Improving synthetic hindered phenol antioxidants: learning from vitamin E

The efficiency of various commercial hindered phenol antioxidants was studied using differential scanning calorimetry (DSC) to determine the oxidation induction time (OIT) of antioxidant solutions in squalane. It was observed that alpha-tocopherol has an exceptionally high antioxidant activity. In fact, after normalisation for the molecular weight and functionality of each antioxidant, alpha-tocopherol was twice as efficient as any of the commercial, synthetic, hindered phenols tested. Through measurements on a series of model compounds, it was possible to identify the aspects of alpha-tocopherol's chemical structure that are responsible for its exceptional antioxidant efficiency. The results showed that the para oxygen in alpha-tocopherol is largely responsible for its exceptionally high antioxidant activity. Most commercial synthetic hindered phenolic antioxidants are based upon 2, 6-di-tert-butyl-4-methylphenol (BHT). We compared the antioxidant efficiency of BHT with that of 2, 6-di-tert-butyl-4-methoxyphenol (BHA) and found that BHA was 94% more efficient. This implies that it may be advantageous to make new commercial hindered phenolic antioxidants that are based in the more effective BHA structure instead of the conventional BHT structure used today. It is expected that addition of a para oxygen (or other electron donating groups) to the aromatic ring of existing hindered phenolic antioxidants would significantly increase their activity. (C) 2000 Elsevier Science Ltd. All rights reserved.