Improving synthetic hindered phenol antioxidants: learning from vitamin E

The eciency of various commercial hindered phenol antioxidants was studied using di€erential scanning calorimetry (DSC) to determine the oxidation induction time (OIT) of antioxidant solutions in squalane. It was observed that a-tocopherol has an exceptionally high antioxidant activity. In fact, after normalisation for the molecular weight and functionality of each antioxidant, a-tocopherol was twice as ecient 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 a-tocopherol's chemical structure that are responsible for its exceptional antioxidant eciency. The results showed that the para oxygen in a-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 eciency of BHT with that of 2, 6-di-tert-butyl-4-methoxyphenol (BHA) and found that BHA was 94% more ecient. This implies that it may be advantageous to make new commercial hindered phenolic antioxidants that are based in the more e€ective 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 signi®cantly increase their activity. # 2000 Elsevier Science Ltd. All rights reserved.