Phosphine (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name: phosphane) is a colorless, flammable, highly toxic compound with the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (). With traces of present, is spontaneously flammable in air (

pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...

), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure. Phosphines are compounds that include and the organophosphines, which are derived from by substituting one or more hydrogen atoms with organic groups. They have the general formula . Phosphanes are saturated phosphorus hydrides of the form , such as triphosphane. Phosphine () is the smallest of the phosphines and the smallest of the phosphanes.

History

Philippe Gengembre (1764–1838), a student of

Lavoisier Antoine-Laurent de Lavoisier ( ; ; 26 August 17438 May 1794),
CNRS (

white phosphorus in an aqueous solution of

potash Potash ( ) includes various mined and manufactured salts that contain potassium in water- soluble form.

(potassium carbonate).For further information about the early history of phosphine, see: * ''The Encyclopædia Britannica'' (1911 edition), vol. 21, p. 480:
Phosphorus: Phosphine.
* Thomas Thomson, ''A System of Chemistry'', 6th ed. (London, England: Baldwin, Cradock, and Joy, 1820), vol. 1
p. 272.
Perhaps because of its strong association with elemental

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

, 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 as ''phosphure d'hydrogène'' (phosphide of hydrogen).Note: *
On p. 222
of his ''Traité élémentaire de chimie'', vol. 1, (Paris, France: Cuchet, 1789), Lavoisier calls the compound of phosphorus and hydrogen ''"phosphure d'hydrogène"'' (hydrogen phosphide). However
on p. 216
, he calls the compound of hydrogen and phosphorus ''"Combinaison inconnue."'' (unknown combination), yet in a footnote, he says about the reactions of hydrogen with sulfur and with phosphorus: ''"Ces combinaisons ont lieu dans l'état de gaz & il en résulte du gaz hydrogène sulfurisé & phosphorisé."'' (These combinations occur in the gaseous state, and there results from them sulfurized and phosphorized hydrogen gas.) * In Robert Kerr's 1790 English translation of Lavoisier's ''Traité élémentaire de chimie'' ... — namely, Lavoisier with Robert Kerr, trans., ''Elements of Chemistry'' ... (Edinburgh, Scotland: William Creech, 1790) — Kerr translates Lavoisier's ''"phosphure d'hydrogène"'' as "phosphuret of hydrogen"
p. 204
, and whereas Lavoisier — on p. 216 of his ''Traité élémentaire de chimie'' ... — gave no name to the combination of hydrogen and phosphorus, Kerr calls it "hydruret of phosphorus, or phosphuret of hydrogen"
p. 198
. Lavoisier's note about this compound — ''"Combinaison inconnue."'' — is translated: "Hitherto unknown." Lavoisier's footnote is translated as: "These combinations take place in the state of gas, and form, respectively, sulphurated and phosphorated oxygen gas." The word "oxygen" in the translation is an error because the original text clearly reads ''"hydrogène"'' (hydrogen). (The error was corrected in subsequent editions.) In 1844, Paul Thénard, son of the French chemist Louis Jacques Thénard, used a cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide, thereby demonstrating that is responsible for spontaneous flammability associated with , and also for the characteristic orange/brown color that can form on surfaces, which is a polymerisation product. He considered diphosphine's formula to be , and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally ) produces more 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 organic

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

s ().In 1857, August Wilhelm von Hofmann announced the synthesis of organic compounds containing phosphorus, which he named " trimethylphosphine" and " triethylphosphine", in analogy with "amine" (organo-nitrogen compounds), "arsine" (organo-arsenic compounds), and "stibine" (organo-antimony compounds). The gas was named "phosphine" by 1865 (or earlier).

Structure and reactions

is a trigonal pyramidal molecule with ''C''_3''v''

molecular symmetry In chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explai ...

. The

length Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most systems of measurement a Base unit (measurement), base unit for length is chosen, ...

of the P−H bond is 1.42 Å, the H−P−H bond angles are 93.5 °. The dipole moment is 0.58 D, which increases with substitution of

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated a ...

s in the series: , 1.10 D; , 1.23 D; , 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting with

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

, which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that in the P−H bonds are almost entirely 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 its ³¹P NMR signal accords with the conclusion that the lone pair electrons occupy the 3s orbital (Fluck, 1973). This electronic structure leads to a lack of nucleophilicity in general and lack of basicity in particular (p''K''_aH = −14), as well as an ability to form only weak

hydrogen bonds In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, covalently bonded to a mo ...

. The aqueous

solubility In chemistry, solubility is the ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

of is slight: 0.22 cm³ of gas dissolves in 1 cm³ of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P−H bonds. It is technically amphoteric in water, but acid and base activity is poor. Proton exchange proceeds via a

phosphonium In chemistry, the term phosphonium (more obscurely: phosphinium) describes polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, organyl or halogen group). These cations have tetrahedral structures. The ...

() ion in acidic solutions and via phosphanide () at high pH, with equilibrium constants ''K''_b = and ''K''_a = . Phosphine reacts with water only at high pressure and temperature, producing

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...

and hydrogen: Burning phosphine in the air produces

Preparation and occurrence

Phosphine may be prepared in a variety of ways. Industrially it can be made by the reaction of white

with

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...

, producing

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

or sodium hypophosphite as a by-product. Alternatively, the acid-catalyzed disproportionation of white

yields

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.

Laboratory routes

It is prepared in the laboratory by disproportionation of

phosphorous acid Phosphorous acid (or phosphonic acid) is the Compound (chemistry), compound described by the chemical formula, formula . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an in ...

: Alternative methods are the hydrolysis zinc phosphide: Some other metal phosphides could be used including aluminium phosphide, or calcium phosphide. Pure samples of phosphine, free from , may be prepared using the action of

on phosphonium iodide:

Occurrence

Phosphine is a worldwide constituent of the Earth's atmosphere at very low and highly variable concentrations. It may contribute significantly to the global phosphorus biochemical cycle. The most likely source is reduction of

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

in decaying organic matter, possibly via partial reductions and disproportionations, since environmental systems do not have known reducing agents of sufficient strength to directly convert phosphate to phosphine. It is also found in

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

's atmosphere.

Possible extraterrestrial biosignature

In 2020 a spectroscopic analysis was reported to show signs of phosphine in the

atmosphere of Venus The atmosphere of Venus is the very dense layer of gases surrounding the planet Venus. Venus's atmosphere is composed of 96.5% carbon dioxide and 3.5% nitrogen, with other chemical compounds present only in trace amounts. It is much denser and ho ...

in quantities that could not be explained by known abiotic processes. 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. The authors of the original study then claimed to detect it with a much lower concentration of 1 ppb.

Applications

Organophosphorus chemistry

Phosphine is a precursor to many

organophosphorus compounds Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbo ...

. It reacts with formaldehyde in the presence of

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

to give tetrakis(hydroxymethyl)phosphonium chloride, which is used in textiles. The hydrophosphination of alkenes is versatile route to a variety of phosphines. For example, in the presence of basic catalysts adds of Michael acceptors. Thus with acrylonitrile, it reacts to give tris(cyanoethyl)phosphine: Acid catalysis is applicable to hydrophosphination with

isobutylene Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value. Product ...

and related analogues: where R is , alkyl, etc.

Microelectronics

Phosphine is used as a

dopant A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optics, optical properties. The amount of dopant is typically very low compared to the material b ...

in the

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

industry, and a precursor for the deposition of compound semiconductors. Commercially significant products include gallium phosphide and indium phosphide.

Fumigant (pest control)

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, for farm use, pellets of aluminium phosphide (AlP), calcium phosphide (), or zinc phosphide () are used. These phosphides release phosphine upon contact with atmospheric water or rodents' stomach acid. These pellets also contain reagents to reduce the potential for ignition or

explosion An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated ...

of the released phosphine. An alternative is the use of phosphine gas itself which requires dilution with either or 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.

Toxicity and safety

Deaths have resulted from accidental exposure to fumigation materials containing aluminium phosphide or phosphine. It can be absorbed either by

inhalation Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

transdermal Transdermal is a route of administration wherein active ingredients are delivered across the skin for systemic distribution. Examples include transdermal patches used for medicine delivery. The drug is administered in the form of a patch or ointm ...

ly. As a respiratory poison, it affects the transport of oxygen or interferes with the utilization of oxygen by various cells in the body. Exposure results in

pulmonary edema Pulmonary edema (British English: oedema), also known as pulmonary congestion, is excessive fluid accumulation in the tissue or air spaces (usually alveoli) of the lungs. This leads to impaired gas exchange, most often leading to shortness ...

(the lungs fill with fluid). Phosphine gas is heavier than air so it stays near the floor. Phosphine appears to be mainly a redox toxin, causing cell damage by inducing

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

and mitochondrial dysfunction. Resistance in insects is caused by a mutation in a mitochondrial metabolic gene. Phosphine can be absorbed into the body by inhalation. The main target organ of phosphine gas is the respiratory tract. According to the 2009 U.S.

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the List of United States federal agencies, United States federal agency responsible for conducting research and making recommendations for the prevention of work-related occ ...

(NIOSH) pocket guide, and U.S.

Occupational Safety and Health Administration The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

(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. The Immediately 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. 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 cause olfactory fatigue.

Fumigation hazards

Phosphine is used for

pest control Pest control is the regulation or management of a species defined as a pest (organism), pest; such as any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the da ...

, but its usage is strictly regulated due to high toxicity. Gas from phosphine has high mortality rate and has caused deaths in Sweden and other countries. Because the previously popular fumigant

methyl bromide Bromomethane, commonly known as methyl bromide, is an organobromine compound with chemical formula, formula Carbon, CHydrogen, H3Bromine, Br. This colorless, odorless, nonflammable gas is Bromine cycle, produced both industrially and biologically ...

has been phased out in some countries under the

Montreal Protocol The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion. It was agreed on 16 ...

, phosphine is the only widely used, cost-effective, rapidly acting fumigant that does not leave residues on the stored product. Pests with high levels of resistance 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 the dihydrolipoamide dehydrogenase gene. Identification of this gene now allows rapid molecular identification of resistant insects.

Explosiveness

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.

In fiction

Anne McCaffrey Anne Inez McCaffrey (1 April 1926 – 21 November 2011) was an American writer known for the ''Dragonriders of Pern'' science fiction series. She was the first woman to win a Hugo Award for fiction (Best Novella, ''Weyr Search'', 1968) an ...

's Dragonriders of Pern series features genetically engineered dragons that breathe fire by producing phosphine by extracting it from minerals of their native planet. In the 2008

pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...

of the crime drama television series ''

Breaking Bad ''Breaking Bad'' is an American crime drama television series created and produced by Vince Gilligan for AMC (TV channel), AMC. Set and filmed in Albuquerque, New Mexico, the series follows Walter White (Breaking Bad), Walter White (Bryan Cran ...

'', 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 contain

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

Notes

References

External links

International Chemical Safety Card 0694
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CDC – Phosphine – NIOSH Workplace Safety and Health Topic
{{Authority control Fumigants Functional groups Industrial gases * Phosphorus hydrides Phosphorus(−III) compounds Blood agents Pyrophoric materials