Phosphorus Nitride, P₃N₅

Phosphorus Nitride or Triphosphorus Pentanitride, P₃N₅, appears to have this composition has been obtained by several methods:—

1. By passing the vapour of phosphorus pentachloride in a current of nitrogen over heated magnesium nitride.
2. The black substance produced by the reaction between liquid ammonia and phosphorus in a sealed tube gave an analysis which agreed fairly well with the foregoing composition.
3. By saturating the pentasulphide, P₂S₅, with pure dry ammonia at ordinary temperatures, and heating the product in a current of ammonia at 850° C.

The product is described as a powder, white to dark red in colour according to the time of heating at 250° C. The density was 2.5. The nitride was tasteless, odourless, and chemically inactive at ordinary temperatures. The heat of formation (from white phosphorus) is given as +81.5 Cals. per mol. The molar heat of combustion was 474.7 Cals. (at constant pressure). The nitride dissociated into its elements in a vacuum at about 760° C. It was reduced to phosphorus and ammonia by hydrogen at a red heat, and burned when heated in oxygen or chlorine. It was hydrolysed by boiling water, thus

P₃N₅ + 12H₂O = 3H₃PO₄ + 5NH₃

It acted as a reducing agent on metallic oxides and was decomposed by many metals from 80° C. upwards, giving phosphides of the metals.