| Résumé | The inhibition of the azobis(isobutyronitrile) thermally initiated autoxidation of styrene at 30°C by 1-thio-α-tocopherol and related 6-hydroxythiochromans has shown that these compounds trap fewer than 2.0 peroxyl radicals per molecule (between 1.0 and 1.8) and that they are only slightly less reactive toward peroxyl radicals than structurally related 6-hydroxychromans. A number of thiochromanoxyl radicals were generated photolytically, and their EPR and ENDOR spectra were recorded. The ENDOR cavity is unique in that it allows photolysis of the sample, and this represents the first report on the ENDOR spectra of transient radicals that must be continuously generated by photolysis. The hyperfine splittings for thiochromanoxyls are similar to those of chromanoxyl radicals, but their g values are higher by 0.0008. The UV-visible absorption spectrum of the thiotocopheroxyl radical has a band maximum at 488 nm, well above the 413 nm of α-tocopheroxyl. An addendum reports that 5-hydroxy-2,4,6,7-tetramethylbenzofuran is only ca. 10% as active toward peroxyl radicals at 30°C as structurally related 2,3-dihydro-5-hydroxybenzofurans, the latter being a class of phenols which we have previously shown to be the most active in trapping peroxyl radicals.5,6 An improved synthesis of 1-thio-α-tocopherol and a correction to earlier reports regarding purported syntheses of this compound are also included. |
|---|
