View source for Phosphorus pentachloride

{{redirect|PCl5|the printer protocol|Printer Command Language}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 455252348
| Name = Phosphorus pentachloride
| ImageFile = Phosphorus-pentachloride-2D-dimensions.png
| ImageSize = 100px
| ImageName = Phosphorus pentachloride (gas phase structure)
| ImageFileL1 = Phosphorus-pentachloride-3D-balls.png
| ImageSizeL1 = 100px
| ImageNameL1 = Phosphorus pentachloride
| ImageFileR1 = Phosphorus-pentachloride-3D-vdW.png
| ImageSizeR1 = 100px
| ImageFile2 = Phosphorus pentachloride ampoule.jpg
| IUPACName = Phosphorus pentachloride<br> Phosphorus(V) chloride
| OtherNames = Pentachlorophosphorane
|Section1={{Chembox Identifiers
| SMILES = ClP(Cl)(Cl)(Cl)Cl
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 23204
| InChI = 1/Cl5P/c1-6(2,3,4)5
| InChIKey = UHZYTMXLRWXGPK-UHFFFAOYAP
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/Cl5P/c1-6(2,3,4)5
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = UHZYTMXLRWXGPK-UHFFFAOYSA-N
| CASNo = 10026-13-8
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = <!-- {{fdite|correct|FDA}} no such template:fdite-->
| UNII = 0EX753TYDU
| PubChem = 24819
| EINECS = 233-060-3           
| RTECS = TB6125000
| UNNumber = 1806
 }}
|Section2={{Chembox Properties
| P=1 | Cl=5
| Appearance = colourless crystals
| Odor = pungent, unpleasant<ref name=PGCH/>
| Density = 2.1&nbsp;g/cm<sup>3</sup>
| Solubility = reacts
| SolubleOther = soluble in [[carbon disulfide|CS<sub>2</sub>]], [[haloalkane|chlorocarbons]], [[benzene]]
| MeltingPtC = 160.5
| BoilingPtC = 166.8
| BoilingPt_notes = sublimation
| VaporPressure = 1.11&nbsp;kPa (80&nbsp;°C)<br> 4.58&nbsp;kPa (100&nbsp;°C)<ref name=nist>{{nist|name=Phosphorus pentachloride|id=C10026138|accessdate=2014-05-15|mask=FFFF|units=SI}}</ref>
 }}
|Section3={{Chembox Structure
| Coordination = ''D''<sub>3h</sub> ([[trigonal bipyramidal]])
| CrystalStruct = tetragonal
| Dipole = 0&nbsp;[[Debye|D]]
 }}
|Section4={{Chembox Thermochemistry
| HeatCapacity = 111.5&nbsp;J/mol·K<ref name=nist />
| Entropy = 364.2&nbsp;J/mol·K<ref name=nist />
| DeltaHf = 
| DeltaGf = 
| DeltaHc = 
 }}
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS05}}{{GHS06}}{{GHS08}}<ref name="sigma">[http://www.sigmaaldrich.com/catalog/product/sial/157775 Phosphorus pentachloride]</ref>
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|302|314|330|373}}<ref name="sigma" />
| PPhrases = {{P-phrases|260|280|284|305+351+338|310}}<ref name="sigma" />
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0544.htm ICSC 0544]
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 2
| NFPA-S = W
| FlashPt = Non-flammable
| LD50 = 660&nbsp;mg/kg (rat, oral)<ref name=IDLH/>
| IDLH = 70&nbsp;mg/m<sup>3</sup><ref name=PGCH>{{PGCH|0509}}</ref>
| LC50 = 205&nbsp;mg/m<sup>3</sup> (rat)<ref name=IDLH>{{IDLH|10026138|Phosphorus pentachloride}}</ref>
| REL = TWA 1&nbsp;mg/m<sup>3</sup><ref name=PGCH/>
| PEL =  TWA 1&nbsp;mg/m<sup>3</sup><ref name=PGCH/>
| LCLo = 1020&nbsp;mg/m<sup>3</sup> (mouse, 10&nbsp;min)<ref name=IDLH/>
 }}
|Section8={{Chembox Related
| OtherAnions = 
| OtherCations = 
| OtherFunction = [[Phosphorus pentafluoride]]<br />[[Phosphorus pentabromide]]<br />[[Phosphorus pentaiodide]]
| OtherFunction_label = phosphorus pentahalides
| OtherCompounds = [[Phosphorus trichloride]]<br />[[Phosphoryl chloride]]
 }}
}}
'''Phosphorus pentachloride''' is the [[chemical compound]] with the formula PCl<sub>5</sub>. It is one of the most important [[phosphorus]] chlorides, others being [[phosphorus trichloride|PCl<sub>3</sub>]] and [[phosphorus oxytrichloride|POCl<sub>3</sub>]]. PCl<sub>5</sub> finds use as a [[Chlorination reaction|chlorinating]] reagent.  It is a colourless, water-sensitive and moisture-sensitive [[solid]], although commercial samples can be yellowish and contaminated with [[hydrogen chloride]].

==Structure==
The structures for the phosphorus chlorides are invariably consistent with [[VSEPR theory|VSEPR]] theory.  The structure of PCl<sub>5</sub> depends on its environment.  Gaseous and molten PCl<sub>5</sub> is a neutral molecule with [[trigonal bipyramidal molecular geometry|trigonal bipyramidal]] geometry and (''D''<sub>3h</sub>) [[Molecular symmetry|symmetry]]. The [[hypervalent]] nature of this species (as well as of {{chem|PCl|6|-}}, see below) can be explained with the inclusion of non-bonding [[molecular orbital]]s ([[molecular orbital theory]]) or [[resonance (chemistry)|resonance]] ([[valence bond theory]]). This trigonal bipyramidal structure persists in nonpolar solvents, such as [[carbon disulfide|CS<sub>2</sub>]] and [[carbon tetrachloride|CCl<sub>4</sub>]].<ref>{{cite book| first = D. E. C. | last=Corbridge| title = Phosphorus: An outline of its chemistry, biochemistry, and uses| year = 1995| publisher = Elsevier Science | isbn = 0-444-89307-5 }}</ref> In the solid state PCl<sub>5</sub> is an [[ionic compound]], formulated {{chem|PCl|4|+|PCl|6|-}}.<ref name="Holleman">{{cite book| first= A. F.|last= Holleman|first2=E.|last2= Wiber |first3=N.|last3= Wiberg | title = Inorganic Chemistry| year = 2001| publisher = Academic Press| isbn = 978-0-12-352651-9 }}</ref>

[[File:EntryWithCollCode76731.png|thumb|left|Structure of solid phosphorus pentachloride, illustrating its autoionization at higher concentrations.<ref>{{cite journal|authors=Finch, A.; Fitch, A.N.; Gates, P.N.|title=Crystal and Molecular structure of a metastable modification of phosphorus pentachloride|journal=Journal of the Chemical Society, Chemical Communications|issue=11|year=1993|pages= 957–958|doi=10.1039/C39930000957}}</ref>]]

In solutions of polar solvents, PCl<sub>5</sub> undergoes self-[[ionization]].<ref>{{cite journal | last1= Suter |first1=R. W.|last2= Knachel |first2=H. C. |last3=Petro |first3=V. P. |last4=Howatson |first4=J. H. |last5= Shore|first5= S. G.  |lastauthoramp=yes | title = Nature of Phosphorus(V) Chloride in Ionizing and Nonionizing Solvents | journal = [[Journal of the American Chemical Society]] | volume = 95 | year = 1978 | pages = 1474–1479 | doi = 10.1021/ja00786a021 | issue = 5}}</ref>  Dilute solutions dissociate according to the following equilibrium:

:PCl<sub>5</sub> {{eqm}} {{chem|PCl|4|+}} + Cl<sup>−</sup>

At higher concentrations, a second equilibrium becomes more prevalent:

:2&nbsp;PCl<sub>5</sub> {{eqm}} {{chem|PCl|4|+}} + {{chem|PCl|6|-}}

The cation {{chem|PCl|4|+}} and the anion {{chem|PCl|6|-}} are [[tetrahedral molecular geometry|tetrahedral]] and [[octahedral molecular geometry|octahedral]], respectively. At one time, PCl<sub>5</sub> in solution was thought to form a dimeric structure, P<sub>2</sub>Cl<sub>10</sub>, but this suggestion is not supported by [[Raman spectroscopy|Raman spectroscopic]] measurements.

===Related pentachlorides===
[[Arsenic pentachloride|AsCl<sub>5</sub>]] and [[Antimony pentachloride|SbCl<sub>5</sub>]] also adopt trigonal bipyramidal structures. The relevant bond distances are 211&nbsp;pm (As−Cl<sub>eq</sub>), 221&nbsp;pm (As−Cl<sub>ax</sub>), 227&nbsp;pm (Sb−Cl<sub>eq</sub>), and 233.3&nbsp;pm (Sb−Cl<sub>ax</sub>).<ref>{{cite journal |last1=Haupt |first1=S. |last2=Seppelt |first2=K. | title = Solid State Structures of AsCl<sub>5</sub> and SbCl<sub>5</sub> | journal = [[Zeitschrift für anorganische und allgemeine Chemie]] | year = 2002 | volume = 628 |pages = 729–734 | doi = 10.1002/1521-3749(200205)628:4<729::AID-ZAAC729>3.0.CO;2-E | issue = 4}}</ref> At low temperatures, SbCl<sub>5</sub> converts to the dimer, dioctahedral Sb<sub>2</sub>Cl<sub>10</sub>, structurally related to [[niobium pentachloride]].

==Preparation==
PCl<sub>5</sub> is prepared by the [[Halogenation|chlorination]] of PCl<sub>3</sub>.<ref>{{cite book|first=R. N.|last=Maxson|chapter=Phosphorus Pentachloride|series=Inorganic Syntheses|date=1939|volume=1|pages=99–100|doi=10.1002/9780470132326.ch34|title=Inorganic Syntheses|isbn=9780470132326}}</ref>  This reaction is used to produce around 10,000 tonnes of PCl<sub>5</sub> per year (as of 2000).<ref name="Holleman" />
:PCl<sub>3</sub> +  Cl<sub>2</sub> {{eqm}} PCl<sub>5</sub> {{pad|3em}} (Δ''H'' = −124&nbsp;kJ/mol)

PCl<sub>5</sub> exists in equilibrium with PCl<sub>3</sub> and [[chlorine]], and at 180&nbsp;°C the degree of dissociation is about 40%.<ref name="Holleman" /> Because of this equilibrium, samples of PCl<sub>5</sub> often contain chlorine, which imparts a greenish coloration.

==Reactions==

===Hydrolysis===
In its most characteristic reaction, PCl<sub>5</sub> [[chemical reaction|reacts]] upon contact with [[water (molecule)|water]] to release [[hydrogen chloride]]. The first hydrolysis product is [[phosphorus oxychloride]]:
:PCl<sub>5</sub> + H<sub>2</sub>O  →  POCl<sub>3</sub> + 2&nbsp;HCl

In hot water, hydrolysis proceeds completely to [[phosphoric acid|orthophosphoric acid]]:
:PCl<sub>5</sub>  +  4&nbsp;H<sub>2</sub>O   →   H<sub>3</sub>PO<sub>4</sub>  +  5&nbsp;HCl

===Lewis acidity===
Phosphorus pentachloride is a Lewis acid.  This property underpins many of its characteristic reactions, autoionization, chlorinations, hydrolysis.  A well studied adduct is PCl<sub>5</sub>(pyridine).<ref>{{cite journal|title=Neutral Six-Coordinate Phosphorus|first1=Chih Y.|last1=Wong|first2=Dietmar K.|last2=Kennepohl|first3=Ronald G.|last3=Cavell|journal=Chemical Reviews|year=1996|volume=96|issue=6|pages=1917–1952|doi=10.1021/cr9410880|pmid=11848816}}</ref>

===Chlorination of organic compounds===
In synthetic chemistry, two classes of chlorination are usually of interest: oxidative chlorinations and substitutive chlorinations. Oxidative chlorinations entail the transfer of Cl<sub>2</sub> from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl<sub>5</sub> can be used for both processes.

Upon treatment with PCl<sub>5</sub>, [[carboxylic acid]]s convert to the corresponding [[acyl chloride]].<ref>{{OrgSynth | authorlink = Roger Adams|last1=Adams |first1=R. |last2=Jenkins |first2=R. L. | title = ''p''-Nitrobenzoyl chloride | collvol = 1 | collvolpages = 394 | prep = cv1p0394 | year = 1941}}</ref> The following mechanism has been proposed:<ref>{{cite book|last=Clayden|first=Jonathan|title=Organic chemistry|year=2005|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-850346-0|edition=Reprinted|url-access=registration|url=https://archive.org/details/organicchemistry00clay_0}}</ref>
:[[File:Phosphorus pentachloride mechanism.png|450px]]

It also converts [[alcohol]]s to [[alkyl halide|alkyl chlorides]]. [[Thionyl chloride]] is more commonly used in the laboratory because the resultant [[sulfur dioxide]] is more easily separated from the organic products than is POCl<sub>3</sub>.

PCl<sub>5</sub> reacts with a tertiary amides, such as [[dimethylformamide]] (DMF), to give dimethylchloromethyleneammonium chloride, which is called the [[Vilsmeier–Haack reaction|Vilsmeier reagent]], [(CH<sub>3</sub>)<sub>2</sub>N=CClH]Cl.  More typically, a related salt is generated from the reaction of DMF and POCl<sub>3</sub>.  Such reagents are useful in the preparation of derivatives of [[benzaldehyde]] by formylation and for the conversion of C−OH groups into C−Cl groups.<ref name="Burks">{{cite encyclopedia|last=Burks Jr. |first=J. E. |title=Encyclopedia of Reagents for Organic Synthesis |chapter=Phosphorus(V) chloride |editor-first=L. |editor-last=Paquette |date=2004 |publisher=J. Wiley & Sons |location=New York, NY |doi=10.1002/047084289X.rp158|isbn=0471936235 }}</ref>

It is especially renowned for the conversion of [[carbonyl|C=O]] groups to CCl<sub>2</sub> groups.<ref>{{OrgSynth | last1= Gross |first1=H. |last2=Rieche |first2=A. |last3=Höft |first3=E. |last4=Beyer |first4=E. | title = Dichloromethyl methyl ether | collvol = 5 | collvolpages = 365 | prep = cv5p0365 | year = 1973}}</ref>  For example, [[benzophenone]] and phosphorus pentachloride react to give the [[diphenyldichloromethane]]:<ref name="Spaggiari2007">{{cite journal|last=Spaggiari|first=A.|first2=D. |last2=Vaccari |first3=P. |last3=Davoli |first4=G. |last4=Torre |first5=F. |last5=Prati |year=2007|title=A Mild Synthesis of Vinyl Halides and ''gem''-Dihalides Using Triphenyl Phosphite−Halogen-Based Reagents|journal=The Journal of Organic Chemistry|volume=72|issue=6|pages=2216–2219|issn=0022-3263|pmid=17295542|doi=10.1021/jo061346g}}</ref> 
:(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>CO  +  PCl<sub>5</sub>  →   (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>CCl<sub>2</sub>  +  POCl<sub>3</sub>

The [[electrophilic]] character of PCl<sub>5</sub> is highlighted by its reaction with [[styrene]] to give, after [[hydrolysis]], [[phosphonic acid]] derivatives.<ref>{{OrgSynth | last= Schmutzler |first=R. | title = Styrylphosphonic dichloride | collvol = 5 | collvolpages = 1005 | prep = cv5p1005 | year = 1973}}</ref>

===Comparison with related reagents===
Both PCl<sub>3</sub> and PCl<sub>5</sub> convert R<sub>3</sub>COH groups to the chloride R<sub>3</sub>CCl.  The pentachloride is however a source of chlorine in many reactions.  It chlorinates allylic and [[benzylic]] CH bonds.  PCl5 bears a greater resemblance to [[sulfuryl chloride|SO<sub>2</sub>Cl<sub>2</sub>]], also a source of Cl<sub>2</sub>.  For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl<sub>5</sub> since the gaseous SO<sub>2</sub> by-product is readily separated.

===Chlorination of inorganic compounds===
As for the reactions with organic compounds, the use of PCl<sub>5</sub> has been superseded by SO<sub>2</sub>Cl<sub>2</sub>.  The reaction of [[phosphorus pentoxide]] and PCl<sub>5</sub> produces [[phosphorus oxychloride|POCl<sub>3</sub>]] (which is an unstable compound):<ref>{{cite book| first= Frank Albert|last= Cotton| title = Advanced Inorganic Chemistry| year = 1999| publisher = Wiley-Interscience| isbn = 978-0-471-19957-1 }}</ref>{{page needed|date=September 2017}}

:6&nbsp;PCl<sub>5</sub>  +  P<sub>4</sub>O<sub>10</sub> → 10&nbsp;POCl<sub>3</sub>

PCl<sub>5</sub> chlorinates [[nitrogen dioxide]] to form unstable [[nitryl chloride]]:

:PCl<sub>5</sub>  +  2&nbsp;NO<sub>2</sub> →  PCl<sub>3</sub> +  2&nbsp;NO<sub>2</sub>Cl
:2&nbsp;NO<sub>2</sub>Cl → 2&nbsp;NO<sub>2</sub> + Cl<sub>2</sub>

PCl<sub>5</sub> is a precursor for [[lithium hexafluorophosphate]], LiPF<sub>6</sub>. Lithium hexafluorophosphate is a commonly employed salt in [[electrolyte]]s in [[lithium ion batteries]].<ref name="Dobrov-2017">{{cite journal |last1=Bushkova |first1=O. V. |last2=Yaroslavtseva |first2=T. V. |last3=Dobrovolsky |first3=Yu. A. |title=New lithium salts in electrolytes for lithium-ion batteries (Review) |journal=Russian Journal of Electrochemistry |date=4 August 2017 |volume=53 |issue=7 |pages=677–699 |doi=10.1134/S1023193517070035}}</ref> {{chem|LiPF|6}} is produced by the reaction of {{chem|PCl|5}} with [[lithium fluoride]], with [[lithium chloride]] as a side product:

:PCl<sub>5</sub>  +  6&nbsp;LiF  →  LiPF<sub>6</sub> +  5&nbsp;LiCl

==Safety==
PCl<sub>5</sub> is a dangerous substance as it reacts violently with water. It is also corrosive when in contact with skin and can be fatal when inhaled.

== History ==

Phosphorus pentachloride was first prepared in 1808 by the English chemist [[Humphry Davy]].<ref>{{cite journal|last1=Davy|first1=Humphry|title=The Bakerian Lecture. An account of some new analytical researches on the nature of certain bodies, particularly the alkalies, phosphorus, sulphur, carbonaceous matter, and the acids hitherto undecomposed; with some general observations on chemical theory|journal=Philosophical Transactions of the Royal Society of London|date=1809|volume=99|pages=39–104|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015034564347;view=1up;seq=53|doi=10.1098/rstl.1809.0005}}  On pp. 94–95, Davy mentioned that when he burned phosphorus in  chlorine gas ("oxymuriatic acid gas"), he obtained a clear liquid (phosphorus trichloride) and a white solid (phosphorus pentachloride).</ref>  Davy's analysis of phosphorus pentachloride was inaccurate;<ref>{{cite journal|last1=Davy|first1=Humphry|title=Researches on the oxymuriatic acid [i.e., chlorine], its nature and combinations; and on the elements of the muriatic acid [i.e., hydrogen chloride]. With some experiments on sulphur and phosphorus, made in the laboratory of the Royal Institution|journal=Philosophical Transactions of the Royal Society of London|date=1810|volume=100|pages=231–257|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015034564339;view=1up;seq=301|doi=10.1098/rstl.1810.0016|doi-access=free}} On p. 257, Davy presented his empirical formula for phosphorus pentachloride:  1 portion of phosphorus to 3 portions of "oxymuriatic gas" (chlorine).</ref> the first accurate analysis was provided in 1816 by the French chemist [[Pierre Louis Dulong]].<ref>{{cite journal|last1=Dulong|title=Extrait d'un mémoire sur les combinaisons du phosphore avec l'oxigène|journal=Annales de Chimie et de Physique|date=1816|volume=2|pages=141–150|url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3dvb;view=1up;seq=147|series=2nd series|trans-title=Extract from a memoir on the compounds of phosphorus with oxygen|language=French}} On p. 148, Dulong presented the correct analysis of phosphorus pentachloride (which is 14.9% phosphorus and 85.1% chlorine by weight, vs. Dulong's values of 15.4% and 84.6%, respectively).</ref>

==See also==
* [[Phosphorus halides]]
* [[Phosphorus trichloride]]
* [[Phosphoryl chloride]]
* [[Phosphorus trifluorodichloride]]

==References==
{{reflist|30em}}

==External links==
{{Commons category|Phosphorus pentachloride}}
* [http://www.chemguide.co.uk/inorganic/period3/chlorides.html The period 3 chlorides]
* [http://www.inchem.org/documents/icsc/icsc/eics0544.htm International Chemical Safety Card 0544]
* [https://www.cdc.gov/niosh/npg/npgd0509.html CDC - NIOSH Pocket Guide to Chemical Hazards]

{{Phosphorus compounds}}

[[Category:Inorganic phosphorus compounds]]
[[Category:Chlorides]]
[[Category:Hypervalent molecules]]
[[Category:Phosphorus(+5) compounds]]