An excess of phosphorus is used in order to prevent formation of PBr5:[1][2] Because the reaction is highly exothermic, it is often conducted in the presence of a diluent such as PBr3.

An important reaction of PBr3 is with alcohols, where it replaces an OH group with a bromine atom to produce an alkyl bromide.

[7] The mechanism for a primary alcohol involves formation of a phosphorous ester (to form a good leaving group), followed by an SN2 substitution.

The overall process can be represented as On a commercial scale, phosphorus tribromide is used in the manufacture of pharmaceuticals such as alprazolam, methohexital and fenoprofen.

In reactions that produce phosphorous acid as a by-product, when working up by distillation be aware that this can decompose above about 160 °C to give phosphine which can cause explosions in contact with air.