Phosphorus pentasulfide

Phosphorus pentasulfide is the chemical compound with the formula P₄S₁₀. This yellow solid is an industrially important inorganic compound of phosphorus and sulfur. Commercial samples often appear greenish-gray. The compound has a low solubilty in carbon disulfide and benzene, but it reacts with many organic compounds such as alcohols and amines. Its molecular structure is related to that of adamantane, a common motif in inorganic chemistry, and is almost identical to the structure of phosphorus pentoxide.^[1]

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Production

Phosphorus pentasulfide is obtained by the reaction of liquid white phosphorus, P₄, with sulfur above 300 °C. Alternatively, P₄S₁₀ can be formed by reacting elemental sulfur or pyrite, FeS₂, with ferrophosphorus, impure Fe₂P (a byproduct of P₄ production from phosphate rock):

4Fe₂P + 18S → P₄S₁₀ + 8FeS

4Fe₂P + 18FeS₂ + heat → P₄S₁₀ + 26FeS

Reactivity

Due to hydrolysis by atmospheric moisture, P₄S₁₀ evolves H₂S, thus P₄S₁₀ is associated with a rotten egg odour. Aside from H₂S, hydrolysis of P₄S₁₀ gives phosphoric acid:

P₄S₁₀ + 16H₂O → 4H₃PO₄ + 10H₂S

Other mild nucleophiles react with P₄S₁₀, including alcohols and amines. Aromatic compounds such as anisole, ferrocene and 1-methoxynapthalene react to form 1,3,2,4-dithiadiphosphetane 2,4-disulfides such as lawesson's reagent.

Related phosphorus sulfides

Aside from the commercially important P₄S₃ and P₄S₁₀, several other phosphorus sulfides are known with the formula P₄S_x where x is less than or equal to 10. 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 on structural principles.^[2] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms.

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 (i) desulfurization, e.g. using triphenylphosphine and, complementarily, (ii) sulfidation using triphenylarsine sulfide.^[3][4]

Applications

Phosphorus pentasulfide is used for manufacturing zinc dialkyl dithio phosphate, insecticides, ore flotation agents, and various organophosphates. It is also a component of some amorphous solid electrolytes (eg. Li₂S-P₂S₅) for some types of lithium batteries.

Phosphorus pentasulfide is a dual-use material, as it can be used for manufacture of the VX nerve agent.

References

1. ^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam 1995. ISBN 0-444-89307-5.
2. ^ Jason, M. E.; Ngo, T.; Rahman, S. (1997). "Products and Mechanisms in the Oxidation of Phosphorus by Sulfur at Low Temperature". Inorg. Chem. 36: 2633-2640. doi:10.1021/ic9614879.
3. ^ 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: 2641-2646. doi:10.1021/ic9614881.
4. ^ Nowottnick, H.; Blachnik, R. "Zwei neue Phosphorsulfide” (Two New Phosphorus Sulfides) Zeitschrift für Anorganische und Allgemeine Chemie 1999, volume 625, pages 1966-1968.