Abstract

Sharif A S. Alkaabi and El-Metwally Nou

The kinetic* of oxidation of iron (Il)-malate complex by molecular oxygen are studied in various alcohol-water mixtures at constant pH=6.4 and at different temperatures. The value of the rate constant, Kobs. for the oxidation is shown to be strongly dependent upon the type and the amount of the added alcohol. The Kobs. decreases with the addition of alcohol to the aqueons solution. For example, the Kobs. values at 30°C are 11 23x10-2, 6.24 x 10-2 3.06 x10-2 and 1.45x10-2 sec-1 for the reaction in the absence of alcohol and in the presence of 3M of methanol, ethanol. and propano) in water alcohol mixtures, respectively. The rate constant also decreases with the increase of the concentration of the alcohol. A linear relationship was obtained between the log Kobs. and the inverse of the dielectric constant of the alcohol-water mixtures. Activation parameters for the reaction in all solvent systems arc reported.! The solvent effects on the kinetics of iron (II)~malate complex has been attributed not to changes in the structure of the coordination sphere of the complex as reported previously on the oxidation of the related iron (II)-tartrate complex but in this case mainly due to the decrease in the macroscopic dielectric constant of the medium upon the addition of alcohol.

Solvent; Oxidation; Alcohol-Water

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