Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. I. Die Festkörperreaktion von β-Ga2O3 mit NiO

The solid state reaction in a sandwich type diffusion couple of NiO and β-Ga₂O₃ has been investigated between 1240 and 1550°C in air and inert gas atmosphere.Optical microscope and X-ray methods are used to identify the reaction product, which is a singlephased spinel of the general formula $\text{Ni}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$. The homogeneity range of the spinel phase was investigated by X-ray methods; there is a high solubility of β-Ga₂O₃ in the spinel lattice.The growth of the thickness of the reaction layer follows a parabolic rate law, and therefore a diffusion process must be rate determining. The activation energy of the rate controlling step is 82 kcal/mole.Pt-marker experiments are not sufficient for determining the reaction mechanism. Investigations with an electron-probe microanalyzer, an connection with a modified marker technique, resulted in a Wagner-mechanism of counterdiffusion of cations for formation of nickel-gallium spinel; the total amount in Ga³⁺ ions is lost for spinel formation before there is an appreciable solubility of gallium in NiO.     

Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. IV. Reaktionen 2. Art im System CoO-β-Ga2O3

The solid-state reaction of the second kind in a sandwich type diffusion couple of $\text{Co}{}_{\mathrm{1?z}}\text{Ga}{}_{\mathrm{<mtext>2z</mtext><mtext>3</mtext>}}\text{O}$ and β-Ga₂O₃ has been investigated between 1249 and 1550°C in air. The quantity z, which corresponds to the saturation concentration of β-Ga₂O₃ in CoO, was determined as a function of temperature by X-ray methods and the optical microscope; the homogeneity range of the spinel phase $\text{Co}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$ was investigated also. The growth of the thickness of the reaction layer follows a parabolic rate law; the activation energy is 71.6 kcal/mole. A comparison of reaction rate constants of the first and second kind in connection with experimental results, achieved with a modified marker technique, leads to confirmation of the Wagner mechanism for the formation of CoGa₂O₄ spinel as supposed before by Laqua. Reaction rate constants of the second kind, calculated from interdiffusion profiles in CoO-β-Ga₂O₃ diffusion couples, are in good agreement with experimental values. Presented data are used for estimating interdiffusion coefficients for the CoO-β-Ga₂O₃ system according to theoretical aspects developed by Pelton, Schmalzried, and Greskovich.     

Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden II. Tracerdiffusion von 63Ni2+ und 67Ga3+ im Nickel-Gallium-Spinell

The self-diffusion coefficients of ⁶³Ni²⁺ and ⁶⁷Ga³⁺ have been measured in nickel-gallium spinels of the general formula $\text{Ni}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$ between 1653 and 1838 K using the restactivity method. Thin radioactive oxide layers are produced on inactive sample surfaces by sedimentation from aqueous solution. The sample composition corresponds to the solubility limit of NiO, respectively, β-Ga₂O₃ in the spinel lattice.It has been concluded that diffusion of Ni²⁺-and Ga³⁺-ions occurs via vacant cation sites.The values obtained for the two cations, which are in the same order of magnitude, are used to calculate the rational reaction constants for NiGa₂O₄ formation after Schmalzried.There is a satisfying agreement between these reaction constants and those values determined by thickness measurement of spinel reaction layers; the agreement between values of activation energy is very good.It is suggested that NiGa₂O₄ formation proceeds after the Wagner mechanism of counterdiffusion of cations.     

Zur Reaktionsweise von Enaminen mit Cyclopropenonen V. Einsatz von β-Carbonyl-enaminen

Diphenylcyclopropenone ( 10 ) was heated with five different β-carbonyl-enamines, namely 4-pyrrolidino-pent-3 E-en-2-one ( 12 ), 4-dimethylamino-pent-3E-en-2-one ( 13 ), 4-dimethylamino-but-E-en-2-one ( 14 ), 3-dimethylamino-1-phenyl-prop-E-en-1-one ( 15 ) and ethyl 3-pyrrolidino-isocrotonate ( 16 ). The resulting reactions were more sluggish than those of 10 with ordinary enamines. The main reaction (between 10 and 69% yield) was in all cases a ‘C, N-insertion’. The major products were: from 12 : an inseparable mixture of 4-methyl-6-oxo-2,3-diphenyl-hepta-2E, 4E-dienoic acid pyrrolidide ( 17 ) and its 2Z, 4E-stereomer ( 18 ); from 13 : 4-methyl-6-oxo-2, 3-diphenyl-hepta-2E-dienoic acid dimethylamide ( 19 ) and its 2Z, 4E-stereomer ( 20 ); from 14 : 6-oxo-2, 3-diphenyl-hepta-2E, 4E-dienoic acid dimethylamide ( 21 ); from 15 : 6-oxo-2,3,6-triphenyl-hexa-2E, 4E-dienoic acid dimethylamide ( 22 ); and from 16 : 5-ethoxycarbonyl-4-methyl-2, 3-diphenyl-penta-2E, 4E-dienoic acid pyrrolidide ( 23 ) and its 2Z, 4E-stereomer ( 24 ). The constitutions of 17 to 24 were derived mainly from spectral properties. For these products the E-configuration at the 4,5-double bond was assigned on the assumption that the insertion of the side-chain (cyclopropenone carbons) between the enamine carbon and nitrogen atoms occurred with retention of configuration, as had been concluded earlier. This was confirmed in the cases of 21 and 22 by the trans-coupling between H? C(4) and H? C(5) in the ¹H? NMR. spectrum, the educts ( 14 and 15 ) having the E-configuration. The configurational difference between the stereomeric products 17 / 18 , 19 / 20 and 23 / 24 was, therefore attributed to the 2,3-double bond. This was confirmed by aqueous acid treatment in the case of the pair 19 / 20 : The 2E-configuration for 19 followed from its conversion to 4-acetonyl-4-methyl- 2,3-diphenyl-isocrotonolactone ( 25 ) and the 2Z-configuration of 20 by its conversion first to a mixture ol two diastereomers of (presumably) 1-acetyl-4-dimethylaminocarbonyl-2-methyl-3- phenyl-l,4-dihydronaphthalene ( 27a ) and then, under more drastic conditions, to 6-methyl-11H-benzo[a]fluorene ( 26 ).The structures of 25 and of 26 were derived from their spectral properties, and that of the 27a -mixture was made probable by the plausibility of its intermediacy on the way to 26 . A pathway for the conversion of 20 to 27a (scheme 3) and of the latter to 26 (scheme 4)is proposed. In the case of the reaction of 10 with 12 , two stereomeric basic by-products were isolated (combined yield 150/,). Their structures as traw- and cis-4-acetonyl-4,5-diphenyl-3-pyrrolidinocyclopent-2-en-ones ( 30 and 31 ) were deduced from their spectral properties and from those of their hydrochlorides 32 and 33 . The enamino-ketone function was found to be resistant to a number of reagents, among which were excess sodium borohydride, which converted 30 to the secondary alcohol 34 , and excess methyllithium, which converted 31 to the tertiary alcohol 35 . A mechanism (called ‘rearrangement’) is proposed (scheme 5) for the formation of the enaminoketones (such as 30 and 31 ), which proceeds via the same ammonio-enolate intermediate ( 36 ) which plays a role in the formation of the major products, the amides (such as 17 to 24 ). It is suggested (scheme 6) that the 3-membered ring of the ammonio-enolate 40 may open in three ways, one of which leads to the amides and another to the enamino-ketones.     

Festkörperaktivität und Mechanismen in Oxidsystemen. X. Untersuchung der Umsetzung von α-Fe2O3 mit BaCO3 mittels RBS-Spektrometrie

Solid State Reactivity and Mechanisms in Oxide Systems. X Investigation of the Reaction of α-Fe₂O₃ with BaCO₃ by RBS-Spectrometry Plate-like shaped α-Fe₂O₃ single crystals with the hexagonal axis perpendicular to the plane are characterized by Rutherford-Back-Scattering measurements. The preparation of dense BaCO₃ layers of a defined thickness is reported. The reaction at 650°C and 800°C leads to the formation of BaFe₂O₄ at the surface. Supported by model calculations the RBS spectra are interpreted by a sequence of phases which are in accordance with the phase diagram. PbO evaporates from the α-Fe₂O₃ single crystal surface at 500°C without reaction.     

Kinetik und Mechanismus der α/β-Umwandlung von Li2ZnGe

Kinetics and Mechanism of the α/βαTransformation of Li₂ZnGe The α/β-transformation of Li₂ZnGe was investigated by differential thermal analysis under nearly isothermal conditions. The possible mechanisms of solid state reactions are represented using the integrated and differentiated kinetic equations. For the investigation of DTA curves soft ware is developed to calculate the activation parameters and to find an adequate kinetic equation. A mechanism for the α/β-transformation of Li₂ZnGe is proposed and discussed.     

Festkörperreaktionen in Katalysatoren und Katalysatorkomponenten. XV. Zum Reduktionsverhalten von Sulfat-lonen in γ-Al2O3

Solid State Reactions in Catalysts and Components of Catalysts. XV. On the Reduction Behaviour of Sulfate Ions in γ-Al₂O₃ Different sulphuric acid modified alumina samples were used as model systems for sulfided and regenerated Al₂O₃ carrier catalysts. From investigations of temperature programmed reduction can be concluded that sulphur is reduced by hydrogen to sulfide state at temperatures between 500 and 750°C. The greater part will desorbed as H₂S but a smaller one remains adsorbed on the alumina surface.     

Die Kristallstruktur von α-CaCr2O4

The Crystal Structure of α-CaCr₂O₄ Single crystals of the high temperature modifikation α-CaCr₂O₄ were investigated by X-Ray goniometer data. (a = 11.059, b = 5.836, c = 5.114 Å, space group D–Pmmn). α-CaCr₂O₄ is isotypic with SrCr₂O₄.     

Zur Lokalisierung funktioneller Gruppen mit Hilfe der Massenspektrometrie. XVII—Massenspektren von 3,6,20β-Trihydroxy-pregnanen

Mass spectra of 3,6,20β-trihydroxypregnanes differ greatly, depending upon the nature of the A/B ring fusion and the positions of the hydroxy groups. Of all the isomers only 3α,6β,20β-trihydroxy-5β-pregnane produces an intense, structurally significant, ion at m/e 263. For 3β,6α,20β-trihydroxy-5α-pregnane an ion of m/e 141 is typical.     

Zur Darstellung von Phosphor(III,V)-oxiden: β-Phase P4O7–P4O8

The previously suggested end member P₄O₇ of the beta;hyphen;phase structure type of phosphorus (III,IV) oxides as well as the mixed-crystal β-phase P₄O₇–P₄O₈ have been prepared by oxidation of phosphorus(III) oxide dissolved in carbon tetrachloride. Without alteration of the crystal structure type, P₄O₇ and P₄O₈ molecules are mutually exchangeable in the phase range P₄O₇–P₄O_7,9, the density of such mixed crystals being strictly determined by the mean composition. The crystal structure of the β-phase is obviously fixed by the P₄O₇ molecular structure and not, as previously supposed, by that of the P₄O₈ molecules. The latter appear to occur in the pure state as, in general, amorphous substances.     

Reaktionen von Organometallverbindungen, 3. Mitt.: Zur Kinetik der Reaktionen von Tetraorganoplumbanen mit Essigsäure

Zusammenfassung Die beiden Reaktionen (1) PbR₄+HacR₃Pbac+HR, (2) R₃Pbac+HacR₂Pbac ₂+HR laufen bei der Umsetzung von Pb(C₂H₅)₄ und Essigsäure in wasserfr. Toluol bei 60°, 80° und 100° als konkurrierende Folgereaktionen 2. Ordnung ab. Der Reaktionsablauf wurde durch Titration der Essigsäure mit KOCH₃-Lösung in wasserfr. Medium verfolgt, wobei die Geschwindigkeitskonstanten und die Aktivierungsenergien der Reaktionen ermittelt wurden.

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During the reaction of Pb(C₂H₅)₄ and acetic acid in anhydrous toluene at 60, 80 and 100° C the two reactions (1) and (2) proceed as competitive consecutive second order reactions. The reaction was studied by nonaqueous titration of acetic acid with KOCH₃-solution. Rate constants and activation energies have been determined.

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Mit 9 Abbildungen.

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Herrn Professor Dr.-Ing. habil.F. Asinger zum 60. Geburtstag gewidmet.

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Auszug aus der PromotionsarbeitH. Horn, Techn. Hochsch. Aachen 1966.

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2. Mitt.:F. Huber, H. Horn undH.-J. Haupt, Z. Naturforschg., im Druck.