[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([F:8])=[CH:4][N+:3]=1[O-:9].S(=O)(=O)(O)O.[N+:15]([O-])([O-:17])=[O:16].[K+].[OH-].[NH4+]>>[Cl:1][C:2]1[CH:7]=[C:6]([N+:15]([O-:17])=[O:16])[C:5]([F:8])=[CH:4][N+:3]=1[O-:9]2-Chloro-5-fluoropyridine-N-oxide (10, 3.5 g, 23.7 mmol) was gradually added to 46 mL of concentrated sulfuric acid, followed by 10 g of potassium nitrate with stirring. The reaction mixture was heated at 120° C. for 2 h, cooled and poured onto 160 g of crushed ice. The solution was neutralized by dropwise addition of 28% ammonium hydroxide with stirring, while the temperature was maintained below 15° C. with an ice bath. The light yellow crystals which precipitated were collected by filtration, washed with ice water, and dried to yield 2.7 g (59%) of product. A small sample was purified by silica gel column chromatography (CH2Cl2/EtOAc, 4:1, v/v, Rf 0.71): mp 131-132° C.; 1H NMR (DMSO-d6) δ8.70 (m, 1 H, 3-H), 9.12 (m, 1 H, 6-H). Analysis calculated for C5H2ClFN2O3: C, 31.19; H, 1.05; N, 14.55. Found: C, 31.36; H, 1.16; N, 14.75.
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