A number of 2,6-di-t-butyl-4-substituted phenols have been prepared and their efficiencies in inhibiting the autoxidation of a saturated white mineral oil have been compared. Electron releasing 4-substituents increase the efficiency of the inhibitors and, provided the substituents are small, the results can be represented by a Hammett ρσ plot. For bulky alkyl substituents in the 4-position, the relative inhibiting efficiencies can be related to the Taft steric substituent constants Es. Replacement of the phenolic hydrogen by deuterium does not affect the efficiency of the inhibitors. It is concluded that the rate controlling step of inhibition involves an addition reaction, perhaps by a charge transfer process, in which the attacking peroxy radical becomes conjugated with the aromatic ring of the inhibitor, probably via the π electrons on the phenolic oxygen atom.
The Journal of Physical Chemistry64, no. 11 (1960): 1636–1642.