EFFECT OF THE OXIDATION NUMBER OF THE SULFUR ATOM ON THE THIOXANTHONES RADICAL-ANIONS STUDIED BY ELECTRONIC ABSORPTION AND ESR-SPECTRA

Electronic absorption and ESR spectra of the radical anions of thioxanthones, (TO-SOn)-•(,M+) (n = 0, 1, and 2; the abbreviation represents both the contact ion pairs and free ions together), and of xanthone were studied under a variety of conditions. The absorption spectra, observed in HMPA (hexamethylphosphoric triamide), were the same as those observed in γ-irradiated glassy MTHF (2-methyltetrahydrofuran) solution, revealing formation of the monomeric free ((TO-SOn)-• radical anions in HMPA. These observations were supported by the lack of alkali metal splitting for the ESR spectra in HMPA. From the change in hfs (hyperfine splitting constants) and λmax resulting from the change in size of countercations of the contact (TO-SOn)-•,M+ ion pairs, the ion pairing effect was discussed. The hfs of (TO-SO)-•,M+ and (TO-SO2)-•,M+ were very similar to those of radical anions of fluorenone, (FO)-•,M+, and the similarity was also observed even in HMPA. Thus, ((TO-SO)-•(,M+) and (TO-SO2)-•(,M+) may exist as the ketyl. It was found from the ESR data in rigid media that (TO-SO)-•,Na+ and (TO-S)-•,Na+ contained a variety of associated ionic species in small amounts, while (TO-S)--,Na+contained such species in large amounts. The data of hfs, λmax, and reduction potentials revealed the similarity in electronic structure between (TO-SO)-•,M+ and (TO-SO2)-•(,M+). The conjugation between two aromatic rings in both the radical anions through the sulfoxide or sulfone moiety was significant. © 1979, American Chemical Society. All rights reserved.