Preparation of symmetric dibromides of 1,10-phenanthroline

Bromation of 1,10-phenanthroline with Br2 proceeds smoothly in the presence of S2Cl2 and pyridine to give 3,8-dibromo-1,10-phenanthroline in good yield. Bromation of 2,9-dibutoxy-1,10-phenanthroline with Br2, in an aqueous medium gives 5,6-dibromo-2,9-dibutoxy-1,10-phenanthroline selectively. Similar bromination of 4,7-dibutoxy-1,10-phenanthroline with Br2 gives 3,8-dibromo-4,7-dibutoxy-1,10-phenanthroline, which forms a 1:1 adduct with Cu(NO3)2. Molecular structure of the 1:1 adduct has been determined by X-ray crystallography. Keywords: bromination, 1,10-phenanthroline, 3,8-dibromo-1,10-phenanthroline.