Phosphorus sulfides
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur. These compounds have the formula  with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide (), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide (), used in the production of "strike anywhere matches". There are several other phosphorus sulfides in addition to  and . Six of these phosphorus sulfides exist as isomers: . 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. is also known but is unstable above −30 °C. 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. 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  can be prepared by treating the corresponding isomers of  with :

 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine. can be prepared by treating stoichiometric amounts of  with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine. The respective product distribution is then analyzed by using 31P-NMR spectroscopy. In particular, α- can be easily made by the photochemical reaction of  with red phosphorus. Note that  is unstable when heated, tending to disproportionate to  and  before reaching its melting point. can be made by abstracting a sulfur atom from  using triphenylphosphine:

Treating α- with  in  also yields α-. The two new polymorphs δ- and ε- can be made by treating α- with  in . is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. β- can be made by treating α- with  in , which yields a mixture between α- and β-. can be made by two methods. One method involves the heating of  in excess sulfur. Another 
method involves the heating of  and  in 1:2 mole ratio, where  is reversibly formed:

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. See also
Diphosphorus trisulfide ()

References

Inorganic phosphorus compounds
Sulfides