[7789-69-7] · Br5P · Phosphorus(V) Bromide · (MW 430.47)
(bromination agent for conversion of alcohols to bromides)
Alternate Name: phosphorus pentabromide.
Physical Data: mp 179-181 °C; The Merck Index (11th ed.) reports dec above 100 °C.
Solubility: sol CS2, CCl4.
Form Supplied in: yellow solid; commercially available.
Preparative Method: from Bromine and Phosphorus(III) Bromide,1 with which it is in equilibrium.
Handling, Storage, and Precautions: corrosive and highly toxic; stable if kept dry, but reacts violently with water; store under N2 at rt; use in a fume hood.
The conversion of alcohols (ROH) into bromides (RBr) using PBr5 would appear to be quite general for alcohols; however, the literature does not report many examples of this reaction. Eliel2 reported that PBr5 is better able to convert 4-t-butylcyclohexanol to 4-t-butylbromocyclohexane than Phosphorus(III) Bromide (eq 1).
In the steroid series, D-ring enlargement accompanies reaction of a secondary alcohol with PBr5 (eq 2).3 It should be noted that reaction of Phosphorus(V) Chloride with this same substrate gave direct replacement of the OH with Cl with inversion of configuration.4 Rearrangement and addition of bromine across a double bond has been noted in the reaction with a propargyl alcohol derivative (eq 3).5
PBr5 has been used to cleave diisopropyl ether to isopropyl bromide.5
A regioselective dibromination of a diketone has been reported (eq 4).6
Many related reagents are available for the conversion of alcohols to bromides (see Phosphorus(III) Bromide and related reagents cited therein).
Bradford P. Mundy
Colby College, Waterville, ME, USA