Correlation pKa – activité catalytique des thiols dans la réaction d'hydrolyse de l'acétate de p-nitrophényle

1984 ◽  
Vol 62 (11) ◽  
pp. 2330-2336 ◽  
Author(s):  
Alain Brembilla ◽  
Denis Roizard ◽  
Jacqueline Schoenleber ◽  
Pierre Lochon
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Second Order ◽  
Species Comparison ◽  
Order Rate ◽  
Thiolate Anion ◽  
Group A ◽  
Hydrolysis Of

The kinetic study of the hydrolysis of p-nitrophenylacetate in the presence of primary thiols indicates the thiolate anion as the sole catalytic species. Comparison of the true second order rate constants (kRS−) reveals that purely aliphatic primary thiols behave differently from aromatic α-substituted primary thiols. In the latter group a correlation can be established between the true second order rate constants and the pKSH values by means of the Brönsted equation log kRS− = βpKSH + C, with β equal to 0.40 and C equal to −0.85.

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.

Kinetic Study on Oxidation of Thiodipropionic Acid by Iron (III)- bipyridine Complex

2016 ◽  
Vol 15 (2) ◽  
pp. 33-44
Author(s):  
John K Adaikalasamy ◽  
Selva A Priya ◽  
Sunaja K R Devi
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Second Order ◽  
Aqueous Acetonitrile ◽  
Order Rate ◽  
Uv Visible

Iron(III)-bipyridine complex was prepared andcharacterized by UV-Visible spectrophotometer. Kineticstudy was carried out by using this iron(III)-bipyridinewith thiodipropionic acid in aqueous acetonitrile solution.The reaction was optimized by studying the effect onsubstrate, solvent, oxidant, acidity and temperature. Firstorder, second order rate constants and activationparameters were calculated. The above reaction wasfound to be second order and proceeded through electrontransfer from thiodipropionic acid to iron(III)-bipyridinecomplex. The product was characterized and confirmedby IR and NMR spectroscopy.Keywords: Thiodipropionic acid, Iron(III)-bipyridine complex,kinetic study of Iron(III)-bipyridyl complexes.

scholarly journals Optimization and a Kinetic Study on the Acidic Hydrolysis of Dialkyl α-Hydroxybenzylphosphonates

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3793
Author(s):  
Nikoletta Harsági ◽  
Zita Rádai ◽  
Áron Szigetvári ◽  
János Kóti ◽  
György Keglevich
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Acidic Hydrolysis ◽  
First Order ◽  
Order Rate ◽  
Rate Determining Step ◽  
Pseudo First Order ◽  
Hydrolysis Of ◽  
Electron Withdrawing Substituents

The two-step acidic hydrolysis of α-hydroxybenzylphosphonates and a few related derivatives was monitored in order to determine the kinetics and to map the reactivity of the differently substituted phosphonates in hydrolysis. Electron-withdrawing substituents increased the rate, while electron-releasing ones slowed down the reaction. Both hydrolysis steps were characterized by pseudo-first-order rate constants. The fission of the second P-O-C bond was found to be the rate-determining step.

The Lewis-acidity of square-planar nickel(II) complexes. III. A kinetic study of the effects of substituents on the addition of 1,10-Phenanthroline to Bis(monothioacetylacetonato)nickel(II) and Bis(dithiophosphato)nickel(II) complexes in toluene

1978 ◽  
Vol 31 (7) ◽  
pp. 1439 ◽  
Author(s):  
MU Fayyaz ◽  
MW Grant
Keyword(s):  
Kinetic Study ◽  
Rate Constants ◽  
Activation Parameters ◽  
Adduct Formation ◽  
Second Order ◽  
Lewis Acidity ◽  
Order Rate ◽  
Measured Rate ◽  
Square Planar ◽  
Inductive Effects

The second-order rate constants and activation parameters for the addition of 1,10-phenanthroline to bis(dialkyldithiophosphato)nickel(II) complexes and substituted bis(monothioacetylacetonato)-nickel(II) complexes in toluene have been measured. Rate constants are in the range 102-108 1. mol-1 s-1 at 25°C, while ΔH‡ is in the range 10-50 kJ mol-1 and ΔS‡ is in the range from -30 to -110 J mol-1 K-1. The higher rate constants, smaller ΔH‡ and more negative ΔS‡ values are associated with complexes with electron- withdrawing substituents. The results are related to the thermo- dynamics of adduct formation, the inductive effects of the substituents and the pKa of the ligands.

Micellar Catalysis of Organic-Reactions. XXI. A Comparison of the Catalytic Activity of Micelles of Cetyltrimethylammonium Bromide and Sulfate on Ester, Amide and Carbamate Hydrolyses

1988 ◽  
Vol 41 (3) ◽  
pp. 325
Author(s):  
TJ Broxton ◽  
JR Christie ◽  
SM Mannas
Keyword(s):  
Catalytic Activity ◽  
Rate Constants ◽  
Cetyltrimethylammonium Bromide ◽  
Second Order ◽  
Phenyl Acetate ◽  
Bond Breaking ◽  
Order Rate ◽  
Cationic Micelles ◽  
Hydrolysis Of ◽  
Reaction In Water

The basic hydrolyses of phenyl acetate, N,4-dimethyl-N-(3′- nitrophenyl ) benzamide , methyl N-methyl-N-(4′-nitrophenyl) carbamate and methyl N-(3′,5′-dinitrophenyl)-N-methylcarbamate have been studied in cationic micelles of cetyltrimethylammonium bromide (ctab) and sulfate (ctas). Hydrolysis of phenyl acetate and the 4′-nitro carbamate, which involve rate-determining hydroxide attack, exhibit weak catalysis by both micelles, and the observed rates in each micelle are similar. The hydrolysis of the benzamide and the 3′,5′-dinitro carbamate, which involve rate determining C-N bond breaking, show larger catalysis, and, furthermore, micelles of ctab are more effective than micelles of ctas. The observed rates can be explained by the pseudo-phase kinetic model. For reactions involving rate-determining hydroxide attack, the calculated second-order rate constants in micelles of ctab and ctas are similar and much less than those for reaction in water. For reactions involving rate-determining C-N bond breaking the calculated second-order rate constants in micelles of ctab are greater than in micelles of ctas, and similar to those for reaction in water.

scholarly journals Reactivities of neutral and cationic forms of 2,2′-dipyridyl disulphide towards thiolate anions. Detection of differences between the active centres of actinidin, papain and ficin by a three-protonic-state reactivity probe

1979 ◽  
Vol 183 (2) ◽  
pp. 233-238 ◽  
Author(s):  
K Brocklehurst ◽  
T Stuchbury ◽  
J P G Malthouse
Keyword(s):  
Rate Constants ◽  
Positive Charge ◽  
Ph Dependence ◽  
Second Order ◽  
Order Rate ◽  
Wide Range ◽  
Thiolate Anion ◽  
Thiolate Anions ◽  
Thiol Proteinase ◽  
Active Centres

The second-order rate constants (k) for the reactions of 2,2′-dipyridyl disulphide (pKa2,45) with 2-mercaptoethanol (pKa9.6) and with benzimidazol-2-ylmethanethiol (pKa values 5.6 and 8.3) were determined at 25 degrees C at I 0.1 by stopped-flow spectral analysis over a wide range of pH. These were used to calculate the pH-independent second-order rate constants (k) for the reactions of neutral 2,2′-dipyridyl disulphide and of its monocation with the 2-mercaptoethanol thiolate anion (associated pKa9.6) and with the benzimidazol-2-ylmethanethiol zwitterion (associated pKa5.6). For both thiolate ions, the rate-enhancement factor (kmonocation/kneutral disulphide) is about 1.5×10(3). The dependence on pH in acidic media of k for the reaction of 2,2′-dipyridyl disulphide with actinidin, the thiol proteinase from Actinidia chinensis, was shown to differ from the forms of pH-dependence observed for the analogous reactions with papain (EC 3.4.22.2) and ficin (3.4.22.3). The reactivity of the 2,2′-dipyridyl disulphide dication and its apparent sensitivity to the presence and location of a positive charge in the attacking thiol are discussed.

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.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

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.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

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