Search results for " rate constant"
showing 10 items of 220 documents
1986
The aminolysis of diphenyl terephthalate by means of hexylamine was studied in dimethyl sulfoxide as a model reaction for polyamidation. The kinetic analysis showed that the two ester groups of the diphenyl ester do not react independently. Furthermore, the reaction of the first ester group was of mixed second and third order, while the reaction of the second ester group contained only a second order term. The rate constants found were used to determine the Arrhenius activation parameters.
Mechanistic Investigations of the BZ Reaction with Oxalic Acid Substrate. I. The Oscillatory Parameter Region and Rate Constants Measured for the Rea…
2004
This paper is the first part of a study reinvestigating the mechanism of the Belousov-Zhabotinsky (BZ) reaction of oxalic acid, which is the simplest organic substrate for a BZ oscillator. New experiments are performed to find the oscillatory region in 1 M sulfuric acid at 20 °C. The removal rate of the end product bromine by an inert gas stream is a critical parameter here: oscillations can be observed only in a window of that parameter. The “rate constant” for the physical removal of bromine is measured as a function of the gas flow rate and reactor volume; furthermore, the rate constants of three component reactions important in this system are also determined. These are oxygen atom tran…
Kinetics of the Strain-Promoted Oxidation-Controlled Cycloalkyne-1,2-quinone Cycloaddition: Experimental and Theoretical Studies
2018
Stimulated by its success in both bioconjugation and surface modification, we studied the strain-promoted oxidation-controlled cycloalkyne–1,2-quinone cycloaddition (SPOCQ) in three ways. First, the second-order rate constants and activation parameters (ΔH⧧) were determined of various cyclooctynes reacting with 4-tert-butyl-1,2-quinone in a SPOCQ reaction, yielding values for ΔH⧧ of 4.5, 7.3, and 12.1 kcal/mol, for bicyclo[6.1.0]non-4-yne (BCN), cyclooctyne (OCT), and dibenzoazacyclooctyne (DIBAC), respectively. Second, their reaction paths were investigated in detail by a range of quantum mechanical calculations. Single-configuration theoretical methods, like various DFT and a range of MP2…
Nitric Oxide-Scavenging Properties of Some Chalcone Derivatives
2002
Abstract The implication of NO in many inflammatory diseases has been well documented. We have previously reported that some chalcone derivatives can control the iNOS pathway in inflammatory processes. In the present study, we have assessed the NO-scavenging capacity of three chalcone derivatives (CH8, CH11, and CH12) in a competitive assay with HbO2, a well-known physiologically relevant NO scavenger. Our data identify these chalcones as new NO scavengers. The estimated second-order rate constants (ks) for the reaction of the three derivatives with NO is in the same range as the value obtained for HbO2, with CH11 exerting the greatest effect. These results suggest an additional action of t…
Selective photocatalytic oxidation of 5-hydroxymethyl-2-furfural in aqueous suspension of polymeric carbon nitride and its adduct with H2O2 in a sola…
2018
Abstract This work reports a study on the reactivity of polymeric carbon nitride (PCN) and PCN-H2O2 adduct samples for sunlight photocatalytic selective oxidation reactions. The characterization of these materials was reported in a previous paper where the reactivity towards the partial oxidation of 5-hydroxymethylfurfural (HMF) was studied by using two different laboratory scale photoreactors; one irradiated by UV lamps and the other one by natural sunlight. In the present study it has been confirmed the effectiveness of these C3N4 based materials for the selective partial oxidation of HMF to FDC (2,5-furandicarboxaldehyde) in aqueous medium in a pilot plant photoreactor irradiated by natu…
A theoretical and experimental study of the formation mechanism of 4-X-chalcones by the Claisen–Schmidt reaction
2000
Abstract A theoretical and experimental study on the formation of 4-X-chalcones (X=H, Cl, F, OCH3, N(CH3)2) was carried out by the Claisen–Schmidt reaction. The influence of pH and temperature was analyzed. Under the adopted experimental conditions 4-X-chalcones were the only reaction products. In the theoretical study, the thermodynamic magnitudes and the reactivity indexes calculated with the AM1 method were used. The mechanism of Nayak and Rout was analyzed critically and a new mechanism was proposed, characterized by: (1) rapid nucleophilic attack of the catalyst (OH−) on the carbon atom of the methyl group of acetophenone; (2) attacks of the acetophenonate ion on the carbon atom of the…
Photocatalytic degradation of 4-Nitrophenol by g-C3N4-MCy: Mechanism study and kinetic modeling
2021
Abstract A graphitic carbon nitride (g-C3N4-MCy) photocatalyst was prepared by thermal condensation of melamine and cyanuric acid with equal proportions. The photocatalyst was characterized by Fourier transform infrared spectroscopy (FTIR), Specific surface area (SSA), X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Transmission electron microscope (TEM), and DRS–UV–Vis spectroscopic methods. We studied the photo-degradation kinetics of 4-nitrophenol using a g-C3N4-MCy. Four parameters were applied including initial concentration of 4-nitrophenol, amount of catalyst, dissolved oxygen content, and photon flux. The reaction rate constant was shown to be correlate…
A molecular electron density theory (MEDT) study of the role of halogens (X2= F2, Cl2, Br2and I2) on the aza-Michael-addition reactions
2020
Using the Molecular Electron Density Theory (MEDT), a set of uncatalyzed and X2 molecule-catalyzed (X2 = F2, Cl2, Br2, or I2) aza Michael addition reactions (aza-MARs) between pyrrolidine (PYR) and methyl acrylate (MA) have been studied in the gas phase and in dichloromethane (DCM) medium from the kinetics and molecular mechanism aspects. Analysis of the conceptual DFT reactivity indices indicates that the coordination of the X2 molecules to the oxygen of the MA's carbonyl group increases both the softness and the electrophilic character of MA, thus explaining the catalytic role of the X2 molecules. The nucleophilic attack of the nitrogen of PYR on the MA's β conjugated carbon is the rate-d…
Kinetics and equilibrium in insulin radioimmunoassay.
2002
The kinetics of insulin reaction has been studied with its specific antibody immobilized on the inner wall of the reaction tube; the radioimmunoanalytical determination of such a substance is based on the reaction. Independent variables were labelled and unlabelled insulin concentrations, temperature, viscosity, and the medium's ionic strength. Biexponential kinetics was found to be dependent on the concentrations fitted to the models discussed in the paper. The effect of temperature shows activation parameters similar to the viscous flow energy of water, which suggests that the reaction is diffusion-controlled. The results of the viscosity analysis points at the clearly negative influence …
Rapid hydrolysis of benzodiazepines to benzophenones in a microwave oven
1989
Abstract A microwave oven is used to carry out the complete hydrolysis of diazepam to the corresponding benzophenone in only 10 min, at 650 W, with good recovery. The reaction yield is evaluated by first-derivative UV spectrophotometry.