Sodium dithiophosphate


Sodium dithiophosphate is the salt with the formula Na3PS2O2. It is usually supplied as the hydrated solid or as an aqueous solution together with other thiophosphates such as sodium monothiophosphate and sodium trithiophosphate. Both Na3PS2O2 and its hydrate are colorless solids, but commercial samples can appear dark owing to the presence of impurities. It is used to facilitate the isolation of molybdenum from its ores.

Preparation

The compound has been prepared in a multistep process starting with the base hydrolysis of phosphorus pentasulfide:
The salt is isolated as the hydrate Na3PO2S2.11. It is prone to hydrolysis, especially when it is heated as an aqueous solutions:
The structure of the anhydrous compound has been examined by X-ray crystallography. The material consists of tetrahedral PO2S23- centers interconnected by Na+ ions. It is assumed that the hydrate retains the tetrahedral PO2S23- centers, but that the Na+ ions are bonded to water.

Applications

The hydrated salt is used as a flotation agent in the purification of molybdenite from other components of the ores. It is a major component of "Nokes reagent". The salt is generated by the reaction of phosphorus pentasulfide with sodium hydroxide, often using impure reagents to obtain a mixture of the desired salt and related thiophosphates and oxidized species. Molybdenite particles, which are normally hydrophobic, become hydrophilic in the presence of this salt.

Related dithiophosphates

Organic esters of dithiophosphate are sometimes also called dithiophosphates. Diethyl dithiophosphoric acid is the parent of one series of these organic compounds. These compounds are salts with the formula . These lipophilic salts have also been used as a flotation "collectors" in the purification of various sulfide minerals. Zinc dithiophosphates also refers to this class of organic compounds.