Phosphine
264583
220542586
2008-06-20T10:58:16Z
192.149.9.30
{{Otheruses4|the chemical|the visual phenomenon|phosphene}}
{{Chembox new
| Name = Phosphine
| ImageFile = Phosphine.png
| ImageSize = 100px
| ImageName = Phosphine
| ImageFileL1 = Phosphine-3D-balls.png
| ImageSizeL1 = 100px
| ImageFileR1 = Phosphine-3D-vdW.png
| ImageSizeR1 = 120px
| IUPACName = Phosphane
| OtherNames = Phosphine<br />Phosphamine<br />Phosphorus hydride<br />Phosphorated hydrogen
| Section1 = {{Chembox Identifiers
| CASNo = 7803-51-2
}}
| Section2 = {{Chembox Properties
| Formula = PH<sub>3</sub>
| MolarMass = 34.00 g/mol
| Appearance = colorless gas
| Density = 1.379 g/l, gas (25 °C)
| Solubility = 31.2 mg/100 ml (17 °C)
| MeltingPt = −134 °C
| BoilingPt = −87.8 °C
}}
| Section3 = {{Chembox Structure
| MolShape = Trigonal pyramidal
| Dipole = 0.58 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| EUClass = Highly flammable ('''F+''')<br />Very toxic ('''T+''')<br />Dangerous for<br />the environment ('''N''')
| NFPA-H = 3
| NFPA-F = 4
| NFPA-R = 2
| RPhrases = {{R12}}, {{R17}}, {{R26}}, {{R34}}, {{R50}}
| SPhrases = {{S1/2}}, {{S28}}, {{S36/37}}, {{S45}},<br />{{S61}}, {{S63}}
| FlashPt = flammable gas
| Autoignition = 38 °C (''see text'')
}}
| Section8 = {{Chembox Related
| OtherCations = [[Ammonia]]<br />[[Arsine]]<br />[[Stibine]]<br />[[Bismuthine]]
| OtherCpds = [[Trimethylphosphine]]<br />[[Triphenylphosphine]]
}}
}}
'''Phosphine''' is the common name for '''phosphorus hydride''' (PH<sub>3</sub>), also known by the [[IUPAC]] name '''phosphane''' and, occasionally, '''phosphamine'''. It is a colorless, flammable gas with a boiling point of −88 °C at [[standard pressure]]. Pure phosphine is odourless, but ''technical grade'' phosphine has a highly unpleasant odor like [[garlic]] or rotting fish, due to the presence of substituted [[phosphine]] and [[diphosphine]] (P<sub>2</sub>H<sub>4</sub>). '''Phosphines''' are also a group of substituted phosphines, with the structure R<sub>3</sub>P, where other functional groups replace hydrogens. They are important in catalysts where they complex to various metal ions; a [[Chirality (chemistry)|chiral]] metal phosphine complex can catalyze a reaction to give chiral products.
Phosphine is highly [[toxin|toxic]]; it kills at low concentrations. Because of this, the gas is used for [[pesticide|pest control]] by [[fumigation]]. For [[agriculture|farm use]], it is often sold in the form of [[aluminium phosphide]], [[calcium phosphide]], or [[zinc phosphide]] pellets, which yield phosphine on contact with atmospheric water or rodents' stomach acid. These pellets also contain other chemicals which evolve [[ammonia]] which helps to reduce the potential for spontaneous [[Combustion|ignition]] or [[explosion]] of the phosphine gas. They may also contain other agents, such as [[methanethiol]], to give the gas a detectable garlic smell to help warn against its presence in the atmosphere.
Phosphine is also used as a [[dopant]] in the [[semiconductor]] industry, and a precursor for the deposition of [[compound semiconductor]]s. Recently [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TJ6-4DHXJV5-8&_user=10&_handle=V-WA-A-W-ABD-MsSAYVA-UUA-U-AAZCEEDYVY-AAZBCDYZVY-ZCZZCDYU-ABD-U&_fmt=summary&_coverDate=12%2F10%2F2004&_rdoc=97&_orig=browse&_srch=%23toc%235302%232004%23997279998%23530941!&_cdi=5302&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d7fa573ff50b10d4975aed0deddcb80a high purity tertiary butyl phosphine (TBP)] has been developed as a less hazardous liquid alternative to highly toxic phosphine gas, for application in Metalorganic Vapor Phase Epitaxy ([[MOVPE]]) of III-V [[compound semiconductor]]s. Alternatively phosphine can be packaged in a cylinder containing a solid microporous adsorbent at 0 PSIG. The system is called a sub-atmospheric gas source. This type of packaging permits the gas to be stored without pressure which significantly reduces the risk of a phosphine gas leak from the cylinder. The system is able to deliver gas by applying vacuum to the cylinder valve outlet. For semiconductor manufacturing, this is a practical approach as the processes usually operate under high vacuum.
Phosphine is probably a normally occurring constituent of the atmosphere at very low and highly variable concentrations and hence may contribute to the global phosphorus biochemical cycle<ref>Gassmann et al, "Phosphine in the lower terrestrial troposphere", ''Naturwissenschaften'', 1996, 83(3), 129-31, (Eng).</ref>. The origin(s) of atmospheric phosphine is not certain. Possible sources include bacterial reduction of phosphate in decaying organic matter, although this is not thermodynamically favorable, and processes related to corrosion of metals containing phosphorus impurities.<ref>J. Roels & W. Verstraete, "Biological formation of volatile phosphorus compounds, a review paper", Bioresource Technology 79 (2001), 243-250.</ref>
==History==
Perhaps because of its strong association with elemental [[phosphorus]], phosphine was once regarded as a gaseous form of the element but [[Lavoisier]] (1789) recognised it as a combination of phosphorus with hydrogen by describing it as “hydruyet of phosphorus, or phosphuret of hydrogen”.
[[Ernst von Meyer]] (1891) described the early history of phosphine research thus:
"The discovery of phosphuretted hydrogen (PH<sub>3</sub>) by [[Gengembre]] in 1783, and the examination of it by [[Pelletier]] (who was the first to prepare it pure), only became fruitful after [[Humphry Davy]]’s investigations; and the last-named elucidated the composition of this gas, and pointed out its analogy to [[ammonia]], this being emphasised still more sharply by H. Rose later on."
[[Thénard]] (1845) used a [[cold trap]] to separate diphosphine from phosphine that had been generated from [[calcium phosphide]], thereby demonstrating that P<sub>2</sub>H<sub>4</sub> is responsible for spontaneous flammability associated with PH<sub>3</sub>, and also for the characteristic orange/brown colour that can form on surfaces, which is a polymerisation product. He considered diphosphine’s formula to be PH<sub>2</sub>, and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally Ca<sub>3</sub>P<sub>2</sub>) produces more P<sub>2</sub>H<sub>4</sub> than other phosphides because of the preponderance of P-P bonds in the starting material.
==Structure and properties==
PH<sub>3</sub> is a trigonal pyramidal molecule with C<sub>3v</sub> [[molecular symmetry]]. The [[bond length|length]] of the P-H bond 1.42 [[angstrom|Å]], the H-P-H [[bond angle]]s are 93.5[[degree (angle)|°]]. The [[dipole moment]] is 0.58 D, which increases with [[substitution (chemistry)|substitution]] of [[methyl group]]s in the series: CH<sub>3</sub>PH<sub>2</sub>, 1.10 D; (CH<sub>3</sub>)<sub>2</sub>PH, 1.23 D; (CH<sub>3</sub>)<sub>3</sub>P, 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting with [[ammonia]], which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that in PH<sub>3</sub> the P-H bonds are almost entirely pσ(P) – sσ(H) and the lone pair contributes only a little to the [[molecular orbital]]s. The high positive chemical shift of the P atom in<sup>31</sup>P NMR spectrum accords with the conclusion that the lone pair electrons occupy the 3s orbital and so are close to the P atom (Fluck, 1973). This electronic structure leads to a lack of [[nucleophilicity]] and an inability to form [[hydrogen bonds]].
The aqueous [[solubility]] of PH<sub>3</sub> is slight; 0.22 mL of gas dissolve in 1 mL of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P-H bonds. It acts as neither an acid nor a base in water. Proton exchange proceeds via a [[phosphonium]] (PH<sub>4</sub><sup>+</sup>) ion in acidic solutions and via PH<sub>2</sub><sup>-</sup> at high pH, with equilibrium constants K<sub>b</sub> = 4 x 10<sup>-28</sup> and K<sub>z</sub> = 41.6 x 10<sup>-29</sup>.
==Chemistry==
Phosphine may be prepared in a variety of ways.<ref>A.D.F. Toy, ''The Chemistry of Phosphorus'', Pergamon Press, Oxford, UK, 1973.</ref> Industrially it can be made by the reaction of white [[phosphorus]] with [[sodium hydroxide]], producing [[sodium hypophosphite]] and sodium [[phosphite]] as a by-product. Alternatively the acid-catalyzed disproportioning of white [[phosphorus]] may be used, which yields [[phosphoric acid]] and phosphine. Both routes have industrial significance, with the acid route as the preferred method if further reaction of the phosphine to substituted phosphines is needed. This latter step requires purification and pressurizing. It can also be made (as described above) by the hydrolysis of a metal phosphide such as [[aluminium phosphide]] or [[calcium phosphide]]. Pure samples of phosphine, free from P<sub>2</sub>H<sub>4</sub>, may be prepared using the action of [[potassium hydroxide]] on [[phosphonium iodide]] (PH<sub>4</sub>I).
===Phosphines===
Related to PH<sub>3</sub> is the class of compounds commonly called '''phosphines'''. These are alkyl or aryl derivatives of phosphine, just as [[amine]]s can be regarded as derivatives of [[ammonia]]. Common examples include [[triphenylphosphine]] ((C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>P) and [[BINAP]], both used as phosphine [[ligand]]s in [[Complex (chemistry)|metal complexes]] such as [[Wilkinson's catalyst]]. Metal phosphine complexes are [[catalyst]]s for reactions such as the [[Sonogashira coupling]]. Most of these phosphines, with the exception of [[triphenyl phosphine]], are made from pressurized, purified phosphine gas as described above.
A large industrial application of phosphine is found in the production of tetrakis(hydroxymethyl) [[phosphonium]] salts, made by passing phosphine gas through a solution of [[formaldehyde]] and a [[mineral acid]] such as [[hydrochloric acid]]. These find application as [[flame retardants]] for textile ("Proban(r) - registered trademark of Rhodia UK Limited") and as [[biocide]]s.
Phosphine is often confused with [[phosgene]], (COCl<sub>2</sub>) which has a similar-sounding name but contains no phosphorus.
==Use as a fumigant==
Phosphine is highly toxic to organisms undergoing [[Oxidative phosphorylation|oxidative respiration]], but is non toxic to organisms kept under low oxygen (<1%) or that can anaerobically respire (i.e. [[fermentation (biochemistry)|ferment]]). Because of these characteristics, phosphine is widely used as a [[fumigant]] of metabolically [[dormancy|dormant]] stored products such as [[cereal|grain]]. The toxicity of phosphine kills insect pests that might infest the grain, but does not affect the viability of the dormant grain.
Because continued use of the previously widely used [[fumigant]] [[methyl bromide]] has been banned under the [[Montreal Protocol]], phosphine is the only widely used, cost effective, rapidly acting fumigant that does not leave residues on the stored product. Pests developing high levels of resistance toward phosphine have become commonplace in many countries of Asia and in Australia as well. Active research in Australia into the mode of action of phosphine and the mechanisms whereby insects acquire resistance is being carried out by the [[CSIRO]] in Canberra, QDPI&F in Queensland and the [[University of Queensland]].
==See also==
*[[Phosphine oxide]] - OPR<sub>3</sub>
*[[Phosphinite]] - P(OR)R<sub>2</sub>
*[[Phosphonite]] - P(OR)<sub>2</sub>R
*[[Phosphite]] - P(OR)<sub>3</sub>
*[[Phosphinate]] - OP(OR)R<sub>2</sub>
*[[Phosphonate]] - OP(OR)<sub>2</sub>R
*[[Phosphate]] - OP(OR)<sub>3</sub>
==References==
<div class="references-small">
<references/>
# E. Fluck, ''The chemistry of phosphine'', Topics in Current Chemistry Vol. 35, 64 pp, 1973.
# WHO (World Health Organisation), ''Phosphine and selected metal phosphides'', Environmental Health Criteria. Published under the joint sponsorship of UNEP, ILO and WHO, Geneva, Vol. 73, 100 pp, 1988.
</div>
==External links==
*[http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc06/icsc0694.htm International Chemical Safety Card 0694]<!-- Syntax: {{ICSC|AllDigits|TwoDigits}} -->
[[Category:Functional groups]]
[[Category:Phosphorus compounds]]
[[Category:Organophosphorus]]
[[Category:Phosphines]]
[[Category:Hydrides]]
[[Category:Fumigants]]
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