Abstract
The corresponding semiquinone radicals are formed via a one-photon reaction during the irradiation of pyridine, quinoline, isoquinoline, pyrazine, pyrimidine, quinoxaline, and acridine in neutral hydrogen-containing solvents such as ether, methanol, or ethanol. In all cases, the dissolved substance in the nπ*-excited (usually singlet) state splits out a hydrogen atom from the solvent. Six-membered monoaza aromatic compounds on irradiation in methanol acidified with HCl are converted to the same semiquinone radicals as in neutral media, but via a two-photon process consisting of electron transfer from an alcohol molecule to the higher excited triplet state of the protonated monoaza aromatic compound. The corresponding cation radicals are formed by UV irradiation of pyrazine, quinoxaline, and phenazine in methanol acididified with HCl. Six-membered o-diaza compounds of the phthalazine and cinnoline type do not react with ether in the absence of a ketone, which acts as a chemical sensitizer. However, they react with methanol via a two-photon mechanism in which the first step is protonation of the dissolved substance, which is followed by electron transfer.
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Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–884, July, 1974.
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Castellano, A., Catteau, J.P., Lablache-Combier, A. et al. Mechanism of the photochemical addition-substitution reactions of six-membered aza aromatic compounds in hydrogen-containing solvents (review). Chem Heterocycl Compd 10, 755–768 (1974). https://doi.org/10.1007/BF00471348
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DOI: https://doi.org/10.1007/BF00471348