Autoxidation and Antioxidants. Basic Principles and New Developments

Abstract

Abstract There is no doubt that liquid-phase hydrocarbon autoxidation is one of the most thoroughly understood reactions in organic chemistry. Our knowledge of the elementary reactions involved in this process is so complete that it should be possible to calculate, with a reasonable degree of precision, the overall rate of autoxidation of a hydrocarbon or mixture of hydrocarbons, provided, of course, that the rate of chain initiation can be estimated. It should also be possible to make a reasonable intelligent guess at the stability of a solid system, with the reservations appropriate to the change of phase. With regard to inhibition, there is probably not a great deal of room for further improvement in the inherent efficiency of H-atom donating antioxidants. This is because a decrease in the strength of the X—H bond makes the hydrogen more susceptible to abstraction by molecular oxygen. Radical scavenging transition metal complexes also suffer from the limitation that the more reactive the complex is to ROO the more reactive it will be to O2. There may, of course, be further improvements in the efficiency of preventative antioxidants, particularly multi-functional antioxidants with the ability to decompose hydroperoxides and peroxides by several non-radical mechanisms and also scavenge free-radicals.