Phosphine(redirected from phosphoniums)
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(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.