Vinyl ether hydrolysis XXVIII. The mechanism of reaction of methyl α-(2,6-dimethoxyphenyl)vinyl ether

1993 ◽  
Vol 71 (1) ◽  
pp. 38-41 ◽  
Author(s):  
J. Jones ◽  
A. J. Kresge
Keyword(s):  
Vinyl Ether ◽  
Nucleophilic Attack ◽  
Tracer Study ◽  
Solvent Isotope Effect ◽  
Methyl Group ◽  
Hydronium Ion ◽  
Mechanism Of Reaction ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of methyl α-(2,6-dimethoxyphenyl)vinyl ether in aqueous solution at 25 °C occurs with the hydronium ion catalytic coefficient [Formula: see text] and gives the solvent isotope effect [Formula: see text] this indicates that reaction occurs by rate-determining proton transfer from the catalyst to the substrate to generate an alkoxycarbocation intermediate. An oxygen-18 tracer study shows further that, despite the steric hindrance provided by its two ortho substituents, this cation then reacts by addition of water to the cationic carbon atom to generate a hemiacetal, and not by nucleophilic attack of water on the methyl group remote from the carbocationic center:[Formula: see text]

scholarly journals Vinyl ether hydrolysis. XXIII. Solvent isotope effect on the reaction of divinyl ether catalyzed by the hydronium ion

1990 ◽  
Vol 68 (12) ◽  
pp. 2129-2130 ◽  
Author(s):  
A. J. Kresge ◽  
M. Leibovitch
Keyword(s):  
Vinyl Ether ◽  
Isotope Effect ◽  
Perchloric Acid ◽  
Divinyl Ether ◽  
Solvent Isotope Effect ◽  
Hydronium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of

Rates of hydrolysis of divinyl ether (CH2=CHOCH=CH2), measured in dilute H2O and D2O solutions of perchloric acid at 25 °C, provide the catalytic coefficients kH+ = 0.0084 M−1 s−1 and kD+ = 0.0028 M−1 s−1, and these lead to the isotope effect kH/kD = 3.0. The magnitude of this isotope effect indicates that this reaction occurs by rate-determining hydron transfer from catalyst to substrate and thus follows the conventional mechanism for vinyl ether hydrolysis. Keywords: divinyl ether, vinyl ether hydrolysis, solvent isotope effect.

Vinyl ether hydrolysis. XXIV. 1-Methoxycyclooctene and the question of reversibility of the carbon protonation step

1991 ◽  
Vol 69 (1) ◽  
pp. 84-87 ◽  
Author(s):  
A. J. Kresge ◽  
Y. Yin
Keyword(s):  
Reaction Mechanism ◽  
Proton Transfer ◽  
Vinyl Ether ◽  
Isotope Effects ◽  
Hydrolysis Rate ◽  
Hydronium Ion ◽  
Mineral Acids ◽  
Dilute Aqueous Solutions ◽  
Solvent Isotope ◽  
Hydrolysis Of

An argument is presented which suggests that hydrolysis of the vinyl ether group of 1-methoxycyclooctene may occur by reversible proton transfer from a catalyzing acid to the β-carbon atom of the substrate, instead of by the conventional reaction mechanism in which this proton transfer is rate determining and not reversible. Hydrolysis of this substrate is then examined by measuring rates of reaction in dilute aqueous solutions of strong mineral acids (perchloric and hydrochloric) as well as in buffer solutions of seven carboxylic acids, biphosphate ion, and 1,1,1,3,3,3-hexafluoro-2-propanol. General acid catalysis is observed and a Brønsted relation with the exponent α = 0.73 is constructed. That, plus the isotope effects kH/kD = 2.9 and 6.0 for catalysis by hydronium ion and acetic acid respectively, as well as the lack of deuterium incorporation into the substrate when the reaction is carried out in D2O with D2PO4−/DPO42− buffer at pD = 8, show that carbon protonation of the substrate is not reversible and that the conventional reaction mechanism is operative. Key words: 1-methoxycyclooctene, vinyl ether hydrolysis, rate-determining proton transfer, Brønsted relation, solvent isotope effect.

Acid-catalyzed hydrolysis of tetramethoxyethene in aqueous solution. Initial state stabilization by the methoxy groups

1990 ◽  
Vol 68 (10) ◽  
pp. 1786-1790 ◽  
Author(s):  
A. J. Kresge ◽  
M. Leibovitch ◽  
K. R. Kopecky
Keyword(s):  
Aqueous Solution ◽  
Dimethyl Acetal ◽  
Initial State ◽  
Olefinic Carbon ◽  
Hydronium Ion ◽  
Methoxy Groups ◽  
Rate Retardation ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of tetramethoxyethene to methyl dimethoxyacetate in aqueous solution at 25 °C was found to occur with the hydronium-ion catalytic coefficient [Formula: see text], to give the solvent isotope effect [Formula: see text], and to provide a Brønsted relation based upon six carboxylic acids with the exponent α = 0.42. These data indicate that the reaction proceeds via rate-determining proton transfer from the catalyzing acid to an olefinic carbon atom of the substrate. They also show tetramethoxyethene to be 1.0 × 106 times less reactive than 1,1-dimethoxyethene (ketene dimethyl acetal), a rate retardation 600 times greater than that expected from initial state stabilization by the two additional methoxy groups in tetramethoxyethene; possible causes of this disparity are discussed. Keywords: tetramethoxyethene, carbon–carbon double bond reactivity, ketene acetal, vinyl ether hydrolysis.

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.

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

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.

Vinyl ether hydrolysis. XVII. Oxacyclonon-2,8-diene and the question of the unorthodox reaction mechanism for 9-methoxyoxacyclonon-2-ene

1984 ◽  
Vol 62 (1) ◽  
pp. 74-76 ◽  
Author(s):  
R. A. Burt ◽  
Y. Chiang ◽  
A. J. Kresge ◽  
S. Szilagyi
Keyword(s):  
Reaction Mechanism ◽  
Vinyl Ether ◽  
Membered Ring ◽  
Specific Rate ◽  
Ether Group ◽  
Reaction Proceeds ◽  
Great Reactivity ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of the nine-membered ring cyclic vinyl ether, oxacyclonon-2,8-diene, occurs with a normal isotope effect, [Formula: see text], which indicates that this reaction proceeds by the conventional vinyl ether hydrolysis mechanism involving rate-determining proton transfer to carbon. The specific rate of this reaction, [Formula: see text], may then be used to show that there is no significant ring-size effect on the rate of hydrolysis of a vinyl ether group in a nine-membered ring. The previously noted unusually great reactivity of the vinyl ether group in 9-methoxyoxacyclonon-2-ene, for which an unorthodox reaction mechanism has been claimed, must therefore be due to some other cause.

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.

Acid-Catalyzed Hydration of Prop-2-en-1-ol and 2-Methylprop-2-en-1-ol: Correlation of Reactivity

1989 ◽  
Vol 42 (8) ◽  
pp. 1345 ◽  
Author(s):  
KP Herlihy
Keyword(s):  
Activation Parameters ◽  
Relative Reactivity ◽  
Nucleophilic Attack ◽  
Alternative Mechanism ◽  
Catalysed Reaction ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Kinetics Of

The kinetics of the acid-catalysed reaction of prop-2-en-1-ol and 2-methylprop-2-en-1-ol have been measured. The relative reactivity, solvent isotope ( kH+/kD +) and change in acidity effects, and activation parameters, have been determined and found to be similar to those of other alkenes. While this correlation of results for the hydration of both these alkenols can be interpreted in terms of the conventional Ad-E2 mechanism, computed values for the lifetime of possible carbocation intermediates suggest that an alternative mechanism for the reaction of prop-2-en-1-ol, in which nucleophilic attack by the solvent is concerted with protonation, is feasible.

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