Phosphorus. P; at. wt 30.97376; at. no. 15; valences 3, 5. One naturally occurring isotope: 31P; artificial, radioactive isotopes: 28-30; 32-34. Abundancc in earth's crust: about 0.12%. Does not occur free in nature; found in the form of phosphates in the minerals chlorapatite [3Ca2(PO4)2.CaCl2], fluorapatite [3Ca(PO4)2.CaF2], vivianite, wavellite and "phosphate rock" or phosphorite; occurs in small quantities in granite rocks; occurs in all fertile soil; an essential constituent of protoplasm, nervous tissue and bones. Discovered in 1669 by Brandt. Prepn: Ullmano, Enzyklopädie der Technischen Chemie 8, 362 (1931); DeWitt, Skolnik, J. Am. Chem. Soc. 68, 2305 (1946); Skolnik et al., ibid. 2310. Lab prepn and purification: Klement in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) pp 518-525. Reviews: J. R. Van Waser, Phosphorus and Its Compounds, 2 vols. (Interscience, New York, 1958, 1961) 2046 pp; Corbridge, "The Structural Chemistry of Phosphorus Compounds" in Topics in Phosphorus Chemistry, Vol. 3, E. J. Griffith, M. Grayson, Eds. (Interscience, New York, 1966) pp 57-394; Toy, "Phosphorus" in Comprehensive Inorganic Chemistry, Vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 389-545; J. R. Van Wazer in Kirk-Othmer Encyclopedia of Chemical Technology vol. 17 (Wiley-Interscience, New York, 3rd ed., 1982) pp 473-490.

Phosphorus exists in three main allotropic forms: white, black, and red. The same liquid ia obtained on melting. Phosphorus atoms exist as symmetrical, tetrahedral P4 mole - cults in the liquid phase and in the vapor phase below 800 molecules dissociate to ~2 above 800~.

White phosphorus. Colorless or white, transparent, cryst solid; waxy appearance; darkens on exposure to light. Sometimes called yellow phosphorus; color due to impurities. Two allotropic modifications: a-form exists at room temp; cubic crystals containing P4 molecules; d 1.83. b-Form prepd by conversion of a-form at -79.6°; hexagonal crystals; d 1.88. mp 44.1° (vapor press. 0.181 mm); bp 280°. Volatile; sublimes in vacuo at ordinary temp when exposed to light. When exposed to air in the dark, emits a greenish light and gives off white fumes. Solubilities in water: one part/300,000 parts water; in abs alc: one g/400 ml; in abs ether: one g/102 ml; in CHCl3: one g/40 ml; in benzene: one g/35 ml; in CS2: one g/0.8 ml. Soly in oils: one gram phosphorus dissolves in 80 ml olive oil, 60 ml oil of turpentine, about 100 ml almond oil. Ignites at about 30° in moist air; the ignition temp is higher when the air is dry. Caution: handle with forceps. Keep under water. The fumes and the element itself are poisonous. Combines directly with the halogens to form tri - or pentahalides; combines with sulfur to form sulfides. Reacts with several metals to form phosphides. Yields orthophosphoric acid when treated with nitric acid. Reacts with alkali hydroxides with formation of phosphine and sodium hypophosphite. Incompat. Sulfur, iodine, oil of turpentine, potassium chlorate.

Black Phosphorus. Polymorphic. Orthorhombic crystalline form: stable in air; resembles graphite in texture; produced from the white modification under high pressures: Bridgman, J. Am. Chem. Soc. 36, 1344 (1914); Jacobs, J. Chem. Phys. 5, 945 (1937); Krebs, Inorg. Syn. 7, 60 (1963). d 2.691. Does not catch fire spontaneously. Insol in organic solvents. Amorphous form prepd at lower pressures: Jacobs, loc. cit. At higher pressure the orthorhombic form undergoes reversible transition to a rhombohedral structure, d 3.56, and a cubic structure, d 3.83: Jamieson, Science 139, 1291 (1963).

Red phosphorus. Red to violet powder; polymorphism: Roth et al., J. Am. Chem. Soc. 69, 2881 (1947); Corbridge, loc. cit. Crystal structure of one form, Hittorf's phosphorus: Thurn, Keebs, Acta Cryst. 25B, 125 (1969). The properties of red phosphorus are intermediate between those of the white and black forms. Sublimes at 416°, triple point 589.5° under 43.1 atm. d 2.34. Insol in organic solvents. Sol in phosphorus tribromide. Less active than the white form; reacts only at high temp. Yields the white modification when distilled at 290°. Catches fire when heated in air to about 260° and burns with formation of the pentoxide. Burns when heated in an atmosphere of chlorine.

Caution: Avoid contact with KClO3, KMnO4, peroxides and other oxidizing agents; explosions may result on contact or friction.

Human Toxicity: Ingestion of even small amounts of white phosphorus may produce severe G.I. irritation, bloody diarrhea, liver damage, skin eruptions, oliguria, circulatory collapse, coma, convulsions, death. The approx fatal dose is 50 to 100 mg. External contact may cause severe burns. Chronic poisoning (from ingestion or inhalation) is characterized by bony necrosis, especially of the mandible, spontaneous fractures, anemia, weight loss. Red phosphorus is relatively nontoxic unless it contains the white form as an impurity: Clinical Toxicology of Commercial Products M. N. Gleason et al., Eds. (Williams & Wilkins, Baltimore, 1969) Section III, pp 192-195.

USE: White phosphorus: manuf rat poisons; for smoke screens, gas analysis. Red phosphorus: pyrotechnics; manuf safety matches; in organic synthesis; manuf phosphoric acid, phosphine. phosphoric anhydride, phosphorus pentachloride, phosphorus trichloride; manuf fertilizers, pesticides, incendiary shells, smoke bombs, tracer bullets.
Ref.: 7321, 1167 pp.
The Merck Index - Eleventh Edition.
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