Phosphine – Preparation, Properties, Reactions and Uses
Phosphine is a colorless gas with a pungent odor, similar to rotten fish or garlic. It is the simplest of the Lewis bases and is very reactive.
Inhalation of phosphine can cause death in humans and animals. Symptoms of poisoning include salivation, restlessness, and dyspnea. Phosphine exposure also causes chromosomal aberrations in lymphocytes.
What is Phosphine?
Phosphine (PH3) is a colourless gas with a garlic-like odour. It is a Lewis base, and reacts with HI, HBr, and HCl to form phosphonium compounds. It is non-flammable and only sparingly soluble in water. It also reacts with phosphide, forming a phosphide-phosphine complex that is highly toxic and combustible.
It is used as an insecticide, rodenticide, and fumigant. It is a powerful pesticide that works well on insects resistant to most other chemicals. It is often formulated with a solvent to help it penetrate insects’ bodies, causing them to die in minutes. Phosphine is also used as a degreasing agent and in the manufacture of semiconductors. It is an important intermediate in the production of tetrakis(hydroxymethyl) phosphonium salts, which find use as textile flame retardants such as Proban® and as biocides.
Preparation of Phosphine
In the laboratory, white phosphorus is heated with a concentrated sodium hydroxide solution in an inert atmosphere of CO2 to produce phosphine. This gas is then purified by distillation to yield high purity phosphine for a variety of industrial applications.
When this chemical is exposed to oxidising agents such as air or hydrogen peroxide it can catch fire and explode violently. It is also a Lewis base and can donate its lone pair of electrons to hydrogen iodide, generating phosphoric acid. It is used in semiconductor industries as a dopant.
Uses of Phosphine
Phosphine is also an essential component of a Holmes signal, which is used to warn ships as they navigate the ocean. The device consists of a container filled with calcium carbide and calcium phosphide. The mixture is pierced and dropped into the sea, resulting in a combustion reaction with water that produces gases such as PH3 and C2H2. These are emitted through a hole in the container and help guide ships across the ocean.
A small amount of phosphine gas can be used to control infestations of stored grain and other agricultural products. It can be applied by spraying or applying it to grain as a preservative, or it can be fumigated at a factory. However, phosphine is not as effective as sulfuryl fluoride. Therefore, it is best used in conjunction with a pest management system. Managing the risks of phosphine gas is a duty of employers and persons conducting a business or undertaking, as outlined in the Work Health and Safety Act.
Preparation of Phosphine
1. In order to prepare phosphine, elemental phosphorus must be converted to phosphorus trichloride (PCl3) first. This is accomplished in a plasma-conversion reactor, where a stream of electronically excited hydrogen is fed into a reaction zone. A stoichiometric amount of hydrogen is necessary to transform the phosphorus into phosphine. Excess hydrogen can be used if desired, but it is not preferable from the standpoint of yields.
2. Another method to make phosphine is by hydrolyzing metallic phosphides with water or dilute mineral acids such as HCl or H2SO4. Phosphorus trichloride can also be prepared by the reduction of methylphosphine. This is a dangerous process, and a gas containing phosphine is explosive when it is ignited.
The phosphine produced in this way is a colorless, odorless gas that smells like rotten fish or garlic. It is soluble in some organic solvents and sparingly soluble in water. It is a powerful Lewis base and donates its lone electron in reaction with hydrogen iodide. It is highly flammable and explodes aggressively when exposed to oxidizing agents.
3. A safer and more reliable preparation of phosphine is to use white phosphorus and concentrated sodium hydroxide. The phosphine so obtained is impure, but when it is heated with an aqueous solution of hydrogen iodide to form PH4I, pure phosphine is produced.
Phosphine is used in a variety of industrial applications and as a precursor for the deposition of compound semiconductors. High purity tertiary butyl phosphine is also being developed as a less hazardous liquid alternative to phosphine for application in metalorganic vapor phase epitaxy of III-V semiconductors. However, it is a volatile and extremely dangerous substance, and its production must be performed in a carefully controlled environment. A high level of safety equipment is required, and the phosphine must be stored in an airtight container with an inert gas such as nitrogen.
Risks Associated With Exposure to Phosphine
Exposure to phosphine can cause a variety of symptoms, including headache, nausea, chest pains, tightness and pain in the throat and abdomen, chills, sweating, and even tremors or coma. Acute exposure can also result in pulmonary edema, cardiac arrhythmias, renal damage, and hepatic damage.
Properties of Phosphine
Phosphine is a colorless, poisonous gas with a rotten fish smell and is slightly soluble in water. It is flammable at ambient temperature and is highly explosive. It can be generated by the vaporization of aluminum or zinc phosphide for grain fumigation, by metal processing and by certain chemical processes. It is also present in some minerals and biological material. The chemical is weakly basic and forms phosphonium salts with halogen acids and coordination compounds with lewis acid such as boron trichloride. It is also toxic to animals and humans.
The chemical has high permeability through the skin and mucous membranes. Its vapor is corrosive and penetrates the lungs, causing irritation and swelling. Acute exposure can cause vomiting, stomach pains, diarrhea, thirst, muscle pain, and difficulty breathing. Higher exposures and longer-term exposure can cause serious harm, including lung damage. NIOSH recommends that workers follow the Hierarchy of Controls to prevent phosphine exposure in the workplace. Workers should always read the label and safety instructions on fumigants and follow them carefully.
Earth bacteria generate phosphine by taking up phosphorus from the environment and adding hydrogen. It is also produced in the atmosphere of Venus by reactions between phosphine and nitrous oxide. This is likely due to the high levels of nitrogen in the planet’s air and low ozone concentrations. The presence of these gases may indicate that there is a significant amount of phosphine on Venus.
Toxicity of Phosphine
Phosphine is extremely toxic to organisms that undergo oxidative respiration and is non-toxic to organisms that anaerobically respire. These properties make it a valuable substance for the fumigation of metabolically dormant stored products, such as grain. It kills insect pests while preserving the viability of the grain.
An acute inhalation study in three turkeys and six hens exposed to phosphine at concentrations of 211, 224, and 250 mg/cu m, respectively, found that the birds exhibited apathy, restlessness, dyspnea, and tonic-clonic convulsions and died after 68, 74, and 80 min, respectively. In addition, the hens developed respiratory failure, and their organs were congested with oxygenated blood. During an in vitro cytogenetic test with Chinese hamster ovary cells, phosphine was found to be clastogenic at 2500 and 5000 ppm without metabolic activation and showed no clastogenic activity at 4.9 ppm during days 6 to 15 of gestation.
Reactions of Phosphine
1. Phosphine reacts with alkenes to form phosphinoethers, which have many uses in organic synthesis. For example, phosphine reacts with methylbenzene to produce a phosphite molecule, which can then be converted into a monodentate phosphine by reductive elimination with sodium borohydride. Alternatively, it can be combined with acetone to produce a diphenylphosphine, which is useful in organometallic reactions because of its strong electron-withdrawing properties.
2. In addition, this chemical can be functionalized on the boron atom by nucleophilic substitution with arenethiols or secondary phosphine-boranes to yield phosphine-borane complexes. These complexes are highly soluble and resorbed readily from solution, making them excellent catalysts for organic reactions.
3. Phosphate ligands can also act as nucleophiles to attack other phosphorus-containing molecules. For example, tertiary phosphines can react with nitrous oxide to form nitrogen dioxide and trifluoroacetic acid. They can also bind to sp-metal centers, giving rise to chiral compounds with a high degree of symmetry. Unlike most phosphines, which are spectator ligands that simply hang on to metal complexes, tertiary phosphines exhibit an unusually high degree of electronic and steric tunability. This allows them to profoundly affect the nature of the metal center to which they are bound.
4. Another interesting reaction involves a reaction between phosphine and tetrafluoroethylene to produce polymers that can be used as packaging materials. The polymers are highly resistant to heat and cold, which makes them useful for industrial applications. They are also biodegradable, which makes them a good substitute for a number of existing packaging materials.
Astrobiologists have recently discovered traces of phosphine in the clouds of Venus, our Solar System neighbor. These traces were detected by observations with the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array, in which ESO is a partner. These tracers will help scientists gather clues on how life could have developed on the planet, and may even contribute to the search for signs of life beyond Earth.
Health Effects of Prolonged Exposure to Phosphine
Phosphine is a colorless gas that has a strong fish- or garlic-like odor. It is toxic if inhaled, and can be explosive if ignited. Long-term exposure can cause a variety of health effects, including nasal and throat irritation, weakness, dizziness, nausea, gastrointestinal, cardiac, and central nervous system symptoms. It is also carcinogenic. The chemical is a fire hazard and can explode when mixed with water.
