Phosphorus is a key element in all known forms of life. Inorganic phosphorus in the form of the phosphate plays a major role in biological molecules such as DNA and RNA. Living cells also utilize phosphate to transport cellular energy via adenosine triphosphate. Nearly every cellular process that uses energy gets it in the form of ATP. Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts are used by animals to stiffen their bones. Phosphorus is an essential mineral macronutrient, which is studied extensively in soil conservation in order to understand plant uptake from soil systems. In ecological terms, phosphorus is often a limiting nutrient in many environments. The availability of phosphorus governs the rate of growth of many organisms. In ecosystems an excess of phosphorus can be problematic, especially in aquatic systems.
Phosphorus was discovered by a German alchemist Hennig Brand in 1669 through a preparation from urine, and in the process he produced a white material that glowed in the dark and burned brilliantly. Phosphorus was first made commercially for the match industry in the 19th century by distilling off phosphorus vapor from precipitated phosphates heated in a retort. The precipitated phosphates made from ground-up bones had been degreased and treated with strong acids. Early matches used white phosphorus in their composition, which was dangerous due to its toxicity. When a safe process of manufacturing red phosphorus was discovered, it become a safer alternative for match manufacture.
Due to its reactivity to air and many other oxygen containing substances, phosphorus is not found free in nature but it is widely distributed in many different minerals. Phosphate rock is an important commercial source of this element. The white allotrope can be produced using several different methods. In one process, tricalcium phosphate, which is derived from phosphate rock, is heated in an electric furnace in the presence of carbon and silica. Elemental phosphorus is then liberated as a vapor and can be collected under phosphoric acid.
Organic compounds of phosphorus form a wide class of materials, some of which are extremely toxic. Fluorophosphate esters are among the most potent neurotoxins known. A wide range organophosphorus compounds are used for their toxicity to certain organisms as pesticides. Most inorganic phosphates are relatively nontoxic and essential nutrients. The allotrope of white phosphorus should be kept under water at all times as it presents a significant fire hazard. When the white form is exposed to sunlight or when it is heated in its own vapor to 250oC, it is transmuted to the red form. The red allotrope does not spontaneously ignite in air and is not as dangerous as the white form. Nevertheless, it should be handled with care because it does revert to white phosphorus in some temperature ranges and it also emits highly toxic fumes that consist of phosphorus oxides when it is heated.