Sodium phosphides

By heating in vacuum at 400° to 450° C. the black product formed by the interaction of sodium and phosphorus, a lemon-yellow substance of the formula Na₂P₅, is obtained. It has a density somewhat above 2, is unstable in air, and is decomposed by water with formation of solid phosphorus hydride.

Tomkinson and Barker describe the product formed by heating sodium and red phosphorus as a grey mass, which reacts violently with water, yielding spontaneously inflammable hydrogen phosphide. They also state that under suitable experimental conditions sodium reacts with yellow phosphorus to form a white, crystalline product.

At low temperatures ammonia reacts with sodium and red phosphorus to form a reddish-brown, amorphous mass, considered by Hugot to be sodium phosphide. With excess of sodium, yellow crystals of the formula Na₃P₂H₃ are formed. They react with water and acids, evolving phosphine:

Na₃P₂H₃+3H₂O = 3NaOH+2PH₃.