Phosphorus sulfides comprise a family ofinorganic compounds containing onlyphosphorus andsulfur. These compounds have the formulaP4Sn withn ≤ 10. Two are of commercial significance,phosphorus pentasulfide (P4S10), which is made on a kiloton scale for the production of other organosulfur compounds, andphosphorus sesquisulfide (P4S3), used in the production of"strike anywhere matches".
There are several other phosphorus sulfides in addition toP4S3 andP4S10. Six of these phosphorus sulfides exist asisomers: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 monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long.[4]
The main method for preparing these compounds isthermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by31P-NMR spectroscopy. More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K,[7] followed by carefulrecrystallization withcarbon disulfide andbenzene. An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent.[8]
The α- and β- forms ofP4S4 can be prepared by treating the corresponding isomers ofP4S3I2 with((CH3)3Sn)2S:[7]
P4S3I2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P4S5 can be prepared by treating stoichiometric amounts ofP4S3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount ofiodine.[9] The respective product distribution is then analyzed by using31P-NMR spectroscopy.
In particular, α-P4S5 can be easily made by thephotochemical reaction ofP4S10 with red phosphorus.[7] Note thatP4S5 is unstable when heated, tending todisproportionate toP4S3 andP4S7 before reaching its melting point.[10]
P4S6 can be made by abstracting a sulfur atom fromP4S7 usingtriphenylphosphine:[7]
Treating α-P4S5 withPh3AsS inCS2 also yields α-P4S6.[5] The two new polymorphs δ-P4S6 and ε-P4S6 can be made by treating α-P4S4 withPh3SbS inCS2.[11]
P4S7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides.[12]
β-P4S8 can be made by treating α-P4S7 withPh3AsS inCS2, which yields a mixture between α-P4S7 and β-P4S8.[5]
P4S9 can be made by two methods. One method involves the heating ofP4S3 in excess sulfur.[7] Another method involves the heating ofP4S7 andP4S10 in 1:2 mole ratio, whereP4S9 is reversibly formed:[11]
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.[13]