What Is Phosphine?
Phosphine, also known as hydrogen phosphide or phosphorus hydride, is an inorganic compound consisting of hydrogen and phosphorus. Its chemical formula is PH3, with a molecular weight of 34.0 g/mol. Its boiling point is -88°C, its density as a gas is 1.38 g/L, and its CAS number is 7803-51-2. Phosphine includes derivatives of phosphine as well.
It is colorless at room temperature and exists as a flammable gas with an unpleasant odor. Its solubility in water is 26 ml per 100 L.
Uses of Phosphine
1. Raw Material for Semiconductors
Phosphine is a crucial raw material in semiconductor manufacturing. Its non-covalent electron pairs and electron-rich nature make it an ideal doping agent for converting silicon into n-type semiconductors. It’s also used to introduce impurities in the production of semiconductors like InGaP (indium gallium phosphide).
These semiconductors are utilized in laser diodes for optical discs such as DVDs, fiber optic communications, light receiving diodes, high brightness light emitting diodes, and electronic devices for cell phones.
2. Production of Phosphorus-Containing Compounds
Through the pyrolysis of high-purity phosphine gas, yellow phosphorus is synthesized, and further heating produces red phosphorus. Phosphine serves as a raw material for a broad spectrum of phosphorus-containing compounds due to its versatility in undergoing radical addition, Michael addition, acid catalysis, and substitution reactions.
Additionally, the proportion of primary, secondary, and tertiary phosphines can be adjusted by modifying the reaction conditions, such as the molar ratio of olefins. Secondary phosphines are oxidized to produce phosphinic acid, used in surface treatments, metal extractions, resin additives, and as a catalyst in reactions.
3. Insecticides
Primarily used in grain storage for fumigation, phosphine effectively controls pests and serves as a fungicide/sterilant. Its ability to evenly disperse through the air allows it to penetrate deep into objects and seed husks.
Properties of Phosphine
Phosphine’s structure is similar to ammonia’s, containing nitrogen from group 15 of the periodic table. However, phosphine’s noncovalent electron pairs are weaker in proton affinity, making it a very weak base compared to ammonia.
Phosphine production includes methods such as reacting tricalcium diphosphide with water and generating crude phosphine gas (a mixture of phosphine and hydrogen gas) by adding sodium hydroxide to yellow phosphorus.
Other Information on Phosphine
1. Phosphine in the Atmosphere
Phosphine is found in trace amounts in the Earth’s atmosphere, believed to originate from the biological decomposition of organic matter. It is also detected in Jupiter’s atmosphere, where it is thought to be produced internally. In Jupiter’s environment, phosphine continually reacts with other substances.
2. Hazards of Phosphine
Phosphine can spontaneously ignite upon reacting with oxygen in the air at room temperature, posing explosion risks. It is extremely toxic, capable of causing pulmonary edema, and potentially fatal if inhaled. It must be strictly stored in cylinders, avoiding any contact with human skin, mouth, or eyes. Phosphine is classified as a poisonous substance under safety laws, and in the GHS classification, it is listed as class 1 for flammability, acute toxicity, and specific target organ toxicity.