Phosphine



Phosphine
IUPAC name Phosphane
Other names Phosphine
Phosphamine
Phosphorus hydride
Phosphorated hydrogen
Identifiers
CAS number 7803-51-2
Properties
Molecular formula PH3
Molar mass 34.00 g/mol
Appearance colorless gas
Density 1.379 g/l, gas (25 °C)
Melting point

−134 °C

Boiling point

−87.8 °C

Solubility in water 31.2 mg/100 ml (17 °C)
Structure
Molecular shape Trigonal pyramidal
Dipole moment 0.58 D
Hazards
EU classification Highly flammable (F+)
Very toxic (T+)
Dangerous for
the environment (N)
NFPA 704
4
3
2
 
R-phrases R12, R17, R26, R34, R50
S-phrases S63
Flash point flammable gas
Autoignition
temperature 		38 °C (see text)
Related Compounds
Other cations Bismuthine
Related compounds Triphenylphosphine
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Phosphine is the common name for phosphorus hydride (PH3), also known by the IUPAC name phosphane and, occasionally, phosphamine. It is a colorless, flammable gas with a boiling point of −88 °C at chiral metal phosphine complex can catalyze a reaction to give chiral products.

Phosphine is highly toxic; it can easily kill in relatively low concentrations. Because of this, the gas is used for methanethiol, to give the gas a detectable garlic smell to help warn against its presence in the atmosphere.

Phosphine is also used as a compound semiconductors.

History

Perhaps because of its strong association with elemental 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 (PH3) by Gengembre in 1783, and the examination of it by Pelletier (who was the first to prepare it pure), only became fruitful after ammonia, this being emphasised still more sharply by H. Rose later on."

cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide, thereby demonstrating that P2H4 is responsible for spontaneous flammability associated with PH3, 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 PH2, and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally Ca3P2) produces more P2H4 than other phosphides because of the preponderance of P-P bonds in the starting material.

Structure and properties

PH3 is a trigonal pyramidal molecule with C3v hydrogen bonds.

The aqueous solubility of PH3 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 (PH4+) ion in acidic solutions and via PH2- at high pH, with equilibrium constants Kb = 4 x 10-28 and Kz = 41.6 x 10-29.

Chemistry

Phosphine may be prepared in a variety of ways[2]. Industrially it can be made by the reaction of white aluminium phosphide or calcium phosphide. Pure samples of phosphine, free from P2H4, may be prepared using the action of potassium hydroxide on phosphonium iodide (PH4I).

Phosphines

Related to PH3 is the class of compounds commonly called phosphines. These are alkyl or aryl derivatives of phosphine, just as 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 hydrochloric acid. These find application as flame retardants for textile ("Proban(r) - registered trademark of Rhodia UK Limited") and as biocides.

Phosphine is often confused with phosgene, (COCl2) which has a similar-sounding name but contains no phosphorus.

Use as a fumigant

Phosphine is highly toxic to organisms undergoing ferment). Because of these characteristics, phosphine is widely used as a fumigant of metabolically dormant stored products such as 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. Given the heavy reliance on phosphine as a means of protecting grain from insect infestation, it is disturbing to note that 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

References

  1. E. Fluck, The chemistry of phosphine, Topics in Current Chemistry Vol. 35, 64 pp, 1973.
  2. A.D.F. Toy, The Chemistry of Phosphorus, Pergamon Press, Oxford, UK, 1973.
  3. 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.
 
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