Phosphine

Description

Phosphine is a colorless, flammable gas that is heavier than air and has a characteristic odor described as being similar to decaying fish. Pure phosphine is claimed to be odorless, even at a level of 200 ppm. The odor threshold for commercially available phosphine ranges from 0.02 ppm to 3 ppm. It has an autoignition temperature of 100°F (37.8°C) and ignites spontaneously when traces of other phosphorous hydrides such as diphosphine are present. For all practical purposes, phosphine should be handled both as a pyrophoric and highly toxic gas.
Phosphine is stable at room temperature and begins to decompose at about 707°F (375°C), with complete decomposition at about 1100°F (593°C). Phosphine is readily oxidized by common oxidizers such as potassium permanganate and sodium hypochlorite. Unlike arsine, it will have some reaction with the alkalis. Phosphine is a strong reducing agent and can precipitate a number of heavy metals from solutions of their salts. It will react violently with oxidizers such as oxygen, chlorine, fluorine, and nitric oxide.
Phosphine is shipped in the pure form as a liquefied gas, and is also commonly available as a mixture when blended with hydrogen or inert gases.

Description

Phosphine, the simplest phosphorus hydride, is a colorless and extremely toxic gas. Some people think it smells like rotting fish; it reminds others of the odor of garlic. In any case, pure phosphine is actually odorless; an impurity, diphosphane (P2H4), is responsible for its foul scent.
Phosphine is formed naturally via the anaerobic decay of phosphorus-containing organic matter. The earliest reported preparation was made by Antoine Lavoisier’s student Philippe Gengembre in the late 18th century.
Phosphine is made industrially from white phosphorus by hydrolysis with an alkali metal hydroxide or an aqueous acid–catalyzed disproportionation reaction. The industrial product is normally shipped as liquefied gas.
Although phosphine’s molecular structure is analogous to that of ammonia, the 3d orbital of its phosphorus atom interacts with its hydrogen atoms to reduce its ability to hydrogen bond. Thus, whereas ammonia is completely miscible in water, the aqueous solubility of phosphine is very low.
The hazard information box shows that phosphine is dangerous in several ways on Earth. But recent findings indicate that its presence in outer space may have had a key role in the beginnings of life.
Ralf I. Kaiser at the University of Hawaii at Manoa (Honolulu) and his colleagues there and in Taiwan and France simulated ices found in space by combining phosphine, carbon dioxide, water, and oxygen at near–absolute zero temperatures. They then bombarded the ices with high-energy electrons (typical of those found in space) to produce several phosphorus oxyacids, including some with the same phosphorus oxidation state that exists in DNA, ATP, and other important biomolecules.
The theme of this year’s National Chemistry Week (which begins today) is “Chemistry Is Out of This World”. Celebrate it by recognizing extraterrestrial phosphine’s potential contribution to life.

Chemical properties

Phosphine is a pyrophoric chemical and spontaneously flammable in air. It is incompatible with strong oxidising agents, halogens, nitric acid. It has the odour of garlic or decaying fish. It is slightly soluble in water. It is flammable and is an explosive gas at ambient temperature. Phosphine decomposes on heating or on burning producing toxic fumes including phosphorus oxides. It reacts violently with air, oxygen, oxidants such as chlorine and nitrogen oxides, metal nitrates, halogens, and other toxic substances, and causes fire and explosion hazard.

Chemical properties

Phosphine is a colorless gas that is shipped as liquefied compressed gas. Odorless when pure. It has the odor of garlic or the foul odor of decaying fish. The level at which humans detect the odor of phosphine (odor threshold) does not provide sufficient warning of dangerous concentrations. Phosphine presents an additional hazard in that it ignites at very low temperatures. Shipped as a liquefied compressed gas. The pure compound is odorless. The Odor Threshold is 0.14 ppm.

Physical properties

Colorless gas with an odor of decaying fish; flammable; burns with a luminous flame; density 1.492 g/L; liquefies at -87.7°C; solidifies at -133°C; critical temperature 51.35°C; critical pressure 64.55 atm; slightly soluble in water; the solution is weakly basic.

Occurrence

Phosphine is produced naturally in small amounts in marshy lands, especially in damp graveyards, resulting from bacterial decay of animal and vegetable matter containing phosphorus. The atmospheric oxidation of impure phosphine (containing trace amounts of diphosphine, P₂H₄) emits pale flickering lights, the so-called “Will o’ the wisps” or “corpse candles” seen on dark nights. The compound has very little commercial application. It is used to prepare phosphonium salts, which also can be made by other processes.

The Uses of Phosphine

Phosphine is used as a fumigant, in the synthesis of many organophosphorus compounds, and as a doping agent for electronic components. It occurs in the waste gases from plants manufacturing semiconductors and thin-film photovoltaic cells. The presence of bound residues of phosphine in fumigated commodities has been reported (Rangaswamy and Sasikala 1986).

The Uses of Phosphine

Phosphine is used in a variety of organic preparations and in the preparation of phosphonium halides. It is commonly used (in gas mixtures) as a doping agent for n-type semiconductors, and as a pure gas in the manufacture of light-emitting diodes. It is also used as a fumigant at low concentrations for grain.

The Uses of Phosphine

Phosphine is the most widely used fumigant for insect con-trol in the durable commodities throughout the world. It is increasingly used as a treatment to re-place methyl bromide especially because of its low cost, fast dispersion in the air and low residues. Versatility of use is a major advantage for phosphine, as it can be used in a variety of storage buildings, during transit (e.g. in ship holds) or in plastic sheet enclosures. It is close to an ideal fumigant except for few drawbacks: slow activity, the rapid increase in insect resistance, flammability at higher concentrations (>900 ppm) and corrosion of copper, silver and gold. The phosphine resistance among the insect populations was found to be the result of selection pressure caused by inadequate fumigations in the storage units; storage facilities not adequately sealed before fumigation; and fumigant concentrations not being monitored. The understanding of phosphine resistance mechanism, improved monitoring tactics and management of resistance are the priorities in tackling the problem (Rajendran, 2001). The other problems like corrosion and flammability were found to be limited by using the combination of heat (30–36℃), carbon dioxide (3–7%) and phosphine at 80–100 ppm, while achieving a complete insect control.

Definition

A colorless gas that is slightly soluble in water. It has a characteristic fishy smell. It can be made by reacting water and calcium phosphide or by the action of yellow phosphorus on a concentrated alkali. Phosphine usually ignites spontaneously in air because of contamination with diphosphine. It decomposes into its elements if heated to 450°C in the absence of oxygen and it burns in oxygen or air to yield phosphorus oxides. It reacts with solutions of metal salts to precipitate phosphides. Like its nitrogen analog ammonia it forms salts, called phosphonium salts. It also forms complex addition compounds with metal ions. As in ammonia, one or more of the hydrogen atoms can be replaced by alkyl groups.

Definition

phosphine: A colourless highlytoxic gas, PH₃; m.p.-133°C; b.p.–87.7°C; slightly soluble in water.Phosphine may be prepared by reactingwater or dilute acids with calciumphosphide or by reactionbetween yellow phosphorus and concentratedalkali. Solutions of phosphineare neutral but phosphinedoes react with some acids to givephosphonium salts containing PH₄⁺ions, analogous to the ammoniumions. Phosphine prepared in the laboratoryis usually contaminated withdiphosphine and is spontaneouslyflammable but the pure compound isnot so. Phosphine can function as aligand in binding to transition-metalions. Dilute gas mixtures of very purephosphine and the rare gases areused for doping semiconductors.

Definition

ChEBI: The simplest phosphine, consisting of a single phosphorus atom with three hydrogens attached.

Production Methods

Phosphine, also known as phosphorated hydrogen or hydrogen phosphide (PH3), has no direct commercial use. However, it may be generated from aluminum or zinc phosphide and water for grain fumigation. It may be present in phosphorus as a polymer or generated at low rates under alkaline conditions and at a temperature of 85
C. The generation of acetylene from calcium carbide containing calcium phosphide as an impurity and metal processing procedures in which phosphides are formed are the most frequent sources of industrial hygiene problems with phosphine.

Preparation

Phosphine, unlike ammonia, is not made by direct union of elements. However, phosphine is prepared from other phosphorus compounds by several methods.
Phosphine can be prepared by alkaline hydrolysis of white phosphorus. Thus, a strong aqueous solution of caustic potash when boiled with white phosphorus yields hypophosphite with liberation of phosphine:
P₄ + 3KOH + 3H₂O → 3KH₂PO₂ + PH₃↑
Caustic soda or barium hydroxide can be used instead of caustic potash. The apparatus should be free from air. Either hydrogen or natural gas may be passed through the generator to purge out all residual oxygen out from the flask to prevent any explosion. A small amount of diphosphine, P₂H₄ also is produced in the reaction. The latter inflames spontaneously in air. Diphosphine, which is an unstable liquid at 20°C, may be removed by condensation in a tube immersed in a freezing mixture; or by passing through concentrated hydrochloric acid; or slowly by photochemical decomposition by exposing to light.
Phosphine also is prepared by reduction of a solution of phosphorus trichloride with lithium aluminum hydride in dry ether under warm conditions. The solution of the latter is added from a dropping funnel to phosphorus trichloride solution in dry ether placed in a water bath.
4 PCl₃ + 3LiAlH₄ → 3 LiCl + 3AlCl₃ + 4PH₃↑
The flask is connected to a reflux condenser to condense down solvent ether back into the flask. Phosphine is collected over water as a moist gas. Dry phosphine may alternatively be condensed in a U-tube placed in freezing mixture.
Phosphine may be produced by mixing a solution of phosphonium iodide with potassium hydroxide:
PH₄I + KOH → KI + H₂O + PH₃↑
Another preparation method involves treating metallic phosphide with dilute acids:
Ca₃P₂ + 6HCl → 3CaCl₂ + 2PH₃↑
This method was applied earlier to produce floating signal flares at sea. Floating cans of calcium phosphide were punctuated to admit sea water to generate phosphine, which ignited spontaneously to emit flares. The flares could not be extinguished by wind or water.

Air & Water Reactions

Highly flammable. Usually ignites spontaneously in air. Burns with a luminous flame [Merck 11th ed. 1989]. Insoluble in water.

Reactivity Profile

Phosphine is a reducing agent. Ignites spontaneously in air when pure [Sidgwick, 1950, p. 729]. Liquefied Phosphine can be detonated [Rust, 1948, p. 301]. Ignites or reacts violently with boron trichloride, dichlorine oxide, halogens (bromine, chlorine, iodine), metal nitrates, nitrogen oxides, nitric acid, nitrous acid, nitrogen trichloride [Bretherick, 5th ed., 1995, p. 1562]. Forms explosive mixtures with even small amounts of oxygen. Autoignites at low pressures [Fisher, E. O. et al., Angew. Chem., 1968, 7, p. 136].

Hazard

Phosphine is a highly toxic and flammable gas. Acute effects are irritation, tightness of chest, painful breathing, and lung damage. High concentration can be fatal. A fire hazard.

Health Hazard

Phosphine is a super- toxic gas with a probable oral lethal dose of 5 mg/kg or 7 drops for a 150 pound person. An air concentration of 3 ppm is safe for long term exposure, 500 ppm is lethal in 30 minutes, and a concentration of 1,000 ppm is lethal after a few breaths.

Health Hazard

Phosphine is a highly poisonous gas. The symptoms of its acute toxic effectsin humans can be respiratory passage irritation, cough, tightness of chest, painful breathing, a feeling of coldness, and stupor. Inhalation of high concentrations of phosphine in air can cause lung damage, convulsion, coma, and death. In addition to damaging the respiratory system, exposure to this compound can cause nausea, vomiting, diarrhea, and depression of the central nervous system. Exposure to a concentration of 1000 ppm in air for 5 minutes can be fatal to humans (NIOSH 1986).
LC50 value, inhalation (rats): 11 ppm (15.3 mg/m³)/4 h
Chronic exposure is likely to cause phosphorus poisoning. Nutritional and toxicological studies indicated that ingestion of a phosphine-fumigated diet by rats for 2 years did not cause marked modification of growth, feed intake, functional behavior, or the incidence or type of tumors (Cabrol Telle et al. 1985).

Fire Hazard

Phosphine can explode with powerful oxidizers. The gas is heavier than air and may travel along the ground to an ignition source. Container may explode in heat of fire. When heated to decomposition, Phosphine emits highly toxic fumes of phosphorus oxides. Reacts violently with: air; boron trichloride; bromine; chlorine; chlorine monoxide; nitric acid; nitric oxide; nitrous oxide; nitrogen trioxide; silver nitrate; nitrous acid; mercuric nitrate; nitrogen trichloride; oxygen; and (potassium plus ammonia). Stable up to 131F. May become unstable at high temperatures.

Flammability and Explosibility

Highly flammable

Agricultural Uses

Fumigant, Insecticide: Phosphine gas is used indoors to control a broad spectrum of insects for non-food/non-feed commodities in sealed containers or structures. There are no homeowner or agricultural row crop uses for this product. The end-use product is a poisonous liquefied gas under pressure, and is A U.S. EPA restricted Use Pesticide (RUP) due to the acute inhalation toxicity of phosphine gas. Phosphine is only occasionally used in industry, and exposure usually results accidentally as a byproduct of various processes. Exposures may occur when acid or water comes in contact with metallic phosphides (aluminum phosphide, calcium phosphide). These two phosphides are used as insecticides or rodenticides for grain, and phosphine is generated during grain fumigation. Phosphine may also evolve during the generation of acetylene from impure calcium carbide, as well as during metal shaving, sulfuric acid tank cleaning, rustproofing, and ferrosilicon, phosphoric acid and yellow phosphorus explosive handling. U.S. EPA restricted Use Pesticide (RUP). Currently listed as “pending” in the EU.

Trade name

ECO2 FUME TM®; VAPORPH3OS®

Materials Uses

Phosphine is noncorrosive and, therefore, may be used with most ofthe commercially available metals. However, since phosphine is mainly used for the electronics industry, type 316 and 316L stainless steel is recommended for the gas delivery systems. Stainless steel regulators should be used for all high purity applications with phosphine and phosphine mixtures. In all cases, systems should be adequately designed to withstand the pressures to be encountered.

Safety Profile

A poison by inhalation. A very toxic gas whose effects are not completely understood. The chef effects are central nervous system depression and lung irritation. There may be pulmonary edema, dilation of the heart, and hyperemia of the visceral organs. Inhalation can cause coma and convulsions leading to death within 48 hours. However, most cases recover without after-effects. Chronic poisoning, characterized by anemia, bronchitis, gastrointestinal disturbances, and visual, speech, and motor disturbances, may result from continued exposure to very low concentrations.Very dangerous fire hazard by spontaneous chemical reaction. Moderately explosive when exposed to flame. Explosive reaction with dichlorine oxide, silver nitrate, concentrated nitric acid, nitrogen trichloride, oxygen. Reacts with mercury(Ⅱ) nitrate to form an explosive product. Ignition or violent reaction with air, boron trichloride, Br2, Cl2, aqueous halogen solutions, iodine, metal nitrates, NOx NCh, NO3, N20, HN02, K + NH3, oxidants. The organic derivatives of phosphine (phosphines) react vigorously with halogens. To fight fire, use CO2, dry chemical, or water spray. Dangerous; when heated to decomposition it emits highly toxic fumes of POx. Used as a fumigant, doping agent for electronic components, and in chemical synthesis

Potential Exposure

Phosphine is used as a fumigant; in the semiconductor industry, as a doping agent for electronic components to introduce phosphorus into silicon crystals; in chemical synthesis; used as a polymerization initiator; as an intermediate for some flame retardants. Also, exposures may occur when acid or water comes in contact with metallic phosphides (aluminum phosphide, calcium phosphide). These two phosphides are used as insecticides or rodenticides for grain, and phosphine is generated during grain fumigation. When phosphine toxicity is suspected, but phosphine exposure is not obvious, one should suspect transdermal contamination and/or ingestion of phosphides. Phosphine may also evolve during the generation of acetylene from impure calcium carbide, as well as during metal shaving; sulfuric acid tank cleaning; rustproofing, ferrosilicon, phosphoric acid; and yellow phosphorus explosive handling.

Physiological effects

Phosphine is a highly toxic gas that can cause death from delayed pulmonary edema or from tissue anoxia secondary to interference with tissue respiration. Phosphine is both an irritant and a general systemic poison. Its action is similar to that of hydrogen sulfide. Symptoms of irritation include lacrimation, substernal chest pain and chest tightness, shortness of breath, a slight cough, and cyanosis. Nonlethal exposures can result in symptoms referable to the gastrointestinal tract and the nervous system. Abdominal symptoms include nausea, vomiting, severe epigastric pain, and diarrhea. Neurologic symptoms include vertigo,headache, restlessness, intentional tremor, lack of muscular coordination, double vision, drowsiness, and a decreased sensation in the extremities. Death in humans has occurred after exposures as low as 8 ppm for 1-2 hours.
Additional acute toxic symptoms involve cardiac abnormalities, liver dysfunction, and kidney inflammation. Agitated psychotic behavior can occur.
ACGIH recommends a Threshold Limit Value-Time-Weighted Average (TLV-TWA) of 0.3 ppm (0.42 mg/m3) for phosphine. The TLV-TWA is the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. ACGIH also recommends a Threshold Limit Value-Short Term Exposure Limit (TLV-STEL) of 1 ppm (1.4 mg/m3) for phosphine. The TLV-STEL is the IS-minute TWA exposure that should not be exceeded at any time during a workday even if the 8-hour TWA is within the TLV-TWA. Exposures above the TLV- TWA up to the STEL should not be longer than 15 minutes and should not occur more than 4 times per day. There should be at least 60 minutes between successive exposures in this range.
OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 0.3 ppm (0.4 mg/m3) for phosphine. TWAPEL is the exposure limit that shall not be exceeded by the 8-hour TWA in any 8-hour work shift of a 40-hour workweek.

Environmental Fate

Because of its very high vapor pressure, phosphine exists in air as a gas and volatilizes from water and surface soil. At high concentrations, the vapors may spontaneously combust in air. Atmospheric phosphine may be degraded by photochemically produced hydroxyl radicals with an expected half-life of less than 1 day. Phosphine can bind to subsurface soils and is degraded quickly. The chemical does not accumulate in the food chain.

storage

Since phosphine is an extremely toxic and flammable gas, appropriate precautions must be taken in its storage and handling. Store and use phosphine and phosphine mixtures only in ventilated gas cabinets, exhaust hoods, or highly ventilated rooms that supply a large volume of forced air ventilation. Explosion-proof forced draft gas cabinets or fume hoods are recommended. Use piping and equipment adequately designed to withstand the pressures to be encountered.
Since phosphine may form explosive mixtures with air, keep it away from heat and all ignition sources such as flames and sparks. All lines, connections, equipment, etc. must be thoroughly checked for leaks and grounded prior to use. Only use spark-proof tools and explosion-proof equipment. The compatibility with plastics and elastomers should be confirmed.
For basic safety information on the handling of compressed gas cylinders, refer to CGA P-I, Safe Handling of Compressed Gases in Containers.

Shipping

UN2199 Phosphine, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 2.1-Flammable gas, Inhalation Hazard Zone A. Cylinders must be transported in a secure upright position, in a well -ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.

Purification Methods

PH3 is best purified in a gas line (in a vacuum) in an efficient fume cupboard. It is spontaneously flammable, has a strong odour of decayed fish and is POISONOUS. The gas is distilled through solid KOH towers (two), through a Dry ice-acetone trap (-78o, to remove H2O, and P2H4 which spontaneously ignites with O2), then through two liquid N2 traps (-196o), followed by distillation into a -126o trap (Dry ice-methylcyclohexane slush), allowed to warm in the gas line and then sealed in ampoules preferably under N2. IR: max 2327 (m), 1121 (m) and 900 (m) cm-1 . [Klement in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 525-530 1963, Gokhale & Jolly Inorg Synth IX 56 1967.] PH3 has also been absorbed into a solution of cuprous chloride in hydrochloric acid (when CuCl.PH3 is formed). PH3 gas is released when the solution is heated, and the gas is purified by passage through KOH pellets and then over P2O5. Its solubility is 0.26mL/1 mL of H2O at 20o, and a crystalline hydrate is formed on releasing the pressure on an aqueous solution.

Toxicity evaluation

Phosphine toxicity occurs in insects, rodents, and humans via a common mechanism of respiratory inhibition. The chemical is a noncompetitive inhibitor of cytochrome oxidase in mitochondria. Human case reports and animal studies have shown that phosphine also inhibits the activity of catalase and cholinesterase, decreases glutathione content, and reacts with hemoglobin. Overall, the studies show oxidative stress as the mechanism of phosphine toxicity.

Incompatibilities

Phosphine reacts with acids, air, copper, moisture, oxidizers, oxygen, chlorine, nitrogen oxides; metal nitrates; halogens, halogenated hydrocarbons; copper and many other substances, causing fire and explosion hazard. Extremely explosive; may ignite spontaneously on contact with air at (or about) 100C. Attacks many metals. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine,fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong acids, amines, ammonia, ethylene oxide, metal nitrates, nitrous acid, phosgene, strong bases.

Waste Disposal

Return refillable compressed gas cylinders to supplier. Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office. Controlled discharges of Phosphine may be passed through 10% NAOH solution in a scrubbing tower. The product may be discharged to a sewer.

GRADES AVAILABLE

Phosphine is supplied in a number of grades, primarily as electronic grade, with a purity of 99.999 percent on a hydrogen-free basis.An MOCVD grade is also offered with a purity of 99.9998 percent.