 | |||
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| Names | |||
|---|---|---|---|
| IUPAC name Phosphane | |||
| Other names Hydrogen phosphide Phosphamine Phosphorus trihydride Phosphorated hydrogen | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider |
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| ECHA InfoCard | 100.029.328 | ||
| EC Number |
| ||
| 287 | |||
| RTECS number |
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| UNII | |||
| UN number | 2199 | ||
| |||
| Properties | |||
| PH3 | |||
| Molar mass | 33.99758 g/mol | ||
| Appearance | Colourless gas | ||
| Odor | odorless as pure compound; fish-like or garlic-like commercially[1] | ||
| Density | 1.379 g/L, gas (25 °C) | ||
| Melting point | −132.8 °C (−207.0 °F; 140.3 K) | ||
| Boiling point | −87.7 °C (−125.9 °F; 185.5 K) | ||
| 31.2 mg/100 ml (17 °C) | |||
| Solubility | Soluble in alcohol,ether,CS2 slightly soluble inbenzene,chloroform,ethanol | ||
| Vapor pressure | 41.3 atm (20 °C)[1] | ||
| Conjugate acid | Phosphonium (PH+4) | ||
Refractive index (nD) | 2.144 | ||
| Viscosity | 1.1×10−5 Pa⋅s | ||
| Structure | |||
| Trigonal pyramidal | |||
| 0.58 D | |||
| Thermochemistry | |||
| 37 J/mol⋅K | |||
Std molar entropy(S⦵298) | 210 J/mol⋅K[2] | ||
Std enthalpy of formation(ΔfH⦵298) | 5 kJ/mol[2] | ||
Gibbs free energy(ΔfG⦵) | 13 kJ/mol | ||
| Hazards | |||
| GHS labelling: | |||
    | |||
| NFPA 704 (fire diamond) | |||
| Flash point | Flammable gas | ||
| 38 °C (100 °F; 311 K)(see text) | |||
| Explosive limits | 1.79–98%[1] | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 3.03 mg/kg (rat, oral) | ||
LC50 (median concentration) | 11 ppm (rat, 4 hr)[3] | ||
LCLo (lowest published) | 1000 ppm (mammal, 5 min) 270 ppm (mouse, 2 hr) 100 ppm (guinea pig, 4 hr) 50 ppm (cat, 2 hr) 2500 ppm (rabbit, 20 min) 1000 ppm (human, 5 min)[3] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA 0.3 ppm (0.4 mg/m3)[1] | ||
REL (Recommended) | TWA 0.3 ppm (0.4 mg/m3), ST 1 ppm (1 mg/m3)[1] | ||
IDLH (Immediate danger) | 50 ppm[1] | ||
| Safety data sheet (SDS) | ICSC 0694 | ||
| Related compounds | |||
Othercations | |||
Related compounds | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Phosphine (IUPAC name:phosphane) is a colorless, flammable, highly toxic compound with thechemical formulaPH3, classed as apnictogen hydride. Pure phosphine is odorless, buttechnical grade samples have a highlyunpleasant odor like rotting fish, due to the presence ofsubstituted phosphine anddiphosphane (P2H4). With traces ofP2H4 present,PH3 is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and isimmediately dangerous to life or health at 50 ppm. Phosphine has atrigonal pyramidal structure.
Phosphines are compounds that includePH3 and theorganophosphines, which are derived fromPH3 by substituting one or more hydrogen atoms with organic groups.[4] They have the general formulaPH3−nRn.Phosphanes are saturated phosphorus hydrides of the formPnHn+2, such astriphosphane.[5] Phosphine (PH3) is the smallest of the phosphines and the smallest of the phosphanes.
Philippe Gengembre (1764–1838), a student ofLavoisier, first obtained phosphine in 1783 by heatingwhite phosphorus in an aqueous solution ofpotash (potassium carbonate).[6][NB 1]
Perhaps because of its strong association with elementalphosphorus, phosphine was once regarded as a gaseous form of the element, but Lavoisier (1789) recognised it as a combination of phosphorus with hydrogen and described it asphosphure d'hydrogène (phosphide of hydrogen).[NB 2]
In 1844, Paul Thénard, son of the French chemistLouis Jacques Thénard, used acold trap to separate diphosphine from phosphine that had been generated fromcalcium phosphide, thereby demonstrating thatP2H4 is responsible for spontaneous flammability associated withPH3, and also for the characteristic orange/brown color that can form on surfaces, which is a polymerisation product.[7] He considered diphosphine's formula to bePH2, and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine.Calcium phosphide (nominallyCa3P2) produces moreP2H4 than other phosphides because of the preponderance of P-P bonds in the starting material.
The name "phosphine" was first used for organophosphorus compounds in 1857, being analogous to organicamines (NR3).[NB 3][8] The gasPH3 was named "phosphine" by 1865 (or earlier).[9]
PH3 is atrigonal pyramidal molecule withC3vmolecular symmetry. Thelength of the P−H bond is 1.42 Å, the H−P−Hbond angles are 93.5°. Thedipole moment is 0.58 D, which increases withsubstitution ofmethyl groups in the series:CH3PH2, 1.10 D;(CH3)2PH, 1.23 D;(CH3)3P, 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting withammonia, which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that inPH3 the P−H bonds are almost entirelypσ(P) – sσ(H) and phosphorus 3s orbital contributes little to the P-H bonding. For this reason, the lone pair on phosphorus is predominantly formed by the 3s orbital of phosphorus. The upfield chemical shift of its31P NMR signal accords with the conclusion that the lone pair electrons occupy the 3s orbital (Fluck, 1973). This electronic structure leads to a lack ofnucleophilicity in general and lack of basicity in particular (pKaH = −14),[10] as well as an ability to form only weakhydrogen bonds.[11]
The aqueoussolubility ofPH3 is slight: 0.22 cm3 of gas dissolves in 1 cm3 of water. Phosphine dissolves more readily innon-polar solvents than in water because of the non-polar P−H bonds. It is technicallyamphoteric in water, but acid and base activity is poor. Proton exchange proceeds via aphosphonium (PH+4) ion in acidic solutions and viaphosphanide (PH−2) at high pH, with equilibrium constantsKb =4×10−28 andKa =41.6×10−29. Phosphine reacts with water only at high pressure and temperature, producingphosphoric acid and hydrogen:[12][13]
Burning phosphine in the air producesphosphoric acid:[14][12]
Phosphine may be prepared in a variety of ways.[15] Industrially it can be made by the reaction of whitephosphorus withsodium orpotassium hydroxide, producingpotassium orsodium hypophosphite as a by-product.
Alternatively, the acid-catalyzeddisproportionation of whitephosphorus yieldsphosphoric acid and phosphine. Both routes have industrial significance; the acid route is the preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification and pressurizing.
It is prepared in the laboratory bydisproportionation ofphosphorous acid:[16]
Alternative methods include the hydrolysis ofzinc phosphide:[17]
Some other metal phosphides could also be used, includingaluminium phosphide orcalcium phosphide. Pure samples of phosphine, free fromP2H4, may be prepared using the action ofpotassium hydroxide onphosphonium iodide:
Phosphine is a worldwide constituent of the Earth's atmosphere at very low and highly variable concentrations.[18] It may contribute significantly to the globalphosphorus biochemical cycle. The most likely source isreduction ofphosphate in decaying organic matter, possibly via partial reductions anddisproportionations, since environmental systems do not have known reducing agents of sufficient strength to directly convert phosphate to phosphine.[19]
It is also found inJupiter's atmosphere.[20]
In 2020 a spectroscopic analysis was reported to show signs of phosphine in theatmosphere of Venus in quantities that could not be explained by knownabiotic processes.[21][22][23] Later re-analysis of this work showed interpolation errors had been made, and re-analysis of data with the fixed algorithm do not result in the detection of phosphine.[24][25] The authors of the original study then claimed to detect it with a much lower concentration of 1 ppb.[26][disputed –discuss]
Phosphine is a precursor to manyorganophosphorus compounds. It reacts with formaldehyde in the presence ofhydrogen chloride to givetetrakis(hydroxymethyl)phosphonium chloride, which is used in textiles. Thehydrophosphination of alkenes is versatile route to a variety of phosphines. For example, in the presence of basic catalystsPH3 adds ofMichael acceptors. Thus withacrylonitrile, it reacts to givetris(cyanoethyl)phosphine:[27]
Acid catalysis is applicable to hydrophosphination withisobutylene and related analogues:
where R isCH3, alkyl, etc.
Phosphine is used as adopant in thesemiconductor industry, and a precursor for the deposition ofcompound semiconductors. Commercially significant products includegallium phosphide andindium phosphide.[28]
Phosphine is an attractive fumigant because it is lethal to insects and rodents, but degrades to phosphoric acid, which is non-toxic. As sources of phosphine, forfarm use, pellets ofaluminium phosphide (AlP),calcium phosphide (Ca3P2), orzinc phosphide (Zn3P2) are used. These phosphides release phosphine upon contact with atmospheric water or rodents' stomach acid. These pellets also contain reagents to reduce the potential forignition orexplosion of the released phosphine.
An alternative is the use of phosphine gas itself which requires dilution with eitherCO2 orN2 or even air to bring it below the flammability point. Use of the gas avoids the issues related with the solid residues left by metal phosphide and results in faster, more efficient control of the target pests.
One problem with phosphine fumigants is the increased resistance by insects.[29]
Deaths have resulted from accidental exposure to fumigation materials containingaluminium phosphide or phosphine.[30][31][32][33] It can be absorbed either byinhalation ortransdermally.[30] As a respiratory poison, it affects the transport of oxygen or interferes with the utilization of oxygen by various cells in the body.[32] Exposure results inpulmonary edema (the lungs fill with fluid).[33] Phosphine gas is heavier than air so it stays near the floor.[34]
Phosphine appears to be mainly a redox toxin, causing cell damage by inducingoxidative stress and mitochondrial dysfunction.[35] Resistance in insects is caused by a mutation in a mitochondrial metabolic gene.[29]
Phosphine can be absorbed into the body by inhalation. The main target organ of phosphine gas is the respiratory tract.[36] According to the 2009 U.S.National Institute for Occupational Safety and Health (NIOSH) pocket guide, and U.S.Occupational Safety and Health Administration (OSHA) regulation, the 8 hour average respiratory exposure should not exceed 0.3 ppm. NIOSH recommends that the short term respiratory exposure to phosphine gas should not exceed 1 ppm. TheImmediately Dangerous to Life or Health level is 50 ppm. Overexposure to phosphine gas causes nausea, vomiting, abdominal pain, diarrhea, thirst, chest tightness,dyspnea (breathing difficulty), muscle pain, chills, stupor or syncope, and pulmonary edema.[37][38] Phosphine has been reported to have the odor of decaying fish or garlic at concentrations below 0.3 ppm. The smell is normally restricted to laboratory areas or phosphine processing since the smell comes from the way the phosphine is extracted from the environment. However, it may occur elsewhere, such as in industrial waste landfills. Exposure to higher concentrations may causeolfactory fatigue.[39]
Phosphine is used forpest control, but its usage is strictly regulated due to high toxicity.[40][41] Gas from phosphine has high mortality rate[42] and has caused deaths in Sweden and other countries.[43][44][45]
Because the previously popularfumigantmethyl bromide has been phased out in some countries under theMontreal Protocol, phosphine is the only widely used, cost-effective, rapidly acting fumigant that does not leave residues on the stored product. Pests with high levels ofresistance toward phosphine have become common in Asia, Australia and Brazil. High level resistance is also likely to occur in other regions, but has not been as closely monitored. Genetic variants that contribute to high level resistance to phosphine have been identified in thedihydrolipoamide dehydrogenase gene.[29] Identification of this gene now allows rapid molecular identification of resistant insects.
Phosphine gas is denser than air and hence may collect in low-lying areas. It can form explosive mixtures with air, and may also self-ignite.[12]
Anne McCaffrey'sDragonriders of Pern series features genetically engineered dragons that breathe fire by producing phosphine by extracting it from minerals of their native planet.
In the 2008pilot of the crime drama television seriesBreaking Bad,Walter White poisons two rival gangsters by adding red phosphorus to boiling water to produce phosphine gas. However, this reaction in reality would require white phosphorus instead, and for the water to containsodium hydroxide.[46]
(From page 524:) The bases Me3P and E3P, the products of this reaction, which we propose to call respectively trimethylphosphine and triethylphosphine, ...
