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Phosphorus is a chemical element; it has Chemical symbol P and atomic number 15. All elemental forms of phosphorus are highly reactive and are therefore never found in nature. They can nevertheless be prepared artificially, the two most common allotropes being white phosphorus and red phosphorus. With as its only stable isotope, phosphorus has an occurrence in Earth's crust of about 0.1%, generally as phosphate rock. A member of the pnictogen family, phosphorus readily forms a wide variety of organic compound and inorganic compounds, with as its main +5, +3 and −3.
The isolation of white phosphorus in 1669 by Hennig Brand marked the scientific community's first discovery since Antiquity of an element. The name phosphorus is a reference to the god of the Morning star in Greek mythology, inspired by the faint glow of white phosphorus when exposed to oxygen. This property is also at the origin of the term phosphorescence, meaning glow after illumination, although white phosphorus itself does not exhibit phosphorescence, but chemiluminescence caused by its oxidation. Its high toxicity makes exposure to white phosphorus very dangerous, while its flammability and pyrophoricity can be weaponised in the form of incendiaries. Red phosphorus is less dangerous and is used in and .
Most industrial production of phosphorus is focused on the mining and transformation of phosphate rock into phosphoric acid for phosphate-based . Phosphorus is an essential and often limiting nutrient for plants, and while natural levels are normally maintained over time by the phosphorus cycle, it is too slow for the regeneration of soil that undergoes intensive cultivation. As a consequence, these fertilisers are vital to modern agriculture. The leading producers of phosphate ore in 2024 were China, Morocco, the United States and Russia, with two-thirds of the estimated exploitable phosphate reserves worldwide in Morocco alone. Other applications of phosphorus compounds include , , and .
Phosphorus is essential to all known forms of life, largely through , organic compounds containing the phosphate ion as a functional group. These include DNA, RNA, ATP, and , complex compounds fundamental to the functioning of all cells. The main component of bones and teeth, bone mineral, is a modified form of hydroxyapatite, itself a phosphorus mineral.
Brand at first tried to keep the method secret, but later sold the recipe for 200 to from Dresden. Kraft toured much of Europe with it, including London, where he met with Robert Boyle. The crucial fact that the substance was made from urine was eventually found out, and Johann Kunckel was able to reproduce it in Sweden in 1678. In 1680, Boyle also managed to make phosphorus and published the method of its manufacture. He was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of modern matches, and also improved the process by using sand in the reaction:
In 1777, Antoine Lavoisier recognised phosphorus as an element after Johan Gottlieb Gahn and Carl Wilhelm Scheele showed in 1769 that calcium phosphate is found in bones by obtaining elemental phosphorus from bone ash. Bone ash subsequently became the primary industrial source of phosphorus and remained so until the 1840s. The process consisted of several steps. First, grinding up the bones into their constituent tricalcium phosphate and treating it with sulfuric acid:
In 1609 Inca Garcilaso de la Vega wrote the book Comentarios Reales in which he described many of the agricultural practices of the Incas prior to the arrival of the Spaniards and introduced the use of guano as a fertiliser. As Garcilaso described, the Incas near the coast harvested guano. In the early 1800s Alexander von Humboldt introduced guano as a source of agricultural fertiliser to Europe after having discovered it in exploitable quantities on islands off the coast of South America. It has been reported that, at the time of its discovery, the guano on some islands was over 30 meters deep. The guano had previously been used by the Moche culture people as a source of fertiliser by mining it and transporting it back to Peru by boat. International commerce in guano did not start until after 1840. By the start of the 20th century guano had been nearly completely depleted and was eventually overtaken with the discovery of methods of production of superphosphate.
Early matches used white phosphorus in their composition, and were very dangerous due to both its toxicity and the way the match was ignited. The first striking match with a phosphorus head was invented by Charles Sauria in 1830. These matches (and subsequent modifications) were made with heads of white phosphorus, an oxygen-releasing compound (potassium chlorate, lead dioxide, or sometimes nitrate), and a binder. They were poisonous to the workers in manufacture, exposure to the vapours causing severe necrosis of the bones of the jaw, known as "phossy jaw". Additionally, they were sensitive to storage conditions, toxic if ingested, and hazardous when accidentally ignited on a rough surface. The very high risks for match workers was at the source of several notable early cases of industrial action, such as the 1888 London Matchgirls' strike.
The discovery of red phosphorus allowed for the development of matches that were both much safer to use and to manufacture, leading to the gradual replacement of white phoshphorus in matches. Additionally, around 1900 French chemists Henri Sévène and Emile David Cahen invented the modern strike-anywhere match, wherein the white phosphorus was replaced by phosphorus sesquisulfide (), a non-toxic and non-pyrophoric compound that ignites under friction. For a time these safer strike-anywhere matches were quite popular but in the long run they were superseded by the modern red phosphorus-based safety match. Following the implementation of these new manufacturing methods, production of white phosphorus matches was banned in several countries between 1872 and 1925, and an international treaty to this effect was signed following the Berne Convention (1906).
Phosphate rock, which usually contains calcium phosphate, was first used in 1850 to make phosphorus. With the introduction of the submerged-arc furnace for phosphorus production by James Burgess Readman in 1888 (patented 1889), the use of bone-ash became obsolete. After the depletion of world guano sources about the same time, mineral phosphates became the major source of phosphate fertiliser production. Phosphate rock production greatly increased after World War II, and remains the primary global source of phosphorus and phosphorus chemicals today.
The electric furnace method allowed production to increase to the point where it became possible that white phosphorus could be weaponised in war. In World War I, it was used in incendiary ammunition, and tracer ammunition. A special incendiary bullet was developed to shoot at hydrogen-filled over Britain (hydrogen being highly flammable).
During World War II, made of phosphorus dissolved in petrol were distributed in Britain to specially selected civilians as part of the preparations for a potential invasion. The United States also developed the M15 white-phosphorus hand grenade, a precursor to the M34 grenade, while the British introduced the similar No 77 grenade. These multipurpose grenades were mostly used for signaling and smoke screens, although they were also efficient anti-personnel weapons. The difficulty of extinguishing burning phosphorus and the very severe burns it causes had a strong psychological impact on the enemy. Phosphorus were used on a large scale, notably to destroy Hamburg, the place where the "miraculous bearer of light" was first discovered.
Two radioactive isotopes of phosphorus have half-lives suitable for biological scientific experiments, and are used as radioactive tracers in biochemical laboratories. These are:
Phosphorus is a member of the (also called group 15) and period 3 elements, and many of its chemical properties can be inferred from its position on the periodic table as a result of periodic trends. Like nitrogen, arsenic and antimony, its main are −3, +3 and +5, with every one in-between less common but known. Phosphorus shows as expected more electronegativity than silicon and arsenic, less than sulfur and nitrogen, but also notably less than carbon, affecting the nature and properties of P–C bonds. It is the element with the lowest atomic number to exhibit hypervalence, meaning that it can form more chemical bond per atom that would normally be permitted by the octet rule.
White phosphorus is a soft, waxy molecular solid that is insoluble in water. It is also very toxic, highly flammable and pyrophoricity, igniting in air at about . Structurally, it is composed of tetrahedra. The nature of bonding in a given tetrahedron can be described by spherical aromaticity or cluster bonding, that is the electrons are highly delocalized. This has been illustrated by calculations of the magnetically induced currents, which sum up to 29 nA/T, much more than in the archetypical Aromaticity molecule benzene (11 nA/T). The molecule in the gas phase has a P-P bond length of 2.1994(3) Å as determined by gas electron diffraction. White phosphorus exists in two crystalline forms named α (alpha) and β (beta), differing in terms of the relative orientation of the constituent tetrahedra. The α-form is most stable at room temperature and has a cubic crystal structure. When cooled down to it transforms into the β-form, turning into an hexagonal crystal structure. When heated up, the tetrahedral structure is conserved after melting at and boiling at , before facing thermal decomposition at where it turns into gaseous diphosphorus (). This molecule contains a triple bond and is analogous to ; it can also be generated as a transient intermediate in solution by thermolysis of organophosphorus precursor reagents. At still higher temperatures, dissociates into atomic P.
When exposed to air, white phosphorus faintly glows green and blue due to oxidation, a phenomenon best visible in the dark. This reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules and that both emit visible light. However, in a pure-oxygen environment phosphorus does not glow at all, with the oxidation happening only in a range of . Derived from this phenomenon, the terms and phosphorescence have been loosely used to describe substances that shine in the dark. However, phosphorus itself is not phosphorescent but chemiluminescent, since it glows due to a chemical reaction and not the progressive reemission of previously absorbed light.
Red phosphorus is in structure. It can be viewed as a derivative of wherein one P-P bond is broken and one additional bond is formed with the neighbouring tetrahedron, resulting in chains of molecules linked by van der Waals forces. Red phosphorus may be formed by heating white phosphorus to in the absence of air or by exposing it to sunlight. In this form phosphorus is amorphous, but can be crystallised upon further heating into violet phosphorus or fibrous red phosphorus depending on the reaction conditions. Red phosphorus is therefore not an allotrope in the strictest sense of the term, but rather an intermediate between other crystalline allotropes of phosphorus, and consequently most of its properties have a range of values. Freshly prepared, bright red phosphorus is highly reactive and ignites at about . After prolonged heating or storage, the color darkens; the resulting product is more stable and does not spontaneously ignite in air.
Violet phosphorus or α-metallic phosphorus can be produced by day-long annealing of red phosphorus above . In 1865, Johann Wilhelm Hittorf discovered that when phosphorus was recrystallised from molten lead, a red/purple form is obtained. Therefore, this form is sometimes known as "Hittorf's phosphorus" .
Black phosphorus or β-metallic phosphorus is the least reactive allotrope and the thermodynamically stable form below . In appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and having puckered sheets of linked atoms. It is obtained by heating white phosphorus under high pressures (about ). It can also be produced at ambient conditions using metal salts, e.g. mercury, as catalysts. Single-layer black phosphorus is called phosphorene, and is therefore predictably analogous to graphene.
Phosphorus has a concentration in the Earth's crust of about one gram per kilogram (for comparison, copper is found at about 0.06 grams per kilogram). It is not found free in nature, but is widely distributed in many , usually as phosphates. Inorganic phosphate rock, which is partially made of apatite, is today the chief commercial source of this element.
Food-grade phosphoric acid (additive E number) is used to acidify foods and beverages such as various and jams, providing a tangy or sour taste. The phosphoric acid also serves as a preservative. Soft drinks containing phosphoric acid, including Coca-Cola, are sometimes called or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion, as well as contribute to the formation of kidney stones, especially in those who have had kidney stones previously.
Calcium phosphates in particular are widespread compounds with many applications. Among them, they are used to improve the characteristics of processed meat and cheese, in baking powder, and in toothpaste. Two of the most relevant among them are monocalcium phosphate, and dicalcium phosphate.
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Most phosphorus pentahalides are common compounds. is a colourless gas and the molecules have a trigonal bipyramidal geometry. With fluoride, it forms , an anion that is isoelectronic with . is a colourless solid which has an ionic formulation of , but adopts a trigonal bipyramidal geometry when molten or in the vapour phase. Both the pentafluoride and the pentachloride are . Meanwhile, is an unstable solid formulated as . is not known.
The most important phosphorus oxyhalide is phosphorus oxychloride (), which is approximately tetrahedral. It is prepared from and used in the manufacture of plasticizers. Phosphorus can also form thiohalides such as , and in rare cases selenohalides.
Phosphine () and its organic derivatives are structural analogues of ammonia (), but the bond angles at phosphorus are closer to 90° for phosphine and its organic derivatives. It is an ill-smelling and toxic gas, produced by hydrolysis of calcium phosphide (). Unlike ammonia, phosphine is oxidised by air. Phosphine is also far less basic than ammonia. Other phosphines are known which contain chains of up to nine phosphorus atoms and have the formula . The highly flammable gas diphosphine () is an analogue of hydrazine.
Some organophosphates are used as flame retardants. Among them, tricresyl phosphate and 2-ethylhexyl diphenyl phosphate are also plasticisers, making these two properties useful in the production of non-flammable plastic products and derivatives.
While many organic compounds of phosphorus are required for life, some are highly toxic. A wide range of organophosphorus compounds are used for their toxicity as and as . Some notable examples include sarin, VX or Tabun. Fluorophosphate (like sarin) are among the most potent known.
According to the U.S. Institute of Medicine, the estimated average requirement for phosphorus for people ages 19 and up is 580 mg/day. The RDA is 700 mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher-than-average requirements. RDA for pregnancy and lactation are also 700 mg/day. For people ages 1–18 years, the RDA increases with age from 460 to 1250 mg/day. As for safety, the IOM sets tolerable upper intake level for phosphorus at 4000 mg/day. Collectively, these values are referred to as the Dietary Reference Intake. The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For people ages 15 and older, including pregnancy and lactation, the AI is set at 550 mg/day. For children ages 4–10, the AI is 440 mg/day, and for ages 11–17 it is 640 mg/day. These AIs are lower than the U.S. RDAs. In both systems, teenagers need more than adults. The EFSA reviewed the same safety question and decided that there was not sufficient information to set a UL.
Phosphorus deficiency may be caused by malnutrition, by failure to absorb phosphate, and by metabolic syndromes that draw phosphate from the blood (such as in refeeding syndrome after malnutrition) or passing too much of it into the urine. All are characterised by hypophosphatemia, which is a condition of low levels of soluble phosphate levels in the blood serum and inside the cells. Symptoms of hypophosphatemia include neurological dysfunction and disruption of muscle and blood cells due to lack of ATP. Too much phosphate can lead to diarrhoea and calcification (hardening) of organs and soft tissue, and can interfere with the body's ability to use iron, calcium, magnesium, and zinc.
Natural phosphorus-bearing compounds are mostly inaccessible to plants because of the low solubility and mobility in soil. Most phosphorus is very stable in the soil minerals or organic matter of the soil. Even when phosphorus is added in manure or fertiliser it can become fixed in the soil. Therefore, the natural phosphorus cycle is very slow. Some of the fixed phosphorus is released again over time, sustaining wild plant growth, however, more is needed to sustain intensive cultivation of crops. Fertiliser is often in the form of superphosphate of lime, a mixture of calcium dihydrogen phosphate (), and calcium sulfate dihydrate () produced reacting sulfuric acid and water with calcium phosphate.
Processing phosphate minerals with sulfuric acid for obtaining fertiliser is so important to the global economy that this is the primary industrial market for sulfuric acid and the greatest industrial use of elemental sulfur.
US production of phosphate rock peaked in 1980 at 54.4 million metric tons. The United States was the world's largest producer of phosphate rock from at least 1900, up until 2006, when US production was exceeded by that of China. In 2019, the US produced 10 percent of the world's phosphate rock.
For the use of phosphorus in drugs, detergents, and foodstuff, the standards of purity are high, which led to the development of the thermal process. In this process, phosphate minerals are converted to white phosphorus, which can be purified by distillation. The white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with a base to give phosphate salts. The thermal process is conducted in a submerged-arc furnace which is energy intensive. Presently, about of elemental phosphorus is produced annually. Calcium phosphate (as Phosphorite), mostly mined in Florida and North Africa, can be heated to 1,200–1,500 °C with sand, which is mostly , and coke to produce . The product, being volatile, is readily isolated:
Side products from the thermal process include ferrophosphorus, a crude form of , resulting from iron impurities in the mineral precursors. The silicate slag is a useful construction material. The fluoride is sometimes recovered for use in water fluoridation. More problematic is a "mud" containing significant amounts of white phosphorus. Production of white phosphorus is conducted in large facilities in part because it is energy intensive. The white phosphorus is transported in molten form. Some major accidents have occurred during transportation.
The countries estimated to have the biggest phosphate rock commercial reserves (in billion metric tons) are Morocco (50), China (3.2), Egypt (2.8), Algeria (2.2), Syria (1.8), Brazil (1.6), Saudi Arabia (1.4), South Africa (1.4), Australia (1.1), United States (1.0), and Finland (1.0). Estimates for future production vary significantly depending on modelling and assumptions on extractable volumes, but it is inescapable that future production of phosphate rock will be heavily influenced by Morocco in the foreseeable future. According to some researchers, Earth's commercial and affordable phosphorus reserves are expected to be depleted in 50–100 years.
In 2023, the United States Geological Survey (USGS) estimated that economically extractable phosphate rock reserves worldwide are 72 billion tons, while world mining production in 2022 was 220 million tons. Assuming zero growth, the reserves would thus last for around 300 years. This broadly confirms a 2010 International Fertilizer Development Center (IFDC) report that global reserves would last for several hundred years. Phosphorus reserve figures are intensely debated. Gilbert suggest that there has been little external verification of the estimate. A 2014 review concluded that the IFDC report "presents an inflated picture of global reserves, in particular those of Morocco, where largely hypothetical and inferred resources have simply been relabeled “reserves".
Sewage treatment plants that have a dedicated phosphorus removal step produce phosphate-rich sewage sludge that can then be treated to extract phosphorus from it. This is done by incinerating the sludge and recovering the resulting ash. Another approach lies into the recovery of phosphorus-rich materials such as struvite from waste processing plants, which is done by adding magnesium to the waste. However, the technologies currently in use are not yet cost-effective, given the current price of phosphorus on the world market.
In practice, the silicon is typically placed near or inside a nuclear reactor generating neutrons. As neutrons pass through the silicon, phosphorus atoms are produced by transmutation. This doping method is far less common than diffusion or ion implantation, but it has the advantage of creating an extremely uniform dopant distribution.
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