Novel and Simple Synthesis of Brominated 1,10-Phenanthrolines

Abstract

A novel, simple, and reasonably efficient synthesis of 3,8-dibromo-1,10-phenanthroline, 3,6-dibromo-1,10-phenanthroline, 3,5,8-tribromo-1,10-phenanthroline, and 3,5,6,8-tetrabromo-1,10-phenanthroline is presented herein. The crucial role of a new catalyst (sulfur dichloride – SCl2) for the bromination of 1,10-phenanthroline is reported. The bromination of 1,10-phenanthroline monohydrate in the presence of SCl2 and pyridine yielded the brominated compounds, previously only possible through the complicated multi-step and tedious Skraup synthesis method. The application of the bromination catalyst SCl2 as a medium-strength Lewis acid is demonstrated for the first time, and the results are compared with the behaviours of known weak (sulfur chloride – S2Cl2) and strong (thionyl chloride – SOCl2) bromination catalysts. A reaction mechanism was proposed.