participation of metal hydride intermediates

Treatment of the complexes [(C(5)H(4)PR(2))(2)Zr(CH(3))(2)](b: R = isopropyl; c: R = cyclohexyl) with the reagent HIr(CO)(PPh(3))(3) (2b) yield the heterobimetallic complexes [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Ir(CO)(PPh(3)))] (4b, 4c) with evolution of methane. The reaction of the -PPh(2) substituted analogue with initially yields an intermediate [(H(3)C)(2)Zr(mu-C(5)H(4)PPh(2))(2)Ir(H)(CO)(PPh(3))] 5a, that still contains both methyl groups at zirconium and does not contain a metal-metal bond. At room temperature, the intermediate reacts further with methane formation to eventually yield the (Zr-Ir) complex 4a. The corresponding [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Rh(CO)(PPh(3)))] complexes 3a (R = Ph) and 3b (R = isopropyl) react cleanly with isopropyl alcohol to liberate methane and yield the corresponding [mu-C(5)H(4)PR(2))(2)(Me(2)CHO-Zr-Rh(CO)(PPh(3)))] products (7a, 7b). Carefully monitoring the reaction of with Me(2)CHOH by NMR revealed that the Zr-Rh functionality is attacked first to give the intermediate [Me(Me(2)CHO)Zr([micro sign]-C(5)H(4)PR(2))(2)Rh(H)(CO)(PPh(3))] (6b). This intermediate then reacts further to cleave off methane and re-form the (Zr-Rh) metal-metal bond to yield the product 7b. The tetrametallic mu-oxo-(Zr-Rh) metallocene derivate 11a was obtained starting from the (Zr-Rh) complex 3a and it was characterized by X-ray diffraction. It may be that this reaction is also initiated by H-OH addition to the [Zr-Rh] metal-metal bond.     

Thermodynamische Untersuchungen im System Gold—Cadmium

Zusammenfassung Flüssige und feste Legierungen im System Au–Cd wurden von 60 bis 90 At% Cd zwischen 653° und 873°K mit derEMK-Methode untersucht und thermodynamische Eigenschaften berechnet. Die Aktivitäten von Cd zeigen stark negative Abweichungen vom idealen Verhalten. Die partiellen molaren Enthalpien sind negativ und verschieben sich mit zunehmender Temperatur zu weniger negativen Werten, die partiellen molaren Entropien sind positiv und nehmen mit zunehmender Temperatur zu. Aus eigenen Werten und Literaturdaten wurden integrale thermodynamische Größen für die Schmelzen im gesamten System Au–Cd bei 1000°K berechnet. Für einige feste Cd-reiche Phasen wurden ebenfalls Aktivitäten erhalten und aus den Knickpunkten derEMK-Temperatur-Kurve Temperaturen von Phasenübergängen bestimmt.

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Thermodynamic investigations in theAu–Cd-system

Liquid and solid alloys in the Au–Cd system were investigated between 60 and 90 at % Cd and 653°–873°K by theemf method, and thermodynamic properties were calculated. The activities of Cd exhibit strong negative deviations from ideal behavior. Partial molar enthalpies are negative and become less so with increasing temperature; partial molar entropies are positive and increase with increasing temperature. A consistent set of integral thermodynamic data for liquid solutions of the entire Au–Cd system at 1000°K were calculated using values taken from the literature. Activities for some solid Cd-rich phases were also obtained. From discontinuities in theemf vs. temperature curve temperatures of phase transitions were determined.

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Herrn Prof. Dr.H. Nowotny gewidmet.     

The probabilistic solution of the dirichlet problem for\tfrac{1}{2}\Delta + \left\langle {a,\nabla } \right\rangle + b with singular coefficients

We investigate weak solutions ofLu=?p, whereL= \(\tfrac{1}{2}\Delta + \left\langle {a,\nabla } \right\rangle + b\) and |a|²,b andp belong to the Kato classK ^d (d≥3). We shall characterize the weak solutions by a probabilistic mean value property. This characterization includes a continuity principle. Our second regularity result states that for a weak solutionu, |?u|² belongs locally to K^d. Regarding the inhomogeneous Dirichlet problem forL, we shall prove the corresponding gauge theorem and an existence and uniqueness result.     

Zur Synthese von Human-Big-Gastrin I

The synthesis of the tetratriacontapeptide amide corresponding to the revised primary structure of human big gastrin I is described. For this purpose the fragments were designed in view of the maximum use of those utilized in our previous synthesis of human big gastrin I according to the first sequence proposal. Consequently the key tripeptide-Pro-Pro-His- (sequence 7–9) was prepared in suitably protected form to be used as amino or carboxyl component for assembly of the segments 1–9 and 1–14, respectively. Final condensation of the latter nona- and tetradecapeptide derivatives with the C-terminal segments 10–34 and 15–34 via the azide and the dicyclohexylcarbodiimide/N-hydroxysuccinimide procedure, respectively, leads to crude fully protected human big gastrin I. Upon deprotection by exposure to trifluoroacetic acid in presence of ethanedithiol-(1,2) as scavanger, ion exchange chromatography and partition chromatography, the desired tetratriacontapeptide amide was isolated in satisfactory yield with a high degree of purity. The identical immunological behaviour of the synthetic material, if compared with that of natural human big gastrin I, represents ulterior strong evidence for the correctness of the newly proposed structure for this putative prohormonal form of the gastrins.

Kurzmitteilung:Wünsch E., Wendlberger G., Mladenova-Orlinova L., Göhring W., Jaeger E., Scharf R., Gregory R. A., Dockray G. J., Hoppe-Seyler's Z. Physiol. Chem.362, 179 (1981).