Phosphorus sulfides

Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur. These compounds have the formula P₄S_n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide (P₄S₁₀), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide (P₄S₃), used in the production of "strike anywhere matches".

There are several other phosphorus sulfides in addition to P₄S₃ and P₄S₁₀. Six of these phosphorus sulfides exist as isomers: P₄S₄, P₄S₅, P₄S₆, P₄S₇, P₄S₈, and P₄S₉. These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure.^[1] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms.^[2] P₄S₂ is also known but is unstable above −30 °C.^[3]

Phosphorus sulfides that exist in isomeric forms

Preparation

The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by ³¹P-NMR spectroscopy. More selective syntheses entail:

desulfurization, e.g. using triphenylphosphine and, complementarily,
sulfidation using triphenylarsine sulfide.^[4]^[5]

P₄S₃

Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K,^[6] followed by careful recrystallization with carbon disulfide and benzene. An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent.^[7]

P₄S₄

The α- and β- forms of P₄S₄ can be prepared by treating the corresponding isomers of P₄S₃I₂ with ((CH₃)₃Sn)₂S:^[6]

P₄S₃I₂ can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.

P₄S₅

P₄S₅ can be prepared by treating stoichiometric amounts of P₄S₃ with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine.^[8] The respective product distribution is then analyzed by using ³¹P-NMR spectroscopy.

In particular, α-P₄S₅ can be easily made by the photochemical reaction of P₄S₁₀ with red phosphorus.^[6] Note that P₄S₅ is unstable when heated, tending to disproportionate to P₄S₃ and P₄S₇ before reaching its melting point.^[9]

P₄S₆

P₄S₆ can be made by abstracting a sulfur atom from P₄S₇ using triphenylphosphine:^[6]

P₄S₇ + Ph₃P → P₄S₆ + Ph₃PS

Treating α-P₄S₅ with Ph₃AsS in CS₂ also yields α-P₄S₆.^[4] The two new polymorphs δ-P₄S₆ and ε-P₄S₆ can be made by treating α-P₄S₄ with Ph₃SbS in CS₂.^[10]

P₄S₇

P₄S₇ is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides.^[11]

P₄ + 7 S → P₄S₇

P₄S₈

β-P₄S₈ can be made by treating α-P₄S₇ with Ph₃AsS in CS₂, which yields a mixture between α-P₄S₇ and β-P₄S₈.^[4]

P₄S₉

P₄S₉ can be made by two methods. One method involves the heating of P₄S₃ in excess sulfur.^[6] Another method involves the heating of P₄S₇ and P₄S₁₀ in 1:2 mole ratio, where P₄S₉ is reversibly formed:^[10]

P₄S₇ + 2 P₄S₁₀ ⇌ 3 P₄S₉

P₄S₁₀

P₄S₁₀ is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube.^[12]

P₄ + 10 S → P₄S₁₀

References

^ Jason, M. E.; Ngo, T.; Rahman, S. (1997). "Products and Mechanisms in the Oxidation of Phosphorus by Sulfur at Low Temperature". Inorg. Chem. 36 (12): 2633–2640. doi:10.1021/ic9614879.
^ Holleman, A. F.; Wiberg, E. Inorganic Chemistry. Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
^ Heal, H. G. The Inorganic Heterocyclic Chemistry of Sulfur, Nitrogen, and Phosphorus Academic Press: London; 1980 ISBN 0-12-335680-6.
^ ^a ^b ^c Jason, M. E. (1997). "Transfer of Sulfur from Arsenic and Antimony Sulfides to Phosphorus Sulfides. Rational Syntheses of Several Less-Common P₄S_n Species". Inorg. Chem. 36 (12): 2641–2646. doi:10.1021/ic9614881.
^ Nowottnick, H.; Blachnik, R. (1999). "Zwei neue Phosphorsulfide (Two New Phosphorus Sulfides)". Zeitschrift für anorganische und allgemeine Chemie. 625 (12): 1966–1968. doi:10.1002/(SICI)1521-3749(199912)625:12<1966::AID-ZAAC1966>3.0.CO;2-B.
^ ^a ^b ^c ^d ^e Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 484. ISBN 978-0-13-175553-6.
^ "Phosphorus trisulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 563.
^ "Phosphorus pentasulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 565.
^ A. Earnshaw; Norman Greenwood (2002). "Phosphorus". Chemistry of the elements, 2nd edition. Butterworth Heinemann. p. 508. ISBN 0750633654.
^ ^a ^b R. Bruce King (2005). "Phosphorus". Encyclopedia of Inorganic Chemistry, 2nd edition. Wiley. p. 3711. ISBN 9780470862100.
^ "Phosphorus heptasulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 566.
^ "Diphosphorus pentasulfide" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 567.