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.

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 P4Sx 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. 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.

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. 2S-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.