Phosphorus Thiophosphites

These salts may be regarded as derived from mono-, H₃PSO₂, di-, H₃PS₂O and tri-thiophosphorous acids, H₃PS₃. They were prepared, with other products, by heating metals with a mixture of sulphur and phosphorus, e.g. Ag₃PS₃, or metallic sulphides with phosphorus sulphides, e.g. Cu₃PS₃ from Cu₂S and P₂S₅. When P₄S₃ was dissolved in alkalies phosphine, hydrogen and phosphorus were produced. By evaporation in vacuo crystals of Na₂H(PSO₂).2H₂O were obtained. With an excess of sodium hydroxide, after long standing, the normal salt Na₃PSO₂ was deposited. When the alkali was replaced by Na₂S the evaporation in vacuo gave Na₂H(PS₂O).2½H₂O. An ammonium salt, (NH₄)₂H(PSO₂).H₂O, has been prepared similarly from P₄S₃ and solution of ammonia after long standing at 0° C. Solutions of these salts gave a characteristic yellow to red precipitate when mixed with a solution of lead acetate. When the salts were heated or their solutions were boiled, H₂S was evolved and phosphites produced.

Thiohypophosphates, for example those of copper, silver and nickel, Cu₂P₂S₆, Ag₄P₂S₆, and Ni₂P₂S₆, respectively, have been prepared by heating the metals with phosphorus and sulphur. The ease with which they are decomposed by water depends on the electroaffinity of the metal. Thus the zinc salt is decomposed by boiling water, while the nickel salt, which forms grey hexagonal crystals, is scarcely affected by water.