Phosphorus sulfide

Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur. These compounds have the formula P₄S_x with x ≤ 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. All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. P₄S₂ is also known but is unstable above −30 °C.

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.

Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, 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.

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

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