Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing
phosphoric acid and fumes of
hydrogen chloride. It is manufactured industrially on a large scale from
phosphorus trichloride
Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic ...
and
oxygen or
phosphorus pentoxide. It is mainly used to make phosphate esters such as
tricresyl phosphate
Tricresyl phosphate (TCP), is a mixture of three isomeric organophosphate compounds most notably used as a flame retardant and as a plasticizer in manufacturing for lacquers and varnishes and vinyl plastics. Pure tricresyl phosphate is a colo ...
.
Structure
Like phosphate, is tetrahedral in shape. It features three P−Cl bonds and one strong P=O double bond, with an estimated
bond dissociation energy of 533.5 kJ/mol. On the basis of bond length and electronegativity, the Schomaker-Stevenson rule suggests that the double bond form is dominant, in contrast with the case of
. The P=O bond involves the donation of the lone pair electrons on oxygen ''p''-orbitals to the antibonding combinations associated with phosphorus-chlorine bonds, thus constituting
''π'' bonding.
Phosphoryl chloride exists as neutral molecules in the
solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
, liquid and gas states. This is unlike
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
which exists as neutral molecules in the gas and liquid states but adopts the
ionic form in the solid state. The average bond lengths in the
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pattern ...
of are 1.98 Å for P–Cl and 1.46 Å for P=O.
Physical properties
With a freezing point of 1 °C and boiling point of 106 °C, the liquid range of is rather similar to water. Also like water,
autoionizes, owing to the reversible formation of
cations and
anions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...
.
Chemical properties
reacts with water to give
hydrogen chloride and
phosphoric acid:
:
Intermediates in the conversion have been isolated, including pyrophosphoryl chloride, .
Upon treatment with excess
alcohols and
phenols, gives
phosphate esters:
:
Such reactions are often performed in the presence of an HCl acceptor such as
pyridine or an
amine.
can also act as a
Lewis base, forming
adducts with a variety of
Lewis acids such as
titanium tetrachloride:
:
The
aluminium chloride adduct () is quite stable, and so can be used to remove from reaction mixtures, for example at the end of a
Friedel-Crafts reaction.
reacts with
hydrogen bromide in the presence of Lewis-acidic catalysts to produce .
Preparation
Phosphoryl chloride can be prepared by many methods. Phosphoryl chloride was first reported in 1847 by the French chemist
Adolphe Wurtz by reacting
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
with water.
By oxidation
The commercial method involves oxidation of
phosphorus trichloride
Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic ...
with
oxygen:
[.]
:
An alternative method involves the oxidation of phosphorus trichloride with
potassium chlorate:
:
Oxygenations
The reaction of
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
() with
phosphorus pentoxide ().
:
The reaction can be simplified by
chlorinating a mixture of and , generating the
''in situ''.
The reaction of
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
with
boric acid or
oxalic acid:
:
:
Other methods
Reduction of
tricalcium phosphate with carbon in the presence of
chlorine gas:
:
The reaction of phosphorus pentoxide with
sodium chloride is also reported:
:
Uses
In one commercial application, phosphoryl chloride is used in the manufacture of phosphate esters. Triarylphosphates such as
triphenyl phosphate and
tricresyl phosphate
Tricresyl phosphate (TCP), is a mixture of three isomeric organophosphate compounds most notably used as a flame retardant and as a plasticizer in manufacturing for lacquers and varnishes and vinyl plastics. Pure tricresyl phosphate is a colo ...
are used as
flame retardants and
plasticisers for
PVC. Trialkylphosphates such as
tributyl phosphate are used as
liquid–liquid extraction
Liquid–liquid extraction (LLE), also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an orga ...
solvents in
nuclear reprocessing and elsewhere.
In the semiconductor industry, is used as a safe liquid phosphorus source in diffusion processes. The phosphorus acts as a dopant used to create
n-type layers on a silicon wafer.
As a reagent
In the laboratory, is a reagent in dehydrations. One example involves conversion of formamides to isonitriles (isocyanides); primary
amides to
nitriles:
:
In a related reaction, certain aryl-substituted amides can be cyclized using the
Bischler-Napieralski reaction.
:
Such reactions are believed to proceed via an
imidoyl chloride. In certain cases, the imidoyl chloride is the final product. For example,
pyridone Pyridone may refer to several organic compounds with the formula :
* 2-Pyridone
* 3-Pyridone
* 4-Pyridone
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