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Abstract

Methods have been developed for the purification of oleic acid, oleyl alcohol and related substrates and for the determination of polyunsaturated impurities and peroxides in these compounds.

The autoxidation of purified oleic acid and oleyl alcohol has been studied in the absence of additives and in the presence of deliberately added impurities. These studies show that impurities, especially polyunsaturated impurities, are of great importance in determining the stability of these substrates.

These studies have been extended to examine the effect of a range of antioxidant types on the oxidation of both pure and deliberately contaminated substrates. The effects of antioxidant type and substrate type are discussed.

Synergism between different antioxidants has been examined and found to be significant. The implication of these results for the stabilisation of fatty substrates in commercial practice is discussed.

The action of the newly developed nickel complex {bis (stilbene dithiolato) nickel (II) } as an antioxidant has been investigated both by oxygen absorption and by inhibitor consumption measurements on both the original complex and a series of related molecules whose syntheses are described. These complexes are found to be efficient antioxidants for oleyl alcohol but are relatively inefficient in oleic acid. The induction periods in all cases are terminated by the onset of a very rapid oxidation which is believed to be catalysed by the presence of free nickel ions which are released during the thermal autoxidation of these nickel chelates.

Furthermore, the observed induction period for oxygen uptake is somewhat larger than the time required to consume all of the initial nickel complex. These results simply imply that the initial products of oxidation of the complex are able to act as efficient inhibitors.

A brief investigation of the action of metal catalysts has been made. The indications are that these metal catalysts act as powerful pro-oxidants in the thermal autoxidation reactions of oleic acid and oleyl alcohol, and the phenomenon of catalyst-inhibitor conversion does not occur in these systems.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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