Evidence for a change in rate-determining step in the acid-catalyzed hydrolysis of a vinyl ether

1971 ◽  
Vol 93 (23) ◽  
pp. 6294-6296 ◽  
Author(s):  
J. D. Cooper ◽  
V. P. Vitullo ◽  
D. L. Whalen
Keyword(s):  
Vinyl Ether ◽  
Rate Determining Step ◽  
Acid Catalyzed ◽  
Hydrolysis Of

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.

ChemInform Abstract: An ab initio Calculation of the Acid-Catalyzed Hydrolysis of N-Nitrosoamines. A Hypothesis on the Rate-Determining Step.

ChemInform ◽  
1987 ◽  
Vol 18 (28) ◽  
Author(s):  
NGUYEN MINH THO NGUYEN MINH THO ◽  
A. F. HEGARTY
Keyword(s):  
Ab Initio ◽  
Ab Initio Calculation ◽  
Rate Determining Step ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Vinyl ether hydrolysis. XIII. The failure of I-strain to produce a change in rate-determining step

1980 ◽  
Vol 58 (2) ◽  
pp. 124-129 ◽  
Author(s):  
Y. Chiang ◽  
W. K. Chwang ◽  
A. J. Kresge ◽  
S. Szilagyi
Keyword(s):  
Vinyl Ether ◽  
Acid Catalysis ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Mineral Acid ◽  
Buffer Solutions ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Acetic Acid Buffer ◽  
Hydrolysis Of

Rates of hydrolysis of 1-ethoxy-3,3,5,5-tetramethylcyclopentene and 1-methoxy-2,3,3,5,5-pentamethylcyclopentene measured in mineral acid and formic and acetic acid buffer solutions show general acid catalysis and give large kinetic isotope effects in the normal direction (kH/kD > 1). This indicates that these reactions proceed by the conventional mechanism for vinyl ether hydrolysis in which proton transfer from the catalyzing acid to the substrate is rate-determining, and that the I-strain in these substrates is insufficiently great to shift the reaction mechanism to rapidly reversible substrate protonation followed by rate-determining hydration of the ensuing cationic intermediate.

scholarly journals The mechanism of the hydrolysis of acylimidazoles in aqueous mineral acids. The excess acidity method for reactions that are not acid catalyzed

1997 ◽  
Vol 75 (8) ◽  
pp. 1093-1098 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Imidazole Ring ◽  
Carbonyl Oxygen ◽  
Pseudo First Order Reaction ◽  
Acid Media ◽  
Tetrahedral Intermediate ◽  
Reaction Rate Constants ◽  
Rate Determining Step ◽  
Reversible Addition ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The mechanism of the hydrolysis of acetylimidazole in aqueous perchloric, sulfuric, and hydrochloric acid mixtures has been determined. Benzoylimidazole was also studied in the latter two acids. The method of analyzing the available data, pseudo-first-order reaction rate constants as a function of acid concentration and, in one case, temperature, is the excess acidity method, here applied to the same reaction in the three different acid media, allowing their comparison. The reaction is not acid catalyzed; the rates decrease with increasing acidity. The substrate reacts in the form that is monoprotonated on the imidazole ring; it is 100% protonated at acidities much lower than those used here. Acetylimidazole is shown to become diprotonated at high acidity [Formula: see text], protonating on the carbonyl oxygen, but the diprotonated form is not reactive. The hydrolysis involves the reversible addition of one water molecule to the substrate to give a tetrahedral intermediate; at low acidities the decomposition of this hydrate is the rate-determining step, but as the acidity increases and the water activity decreases its formation becomes rate limiting. Hydroxide catalysis was also observed in dilute perchloric acid, but this is swamped by nucleophilic catalysis by the acid anion in HCl and H2SO4. Keywords: acylimidazoles, excess acidity, hydrolysis, protonation, tetrahedral intermediate.

Acid-catalyzed hydrolysis of 4-diazo-isothiochroman-3-one. Comparison with the acyclic analog and the corresponding oxygen system

1997 ◽  
Vol 75 (1) ◽  
pp. 56-59 ◽  
Author(s):  
E.A. Jefferson ◽  
A.J. Kresge ◽  
S.W. Paine
Keyword(s):  
Carbon Atom ◽  
Negative Charge ◽  
Molecular Orbital Calculations ◽  
Am1 Calculations ◽  
Charge Delocalization ◽  
Rate Determining Step ◽  
Hydronium Ion ◽  
Acid Catalyzed ◽  
Group Migration ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of the cyclic diazothiolactone, 4-diazoisochroman-3-one (3) was found to occur with the hydronium-ion isotope effect, [Formula: see text] and to give the ring-contracted product, 1,3-dihydrobenzo[c]thiophene-1-carboxylic acid (4). This shows that protonation of the diazo carbon atom occurs in the rate-determining step and that the reaction also involves migration of the thio group. The hydronium-ion catalytic coefficient for this reaction, [Formula: see text], is 45 times less than that for hydrolysis of its acyclic thio ester analog, S-methyl phenyldiazothioacetate (5). Semiempirical AM1 molecular orbital calculations support the idea that this difference in reactivity is the result of increased delocalization of negative charge into the aromatic ring in the case of the cyclic substrate, which reduces the negative charge on the diazo carbon atom and makes it less susceptible to protonation. Key words: hydrolysis, diazoalkanes, charge delocalization, AM1 calculations, thio group migration.

ChemInform Abstract: Acid-Catalyzed Hydrolysis of Vinyl Acetals. Reaction Through the Acetal Rather Than the Vinyl Ether Functional Group.

ChemInform ◽  
1989 ◽  
Vol 20 (49) ◽  
Author(s):  
Y. CHIANG ◽  
W. K. CHWANG ◽  
A. J. KRESGE ◽  
Y. YIN
Keyword(s):  
Vinyl Ether ◽  
Functional Group ◽  
Acid Catalyzed ◽  
Vinyl Acetals ◽  
Hydrolysis Of

Acid-catalyzed hydrolysis of 1,1-bis(methylthio)ethene. Buffer- and thiol-dependent changes in the rate-determining step

1983 ◽  
Vol 105 (10) ◽  
pp. 3220-3226 ◽  
Author(s):  
Tadashi Okuyama ◽  
Shoji Kawao ◽  
Takayuki Fueno
Keyword(s):  
Rate Determining Step ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Acid-catalyzed hydrolysis of vinyl acetals. Reaction through the acetal rather than the vinyl ether functional group

1989 ◽  
Vol 111 (18) ◽  
pp. 7185-7190 ◽  
Author(s):  
Y. Chiang ◽  
W. K. Chwang ◽  
A. J. Kresge ◽  
Y. Yin
Keyword(s):  
Vinyl Ether ◽  
Functional Group ◽  
Acid Catalyzed ◽  
Vinyl Acetals ◽  
Hydrolysis Of

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]

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