Unexpected Acid Catalysis in Reactions of Peroxyl Radicals with Phenols

摘要

The formal transfer of a hydrogen atom from a phenol to a peroxyl radical [Eq. (1)] is a reaction widely recognized for its central role in the radical-trapping antioxidant activity of phenols, such as α-tocopherol (1), and as a model for formal hydrogen-atom-transfer processes involving tyrosine (and tyrosyl radicals) in enzymatic reactions (e.g. prostaglandin and DNA biosynthesis). The past ten years have brought a wealth of contributions that greatly enhance our understanding of this reaction, including the realization that it probably occurs by a concerted proton-coupled electron transfer (PCET) mechanism, and that have clarified the basis for the long-observed structure-reactivity relationships, whereby electron-rich phenols react fastest because of weaker O-H bonds.