Search results for "Molecular oxygen"
showing 10 items of 22 documents
Oxidation of adrenaline and noradrenaline by solved molecular oxygen in a FIA assembly.
2002
A simple and effective procedure is proposed for the study and simultaneous determination of adrenaline and noradrenaline. The fluorimetric determination of both substances is performed in a flow injection assembly and by oxidation of both drugs with the solved molecular oxygen. The influence of different parameters is empirically studied and the interpretation of the reaction mechanism is also added. The determination of adrenaline is monitored at 450 nm and the outputs at 520 nm correspond to the adrenaline and noradrenaline global amount; for both lectures lambda(exc) 329 nm. The influence of temperature is relevant and analytical determination occurred at 55 degrees C by immersing the s…
Der nachweis der primärreaktion bei der autoxydation des tetralins
1964
Die Autoxydation des Tetralins wurde bei kleinen Umsatzen durch polarographische oder kolorimetrische Bestimmung des Peroxidgehaltes verfolgt und eine Anfangsgeschwindigkeit gefunden, die groser ist, als sie nach dem Peroxidgehalt des Tetralins sein sollte. Diese zusatzliche Reaktionsgeschwindigkeit ist die der Primarreaktion der Autoxydation. Dabei bilden sich aus Tetralin und molekularem Sauerstoff Radikale. Diese Primarreaktion ist nur dann beobachtbar, wenn der Peroxidgehalt des Tetralins etwa 10−5 Mol/l betragt oder kleiner ist. The autoxidation of tetraline was measured to a low degree of conversion by polarographic or colorimetric determination of tetraline hydroperoxide. The extrapo…
Reaktionskinetik der polymerisationshemmung durch molekularen sauerstoff. (Versuche mit methylmethacrylat)
1956
Wahrend der Inhibierungsperiode findet eine streng alternierende Copolymerisation zwischen molekularem Sauerstoff und dem monomeren Methacrylat statt. Die Alternierung kommt dadurch zustande, das die Anlagerung von O2 an ein radikalisches Kettenende mit einer um mindestens 5 Grosenordnungen hoheren Geschwindigkeitskonstante erfolgt als die Anlagerung des Monomeren. Die Reaktionsfahigkeit des Sauerstoffs bei dieser Reaktion entspricht somit der eines freien Radikals. Die Lange der hierbei auftretenden Reaktionsketten liegt in der Grosenordnung 102, das ist 2 Grosenordnungen kleiner als die Ketten bei der normalen Polymerisation. Der Abbruch der Copolymerisationsketten erfolgt zwischen zwei R…
Oxygen Incorporation Reaction into Mixed Conducting Perovskites: a Mechanistic Analysis for (La,Sr)MnO3 Based on DFT Calculations
2009
Based on DFT calculations of intermediates and transition states, several hypothetical mechanisms for oxygen incorporation into mixed conducting La1-xSrxMnO3{plus minus}d perovskites are discussed. In the most probable mechanism, the rate-determining step comprises the encounter of a highly mobile surface oxygen vacancy and a molecular oxygen adsorbate. Starting from these results, the variation of reaction rates for different materials is explored.
Highly dispersed encapsulated AuPd nanoparticles on ordered mesoporous carbons for the direct synthesis of H2O2 from molecular oxygen and hydrogen
2012
AuPd nanoparticles (<3 nm) have been encapsulated on the pores of a nanostructured CMK-3 carbon prepared by a nanocasting procedure. This material has been shown to be an excellent catalyst for the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen.
A Superoxovanadium(V) Complex Linking the Peroxide and Dioxygen Chemistry of Vanadium.
2001
A missing link: A superoxovanadium(V) complex is the first reaction intermediate in the oxidative conversion of a peroxovanadium(V) complex into a vanadyl(IV) complex and molecular oxygen. The superoxo species appears also to play an essential role in the formation of the peroxovanadium(V) complex from the vanadyl(IV) complex and molecular oxygen.
First transformations of pyrano[3,4-b]indol-3-ones to salvadoricine and 2,3-diacylindoles
1992
The readily available methylated pyrano[3,4-b]indol-3-ones 1a and 1b were hydrolyzed to furnish the 2-acetylindol-3-alkanoic acids 2 and 4. Compound 2 was easily transformed selectively to 2-acetyl-3-methylindole (3, salvadoricine). Substrate 1b reacts with molecular oxygen from the air only in the presence of a catalyst to give 2,3-diacetylindole (5) while 1a reacts with nitrosobenzene via a proposed Diels-Alder step to yield 2-acetylindole-3-carbaldehyde (6). The latter product can also be obtained in low yield from the reaction of 1a with molecular oxygen from the air.
Influence of stoichiometry on high temperature intrinsic defects in fused silica
1992
Abstract The set of intrinsic defects, their generation, interactions and recombination reactions are discussed, including the participation of atomic and molecular oxygen, which allows one to take into account the stoichiometry of fused silica. The mathematical solution of the set of equations, which characterizes the equilibrium concentrations of intrinsic defects, gives the specific values of intrinsic defect concentrations at different temperatures and stoichiometries. The influence of such intrinsic defects frozen in at room temperature on the spectroscopic characteristics of fused silica is analyzed.
FIA-fluorimetric determination of adrenaline in pharmaceutical formulations by oxidation with molecular oxygen
1998
The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h−1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl−1.
Reaktionskinetik der Polymerisationshemmung durch molekularen Sauerstoff
1957
Die Polymerisationshemmung geschieht bei Styrol nach demselben Mechanismus wie er kurzlich fur Methylmethacrylat berichtet wurde1. Wahrend der Inhibierungsperiode findet streng alternierende Copolymerisation zwischen molekularem Sauerstoff und dem monomeren Styrol statt. Die fur die Anlagerung von O2 an das Radikal RM · masgebende Konstante kMO2 ist etwa von der Grosenordnung 106–107, d. h. die Reaktionsfahigkeit des Sauerstoffs in dieser Reaktion entspricht der eines Radikals. Bruttogeschwindigkeit und kinetische Kettenlange wahrend der Inhibierungsperiode werden auf Grund des Reaktionsmechanismus berechnet und experimentell bestatigt. The inhibition mechanism in the polymerization of styr…