Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula PH3, classed as a pnictogen hydride.

Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm.

Phosphines are compounds that include PH3 and the organophosphines, which are derived from PH3 by substituting one or more hydrogen atoms with organic groups.

Philippe Gengembre (1764–1838), a student of Lavoisier, first obtained phosphine in 1783 by heating white phosphorus in an aqueous solution of potash (potassium carbonate).

[NB 2] In 1844, Paul Thénard, son of the French chemist Louis Jacques Thénard, used a cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide, thereby demonstrating that P2H4 is responsible for spontaneous flammability associated with PH3, and also for the characteristic orange/brown color that can form on surfaces, which is a polymerisation product.

The upfield chemical shift of it 31P NMR signal accords with the conclusion that the lone pair electrons occupy the 3s orbital (Fluck, 1973).

Proton exchange proceeds via a phosphonium (PH+4) ion in acidic solutions and via phosphanide (PH−2) at high pH, with equilibrium constants Kb = 4×10−28 and Ka = 41.6×10−29.

[20] In 2020 a spectroscopic analysis was reported to show signs of phosphine in the atmosphere of Venus in quantities that could not be explained by known abiotic processes.

Thus with acrylonitrile, it reacts to give tris(cyanoethyl)phosphine:[27] Acid catalysis is applicable to hydrophosphination with isobutylene and related analogues: where R is CH3, alkyl, etc.

[28] Phosphine is an attractive fumigant because it is lethal to insects and rodents, but degrades to phosphoric acid, which is non-toxic.

Use of the gas avoids the issues related with the solid residues left by metal phosphide and results in faster, more efficient control of the target pests.

[34] Phosphine appears to be mainly a redox toxin, causing cell damage by inducing oxidative stress and mitochondrial dysfunction.

NIOSH recommends that the short term respiratory exposure to phosphine gas should not exceed 1 ppm.

Genetic variants that contribute to high level resistance to phosphine have been identified in the dihydrolipoamide dehydrogenase gene.

[12] Anne McCaffrey's Dragonriders of Pern series features genetically engineered dragons that breathe fire by producing phosphine by extracting it from minerals of their native planet.

In the 2008 pilot of the crime drama television series Breaking Bad, Walter White poisons two rival gangsters by adding red phosphorus to boiling water to produce phosphine gas.