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Acceleration Effect (acceleration + effect)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

ChemInform Abstract: Acceleration Effect of an Allylic Hydroxy Group on Ring-Closing Enyne Metathesis of Terminal Alkynes: Scope, Application, and Mechanistic Insights.

CHEMINFORM, Issue 13 2009
Tatsushi Imahori
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Significant Self-Acceleration Effects of Nitrile Additives in the Rhodium-Catalyzed Conversion of Aldoximes to Amides: A New Mechanistic Aspect

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009
Min Kim
Abstract It was found that the catalytic activity of rhodium complexes was highly sensitive to the type of N-heterocyclic carbene (NHC) ligands in the conversion of aldoximes to amides. Among those species examined, the (cyclooctadiene)rhodium chloride-carbene complex Rh(cod)(IMes)Cl exhibited the highest reactivity when it was employed in combination with a Brønsted acid, thus allowing mild reaction conditions. A significant rate acceleration effect resulting from the addition of nitrile additives was also observed. With the new protocol, the substrate scope of aldoximes has been widely expanded to include sterically congested and electronically varied derivatives. On the basis of detailed mechanistic studies, it is proposed that the reaction proceeds mainly via intramolecular electrophilic addition of aldoxime to rhodium-bound nitrile, which is different from the generally postulated two-step route: dehydration of aldoxime to nitrile followed by hydration of the latter intermediate. [source]

New efficient copper fluoride-based catalyst for enantioselective hydrosilylation of ketones in aerobic conditions

ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2001
James Courmarcel
A new copper(II) fluoride,chiral diphosphines catalytic system was developed. This one is very efficient and selective for the hydrosilylation of several substituted or unsubstituted aromatic ketones in so far as moderate to excellent enantioselectivities were obtained. An oxygen acceleration effect was observed that led us to propose a practical protocol with a low amount of catalyst. [source]

Mass transport and flow regimes in centrifugal partition chromatography

AICHE JOURNAL, Issue 8 2002
L. Marchal
Centrifugal partition chromatography (CPC) is a support-free liquid,liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane-methanol two-phase system, three main flow regimes,stuck film, oscillating sheet, and atomization,are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Péclet number, partition ratio, and mass-transfer coefficient) are fitted on solute residence-time distribution. Off-column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed. [source]