3,8-Dibromo-1,10-phenanthroline-5,6-dione was prepared as follows: 1,10-phenanthroline· monohydrate (22 g), disulfur dichloride (49 g), pyridine (30 mL), and 1-chlorobutane (300 mL) were added dropwise with stirring while adding bromine (57 g) to a reaction vessel where nitrogen substitution was performed. Next, the mixture was heated while stirring and heated to reflux for 6 hours. After cooling to room temperature, 18M aqueous sodium hydroxide solution (300mL), chloroform (400mL) were added and stirred at room temperature for 1 hour, and then filtered using zeolite as an aid. Extraction operation was carried out to take the chloroform layer, which was washed using saturated brine and then distilled to remove the solvent. The residue was purified by using column chromatography to give 3,8-dibromo-1,10-phenanthroline (50% yield). The resulting 3,8-dibromo-1,10-phenanthroline (10 g), potassium bromide (5 g) were added to a reaction vessel where nitrogen substitution was carried out, and a sulfuric acid-nitric acid mixture was added dropwise over 30 min. Then, the reaction was heated while stirring and heated to reflux for 1 hour. After cooling to room temperature, the reaction solution was injected into ice water and aqueous sodium hydroxide solution was carefully added until the pH of the solution reached 5. The extraction operation was carried out using chloroform and the solvent was removed by distillation after drying it with anhydrous magnesium sulfate. The resulting residue was washed with ethanol to give 3,8-dibromo-1,10-phenanthroline-5,6-dione (98% yield).
