Phosphorus trichloride
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2008-03-03T04:01:59Z
Insanity Incarnate
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Reverted edits by [[Special:Contributions/70.241.1.80|70.241.1.80]] ([[User talk:70.241.1.80|talk]]) to last version by Edgar181
{{Chembox new
| Name = Phosphorus trichloride
| ImageFile = Phosphorus-trichloride-2D-dimensions.png
<!-- | ImageSize = 150px -->
| ImageName = Phosphorus trichloride
| ImageFile1 = Phosphorus-trichloride-3D-vdW.png
<!-- | ImageSize1 = 150px -->
| ImageName1 = Phosphorus trichloride
| IUPACName = Phosphorus trichloride
| OtherNames = Phosphorus(III) chloride<br />Phosphorous chloride<br />Monophosphorus trichloride
| Section1 = {{Chembox Identifiers
| CASOther = [7719-12-2]
| EINECS = 231-749-3
| RTECS = TH3675000
}}
| Section2 = {{Chembox Properties
| Formula = PCl<sub>3</sub>
| MolarMass = 137.33 g/mol
| Appearance = colourless liquid
| Solvent = other solvents
| SolubleOther = [[Water (molecule)|Water]]: [[Hydrolysis reaction|hydrolysis]]<br />[[Methanol]]: [[Decomposition|decomposes]]<br />[[Benzene]]: soluble<br />[[Chloroform]]: soluble<br />[[Diethyl ether]]: soluble
| MeltingPt = -93.6 °C (179.6 K)
| BoilingPt = 76.1 °C (349.3 K)
| Dipole = 0.97 [[Debye|D]]
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −319.7 [[kilojoule|kJ]]/ [[mole (unit)|mol]] (liquid)
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = Corrosive, toxic<br />releases HCl
| FlashPt = ?°C
| RPhrases = 14-26/28-29-35-48/20
| SPhrases = 26-36/37/39-45-7/8
}}
| Section8 = {{Chembox Related
| Function = phosphorus<br />compounds
| OtherFunctn = [[Phosphorus pentachloride|PCl<sub>5</sub>]]<br />[[Phosphorus oxychloride|POCl<sub>3</sub>]]<br />[[Diphosphorus tetrachloride|P<sub>2</sub>Cl<sub>4</sub>]]
}}
}}
'''Phosphorus trichloride''' (formula [[Phosphorus|P]][[Chlorine|Cl]]<sub>3</sub>) is the most important of the three [[phosphorus chlorides]]. It is an important [[Chemical industry|industrial chemical]], being used for the manufacture of organophosphorus compounds for a wide variety of applications.
==Chemical properties==
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 -1 oxidation state. Most of its reactivity is consistent with this description.
===Redox reactions===
PCl<sub>3</sub> is a precursor to other phosphorus compound, undergoing [[Redox|oxidation]] to e.g. [[phosphorus pentachloride]] (PCl<sub>5</sub>), [[thiophosphoryl chloride]] (PSCl<sub>3</sub>), or [[phosphorus oxychloride]] (POCl<sub>3</sub>).
If an [[Electrostatic discharge|electric discharge]] is passed through a mixture of PCl<sub>3</sub> vapour and [[hydrogen]] gas, a rare chloride of phosphorus is formed, [[diphosphorus tetrachloride]] (P<sub>2</sub>Cl<sub>4</sub>).
===PCl<sub>3</sub> as an electrophile===
Phosphorus trichloride is the precursor to [[organophosphorus compound]]s that contain one or more (P<sup>3+</sup>) atoms, most notably phosphites and phosphonates. These compounds do not usually contain the chlorine atoms found in PCl<sub>3</sub>.
PCl<sub>3</sub> reacts rapidly and [[exothermic]]ally with [[water (molecule)|water]] to form [[phosphorous acid]], H<sub>3</sub>PO<sub>3</sub> and [[hydrochloric acid|HCl]]. A large number of similar substitution reactions are known, the most important of which is the formation of [[phosphite ester]]s by reaction with [[alcohol]]s or [[phenols]]. For example, with [[phenol]], triphenyl phosphite is formed:
:3 [[Phenol|PhOH]] + PCl<sub>3</sub> → [[Triphenyl phosphite|P(OPh)<sub>3</sub>]] + 3 HCl
where "Ph" stands for [[phenyl]] group, -C<sub>6</sub>H<sub>5</sub>. [[Alcohol]]s such as ethanol react similarly in the presence of a [[Base (chemistry)|base]] such as :<ref>{{OrgSynth | author = A. H. Ford-Moore and B. J. Perry | title = Triethyl Phosphite | collvol = 4 | collvolpages = 955 | year = 1963 | prep = CV4P0955}}</ref>
:PCl<sub>3</sub> + 3 EtOH + 3 R<sub>3</sub>N → P(OEt)<sub>3</sub> + 3 R<sub>3</sub>NH<sup>+</sup>Cl<sup>-</sup>
Of the many related compounds can be prepared similarly, triisopropyl phosphite is an example (b.p. 43.5 °C/1.0 mm; CAS# 116-17-6).
In the absence of base, however, the reaction affords a dialkyl [[phosphonate]] and an [[alkyl chloride]], according to the following stoichiometry:
:PCl<sub>3</sub> + 3 C<sub>2</sub>H<sub>5</sub>OH → (C<sub>2</sub>H<sub>5</sub>O)<sub>2</sub>P(=O)H + [[Chloroethane|C<sub>2</sub>H<sub>5</sub>Cl]] + 2 HCl
[[Amine]]s, R<sub>2</sub>NH, form P(NR<sub>2</sub>)<sub>3</sub>, and [[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
Aminophosphonates are widely used as sequestring and antiscale agents in water treatment. The large volume 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#chemistry|phosphine]]s with the formula R<sub>3</sub>P (sometimes called phosphanes) such as triphenylphosphine, Ph<sub>3</sub>P.
:3 PhMgBr + PCl<sub>3</sub> → [[Triphenylphosphine|Ph<sub>3</sub>P]] + 3 MgBrCl
Under controlled conditions PCl<sub>3</sub> can be used to prepare PhPCl<sub>2</sub> and Ph<sub>2</sub>PCl.
===PCl<sub>3</sub> as a nucleophile===
Phosphorus trichloride has a lone pair, and therefore can act as a [[Lewis base]], for example with the [[Lewis acid]]s BBr<sub>3</sub><sup>[5]</sup> it forms a 1:1 adduct, Br<sub>3</sub>B<sup>−</sup>−<sup>+</sup>PCl<sub>3</sub>. Metal complexes such as Ni(PCl<sub>3</sub>)<sub>4</sub> are known. This Lewis basicity is exploited in one useful route to organophosphorus compounds:
:PCl<sub>3</sub> + [[Alkyl|R]]Cl + [[Aluminium chloride|AlCl<sub>3</sub>]] → (RPCl<sub>3</sub>)<sup>+</sup><sup>−</sup>AlCl<sub>4</sub>
The (RPCl<sub>3</sub>)<sup>+</sup> product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl<sub>2</sub>.
==Preparation==
World production exceeds one-third of a million [[tonne]]s<sup>[1]</sup>. Phosphorus trichloride is prepared industrially by the reaction of [[chlorine]] with a [[reflux]]ing solution of white [[phosphorus]] in phosphorus trichloride, with continuous removal of PCl<sub>3</sub> as it is formed.
:[[Phosphorus|P<sub>4</sub>]] + 6 [[Chlorine|Cl<sub>2</sub>]] → 4 PCl<sub>3</sub>
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]].In the laboratory it may be more convenient to use the less toxic red phosphorus<sup>[6]</sup>. It is sufficiently inexpensive that it would not be synthesized for laboratory use.
==Uses==
PCl<sub>3</sub> is important indirectly as a precursor to [[Phosphorus pentachloride|PCl<sub>5</sub>]], [[Phosphorus oxychloride|POCl<sub>3</sub>]] and [[Thiophosphoryl chloride|PSCl<sub>3</sub>]]. which in turn enjoy many applications in [[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 [[Georg Wittig|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]]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><sup>[8]</sup>.
==Precautions==
PCl<sub>3</sub> is toxic, with a concentration of 600 [[Parts per million|ppm]] being lethal in just a few minutes<sup>[7]</sup>. PCl<sub>3</sub> is classified as [[toxic|''very toxic'']] and [[corrosive|''corrosive'']] under [[European Union|EU]] [[Directive 67/548/EEC]], and the [[List of R-phrases|risk phrases]] R14, R26/28, R35 and R48/20 are obligatory.
==References==
{{Citationstyle|date=September 2007}}
<references/>
# 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.
# R. R. Holmes, ''Journal of Inorganic and Nuclear Chemistry'' '''12''', 266-275 (1960).
# M. C. Forbes, C. A. Roswell, R. N. Maxson, ''Inorganic Syntheses'', Vol. II, 145-7 (1946).
# 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.
[[Category:Chlorides]]
[[Category:Phosphorus compounds]]
[[Category:Nonmetal halides]]
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