Search results for "Catalysis"

Kinetics and mechanism of group transfer polymerization of N-butyl acrylate catalyzed by Hgl2 /(CH3 )3 Sil in toluene

1994

The group transfer polymerization (GTP) of n-butyl acrylate (nBuA) using 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene (MTS) as an initiator, mercuric iodide (HgI2) as a catalyst in toluene at room temperature gives a very good control of molecular weight and narrow molecular weight distribution. (Mw/Mn < 1.2). Kinetic studies in this system reveal that this reaction is rather slow, half-lives being in the range of hours. The kinetic order of the apparent rate constant of propagation with respect to initiator and catalyst concentrations were found to be near to unity. However, the first-order time-conversion plots exhibit considerable induction periods. Upon addition of trimethylsilyl io…

An experimental method for the determination of the photon flow reflected and absorbed by aqueous dispersions containing polycrystalline solids in he…

1991

An experimental method for the evaluation of the photon flow reflected and absorbed by aqueous dispersions containing polycrystalline solids is proposed. The method is based on actinometric measurements. It is shown that the values obtained are independent of the particle sizes and of the concentration of the solids at least in the experimental conditions and in the range used in the present study (particle size range: 40–500 μm; solids concentration: 0.1–2 g liter−1). The results suggest that the values obtained should be attributed to the interfaces formed between the surface of the solids and the medium. The method is applied to a photocatalytic reaction, namely to the photodegradation o…

Study of Ni, Pt, and Ru Catalysts on Wood-based Activated Carbon Supports and their Activity in Furfural Conversion to 2-Methylfuran

2018

Bio‐based chemicals can be produced from furfural through hydrotreatment. In this study, 2‐methylfuran (MF), a potential biofuel component, was produced with Pt, Ru, and Ni catalysts supported on wood‐based activated carbons. The catalytic hydrotreatment experiments were conducted in a batch reactor at 210–240 °C with 2‐propanol as solvent and 40 bar H2 pressure. Two types of activated carbon supports were prepared by carbonization and activation of lignocellulosic biomass (forest‐residue‐based birch and spruce from Finland). Both types of activated carbons were suitable as catalyst supports, giving up to 100 % furfural conversions. The most important factors affecting the MF yield were the…

Halogenated (arylsulfanyl)pyridines syntheses and their derivatives by C-S and C-X couplings catalyzed by palladium complexes

2018

C–H activation of aryl compounds directed by 2-sulfonylpyridine and 2-sulfanylpyridine moiety for the formation of C–X (X = F, Cl, Br, I) bonds was studied. First, the syntheses of thioethers (2-(arylsulfanyl)pyridines) and sulfones (2-(arylsulfonyl)pyridines) were necessary for the progress of this project. A C–S coupling catalyzed by palladium complexe between thioaryls and halogenated heterocycles was performed for the synthesis of thioethers. The cheap ligand bis(diphenylphosphino)ferrocene (dppf) was used for this convenient reaction. Then, oxidation of thioethers was performed to synthesize sulfones. Halogenation of these compounds was studied with ortho-directed C–H activation cataly…

The sustainable synthesis of levetiracetam by an enzymatic dynamic kinetic resolution and an ex-cell anodic oxidation

2021

Levetiracetam is an active pharmaceutical ingredient widely used to treat epilepsy. We describe a new synthesis of levetiracetam by a dynamic kinetic resolution and a ruthenium-catalysed ex-cell anodic oxidation. For the enzymatic resolution, we tailored a high throughput screening method to identify Comamonas testosteroni nitrile hydratase variants with high (S)-selectivity and activity. Racemic nitrile was applied in a fed-batch reaction and was hydrated to (S)-(pyrrolidine-1-yl)butaneamide. For the subsequent oxidation to levetiracetam, we developed a ligand-free ruthenium-catalysed method at a low catalyst loading. The oxidant was electrochemically generated in 86% yield. This route pro…

Phase Equilibrium for the Esterification Reaction of Acetic Acid + Butan-1-ol at 101.3 kPa

2007

In this work, the thermodynamic behavior of catalytic esterification reaction equilibrium and vapor–liquid equilibria (VLE) for the quaternary reactive system acetic acid + butan-1-ol + butyl acetate + water and constituent binary systems acetic acid + butyl acetate, butan-1-ol + butyl acetate, and butan-1-ol + water have been determined at 101.3 kPa, and liquid–liquid equilibria (LLE) of the binary system butan-1-ol + water have also been determined. The esterification reaction rate of the acetic acid and butan-1-ol mixture is very slow. So, in this study, p-toluenesulfonic acid was selected as the catalyst to accelerate the chemical reaction. The measured VLE data were correlated by the N…

Selective derivatisation of resorcarenes. Part 5. Acylation of tetrabenzoxazine derivatives

2000

The reaction of the tetrabenzoxazines 2 with acetic anhydride under mild conditions leads selectively and exclusively to the tetraamides 3 in which the oxazine rings are opened; their structure was deduced from their 1H NMR spectra and confirmed for one example by an X-ray single crystal structure analysis; acylation of the hydroxy groups was not observed.

Cure behaviour of epoxy resin matrices for carbon fibre composites

1999

The cure behaviour of two resin formulations (with high and low curing agent content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of this work is to investigate the kinetics of this specific epoxy system in order to be able to choose a proper set of processing parameters which will give good composite material properties. The shape of the conversion curves gives evidence of the differences in the cure kinetics of the two systems. Furthermore, the values of the activation energies were determined both for formulation in the conversion range where vitrification occurs, following a phenomenological approa…

Enantioselective Addition of Dimethylzinc to Aldehydes Catalyzed by N-Substituted Mandelamide-Ti(IV) Complexes.

2005

Abstract Amides derived from ( S )-(+)-mandelic acid in the presence of titanium isopropoxide catalyze the enantioselective addition of dimethylzinc to aromatic aldehydes with good yields and ee up to 90%.

2014

Carbon-centered radicals represent highly useful reactive intermediates in organic synthesis. Their nucleophilic character is reflected by fast additions to electron deficient C=X double bonds as present in iminium ions or cationic heterocycles. This review covers diverse reactions of preformed or in situ-generated cationic substrates with various types of C-radicals, including alkyl, alkoxyalkyl, trifluoromethyl, aryl, acyl, carbamoyl, and alkoxycarbonyl species. Despite its high reactivity, the strong interaction of the radical’s SOMO with the LUMO of the cation frequently results in a high regioselectivity. Intra- and intermolecular processes such as the Minisci reaction, the Porta react…