Chain scission of butyl rubber by nitrogen dioxide in absence and presence of air

The chain scission reaction suffered by butyl rubber due to NO₂ (0.01-1 mm Hg) has been studied in the presence and absence of air. It has also been studied as a function of temperature (25–65°C) at constant NO₂ pressure, again in absence and presence of 1 atm of air. Reaction mechanisms which are in good agreement with the experimental results have been formulated. The synergistic action of O₂ and NO₂ has been pointed out.     

Melting of gold microclusters

The transition from solid-like to liquid-like behavior in Au _n ,n=6, 7, 13, clusters is studied using molecular dynamics simulations. A Gupta-type potential with all-neighbour interactions is employed to incorporaten-body effects. The melting-like transition is described in terms of short-time averages of the kinetic energy per particle, root-mean-square bond length fluctuations and mean square displacements. A comparison between melting temperatures of Au _n and Ni _n clusters is presented.     

Literatur

Ohne Zusammenfassung     

Poly(galacturonic acid)–bivalent metal complexes

Complexation or stability constants have been determined for complexes of poly-(galacturonic acid) with Cu, Cd, Zn, and Ni. The stability of complexation decreases as follows: Cu > Cd > Zn > Ni.     

Literatur

Ohne Zusammenfassung     

Kohlenhydrate

Ohne Zusammenfassung     

Katalytische Reaktionen in der Spurenanalyse und Untersuchung ihrer Mechanismen. VII

Zusammenfassung Für die Bestimmung von Vanadinspuren eignet sich die Bromat-Ascorbinsäure-Reaktion vom Landolt-Typ, für die das Gesehwindigkeitsgesetz in folgender Form Gültigkeit hat: –d[BrO₃ ^–]/d=[BrO₃ ^– K ₁([(₆H₈O₆+K _v[v]+K ₂ [Br^–][H⁺]²). Die Verfasser bestimmten auf Grund der Daten für die Reaktionszeit der Landolt-Reaktion den Wert vonK ₁ und die Aktivierungsenergie der Bromat-Ascorbinsäure-Reaktion.K ₁=2,5·10^–/Mol^–1 · min^–1 (25° C) bzw. 15,408 Kcal/Mol.

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Catalytic reactions in trace analysis and investigation of their mechanisms. VII

Summary The bromate-ascorbic acid reaction of the Landolt type is suited to the determination of traces of vanadium. The velocity law is valid in the following form: –d[BrO₃ ^–]/d=[BrO₃ ^– K ₁([(₆H₈O₆+K _v [v]+K ₂[Br^–][H ⁺]²). Using the data for the reaction time of the Landolt-reaction, the authors determined the value ofK ₁ and the activation energy of the bromate-ascorbic acid reaction.K ₁=2.5 · 10^–2/mol^–1 · min^–1 (25° C) or 15.408 kcal/mol.

     

Evolution of H2O and CO2 during the copper-catalyzed oxidation of isotactic polypropylene

The kinetics and mechanism of H₂O and CO₂ evolution during uncatalyzed and copper(oxide)-catalyzed (Cu, CuO, CuO_0.67) oxidation of isotactic polypropylene have been investigated in detail for various catalysts over a range of temperatures (90–150°C). These volatiles were determined chromatographically; H₂O and CO₂ represent the main volatiles of the oxidation, comprising about 80 mol % of all volatiles. Uncatalyzed oxidation evolves ca. 1 mol of H₂O and 1 mol of CO₂ for each unit mole of polymer oxidized, while catalyzed oxidation produces 2 mol of H₂O and ca. 1.2 mol of CO₂ for each unit mole of polymer. These results indicate that secondary as well as tertiary H atoms on the polymer chains are involved in hydroperoxide formation and decay. The oxidation mechanism has been formulated and evaluated on this basis. It consists essentially of two parallel oxidation reactions involving tertiary and secondary groups (H atoms and hydroperoxides), respectively. The mechanism can be represented by first- and pseudo-first-order reactions in series: (1) oxygen absorption showing induction periods; (2) hydroperoxide formation and decay (plateaus are reached); (3) H₂O evolution from the decay of hydroperoxides; and (4) subsequent CO₂ production involving chain scission. Arrhenius parameters for all oxidation reactions (uncatalyzed and catalyzed) are also presented. It appears that CuO_0.67 is the most efficient catalyst of those investigated.