Sulfuric Acid → 5-Fluoro-2-methyl-4-nitropyridin-1-ium-1-olate

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Reaction Steps

The reaction was carried out in a flask vented to a gas scrubber containing aqueous sodium hydroxide solution. The product of Step 5, 5-fluoro-2-picoline-N-oxide (1.0 g, 7.86 mmol) was cooled to 0° C. and concentrated sulfuric acid (4.2 mL) was slowly added, with stirring. Solid potassium nitrate (1.27 g, 12.5 mmol) was then added to this mixture at 0° C., in small portions over a 45 minute period. The reaction mixture was allowed to warm to ambient temperature and was stirred at ambient temperature for 1 hour. Not all of the potassium nitrate had dissolved and the reaction mixture was heated at 50° C. for 0.5 hours and then at 100° C. for 18 hours. The homogeneous reaction solution was poured over ice and the resultant aqueous solution was adjusted to pH 9 with solid potassium carbonate. The aqueous solution was then extracted with 3×80 mL of methylene chloride. The combined organic extract was dried over anhydrous sodium sulfate, filtered and concentrated in vacuo to give 1.084 g (80% yield) of the title compound as a yellow solid, m.p. 107°-108° C.; MS DCI-NH3M/Z: 190 (M+NH4)+ 10%, 173 (M+H)+ 30%, 157 (M-O)+ 50%; 1H NMR (CDCl3) d 2.48 (s, 3H), 8.05 (d, 1H, J=9.0 Hz), 8.31 (d, 1H, J=6.0 Hz).

Provenance & Evidence