Phenolic antioxidants-effect of ortho-substituents

The effect of o-substituents, other than alkyls, of phenols was studied. In this case, an a-hydrogen of an o-substituent was found to be abstracted by a phenoxy radical, resulting in the regeneration of a new phenol to enhanc e the activities, especially n value, of a phenol. The substituent effect p roposed so far was not observed on ortho position. New effects, however, ar e found; it can probably change the distribution of the electron of a pheno xy radical and an electron-withdrawing group on the a-carbon of the o-subst ituent can enhance the activity of a phenol, or an o-substituent such as ac etyl deactivates a phenol by hydrogen bonding. In conclusion, an o-acetyl s ubstituent lowered the activity of phenol (n = 0.7) compared with that of B HT, but an o-monochloroacetyl substituent having electron-withdrawing natur e enhanced the activity (n = 3.6) considerably. (C) 2000 Elsevier Science L td. All rights reserved.