100 mL of pyridine hydrofluoride (Py-(HF)x, 70% hydrogen fluoride and 30% pyridine, purchased from Fluka) was cooled at 0°C. 3.7 g of 2-amino-3-hydroxypyridine (molecular weight: 110.12, 33.6 mmol) and 3 g of NaNO2 (molecular weight: 69.00, 43.5 mmol) were added to it in sequence, handling with caution. The reaction mixture was stirred at 0 °C for 1 h, followed by slow alkalinization with 10 N NaOH aqueous solution. The mixture was transferred to a partition funnel and extracted with EtOAc. The organic phases were combined, washed sequentially with water and brine, dried over Na2SO4 and concentrated to dryness. The residue was purified by silica gel column chromatography (eluent: heptane/EtOAc, 50/50) to give 2.5 g (65% yield) of solid 2-fluoro-3-hydroxypyridine, which did not require further purification. Thin layer chromatography (TLC) Rf value (EtOAc/heptane, 80/20): 0.65. melting point: 131 °C. 1H NMR (DMSO-d6, 298 K): δ 10.41 (s, 1H), 7.64 (td, J=1.7 and 4.7 Hz, 1H), 7.42 (dd, J=1.7,1.7 and 10.8 Hz, 1H). 7.17 (ddd, J=1.3,4.7 and 7.8 Hz, 1H).13C NMR (DMSO-d6, 298K): δ 152.8 (d, J1F-C=233 Hz, C), 140.2 (d, J2F-C=27 Hz, C), 135.6 (d, J3F-C=13 Hz, CH), 126.2 (d, J3F -C=5 Hz, CH), 122.6 (CH). Mass spectrum (DCI/NH4+): C5H4FNO: 131 [M+NH4+], 114 [M+H+]. Elemental analysis (C5H4FNO) is consistent with theoretical values for C, H, and N.
