POBr3 is an important brominating agent. The improved method is to directly prepare POBr3 by the reaction of PBr3, Br2 and P2O5. The result is satisfactory. It avoids the use of CS2 and nitrobenzene in the preparation of PBr5, which are more toxic solvents, and simplifies the operation.
In a three-necked flask equipped with a magnetic stirrer, a thermometer, a drying tube with NaOH and CaCl2 (the drying tube is filled with NaOH and then CaCl2), a condenser tube and a constant pressure funnel, add the newly opened P2O524g 0.17mol) and PBr3135g (0.50mol). Start the stirrer, add Br284g (0.53mol) dropwise within 2h at room temperature, after the dropwise addition of bromine, use an oil bath to raise the temperature to 150℃, and react for 5h. After a little cooling, 10gBr2 and 3gP2O5 were added, and the reaction was continued at 150℃ for 7h. After cooling, the vacuum distillation device was used, and a NaOH drying tower was installed between the receiver and the safety bottle. Under reduced pressure distillation, after removing the initial fractions Br2 and PBr3, they were trapped to obtain 173g of phosphorus oxybromide white crystals. The yield was 72.6% (calculated as PBr3).