Étude cinétique de la N-chloration de la succinimide en phase aqueuse

1992 ◽  
Vol 70 (1) ◽  
pp. 89-99 ◽  
Author(s):  
Denise Matte ◽  
Bernard Solastiouk ◽  
André Merlin ◽  
Xavier Deglise
Keyword(s):  
Aqueous Medium ◽  
Rate Constants ◽  
Low Ph ◽  
Chloride Ions ◽  
Nucleophilic Attack ◽  
Stopped Flow ◽  
Molecular Chlorine ◽  
Kinetics Of ◽  
Limiting Values ◽  
Phase Aqueuse

A kinetic study of the N-chlorination, in aqueous medium, of succinimide (SH) at low pH (<5) and at high pH (>9) is presented. We have derived the rate constants and activation energies of the processes involved. A stopped-flow spectrophotometric technique was used to study the kinetics. Without chloride ions, our experimental results can be interpreted by two kinetically indistinguishable mechanisms:[Formula: see text]The limiting values of the rate constants for the case in which only one process is involved in the kinetics of chlorination were evaluated: [Formula: see text]; [Formula: see text].In acid medium, in the presence of chloride ions, we observe a nucleophilic attack of the S− ion on molecular chlorine Cl2. This process is added to the two former processes. Keywords: kinetics, N-chlorination, succinimide, aqueous medium, stopped flow.

Étude cinétique de la N-chloration de l'acide cyanurique en phase aqueuse

1990 ◽  
Vol 68 (2) ◽  
pp. 307-313 ◽  
Author(s):  
Denise Matte ◽  
Bernard Solastiouk ◽  
André Merlin ◽  
Xavier Deglise
Keyword(s):  
Aqueous Medium ◽  
Rate Constants ◽  
Cyanuric Acid ◽  
Stopped Flow ◽  
Experimental Values ◽  
Kinetics Of Reaction ◽  
Limiting Case ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Phase Aqueuse

A complete kinetic study of the N-chlorination, in basic aqueous medium, of cyanuric acid by the stopflow spectrophotometric method is presented. Our experimental results can be interpreted by two pairs of kinetically indistinguishable mechanisms.[Formula: see text]or[Formula: see text]and[Formula: see text]or[Formula: see text]The rate constants and their corresponding activation energies were determined in the limiting case where one of the elementary steps in each pair is involved alone in the kinetics of reaction.[Formula: see text]The rate constants for hydrolysis of the monochlorinated cyanuric acid derivatives were derived from our experimental values. Keywords: kinetics, N-chlorination, 1,3,5-triazine-2,4,6-trione, aqueous medium, stopped flow.

scholarly journals Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

Synthesis ◽  
2019 ◽  
Vol 51 (05) ◽  
pp. 1157-1170 ◽  
Author(s):  
Artem Leonov ◽  
Daria Timofeeva ◽  
Armin Ofial ◽  
Herbert Mayr
Keyword(s):  
Rate Constants ◽  
Correlation Equation ◽  
Stopped Flow ◽  
Quinone Methides ◽  
Enol Ethers ◽  
Reactivity Descriptors ◽  
Silyl Enol Ethers ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Least Squares Minimization

The kinetics of the reactions of trimethylsilyl enol ethers and enamines (derived from deoxybenzoin, indane-1-one, and α-tetralone) with reference electrophiles (p-quinone methides, benzhydrylium and indolylbenzylium ions) were measured by conventional and stopped-flow photometry in acetonitrile at 20 °C. The resulting second-order rate constants were subjected to a least-squares minimization based on the correlation equation lg k = s N(N + E) for determining the reactivity descriptors N and s N of the silyl enol ethers and enamines. The relative reactivities of structurally analogous silyl enol ethers, enamines, and enolate anions towards carbon-centered electrophiles are determined as 1, 107, and 1014, respectively. A survey of synthetic applications of enolate ions and their synthetic equivalents shows that their behavior can be properly described by their nucleophilicity parameters, which therefore can be used for designing novel synthetic transformations.

scholarly journals The Kinetics of Peroxynitrite on Insulin Nitration Damage

2020 ◽  
Author(s):  
Congxiao Zhang ◽  
Fusheng Sun ◽  
Congjiang Zhang ◽  
Yunjing Luo
Keyword(s):  
Activation Energy ◽  
Biological Activity ◽  
Glucose Metabolism ◽  
Rate Constants ◽  
The Body ◽  
Stopped Flow ◽  
Tyrosine Nitration ◽  
Protein Nitration ◽  
Physiological Conditions ◽  
Kinetics Of

Abstract Background: Insulin is one of the most important versatile hormones that is central to regulating the energy and glucose metabolism in the body. There has been accumulating evidence supporting that diabetes was associated with peroxynitrite and protein nitration, and insulin nitration induced by peroxynitrite affected its biological activity. Methods: In this paper, the kinetics of insulin nitration by peroxynitrite in physiological conditions was studied by the stopped flow technique. Results: We determined the values of the reactive rate constants of peroxynitrite decomposition and peroxynitrite-induced tyrosine nitration in the presence of insulin. The activation energy of peroxynitrite decomposition and 3-nitrotyrosine yield in the presence of insulin is 48.8 kJ·mol−1 and 42.7 kJ·mol−1 respectively. Conclusions: It is inferred that the glutamate residue of insulin accelerated peroxynitrite decomposition and tyrosine nitration by reducing the activation energy of reactions. The results could be beneficial for exploring the molecular mechanism of diabetes and offering a new target for diabetes therapies.

Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

1978 ◽  
Vol 56 (23) ◽  
pp. 2970-2976 ◽  
Author(s):  
Oswald S. Tee ◽  
David C. Thackray ◽  
Charles G. Berks
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Aqueous Media ◽  
Stopped Flow ◽  
Flow Method ◽  
High Acidity ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of bromination of the 1,2-dihydro-1,3-dimethyl-2-oxopyrimidinium cation (Q+) in aqueous media (pH 0–5) have been studied using the stopped-flow method. At the higher acidities (pH < 2) the results are consistent with rate determining attack by bromine upon the pseudobase (QOH), whereas at low acidities (pH > 4) it appears that pseudobase formation is rate determining. The change occurs because at high acidity the reversal of the pseudobase QOH to the cation is fast relative to bromine attack, whereas at low acidity the converse is true. Results obtained at intermediate acidities (pH 2–4) are consistent with this interpretation.A separate kinetic study of pseudobase formation (and decomposition) yielded rate constants in good agreement with those derived from the bromination study.

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

Kinetics of oxidation of thiocyanate by aqueous iodine

1973 ◽  
Vol 26 (9) ◽  
pp. 1863 ◽  
Author(s):  
GT Briot ◽  
RH Smith
Keyword(s):  
Rate Constants ◽  
Activation Energies ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
General Base ◽  
Present Rate ◽  
Rapid Equilibrium ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of thiocyanate to sulphate by aqueous iodine in the pH range 9.2-12.5 have been studied using a spectrophotometric stopped flow technique. The reaction is general base-catalysed, having the rate law ��������������������� -d[I2]a/dt = ([SCN-][I3-]/[I-]2)Σ kB[B] where [I2]a is the total analytical concentration of iodine, [B] is the concentration of base, and where the summation is taken over all bases present. Rate constants, kB, and activation energies have been measured for the bases, OH-, PO43- and CO32-. ��� A mechanism involving the initial steps ����������������� I2+SCN- ↔ ISCN+I- �����������������(rapid equilibrium) ������������� ISCN+H2O+B → HOSCN+I- + HB+ �����������(rate determining) followed by rapid reactions of HOSCN with itself or with iodine is proposed.

scholarly journals Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique

2012 ◽  
Vol 19 (1) ◽  
pp. 55-66 ◽  
Author(s):  
Marta Siemieniec ◽  
Hanna Kierzkowska-Pawlak ◽  
Andrzej Chacuk
Keyword(s):  
Carbon Dioxide ◽  
Reaction Kinetics ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Good Agreement

Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique The pseudo-first-order rate constants (kOV) for the reactions between CO2 and diethanolamine have been studied using the stopped-flow technique in an aqueous solution at 293, 298, 303 and 313 K. The amine concentrations ranged from 167 to 500 mol·m-3. The overall reaction rate constant was found to increase with amine concentration and temperature. Both the zwitterion and termolecular mechanisms were applied to correlate the experimentally obtained rate constants. The values of SSE quality index showed a good agreement between the experimental data and the corresponding fit by the use of both mechanisms.

scholarly journals Kinetics of the Reversible Transformation of 2,3-Dioxogulonic Acid into its Enol as a Function of the pH of the Medium

1978 ◽  
Vol 33 (10) ◽  
pp. 1184-1189
Author(s):  
J. Zuluaga ◽  
P. Martínez
Keyword(s):  
Kinetic Study ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Disodium Salt ◽  
Stopped Flow ◽  
Free Energies ◽  
Reversible Transformation ◽  
Flow Method ◽  
Kinetic Coefficients ◽  
Kinetics Of

Abstract 2,3-dioxogulonic acid and the disodium salt of its enol were synthesised, isolated and identified both chemically and spectroscopically. A kinetic study was carried out on its equilibrium by means of the “stopped flow” method for rapid processes, and the rate constants for the forward and backward reaction were determined as a function of the pH of the medium. The kinetic coefficients involved, equilibrium constant and Gibbs free energies were also determined.

scholarly journals The kinetics of formation of horseradish peroxidase compound I by reaction with peroxobenzoic acids. pH and peroxo acid substituent effects

1976 ◽  
Vol 157 (1) ◽  
pp. 247-253 ◽  
Author(s):  
D M Davies ◽  
P Jones ◽  
D Mantle
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Rate Constants ◽  
Ph Effect ◽  
Substituent Effects ◽  
Nucleophilic Attack ◽  
Compound I ◽  
Active Intermediate ◽  
Kinetics Of Formation ◽  
Kinetics Of

1. The kinetics of formation of horseradish peroxidase Compound I were studied by using peroxobenzoic acid and ten substituted peroxobenzoic acids as substrates. Kinetic data for the formation of Compound I with H2O2 and for the reaction of deuteroferrihaem with H2O2 and peroxobenzoic acids, to form a peroxidatically active intermediate, are included for comparison. 2. The observed second-order rate constants for the formation of Compound I with peroxobenzoic acids decrease with increasing pH, in the range pH 5-10, in contrast with pH-independence of the reaction with H2O2. The results imply that the formation of Compound I involves a reaction between the enzyme and un-ionized hydroperoxide molecules. 3. The maximal rate constants for Compound I formation with unhindered peroxobenzoic acids exceed that for H2O2. Peroxobenzoic acids with bulky ortho substituents show marked adverse steric effects. The pattern of substituent effects does not agree with expectations for an electrophilic oxidation of the enzyme by peroxoacid molecules in aqueous solution, but is in agreement with that expected for a reaction involving nucleophilic attack by peroxo anions. 4. Possible reaction mechanisms are considered by which the apparent conflict between the pH-effect and substituent-effect data may be resolved. A model in which it is postulated that a negatively charged ‘electrostatic gate’ controls access of substrate to the active site and may also activate substrate within the active site, provides the most satisfactory explanation for both the present results and data from the literature.

Cinétique d'oxydation des oximes du benzaldéhyde et de l'acétophénone par l'ion thallique

1980 ◽  
Vol 58 (13) ◽  
pp. 1305-1310 ◽  
Author(s):  
Robert Lortie ◽  
Miklos Zador
Keyword(s):  
Reaction Mechanism ◽  
Aqueous Medium ◽  
Rate Equation ◽  
Chloride Ions ◽  
Kinetics Of Oxidation ◽  
Kinetics Of

The kinetics of oxidation of benzaldehyde and acetophenone oximes by Tl(III) in aqueous medium has been studied. The reaction occurs in two consecutive steps: formation of a nitroso intermediate and its decomposition. The oxime forms a complex with Tl(III) leading to the rate equation: −d[oxime]/dt = K1/k2[oxime][Tl(III)]/(1 + K1[Tl(III)]). The formation of the final carbonyl product is inhibited by Tl(III), a resuit of the formation of a complex resistant to decomposition. Coordination of Tl(III) by chloride ions affects the rate of the above two steps. The reaction mechanism is discussed. [Journal translation]

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