General procedure for the synthesis of 3-chloro-5-nitro-1H-pyrazole using 3-chloro-1-nitro-1H-pyrazole as starting material: 3-chloro-1-nitro-1H-pyrazole (4.0 g, 27 mmol) was dissolved in anisole (20 mL), and the resulting solution was transferred to an autoclave. The reaction system was heated to 140 °C and the reaction was continuously stirred at this temperature overnight. Upon completion of the reaction, the reaction mixture was cooled to 0 °C and subsequently diluted with hexane (200 mL) and stirring was continued at 0 °C for 30 min. The solid product was isolated by filtration and the solid was washed with cold hexane (10 mL) and dried to give the target compound 3-chloro-5-nitro-1H-pyrazole (2.1 g, 51% yield) as a yellow solid. The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 14.96 (broad single peak, 1H), 7.30 (single peak, 1H).
