Ketene Acetals. XXIX. The Mechanism of the Reaction of Ketene Acetal with Various Halides

1952 ◽  
Vol 74 (10) ◽  
pp. 2662-2667 ◽  
Author(s):  
S. M. McElvain ◽  
Herbert F. McShane
Keyword(s):  
Ketene Acetal ◽  
Ketene Acetals ◽  
Mechanism Of The Reaction

Reactions of Ketene Acetals. IV. A New Synthesis of α-Pyrones. III

1975 ◽  
Vol 53 (2) ◽  
pp. 201-208 ◽  
Author(s):  
Alain Bélanger ◽  
Paul Brassard
Keyword(s):  
New Synthesis ◽  
One Step ◽  
Ketene Acetals ◽  
Mechanism Of The Reaction

A simple one-step synthesis of α-pyrones and 3-chloro-α-pyrones from β-functionalized α, β-enones and ketene acetals has been devised. The method has also been adapted to the preparation of some 4-methoxy-α-pyrones. Finally the mechanism of the reaction has been investigated.

Synthèse totale des acides (+) et (–) nonactique à partir de carbohydrates

1981 ◽  
Vol 59 (3) ◽  
pp. 572-583 ◽  
Author(s):  
Robert E. Ireland ◽  
Jean-Paul Vevert
Keyword(s):  
Carbon Atom ◽  
Absolute Configuration ◽  
Claisen Rearrangement ◽  
Sigmatropic Rearrangement ◽  
Chiral Carbon ◽  
Ketene Acetal ◽  
Boat Form ◽  
Aliphatic Esters ◽  
Ketene Acetals

The synthesis of (−) and (+) nonactic acids (2a) and (2b) has been achieved starting from D-mannose (7) and D-gluono-γ-lactone (22) respectively. The key step in the synthesis is the [3,3]-sigmatropic rearrangement of the silylated ketene-acetals IV leading to control of the C-2 configuration of nonactic acid. The ketene-acetals were prepared from aliphatic esters of furanoid-glycals II, which were prepared in ten steps from the carbohydrate precursor. The chiral sites of the glycals arise from the corresponding centres in the starting monosaccharide. This type of ketene-acetal Claisen rearrangement leads to products containing the aldol portion required. At the same time knowledge of the absolute configuration of the chiral carbon atom of nonactic acid allows for the determination of the chair or boat form of the transition state of the [3,3]-sigmatropic rearrangement. [Journal translation]

A comprehensive kinetic study of the conventional free-radical polymerization of seven-membered cyclic ketene acetals

2017 ◽  
Vol 8 (34) ◽  
pp. 5139-5147 ◽  
Author(s):  
Antoine Tardy ◽  
Jean-Claude Honoré ◽  
Didier Siri ◽  
Julien Nicolas ◽  
Didier Gigmes ◽  
...  
Keyword(s):  
Free Radical ◽  
Kinetic Study ◽  
Kinetic Analysis ◽  
Radical Polymerization ◽  
Free Radical Polymerization ◽  
Ketene Acetal ◽  
Cyclic Ketene Acetals ◽  
Ketene Acetals

The current study reports on the kinetic analysis of the free-radical polymerization of several seven-membered cyclic ketene acetal monomers.

Ketene Acetals. XIV. The Reactions of Ketene Acetal with Quinones

1944 ◽  
Vol 66 (7) ◽  
pp. 1077-1083 ◽  
Author(s):  
S. M. McElvain ◽  
Edward L. Engelhardt
Keyword(s):  
Ketene Acetal ◽  
Ketene Acetals

Ketene acetals from thermolysis of aryloxy methoxy oxadiazolines. Evidence for carbonyl ylide intermediates

1997 ◽  
Vol 75 (3) ◽  
pp. 326-332 ◽  
Author(s):  
Philippe Couture ◽  
Manal El-Saidi ◽  
John Warkentin
Keyword(s):  
Pure Form ◽  
Second Step ◽  
Carbonyl Ylide ◽  
Ketene Acetal ◽  
Ketene Acetals

Thermolysis of oxadiazolines (5) in benzene at 110 °C leads to ketene acetals (11) as minor products. Carbonyl ylide intermediates (6), and oxiranes (7), presumably in equilibrium with those ylides, are implicated as unstable precursors of the ketene acetals although none of the oxiranes (carbonyl protected α-lactones) were isolable and only one of the ketene acetals was isolable in pure form. The evidence points to the two-step sequence of thermolysis of oxadiazolines, namely, initial cycloreversion to N2 and carbonyl ylide (6), rather than concerted fragmentation to N2, acetone, and carbene (12). The first-formed ylide does fragment to carbene and acetone in a second step that competes with oxirane formation. A tentative mechanism for reaction of 7 with 12, to afford 11, is advanced. Keywords: carbonyl ylide, dioxy oxirane, ketene acetal, oxadiazoline.

Acetolysis of 4β-methanesulphonyloxy-6β,7aβ-cyclo-B-homo-5α-cholestane

1979 ◽  
Vol 44 (11) ◽  
pp. 3308-3320 ◽  
Author(s):  
Ladislav Kohout ◽  
Jan Fajkoš
Keyword(s):  
Mechanism Of The Reaction

Synthesis of 4β-methanesulphonyloxy-6β,7aβ-cyclo-B-homo-5α-cholestane is described. During its acetolysis a kind of conjugative stabilization of the carbocation formed was observed. The mechanism of the reaction is discussed.

Kinetics and mechanism of the reaction of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione

1990 ◽  
Vol 55 (8) ◽  
pp. 1984-1990 ◽  
Author(s):  
José M. Hernando ◽  
Olimpio Montero ◽  
Carlos Blanco
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Activation Parameters ◽  
Enol Form ◽  
Kinetics And Mechanism ◽  
Kinetic Constants ◽  
Steric Factors ◽  
Kinetics Of ◽  
Mechanism Of The Reaction

The kinetics of the reactions of iron(III) with 6-methyl-2,4-heptanedione and 3,5-heptanedione to form the corresponding monocomplexes have been studied spectrophotometrically in the range 5 °C to 16 °C at I 25 mol l-1 in aqueous solution. In the proposed mechanism for the two complexes, the enol form reacts with the metal ion by parallel acid-independent and inverse-acid paths. The kinetic constants for both pathways have been calculated at five temperatures. Activation parameters have also been calculated. The results are consistent with an associative activation for Fe(H2O)63+ and dissociative activation for Fe(H2O)5(OH)2+. The differences in the results for the complexes of heptanediones studied are interpreted in terms of steric factors.

Kinetics and mechanism of the reaction between oxidized cytochrome c and ascorbic acid

1991 ◽  
Vol 56 (2) ◽  
pp. 478-490 ◽  
Author(s):  
Joaquin F. Perez-Benito ◽  
Conchita Arias
Keyword(s):  
Ascorbic Acid ◽  
Cytochrome C ◽  
Redox Reactions ◽  
Arrhenius Equation ◽  
Horse Heart Cytochrome ◽  
First Order ◽  
Acidic Form ◽  
Ph Range ◽  
Horse Heart Cytochrome C ◽  
Mechanism Of The Reaction

The reaction between horse-heart cytochrome c and ascorbic acid has been investigated in the pH range 5.5 – 7.1 and at 10.0 – 25.0 °C. The rate shows a first-order dependence on the concentration of cytochrome c, it increases in a non-linear way as the concentration of ascorbic acid increases, it increases markedly with increasing pH and, provided that the ionic strength of the medium is high enough, it fulfills the Arrhenius equation. The apparent activation energy increases as the pH of the solution increases. The results have been explained by means of a mechanism that includes the existence of an equilibrium between two forms (acidic and basic) of oxidized cytochrome c: cyt-H+ -Fe3+ + OH- cyt -Fe3+ + H2O, whose equilibrium constant is (6.7 ± 1.4). 108 at 25.0 °C, the acidic form being more reducible than the basic one. It is suggested that there is a linkage of hydrogenascorbate ion to both forms of cytochrome c previous to the redox reactions. Two possibilities for the oxidant-reductant linkage (binding and adsorption) are discussed in detail.

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