Antioxidant activities of phenols having a fused oxygen-containing heterocyclic ring

The oxygen uptake method was used to evaluate the antioxidant activities, R -inh/R-0, and induction period, t(inh), for vitamin E (alpha-Toc), 2,6-di-t ert-butyl-4-methylphenol (BHT), hydroxychromanones (I), dihydroxyxanthenes (II), and hydroxybenzofurans (III) during thermally initiated oxidation of tetralin at 61 degrees C. 1,3,4,5,6,8-Hexamethylxanthene-2,7-diols IIa-b an d 2-ethoxycarbonyl-5,6-dihydroxy-2,3-dihydrobenzofuran IIIc exhibited a low er R-inh/R-0, and a higher induction period than that for BHT. The higher a ntioxidant activities of IIa-b and IIIc are mainly attributed to two factor s: (i) the p-type lone pair on the ether type oxygen atom can help stabiliz e the phenoxyl radical formed upon abstraction of the phenolic hydrogen and (ii) the antioxidant activities of IIa-b and IIIc are dependent on the ini tial hydrogen abstraction from the phenolic OH group as well as on further hydrogen abstraction from the benzylic hydrogen atom or the hydrogen attach ed to the alpha-carbon of the ester group. (C) 2000 Elsevier Science Ltd. A ll rights reserved.