Reacivity of Phosphorus-Centered Radicals Generated during the Photoreaction of Diphenylphosphinous Acid with 10-Methylacridinium Salt

Article abstract of DOI:10.1021/jo00112a034

Diphenylphosphinous acid (1) reacts with 10-methylacridinium iodide (2a) in aqueous acetonitrile during irradiation by visible light under an argon atmosphere at 20 deg C to afford diphenylphosphinic acid (3) and 10-methylacridan (4).The effects of the solvent and atmosphere and the effect of added iodide ion (I(1-)) or iodine (I2) on the product distribution show that the mechanism involves initial single-electron transfer (SET) from 1 to 2a in the photoexcited state, by which cation radical 1(1+.) and dihydroacridinyl radical 2(.), are generated.Cation radical 1(1+.) undergoes electrophylic reaction with water in the solvent, and the resulting phosphoranyl radical decomposes through SET to iodine atom (I(.)) rather than unergoing β-scission, eventually giving 3.Protonation to 2(.) followed by reduction by I(1-) affords 4.These reaction sequences make up the catalytic I(.)/I(1-) couple.The results are interpreted on the basis of reported redox potentials.