Carboxylate anion stabilization of a developing carbonium ion in acetal hydrolysis. Hydrolysis of phthalaldehydic acid acetals

1977 ◽  
Vol 99 (20) ◽  
pp. 6693-6699 ◽  
Author(s):  
Thomas H. Fife ◽  
Theodore J. Przystas
Keyword(s):  
Carboxylate Anion ◽  
Carbonium Ion ◽  
Hydrolysis Of

Cyclopropylcarbinyl-oxo-carboniumions. A solvolytic basis for the cyclopropylcarbinyl-oxo-carbonium ion

1970 ◽  
Vol 48 (13) ◽  
pp. 2146-2148 ◽  
Author(s):  
Bert Fraser-Reid ◽  
Bruno Radatus
Keyword(s):  
Silver Ion ◽  
Resonance Contribution ◽  
Conjugated Diene ◽  
Carbonium Ion ◽  
Neutral Media ◽  
Ion Assistance ◽  
Hydrolysis Of

Hydrolysis of 4,6-O-benzylidene-3-deoxy-3-C-(iodomethyl)-D-allal (1) in neutral buffered medium with or without silver ion assistance gives the cyclopropyl aldehyde 4 as the only product. Methanolysis of 1 gives an equal mixture of the α and β anomers of methyl 4,6-O-benzylidene-2,3-C-methylene-2,3-dideoxy-D-allopyranosides (6 and 7). These results indicate that the cyclopropylcarbinyl-oxo-carboniumion (2), is produced with unit efficiency in solvolyses in neutral media, and the formation of both diasteriomers (6 and 7) requires the complete absence of bicyclobutonium ion (9) resonance contribution to the stabilized intermediate, and implies a strong contribution from the oxo-carbonium ion 10. In basic media compound 1 undergoes quantitative dehydroiodination to the conjugated diene, 4,6-O-benzylidene-1,2,3-trideoxy-3-C-methylene-D-ribo-hex-1-enopyranose(8).

A mechanistic study of the base-catalyzed methanolysis and hydrolysis of the hydrogen phthalate ester of 4-bromo-4′-nitrobenzhydrol

1969 ◽  
Vol 47 (9) ◽  
pp. 1487-1493
Author(s):  
K. G. Rutherford ◽  
O. A. Mamer ◽  
B. K. Tang
Keyword(s):  
Carboxylate Anion ◽  
Phthalate Ester ◽  
Mechanistic Study ◽  
Hydrogen Phthalate ◽  
Isotope Studies ◽  
O Isotope ◽  
Hydrolysis Of

The hydrogen phthalate ester of 4-bromo-4′-nitrobenzhydrol has been subjected to base-catalyzed methanolysis and hydrolysis. In both cases the BAC2 mechanism has been observed. There is no evidence of ortho-carboxylate anion participation (BAC1 mechanism). The results have been substantiated by kinetics, stereochemistry, and 18O isotope studies.

Mechanism and Stereochemistry of the Hydrolysis of 4-Arylamino-1,2,3,4- tetrahydroquinaldines

1974 ◽  
Vol 52 (6) ◽  
pp. 884-887 ◽  
Author(s):  
T. P. Forrest ◽  
G. A. Dauphinee ◽  
W. F. Miles
Keyword(s):  
Nitrogen Atom ◽  
Equilibrium Mixture ◽  
Hydroxyl Group ◽  
Amino Group ◽  
Heterocyclic Nitrogen ◽  
Carbonium Ion ◽  
Kinetically Controlled ◽  
Leaving Group ◽  
Acid Catalyzed ◽  
Hydrolysis Of

Rates of acid-catalyzed hydrolysis of the benzylic amino group in stereoisomers of 4-arylamino-1,2,3,4-tetrahydroquinaldines have been determined by n.m.r. spectroscopy. Those isomers which have a pseudo-axial leaving group react more rapidly than those with a pseudo-equatorial leaving group, forming in each case the isomer with a pseudo-axial hydroxyl group as the kinetically controlled product. This product is converted in time to an equilibrium mixture of the two stereoisomeric alcohols. The reaction is inhibited by excess acid and appears to proceed through an intermediate carbonium ion which is stabilized by the heterocyclic nitrogen atom.

Studies in solvolysis. Part I. The neutral hydrolysis of some alkyl trifluoroacetates in water and deuterium oxide

1968 ◽  
Vol 46 (18) ◽  
pp. 2887-2894 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Activation Process ◽  
Rate Data ◽  
Methyl Ethyl ◽  
Light Water ◽  
Carbonium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The temperature dependence of the rates of neutral hydrolysis of a series of alkyl trifluoroacetates (CF3COOR; R = methyl, ethyl, s-propyl, t-butyl) has been determined in both light and heavy water. From these studies the thermodynamic parameters (ΔH≠, ΔS≠) which characterize the activation process have been calculated. Sufficient rate data have been obtained in the case of the ethyl ester to calculate the heat capacity of activation (ΔCP≠) for the hydrolysis of this compound in light water. Both the entropies and enthalpies of activation as well as the solvent isotope effects are consistent with the proposal that the primary and secondary esters react by an acyl–oxygen BAc2 mechanism, in contrast to the tertiary ester, which appears to react either by a carbonium ion (SN1) process or by a route which combines both the BAc2 and SN1 paths.

Vinyl sulfide hydrolysis

1977 ◽  
Vol 55 (3) ◽  
pp. 548-551 ◽  
Author(s):  
Robert A. McClelland
Keyword(s):  
Double Bond ◽  
Proton Transfer ◽  
Acid Solutions ◽  
Vinyl Ethers ◽  
Vinyl Sulfide ◽  
Carbonium Ion ◽  
Carbon Double Bond ◽  
Carbonium Ions ◽  
Vinyl Sulfides ◽  
Hydrolysis Of

The hydrolysis of vinyl sulfides in acid solutions is shown to proceed via a mechanism analogous to that of vinyl ethers, with slow proton transfer to the carbon–carbon double bond to produce a sulfur stabilized carbonium ion. Relative rates of hydrolysis of compounds RXCH=CH2 are CH3S—, 41; CH3O—, 1500; C6H5S—, 1; and C6H5O—, 10.5. This order is compared with that of other systems which produce similar stabilized carbonium ions.

Vinyl ether hydrolysis. XII. Use of cis–trans isomerism to probe the reaction mechanism

1978 ◽  
Vol 56 (4) ◽  
pp. 461-464 ◽  
Author(s):  
Y. Chiang ◽  
A. J. Kresge ◽  
C. I. Young
Keyword(s):  
Reaction Mechanism ◽  
Vinyl Ether ◽  
Hydrolysis Reaction ◽  
Trans Isomers ◽  
Vinyl Methyl ◽  
Reaction Conditions ◽  
Carbonium Ion ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Hydrolysis Of

Rates of hydrolysis of cis- and trans-β-phenylvinyl methyl ethers, cis- and trans-β-(p-nitrophenyl)vinyl methyl ethers, and cis- and trans-β-cyanovinyl ethyl ethers were measured in concentrated (10–55 wt%) aqueous perchloric acids. The results show that these cis and trans isomers do not interconvert under the hydrolysis reaction conditions, and that formation of the alkoxy carbonium ion intermediate in these reactions is therefore not reversible.

scholarly journals Oxygen-17 splitting of the very rapid molybdenum(V) e.p.r. signal from xanthine oxidase. Rate of exchange with water of the coupled oxygen atom

1980 ◽  
Vol 189 (3) ◽  
pp. 615-623 ◽  
Author(s):  
S Gutteridge ◽  
R C Bray
Keyword(s):  
Exchange Rate ◽  
Oxygen Atom ◽  
Xanthine Oxidase ◽  
Transient Signal ◽  
Carbonium Ion ◽  
Oxygen Ligand ◽  
Exchange Rate Constant ◽  
Single Oxygen Atom ◽  
Single Oxygen ◽  
Hydrolysis Of

Studies have been carried out of effects of 17O substitution on a Mo(V) e.p.r. signal from xanthine oxidase, known as Very Rapid. This transient signal is believed to represent an intermediate in enzymic turnover. When Very Rapid was developed from enzyme equilibrate with 17O-enriched water, strong coupling of Mo(V) to a single oxygen atom was observed, with A(17O)1,2,3 1.34, 1.40, 1.36 mT. The isotropic character of the splittings is interpreted as favouring a structure of the type Mo–O–C. The rate of exchange with water of the oxygen atom detected in the signal was studied. In oxidized enzyme, which contains a terminal oxygen ligand, the exchange rate constant was 2–4 h-1 (pH 5.9–7.8 and about 20 degrees C). However, if the exchange was allowed to take place whilst the enzyme was turning over a substrate, then the process occurred within a few seconds. The present and previous results are interpreted as favouring an enzymic mechanism in which a terminal oxygen ligand reacts, as a nucleophile, with a substrate carbonium ion. To complete the reaction, product liberation, by hydrolysis of the enzyme-bound species, occurs in such a way as to cleave the Mo–O bond, thus explaining the fast oxygen exchange in the presence of the substrate.

scholarly journals Vinyl ether hydrolysis. XI. The effect of α-phenyl substitution

1978 ◽  
Vol 56 (4) ◽  
pp. 456-460 ◽  
Author(s):  
Y. Chiang ◽  
W. K. Chwang ◽  
A. J. Kresge ◽  
L. H. Robinson ◽  
D. S. Sagatys ◽  
...  
Keyword(s):  
Transition State ◽  
Carboxylic Acids ◽  
Vinyl Ether ◽  
Phenyl Group ◽  
Marcus Theory ◽  
Methyl Substituent ◽  
Initial State ◽  
Carbonium Ion ◽  
Weak Resonance ◽  
Hydrolysis Of

The unexpected inability of an α-phenyl group to accelerate the rate of vinyl ether hydrolysis more strongly than an α-methyl substituent, k(CH2=CPhOEt)/k(CH2=CMeOEt) = 0.2 for catalysis by H3O+ at 25 °C, is examined and is found to be the result of two effects: (i) preferential initial state stabilization by phenyl and (ii) weak resonance interaction with the developing alkoxy carbonium ion in the transition state induced by the reactant-like character of the latter. A curved Brønsted relation for the hydrolysis of 3-methoxyindene catalyzed by carboxylic acids and monohydrogen phosphonate anions gives the Marcus theory parameters ΔG0≠ = 3 ± 1 kcal/mol and wr = 12 ± 1 kcal/mol.

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