Hydrolysis of sulfamoyl chlorides. I. Hydrolysis of dimethylsulfamoyl chloride. Heat capacity of activation, the secondary .gamma.-deuterium isotope effect, and solvent isotope effect

1972 ◽  
Vol 94 (2) ◽  
pp. 573-575 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Solvent Isotope ◽  
Hydrolysis Of

The Mechanism for Hydrolysis of Primary Alkyl Chlorosulfates in Water. The Kinetic Solvent Isotope Effect and the Secondary Deuterium Isotope Effect

1972 ◽  
Vol 50 (3) ◽  
pp. 434-437 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Sulfonyl Chloride ◽  
Alkyl Halides ◽  
Activation Process ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Temperature Coefficients ◽  
Enthalpy Of Activation ◽  
Solvent Isotope ◽  
Hydrolysis Of

The temperature coefficients of the enthalpy of activation [Formula: see text] for the hydrolysis of the three chlorosulfates, methyl, ethyl, and β-chloro, are shown to have values of −50,−55, and −60 cal deg−1 mol−1; values in the same range as previously reported for the hydrolysis of the sulfonyl chlorides. The corresponding value for the β-methoxy isomer was −40 cal deg−1 mol−1, about the same as found for the p-methoxybenzenesulfonyl chloride. The kinetic solvent isotope effect, however, was significantly lower than reported for the sulfonyl chloride series, being about the same as found for the hydrolysis of the alkyl halides. While some degree of nucleophilic overlap is probably required in the activation process, the requirement here is reduced to about the same level as that for the primary halides, and there is no need to postulate a different mechanism on passing from the methyl to the ethyl member of the series, confirming the earlier conclusion of Buncel and Millington.

Hydrolysis of Sulfamoyl Chlorides. II. Hydrogen Participation in the Hydrolysis of Diethyl and Methylethylsulfamoyl Chlorides

1972 ◽  
Vol 50 (6) ◽  
pp. 946-951 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Temperature Coefficient ◽  
Isotope Effect ◽  
Mixed Solvents ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Enthalpy Of Activation ◽  
Exclusion Experiments ◽  
Solvent Isotope ◽  
Intermediate Value ◽  
Hydrolysis Of

Diethylsulfamoyl chloride (2) hydrolyzes eight times faster than dimethylsulfamoyl chloride (1). In 2 the secondary deuterium isotope effect was found to be about 2, hence hydrogen participation is important in the hydrolysis of this compound. The temperature coefficient of the enthalpy of activation [Formula: see text] is exceptional (−39 cal mol−1 deg−1) for a reaction presumably following an SN1 mechanism. The kinetic solvent isotope effect was normal for such a mechanism. The corresponding value of [Formula: see text] for the hydrolysis of piperidylsulfamoyl chloride (4) was about the same as found for 2 while the value for the methylethyl isomer (3) was −66 cal deg−1 mol−1, an intermediate value supporting an explanation based on solvent exclusion. Experiments in mixed solvents support the hypothesis that solvent reorganization is the major factor in determining the value of [Formula: see text]for 2 but not for 4.

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 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>

The solvent deuterium isotope effect on the hydroxide-ion-catalyzed conversion of acetaldehyde to its enolate ion

1988 ◽  
Vol 66 (9) ◽  
pp. 2440-2442
Author(s):  
J. R. Keeffe ◽  
A. J. Kresge
Keyword(s):  
Water Molecule ◽  
Proton Transfer ◽  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Fractionation Factor ◽  
Hydroxide Ion ◽  
Solvent Isotope

Rates of proton transfer from acetaldehyde to the hydroxide ion were measured by iodine scavenging in H2O and in D2O solution at 25 °C; the results give the solvent isotope effect [Formula: see text]. This value is somewhat more consistent with an estimate, made using fractionation factor theory, for hydron transfer directly from the substrate to the hydroxide ion than with another estimate, made similarly, for hydron transfer through an intervening water molecule.

Kinetic Solvent Isotope Effect for the Spontaneous Solvolysis Acetic and Propionic Anhydrides

1971 ◽  
Vol 49 (22) ◽  
pp. 3665-3670 ◽  
Author(s):  
R. E. Robertson ◽  
B. Rossall ◽  
W. A. Redmond
Keyword(s):  
Acetic Anhydride ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Temperature Dependency ◽  
Solvent Isotope Effect ◽  
Propionic Anhydride ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The large kinetic solvent isotope effects for the neutral hydrolysis of acetic and propionic anhydride show unusual temperature dependency; the former passing through a maximum at about 15°, the latter showing a minimum at 30°. This unusual temperature dependency is the consequence of widely different values of the apparent ΔCp≠ in H2O and D2O: the value for acetic anhydride in H2O being −74 ± 2 cal deg−1 mol−1 but −32 ± 4 in D2O. The corresponding values for propionic anhydride being −31 ± 2 in H2O but −94 ± 10 in D2O. The implications of these differences are discussed.

scholarly journals pH-Rate Profile for Hydrolysis of 4-Nitrophenyl β-D-Glucopyranoside: Unimolecular, Bimolecular and Intramolecular Cleavage Mechanisms

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 ◽  
Rate Profile ◽  
Solvent Isotope ◽  
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 of <i>k</i>(H<sub>3</sub>O<sup>+</sup>)/<i>k</i>(D<sub>3</sub>O<sup>+</sup> = 0.65 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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