3,5-Dinitropyridin-2-amine (4.0 g, 21.7 mmol) was used as starting material and suspended in methanol (150 mL). Subsequently, 20% aqueous ammonium sulfide solution (31.7 mL, 109 mmol, 5 eq.) was slowly added to the suspension. The reaction mixture was heated to 75 °C and kept at this temperature for 30 minutes. Upon completion of the reaction, the mixture was allowed to cool naturally to room temperature and was subsequently cooled in an ice bath to promote the formation of a precipitate. The precipitate was collected by filtration to afford the target product 5-nitropyridine-2,3-diamine (3.4 g, 100% yield) as a solid. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 8.28-8.29 (m, 1H), 7.35-7.37 (m, 1H), 6.99 (br s, 2H), 5.32 (br s, 2H).
