Kinetic solvent isotope effect on acid-catalyzed hydrolysis of hydroxamic acids

1991 ◽  
Vol 45 (1) ◽  
pp. 79-84 ◽  
Author(s):  
Kallos K. Ghosh ◽  
Shiv G. Tandon
Keyword(s):  
Isotope Effect ◽  
Hydroxamic Acids ◽  
Solvent Isotope Effect ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Hydrolysis Of

Reactivity of Organophosphates. IV. Acid-catalyzed Hydrolysis of Triethyl Phosphate: a Comparison with Ethyl Acetate

1974 ◽  
Vol 52 (7) ◽  
pp. 1066-1071 ◽  
Author(s):  
Edward P. Lyznicki Jr. ◽  
Kiyotaka Oyama ◽  
Thomas T. Tidwell
Keyword(s):  
Ethyl Acetate ◽  
Isotope Effect ◽  
Bond Cleavage ◽  
Triethyl Phosphate ◽  
Solvent Isotope Effect ◽  
Mechanism Of Hydrolysis ◽  
Acid Catalyzed ◽  
Neutral Water ◽  
Solvent Isotope ◽  
Hydrolysis Of

The hydrolysis of triethyl phosphate in water and in 35% dioxane – 65% water has been examined. Hydrolysis in neutral water proceeds with a rate constant of 8.35 × 10−6 s−1 at 101°, ΔH* = 23.4 kcal/mol, ΔS* = −20 e.u., a solvent isotope effect [Formula: see text] of 1.3, C—O bond cleavage as shown by 18O labeling, and no catalysis by 0.5 M sulfuric acid. These results are consistent with the BAL2 mechanism of hydrolysis and the same pathway is indicated for the reaction in neutral 35% dioxane –65% water. Perchloric acid catalyzes the reaction in dioxane–water with C—O bond cleavage in 0.904 M acid, ΔH* = 24.1 kcal/mol, ΔS* = −17 e.u., and the solvent isotope effect [Formula: see text] in 0.556 M acid. These results indicate that the AAL2 pathway of hydrolysis is followed under these conditions. The reactivity of triethyl phosphate is compared with that of ethyl acetate.

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

1975 ◽  
Vol 53 (6) ◽  
pp. 869-877 ◽  
Author(s):  
B. Rossall ◽  
R. E. Robertson
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Solvent Isotope Effect ◽  
Acyl Carbon ◽  
Rate Of Hydrolysis ◽  
Solvent Isotope ◽  
Neutral Conditions ◽  
Hydrolysis Of

The temperature dependence of the rate of hydrolysis of benzoic, phthalic, and succinic anhydrides have been determined in H2O and D2O under "neutral" conditions. Corresponding data have been obtained for methyl trifluoroacetate. While both series supposedly react by the same BAc2 mechanism, remarkable differences are made obvious by this investigation. Possible sources of such differences are proposed.

scholarly journals One-proton catalysis by the α-l-arabinofuranosidase III of Monilinia fructigena

1988 ◽  
Vol 254 (3) ◽  
pp. 899-901 ◽  
Author(s):  
T Selwood ◽  
M L Sinnott
Keyword(s):  
Isotopic Composition ◽  
Isotope Effect ◽  
Solvent Isotope Effect ◽  
Monilinia Fructigena ◽  
Single Proton ◽  
Solvent Isotope ◽  
Hydrolysis Of

1. Michaelis-Menten parameters for the hydrolysis of p-nitrophenyl alpha-L-arabinofuranoside were measured as a function of pL (pH or pD) in both 1H2O and 2H2O. 2. The variation of both Vmax. and Vmax./Km with pL is sigmoid, the pK governing Vmax. shifting from 6.34 +/- 0.05 in 1H2O to 6.84 +/- 0.07 in 2H2O, and that governing Vmax./Km from 5.89 +/- 0.03 in 1H2O to 6.38 +/- 0.05 in 2H2O. 3. In the plateau regions there is a small inverse solvent isotope effect on Vmax./Km (0.92), and one of 1.45 on Vmax. 4. The variation of Vmax. with isotopic composition is strictly linear, indicating that the isotope effect arises from the transfer of a single proton.

Solvent isotope effect in the acid-catalyzed isomerization of cis-stilbenes

1968 ◽  
Vol 33 (11) ◽  
pp. 4260-4261 ◽  
Author(s):  
Donald S. Noyce ◽  
Donald R. Hartter ◽  
Frank B. Miles
Keyword(s):  
Isotope Effect ◽  
Solvent Isotope Effect ◽  
Acid Catalyzed ◽  
Solvent Isotope

Solvent isotope effects in the oxidation of dipeptides by aqueous chlorine

1999 ◽  
Vol 77 (5-6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Armesto ◽  
M Canle L. ◽  
V García ◽  
J A Santaballa
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Second Step ◽  
Solvent Isotope Effect ◽  
General Base ◽  
Peptide Oxidation ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

A kinetic study of the mechanism of oxidation of Ala-Gly and Pro-Gly by aqueous chlorine has been carried out. Among other experimental facts, the deuterium solvent isotope effects were used to clarify the mechanisms involved. In a first stage, N-chlorination takes place, and then the (N-Cl)-dipeptide decomposes through two possible mechanisms, depending on the acidity of the medium. The initial chlorination step shows a small isotope effect. In alkaline medium, two consecutive processes take place: first, the general base-catalyzed formation of an azomethine (β ca. 0.27), which has an inverse deuterium solvent isotope effect (kOH-/kOD- ~ 0.8). In a second step, the hydrolysis of the azomethine intermediate takes place, which is also general base-catalyzed, without deuterium solvent isotope effect, the corresponding uncatalyzed process having a normal deuterium solvent isotope effect (kH2O/kD2O ~ 2). In acid medium, the (N-Cl)-dipeptide undergoes disproportionation to a (N,N)-di-Cl-dipeptide, the very fast decomposition of the latter in deuterium oxide preventing a reliable estimation of the solvent isotope effect.Key words: chlorination, deuterium isotope effects, fractionation factors, peptide oxidation, water treatment.

Solvolysis of sulphonyl halides. V. Hydrolysis and deuterolysis of methanesulphonyl chloride

1970 ◽  
Vol 23 (12) ◽  
pp. 2427
Author(s):  
ML Tonnet ◽  
AN Hambly
Keyword(s):  
Transition State ◽  
Thermodynamic Parameters ◽  
Isotope Effect ◽  
Large Reduction ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Initial State ◽  
Solvent Isotope ◽  
Hydrolysis Of

The values of the thermodynamic parameters of activation have been determined for the solvolysis of methanesulphonyl chloride in H2O and D2O and their mixtures with moderate amounts of dioxan. Some of the data are not in agreement with the postulate that the kinetic solvent isotope effect and the maximum in the rate of solvolysis produced by the addition of dioxan are due to changes in the initial state of the reacting system rather than to changes in the transition state. The addition of dioxan does not produce a large reduction in the solvent isotope effect as reported for the hydrolysis of t-butyl chloride and predicted to be general. The relative rates of solvolysis in mixtures of H2O and D2O are not in agreement with the analysis of such reactions by Swain and Thornton.

scholarly journals pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

2021 ◽  
Author(s):  
Amani Alhifthi ◽  
Spencer Williams
Keyword(s):  
Isotope Effect ◽  
Nucleophilic Aromatic Substitution ◽  
Aromatic Substitution ◽  
Solvent Isotope Effect ◽  
Dissociative Mechanism ◽  
Neighboring Group ◽  
Rate Determining Step ◽  
Solvent Isotope ◽  
A Minor ◽  
Hydrolysis Of

1,2-<i>trans</i>-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of<i> </i>4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (<i>k</i>(H<sub>3</sub>O<sup>+</sup>)/<i>k</i>(D<sub>3</sub>O<sup>+</sup>) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of <i>k</i><sub>H</sub>/<i>k</i><sub>D</sub> = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect <i>k</i>(H<sub>2</sub>O)/<i>k</i>(D<sub>2</sub>O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in <sup>18</sup>O-labelled water and H<sub>2</sub>O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of <i>k</i>(HO<sup>–</sup>)/<i>k</i>(DO<sup>–</sup>) = 0.5 and a strongly negative entropy of activation (D<i>S</i><sup>‡</sup> = –13.6 cal mol<sup>–1</sup> K<sup>–1</sup>). Finally, at high pH, an inverse solvent isotope effect of <i>k</i>(HO<sup>–</sup>)/<i>k</i>(DO<sup>–</sup>) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.<br>

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