Photochemistry of Heterocyclic Compounds. VI. The Photochemical Behavior of Phenazine in Hydroxylic Solvents

The photochemical behavior of phenazine in acidified hydroxylic solvents varied with the concentration of acids present in the solutions. Irradiation of phenazine in an aqueous phosphoric acid afforded a 1 : 1 mixture of phenazinium and 1-hydroxyphenazinium cation radicals which were converted to a mixture of phenazine and 1-hydroxyphenazine. Irradiation in moderately strongly acidified alcohols (0.1–1.0 M HCl in alcohols) or in acetic acid containing 0.1 M p-toluenesulfonic acid yielded a 1 : 1 mixture of phenazine and the corresponding 1-alkoxyphenazines or 1-acetoxyphenazine after work-up of the reaction mixture. On the other hand, irradiation in a very strongly acidified methanol (5.6–9.6 M HCl in methanol) gave only the phenazinium cation radical. Mechanistic studies revealed that in the moderately strongly acidified media the reaction proceeds through a solvent-addition to the excited singlet phenazinium monocation, and in the very strongly acidified methanol the reaction proceeds through an electron transfer from the solvent to the excited singlet phenazinium dication.