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

• Published in: Bulletin of the Chemical Society of Japan Vol. 47; no. 5; pp. 1251 - 1256
• Main Authors: Wake, Shigeo, Otsuji, Yoshio, Imoto, Eiji
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.05.1974; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.47.1251

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.