In each case the vicinal diphenol is re-created to react again, but then the alkyl substitution of the ring lowers the pKa (the pH at which ionization is 50%) of phenolate oxidation from about 9.0 to 8.5, effectively doubling reaction speed. This explains Ducournau’s surprising early discovery that oxygenated wines at first increase in reductive strength. Feed a wine oxygen, and its appetite increases. It’s like bodybuilding—do it right, and you get stronger, not weaker. Oxygenation is not oxidation.
