Polymerization of ethylene: Some aspects of metallocene catalyst stabilization under homogeneous and heterogeneous reaction conditions

2010 ◽  
Vol 119 (5) ◽  
pp. 3051-3057 ◽  
Author(s):  
A. J. D. de Freitas ◽  
J. H. Z. dos Santos ◽  
S. M. P. Meneghetti ◽  
M. R. Meneghetti
Keyword(s):  
Heterogeneous Reaction ◽  
Metallocene Catalyst ◽  
Reaction Conditions ◽  
Catalyst Stabilization ◽  
Heterogeneous Reaction Conditions

Effects of salts on the kinetics of oxidation of alkenes by thallic salts in aqueous solutions

1981 ◽  
Vol 46 (3) ◽  
pp. 693-700 ◽  
Author(s):  
Milan Strašák ◽  
Jaroslav Majer
Keyword(s):  
Aqueous Solutions ◽  
Phase Transfer ◽  
Heterogeneous Reaction ◽  
Qualitative Model ◽  
Kinetic Effect ◽  
Tetraalkylammonium Salts ◽  
Reaction Conditions ◽  
Kinetics Of Oxidation ◽  
Kinetics Of ◽  
Heterogeneous Reaction Conditions

The kinetics of oxidation of alkenes by thallic sulphate in aqueous solutions, involving the two reaction steps-the hydroxythallation and the dethallation - was studied, and the effect of salts on the kinetics was examined; this made it possible to specify more precisely the reaction mechanism and to suggest a qualitative model of the reaction coordinate. It was found that in homogeneous as well as in heterogeneous reaction conditions, the reaction can be accelerated appreciably by adding tetraalkylammonium salts. These salts not only operate as catalysts of the phase transfer, but also exert a significant kinetic effect, which can be explained with a simplification in terms of a stabilization of the transition state of the reaction.

scholarly journals Two Fungal Flavonoid-specific Glucosidases/rutinosidases for Rutin Hydrolysis and Rutinoside Synthesis Under Homogeneous and Heterogeneous Reaction Conditions

2021 ◽  
Author(s):  
Michael Kotik ◽  
Hana Javůrková ◽  
Katerina Brodsky ◽  
Helena Pelantová
Keyword(s):  
Dimethyl Sulfoxide ◽  
Biochemical Characterization ◽  
Heterogeneous Reaction ◽  
Mucor Circinelloides ◽  
Product Inhibition ◽  
Sequence Alignments ◽  
Reaction Conditions ◽  
Multiple Sequence ◽  
Hydrolytic Activities ◽  
Heterogeneous Reaction Conditions

Abstract The glycosidases within GH5-23 cleave the glycosidic bond of β-glucosylated or rutinosylated flavonoids. Moreover, by virtue of their transglycosylation activity, glycoconjugates with glucosyl and rutinosyl moieties are accessible. Here we report the biochemical characterization and biotechnological assessment of two heterologously expressed members of GH5-23 – McGlc from Mucor circinelloides and PcGlc from Penicillium chrysogenum. Both enzymes exhibited the highest hydrolytic activities with quercetin-3-β-O-glucopyranoside, whereas lower specificity constants were determined with the rutinosides narcissin, rutin and hesperidin. High stabilities against thermal, ethanol and dimethyl sulfoxide-induced inactivation, a very limited secondary hydrolysis of the formed transglycosylation products, and no detectable product inhibition were additional features appropriate for biotechnological applications. The enzymes were compared in their efficiencies to hydrolyze rutin and to synthesize 2‑phenylethyl rutinoside under homogeneous and heterogeneous reaction conditions using high rutin concentrations of 100 and 300 mM. Highest transglycosylation efficiencies were achieved with fully dissolved rutin in reaction mixtures containing 25 % dimethyl sulfoxide. Molecular docking and multiple sequence alignments suggest that the hydrophobic environment of aromatic residues within the +1 subsite of GH5-23 glycosidases is very important for the binding of flavonoid glucosides and rutinosides.

Tyrosinase-catalyzed modification of Bombyx mori silk fibroin: Grafting of chitosan under heterogeneous reaction conditions

2006 ◽  
Vol 125 (2) ◽  
pp. 281-294 ◽  
Author(s):  
Giuliano Freddi ◽  
Anna Anghileri ◽  
Sandra Sampaio ◽  
Johanna Buchert ◽  
Patrizia Monti ◽  
...  
Keyword(s):  
Bombyx Mori ◽  
Silk Fibroin ◽  
Heterogeneous Reaction ◽  
Reaction Conditions ◽  
Bombyx Mori Silk ◽  
Heterogeneous Reaction Conditions

scholarly journals Reactivity of substrates with multiple competitive reactive sites toward NBS under neat reaction conditions promoted by visible light

2021 ◽  
Author(s):  
Blaž Grjol ◽  
Marjan Jereb
Keyword(s):  
Visible Light ◽  
Heterogeneous Reaction ◽  
Bromine Atom ◽  
Radical Scavenger ◽  
Reaction Conditions ◽  
Gas Atmosphere ◽  
Methoxy Groups ◽  
Radical Initiators ◽  
Aromatic Bromination ◽  
Heterogeneous Reaction Conditions

AbstractRegioselectivity of visible-light-induced transformations of a range of (hetero)aryl alkyl-substituted ketones bearing several competitive reactive sites (α-carbonyl, benzyl and aromatic ring) with N-bromosuccinimide (NBS) was studied under solvent-free reaction conditions (SFRC) and in the absence of inert-gas atmosphere, radical initiators and catalysts. An 8-W energy-saving household lamp was used for irradiation. Heterogeneous reaction conditions were dealt with throughout the study. All substrates were mono- or dibrominated at the α-carbonyl position, and additionally, some benzylic or aromatic bromination was observed in substrates with benzylic carbon atoms or electron-donating methoxy groups, respectively. Surprisingly, ipso-substitution of the acyl group with a bromine atom took place with (4-methoxynaphthyl) alkyl ketones. While the addition of the radical scavenger TEMPO (2,2,6,6-tetramethylpiperidin-1-yloxy) decreased the extent of α- and ring bromination, it completely suppressed the benzylic bromination and α,α-dibromination with NBS under SFRC.

scholarly journals Catalytic Synthesis of Pyrano- and Furoquinolines Using Nano Silica Chromic Acid at Room Temperature

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Ali Gharib ◽  
Manouchehr Jahangir
Keyword(s):  
Room Temperature ◽  
Chromic Acid ◽  
Heterogeneous Reaction ◽  
Similar Reaction ◽  
Coupling Reactions ◽  
Nano Silica ◽  
Reaction Conditions ◽  
Enol Ethers ◽  
High Yields ◽  
Heterogeneous Reaction Conditions

Nano silica chromic acid (nano-SCA) is found to catalyze efficiently the three component-coupling reactions of aldehydes, amines, and cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild conditions to afford the corresponding pyrano- and furanoquinolines in excellent yields with high endoselectivity. Interestingly, 2,3-dihydrofuran afforded selectively endoproducts under the similar reaction conditions. Heterogeneous reaction conditions, easy procedure, short reaction time, and high yields are some important advantages of this method.

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