Phosphine

(also hydrogen phosphide), PH₃, a colorless gas with the odor of rotten fish. Phosphine has a density of 1.55 g/liter, a melting point of –133.8°C, and a boiling point of – 87.8°C at 25°C and a pressure of 0.1 meganewton/m² (1 kilogram-force/cm²); 1 volume of water dissolves approximately 0.25 volume of PH₃. When heated, phosphine decomposes into phosphorus and hydrogen. The chemical properties of phosphine are somewhat similar to those of ammonia; the compound forms phosphonium salts, for example, PH₄I. Phosphine is a strong reducing agent. It ignites in air at temperatures above 100°C; in the presence of a small amount of diphosphine vapor, it ignites spontaneously to form a white smoke—phosphorus pentoxide. Mixtures of PH₃ and oxygen are explosive (the reaction proceeding by a chain mechanism).

Phosphine (with P₂H₄ vapors present as an impurity) is produced by the reaction of calcium phosphide (Ca₃P₂) with water; by heating white phosphorus with a caustic alkali solution (the method used by the French chemist P. Gengembre, who in 1783 was the first to produce phosphine); by thermal decomposition of phosphorous or hypophosphorous acid; and by the reaction of alkalies with phosphonium halides. PH₃ is invariably formed during the electrothermal production of white phosphorus from phosphates.

PH₃ is exceedingly toxic. In the event of poisoning, the victim must be exposed to fresh air and given artificial respiration.

Also known are self-igniting diphosphine (P₂H₄; boiling point, 56°C) and a solid form of the compound, the structure of which has not been determined.