Polymorphic modifications of barium metagermanate

Polymorphic transformations of BaGeO₃ were investigated by DTA and X-ray diffraction methods and the data obtained were compared with those previously published. BaGeO₃ undergoes a reversible phase transformation at 1100° from a low-temperature hexagonal polymorph to a medium-temperature polymorph having an unknown crystal structure, which undergoes a further reversible transformation at 1200° to a high-temperature orthorhombic polymorph found to be stable up to the melting temperature of 1287°. On cooling from the melt, the high-temperature form can be retained metastably at room temperature, but transforms to the low-temperature form at 900°.

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Zusammenfassung Polymorphe Umwandlungen von BaGeO₃ wurden unter Anwendung der DTA- und Röntgendiffraktionsmethoden untersucht und die erhaltenen Angaben mit den früher veröffentlichten verglichen. Bei 1100° vollzieht sich eine reversible Phasentransformation der BaGeO₃ von der hexagonalen Struktur bei niedrigen Temperaturen in eine Verbindung unbekannter Kristallstruktur bei mittleren Temperaturen, welche wiederum bei 1200° eine weitere reversible Umwandlung in eine orthorhombische Struktur erfuhr und sich bis zur Schmelztemperatur von 1287° als stabil erwies. Beim Abkühlen der Schmelze kann die Form bei hohen Temperaturen bei Zimmertemperatur in metastabilem Zustand erhalten bleiben, wird jedoch bei 900° in die Form bei niedrigen Temperaturen umgewandelt.

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Résumé On a étudié les transformations polymorphiques de BaGeO₃ par ATD et diffraction des rayons X et comparé les résultats avec ceux obtenus antérieurement. A 1100° C BaGeO₃ subit une transformation de phase réversible de la forme hexagonale stable à basse température à la forme stable à moyenne température, de structure cristalline inconnue, qui se transforme réversiblement à 1200° C en une phase orthorhombique qui reste stable jusqu'à 1287° C. Au refroidissement, la forme stable à haute température peut être maintenue à l'état métastable à la température ambiante, mais elle se transforme à 900° C en la forme stable à basse température.

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BaGeO₃ . BaGeO₃ 1100° - - 1200° , 1287°. - , - 900°.

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This investigation was supported by the Boris Kidri Foundation for Scientific Research     

Permanganate oxidations in strongly basic solutions

In strongly basic solutions the permanganate ion oxidation of C₁ and C₂ alcohols, aldehydes and acids obeys a second-order kinetic law of the type rate=k_o [S]_o [MnO ₄ ^– ], where S is the substrate. The rate constant k for both alcohols and aldeydes is proportional to the OH^– ion concentration. This behavior is interpreted in terms of a deprotonation equilibrium followed by rate-determining hydride ion transfer to MnO ₄ ^– .

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, C₁ C₂ W=k_o [S]_o [MnO ₄ ^– , S — . OH^–. MnO ₄ ^– , .

     

Reforming type Pt/Al2O3 catalyst prepared from [(CH3)3PtX]4 complexes by thermal decomposition

Pt/Al₂O₃ catalysts with good reforming activity were prepared from [(CH₃)₃PtX]₄ (X=Cl, Br, I) complexes and tested in pulse and continuous-flow reactors in n-hexane dehydrocyclization. It has been demonstrated that [(CH₃)₃PtX]₄ complexes are excellent precursors of supported platinum catalysts.

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Pt/Al₂O₃ [(CH₃)₃ PtX]₄ (X=Cl, Br, I) -. , [(CH₃)₃PtX]₄ .

     

Steroid alcohols from the ascidianHalocynthia aurantium

The total sterols have been isolated fromHalocynthia aurantium by column chromatography on silica gel. The following steroid alcohols have been identified in it with the aid of GLC, GLC-MS, and¹H NMR: 5-cholestan-3-ol, 24-methylcholestan-3-ol, 24-ethylcholestan-3-ol, 4-methyl-24-ethyl-5-cholestan-3-ol, cholest-5-en-3-ol, 24-methylcholest-5-en-3-ol, 24-ethylcholes-5-en-3-ol, 5-cholest-22-en-3-ol, 24-nor-5-cholest-22-en-3-ol, cholesta-5,22-dien-3-ol, 24-methylcholesta-5,22-dien-3-ol, 24-norcholesta-5,22-dien-3-ol, 24-ethylcholesta-5,24(28)-dien-3-ol, and 24-methylcholesta-5,24(28)-dien-3-ol.Pacific Ocean Institute of Bioorganic Chemistry of the Far Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok, and Far-Eastern State University, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 581–585, September–October, 1981.     

Hydrocondensation of CO on iron-alumina catalysts. Influence of ethylene

The transformations of H₂/C₂H₄ and H₂/C₂H₄/CO mixtures on activated and carbided 10% Fe/Al₂O₃ catalysts have been studied in terms of the role of ethylene in Co hydrocondensation, and specifically its influence on the selectivity to C₃–C₄ hydrocarbons.

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H₂/C₂H₄ H₂/C₂H₄/CO 10% Fe/Al₂O₃ CO C₃–C₄ .

     

Influence of Cr loading on the catalytic properties of CrO3/SiO2 catalysts in 2-propanol conversion

Catalytic activity of CrO₃/SiO₂ samples for 2-propanol conversion is governed by only a small amount of active centers (estimated to be around 10¹⁷ per gram of catalyst), whereas excess chromium neither develops catalytic activity nor inhibits the reaction on the active sites. Only when the chromium loading is high enough to allow formation of bulk-like agglomerates (5 wt.% Cr) is 2-propanol converted also on this CrO_x surface phase, but with a significant higher activation energy.

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CrO₃/SiO₂ 2- ( 10¹⁷ ), . , - (5 .% Cr), 2- CrO_x , .

     

AlPO4 as catalyst in organic reactions. IV. Transesterification of methyl methacrylate

Coke deposition on monometallic Pt, Re, Ir, Ge and Sn catalysts supported on -Al₂O₃, and its influence on activity and selectivity over methylcyclopentene reforming was studied. As a result the effect can be interpreted in terms of metal-support interactions that modify the overall catalytic deactivation rates.

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Pt, Re, Ir, Ge Sn, -Al₂O₃ . , .

     

Non quasi-stationary state pyrolysis. Induction period of neopentane pyrolysis

The principle of an apparatus using an isothermal continuous flow stirred tank reactor to study homogeneous gas phase reactions at space times of the order of 1 sec is given. With this apparatus, the induction period of neopentane pyrolysis (as an example) has been clearly shown.

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, , 1 . , , .

     

Triterpene Glycosides and Their Genins from Tragacantha stipulosa. Structure of Cyclostipuloside C

A new cycloartane glycoside of the cyclostipuloside C series, 3-O--D-xylopyranoside-6,16-di-O--D-glucopyranoside-20S-24R-epoxycycloartan-3,6,16,25-tetraol is isolated from aerial organs of Tragacantha stipulosa Boriss.     

Selective catalytic hydrogenation of double bonds in unsaturated furan ketones

In the hydrogenation of unsaturated furan ketones in solvents at atmospheric pressure and room temperature the Raney Pd–Al catalyst is highly active and selective towards the hydrogenation of double bonds. The only reaction products are the respective saturated ketones.

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, Pd–Al . . .

     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Preparation and stereochemical characterization of some N-acyl-[1]benzopyrano[3,4-c]pyrazole derivatives from rotenoids

Summary Several new N-acyl derivatives of 1-(4-hydroxy-2,3-dihydrobenzofuran-5-yl)-7,8-di methoxy-1,9 b,2,3,3 a,4-hexahydro-[1]benzopyrano[3,4-c]pyrazole-1-ene have been prepared by appropriate chemical transformation of isohydrazones of rotenone and amorphigenin. A study of their¹H- and¹³C-NMR spectra confirmed the presence of the twocis 3a, 9b, 2 and 3a, 9b, 2 diastereomers in the parent isohydrazones and revealed the strong predominance of the conformers withendo orientation of the 3-NAc group. The conformations due to rotation about the 1,5-bond between rings C and D in the 4-OH and 4-O-substituted compounds were also determined by taking into account the anisotropic effect of aromatic rings A and D, and the hydrogen bond between 4-OH and the 2-N atom, as well as by inspecting the Dreiding models.

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Darstellung und stereochemische Charakterisierung einiger N-Acyl-[1]benzopyrano[3,4-c]pyrazol-Derivate von Rotenoiden

Zusammenfassung Mittels geeigneter chemischer Transformationen von Isohydrazonen von Rotenon und Amorphigenin wurden einige neue N-Acyl-Derivate von 1-(4-Hydroxy-2,3-dihydrobenzofuran-5-yl)-7,8-dimethoxy-1,9 b,2,3,3 a,4-hexahydro-[1]benzopyrano[3,4-c]pyrazol-1-en hergestellt. Eine Untersuchung ihrer¹H und¹³C-NMR-Spektren zeigt die Gegenwart von zweicis 3a, 9b, 2- und 3a, 9b, 2-Diastereomeren in den Ausgangs-Isohydrazonen und eine starke Bevorzugung der Konformeren mitendo-Orientierung der 3-NAc-Gruppe. Die Konformationen bezüglich der Rotation um die 1,5-Bindung zwischen Ring C und D werden für die 4-OH und 4-O-substituierten Verbindungen unter Berücksichtigung von Anisotropie-Effekten der aromatischen A- und D-Ringe, der Wasserstoffbrücken zwischen 4-OH und dem 2-N Atom und auch der Betrachtung der entspechenden Dreiding-Modelle diskutiert.

     

The effect of outer sphere cations on the thermal stability of nitritocuprates(II)

Thermal analyses by Derivatograph were made for salts of the general formula M ₂ ^I M^II[Cu(NO₂)₆] where M^I=K⁺, Rb⁺ or Cs⁺; and M^II=Ca²⁺, Sr²⁺, Ba²⁺ or Pb²⁺. From the results and the chemical and diffractometric analysis of sinters of chosen salts, the mechanism of thermal decomposition was established. Some conclusions concerning the effects of outer sphere cations on the thermal stabilities of these salts are also drawn.

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Zusammenfassung Es wurden thermische Analysen mit einem Derivatographen für die Salze der allgemeinen Formel M₂ ^IM^II [Cu(NO₂)₆] durchgeführt [M^I=K⁺, Rb⁺, Cs⁺; M^II=Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺]. Aus den Ergebnissen dieser sowie der chemischen und diffraktometrischen Analysen der Sinterprodukte der jeweiligen Salze wurde der Mechanismus ihrer chemischen Zersetzung ermittelt. Einige Folgerungen bezüglich der Wirkung von Kationen der äusseren Sphäre auf die thermische Stabilität konnten ebenfalls gemacht werden.

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Résumé Le mécanisme de la décomposition thermique des sels de formule générale M₂ ^IM^II [Cu(NO₂)₆] où M^I=K⁺, Rb⁺, Cs⁺ et M^II=Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ a été établi à partir des données thermiques obtenues à l'aide d'un Derivatograph, ainsi que par des analyses thermiques et diffractométriques sur les produits frittés. L'effet des cations de la couche externe sur la stabilité thermique de ces sels est discuté.

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M ₂ ^I M^II[Cu(NO₂)₆], M^I=K⁺, Rb⁺, Cs⁺; M^II=Ca²⁺, Sr²⁺, Ba²⁺, b²⁺. , , . , .

     

Kinetics of the acid-catalyzed equilibration of methylenecyclohexane and 1-methylcyclohexene

The rates of isomerization of methylenecyclohexane and 1-methylcyclohexene have been measured in acetic acid, usingp-toluenesulfonic acid as a catalyst, at temperatures of 20.30, 24.07, 30.00, 32.30, 39.85 and 40.21 °C. The overall forward and reverse rate constants can be expressed as k ₁ ⁰ =4.41×10⁸ exp (–17.6×10³/RT) s^–1 and k ₂ ⁰ =0.64×10⁸ exp ((–19.5×10³/RT) s^–1. From the difference in the activation energies the heat of isomerization is estimated as 7.9 kJ mol^–1.

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1- , - 20,30, 24,07, 30,00, 32,30, 39,85 40,21 °C. k ₁ ⁰ =4.41×10⁸ exp (–17.6×10³/RT) ^–1 k ₂ ⁰ =0.64×10⁸ exp (–19.5×10³/RT) ^–1. 7,9 /.

     

Dynamic light scattering of CTAB:NaSal threadlike micelles in the semidilute regime. II. effect of surfactant concentration

Dynamic light scattering measurements are made on networks formed by elongated threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at 25°C. The surfactant concentrationC _D of the samples is varied from 0.006 to 0.3 M and the ratio of the salt concentrationC _s toC _D is fixed at unity. The time correlation functionA _q (t) of light intensity scattered from the solutions exhibits transition from the unimodal to the bimodal distribution of the decay rate at aroundC _D=0.05 M. The dependence of the first cumulant _e on the scattering vectorq for the samples withC _D0.03 M is described by the dynamic scaling law. The cooperative diffusion coefficientD _c is obtained from extrapolation of _e/q² for the samples withC _D0.03 M and of _f/q² forC _D0.05 M where _f is the first cumulant from the fast mode. TheD _c is found in proportion toC _D ^0.45, being in agreement with the theoretical prediction for a rigid rod in the semidilute regime by the scaling law. The decay rate _s characteristic of the slow mode is independent ofq, and _s ^–1 roughly agrees with the mechanical relaxation time estimated from a fit of the dynamic viscoelastic data of the same samples by a Maxwell type of model with the single relaxation time .     

Preparation of cobalt doped γ-Fe2O3 and Mn-Zn ferrites by the thermal decomposition of the hydrazine precursors

Fine particle cobalt doped-Fe₂O₃ and Mn-Zn ferrites have been prepared by the thermal decomposition of N₂H₅Co _x Fe_1–x (N₂H₃COO)₃.H₂O wherex=1–10 atom% and (N₂H₅)₃Mn_xZn_1–x Fe₂(N₂H₃COO)₉· 3H₂O wherex=0.2–0.8, respectively. Formation of these oxide materials has been confirmed by thermogravimetry and X-ray powder diffraction patterns. The fine particle nature of these oxide materials is evident from particle size analysis and surface area measurements.

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Zusammenfassung Mit fein verteiltem Kobalt versetztes-Fe₂O₃ sowie Mn-Zn Ferrite wurden durch thermische Zersetzung von N₂H₅Co _x Fe_1–x (N₂H₃COO)₃·H₂O mit jc=1–10 Atomprozent bzw. (N₂H₅)₃Mn _x Zn_1–x Fe₂(N₂H₃COO)₉·3H₂O mitx=0,2–0,8 hergestellt. Die Bildung dieser Oxidstoffe wurde durch Thermogravimetrie und Pulverdiffraktionsmethoden bekräftigt. Die Feinkornstruktur dieser Oxidstoffe wird durch Korngrößenverteilungs- und Oberflächenmessungen augenscheinlich.

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N₂H₅Co _x Fe_1–x (N₂H₃COO)₃·H₂O, x-1–10 %, (N₂H₅)₃Mn _x Zn_1–x Fe₂(N₂H₃COO)₉ · 3H₂O, x=0,2–0,8, , , -Fe₂O₃ Mn-Zn . . .

     

Kinetics and mechanism of the hydrolysis of sodium carboxymethylcellulose (Na-CMC) by a cellulase complex

TheSomogyi-Nelson colorimetric method is applied in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of sodium carboxymethylcellulose (Na-CMC) catalyzed by the cellulase complex. By means of selective inhibition of a chosen enzyme from the cellulase complex it became possible to trace the effect of the other enzymes included in its composition.

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Kinetik und Mechanismus der Hydrolyse von Natriumcarboxymethylcellulose (Na-CMC) durch einen Cellulase-Komplex

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Natriumcarboxymethylcellulose (Na-CMC), katalysiert durch den Cellulase-Komplex, angewandt. Durch selektive Inhibierung eines bestimmten Enzyms des Cellulase-Komplexes kann man die Wirkung der anderen zu seiner gesamten Zusammensetzung gehörenden Enzyme verfolgen.

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Symbols Used E enzyme (E—cellulase;E—exo-cellobiohydrolase;E—-glucosidase) - [E] _w weight concentration of enzymeE - S substrate (Na-CMC—sodium carboxymethylcellulose) - [S]₀ weight concentration of substrateS - I inhibitor (I—lactose;I—calcium chloride;I—condurrite-B-epoxide) - P product (P—oligosaccharides;P—cellobiose;P—D-glucose) - P end product (K , K , K ) - DP degree of polymerization - DS degree of substitution - ES enzyme-substrate complex (E S, E S, E S) - EP enzyme-product complex (E P, E P) - EI enzyme-inhibitor complex (E I, E I, E I) - M _s molecular mass of substrateS - K _s substrate constant (K _s , K _s , K _s ) - K _I inhibitor constant (K _I , K _I , K _I ) - K _m Michaelis-Menten constant - k ₊₁,k ₊₂ (k ₊₂ ,k ₊₂ ,k ₊₂ ) forward rate constants - k _–1 reverse rate constant - ₀ initial rate of reaction - V maximal reaction rate - A change in absorbance - molar absorption coefficient - wavelength Herrn Prof. Dr.Hans Tuppy zum 60. Geburtstag herzlichst gewidmet.     

Thiolactame als Reagenzien in der quantitativen Analyse. IX

Zusammenfassung Thiocaprolactam (T) eignet sich zur Goldbestimmung im Konzentrationsbereich 10 bis 130 g Au/ml mit einem Fehler von ±0,5g. Thiocaprolactam bildet mit [AuCl₄]^– eine Verbindung im molaren Verhältnis TAuCl=112, mit [AuJ₄]^– im molaren Verhältnis TAuJ=213. Dagegen bilden sich im System T:Au:Br zwei verschiedene Verbindungen: Ein Bromidkomplex mit höherem Goldgehalt TAu=12, der mit Chloroform extrahierbar ist, und eine sich als Niederschlag ausscheidende Verbindung mit dem Verhältnis TAuBr=112.

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Thiolactams as reagents in quantitative analysis. IX

Summary Thiocaprolactam (T) is suitable for the determination of gold in the concentration range 10–130g Au/ml with an error of ±0.5g. Thiocaprolactam yields with [AuCl₄]^– a compound in the molar ratio TAuCl=112, with [Aul₄]^– in the molar ratio TAuI=213. On the other hand various compounds result in the system TAu Br. The molar ratio in the case of the bromide complex has a higher gold content, namely TAu=12; this product is extractable with chloroform and a compound that comes down as a precipitate shows the ratioT Au Br=112.

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Herrn Dr.K. Czerepko möchte ich hiermit meinen Dank für die Diskussion der Ergebnisse aussprechen.     

Thermal effects on cation distribution of CuCr2O4

Thermal studies on CuCr₂O₄ spinel indicated the phase present above 870 K to be cubic CuCr₂O₄. However, when the substance was quenched from 1023 K, 1173 K, 1273 K and 1473 K, only the tetragonal phase of CuCr₂O₄ was obtained. This is because the first-order, diffusionless, tetragonal to cubic phase transition at 865 K occurs reversibly at a very fast rate. Thec/a ratio for CuCr₂O₄ present in the various quenched samples did not change when the quenching temperature was raised. A strong preference of the Cr³⁺ ion for the B site prevents it from interchanging sites with Cu²⁺ ions, thus keeping the lattice parametersc anda unchanged.

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Zusammenfassung Thermische Untersuchungen am CuCr₂O₄ Spinell zeigten, daß die Phase oberhalb von 870 K aus kubischem CuCr₂O₄ besteht. Wenn jedoch von 1023 K, 1173 K, 1273 KL und 1473 K schnell abgekühlt wurde, entsteht nur die tetragonale Phase von CuCr₂O₄. Der Grund hierfür ist, daß der diffusionsfreie Übergang erster Ordnung von der tetragonalen zur kubischen Phase bei 865 K reversibel mit sehr großer Geschwindigkeit vor sich geht. Das Verhältnisc/a von CuCr₂O₄ in den verschiedenen schnell abgekühlten Phasen verändert sich durch das Erhöhen der Ausgangstemperatur der Abkühlung nicht. Ein starker Vorrang des Cr³⁺-Ions für die B Plätze verhindert den Austausch von Plätzen mit Cu²⁺-Ionen, wodurch die Gitterparameter c und a unverändert bleiben.

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Résumé L'étude des propriétés terhmiques du spinelle CuCr₂O₄ indique que la phase présente au-dessus de 870 K consiste en CuCr₂O₄ cubique. Cependant, en refroidissant très rapidement à partir de 1023, 1173, 1273 et 1473 K on n'a obtenu que la phase tétragonale de CuCr₂O₄. Ce résultat est dû au fait que la transition sans diffusion du premier ordre de la phase tétragonale en la phase cubique s'effectue réversiblement, à une vitesse très élevée, à 865 K. Le rapportc/a de CuCr₂O₄ présent dans les divers prélèvements refroidis rapidement, n'a pas été modifié en augmentant la température de départ du refroidissement rapide. Une forte préférence de l'ion Cr³⁺ pour les sites B empêche celui-ci d'échanger ses sites avec les ions Cu²⁺, maintenant ainsi les paramètres du réseau c et a inchangés.

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CuCr₂O₄ , 870 . , 1023 , 1173 , 1273 1473 . , 865 . / . Cr³⁺ , Cu²⁺, «c» «a».