Phosphoryl chloride
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<!--<nowiki> Submit {{subst:chembox}} to get this template</nowiki> -->{{Chembox new
| Name = Phosphoryl chloride
| ImageFile = Phosphorus oxytrichloride.PNG
<!-- | ImageSize = 150px -->
| ImageName = Phosphoryl chloride
| ImageFile1 = Phosphoryl-chloride-3D-vdW.png
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| IUPACName = Phosphoryl chloride or<br />Phosphorus oxide trichloride
| OtherNames = Phosphorus oxychloride<br />Phosphoric trichloride
| Section1 = {{Chembox Identifiers
| CASNo = 10025-87-3
| RTECS = TH4897000
}}
| Section2 = {{Chembox Properties
| Formula = POCl<sub>3</sub>
| MolarMass = 153.33 g/mol
| Appearance = Clear, colourless liquid,<br />fumes in moist air
| Density = 1.645 g/cm<sup>3</sup>, liquid
| Solubility = Reacts
| MeltingPt = 1.25 °C (274.4 K)
| BoilingPt = 105.8 °C (379.0 K)
| Viscosity = ? c[[Poise|P]] at ? °C<!-- Liquids only, omit if data unavailable. You may use [[Pascal-second|Pa.s]] if you prefer -->
}}
| Section3 = {{Chembox Structure
| MolShape = [[tetrahedral]]
| Dipole = 2.54 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| MainHazards = Highly corrosive,<br />lachrymator, toxic
| RPhrases = 14-22-26-29-35-48/23
| SPhrases = 26-45-7/8
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Thiophosphoryl chloride]]<br />
[[Phosphorus oxybromide]]<br />
[[Phosphorus trichloride]]<br />
[[Phosphorus pentachloride]]
}}
}}
'''Phosphoryl chloride''' (commonly called '''phosphorus oxychloride''') is a colourless liquid with the formula {{Phosphorus}}{{Oxygen}}{{Chlorine}}<sub>3</sub>. It hydrolyses in moist air to [[phosphoric acid]] to release choking fumes of [[hydrogen chloride]]. It is manufactured industrially on a large scale from [[phosphorus trichloride]] and [[oxygen]] or [[phosphorus pentoxide]]. It is mainly used to make phosphate esters such as [[tricresyl phosphate]].
==Structure ==
Like phosphate, phosphoryl chloride is tetrahedral in shape. It features three P-Cl bonds and one very 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 very dominant (in contrast with POF<sub>3</sub>). The P=O bond does not resemble the [[Pi bond|π bond]] in a [[carbonyl]] group as in a ketone. The appropriate description of the P-O interaction is a matter of long discussion. Older textbooks favor a description that invokes participation of the [[d-orbital|''d''-orbital]]s on phosphorus. Some of these d-orbitals project toward the O atom, overlapping with [[p-orbital|''p''-orbital]]s on oxygen. More modern texts seem to favor a description where the P-O [[Pi bond|π bond]]ing involves the sigma* components of the P-Cl bonds. These descriptions do not consider a role for d-orbitals.
[[Image:POCl3 structure.png|300px]]
:::<small>where pm = picometers</small>
==Chemical properties==
POCl<sub>3</sub> reacts with water and [[alcohol]]s to give [[phosphoric acid]] or [[phosphate ester]]s, respectively, for example
:O=PCl<sub>3</sub> + 3 H<sub>2</sub>O → [[Phosphoric acid|O=P(OH)<sub>3</sub>]] + 3 [[Hydrogen chloride|HCl]]
If the water is replaced by an [[alcohol]], the trialkyl phosphate esters result. Such reactions are often performed in the presence of an HCl acceptor such as [[pyridine]] or an [[amine]]. If POCl<sub>3</sub> is heated with an excess of a [[phenols|phenol]] ([[Aryl|Ar]]OH) in the presence of a [[Lewis acid]] catalyst such as [[magnesium chloride]] a triaryl phosphate ester is formed, for example:
:3 [[Phenol|C<sub>6</sub>H<sub>5</sub>OH]] + O=PCl<sub>3</sub> → [[Triphenyl phosphate|O=P(OC<sub>6</sub>H<sub>5</sub>)<sub>3</sub>]] + 3 [[Hydrogen chloride|HCl]]
POCl<sub>3</sub> can also act as a [[Lewis base]], forming [[:Wiktionary:adduct|adduct]]s with a variety of Lewis acids such as [[titanium tetrachloride]]:
:Cl<sub>3</sub>P<sup>+</sup>-O<sup>−</sup> + TiCl<sub>4</sub> → Cl<sub>3</sub>P<sup>+</sup>-O-<sup>−</sup>TiCl<sub>4</sub>
The [[aluminium chloride]] adduct (POCl<sub>3</sub>·AlCl<sub>3</sub>) is quite stable, and so POCl<sub>3</sub> can be used to remove AlCl<sub>3</sub> completely from reaction mixtures at the end of a [[Friedel-Crafts reaction]]. POCl<sub>3</sub> reacts with [[hydrogen bromide]] in the presence of AlCl<sub>3</sub> to produce POBr<sub>3</sub>.
==Preparation==
Phosphoryl chloride can be prepared by the reaction of [[phosphorus trichloride]] with [[oxygen]] at 20-50 °C (air is ineffective):
2 [[phosphorus trichloride|PCl<sub>3</sub>]] + [[Oxygen|O<sub>2</sub>]] → 2 O=PCl<sub>3</sub>
An alternative synthesis involves the reaction of [[phosphorus pentachloride]] and [[phosphorus pentoxide]]. Since these compounds are both solids, a convenient way of performing the reaction is to [[Chlorination|chlorinate]] a mixture of PCl<sub>3</sub> and P<sub>4</sub>O<sub>10</sub>, which generates the PCl<sub>5</sub> [[:Wiktionary:in situ|''in situ'']]. As the PCl<sub>3</sub> is consumed, the POCl<sub>3</sub> becomes the reaction solvent.
6 [[phosphorus trichloride|PCl<sub>3</sub>]] + 6 [[Chlorine|Cl<sub>2</sub>]] → 6 [[Phosphorus pentachloride|PCl<sub>5</sub>]]
6 [[Phosphorus pentachloride|PCl<sub>5</sub>]] + [[Phosphorus pentoxide|P<sub>4</sub>O<sub>10</sub>]] → 10 POCl<sub>3</sub>
Phosphorus pentachloride also forms POCl<sub>3</sub> by reaction with water, but this reaction is less easily controlled than the above reaction.
==Uses==
The most important use for phosphoryl chloride is in the manufacture of triarylphosphate esters (as described [[#Chemical properties|above]]) such as [[triphenyl phosphate]] and [[tricresyl phosphate]]. These esters have been used for many years as [[flame retardant]]s and [[plasticiser]]s for [[Polyvinyl chloride|PVC]]. Meanwhile trialkyl esters such as [[tributyl phosphate]] (made similarly from [[butan-1-ol]]) are used as [[liquid-liquid extraction]] solvents in [[nuclear reprocessing]] and elsewhere.
In the semiconductor industry, POCl<sub>3</sub> 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.
In the laboratory, POCl<sub>3</sub> is widely used as a dehydrating agent, for example the conversion of [[amide]]s to [[nitrile]]s. Similarly, certain cyclic amides can be cyclised to dihydro[[isoquinoline]] derivatives using the [[Bischler-Napieralski reaction]].
[[Image:POCl3 organic uses.png|center|600px|Two uses for phosphorus oxychloride in organic chemistry]]
Such reactions are believed to go via an [[imidoyl chloride]]; in certain cases where it is stable, the imidoyl chloride is the final product. For example [[pyridone]]s and pyrimidones can be converted to chloro- derivatives of [[pyridine]]s and [[pyrimidine]]s, which are important intermediates in the pharmaceutical industry. Likewise [[barbituric acid]] is converted to 2,4,6-trichloropyrimidine.<sup>[8]</sup> by reaction with POCl<sub>3</sub> at 140 °C.
[[Image:POCl3 246trichloropyridine.png|center|300px]]
Related to this chemistry is the use of POCl<sub>3</sub> in acylation of activated [[aromatic ring]]s via the [[Vilsmeier-Haack reaction]] to produce [[aryl]] [[aldehyde]]s and [[ketone]]s. The reaction most often uses a formamide such as [[dimethylformamide|DMF]] or ''N''-phenyl-''N''-methylformamide, and it produces an iminium salt which is easily hydrolysed to the aldehyde upon workup. For example [[anthracene]] gives 9-anthraldehyde:
[[Image:Vilsmeier reaction example2.gif|center|Vilsmeier-Haack formylation of anthracene]]
==References==
{{Citationstyle|date=September 2007}}
{{reflist}}
# N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
# ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
# J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992.
# ''The Merck Index'', 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
# A. D. F. Toy, ''The Chemistry of Phosphorus'', Pergamon Press, Oxford, UK, 1973.
# L. G. Wade, Jr., ''Organic Chemistry'', 6th ed., p. 477, Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA, 2005.
# B. J. Walker, ''Organophosphorus chemistry'', p101-116, Penguin, Harmondsworth, UK, 1972.
# R. C. Elderfield, ''Heterocyclic Compounds'', Vol. 6, p 265-266, Wiley, New York, 1957. For trichloropyrimidine prep. see Gabriel & Colman, ''Berichte'' '''37''', 3657 (1904).
# Formylation of [[anthracene]]. ''[[Organic Syntheses]]'', Coll. Vol. 3, p.98; Vol. 20, p.11. ([http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0098 Article])
[[Category:Acyl halides]]
[[de:Phosphoroxychlorid]]
[[fr:Trichlorure de phosphoryle]]
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[[sv:Fosforoxitriklorid]]
[[zh:三氯氧磷]]