Phosphorus
Phosphorus is a chemical element; it has 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 and inorganic compounds, with as its main oxidation states +5, +3 and −3.
The isolation of white phosphorus in 1669 by Hennig Brand marked the scientific community's first discovery of an element since antiquity. 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 matches and fire retardants.
Most industrial production of phosphorus is focused on the mining and transformation of phosphate rock into phosphoric acid for phosphate-based fertilisers. 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 pesticides, food additives, and detergents.
Phosphorus is essential to all known forms of life, largely through organophosphates, organic compounds containing the phosphate ion as a functional group. These include DNA, RNA, ATP, and phospholipids, 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.
History
Phosphorus was the first element to be "discovered", in the sense that it was not known since ancient times. The discovery is credited to the Hamburg alchemist Hennig Brand in 1669, who was attempting to create the fabled philosopher's stone. To this end, he experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism. By letting the urine rot, boiling it down to a paste, then distilling it at a high temperature and leading the resulting vapours through water, he obtained a white, waxy substance that glowed in the dark and burned brilliantly. He named it in. The word phosphorus itself originates from Greek mythology, where it references the god of the morning star, also known as the planet Venus.Brand at first tried to keep the method secret, but later sold the recipe for 200 thalers 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:
Boyle's assistant Ambrose Godfrey-Hanckwitz later made a business of the manufacture of phosphorus.
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:
Then, dehydrating the resulting monocalcium phosphate:
Finally, mixing the obtained calcium metaphosphate with ground coal or charcoal in an iron pot, and distilling phosphorus vapour out of a retort:
This way, two-thirds of the phosphorus was turned into white phosphorus while one-third remained in the residue as calcium orthophosphate. The carbon monoxide produced during the reaction process was burnt off in a flare stack.
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 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 were made with heads of white phosphorus, an oxygen-releasing compound, 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 phosphorus 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.
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, 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, smoke screens and tracer ammunition. A special incendiary bullet was developed to shoot at hydrogen-filled Zeppelins over Britain.
During World War II, Molotov cocktails 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 incendiary bombs were used on a large scale, notably to destroy Hamburg, the place where the "miraculous bearer of light" was first discovered.
Characteristics
Isotopes
There are 22 known isotopes of phosphorus, ranging from to. Only is stable and, therefore, has 100% abundance. The nuclear spin of 1/2 and high abundance of make phosphorus-31 nuclear magnetic resonance spectroscopy a very useful analytical tool in studies of phosphorus-containing samples.Two radioactive isotopes of phosphorus have half-lives suitable for biological scientific experiments, and are used as radioactive tracers in biochemical laboratories. These are:
- , a beta-emitter with a half-life of 14.3 days, which is used routinely in life-science laboratories, primarily to produce radiolabeled DNA and RNA probes, e.g. for use in Northern blots or Southern blots.
- , a beta-emitter with a half-life of 25.4 days. It is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as DNA sequencing.