General procedure for the synthesis of 3,5-dibromo-1H-1,2,4-triazole from 1H-1,2,4-triazole: a solution of bromine (6.1 mL, 119 mmol) in dichloromethane (DCM, 15 mL) and sodium hydroxide (6.78 g, 169 mmol) in water (20 mL) were added simultaneously and slowly dropwise to the stirred 1H-1,2,4- triazole (3.9 g, 56 mmol), water (50 mL) and DCM (15 mL) mixture at 0°C. The reaction temperature was controlled to be below 20°C during the dropwise addition. The reaction mixture was stirred at room temperature overnight. Subsequently, concentrated hydrochloric acid (2.0 mL, 66 mmol) was added to the reaction solution. The solid product was isolated by filtration, washed with water and dried under vacuum to afford the title compound 3,5-dibromo-1H-1,2,4-triazole as a solid (8.3 g, 65% yield). Mass spectrum (ESI) m/z 224 [M-H]-.
