Phosphorus pentabromide is a reactive, yellow solid of formula , which has the structure (tetrabromophosphonium bromide) in the solid state but in the

vapor In physics, a vapor (American English) or vapour (Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R ...

phase is completely dissociated to and . Rapid cooling of this phase to 15 K leads to formation of the ionic species

phosphorus heptabromide Phosphorus heptabromide is an inorganic compound with the chemical formula . It is one of the phosphorus bromides. At normal conditions, it forms red prismatic crystals. can be prepared by the sublimation of a mixture of phosphorus pentabromi ...

(tetrabromophosphonium tribromide ). It can be used in organic chemistry to convert

carboxylic acids In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

acyl bromides In chemistry, an acyl group is a moiety (chemistry), moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group () or hydrogen in the case ...

. It is highly corrosive. It strongly irritates skin and eyes. It decomposes above 100 °C to give

phosphorus tribromide Phosphorus tribromide is a colourless liquid with the formula P Br3. The liquid fumes in moist air due to hydrolysis and has a penetrating odour. It is used in the laboratory for the conversion of alcohols to alkyl bromides. Preparation PBr3 ...

and

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

: : Reversing this equilibrium to generate by addition of to is difficult in practice because the product is susceptible to further addition to yield phosphorus heptabromide .

References

Phosphorus bromides Phosphorus(V) compounds {{Inorganic-compound-stub