Phenols as antioxidants

Substances that are sensitive to air oxidation, such as foods and lubricating oils, can be protected by phenolic additives. Phenols function as antioxidants. They react with and destroy peroxy (ROO )and hydroxy (HO ) radicals, which otherwise react with the alkenes present in foods and oils to cause their degradation. The peroxy and hydroxy radicals abstract the phenolic hydrogen atom to produce more stable phenoxy radicals that cause less damage to the alkenes (eq. 7.45). 

PROBLEM 7.22 Write resonance structures that indicate how the unpaired electron in the phenoxy radical can be delocalized to the ortho and para positions (reason by analogy with the resonance structures for the phenoxide anion on page 215). 

Two commercial phenolic antioxidants are BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene). BHA is used as an antioxidant in foods, especially meat products. BHT is used not only in foods, animal feeds, and vegetable oils, but also in lubricating oils, synthetic rubber, and various plastics. 

PROBLEM 7.23 Write an equation for the reaction of BHT with hydroxy radical. 

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WILLIAMSON G, FAULKNER K, PLUMB G w (1998) Glucosuiolates and phenolics as antioxidants from plant foods. Eur J Cancer Prev. 7 17-21. 

Oxidative stress has been implicated in a variety of neuropathologies, including stroke, trauma, and diseases such as AD and PD. It should be reasonable to use antioxidant strategies to prevent or treat these diseases. In the following sections are discussed the use of several natural phenolics as antioxidants and the potential actions on neurodegenerative diseases. 

Triarylphosphites such as tris(nonyl)phosphite or tris(2,4-di-tert.-butylphenyl)phosphite are utilized together with phenols as antioxidants in numerous plastics and rubbers. 

In Sections I-III our review of antioxidant activities is based entirely on experimental observations with interpretations of relative activities based upon classical concepts of electronic and steric effects operating on phenoxyl radicals. In the last decade there have been some applications of chemical calculations on phenols as antioxidants, with applications to interpretation on known phenols and extension of this to predictions of activities of novel molecules. In general, the thrust of the theoretical approaches endeavor to (1) clarify the antioxidant mechanism of phenols, (2) calculate antioxidant activities and (3) make predictions on potentially new antioxidants. 

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