View source for Phosphorus trichloride

{{Use dmy dates|date=February 2022}}
{{chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 450796811
| Name           = Phosphorus trichloride
| ImageFile      = Phosphorus-trichloride-2D-dimensions.png
| ImageClass     = skin-invert 
| ImageName      = Phosphorus trichloride
| ImageSize      = 190px
| ImageFile1     = Phosphorus-trichloride-3D-vdW.png
| ImageClass1    = bg-transparent 
| ImageName1     = Phosphorus trichloride
| ImageSize1     = 170px
| ImageFile2     = Phosphorus trichloride 25ml.jpg
| ImageSize2     = 250px
| IUPACName      = Phosphorus trichloride
| SystematicName = Trichlorophosphane
| OtherNames     = Phosphorus(III) chloride<br/>Phosphorous chloride
| Section1       = {{Chembox Identifiers
| CASNo = 7719-12-2
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = M97C0A6S8U
| EINECS = 231-749-3
| PubChem = 24387
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 22798
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 30334
| SMILES = ClP(Cl)Cl
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI=1S/Cl3P/c1-4(2)3
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = FAIAAWCVCHQXDN-UHFFFAOYSA-N
| RTECS = TH3675000
| UNNumber = 1809
  }}
| Section2       = {{Chembox Properties
| Formula = PCl<sub>3</sub>
| MolarMass = 137.33 g/mol
| Appearance = Colorless to yellow fuming liquid<ref name=PGCH/>
| Odor = unpleasant, acrid, like [[hydrochloric acid]]<ref name=PGCH/>
| Solubility = [[Hydrolysis reaction|hydrolyzes]]
| Solvent = other solvents
| SolubleOther = soluble{{vague|date=February 2013}} in [[benzene]], [[carbon disulfide|CS<sub>2</sub>]], [[diethyl ether|ether]], [[chloroform]], [[carbon tetrachloride|CCl<sub>4</sub>]], halogenated [[organic solvents]] <br/> reacts with [[ethanol]]
| MeltingPtC = -93.6
| BoilingPtC = 76.1
| Density = 1.574 g/cm<sup>3</sup>
| Dipole = 0.97 [[Debye|D]]
| RefractIndex = 1.5122 (21 °C)
| Viscosity = 0.65 cP (0 °C) <br/> 0.438 cP (50 °C)
| VaporPressure = 13.3 kPa
| MagSus = &minus;63.4·10<sup>−6</sup> cm<sup>3</sup>/mol
  }}
| Section4       = {{Chembox Thermochemistry
| DeltaHf = &minus;319.7 kJ/mol
  }}
| Section7       = {{Chembox Hazards
| MainHazards = Highly toxic,<ref>Phosphorus trichloride toxicity</ref> corrosive 
| ExternalSDS = [https://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc06/icsc0696.htm ICSC 0696]
| GHSPictograms = {{GHS06}} {{GHS08}} {{GHS05}}
| GHSSignalWord = Danger
| GHS_ref  = <ref name ="Sigma">{{Sigma-Aldrich|id=310115|name=Phosphorus trichloride|access-date=28/1/2020}}</ref>
| HPhrases = {{H-phrases|300|301|330|314|373}}
| PPhrases = {{P-phrases|260|273|284|305+351+338|304+340+310|303+361+353}}
| NFPA-H = 4
| NFPA-F = 0
| NFPA-R = 2
| NFPA-S = W
| FlashPt =
| LD50 = 18 mg/kg (rat, oral)<ref name=IDLH>{{IDLH|7719122|Phosphorus trichloride}}</ref>
| IDLH = 25 ppm<ref name=PGCH>{{PGCH|0511}}</ref>
| LC50 = 104 ppm (rat, 4 hr)<br/>50 ppm (guinea pig, 4 hr)<ref name=IDLH/>
| REL = TWA 0.2 ppm (1.5 mg/m<sup>3</sup>) ST 0.5 ppm (3 mg/m<sup>3</sup>)<ref name=PGCH/> 
| PEL = TWA 0.5 ppm (3 mg/m<sup>3</sup>)<ref name=PGCH/>
  }}
| Section8       = {{Chembox Related
| OtherFunction_label = phosphorus chlorides
| OtherFunction = [[Phosphorus pentachloride]]<br/>[[Phosphorus oxychloride]]<br/>[[Diphosphorus tetrachloride]]
| OtherCompounds = [[Phosphorus trifluoride]]<br/>[[Phosphorus tribromide]]<br/>[[Phosphorus triiodide]]
  }}
}}

'''Phosphorus trichloride''' is an [[inorganic compound]] with the [[chemical formula]] PCl<sub>3</sub>. A colorless liquid when pure, it is an important [[Chemical industry|industrial chemical]], being used for the manufacture of [[phosphite]]s and other [[organophosphorus compound]]s. It is toxic and reacts readily with water to release [[hydrogen chloride]].

== History ==
Phosphorus trichloride was first prepared in 1808 by the French chemists [[Joseph Louis Gay-Lussac]] and [[Louis Jacques Thénard]] by heating [[mercury(I) chloride|calomel]] (Hg<sub>2</sub>Cl<sub>2</sub>) with [[phosphorus]].<ref>{{cite journal|last1=Gay-Lussac|last2=Thénard|title=Extrait de plusieurs notes sur les métaux de la potasse et de la soude, lues à l'Institut depuis le 12 janvier jusqu'au 16 mai|journal=Gazette Nationale, Ou le Moniteur Universel|date=27 May 1808|volume=40|issue=148|pages=581–582|url=https://books.google.com/books?id=GRROAAAAcAAJ&pg=PA581|trans-title=Extracts from several notes on the metals potassium and sodium, read at the Institute from the 12th of January to the 16th of May|language=fr}} From p. 582:  ''"Seulement ils ont rapporté qu'en traitant le mercure doux par le phosphure, dans l'espérance d'avoir de l'acide muriatique bien sec, il ont trouvé une liqueur nouvelle très limpide, sans couleur, répandant de fortes vapeurs, s'enflammant spontanément lorsqu'on en imbibe le papier joseph; laquelle ne paraît être qu'une combinaison de phosphore, d'oxigène et d'acide muriatique, et par conséquent analogue à cette qu'on obtient en traitant le soufre par le gas acide muriatique oxigèné."'' (Only they reported that by treating calomel with phosphorus, in the hope of obtaining very dry hydrogen chloride, they found a new, very clear liquid, colorless, giving off strong vapors, spontaneously igniting when one soaks filter paper in it; which seems to be only a compound of phosphorus, oxygen, and hydrochloric acid, and thus analogous to what one obtains by treating sulfur with chlorine gas.)</ref>  Later during the same year, the English chemist [[Humphry Davy]] produced phosphorus trichloride by burning phosphorus in chlorine gas.<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|url-access=subscription}}  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>

==Preparation==
World production exceeds one-third of a million [[tonne]]s.<ref>{{Greenwood&Earnshaw2nd}}</ref> Phosphorus trichloride is prepared industrially by the reaction of [[chlorine]] with [[white phosphorus]], using phosphorus trichloride as the solvent. In this continuous process PCl<sub>3</sub> is removed as it is formed in order to avoid the formation of PCl<sub>5</sub>.

:P<sub>4</sub> + 6 Cl<sub>2</sub> → 4 PCl<sub>3</sub>

==Structure and spectroscopy==
It has a trigonal pyramidal shape.  Its {{chem2|^{31}P}} [[Phosphorus NMR|NMR]] spectrum exhibits a singlet around +220 ppm with reference to a phosphoric acid standard.{{fact|date=February 2022}}

==Reactions==
The [[phosphorus]] in PCl<sub>3</sub> is often considered to have the +3 [[oxidation state]] and the [[chlorine]] atoms are considered to be in the &minus;1 oxidation state.  Most of its reactivity is consistent with this description.<ref>{{Cite web |title=Phosphorus trichloride (PCl3) |url=https://www.simply.science/images/content/chemistry/metals_and_non_metals/nitrogen_family/conceptmap/Phosphorus_chloride.html |access-date=2023-02-15 |website=www.simply.science}}</ref>

===Oxidation===
PCl<sub>3</sub> is a precursor to other phosphorus compounds, undergoing [[Redox|oxidation]] to [[phosphorus pentachloride]] (PCl<sub>5</sub>), [[thiophosphoryl chloride]] (PSCl<sub>3</sub>), or [[phosphorus oxychloride]] (POCl<sub>3</sub>).

===PCl<sub>3</sub> as an electrophile===
PCl<sub>3</sub> reacts vigorously with [[water (molecule)|water]] to form [[phosphorous acid]] (H<sub>3</sub>PO<sub>3</sub>) and [[hydrochloric acid]]:
:PCl<sub>3</sub> + 3 H<sub>2</sub>O → H<sub>3</sub>PO<sub>3</sub> + 3 HCl

Phosphorus trichloride is the precursor to [[organophosphorus compound]]s. It reacts with [[phenol]] to give [[triphenyl phosphite]]:
:{{chem2|1=3 PhOH + PCl3 → P(OPh)3 + 3 HCl  (Ph = C6H5)}}
[[Alcohol (chemistry)|Alcohol]]s such as ethanol react similarly in the presence of a [[Base (chemistry)|base]] such as a tertiary amine:<ref>{{OrgSynth | author = A. H. Ford-Moore | author2 = B. J. Perry | name-list-style=amp | title = Triethyl Phosphite | collvol = 4 | collvolpages = 955 | year = 1963 | prep = CV4P0955}}</ref>
:{{chem2|PCl3  + 3 EtOH  +  3 R<sub>3</sub>N  →  P(OEt)3  +  3 R3NH(+)Cl(-)}}
With one equivalent of alcohol and in the absence of base, the first product is alkoxyphosphorodichloridite:<ref>{{cite journal |doi=10.1039/JR9530001920|title=394. Interaction of phosphorus trichloride with alcohols and with hydroxy-esters |year=1953 |last1=Gerrard |first1=W. |last2=Isaacs |first2=M. J. D. |last3=Machell |first3=G. |last4=Smith |first4=K. B. |last5=Wyvill |first5=P. L. |journal=Journal of the Chemical Society (Resumed) |page=1920 }}</ref>
:{{chem2|PCl3  + EtOH  →  PCl2(OEt)  +  HCl}}

In the absence of base, however, with excess alcohol, phosphorus trichloride converts to [[diethylphosphite]]:<ref>{{cite book|chapter=Diethyl phosphite|author=Malowan, John E.|title=Inorganic Syntheses|year=1953|volume=4|pages=58–60|doi=10.1002/9780470132357.ch19|isbn=9780470132357}}</ref><ref name='CSSP488'>{{cite journal|last = Pedrosa|first = Leandro|year = 2011|url = https://cssp.chemspider.com/488|title = Esterification of Phosphorus Trichloride with Alcohols; Diisopropyl phosphonate|journal = ChemSpider Synthetic Pages|pages=488|doi = 10.1039/SP488|publisher = Royal Society of Chemistry|doi-access = free}}</ref> 
:PCl<sub>3</sub> + 3 EtOH → (EtO)<sub>2</sub>P(O)H + 2 HCl + EtCl

Secondary [[amine]]s (R<sub>2</sub>NH) form [[aminophosphine]]s.  For example, [[bis(diethylamino)chlorophosphine]], (Et<sub>2</sub>N)<sub>2</sub>PCl, is obtained from [[diethylamine]] and PCl<sub>3</sub>.  [[Thiol]]s (RSH) form P(SR)<sub>3</sub>.  An industrially relevant reaction of PCl<sub>3</sub> with amines is phosphonomethylation, which employs [[formaldehyde]]:
: R<sub>2</sub>NH + PCl<sub>3</sub>  +  CH<sub>2</sub>O  → (HO)<sub>2</sub>P(O)CH<sub>2</sub>NR<sub>2</sub>  +  3 HCl
The herbicide [[glyphosate]] is also produced this way. 

The reaction of PCl<sub>3</sub> with [[Grignard reagent]]s and [[organolithium reagent]]s is a useful method for the preparation of organic [[Phosphine#Organophosphorus chemistry|phosphine]]s with the formula R<sub>3</sub>P (sometimes called phosphanes) such as [[triphenylphosphine]], Ph<sub>3</sub>P.

:{{chem2|3 RMgBr + PCl3  ->  R3P + 3 MgBrCl}}
Triphenylphosphine is produced industrially by the reaction between phosphorus trichloride, [[chlorobenzene]], and sodium:<ref name= Corbridge>{{cite book | author = Corbridge, D. E. C. | title = Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology | year = 1995 | edition = 5th | publisher = Elsevier | location = Amsterdam | isbn = 0-444-89307-5}}</ref>
:{{chem2|PCl3  +  3 PhCl  +  6 Na  ->  PPh3  +  6 NaCl}},  where Ph = {{chem2|C6H5}}

Under controlled conditions or especially with bulky R groups, similar reactions afford less substituted derivatives such as [[chlorodiisopropylphosphine]].

===Conversion of alcohols to alkyl chlorides===
Phosphorus trichloride is commonly used to convert primary and secondary alcohols to the corresponding chlorides.<ref>{{cite book |doi=10.1002/9780470771259.ch11|chapter=Displacement of Hydroxyl Groups |title=The Hydroxyl Group (1971) |year=1971 |last1=Brown |first1=Geoffrey W. |series=PATai's Chemistry of Functional Groups |pages=593–639 |isbn=9780470771259 }}</ref> As discussed above, the reaction of alcohols with phosphorus trichloride is sensitive to conditions.  The mechanism for the ROH →RCl conversion involves the reaction of HCl with phosphite esters:
:{{chem2|P(OR)3  +  HCl  <->  HP(OR)3(+)Cl(-)}}
:{{chem2|HP(OR)3(+)Cl(-)  ->  RCl  +  HOP(OR)2}}.

:{{chem2| HOP(OR)2  +  HCl  <->  H2OP(OR)2(+)Cl(-)}}
:{{chem2|H2OP(OR)2(+)Cl(-)  ->  RCl  +  (HO)2P(OR)}}

:{{chem2| (HO)2P(OR)  +  HCl  <->  H(HO)2P(OR)(+)Cl(-)}}
:{{chem2|H(HO)2P(OR)(+)Cl(-)  ->  RCl  +  (HO)3P}}
The first step proceeds with nearly ideal stereochemistry but the final step far less so owing to an SN1 pathway.

===Redox reactions===
Phosphorus trichloride undergoes a variety of redox reactions:<ref name= Corbridge/>
:{{chem2|3PCl3  +  2 CrO3  ->  3POCl3  +  Cr2O3  }}
:{{chem2|PCl3  +  SO3  ->  POCl3  +  SO2}}
:{{chem2|3 PCl3  +  SO2  ->  2POCl3  +  PSCl3}}

===PCl<sub>3</sub> as a nucleophile===
Phosphorus trichloride has a lone pair, and therefore can act as a [[Lewis base]],<ref>{{cite journal | author = R. R. Holmes | journal = Journal of Inorganic and Nuclear Chemistry | volume = 12 | issue = 3–4 | pages = 266–275 | year = 1960 | doi = 10.1016/0022-1902(60)80372-7 | title = An examination of the basic nature of the trihalides of phosphorus, arsenic and antimony}}</ref> e.g., forming a 1:1 adduct Br<sub>3</sub>B-PCl<sub>3</sub>.  Metal complexes such as Ni(PCl<sub>3</sub>)<sub>4</sub> are known, again demonstrating the ligand properties of PCl<sub>3</sub>.

This Lewis basicity is exploited in the [[Kinnear–Perren reaction]] to prepare alkylphosphonyl dichlorides (RP(O)Cl<sub>2</sub>) and alkyl[[phosphonate]] esters (RP(O)(OR')<sub>2</sub>).  Alkylation of phosphorus trichloride is effected in the presence of [[aluminium trichloride]] give the alkyltrichlorophosphonium salts, which are versatile intermediates:<ref name = Svara>{{ Ullmann | author = Svara, J. | author2 = Weferling, N. | author3 = Hofmann, T. | title = Phosphorus Compounds, Organic | doi = 10.1002/14356007.a19_545.pub2}}</ref>
:PCl<sub>3</sub> + RCl + AlCl<sub>3</sub> → RPCl{{su|b=3|p=+}} + AlCl{{su|b=4|p=&minus;}}
The RPCl{{su|b=3|p=+}} product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl<sub>2</sub>.

===PCl<sub>3</sub> as a ligand===
PCl<sub>3</sub>, like the more popular [[phosphorus trifluoride]], is a ligand in [[coordination chemistry]].  One example is Mo(CO)<sub>5</sub>PCl<sub>3</sub>.<ref>{{cite journal |doi=10.1021/om020311d|title=Nature of the Metal−Ligand Bond in M(CO)<sub>5</sub>PX<sub>3</sub> Complexes (M = Cr, Mo, W; X = H, Me, F, Cl): Synthesis, Molecular Structure, and Quantum-Chemical Calculations|year=2002|last1=Frenking|first1=Gernot|last2=Wichmann|first2=Karin|last3=Fröhlich|first3=Nikolaus|last4=Grobe|first4=Joseph|last5=Golla|first5=Winfried|last6=Van|first6=Duc Le|last7=Krebs|first7=Bernt|last8=Läge|first8=Mechtild|journal=Organometallics|volume=21|issue=14|pages=2921–2930}}</ref>

==Uses==
PCl<sub>3</sub> is important indirectly as a precursor to [[Phosphorus pentachloride|PCl<sub>5</sub>]], [[Phosphoryl chloride|POCl<sub>3</sub>]] and [[Thiophosphoryl chloride|PSCl<sub>3</sub>]], which are used in many applications, including [[herbicide]]s, [[insecticide]]s, [[plasticiser]]s, [[oil additive]]s, and [[flame retardant]]s.

For example, oxidation of PCl<sub>3</sub> gives [[Phosphorus oxychloride|POCl<sub>3</sub>]], which is used for the manufacture of [[triphenyl phosphate]] and [[tricresyl phosphate]], which find application as [[flame retardant]]s and [[plasticiser]]s for [[Polyvinyl chloride|PVC]].  They are also used to make [[insecticide]]s such as [[diazinon]]. Phosphonates include the [[herbicide]] [[glyphosate]].

PCl<sub>3</sub> is the precursor to [[triphenylphosphine]] for the [[Wittig reaction]], and [[phosphite ester]]s which may be used as industrial intermediates, or used in the [[Horner-Wadsworth-Emmons reaction]], both important methods for making [[alkene]]s. It can be used to make [[trioctylphosphine oxide]] (TOPO), used as an extraction agent, although TOPO is usually made via the corresponding phosphine.

PCl<sub>3</sub> is also used directly as a [[reagent]] in [[organic synthesis]]. It is used to convert primary and secondary [[Alcohol (chemistry)|alcohol]]s into [[alkyl chloride]]s, or [[carboxylic acid]]s into [[acyl chloride]]s, although [[thionyl chloride]] generally gives better yields than PCl<sub>3</sub>.<ref>{{cite book | author = L. G. Wade Jr. | title = Organic Chemistry | edition = 6th | page = 477 | publisher = Pearson/Prentice Hall | location = Upper Saddle River, New Jersey, USA | year = 2005}}</ref>

==Safety==
* 600 [[Parts per million|ppm]] is lethal in just a few minutes.<ref>{{cite book | author = A. D. F. Toy | title = The Chemistry of Phosphorus | publisher = Pergamon Press | location = Oxford, UK | year = 1973}}</ref>
* 25 ppm is the US [[National Institute for Occupational Safety and Health|NIOSH]] "[[Immediately Dangerous to Life and Health]]" level<ref>[https://www.cdc.gov/niosh/idlh/7719122.html Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)]</ref>
* 0.5 ppm is the US [[Occupational Safety and Health Administration|OSHA]] "[[permissible exposure limit]]" over a time-weighted average of 8 hours.<ref>[https://www.osha.gov/chemicaldata/chemResult.html?RecNo=629 OSHA: Phosphorus Trichloride]</ref>
* 0.2 ppm is the US [[National Institute for Occupational Safety and Health|NIOSH]] "[[recommended exposure limit]]" over a time-weighted average of 8 hours.<ref>[https://www.cdc.gov/niosh/npg/npgd0511.html CDC - NIOSH Pocket Guide to Chemical Hazards]</ref>
* Under [[European Union|EU]] [[Directive 67/548/EEC]], PCl<sub>3</sub> is classified as [[toxic|''very toxic'']] and ''[[corrosive]]'' , and the [[List of R-phrases|risk phrases]] R14, R26/28, R35 and R48/20 are obligatory.

Industrial production of phosphorus trichloride is controlled under the [[Chemical Weapons Convention]], where it is listed in [[List of Schedule 3 substances (CWC)|schedule 3]], as it can be used to produce [[mustard gas|mustard agents]].<ref>{{cite book |author1=M. C. Forbes |author2=C. A. Roswell |author3=R. N. Maxson |title=Inorganic Syntheses |chapter=Phosphorus(III) Chloride | journal = [[Inorg. Synth.]] | volume = 2 | pages = 145–7 | doi = 10.1002/9780470132333.ch42 |date=2007 |isbn=9780470132333 }}</ref>

==See also==
*[[Phosphorus pentachloride]]
*[[Phosphoryl chloride]]
*[[Phosphorus trifluorodichloride]]

==References==
{{Reflist}}
<!-- Dead note "2": ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990. -->
<!-- Dead note "3": J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992. -->
<!-- Dead note "4": ''The Merck Index'', 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960. -->

{{Phosphorus compounds}}
{{Chlorides}}
{{Chemical agents}}

[[Category:Inorganic phosphorus compounds]]
[[Category:Phosphorus chlorides]]
[[Category:Phosphorus(III) compounds]]
[[Category:Pulmonary agents]]