Tetrafluoroboric acid → 4-Fluoro-3-methyl-2-(trifluoromethyl)benzonitrile

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4-amino-3-methyl-2-(trifluoromethyl)benzonitrile (CAS 573764-86-0, 2.0 g, 9.99 mmol) was dissolved in fluoroboric acid, HBF4 solution (15 mL) at −10° C. (ice/MeOH). To the pre-cooled solution was added NaNO2(689 mg, 9.992 mmol) in 2 mL H2O drop by drop under constant stirring. The reaction mixture was allowed to stir for 15 min at −10° C. and filtered off. The white residue was washed with cold EtOH and cold ether to get the diazosalt as a white crystalline solid. The salt is dried over high vacuum for 4-5 h. to provide 1.9 g. The salt was heated up (>250° C.) and sublimed under reduced pressure to get the crude fluoro compound as an oil. The oil is chromatographed to get the pure 4-fluoro-3-methyl-2-(trifluoromethyl)benzonitrile as a clear oil (700 mg): 1H NMR (400 MHz, CDCl3, δ in ppm) 7.68 (dd, J=5.0, 9.0 Hz, 1H), 7.33 (t, J=9 Hz, 1H), 2.43 (quin, J=2 Hz, 3H).

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