The Defluorination of Tetrafluorobenzene with Ntaphthalene Radical Anion and Unsolvated Hydroxide lon

Abstract

The reaction of 1, 2, 4, 5-tetrafluorobenzene (TFB) [1] with sodium dihydronaphthylide (C₁₀H₈^-Na⁺) [9] was investigated as a defluorination model of polyfluo rinated aromatic compounds. When [1] was treated in THF at 0°C for 30 min with 1.5 equiv of [9] per fluorine atom, organic fluorine atom was removed effectively (defluorination efficiency: 100%). α, α, α-Trifluorotoluene [2] was also defluorinated effectivelyd (100%) under the same conditions. The defluorination of [1] under N₂ at 50°C in THF with unsolvated KOH which was prepared from C₁₀H₈^-K⁺ afforded 2, 4, 5-trifluorophenol [3] (83.4%) as the major product. Under an oxygen atmosphere, however, 2, 3, 5, 6-tetrafluorophenol. [4] (46.3%) was predominantly produced besides [3] (25.8%). Thus, the initial likely intermediate is 2, 3, 5, 6tetrafluorobenzenide anion, which undergoes either elimination of fluoride ion to generate trifluorobenzyne or air oxidation to yield tetrafluorophenol [4] as the final oxidation product.