Thermal Expansion of Mixed Zirconium Phosphates

A series of framework phosphates with varied ratio of cations Na_5-2x B _x ^IIZr(PO₄)₃, B^II = Mg, Ca, Sr, Ba (0 x 2) and Na_5-3x Fe _x Zr(PO₄)₃ (0 x 1.33) were synthesized and studied under heating. The coefficients of thermal expansion along crystal axes _a and _c were calculated, and their dependences on the cationic composition (nature and concentration) and on the occupancy of out-of-framework structural positions were established.     

Extractive spectrophotometric determination of niobium(V) using 3-hydroxyflavone

A simple, rapid method for the spectrophotometric determination of niobium in trace amounts is presented, employing 3-hydroxyflavone as a ligand for the complexation of the metal ion and extracting the coloured complex into chloroform from 4M HClO₄ solution. Beer's law is obeyed in the range 0.0 to 3.2 g ml^–1 Nb(V), with a lower working limit of 0.1 g ml^–1 Nb(V). Molar absorptivity and Sandell's sensitivity of the complex at 395 nm are 4.088 × 10⁴l mol^–1 cm^–1 and 0.002g Nb(V) cm^–2, respectively. The stoichiometry of the complex is established as 12 by Job's and mole ratio methods. The method is free from the interference of a large number of analytically important elements. The proposed system handles satisfactorily the analysis of several samples of varying complexity. The results are highly reproducible with a relative standard deviation of 0.34% for 20 g of Nb.     

Triterpene glycosides ofHedera taurica XIV. Structures of glycosides St-G0–2, St-J, and St-K from the stems of Crimean ivy

The structures of new triterpene glycosides isolated from the stems of Crimean ivyHedera taurica Carr. (fam. Araliaceae) — St-J, St-K, and St-G_0–2 — have been established as the 3-0--L-glucopyranuronoside 28-O-[O-L-rhamnopyranosyl-(14)-O--D-glucopyranosyl-(16)--D-glucopyranoside]s of oleanolic acid and of hederagenin and the 3–0(6-O-ethyl--D-glucopyranuronoside) 28-O-[O-L-rhamnopyranosyl0(14)-O--D-glucopyranosyl-(16)-glucopyranoside of hederagenin, respectively.Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii No. 3, pp. 397–403, May–June, 1997.     

Synergetic effect of silver and molybdenum (VI) oxide additives in vanadia catalysts for the selective oxidation of benzene

It has been shown that the selectivity of V₂O₅–MoO₃ catalysts for benzene oxidation to maleic anhydride can be enhanced by small amounts of silver introduced by impregnation with AgNO₃ solution. The effect of Ag₂O additive is synergetic and increases with increasing concentration of MoO₃ up to 28.5 mol %. The best effect was obtained when about 7 Ag atoms were introduced for 1000 (V+Mo) atoms at the surface.

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, V₂O₅–MoO₃ - AgNO₃. Ag₂O MoO₃ 28,5 . %. , 7 Ag 1000 (V+Mo).

     

The dissociation of phosphoric acid in NaCl and NaMgCl solutions at 25°C

The pK ₁ ^* , pK ₁ ^* and pK ₃ ^* for the dissociation of H₃PO₄ have been measured in NaCl solutions from 0.5 to 6m at 25°C. The results have been used to evaluate Pitzer interaction parameters (NaClH₂PO₄)=–0.028±0.005, (NaH₃PO₄)=–0.075±0.025, (HPO₄Cl)=0.105±0.009, (PO₄Cl)=–0.59±0.02 and (NaClHPO₄)=–0.003±0.004, (PO₄NaClH)=0.110±0.008. These parameters yield values of pK ₁ ^* , pK ₂ ^* and pK ₃ ^* in NaCl that agree with the measured values with average deviations of ±0.04, ±0.03 and ±0.05 in pK ₁ ^* . Measurements of pK ₁ ^* and pK ₂ ^* were also made in NaMgCl solutions. These results have been used to evaluate ^(O)(MgH ₂ PO ₄)=–3.55±0.07,⁽¹⁾(MgH ₂ PO ₄=–16.9±0.03, ^(O)(MgH ₂ PO ₄=–17.5±0.03 and ⁽¹⁾(MgH ₂ PO ₄)=27.4±0.8 at 25°C. The results for pK ₂ ^* in NaMg–Cl solutions were also used to calculate log K _MX ^* =3.2±0.1 for the formation of the ion pair MgHPO ₄ ^o .     

Triterpene glycosides of alfalfa VIII. Medinoside E from the leaves

From the leaves ofMedicago sativa L. (Leguminosae) we have isolated the glycoside soyasapogenol B — medinoside E. Medinoside E has the structure of olean-12-ene-3,22,24-triol 3-O-[O--L-rhamnopyranosyl-(12)-O--D-galactopyranosyl-(12)-O--D-glucopyranosyl-(12)--D-glucopyranuronoside].Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan Tashkent. Institute of Organic Chemistry, Russian Academy of Sciences, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 705–710, September–October, 1993.     

Thermal degradation of the transition metal carbonyl complexes

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅(dppm) (whereM=Cr, Mo and W;dppm=Bis-(diphenylphosphino)-methane) has been studied using TG and DSC technics and their results reported. All the complexes facilely lose a carbonyl ligand (CO) below 200 °C. The kinetic analysis on the molybdenum complex suggested a first order dissociation pathway for this decarbonylation process. Dephosphination occurred at high temperature, followed by further decarbonylations. The enthalpy changes associated with the first decarbonylation are reported. The measured kinetic parameters are in good agreement with the literature values on similar systems obtained from solution studies.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonyl-Komplexen des Typs M(CO)₅(dppm) (M=Cr, Mo oder W; dppm=Bis-(diphenylphosphino)-methan) wurden mittels TG und DSC untersucht. Alle diese Komplexe geben unterhalb 200 °C leicht einen Carbonylliganden (CO) ab. Die für den Molybdänkomplex ausgeführte kinetische Analyse deutet auf einen Dissoziationsverlauf erster Ordnung für diesen Decarbonylierungsprozeß hin. Bei hohen Temperaturen erfolgt Dephosphinierung, gefolgt von weiterer Decarbonylierung. Die sich auf den ersten Decarbonylierungsschritt beziehenden Enthalpieänderungen werden angegeben. Die gemessenen kinetischen Parameter stimmen gut mit Literaturwerten ähnlicher Systeme überein.

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M(CO)₅(dppm), M=Cr, W;dppm=-. 200° . . , . , . , .

     

Adsorptive Catalytic Voltammetry of Physcion in the Presence of Dissolved Oxygen at a Carbon Paste Electrode

A novel electroanalytical method for the determination of physcion is described for the first time. Physcion yields an adsorption catalytic voltammetric peak at –0.74V (vs. SCE) in 0.4molL^–1 NH₄Cl–NH₃·H₂O buffer solution (pH 10.5) at a carbon paste electrode (CPE). The experimental results indicated that physcion is efficiently accumulated at a CPE by adsorption. In the subsequent potential scan, physcion was reduced to a homologous anthrahydroquinone compound. The compound was then immediately oxidized to physcion by the dissolved oxygen in the solution, and then physcion was again reduced at the CPE. As a result, a cyclic catalytic reaction was established. The second-order derivative peak current is proportional to the physcion concentration in the ranges of 2.0×10^–104.0×10^–9molL^–1 (accumulation 90s) and 4.0×10^–92.0×10^–8molL^–1 (accumulation 60s). The limit of detection is 8×10^–11molL^–1 (S/N=3) for a 120s accumulation time. The method was applied to the direct determination of physcion in the medicinal plant polygonum multiflorum Thumb with satisfactory results.     

Thermoanalytische Untersuchungen zur Zersetzung von MgCl2 · 6 H2O unter quasiisobaren Bedingungen

Zusammenfassung Vergleichende thermoanalytische Untersuchungen der thermischen Zersetzung von MgCl₂ · 6 H₂O bis 400° C bei p=1 bar unter quasiisothermen und temperaturdynamischen Bedingungen bei simultaner Gasanalyse (EGA) und Variation des H₂O- und HCl-Partialdrucks über der Substanz. Die H₂O- und HCl-Abspaltung erfolgt in Stufen, deren Temperatur vom H₂O-HCl-Partialdruck beeinflußt wird. In Abhängigkeit von den Bedingungen ist die Überführung in MgCl₂ · 4 H₂O direkt aus dem Feststoff oder aus einer Schmelze in einem nichtisothermen Schritt möglich. Die Zersetzung von MgCl₂ · 4 H₂O vollzieht sich unter quasiisobaren Verhältnissen in weiteren drei isothermen Reaktionen über MgCl₂ · 2 H₂O und thermisch stabile basische Magnesiumchloride.

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The decomposition of magnesium chloride hexahydrate was followed by differential thermal analysis and thermogravimetry in combination with evolved gas analysis. The examinations were carried out by means of a Q-derivatograph (temperature range 20–400°; pressure 1 bar) under quasiisothermal and dynamic heating conditions, with variation of the crucible type. The temperatures of the stepwise decomposition of H₂O and HCl are influenced by the partial pressures of H₂O and HCl. Depending on the conditions, it is possible to remove 2 moles of water from solid MgCl₂ · 6 H₂O or from a melt in a nonisothermal step. Under quasiisobaric conditions MgCl₂ · 4 H₂O is transformed in isothermal steps to MgCl₂ · 2 H₂O and stable basic magnesium chlorides.

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Résumé On a étudié la décomposition du chlorure de magnésium hexahydraté par analyse thermique différentielle et par thermogravimétrie combinée avec l'analyse des gaz dégagés. On a effectué les examens avec un dérivatographe-Q (entre 20 et 400°, sous une pression de 1 bar) en conditions de chauffage quasi-isotherme et dynamique, en changeant le type de creuset. La température de l'élimination étagée de H₂O et HCl est influencée par le pression partielle de H₂O et HCl. Suivant les conditions, il est possible d'éliminer deux moles d'eau de MgCl₂ · 6H₂O solide ou fondu, en une étape non-isotherme. En conditions quasi-isobares, MgCl₂ · 4H₂O réagit, par étapes isothermes, pour donner MgCl₂ · H₂O et des chlorures basiques de magnésium stables.

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. Q- ( 20–400°, 1 ) . H₂O HCl H₂O HCl. , , 2 MgCl₂ · 6H₂O , . MgCl₂ · 4H₂O MgCl₂ · 2H₂O .

     

A reanalysis of the kinetic data on the boat pathway of the cope rearrangement of 1,5-hexadiene by comparing with quantum-chemical MINDO/3 results

An attempt has been made to match the availble kinetic data on the title process with the theoretical discovery that it is realized via an intermediate. A new fitting procedure is suggested which takes into account the presence of the intermediate.

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, . , .

     

The effect of defect structure due to doping and irradiation on the thermal decomposition of potassium chlorate

The thermal decomposition of potassium chlorate was investigated as a function of doping and there seems to be a correlation between the polarizing nature of the dopant cation and the thermal degradation temperature of potassium chlorate. In particular, transition metal cations influence strongly the temperature of decomposition. Irradiation and mechanical shock defects influence also the process. A possible mechanism in terms of the semi-conductive properties of the defective chlorates is discussed.

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Zusammenfassung Die thermische Zersetzung von Kaliumchlorat wurde in Abhängigkeit von der Zugabe von Zusätzen untersucht und es scheint eine Korrelation zwischen der polarisierenden Beschaffenheit des Additivkations und der thermischen Zersetzungstemperatur von Kaliumchlorat zu bestehen. Besonders die Übergangsmetallkationen beeinflussen die Zersetzungstemperatur stark. Bestrahlung und mechanische Stoßdefekte beeinflussen den Vorgang ebenfalls. Ein möglicher Mechanismus wird anhand der Halbleiter-Eigenschaften der defekten Chlorate erörtert.

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Résumé On a étudié la décomposition thermique du chlorate de potassium en fonction de l'ajout d'additifs. Il semble qu'une corrélation existe entre la nature polarisante du cation de l'additif et la température de la dégradation thermique du chlorate de potassium. Enparticulier, ce sont les cations des métaux de transition, qui exercent une forte influence sur la température de décomposition. L'irradiation et des défauts causés par choc mécanique influencent aussi le processus. On discute un mécanisme possible à partir des propriétés semi-conductrices des chlorates présentant des défauts.

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. . , , . .

     

High-Performance Liquid Chromatographic Determination of Quinolizidine Alkaloids in Radix Sophora Flavescens Using Tris(2,2′-Bipyridyl)Ruthenium(II) Electrochemiluminescence

Electrogenerated chemiluminescences (ECLs) of quinolizidine alkaloids including matrine (MT), sophocarpine (SC), and sophoridine (SRI) are studied. The light emission is caused by an electro-oxidation reaction between Ru(bpy)₃²⁺ and the tertiary amino group on the alkaloid compounds. A thin-layer flow cell equipped with a glassy carbon disk electrode (22.1mm²) at the potential of ⁺1.30V (vs. Ag/AgCl) was applied for ECL observation. MT, SC and SRI were separated and quantitatively determined within 25min by an ODS-80 Ts reversed-phase column with a mobile phase containing 80mmolL^–1 NaH₂PO₄–K₂HPO₄ buffer+acetonitrile (7:3)+40mmolL^–1 sodium dodecyl sulfate (pH 6.5). The determination limit at an S/N of 3 ranged from 3×10^–9gmL^–1 for MT, 6×10^–9gmL^–1 for SC and 1×10^–9gmL^–1 for SRI. The recoveries are from 92 to 108%, with repeatability ranging from 1.3 to 4.5% (relative standard deviation). The method was successfully applied to the determination of quinolizidine alkaloids in Sophora flavescens samples.     

Trans-cis Photoisomerization of 1-Methyl-4-(4′-hydroxystyryl)pyridinium in inclusion complexes ofβ-cyclodextrin and its derivatives

The effects of -cyclodextrin (-CyD), heptakis(2,6-di-O-methyl)--cyclodextrin (DMCyD) and heptakis(2,3,6-tri-O-methyl)--cyclodextrin (TMCyD) ontrans-cis photoisomerization of 1-ethyl-4-(4-hydroxystyryl)pyridinium (POH) have been studied in aqueous solutions. The ratio of [cis]/[trans] for POH in the photostationary state at pH 8.54 was remarkably reduced by the presence of CyD or DMCyD. The reduction of the [cis]/[trans] ratio in the photostationary state was explained in terms of the shift of the equilibrium of POH ₊ ^trans PO _trans + H^– toward PO _trans formation. The binding constants of CyD and DMCyD for PO _trans were 2.00- and 1.36-fold larger than those for POH ₊ ^trans , respectively. The binding constants of TMCyD for both species are much smaller than those of CyD and DMCyD. This result indicates that PO _trans , which has a betain structure, forms stable complexes with CyD and DMCyD with its hydrophobic parts inside and the charged parts outside the CyD cavities.     

Magnetische Messungen im System Fe—Te

In the binary Fe–Te system six intermediate solid phases exist with varying ranges of homogeneity. With the exception of the high temperature -phase the magnetic behavior of these phases and in some cases the variation of magnetic properties with composition were investigated by susceptibility measurements in the temperature range from 100 to 300 K. Both the -phase (FeTe_1–x ) and the -phase (Fe₅Te₆) follow theCurie—Weiss law and can be designated as antiferromagnetic compounds according to the negativeWeiss constants of –192 K and –314 K, resp. The magnetic moments identify these two phases as high-spin compounds of Fe. The observed increase of the magnetic moments towards the Ferich limit of the -phase is due to the occupation of the octahedral interstices in the anion sublattice by excess iron and it was explained by a simple model. The magnetic moment of the hypothetical equiatomic compounds FeTe, obtained by extrapolation (3.87 _B), as well as the moment of the -phase (3.83 _B) are nearly identical and can be interpreted as being due to the existence of three unpaired 3d-electrons per formula unit. For the Te-rich (Fe_1–x Te)-, (Fe_1–x Te)- and (FeTe₂)-phases the transition metal is supposed to be in the low-spin state. The observedPauli paramagnetism is not temperature independent but decreases with decreasing temperature. Below 100 K FeTe₂ appears to be diamagnetic.

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Mit 7 Abbildungen     

Synthesis and structures of substituted 5,6-dihydro-spiro(benz[4,5]imidazo[1,2-<Emphasis Type="Italic">c</Emphasis>]quinazoline-6,3′-indolin)-2′-ones

The reactions of 2-(2-aminophenyl)benzimidazole with substituted isatins afforded the corresponding 5,6-dihydrospiro(benz[4,5]imidazo[1,2-c]quinazoline-6,3indolin)-2-ones. The spirocyclic structure of the reaction products was established by NMR spectroscopy and X ray diffraction analysis.Results of the study were presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (May 30–June 4, 2004, Moscow).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1987–1989, September, 2004.     

Catalytic reaction of tetrahydrofuran with H2S

The reaction of tetrahydrofuran with H₂S catalyzed by acid-base catalysts has been studied. Catalysts containing an acid-base pair, i.e. a Lewis acid center and a base center, are the most active and selective towards thiolane. Proton donor catalysts and those containing only basic centers are of low activity and selectivity.

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H₂S - . , - : - , . , , .

     

The Electrochemical Behavior of p-Aminophenol at a ω-Mercaptopropionic Acid Self-Assembled Gold Electrode

A -mercaptopropionic acid (MPA) self-assembled monolayer modified electrode (MPA/SAM/Au) on a gold electrode has been fabricated. The characterization of the MPA/SAM/Au was investigated using attenuated total reflection-fourier transform infrared (ATR-FTIR) and A.C. impedance. The electrochemical behaviors of p-aminophenol (p-AP) were studied at the MPA/SAM/Au by cyclic voltammetry and semi-derivative voltammetry (SDV) in BR buffer solution. The modified electrode shows excellent electrocatalytic activity for the redox of p-AP and accelerates the electron transfer rate. The diffusion coefficient (D) is 4.55×10^–6cm²s^–1. The oxidative peak current increases linearly with the concentration of p-AP in the range of 4.0×10^–88×10^–6molL^–1 and 1.0×10^–52×10^–4molL^–1 by square wave voltammetry response, respectively. The detection limit (three times the signal blank/slope) is up to 1.2×10^–8molL^–1. The modified electrode is able to eliminate the interference of p-benzenediol, o-benzenediol and o-AP at a 40-, 90- or 70-fold concentration of p-AP, and it has been satisfactorily used for the determination of the real sample.     

A remark on the applicability of DTA and the reliability of non-isothermal determination for the crystallization kinetics of glasses

The most decisive phenomena arising either from specific DTA measurements (heat inertia, temperature deviation, self-heating) or from non-isothermal kinetic treatment (overlapping models, characteristics determinations) are discussed.

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Zusammenfassung Die entscheidensten Phänomene werden diskutiert, die entweder bei spezifischen DTA-Messungen (Wärmeträgheit, Temperaturabweichungen, Selbsterhitzung) oder bei der nichtisothermen kinetischen Behandlung (überlappende Modelle, Charakteristikbestimmungen) auftreten.

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, ( , , ) ( , ).

     

Electroconduction of Potassium Orthophosphate Modified with Triple-Charged Cations

Solid electrolytes in the systems K_{3 – 3x} Me _x PO₄ (Me = Sc, Y, In, La, Nd, Gd, Tb) are synthesized. Their phase composition and the temperature and concentration dependences of their electroconductivity are studied. In all the systems there form solid solutions based on K₃PO₄, which have a high potassium cation conductance. The latter is due to the formation of potassium vacancies at substitutions 3K⁺ Me³⁺ and, at lower temperatures, to stabilization of a high-temperature -modification of potassium orthophosphate. The electroconductivity of synthesized solid solutions, which equals (4–7) × 10^–3 and 10^–1 S cm^–1 at 300 and 700°C, is similar to that of solid electrolytes K_{3 – x} P_{1 – x} E _x ^VIO₄ and K_{3 – 4x} E _x ^IVPO₄.