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

Ladislav Kohout; Jan Fajkoš

doi:10.1135/cccc19793308

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

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19793308 ◽

1979 ◽

Vol 44 (11) ◽

pp. 3308-3320 ◽

Cited By ~ 2

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.

Download Full-text

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

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19901984 ◽

1990 ◽

Vol 55 (8) ◽

pp. 1984-1990 ◽

Cited By ~ 1

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.

Download Full-text

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

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19910478 ◽

1991 ◽

Vol 56 (2) ◽

pp. 478-490 ◽

Cited By ~ 2

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.

Download Full-text