T. Umemoto, M. Nagayoshi, K. Adachi
May 15, 1998
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Journal
Journal of Organic Chemistry
Abstract
N,N‘-Difluoro-2,2‘-, -2,4‘-, -3,3‘-, -4,4‘-bipyridinium and substituted N,N‘-difluoro-2,2‘-bipyridinium bis(triflates), bis(tetrafluoroborates), bis(hexafluorophosphates), and bis(hexafluoroantimonates) 1−9 were synthesized in high yields by the direct fluorination of a mixture of a bipyridyl and a Lewis acid, a Bronsted acid, or the alkali metal salt of an acid. The higher homologues, trimer 10 and polymer 11, were also synthesized. Unsubstituted or electron-donating group-substituted N,N‘-difluorobipyridinium salts are stable nonhygroscopic crystals, while the electron-withdrawing group-substituted N,N‘-diflurobipyridinium salts 3, 5, and 6 are moisture-sensitive crystals. Hydrolysis of 1b in boiling water gave 3,3‘-dihydroxy-2,2‘-bipyridyl. The reactivity determination indicated that the fluorinating capability decreased in the order 2,2‘- ≫ 2,4‘ > 3,3‘- ≈ 4,4‘-isomer ≫ N-fluoropyridinium salt and that the two N−F moieties in a molecule were effective for fluorination. This fluorination occurred in a s...