Triphenylphosphine sulfide

Triphenylphosphine sulfide (IUPAC name: triphenyl-λ5-phosphanethione) is the organophosphorus compound with the formula (C6H5)3PS, usually written Ph3PS (where Ph = phenyl). It is a colourless solid, which is soluble in a variety of organic solvents.

Structurally, the molecule resembles the corresponding oxide, with idealized C3 point group symmetry. It is weakly nucleophilic at the sulfur atom.

Organic synthesis
Triphenylphosphine sulfide is useful for the conversion of epoxides to the corresponding episulfides:
 * Ph2C2H2O + Ph3PS → Ph2C2H2S + Ph3PO

It also reacts with ketenes to form thioketenes:
 * Ph2CCO + Ph3PS → Ph2CCS + Ph3PO

Analytical chemistry
In analytical chemistry, triphenylphosphine is used for the analysis of certain kinds of sulfur compounds. Elemental sulfur (S8), as occurs in some oils, and labile organosulfur compounds, such as organic trisulfides, react with triphenylphosphine to give Ph3PS, which can be detected by gas chromatography.