ON THE KINETICS OF THE AUTOXIDATION OF FATS .2. MONOUNSATURATED SUBSTRATES

The autoxidation of methyl oleate and oleic acid shows some differences as compared to the autoxidation of linoleate, e.g., the formation of water at an early stage. Linearization of experimental data on the autoxidation to high oxidation degrees of methyl oleate and other monounsaturated substrates shows that the rate equations previously derived for methyl linoleate in the range of 1-25% oxidation are valid, provided the correct expression for the remaining unreacted substrate is used. With monounsaturated substrates, part of the oxygen is consumed by a secondary oxidation reaction almost from the beginning, and only a certain constant fraction a of the total O2 consumption is consumed in hydroperoxide formation. The fraction alpha is different for methyl oleate, oleyl alcohol, oleic acid and cis 9-octadecene, but the rate constant for the hydroperoxide formation is the same for all of them when experimental conditions are the same. The main difference between oleate and linoleate autoxidation is the much faster decomposition of the oleate hydroperoxides relative to their slow formation.