Thermal studies on dithionate compounds

TG and DTG studies have been carried out on CoS₂O₆ · 6H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O and CdS₂O₆ · 4H₂O. After partial dehydration, the dithionates of Co(II), Ni(II), Cu(II) and Zn(II) lose water and sulfur dioxide simultaneously to yield the stable metal sulfates in the final step of decomposition. The CdS₂O₆ · 4H₂O dehydrates completely in the first two steps of decomposition with two water molecules being lost in each step. In the third step, it loses only SO₂ to yield CdSO₄. Kinetic parameters are presented for these reactions.

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Zusammenfassung TG- und DTG-Untersuchungen von CoS₂O₆ · 4 H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O und CdS₂O₆ · 4 H₂O wurden ausgeführt. Nach partieller Dehydratisierung geben die Dithionate von Co(II), Ni(II), Cu(II) und Zn(II) im letzten Schritt des Abbaus gleichzeitig Wasser und Schwefeldioxid unter Bildung der stabilen Metallsulfate ab. CdS₂O₆ · 4 H₂O wird in den ersten beiden Zersetzungsschritten unter Abgabe von je 2 Wassermolekülen vollständing zersetzt. Im dritten Schritt wird nur SO₂ unter Bildung von CdSO₄ abgegeben. Kinetische Parameter dieser Reaktionen werden angegeben.

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CoS₂O₆ · 6 H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O CdS₂O₆ · 4 H₂O. , , , , . , . , . .

     

Intramolecular cyclization of Z,E,E-1,5,9,-cyclododecatriene by the Cp2TiCl2?LiAlH4 system

The system Cp₂TiCl₂–LiAlH₄, in the absence of ethereal solvents, catalyzes the intramolecular cyclization of Z,E,E-1,5,9-cyclododecatriene, yielding a mixture of C₁₂ hydrocarbons consisting mainly of cis, anti, cis-and cis, syn, trans-tricyclo [7.3.0.0^2,6] dodec-7-ene and 5,6,7,8,9,10-hexahydrobenzocyclooctene.

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Cp₂TiCl₂–LiAlH₄, , Z,E,E,-1,5,9-, C₁₂, , , - , , - [7.3.0.0.^2,6] -7, 5,6,7,8,9,10-.

     

Methodical aspects in thermal analysis of liquid crystalline substances

On the basis of experience in liquid crystal research, the optimum conditions are presented for the use of thermo-microscopy and microcalorimetry (DSC) in preliminary investigations of the general chemical, thermodynamic and kinetic behaviour. In the second step, special measurements are necessary to obtain exact results on purities, phase types, temperatures, enthalpies, and kinetic parameters of transitions in stable and metastable states.

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Zusammenfassung Ausgehend von den Erfahrungen auf dem Gebiet der Flüssigkristalle wird der optimale Einsatz von Thermomikroskopie und Mikrokalorimetrie (DSC) für allgemein-chemische, thermodynamische und kinetische Voruntersuchungen beschrieben. In einer zweiten Untersuchungsphase sind spezielle Messungen notwendig, um exakte Ergebnisse bezüglich Reinheit und Phasentypen zu erhalten sowie Temperaturen, Enthalpien und kinetische Parameter von stabilen und metastabilen Zustandsänderungen zu bestimmen.

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() , . , , , .

     

Cluster and ligand effects in CO adsorption on high dispersity supported Ni?Cu alloys

IR spectroscopic studies of CO chemisorption on SiO₂-supported Ni and Ni–Cu microcrystals have revealed that the alloy composition affects the intensity and frequency of absorption bands of the linear form of chemisorbed CO. Chemisorbed hydrogen is shown to shift its absorption band to the high-frequency region on pure Ni and low-copper Ni–Cu alloys and does not affect it on high-copper ones. The presence of Cu in the alloy increases significantly the reactivity of chemisorbed oxygen in the reaction with CO. The results are treated in terms of the concepts of cluster and ligand effects.

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- CO SiO₂ Ni Ni–Cu. CO. CO Ni–Cu , Cu CO , Cu. Cu CO. .

     

Acidity and catalytic activity of rare-earth containing X zeolites

The acidity of LaX and CeX zeolites evaluated by the IR-spectra of adsorbed pyridine is compared with their activities in cumene cracking. The definitive role of the rare-earth cations in the catalytic activity, in Brönsted acidity as well as in Lewis active sites has been confirmed.

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LaX CeX . , , .

     

Ammonia Formation on (Ru + Cs)/C Catalysts by the Interaction of Adsorbed Nitrogen with Hydrogen That Diffused from the Bulk of Cesium–Ruthenium Particles

The high-temperature (T _max = 625 ) and (T _max = 750 ) states of ammonia and (T _max = 550–750 ), (T _max = 750–900 ), and (T _max > 900 K) states of hydrogen were detected on (Ru + Cs)/C catalysts for ammonia synthesis activated under the reaction conditions (P = 30 atm; T = 650 K; the initial pressure ratio P_{N 2}/P_{H 2} = 1/3). A mechanism was proposed for the formation of ammonia as a result of the interaction of chemisorbed nitrogen with hydrogen that diffused from the bulk of cesium–ruthenium particles.     

Two Algorithms for Computing the Randles–Sevcik Function from Electrochemistry

We derive two expansions of the Randles–Sevcik function : an asymptotic expansion of for x and its Taylor expansion at any x ₀ . These expansions are accompanied by error bounds for the remainder at any order of the approximation.     

Phase-fixed double-group 3-Γ symbols. V. 3-Γ symbols and coupling coefficients for all the octahedral double group-subgroup hierarchies

For all the subgroup hierarchies descending from the octahedral double group O ^*, we have obtained sets of 3- symbols and discuss here their properties. We have entirely real sets of 3- symbols for the tetrahedral and tetragonal hierarchies as well as for O ^* C ₃ ^* . For the latter hierarchy and the tetragonal ones, formalisms almost as powerful as the classical one for the rotation group may be established. We also discuss results obtained for cases with strict adaption to D ₃ ^* where it is now known that non-real 3- symbols are unavoidable.The 3- symbols are phase-fixed by the specification of basis functions (or, equivalently, subduction coefficients) generating them.The significance of the concept of associated representations of O* is discussed. The problems raised by the two multiplicity triples UT₁U and UT₂U in O* are given particular attention.     

Influence of water on the mechanism of the electroreduction of 9-nitroanthracene in DMF

The comparison of the data on the preparative electroreduction of 9-nitroanthracene in the mixtures of DMF-H₂O was performed for the potentials of the first and second stages. It was shown that the protonation of the anion radicals of 9-nitroanthracene by water has virtually no influence on the course of their dimerization up to the content of the H₂O in the DMF equal to 50%. The sharp change in the ratio of the electrolysis products under the conditions of the two-electron ER of (I) when water is present in the solvent is explained by the high rate of protonation of the dianion of 9,9-dinitro-9,9, 10,10-tetrahydro-10,10-bianthryl by water and the subsequent reduction of this hydrodimer. The PMR spectra of the cis and trans isomers of 9,9-dihydroximino-9,9,10,10-tetrahydrobianthryl, which are formed by the reaction of the dimeric dianion with MeI and the subsequent thermal decomposition of the nitron ether, were studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 873–877, April, 1991.     

Analytical Electron Microscopy in a Discontinuous Precipitated Cu–In Alloy

The morphology and kinetics of the discontinuous precipitation reaction in a Cu-4.5 at.% In alloy were studied by means of analytical electron microscopy. Upon discontinuous precipitation an /(Cu₇In₃) lamellar two-phase microstructure was observed, where is the In-depleted solid solution and the precipitate phase. Indium concentration profiles were determined parallel to the moving reaction front for individual lamellae. A local analysis was applied to characterize the kinetics of the discontinuous precipitation reaction and allowed the determination of the local grain-boundary diffusivity.     

Applications of a new low temperature differential scanning calorimeter

A new low temperature differential scanning calorimeter is described which operates over the temperature range –150 °C to 700 °C. The equipment features a chromel heat flux DSC sensor plate located in a cobalt alloy heating chamber, enabling work to be carried out in oxidizing atmospheres to above 600 °C. Full data processing and programme control facilities are provided by an IBM compatible computer system. The performance of the instrument is illustrated by experiments on indium and poly (vinyl chloride).

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Zusammenfassung Ein neues Tieftemperatur-Differential-Scanning-Kalorimeter für den Bereich von –120 °C bis+700 °C wird beschrieben. Das Gerät enthält eine Wärmefluss-DSC-Sensorplatte aus Chromel in einer Heizkammer aus einer Kobaltlegierung, was Arbeiten in oxidierender Atmosphäre bis über 600 °C ermöglicht. Ein IBM-kompatibles Computersystem bietet alle Möglichkeiten der Datenverarbeitung und Programmregelung. Die Leistungsfähigkeit des Geräts wird an Hand von Experimenten mit Indium und Polyvinylchlorid demonstriert.

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, —150° 700°. , 600°. IBM . .

     

Thermodynamic limitations in searching for regions of optimal performance of complex chemical reactions (exemplified by conversion of hydrocarbons)

An algorithm of searching for optimal nonequilibrium reaction mixture compositions accounting for thermodynamic limitations is suggested. It is exemplified by the analysis of a steam conversion of hydrocarbons.

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, . .

     

Subshell-pair interelectronic angles of atoms

For the 102 atoms from He to Lr in their ground states, the average interelectronic angles <₁₂> _{nl, n'l'} between an electron in a subshellnl and another electron in a subshell n'l' are examined, where n and l are the principal and azimuthal quantum numbers, respectively. Theoretical study clarifies that <₁₂> _nl,n'l' are 90° precisely if l–l' are even, while they are larger than 90° if l–l' are odd. Numerical analysis of 3,275 subshell pairs with odd l–l' of the 102 atoms shows that the increases in the total average interelectronic angles <₁₂> from 90° are attributed predominantly to subshell pairs with n=n' and l–l'=1.     

Solubility of Oxygen in Some 1-1, 2-1, 1-2, and 2-2 Electrolytes as a Function of Concentration at 25°C

The solubility of oxygen has been measured in a number of electrolytes [(LiCl, KCl, RbCl, CsCl, NaF, NaBr, NaI, NaNO₃, KBr, KI, KNO₃, CaCl₂, SrCl₂, BaCl₂, Li₂SO₄, K₂SO₄, Mn(NO₃)₃)] as a function of concentration at 25°C. The solubilities, mol (kg-H₂O)^–1, have been fitted to a function of the molality m (standard deviation < 3mol-kg^–1)

Hydroperoxidation of alkanes by atmospheric oxygen in the presence of hydroquinone or quinone catalyzed by copper(II) acetate under visible light irradiation

When a solution of an alkane and hydroquinone (or quinone) in CH₃CN irradiated in air by visible light in the presence of catalytic amounts of Cu(OCOCH₃)₂, the alkyl hydroperoxide is formed.

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( ) CH₃CN Cu(OCOCH₃)₂ .

     

Studies on nickel oxide mixed catalysts, V. Propene dimerization on Nio?Al2O3/SiO2 catalysts

The catalytic activity of various NiO–Al₂O₃/SiO₂ catalysts has been investigated in a tubular fixed-bed reactor at high pressure. High selectivities to propene dimers were obtained on catalysts with a high Ni/Al ratio. The surface acidity of the catalysts influences strongly the selectivity and the product distribution.

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NiO–Al₂O₃/SiO₂ . , Ni/Al . .

     

Solution of the generalized eigenvalue equation perturbed by a generalized low rank perturbation

Summary The problem of finding eigenvalues and eigenstates of the generalized perturbed eigenvalue equation = g3(+) is considered. The eigenvalues and the eigenstates of the unperturbed eigenvalue equation = are assumed to be known. Matrices , and can be arbitrary, except for the requirement that be nonsingular and that the eigenstates of the unperturbed equation be complete. It is shown that the eigenvalues and the eigenstates of the perturbed equation can be easily obtained if the rank of the generalized perturbation , is small. A special case of low rank perturbations are piecewise local perturbations which are common in physics and chemistry. If the perturbation is piecewise local with fixed localizability, the operation count for the derivation of a single eigenvalue and/or a single eigenstate is (n). If the perturbation has a fixed rank, the operation count for the derivation of all eigenvalues and/or all eigenstates is (n ²).Research supported by the Welch Foundation of Houston, Texas, and by the Yugoslav Ministry for Development (Grant P-96)     

Studies of the energy spectrum of α, ω- substituted polymethine chains. II. Polymethine chains with odd number of methine groups

The analysis of the experimental data for the energy of the longest wavelength optical transitions _n,opt of substituted polymethines X (CH)_2n+1 X shows that in the asymptotic case (n) _,opt does not tend to zero, as it follows from the empirically established correlations, but has a finite, non-zero value. It is shown that the energy gap of odd polymethines is the same as that of the even polymethines - the polyenes (E 2 eV). The substituents (X N, O, B) are responsible for the appearance of levels in the gap. These, depending on the substituent character, are vacant (X B) or occupied (X N, O). The transition from or to such a level determines the longest wavelength optical transition energy of polymethines.     

Alkali-promoted AlPO4 catalysts, II. Cyclohexene skeletal isomerization to 1- and 3-methylcyclopentenes

Skeletal isomerization of cyclohexene to 1- and 3-methylcyclopentenes has been carried out at temperatures ranging from 250–400 °C using a microcatalytic pulse technique, over AlPO₄ catalysts having various amounts of alkali cations (1–5 wt.%, Li, Na and K). Apparent rate constants and activation energies were calculated in terms of Bassett and Habgood's kinetic model for first order processes in which the surface reaction is the controlling step and partial pressure of the reactant is low. The results show that alkali-containing catalysts exhibit lower activity and higher selectivity to 1-methylcyclopentene than pure AlPO₄ due to the modification of the surface acidity by alkali impregnation.

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1- 3- 250–400°C AlPO₄ (1–5 .% Li, Na K). , . 1-, AlPO₄ .

     

Possibilities of applying the piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and their derivatives

Piloyan activation energiesE as well as initals of exothermT _D of sevenN-monoalkyl and fiveN,N-dialkyl-2,4-dinitroanilines were determined. Relationships were found between the T_D values and R_f factors as well asE values and those R_M functions and also theET _D ^–1 term and R_M functions.

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Zusammenfassung Die AktivierungsenergienE nach Piloyan sowie die Anfangswerte der ExothermenT _D wurden für siebenN-Monoalkyl- und fünfN,N-Dialkyl-2,4-dinitroaniline bestimmt. Die Zusammenhänge zwischen denT _D-Werten und den papierchromatographischenR _f-Faktoren der gemessenen Dinitroaniline wurden abgeleitet und erörtert. Desgleichen wurden auch die Zusammenhänge zwischen denE-Werten und denR _M-Funktionen der Papierchromatographie abgeleitet und erörtert. Auch zwischen dem AusdruckE ·T _D ^–1 und denR _M-Funktionen wurde ein Zusammenhang gefunden.

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Résumé On a déterminé les températures initialesT _D de l'effet exothermique ainsi que les énergies d'activationE d'après la méthode de Piloyan, de sept N-mono alcoyl et cinqN,N-dialcoyl-2, 4-dinitroanilines. Une corrélation entre les valeursT _D et les facteursR _f de la Chromatographie sur papier des dinitroanilines étudiées a été trouvée et discutée, ainsi qu'entre les valeursE et les fonctionsR _M de la Chromatographie sur papier. Une relation entre le termeE ·T _D ^–1 et les fonctionsR _M a également été trouvée.

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E T _D N- N,N- -2,4- . _D R _f , E R _M. E. _D ^–1 R _M.

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The authors would like to thank Mrs. Anna Collàkovà for careful DTA measurements, and Dr. Ladislav Smolka for help in treatment of the measured results with the Wang 600 computer.