Phosphine PH3
Phosphine PH3 is a colorless and extremely toxic gas, which smells slightly of garlic or bad fish. It is highly reactive. It can be formed either by hydrolysing metal phosphides such as Na3P or Ca3P2 with water, or by hydrolysing white phosphorus with NaOH solution.
Structure of Phosphine
Phosphine has a pyramidal structure, the H–P–H bond angle is 93.5°. PH3 unlike NH3, is not very soluble in water; aqueous solutions are neutral. It is more soluble in CS2 and other organic solvents.
Phosphonium salts such as [PH4]+ Cl– can be formed, but require PH3 and anhydrous HCl. Pure PH3 is stable in air, but it catches fire when heated to about 150°C. PH3 frequently contains traces of diphosphine P2H6 which cause it to catch fire spontaneously. This is the origin of the flickering light called will–o'–the wisp, which is sometimes seen in marshes.
Phosphine is used as an insecticide for the fumigation of grains, animal feed, and leaf–stored tobacco, and as a rodenticide.
Phosphine is also used as an intermediate in the synthesis of flame retardants for cotton fabrics, as a doping agent for n–type semiconductors, a polymerization initiator and a condensation catalyst.