Mechanism of alkyl iodide reduction to alkanes in aqueous solutions of Na2PtCl4?NaI?HClO4

Platinum(II) catalyzes the reduction of alkyl iodides to alkanes according to a mechanism involving oxidative addition of RI to Pt(II), reduction of the product complex RPt(IV) to RPt(II) by iodide ions and protolysis of the latter particle.

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(II) , RI Pt^II, - RPt^IV RPt^II .

     

Multivariate Statistical Assessment of Air Quality: A Case Study

The present paper deals with the application of several chemometrical methods (cluster and principal components analysis, source apportioning on absolute principal components scores) to an aerosol data collection from Unterloibach, Austria. It is shown that seven latent factors explaining almost 80% of the total variance are responsible for the data structure and are conditionally identified as secondary aerosol, mineral dust, oil burning, lead smelter, coal burning, salt and fertilizer emission sources. Furthermore, the contribution of each identified source to the formation of the particle total mass and chemical compounds total concentration is calculated. Thus, a reliable assessment of the air quality in the region is performed. The requirements of the sustainability concept for ecological indicators in this case is easily transformed into a multivariate statistical problem taking into account not separate indicators but the specific multivariate nature of aerosol pollution.     

Quantitative phase analysis from permeability versus temperature curves

The expressions for quantitative phase analysis from permeability versus temperature curves are discussed, and the results are illustrated by the determination of magnetic Co₂ Y remnants (2CoO·2BaO·6Fe₂O₃) in Co₂Z (2CoO·3BaO·12Fe₂O₃) samples. The method is well suited for the determination of small inclusions of a magnetic phase in a given magnetic material, in a range where X-ray methods become useless as a rule.

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Zusammenfassung Zwecks quantitativer Phasenuntersuchungen wird die Auswertung von Permeabilitäts-Temperatur Diagrammen näher beschrieben und die Ergebnisse mit der Bestimmung von magnetischen Co₂Y Resten (2CoO · 2BaO · 6Fe₂O₃) in Co₂Z (2CoO·3BaO·12Fe₂O₃) Proben illustriert. Diese Methode ist zur Bestimmung von geringen, mittels röntgenographischen Verfahren nicht feststellbaren magnetischen Phaseneinschlüssen in einem bestimmten magnetischen Material sehr geeignet.

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, Co₂Y (2CoO·2BaO·6Fe₂O₃) Co₂Z (2CoO·3BaO·12Fe₂O₃). , , , .

     

Der o-Effekt in den Massenspektren aromatischer Verbindungen

Zusammenfassung Das Massenspektrum des O-Äthylsalicylsäureamides VII b ist von dem seiner m- und p-isomeren Verbindung völlig verschieden und zeigt einen typischen massenspektrometrischen o-Effekt.Die bisher aufgefundenen Verbindungen mit massenspektro-metrischem o-Effekt gehören einem relativ kleinen Kreis von Aromaten mit ganz bestimmten Strukturmerkmalen an. Die Bildung der für den o-Effekt charakteristischen Bruchstücke kann in allen diesen Fällen nach einem vonMcLafferty aufgestellten Mechanismus zwanglos erklärt werden. Verbindung VIIb hätte unter der Voraussetzung, daß eine Entstehung der für den o-Effekt typischen Fragmente nur nach diesem Mechanismus möglich ist, keinen o-Effekt zeigen dürfen.Das Auftreten des o-Effektes im Massenspektrum von VIIb läßt erkennen, daß die Bedingung zur Bildung der für den o-Effekt charakteristischen Bruchstücke lediglich in der Möglichkeit zur Ausbildung stabiler Spaltprodukte zu suchen ist, und daß daher weit mehr Verbindungen einen o-Effekt zeigen sollten als bisher anzunehmen war.Mit 1 Abbildung     

Natural flavours of wine: correlation between instrumental analysis and sensory perception

Summary The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. The aroma extracts — received by extraction with trichlorofluoromethane — are separated by gas chromatography. There are significant varietal differences between the aromagrams (fingerprint pattern). Thus the amount of some flavour compounds (key substances) shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties.The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes (terpene profile). These groups are: Riesling type, Muscat type and Silvaner-Weißburgunder type. Such terpene profiles are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods as for example linear discriminant analysis even the different varieties within the mentioned groups (for instance the Riesling-group: Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other.To identify compounds causing off-flavours the sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatography separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, mousiness, corkiness etc. in wine could be found in this way.     

ESR studies of photoinduced centers on weakly reduced anatase

The paramagnetic centers of reduced anatase (g₁=1.999, g₂=1.984, g₃=1.979) and (g₁=2.046, g₂=2.008), assigned to the stabilization of photoinduced holes near anion vacancies, have been studied. For the reduced oxide a new type of O₂ photoadsorption at h >1 eV due to the generation of only electron surface centers has been discovered.

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, : (g₁=1,999, g₂=1,984, g₃=1,979) (g₁=2,046, g₂=2,008), . O₂ h>1 , .

     

Determination of total,and bound Se in sera by INAA

In this study we report on the comparison between the total selenium in serum (total Se) with that which is apparently bound to high molecular weight (>12,000 D) species, presumably proteins (bound Se). Nine hundred seventy seven (977) serum samples arising out of a population-based epidemiological study were prepared in duplicate for the determination of total Se by pipeting directly into irradiation vials; and separate duplicate aliquots were dialyzed against DI water for the determination of bound Se. All samples were analyzed by neutron activation analysis via^77mSe (17.4 s). A small dialyzable Se component (6%) (free Se), defined as the difference between the total Se minus the bound Se, was identified.     

Kinetics of autoxidation of potassium O-butyl dithiocarbonate catalyzed by cobalt(II) tetrasulfophthalocyanine

Autoxidation kinetics of potassium O-butyl dithio-carbonate catalyzed by cobalt(II) tetrasulfophthalocyanine has been studied polarographically. The reaction follows two parallel pathways of zero and first order with respect to dioxygen, each being a Michaelis function of the substrate concentration. On the basic of data obtained and those reported previously for cysteine autoxidation, a general reaction mechanism is suggested.

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O- , - (II). , , . , , .

     

To the Theory of the Aggregation of Polydisperse Colloids

Particle aggregation in polydisperse colloids is studied theoretically. It is assumed that the aggregation follows phase transition scenario with the formation of dense uniform colloidal phases. Bidisperse model corresponding to the system of relatively large and small particles is considered. Van der Waals attraction between large particles and the action of relevant entropy forces due to the presence of depleted layers of small particles are taken into account. The diagrams of equilibrium phase transitions of gas–liquid and gas–solid types occurring in the ensemble of large particles are constructed. The influence of size and concentration of small particles on the pattern and structure of phase diagrams is studied. It is shown that an increase in the concentration of small particles leads, on the one hand, to a rise of phase transition temperature and, on the other hand, to an increase in the threshold concentration of large particles.     

Beiträge zur Chemie der Pyrrolpigmente, 72. Mitt.

A strategy for the synthesis of bilatrienes-abc bridged between rings A and C has been developed and tested in case of a bibenzylethane bridging fragment. This strategy was then applied to the synthesis of a 2,3-dihydrobilatriene-abc bridged by a (S)-lysine moiety from ring A to ring C (positions 3 and 12) by means of peptide bonds between the two amino groups of lysine and the acetic and propionic acid side chains of the chromophoric unit. The two diastereomers resulting from the two chiral centers of the lysine residue and at position 3 of the chromophore were separated by chromatography.

     

Effect of composition of the solvent on the selectivity of competitive hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene

The selectivity of competitive hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene on 5% Pt on silica gel catalyst at 20°C and atmospheric pressure was investigated, and the effect of changes in the composition of the solvent on the selectivity of hydrogenation was examined. Three solvent systems have been used: methanol-water, 1-heptanol-cyclohexane and ethanol-cyclohexane mixtures. The causes underlying changes in the selectivity of hydrogenation with changing composition of the solvent are discussed.

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2--3--2- 1- 5% Pt 20°C . . 1- . .

     

Methanol oxidation on copper-oxide catalysts

Complete oxidation of methanol on CuO and CuO/Al₂O₃ catalysts has been studied. The main kinetic parameters have been determined. A possible mechanism and the nature of the rate-determining step are discussed.

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CuO CuO/Al₂O₃. . .

     

Analytical Chemistry — today''s definition and interpretation

Conclusion Although this multidisciplinary branch of science is growing rapidly today, yet two main points remain unchanged. On the one hand, it is analytical in essence; on the other, the information which it aims to acquire is chemical in nature, i.e. within the domain of chemistry. Accordingly it seems pertinent to reserve the term Analytical Chemistry for it. Other terms like analytical physics and chemical characterization are one-sided, with the aim or essence missing. The same is true of analytics and analytical science. Moreover, they should, literally speaking, include analytic geometry, analytical mechanics and so on.     

Elemental assay of materials by NA and gamma-ray spectroscopy without standards and neutron flux monitoring

The theoretical expression of the induced radioactivity of a nuclide activated by neutron reactions is basically used to develop a mathematical model and an accurate method of evaluating concentrations of elements producing -ray emitting isotopes, without use of standards and of neutron flux monitoring. This initial Without Standard method is mainly applicable to materials obtained by special or industrial technologies, when precise values of the elemental concentrations, after the synthesis process, are required. A preliminary test of the method, using a Goodfellow Metals stainless steel material irradiated in a thermal neutron field is reported. The results confirm the applicability of the Without Standard method to the NAA experiments for the elemental analysis of materials.Presented at the MTAA-8 Conference, September 16–20, 1991, Vienna, Austria.     

Determination of trace element concentrations of Libyan chewing and cigarette tobacco by instrumental neutron activation analysis

The concentration of 12 trace elements in the chewing tobacco and two different brands of Libyan cigarette Atlas and Sport has been measured by instrumental neutron activation analysis and compared to the results of cigarette tobacco from India, USA, Iran and Yugoslavia. These elements are Co, Cr, Cu, Fe, Hf, Mn, Rb, Sc, Th, U, V and Zn.     

A definitive method for the determination of trace amounts of cobalt in biological materials by neutron activation analysis

A new, very accurate (definitive) method for the determination of trace amounts of cobalt in biological materials has been devised. The method is based on combination of neutron irradiation with quantitative and selective post-irradiation separation of cobalt from all accompanying radionuclides followed by measurement by -ray spectrometry. Column chromatography in which owing to addition of Co carrier the course of separation can be followed visually is the key element of the separation scheme. Several criteria have been formulated which must be simultaneously fulfilled in order to acknowledge the result as obtained by a definitive method. The high accuracy of the method has been demonstrated by the analysis of several certified reference materials of widely different Co contents.     

Epithermal neutron flux characterization of the Triga Mark III reactor, Salazar, Mexico, for use in INAA

The nonideality of the epithermal neutron flux distribution at a reactor site parameter () and the thermal-to-epithermal neutron ratio (f) were determined in 3 typical irradiation positions of the Triga Mark III reactor of the National Nuclear Research Institute, Salazar, Mexico, using the Cd-ratio for multimonitor and bare bi-isotopic monitor methods, respectively. This characterization is to be used in theK ₀-method of NAA, recently introduced at the Institute.     

Philosophical aspects of chemometrical strategy in Analytical Chemistry

Summary This paper discusses the philosophical aspects of the three main chemometrical strategies in analytical chemistry: statistical data treatment, optimization and modelling, pattern recognition. It is possible by a more general consideration of these approaches to find a proper place of different philosophical categories such as form and content, induction and deduction, concrete and general in analytical chemistry. The philosophical aspect of the considerations allows a deeper penetration into the theoretical basis of chemical analysis.

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Philosophische Betrachtungen zu chemometrischen Strategien in der Analytischen Chemie

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Presented at the First International Symposium on History and Philosophy in Analytical Chemistry, Vienna, November 22–23, 1985     

The use of a modified Westcott-formalism in thek o-standardization of NAA: The state of affairs

Recently, the introduction was proposed of the Westcott-formalism in the k_o-standardization method, in order to enable the handling of analytically important non-1/v (n, ) reactions. In the present paper some elucidations are given to the Westcott-basedk _o-method: the black box of Westcott's g+rs formalism is opened; procedures and formulas are given for the experimental determination of the flux parameters and a survey is presented of the status of the nuclear data.