Etude cinétique de la réduction des ozonides de styrènes substitués dans le noyau par la triphénylphosphine

1970 ◽  
Vol 48 (8) ◽  
pp. 1309-1316 ◽  
Author(s):  
J. Carles ◽  
S. Fliszár
Keyword(s):  
Solvent Effect ◽  
Rate Constants ◽  
Chloroform Solution ◽  
Membered Ring ◽  
Second Order ◽  
Nucleophilic Attack ◽  
Hammett Equation ◽  
Order Rate ◽  
Rate Determining Step

The rates of reduction k[ozonide][triphenylphosphine] have been studied, in chloroform solution, for ozonides of ring-substituted styrenes. The second order rate constants k fit the Hammett equation with ρ = 0.72, thus confirming that the reduction proceeds via a nucleophilic attack of the triphenylphosphine on the ozonide ring. The absence of any significant kinetic solvent effect indicates that the rate determining step is in the formation of an unstable six-membered ring oxyphosphorane intermediate.

Effect of pH on the reaction of 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole with 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione

1970 ◽  
Vol 48 (19) ◽  
pp. 3104-3107 ◽  
Author(s):  
James Leslie
Keyword(s):  
Rate Constants ◽  
Ionic Species ◽  
Second Order ◽  
Hydrogen Ion ◽  
Effect Of Ph ◽  
Order Rate ◽  
Rate Determining Step ◽  
Ion Activity ◽  
Kinetics Of ◽  
Linear Manner

The kinetics of the oxidation of 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione with 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole (1) have been examined at pH 4–5.6. The reaction is second-order, which can be explained by a rate-determining step involving the reaction of one molecule of the thiol with one molecule of 1. The second-order rate constants vary in a linear manner with the reciprocal of the hydrogen ion activity. The ionic species involved in the reaction are discussed.

Structure-reactivity correlations in the reaction of 2,4-dinitrophenyl X-substituted benzoates with alicyclic secondary amines

1999 ◽  
Vol 77 (5-6) ◽  
pp. 659-666 ◽  
Author(s):  
Ik-Hwan Um ◽  
Ji-Sook Min ◽  
Hye-Won Lee
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Secondary Amines ◽  
Electronic Nature ◽  
Order Rate ◽  
Rate Determining Step ◽  
Acyl Substituent ◽  
Plot Structure ◽  
Rate Limiting

Apparent second-order rate constants (kapp) have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl X-substituted benzoates with a series of alicyclic secondary amines in H2O containing 20 mol% DMSO at 25°C. The microconstants involved in the reaction (k-1/k2, k1, and k1k2/k-1) have also been calculated. The magnitude of kapp, k1, and k1k2/k-1 values increases with increasing amine basicity and with increasing acid strengthening ability of the acyl substituent X. The k-1/k2 value decreases from ca. 6.5 to 0.3 with increasing the amine basicity, but remains almost constant upon changing the acyl substituent X for a given amine, indicating that the rate-determining step is governed by the basicity of amine but not by the electronic nature of the acyl substituent X. The Brønsted-type plots for kapp show a break at pKa = 9.1, supporting the assumption that a change in the rate-determining step occurs from rate-limiting breakdown to formation of the addition intermediate as amine basicity increases. The corresponding Brønsted-type plots for k-1/k2, k1, and k1k2/k-1 are linear but their β values are different. σ+ constants show better correlation with log kapp, log k1 and log k1k2/k-1 for the reaction with low basic amines (pKa < 9.1), while σ constants exhibit better correlation for the reaction with highly basic amines (pKa > 9.1). The magnitude of ρ1 is identical to that of ρapp and ρeq for a given amine.Key words: aminolysis, Brønsted-type plot, structure-reactivity correlations, rate-determining step.

Kinetics and mechanism of oxidation of Cr(II) ions by tetrachloromethane

1980 ◽  
Vol 45 (1) ◽  
pp. 21-25 ◽  
Author(s):  
Peter Ševčík ◽  
Miroslav Khír
Keyword(s):  
Rate Constants ◽  
Redox Reaction ◽  
Second Order ◽  
Kinetics And Mechanism ◽  
Bridge Structure ◽  
Order Rate ◽  
Rate Determining Step ◽  
Inner Sphere ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

Kinetics of the redox reaction of Cr(II) ions with tetrachloromethane has been studied in H2O-CH3OH-HClO4 and H2O-CH3COOH-HClO4. In the redox reaction 2 moles of Cr(II) are consumed per one mol of CCl4, and CrCl2+ and CrCCL2+3 ions are formed in the same amounts. Second order rate constants (k293 = 2.31 mol-1 s -1 in 50% CH3OH, k293 = 1.66 l . mol-1 s-1 in 50% CH3COOH) are independent of H+ ions concentration.The rate determining step is an inner sphere transfer of the halogen from CCl4 to Cr(II), the Cr-Cl-C bridge structure being retained in both media.

Mutarotation of D(+)-glucose. I. Evidence of electrophilic attack by hydrated monomeric and dimeric copper(II) species

1982 ◽  
Vol 35 (5) ◽  
pp. 951 ◽  
Author(s):  
CJ O'Conner ◽  
AL Odell ◽  
AAT Bailey
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Order Rate Constant ◽  
Second Order ◽  
Electrophilic Attack ◽  
Order Rate ◽  
Rate Determining Step ◽  
Entropy Of Activation ◽  
Ph Range

The rate of mutarotation of α-D(+)-glucose is markedly affected by the addition of electrolytes. At 293 K the rate constants for reaction with H2O, HClO4, NaClO4 and CU(ClO4)2 are 4.6 × 10-6, 5.9 × 10-3,1.2 × 10-4 and 4.6 × 10-3 dm3 mol-1 s-1 respectively. In the pH range 3.5 - 4.4 the rate of mutarotation increases sharply in solutions of Cu(ClO4)2 because of the presence of small concentrations of Cu((OH)2CU)2+ for reaction with which the second-order rate constant is 4.0 dm3 mol-1 s-1. A model for mutarotation is proposed which involves a specifically oriented aquation sheath about the charged ion which then acts as an enhanced electrophile in the rate-determining step to form the aldehyde intermediate. In the presence of mixed cationic catalysts, additivity rather than competition is observed between the effect of two catalysts. This result and the observed increase in the entropy of activation in the presence of aquated copper(II) support this model.

Inhibition in Purified Systems and in Human Plasma of Chimaeric Plasminogen Activators Consisting of the NH2-Terminal Region of Tissue-Type Plasminogen Activator and the COOH-Terminal Region of UrokinaseType Plasminogen Activator

1988 ◽  
Vol 60 (02) ◽  
pp. 247-250 ◽  
Author(s):  
H R Lijnen ◽  
L Nelles ◽  
B Van Hoef ◽  
F De Cock ◽  
D Collen
Keyword(s):  
Plasminogen Activator ◽  
Rate Constants ◽  
Plasminogen Activators ◽  
Second Order ◽  
Tissue Type ◽  
Single Chain ◽  
Chain Molecules ◽  
Order Rate ◽  
Type Plasminogen Activator ◽  
Urokinase Type Plasminogen Activator

SummaryRecombinant chimaeric molecules between tissue-type plasminogen activator (t-PA) and single chain urokinase-type plasminogen activator (scu-PA) or two chain urokinase-type plasminogen activator (tcu-PA) have intact enzymatic properties of scu-PA or tcu-PA towards natural and synthetic substrates (Nelles et al., J Biol Chem 1987; 262: 10855-10862). In the present study, we have compared the reactivity with inhibitors of both the single chain and two chain variants of recombinant u-PA and two recombinant chimaeric molecules between t-PA and scu-PA (t-PA/u-PA-s: amino acids 1-263 of t-PA and 144-411 of u-PA; t-PA/u-PA-e: amino acids 1-274 of t-PA and 138-411 of u-PA). Incubation with human plasma in the absence of a fibrin clot for 3 h at 37° C at equipotent concentrations (50% clot lysis in 2 h), resulted in significant fibrinogen breakdown (to about 40% of the normal value) for all two chain molecules, but not for their single chain counterparts. Preincubation of the plasminogen activators with plasma for 3 h at 37° C, resulted in complete inhibition of the fibrinolytic potency of the two chain molecules but did not alter the potency of the single chain molecules. Inhibition of the two chain molecules occurred with a t½ of approximately 45 min. The two chain variants were inhibited by the synthetic urokinase inhibitor Glu-Gly-Arg-CH2CCl with apparent second-order rate constants of 8,000-10,000 M−1s−1, by purified α2-antiplasmin with second-order rate constants of about 300 M−1s−1, and by plasminogen activator inhibitor-1 (PAI-1) with second-order rate constants of approximately 2 × 107 M−1s−1.It is concluded that the reactivity of single chain and two chain forms of t-PA/u-PA chimaers with inhibitors is very similar to that of the single and two chain forms of intact u-PA.

Determination of the Nucleophilicity of Tricarbonyliron Coordinated Cyclohepta-1,3,5-triene

1999 ◽  
Vol 64 (11) ◽  
pp. 1770-1779 ◽  
Author(s):  
Herbert Mayr ◽  
Karl-Heinz Müller
Keyword(s):  
Gibbs Energy ◽  
Ambient Temperature ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Electrophilic Additions ◽  
Kinetics Of

The kinetics of the electrophilic additions of four diarylcarbenium ions (4a-4d) to tricarbonyl(η4-cyclohepta-1,3,5-triene)iron (1) have been studied photometrically. The second-order rate constants match the linear Gibbs energy relationship log k20 °C = s(E + N) and yield the nucleophilicity parameter N(1) = 3.69. It is concluded that electrophiles with E ≥ -9 will react with complex 1 at ambient temperature.

Luminescence Quenching of Rhodamines by Cyclooctatetraene

1987 ◽  
Vol 42 (9) ◽  
pp. 1009-1013 ◽  
Author(s):  
P. Targowski ◽  
B. Ziętek ◽  
A. Bączyński
Keyword(s):  
Rhodamine B ◽  
Rate Constants ◽  
Internal Conversion ◽  
Rhodamine 6G ◽  
Second Order ◽  
Luminescence Quenching ◽  
Intersystem Crossing ◽  
Order Rate ◽  
Quenching Process

Cyclooctatetraene (COT) as a quencher of fluorescence of a series of Rhodamine solutions was studied. The second order rate constants for the quenching process of Rhodamine 110, Rhodamine 19 pchl., Rhodamine 6G pchl., Rhodamine 6G, Tetramethylrhodamine, Rhodamine B and Rhodamine 3B pchl. are given. It was found that COT enhances rather intersystem crossing than internal conversion.

A Study on the β-Elimination Reaction from N-[2-(p-nitrophenyl)ethyl]quinuclidinium and 2-(p-nitrophenyl)ethyl bromide induced by amines in dimethylsulfoxide with formation of p-nitrostyrene

2000 ◽  
Vol 2000 (2) ◽  
pp. 62-63
Author(s):  
Sergio Alunni ◽  
Arianna Rocchi
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Ethyl Bromide ◽  
Elimination Reaction ◽  
Order Rate

Second order rate constants kE M−1 s−1 for the β-elimination reaction from N-[2-( p-nitrophenyl)ethyl]quinuclidinium and 2-( p-nitrophenyl)ethyl bromide induced by amines of different structure in dimethylsulfoxide at 50 °C have been measured. Application of the Brønsted equation shows a similar behaviour of the two substrates, with values of β = 0.649 and 0.584 respectively.

Substituent effects of cis-dioxobis(dithiocarbamato) molybdenum(VI) on redox properties: redox potentials for one-electron reduction and second-order rate constants for oxygen atom transfer

1998 ◽  
Vol 269 (2) ◽  
pp. 260-268 ◽  
Author(s):  
Kei Unoura ◽  
Akira Yamazaki ◽  
Akira Nagasawa ◽  
Yoshikiyo Kato ◽  
Hiroki Itoh ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
Rate Constants ◽  
Substituent Effects ◽  
Second Order ◽  
Redox Properties ◽  
Atom Transfer ◽  
Redox Potentials ◽  
Oxygen Atom Transfer ◽  
Order Rate ◽  
Electron Reduction

KINETICS OF THE AQUEOUS ALKALINE HOMOGENOUS HYDROLYSIS OF HIGH EXPLOSIVE 1, 3,5,7-TETRAAZA- 1, 3,5,7-TETRANITROCYCLOOCTANE (HMX)

1994 ◽  
Vol 30 (3) ◽  
pp. 53-61 ◽  
Author(s):  
Harro M. Heilmann ◽  
Michael K. Stenstrom ◽  
Rolf P. X. Hesselmann ◽  
Udo Wiesmann
Keyword(s):  
Temperature Dependence ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Elevated Temperatures ◽  
Second Order ◽  
Order Rate ◽  
Subsequent Calculation ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Order Rate Equation

In order to get basic data for the design of a novel treatment scheme for high explosives we investigated the kinetics for the aqueous alkaline hydrolysis of 1,3,5,7-tetraaza-1,3,5,7-tetranitrocyclooctane (HMX) and the temperature dependence of the rate constants. We used an HPLC procedure for the analysis of HMX. All experimental data could be fit accurately to a pseudo first-order rate equation and subsequent calculation of second-order rate constants was also precise. Temperature dependence could be modeled with the Arrhenius equation. An increase of 10°C led to an average increase in the second-order rate constants by the 3.16 fold. The activation energy of the second-order reaction was determined to be 111.9 ±0.76 kJ·moJ‒1. We found the alkaline hydrolysis to be rapid (less than 2.5% of the initial HMX-concentration left after 100 minutes) at base concentrations of 23 mmol oH‒/L and elevated temperatures between 60 and 80°C.

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