Free radical oxidation
2012; Elsevier BV; Linguagem: Inglês
10.1533/9780857097927.15
Autores Tópico(s)Porphyrin and Phthalocyanine Chemistry
ResumoAutoxidation is the direct reaction of molecular oxygen with organic compounds under mild conditions. Oxygen has a special nature in behaving as a biradical by having two unpaired electrons ('O–O') in the ground state and is said to be in a triplet state. The oxidation of lipids proceeds like that of many other organic compounds by a free radical chain mechanism, which can be described in terms of initiation, propagation, and termination processes. These processes often consist of a complex series of sequential and overlapping reactions. Many of the classical mechanistic concepts of lipid oxidation were formulated on the basis of kinetic studies. Later developments in support of the general free radical mechanism of oxidation were based on structural studies of the primary hydroperoxide products. To simplify the kinetics of linoleate oxidation, the reactions were studied at early stages of oxidation, at low levels of conversion, at lower temperatures, and in the presence of an appropriate initiator. Under these conditions, the propagation reactions producing hydroperoxides in high yields are emphasized and the decomposition of hydroperoxides is minimized or considered insignificant. However, the kinetics becomes much more complex when autoxidation is carried out to high conversions, or at elevated temperatures, or in the presence of metals.
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