General procedure for the synthesis of 2-amino-4-fluoropyridine from 2-amino-4-chloropyridine: 28 g of 2-amino-4-chloropyridine was dissolved in 100 ml of N,N-dimethylformamide, followed by the addition of 46 g of sodium fluoride. The reaction mixture was heated to 140°C and kept reacting for 5 to 8 hours. Upon completion of the reaction, the mixture was cooled to 80 °C and the solvent was subsequently recovered by distillation under reduced pressure. The residue was dissolved in dichloromethane and washed with saturated saline. The organic phase was separated and after evaporation of the solvent, recrystallized from ethanol to give 22 g of white solid 2-amino-4-fluoropyridine in 90% yield.
