To a reflux apparatus add 40 mL of bromine, with stirring start adding 20 g of red phosphorus in small portions, the reaction is very violent. After addition, start a reflux, add some more red phosphorus if the red to brownish color doesn’t disappear, reflux until the reflux condenser is clear. Then distill, the residual red phosphorus in the RBF can be reused to make phosphorus tribromide. Store in glass ampoules.
P4 + 6 Br2 = 4 PBr3
PBr3 + Br2 = PBr5
Phosphorus reacts violently with the bromine
The mixture after completion
Heat to reflux, refluxing cleans the glassware and it indicates that the reaction is complete
The refluxing is complete
Pure phosphorus tribromide