white phosphorus

File:White_phosphorus.png

White phosphorus exists as molecules of four phosphorus atoms in a tetrahedral structure, joined by six phosphorus—phosphorus single bonds. The tetrahedral arrangement results in ring strain and instability.{{Housecroft2nd|page=392}} Although both are called "white phosphorus", in fact two different crystal allotropes are known, interchanging reversibly at 195.2 K.{{cite book |last1=Durif |first1=A. |title=Topics in phosphate chemistry |last2=Averbuch-Pouchot |first2=M.T. |date=1996 |publisher=World Scientific |isbn=978-981-02-2634-3 |location=Singapore [u.a.] |page=3}} The element's standard state is the body-centered cubic α form, which is actually metastable under standard conditions. The β form is believed to have a hexagonal crystal structure.

Molten and gaseous white phosphorus also retains the tetrahedral molecules, until {{convert|800|C|F K|-2}} when it starts decomposing to {{chem|P|2}} molecules.{{Cite journal |author=Simon, Arndt |last2=Borrmann |first2=Horst |last3=Horakh |first3=Jörg |date=1997 |title=On the Polymorphism of White Phosphorus |journal=Chemische Berichte |volume=130 |issue=9 |pages=1235–1240 |doi=10.1002/cber.19971300911}} The {{chem|P|4}} molecule in the gas phase has a P-P bond length of r_g = 2.1994(3) Å as was determined by gas electron diffraction.{{Cite journal |last1=Cossairt |first1=Brandi M. |last2=Cummins |first2=Christopher C. |last3=Head |first3=Ashley R. |last4=Lichtenberger |first4=Dennis L. |last5=Berger |first5=Raphael J. F. |last6=Hayes |first6=Stuart A. |last7=Mitzel |first7=Norbert W. |last8=Wu |first8=Gang |date=2010-06-01 |title=On the Molecular and Electronic Structures of AsP3 and P4 |journal=Journal of the American Chemical Society |volume=132 |issue=24 |pages=8459–8465 |doi=10.1021/ja102580d |issn=0002-7863 |pmid=20515032|bibcode=2010JAChS.132.8459C }} The β form of white phosphorus contains three slightly different {{chem|P|4}} molecules, i.e. 18 different P-P bond lengths — between 2.1768(5) and 2.1920(5) Å. The average P-P bond length is 2.183(5) Å.{{Cite journal |author=Simon, Arndt |last2=Borrmann |first2=Horst |last3=Horakh |first3=Jörg |date=1997 |title=On the Polymorphism of White Phosphorus |journal=Chemische Berichte |volume=130 |issue=9 |pages=1235–1240 |doi=10.1002/cber.19971300911}}

Despite white phosphorus not being the most stable allotropes of phosphorus, its molecular nature allows it to be easily purified. Thus, it is defined to have a zero enthalpy of formation.

In base, white phosphorus spontaneously disproportionates to phosphine and various phosphorus oxyacid salts.{{cite book |last1=Engel |first1=Robert |title=Synthesis of Carbon-Phosphorus Bonds |last2=Cohen |first2=JaimeLee Iolani |publisher=CRC Press |year=2004 |isbn=0-8493-1617-0 |edition=2nd |location=Boca Raton |at=§2.3 |lccn=2003060796}}

Many reactions of white phosphorus involve insertion into the P-P bonds, such as the reaction with oxygen, sulfur, phosphorus tribromide and the NO⁺ ion.

It ignites spontaneously in air at about {{convert|50|C}}, and at much lower temperatures if finely divided (due to melting-point depression). Phosphorus reacts with oxygen, usually forming two oxides depending on the amount of available oxygen: {{chem2|P4O6}} (phosphorus trioxide) when reacted with a limited supply of oxygen, and {{chem2|P4O10}} when reacted with excess oxygen. On rare occasions, {{chem2|P4O7}}, {{chem2|P4O8}}, and {{chem2|P4O9}} are also formed, but in small amounts. This combustion gives phosphorus(V) oxide:

: {{chem2|P4 + 5 O2 → P4O10}}

The white allotrope can be produced using several methods. In the industrial process, phosphate rock is heated in an electric or fuel-fired furnace in the presence of carbon and silica.Threlfall, R.E., (1951). 100 years of Phosphorus Making: 1851–1951. Oldbury: Albright and Wilson Ltd Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid. An idealized equation for this carbothermal reaction is shown for calcium phosphate (although phosphate rock contains substantial amounts of fluoroapatite, which would also form silicon tetrafluoride):

:{{chem2|2 Ca3(PO4)2 + 6 SiO2 + 10 C → 6 CaSiO3 + 10 CO + P4}}

In this way, an estimated 750,000 tons were produced in 1988.

Most (83% in 1988) white phosphorus is used as a precursor to phosphoric acid, half of which is used for food or medical products where purity is important. The other half is used for detergents.{{Needs update|reason=Phosphates were removed from consumer detergents quite a while ago in the global movement to make ordinary consumer goods stop working in the name of the environment while still allowing the heavier commercial users to access them easily..|date=November 2024}} Much of the remaining 17% is mainly used for the production of chlorinated compounds phosphorus trichloride, phosphorus oxychloride, and phosphorus pentachloride:{{Cite book |url=https://ncert.nic.in/ncerts/l/lech107.pdf |title=Chemistry Part I Class XII |publisher=NCERT |date=January 2019 |isbn=978-81-7450-648-1 |edition=Reprinted |location=India |pages=177 |language=English}}

:{{chem2|P4 + 10Cl2 -> 4PCl5}}

Other products derived from white phosphorus include phosphorus pentasulfide and various metal phosphides.{{cite book |doi=10.1002/14356007.a19_505 |chapter=Phosphorus |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Diskowski |first1=Herbert |last2=Hofmann |first2=Thomas |isbn=978-3-527-30385-4 }}

Although white phosphorus forms the tetrahedron, the simplest possible Platonic solid, no other polyhedral phosphorus clusters are known.{{wikicite|reference=Corbridge, D. E. C. (1995) "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. § 4.1.12. {{ISBN|0-444-89307-5}}.|ref={{harvid|Corbridge|1995}}}} White phosphorus converts to the thermodynamically-stabler red allotrope, but that allotrope is not isolated polyhedra.

A cubane-type cluster, in particular, is unlikely to form, and the closest approach is the half-phosphorus compound {{chem2|P4(CH)4}}, produced from phosphaalkynes.{{cite journal|doi=10.1002/anie.199504361|title=Phosphaalkyne Cyclooligomers: From Dimers to Hexamers—First Steps on the Way to Phosphorus–Carbon Cage Compounds|year=1995|last1=Streubel|first1=Rainer|journal=Angewandte Chemie International Edition in English|volume=34|pages=436–438|issue=4}} Other clusters are more thermodynamically favorable, and some have been partially formed as components of larger polyelemental compounds.

White phosphorus is acutely toxic, with a lethal dose of 50-100 mg (1 mg/kg body weight). Its mode of action is not known but is thought to involve its reducing properties, possibly forming intermediate reducing compounds such as hypophosphite, phosphite, and phosphine. It damages the liver, kidneys, and other organs before eventually being metabolized to non-toxic phosphate. Chronic low-level exposure leads to tooth loss and phossy jaw which appears to be caused by the formation of amino bisphosphonates.{{Citation |last=Obscurants |first=National Research Council (US) Subcommittee on Military Smokes and |title=White Phosphorus Smoke |date=1999 |work=Toxicity of Military Smokes and Obscurants: Volume 2 |url=https://www.ncbi.nlm.nih.gov/books/NBK224560/ |access-date=2025-02-04 |publisher=National Academies Press (US) |language=en}}{{Cite report |url=https://www.atsdr.cdc.gov/toxprofiles/tp103.pdf |title=Toxicological Profile for White Phosphorous [sic]|date=September 1997 |publisher=U.S. Department of Health and Human Services |access-date=2025-02-05 |archive-url=https://web.archive.org/web/20250118100739/https://www.atsdr.cdc.gov/toxprofiles/tp103.pdf |archive-date=2025-01-18 |url-status=live}}

White phosphorus is used as a weapon because it is pyrophoric. For the same reasons, it is dangerous to handle. Measures are taken to protect samples from air since it will react with oxygen at ambient temperatures, and even in small samples this can lead to self-heating and eventual combustion. There are anecdotal reports of problems for beachcombers who may collect washed-up samples while unaware of their true nature.{{cite web |last=Winter |first=George |date=1 October 2017 |title=A dangerous guide to beachcombing |url=https://www.chemistryworld.com/news/a-dangerous-guide-to-beachcombing/3008056.article |website=Chemistry World}}{{cite web |last=Staudenmaier |first=Rebecca |date=May 8, 2017|title=Woman mistakes WWII-era munition for precious stone on German beach {{pipe}} DW {{pipe}} 05.08.2017 |url=https://www.dw.com/en/woman-mistakes-wwii-era-munition-for-precious-stone-on-german-beach/a-39977702 |website=Deutsche Welle}}{{dubious|date=December 2024}}

• Red phosphorus
• Allotropes of phosphorus
• Phosphorus

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Category:Allotropes