Formula Na3PS2O2 | Molar mass 196.072 g/mol | |
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Sodium dithiophosphate is the salt with the formula Na3PS2O2, although the solid is usually encountered as the hydrate. It is also supplied as an aqueous solution together with other thiophosphates. It is a colorless compound, but commercial samples can appear dark owing to the presence of impurities. It is used to facilitate the isolation of molybdenum from its ores.
Contents
Preparation
The compound has been prepared in a multistep process starting with the base hydrolysis of phosphorus pentasulfide to give dithiophosphate, which is isolated as its barium salt:
P2S5 + 6 NaOH → 2 Na3PO2S2 + H2S + 2 H2OThe salt is isolated as the hydrate Na3PO2S2.(H2O)11. It is prone to hydrolysis, especially when it is heated as an aqueous solutions:
Na3PO2S2 + 2 H2O → Na3PO3S + H2SApplications
This salt is used as a flotation agent in molybdenite mineral concentration from ores, where it is usually known as "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. In this context, the Nokes reagent is called a "depressant," since it suppresses the flotation tendency of the solids.