Revised mechanism for the hydrolysis of ethers in aqueous acid

2012 ◽  
Vol 90 (10) ◽  
pp. 811-818 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Positive Charge ◽  
Bond Cleavage ◽  
Aqueous Media ◽  
Nucleophilic Attack ◽  
Subsequent Paper ◽  
Reaction Intermediates ◽  
Aqueous Acid ◽  
Acid Catalyzed ◽  
Protonated Species ◽  
Hydrolysis Of

It has been shown recently that many supposed reaction intermediates in aqueous media do not have lifetimes long enough for them to serve this purpose. Among these are oxygen-protonated species where the positive charge is not delocalized, primary and secondary carbocations, and the commonly written species H3O+ and HO–. This means that the mechanisms for many of the organic reactions that take place in aqueous media are in need of revision. This paper concerns the acid hydrolysis of simple ethers, many of which cannot form carbocations stable enough to exist in water. Rather than an A1 process in which an oxygen-protonated species dissociates into an alcohol and a carbocation, which is then quenched by water, or an A2 process in which a water molecule or another nucleophilic species assists in this, the mechanism for most ethers is a general-acid-catalyzed process in which proton transfer to oxygen is concerted with C–O bond cleavage in cases where a stable carbocation can exist, or additionally concerted with nucleophilic attack for those cases in which stable carbocation formation is not possible. All of the cases for which rate constant data could be found in the literature are analyzed and discussed in this paper, with the exception of the hydrolyses of several azoethers, where additional hydrolysis mechanisms are possible. These will be discussed in a subsequent paper.

scholarly journals Unveiling the crucial intermediates in androgen production

2015 ◽  
Vol 112 (52) ◽  
pp. 15856-15861 ◽  
Author(s):  
Piotr J. Mak ◽  
Michael C. Gregory ◽  
Ilia G. Denisov ◽  
Stephen G. Sligar ◽  
James R. Kincaid
Keyword(s):  
Bond Cleavage ◽  
Nucleophilic Attack ◽  
Reaction Intermediates ◽  
Structural Determinants ◽  
Initial Product ◽  
Androgen Synthesis ◽  
Ferric Peroxo ◽  
Enzymatic Mechanisms ◽  
Primary Substrate

Ablation of androgen production through surgery is one strategy against prostate cancer, with the current focus placed on pharmaceutical intervention to restrict androgen synthesis selectively, an endeavor that could benefit from the enhanced understanding of enzymatic mechanisms that derives from characterization of key reaction intermediates. The multifunctional cytochrome P450 17A1 (CYP17A1) first catalyzes the typical hydroxylation of its primary substrate, pregnenolone (PREG) and then also orchestrates a remarkable C17–C20 bond cleavage (lyase) reaction, converting the 17-hydroxypregnenolone initial product to dehydroepiandrosterone, a process representing the first committed step in the biosynthesis of androgens. Now, we report the capture and structural characterization of intermediates produced during this lyase step: an initial peroxo-anion intermediate, poised for nucleophilic attack on the C20 position by a substrate-associated H-bond, and the crucial ferric peroxo-hemiacetal intermediate that precedes carbon–carbon (C-C) bond cleavage. These studies provide a rare glimpse at the actual structural determinants of a chemical transformation that carries profound physiological consequences.

Bond cleavage in acid-catalyzed hydrolysis of vinyl phosphates

1972 ◽  
Vol 94 (10) ◽  
pp. 3676-3677 ◽  
Author(s):  
Edward P. Lyznicki ◽  
Thomas T. Tidwell
Keyword(s):  
Bond Cleavage ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Amide directed hydrocarboxylation of N-allylacetamide catalyzed by the aqueous Pd - tppts - Brønsted acid system (tppts = P(C6H4-m-SO3Na)3)1

2001 ◽  
Vol 79 (5-6) ◽  
pp. 688-692 ◽  
Author(s):  
Göran Verspui ◽  
Gábor Besenyei ◽  
Roger A Sheldon
Keyword(s):  
Substitution Reaction ◽  
Aqueous Media ◽  
Propanoic Acid ◽  
Allylic Substitution ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Mild Conditions ◽  
Brönsted Acid ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The Pd - tppts - HOTs (tppts = P(C6H4-m-SO3Na)3, HOTs = p-toluenesulfonic acid) catalyzed hydrocarboxylation of N-allylacetamide in an aqueous medium afforded 4-acetamidobutyric acid and 3-acetamido-2-methylpropanoic acid under mild conditions, with a high regioselectivity towards the linear isomer. During the hydrocarboxylation an acid catalyzed hydrolysis of the amide moieties of both the substrate and the products took place, as well as the formation of acetamide and propanal, presumably via a Pd-catalyzed allylic substitution reaction of N-allylacetamide. The hydrolysis reaction was suppressed by lowering the amount of Brønsted acid cocatalyst (HOTs) or by employing a weaker Brønsted acid such as propanoic acid. The allylic substitution reaction was minimized by increasing the CO pressure but unfortunately this caused a decrease in the regioselectivity. A sudden inhibition took place after ca. 70% conversion, presumably caused by one of the side products. By increasing the tppts concentration to 13.1 mmol L-1 (20 equiv per Pd) the inhibition was circumvented and a quantitative conversion of N-allylacetamide was achieved.Key words: aqueous media, olefins, palladium, hydrocarboxylation, N-allylacetamide.

Transition state activity coefficients in the acid-catalyzed hydrolysis of amides

1977 ◽  
Vol 55 (16) ◽  
pp. 3050-3057 ◽  
Author(s):  
Tomasz A. Modro ◽  
Keith Yates ◽  
Françoise Beaufays
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Protonated Form ◽  
State Activity ◽  
Alkyl Derivatives ◽  
Amide Hydrolysis ◽  
Conjugate Acid ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Nitrogen Bond

The transition-state activity coefficient [Formula: see text] approach has been applied to the acid-catalyzed hydrolysis of benzamide and its N-alkyl derivatives. For all systems (with the exception of the N-tert-butyl derivative which reacts via carbon–nitrogen bond cleavage) a uniform type of medium dependence of [Formula: see text] is observed. The reaction shows a pronounced destabilization of S≠ over the whole region of acidity studied, practically identical to that found for the AAc-2 type of ester hydrolysis. This is interpreted in terms of an AoT2 mechanism of amide hydrolysis, that is the rate-determining formation of the oxonium-type tetrahedral intermediate from the O-protonated form of substrate conjugate acid.

PRESSURE EFFECT AND MECHANISM IN ACID CATALYSIS: VII. HYDROLYSIS OF METHYL, ETHYL, AND t-BUTYL ACETATES

1961 ◽  
Vol 39 (5) ◽  
pp. 1094-1100 ◽  
Author(s):  
A. R. Osborn ◽  
E. Whalley
Keyword(s):  
Hydrochloric Acid ◽  
Water Molecule ◽  
Butyl Acetate ◽  
Carbonyl Oxygen ◽  
Methyl Ethyl ◽  
Dilute Acid ◽  
Aqueous Acid ◽  
Ether Oxygen ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The effect of pressures up to 3 kbar on the rate of the acid-catalyzed hydrolysis of methyl, ethyl, and t-butyl acetates in dilute aqueous acid and of ethyl acetate in concentrated hydrochloric acid has been measured. The volume of activation for t-butyl acetate is zero within experimental error, showing that the mechanism is unimolecular. Those for methyl and ethyl acetates are near –9 cm3mole−1 in both dilute and concentrated acid. We deduce from this that the mechanism is the same in 9.2-M hydrochloric acid as in dilute acid, that the transition state is not highly polar, and that if the proton in the reactive protonated ester is on the carbonyl oxygen then the attacking water molecule adds, and if the proton is on the ether oxygen then the attacking water molecule substitutes.

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]

ChemInform Abstract: The Broensted Acid-Catalyzed Hydrolysis of Acyl Fluorides in Aqueous Media

ChemInform ◽  
2010 ◽  
Vol 24 (38) ◽  
pp. no-no
Author(s):  
R. E. MOTIE ◽  
D. P. N. SATCHELL ◽  
W. N. WASSEF
Keyword(s):  
Aqueous Media ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Hydrogen generation from aqueous acid-catalyzed hydrolysis of sodium borohydride

2010 ◽  
Vol 35 (22) ◽  
pp. 12239-12245 ◽  
Author(s):  
Hyun Jae Kim ◽  
Kyoung-Jin Shin ◽  
Hyun-Jong Kim ◽  
M.K. Han ◽  
Hansung Kim ◽  
...  
Keyword(s):  
Sodium Borohydride ◽  
Hydrogen Generation ◽  
Aqueous Acid ◽  
Acid Catalyzed ◽  
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.

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