Phosphorus pentabromide
Encyclopedia
Phosphorus pentabromide is a reactive, yellow solid of formula P
Br
5, which has the structure PBr4+ Br
− in the solid state but in the vapor
phase is completely dissociated to PBr3 and Br2. Rapid cooling of this phase to 15 K
leads to formation of an ionic species [PBr4]+[Br3]-.
It can be used in organic chemistry to convert carboxylic acids to acyl bromides
. It is highly corrosive and should be handled with care. It decomposes above 100 °C to give phosphorus tribromide
and bromine
:
Reversing this equilibrium to generate PBr5 by addition of Br2 to PBr3 is difficult in practice because the product is susceptible to further addition to yield PBr7.
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
Br
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
5, which has the structure PBr4+ Br
Bromide
A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...
− in the solid state but in the vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
phase is completely dissociated to PBr3 and Br2. Rapid cooling of this phase to 15 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
leads to formation of an ionic species [PBr4]+[Br3]-.
It can be used in organic chemistry to convert carboxylic acids to acyl bromides
Acyl halide
An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group....
. It is highly corrosive and should be handled with care. It decomposes above 100 °C to give phosphorus tribromide
Phosphorus tribromide
Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...
and bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
:
- PBr5 → PBr3Phosphorus tribromidePhosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...
+ Br2BromineBromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
Reversing this equilibrium to generate PBr5 by addition of Br2 to PBr3 is difficult in practice because the product is susceptible to further addition to yield PBr7.