Katalytische Bestimmung von Vanadinspuren mit Hilfe einer Landolt-Reaktion auf „Bromgrundlage“

Zusammenfassung Unter geeigneten Versuchsbedingungen sind die Bromat-Askorbinsäure- bzw. die Bromat-Bromid-Askorbinsäure-Reaktion Landolt-Reaktionen auf Bromgrundlage, die von Vanadin stark katalysiert werden. Das beim Reaktionsendpunkt ausgeschiedene Brom läßt sich mit o-Tolidin oder Azokarmin GX indizieren. Zur Bestimmung von Vanadinspuren mittels der Bromat-Bromid-Askorbinsäure-Reaktion wurde die chronometrische und die Simultankomparationsmethode angewandt. Die Nachweisgrenze der Reaktion beträgt 0,01g V, die Grenzkonzentration 15 · 10⁸. Der optimale Konzentrationsbereich liegt zwischen 0,05 und 1,50g V/5 ml, der relative Fehler der Simultankomparationsmethode innerhalb von 2%. Der Einfluß von Fremdionen wird angegeben.Die Bromat-Bromid-Hydrazin-Reaktion gehört ebenfalls zu den Landolt-Reaktionen auf Bromgrundlage. Vanadin übt auch auf dieses System eine katalytische Wirkung aus.

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Summary Under suitable conditions, the bromate-ascorbio acid and the bromate-bromide-ascorbio acid undergo the Landolt reactions based on bromine that are strongly catalyzed by vanadium. The bromine released at the endpoint of the reaction can be indicated by means ofo-tolidine or azocarmine GX. The chronometric and the simultaneous comparation methods were employed in the determination of traces of vanadium by means of the bromate-bromide-ascorbic acid reaction. The detection limit of the reaction is 0.01g V, the concentration limit is 1 5 · 10⁸. The optimal concentration range is between 0.05 and 1.50g V/5 ml. The relative error of the simultaneous comparation method is within 2%. The influence of foreign ions is stated.The bromate-bromide-hydrazine reaction also belongs among the Landolt reactions «based on bromine». This system is likewise catalyzed by vanadium.

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Résumé Dans des conditions expérimentales précises, la réaction acide ascorbiquebromate ou la réaction acide ascorbique-bromure-bromate sont des réactions de Landolt, «avec brome», fortement catalysées par le vanadium. On peut prendre l'o-tolidine ou l'azocarmin GX comme indicateur du brome qui se sépare au point équivalent. Pour doser les traces de vanadium à l'aide de la réaction acide ascorbique-bromate-bromure, on a utilisé la méthode chronométrique et la méthode de comparaison simultanée. La limite de dilution de la réaction s'élève à 0,01 g V, la concentration limite à 1 5 · 10⁸. Le domaine optimal de concentration se situe entre 0,05 et 1,50g V/5 ml, l'erreur relative de la méthode de comparaison simultanée se trouve comprise dans les limites de 2%. On décrit l'influence des ions gênants.La réaction hydrazine-bromure-bromate appartient également aux réactions de Landolt «avec brome«. Le vanadium exerce aussi une action catalytique sur ce système.

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Herrn Professor Dr.I. M. Kolthoff zum 70. Geburtstag gewidmet.     

Diffusion of Cu2+ catalysts from Cu-metal polymer or Cu-oxide/polymer interfaces into isotactic polypropylene

Diffusion coefficients of Cu²⁺ in the form of its carboxylate have been measured in isotactic polypropylene as a function of temperature (90–128°C) and extent of preoxidation. Diffusion take place from the metal catalyst/polymer interface into the bulk polymer. The diffusion is dependent on the extent of preoxidation and temperature but not on the type of catalyst (Cu, CuO, CuO_0.67). Analysis of polymer sections for Cu²⁺ ions was carried out with a selective Cu²⁺ electrode. Diffusion in isotactic polypropylene is about 1000 times faster than in lowdensity polyethylene. The carboxylate anion appears to have about 7 C-atoms for diffusion in isotactic polypropylene compared with 29 C-atoms for low-density polyethylene.     

Thermal degradation of poly-p-oxybenzoate under vacuum

The thermal degradation of poly-p-oxybenzoate in vacuo as function of temperature has been studied. The energy of activation of the process up to about 30% volatile formation is 59.6 kcal/mole. The degradation is preceded by induction periods, which have been shown to be due to poor heat conductivity of the polymer powder. CO, CO₂, phenol, and an unknown compound of molecular weight larger than 200 are the main degradation products found by chromatographic analysis. Infrared spectra of the original polymer, the polymer residue after degradation and of a degradation product solid at room temperature are presented. The possible reactions taking place have been indicated. The heat stability of the polymer in vacuo lies between those of polytetra-fluoroethylene and polyethylene.     

Literatur

Ohne Zusammenfassung     

Properties of rotating nanoalloys formed by cluster collision: a computer simulation study

Results of dynamical simulations of collision-induced formation and properties of bimetallic nanoparticles are presented and analyzed. The analysis includes the effects of the collision energy and the impact parameter. For nonzero impact parameters, the formed (in many cases Janus-type) nanoparticles are rotating. The energy of the rotating nanoparticles is decomposed into the rotational and vibrational components, and the structural effects of these components are analyzed. Comparison is made with the case of the corresponding homoatomic systems, formed by collision of nanoparticles with the same elemental composition.