405230-79-7

405230-80-0

General procedure for the synthesis of 2-chloro-5-fluoro-4-nitropyridine-1-oxide (11) from 2-chloro-5-fluoropyridine-1-oxide: 2-chloro-5-fluoropyridine-1-oxide (10, 3.5 g, 23.7 mmol) was slowly added to 46 mL of concentrated sulfuric acid, followed by 10 g of potassium nitrate under stirring conditions. The reaction mixture was heated at 120 °C for 2 h, cooled and poured into 160 g of crushed ice. The reaction solution was neutralized by dropwise addition of 28% ammonium hydroxide solution under cooling in an ice bath, keeping the temperature below 15 °C. The precipitated light yellow crystals were collected by filtration, washed with ice water and dried to give 2.7 g (59% yield) of the target product. A small amount of the sample was purified by silica gel column chromatography (eluent: dichloromethane/ethyl acetate, 4:1, v/v, Rf 0.71) with a melting point of 131-132 °C. 1H NMR (DMSO-d6) δ 8.70 (m, 1H, 3-H), 9.12 (m, 1H, 6-H). Elemental analysis (C5H2ClFN2O3) Calculated values: C, 31.19; H, 1.05; N, 14.55. Measured values: C, 31.36; H, 1.16; N, 14.75.