Kinetic and Thermodynamic Study of the Acid-Catalysed Hydrolysis of Diethylmalonate in Dioxane-Water Mixtures

A kinetic study of the acid-hydrolysis of diethylmalonate in water and dioxane-water mixtures covering the range 0-95% (w/w) of dioxane is reported. The reaction rate is inversely proportional to the organic content of the medium up to about 80% (w/w) then, after passing through a minimum, it becomes directly proportional as the dioxane cosolvent is further added. The kinetic ratio k1/k2 is independent of the solvent composition. The observed activation energies, thermodynamic parameters and radii of the activated complexes along the whole range of solvent composition, for the two consecutive steps of the reaction, are computed. Electrostatic theories favour an interaction in which an ion and a molecular dipole are involved. Application of the reactivity-selectivity principle (RSP) to the present reaction in comparison with that for diethylsuccinate. under different conditions of temperature and solvent composition, is presented.

Download Full-text

Kinetics of Acid-Catalysed Hydrolysis of Diethylsuccinate in Dioxane-Water Mixtures

Zeitschrift für Naturforschung A ◽

10.1515/zna-1982-0415 ◽

1982 ◽

Vol 37 (4) ◽

pp. 390-394

Author(s):

Fayez Y . Khalil ◽

F. M. Abdel-Halim ◽

Adel N. Asaad

Keyword(s):

Dielectric Constant ◽

Thermodynamic Parameters ◽

Rate Constants ◽

Solvent Composition ◽

Specific Rate ◽

Molecular Dipole ◽

First Order ◽

Kinetics Of ◽

Hydrolysis Of ◽

Activated Complex

Abstract The specific rate constants k1 and k2 of the consecutive first-order acid-catalysed hydrolysis steps of diethylsuccinate in dioxane-water mixtures covering the range 0-95% (w/w) of dioxane are determined at 25-55 °C. As the concentration of dioxane increases, the rate of the reaction decreases to a minimum at about 90% (w/w) dioxane, after which it increases again. The ratio k1/k2 was found to be almost constant at the value 2.0. The activation energies of the reaction are independent of solvent composition. Available electrostatic theories regarding the effect of the dielectric constant on the rate are presented, from which the reaction is shown to be an ion-molecular dipole type of interaction. The thermodynamic parameters and the radii of the activated complex at different solvent compositions are calculated and discussed.

Download Full-text

Solvent Effects on the Kinetics and Mechanism of the Acid-Catalysed Hydrolysis of Diterf.-butylsuccinate in Dioxane-Water Mixtures

Zeitschrift für Naturforschung A ◽

10.1515/zna-1985-0115 ◽

1985 ◽

Vol 40 (1) ◽

pp. 84-91 ◽

Cited By ~ 2

Author(s):

Adel N. Asaad ◽

Fayez Y. Khalil

Keyword(s):

Dielectric Constant ◽

Solvent Effects ◽

Rate Constants ◽

Mixed Type ◽

Reaction Rate ◽

Solvent Composition ◽

Water Molecules ◽

Molecular Dipole ◽

First Order ◽

Hydrolysis Of

The acid-catalysed hydrolysis of ditert.-butylsuccinate in dioxane-water mixtures proceeds via consecutive first-order reactions. The rate constants kI and kII corresponding to the two steps decrease with increasing dioxane content of the medium. After reaching a minimum at 90% (w/w) dioxane, both rate constants increase again with further addition of dioxane. The kinetic ratio kI/kII is smaller than the statistical value 2.0, and is markedly affected both by solvent composition and temperature. The maximum concentration of the intermediate half ester decreases with increasing dioxane content. The observed activation energies EI and EII of the two steps of the reaction are largely dependent on temperature as well as solvent composition indicating a mixed type of bond fission represented by the AAl 1 and AAC 2 mechanisms, whose relative contributions in the overall rate constants kI and kIIcould be calculated on the basis of the number of water molecules incorporated in the corresponding transition states. The effect of bulk dielectric constant on the reaction rate was investigated in the light of the available electrostatic theories and showed the reaction to be an ion-molecular dipole type of interaction. The activation thermodynamic parameters were computed and discussed as criteria of solvent effect and mechanism.

Download Full-text

A kinetic study of the acid autoxidation of tryptophan

Australian Journal of Chemistry ◽

10.1071/ch9722139 ◽

1972 ◽

Vol 25 (10) ◽

pp. 2139 ◽

Cited By ~ 8

Author(s):

M Stewart ◽

CH Nicholls

Keyword(s):

Free Radical ◽

Amino Acid ◽

Kinetic Study ◽

Acid Hydrolysis ◽

Soda Glass ◽

Glass Containers ◽

Hydrolysis Of

The decomposition of tryptophan in aqueous HC1 at 100�C has been shown to proceed by a free-radical autoxidation mechanism. The acid functions by protonating the amino acid at either the 1- or 3-positions prior to autoxidation and so 1-methyltryptophan is also decomposed under these conditions. Impurities present in the soda glass containers used are shown to be responsible for the initiation of the reaction. The decomposition of tryptophan during the acid hydrolysis of proteins is considered in the light of these results.

Download Full-text