Phosphorus pentachloride: Difference between revisions

{{Redirect|PCl5|the printer protocol|Printer Command Language}}

{{Chembox

| Verifiedfields = changed

| verifiedrevid =

| Name = Phosphorus pentachloride

| ImageFile = Phosphorus-pentachloride-2D-dimensions.png

| ImageSize =

| ImageName = Phosphorus pentachloride (gas phase structure)

| = Phosphorus-pentachloride-3D-balls.png

| =

| = Phosphorus pentachloride

| = Phosphoruspentachloride.

| ImageSizeR1 = 100px

| ImageFile2 = Phosphorus pentachloride ampoule.jpg

| IUPACName = Phosphorus pentachloride<br> Pentachloro-λ⁵-phosphane

| 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 = yellowish white crystals

| Odor = pungent, unpleasant<ref name=PGCH/>

| Density = 2.1&nbsp;g/cm³

| Solubility = reacts

| SolubleOther = soluble in [[carbon disulfide|CS₂]], [[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''_3h ([[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 />

| =

| 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/m³<ref name=PGCH>{{PGCH|0509}}</ref>

| LC50 = 205&nbsp;mg/m³ (rat)<ref name=IDLH>{{IDLH|10026138|Phosphorus pentachloride}}</ref>

| REL = TWA 1&nbsp;mg/m³<ref name=PGCH/>

| PEL = TWA 1&nbsp;mg/m³<ref name=PGCH/>

| LCLo = 1020&nbsp;mg/m³ (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 PCl₅. It is one of the most important phosphorus chlorides, others being [[phosphorus trichloride|PCl₃]] and [[phosphorus oxytrichloride|POCl₃]]. PCl₅ finds use as a [[]]. It is a colourless, water-sensitive [[solid]], although commercial samples can be yellowish and contaminated with [[hydrogen chloride]].

The structures for the phosphorus chlorides are invariably consistent with [[VSEPR theory. The structure of PCl₅ depends on its environment. Gaseous and molten PCl₅ is a neutral molecule with trigonal bipyramidal (''D''_3h) [[ |symmetry]]. The [[hypervalent]] nature of this species (as well as {{|6|}}, see below) can be explained with [[ ]] . This trigonal bipyramidal structure persists in solvents, such as [[carbon disulfide|CS₂]] and [[carbon tetrachloride|CCl₄]].<ref>D. E. C. Corbridge Phosphorus: An of its , , and Elsevier 0-444-89307-5</ref> In the solid state PCl₅ is ionic formulated {{|4|+PCl|6|}}.<ref name="Holleman"> A. F. E. Inorganic Chemistry 0-12-352651-</ref>

[[File:EntryWithCollCode76731.png|thumb|left|Structure of solid phosphorus pentachloride, illustrating its autoionization at higher concentrations.<ref>{{cite journal|author1=Finch, A. |author2=Fitch, A.N. |author3=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, PCl₅ 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. |name-list-style=amp | 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:

:PCl₅ {{eqm}} {{chem|PCl|4|+}} + Cl⁻

At higher concentrations, a second equilibrium becomes more prevalent:

:2&nbsp;PCl₅ {{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, PCl₅ in solution was thought to form a dimeric structure, P₂Cl₁₀, but this suggestion is not supported by [[Raman spectroscopy|Raman spectroscopic]] measurements.

===Related pentachlorides===

[[Arsenic pentachloride|AsCl₅]] and [[Antimony pentachloride|SbCl₅]] also adopt trigonal bipyramidal structures. The relevant bond distances are 211&nbsp;pm (As−Cl_eq), 221&nbsp;pm (As−Cl_ax), 227&nbsp;pm (Sb−Cl_eq), and 233.3&nbsp;pm (Sb−Cl_ax).<ref>{{cite journal |last1=Haupt |first1=S. |last2=Seppelt |first2=K. | title = Solid State Structures of AsCl₅ and SbCl₅ | 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| doi-access = free }}</ref> At low temperatures, SbCl₅ converts to the dimer, dioctahedral Sb₂Cl₁₀, structurally related to [[niobium pentachloride]].

PCl₅ is prepared by the [[Halogenation|chlorination]] of PCl₃. This reaction used to produce 10,000 of PCl₅ 2000.<ref name="Holleman" />

:PCl₃ + Cl₂ {{eqm}} PCl₅ (H = −124kJ/mol)

PCl₅ exists in equilibrium with PCl₃ and [[chlorine]], and at 180°C the degree of dissociation is 40%.<ref name="Holleman" /> Because of this equilibrium, samples of PCl₅ often contain chlorine, which imparts a greenish .

In its most characteristic reaction, PCl₅ [[chemical reaction|]] upon contact with [[water (molecule)|water]] to release [[hydrogen chloride]] and give phosphorus oxides.

:PCl₅ + H₂O → POCl₃ + 2&nbsp;HCl

In hot water, hydrolysis proceeds completely to [[phosphoric acid]]:

:PCl₅ + H₂O → H₃PO₄ + 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 PCl₅(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>

In synthetic chemistry, two classes of chlorination are usually of interest Oxidative chlorinations entail the transfer of Cl₂ from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl₅ can be used for both processes.

PCl₅ [[carboxylic acid]]s to the corresponding [[acyl chloride]]<ref>{{OrgSynth | = Roger Adams|Adams R. Jenkins R. L. | title = ''p''-Nitrobenzoyl chloride | collvol = 1 | collvolpages = 394 | prep = cv1p0394 | year = 1941}}</ref> | /</>

:[[File:Phosphorus pentachloride mechanism.png|450px]]

It also converts [[Alcohol (chemistry)|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 POCl₃.

PCl₅ reacts with a tertiary amides, such as [[]], to give dimethylchloromethyleneammonium chloride, which is called the [[ reaction|Vilsmeier reagent]], [(CH₃)₂]Cl. More typically, a related salt is generated from the reaction of DMF and POCl₃. Such reagents are useful in the preparation of derivatives of [[benzaldehyde]] by formylation and for the conversion of groups into groups.<ref name="Burks" />

is especially renowned for the conversion of C=O groups to CCl₂ groups.<ref>{{OrgSynth | = Gross H. Rieche A. Höft E. Beyer E. | title = Dichloromethyl | collvol = 5 | collvolpages = 365 | prep = cv5p0365 | year = 1973}}</ref>

:(C₆H₅)₂CO + PCl₅ → (C₆H₅)₂CCl₂ + POCl₃

The [[electrophilic]] character of PCl₅ is highlighted by its reaction with [[styrene]] to give, after [[hydrolysis]], phosphonic acid derivatives.<ref>{{OrgSynth | = Schmutzler R. | title = Styrylphosphonic dichloride | collvol = 5 | collvolpages = 1005 | prep = cv5p1005 | year = 1973}}</ref>

===Comparison with related reagents===

Both PCl₃ and PCl₅ convert R₃COH groups to the chloride R₃CCl. 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|SO₂Cl₂]], also a source of Cl₂. For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl₅ since the gaseous SO₂ by-product is readily separated.

As for the reactions with organic compounds, the use of PCl₅ has been superseded by SO₂Cl₂. The reaction of [[phosphorus pentoxide]] and PCl₅ produces [[phosphorus oxychloride|POCl₃]]:<ref> Advanced Inorganic Chemistry Wiley- 0-471-19957-</ref>

:6PCl₅ + P₄O₁₀ → 10POCl₃

PCl₅ chlorinates [[nitrogen dioxide]] to form [[ ]]:

:PCl₅ + 2NO₂ → PCl₃ + 2NO₂Cl

:2&nbsp;NO₂Cl → 2&nbsp;NO₂ + Cl₂

PCl₅ is a precursor for [[lithium hexafluorophosphate]], LiPF₆ [[electrolyte]] in [[lithium ion batteries]]. {{chem|LiPF|6}} is produced by the reaction of {{chem|PCl|5}} with [[lithium fluoride]], with [[lithium chloride]] as a sideproduct:

:PCl₅ + 6LiF → LiPF₆ + 5LiCl

PCl₅ is a dangerous substance as it reacts violently with water.

== 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|s2cid=98814859}} 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=|s2cid=95219058 }} 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=fr}} 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>

*[[Phosphorus halides]]

* [[Phosphorus trichloride]]

* [[Phosphoryl chloride]]

* [[Phosphorus trifluorodichloride]]

{{}}

{{Commons category|Phosphorus pentachloride}}

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* [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]

{{Chlorides}}

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