Photochemical Reaction in Chlorinated Solvents in the Presence of Halogenated p-Benzoquinones. I Photochemically Induced Acidification of Solution and Protonation on Octaethylporphyrin in Dichloromethane or Chloroform

Abstract Irradiation of visible light on a dichloromethane or chloroform solution in the presence of halogenated p-benzoquinones, such as fluoranil, chloranil, and bromanil, caused the formation of an acid, HCl. In the presence of octaethylporphyrin in those solutions, the photoinduced protonations of porphyrins were observed. Stepwise spectral changes suggested the formations of monocationic and dicationic species and an “intermediate” which had a spectrum with maximum wavelength at 717 nm. The unstable intermediate was suggested to be octaethylphlorin. But the trial to isolate the intermediate gave octaethylbilindione. Dioxygen was found to exert both negative and positive effects on the acidification of solvents and on the protonation on porphyrin in the octaethylporphyrin–bromanil systems. The mechanisms of these photochemically induced reactions are discussed.