Deprotonation of organic radical cations. Chemical evidence for proton transfer between 9,10-dihydroanthracence radical cations and superoxide radical anions

Abstract

Photoinduced electron-transfer oxygenation of 9,lO-dihydroanthracene was carried out with 2,4,6-triphenylpyrylium tetrafluoroborate (TPP) and 9,lO-dicyanoanthracene (DCA) as sensitizers. The time course of the oxygenation products was studied, and the results showed that anthrone was formed as a primary product in the DCA-sensitized oxygenation whereas in the TPP-sensitized oxygenation anthracene was the primary, major product which under the reaction conditions was converted to anthrone. A mechanism involving proton transfer in the radical ion pair consisting of 9,10-dihydronathracene radical cation and superoxide radical anion, which cannot occur in the TPP-sensitized oxygenation, was proposed to rationalize the difference in the product distribution in the two sensitized oxygenation reactions.