Phosphorus pentabromide is a reactive, yellow solid of formula
P Br5, which has the structure PBr
4+ Br− in the solid state but in the
vapor
In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...
phase is completely dissociated to PBr
3 and Br
2. Rapid cooling of this phase to 15
K leads to formation of the ionic species
phosphorus heptabromide (
4">Br4sup>+
3">r3sup>−).
It can be used in organic chemistry to convert
carboxylic acids to
acyl bromides. It is highly corrosive. 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 with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
:
:PBr
5 →
PBr3 +
Br2
Reversing this equilibrium to generate PBr
5 by addition of Br
2 to PBr
3 is difficult in practice because the product is susceptible to further addition to yield phosphorus heptabromide (PBr
7).
References
Phosphorus bromides
Phosphorus(V) compounds
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