Commercially available 1,10-phenanthroline monohydrochloride monohydrate reacts with bromine, giving 3,8-dibromo-1,10-phenanthroline as major products in a one-step reaction.
In a typical procedure, a solution of 1,10-phenanthroline monohydrochloride monohydrate (10 g, 43 mmol) in nitrobenzene (20 ml) was heated to 130-140 ℃ in a 250 ml 3-neck flask. Bromine (3.3 ml, 64 mmol in 9.3 ml nitrobenzene) was added dropwise throughout 1 h. The raw material was added to the solution after adding bromine. After stirring for 3 h at the same temperature, the reaction mixture was cooled to room temperature, treated with concentrated ammonium hydroxide, and extracted with dichloromethane. The combined organic layers were washed with water and dried (MgSO4). Concentration in a vacuum afforded a suspension of the products in nitrobenzene. The nitrobenzene was removed by dissolving the suspension in dichloromethane (I0 ml) and filtering it through silica gel (300 ml) using dichloromethane as the eluent. After the nitrobenzene eluted out, the products were recovered by gradually increasing the polarity of the eluent up to 10% MeOH in CH2C12. Flash column chromatography afforded production (2.4 g, 17 % yield) as white powders[1].
[1] Dimitrios Tzalis. “Simple one-step synthesis of 3-bromo- and 3,8-dibromo-1,10-phenanthroline: Fundamental building blocks in the design of metal chelates.” Tetrahedron Letters 36 1 (1995): 3489–3490.
