Preparation
Electrolytic Cr powder is spread in a thin layer in a quartz reactor tube and bromine vapor, predried over PSO5, is passed over the Cr in a stream of O2-free, dry N2 or Ar. The quartz tube is heated to about 1000°C, after that the two elements combine with incandescence at the beginning of the reaction. The unconverted Br2 is condensed in a receiver cooled in an ice-salt mixture. After 45-60 minutes, the material can cool while maintaining the gas stream. The lustrous black, leafy crystals of CrBr3 are purified by several extractions with absolute ether and decantations with ice water (to remove traces of adhering CrBr2).
