Search results for "Catalysis"

Die acidolytische depolymerisation von trioxan in stationärer phase. 21. Mitt. über polyoxymethylene1

1964

Die Depolymerisation von Trioxan mit verschiedenen Phosphorsauren wurde im Temperaturbereich von 100–160°C untersucht. Sie fuhrt zu einem temperaturabhangigen Gleichgewicht zwischen Trioxan und Formaldehyd, das oberhalb 180°C weitgehend auf der Seite des Formaldehyds liegt. Zu einer schnellen Einstellung des Gleichgewichtes eignen sich Ortho- und Pyrophosphorsaure. Die bevorzugte Nebenreaktion ist die Bildung von Methylformiat; die Ausbeute an Methylformiat wird durch Erhohung der Reaktionszeit und der Katalysatoroberflache vergrosert. Das geschilderte Verfahren eignet sich zur Darstellung von monomerem Formaldehyd (Reinheitsgrad etwa 99,8%) im Laboratorium. Depolymerization of trioxane by …

ChemInform Abstract: Stereoselective Synthesis of Quinolizidine Alkaloids: (-)-Lasubin II.

2008

Initially, lasubin II was synthesized diastereoselectively in racemic form [3]. Asymmetric syntheses of lasubin II were achieved based on stereoselective transformations of enantiomerically pure substrates [4] or, for example, via a diastereoselective aza-Diels-Alder reaction using a resolved chiral arylaldehyde tricarbonylchromium complex [5]. Recently, an enantioselectively catalyzed aza-Diels-Alder reaction [6] and a [2+2+2] cycloaddition reaction [7] were successfully used for the synthesis of enantiomerically pure lasubin II.

Stereoselective Synthesis of Quinolizidine Alkaloids: (–)-Lasubin II

2008

Initially, lasubin II was synthesized diastereoselectively in racemic form [3]. Asymmetric syntheses of lasubin II were achieved based on stereoselective transformations of enantiomerically pure substrates [4] or, for example, via a diastereoselective aza-Diels-Alder reaction using a resolved chiral arylaldehyde tricarbonylchromium complex [5]. Recently, an enantioselectively catalyzed aza-Diels-Alder reaction [6] and a [2+2+2] cycloaddition reaction [7] were successfully used for the synthesis of enantiomerically pure lasubin II.

Magnetization Relaxation in a Three‐Dimensional Ligated Cobalt Phosphonate Containing Ferrimagnetic Chains

2010

Electrochemical Syntheses Involving Carbon Dioxide

1990

The recent developments of electrosynthetic processes involving carbon dioxide are reviewed. Both processes involving carbon dioxide alone and electrocarboxylations are taken under consideration. The first of these two fields, mainly projected towards the production of basic chemicals such as methanol or carbon monoxide, is at present at a stage of fundamental research. Some interesting developments have recently appeared in the literature, concerning the use of electrode materials, or of transition metal complexes with particular catalytic activity. Electrocarboxylations are at a stage of more applicative development: some processes have reached the stage of pilot plant, and other have int…

Inversion of the Triphenylamine Molecule

1964

Book Review: Cycloaddition Reactions in Organic Synthesis. By W. Carruthers

1992

Challenges in the Electrochemical Synthesis of Si 2 Cl 6 Starting from Tetrachlorosilane and Trichlorosilane

2022

1975

In the polymerization of isobutene catalyzed by aluminium tribromide and in the polymerization of styrene catalyzed by trifluoromethanesulphonic acid it is supposed that an inactive catalyst monomer complex is formed which is in equilibrium with other active species. The monomer complexation of the catalyst explains the S-shaped conversion curves and the complex kinetics of the polymerization. The value of the equilibrium constant Km (complexation constant) expresses what part of the catalyst may take part in the polymerization process as an active initiating species. For the system isobutene/AlBr3, Km was found to be 0,62 1/mol. In the system styrene/CF3SO3H, the high value of the complexa…

Über die polymerisation von styrol in flüssigem schwefeldioxyd

1963

In uberschussigem flussigem Schwefeldioxyd gelostes Styrol kann durch Zugabe von Hydroperoxyden oder Persaren polymerisiert werden. Innerhalb weniger Minuten entstehen in hohen Ausbeuten nach einem kationischen Mechanismus hochmolekulare Polystyrole. Der Einflus der Monomeren-Konzentration, der Temperatur, der Losungsmittel und sonstiger Zusatze wird studiert. Bei Anwesenheit bestimmter Losungsmittel entstehen mit den gleichen Katalysatoren bei stark verminderter Reaktionsgeschwindigkeit durch radikalische Copolymerisation Polystyrolsulfone. Styrene, dissolved in excess liquid SO2 can be polymerized by addition of hydroperoxides or peracids. In a few minutes high yields of high molecular po…