Search results for "Reaction"
showing 10 items of 6134 documents
Step-growth Polymerization ofBistriazolinediones with1,1-Diphenylethylene
1996
The reactions of 4-ethyl-1,2,4-triazoline-3,5-dione (ETD) (1) and 4-phenyl-1,2,4-triazoline-3,5-dione (PhTD) (2) with 1,1-diphenylethylene (DPE) (3) were investigated at room temperature. The reactions are very fast and are completed in less than 4 min. These reactions lead to the formation of two 2 :1 adducts via double Diels-Alder and Diels-Alder-ene reactions in a ratio of 1.35 : 1. The structure of these adducts where R = Et were determined by X-ray analysis of a single crystal. These compounds were used as models for the polymerization reactions. The reaction of bistriazolinediones (1,6-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)hexane and bis-(p-3,5-dioxo-1,2,4-triazoline-4-ylphenyl)methane…
Cyclodextrins in Polymer Synthesis: Enantiodiscrimination in Free-Radical Polymerization of Cyclodextrin-Complexed Racemic N -Methacryloyl-D,L -pheny…
2003
The enantiodiscriminating polymerization of racemic cyclodextrin-complexed N-methacryloylphenylalanine methyl ester is investigated 1 H NMR spectra of the complexes with methylated β-cyclodextrin in D 2 O manifest splittings due to chiral recognition. The different stabilities of the diastereomeric complexes influence the kinetics of the homopolymerization, particularly at 0°C. An enrichment of the residual N-methacryloyl-L-phenylalanine methyl ester of 14% was achieved after 21 h of polymerization.
NMR and Quantum-Chemical Study on the Structure of Ester Enolate−Aluminum Alkyl Complexes as Models of the Active Center in the Anionic Polymerizatio…
1999
6Li and 13C NMR on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were used to elucidate the structure of the active center in the anionic polymerization of methacrylates in the presence of triethylaluminum (AlEt3) in toluene. This study reveals ester enolate/aluminum alkyl complexes with different degrees of association, (MiBLi·AlEt3)n (n = 1, 2, 4), and different stoichiometries, MiBLi·xAlEt3 (x = 1, 2). In the presence of methyl pivalate (MPiv), which is taken as a model compound for the monomer and polymer, complexes such as (MiBLi·MPiv·AlEt3)n (n = 1, 2) are formed. These complexes can dissociate into MiBLi·2AlEt3 and MPi…
Polymerization of ε-caprolactone using heterobimetallic lanthanocene complexes
1997
The chiral heterobimetallic complexes Li[Ln(η 5 :η 1 -C 5 R 4 1 SiMe 2 NCH 2 CH 2 R 2 ) 2 ] (ln= Y, Lu; C 5 R 4 1 = C 5 Me 4 , C 5 H 4 , 3-C 5 H 3 tBu; R 2 = OMe, NMe 2 ) have been found to polymerize e-caprolactone to give a polymer of high molecular weight (M n > 20000) and moderate polydispersity (M w /M n < 2). Failure to observe a correlation between monomer/initiator ratio and molecular weight suggest a polymerization mechanism different from a pseudo-anionic mechanism
Overview on oxidation mechanisms of organic compounds by TiO2 in heterogeneous photocatalysis
2012
This review provides the reader with a general overview on heterogeneous photocatalytic oxidation mechanisms in the presence of TiO2, with a special address to conversion of aliphatic and aromatic organic species. The aim was to clarify the steps of the photo-oxidation of the various classes of compounds and to relate them with the properties of the catalysts and the experimental conditions used. Reactions carried out to perform complete degradation and photocatalytic partial oxidations have been deeply discussed. Recent isotopic studies highlighted new reaction pathways concerning partial oxidation of alcohols to aldehyde and oxidation of benzene while EPR investigations confirmed that not…
Zum Ligandenaustausch des Ferrocens mit Methyl- und Ethyl-substituierten Naphthalinen
1988
Abstract The replacement of a Cp ligand of ferrocene by each of ten unsymmetrically substituted naphthalenes yields pairs of complex ions [arene-FeCp] + , which have been identified from their 1 H NMR spectra. The influence of the substituent on the ratio of the two isomers, and its temperature dependence implies a complex reaction mechanism involving an η 2 -bound intermediate of the associated naphthalene. The proton resonances of the alkyl groups of the naphthalenes are shifted to lowfield by complexation; this effect decreases with increasing distance from the iron. The resonance shift of the arene protons has a different sign for the complexed (highfield) and the uncomplexed part (lowf…
ChemInform Abstract: Substituent Effect on Oxidative Cyclization of Aldehyde Thiosemicarbazones with Ferric Chloride.
2010
The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.
Electrochemical Oxidation of Carboxylic Acids in Water at Boron-Doped Diamond (BDD) Anodes in the Range of Potential of Oxygen Evolution: Detection M…
2013
The electrochemical oxidation in water solutions of selected carboxylic acids (namely oxalic, formic, acetic, maleic, and succinic) at boron-doped diamond (BDD) anodes was investigated by polarization and chronoamperometric measurements. In the presence of low concentrations of carboxylic acids, current densities changed approximately linearly with the acid concentrations. Furthermore, when the current densities were plotted as a function of the chemical oxygen demand, a similar response was observed for all the investigated acids with the exception of oxalic acid. For high carboxylic acid concentrations, the linear variation is often loosen and different behaviors are observed depending on…
Mechanism of Trichloroethene Hydrodehalogenation: A First-Principles Kinetic Monte Carlo Study
2014
A hydrodehalogenation (HDC) reaction of trichloroethene (TCE) has gained a lot of interest due to its possible application in water purification, but the reaction mechanism has been subject to much controversy. In this work, HDC of TCE on Pd(111) was examined by carrying out kinetic Monte Carlo simulations based on DFT-calculated thermodynamic and kinetic parameters. Obtained kMC results show that the HDC follows a so-called direct pathway, which means that, after adsorption on a catalyst, TCE quickly dechlorinates, producing CH–C and then, more slowly, hydrogenates to form hydrocarbon products. This is reflected in the surface coverage snapshots, where intermediates corresponding to the di…
The skeletal isomerization of but-1-ene catalyzed by theta-1 zeolite
2001
The complete mechanism for the skeletal isomerization of but-1-ene catalyzed by theta-1 zeolite was investigated theoretically by means of DFT calculations, and the influence of the local geometry of the active site and of electrostatic effects on the geometries of the species involved and on activation and reaction energies were analyzed. It was found that whereas the geometry and stability of alkoxide intermediates are strongly influenced by the local geometry of the active site, the ionic transition states are mainly stabilized by electrostatic effects. Both aspects result in a lowering of the activation energies of the elementary steps that form the mechanism and therefore in enhanced r…