Phosphorus Hydrogen Compounds

The most important hydride of phosphorus is phosphine, PH₃, a gaseous analog of ammonia in terms of both formula and structure. Unlike ammonia, it is not possible to form phosphine by direct union of the elements. There are two methods for the preparation of phosphine. One method is by the action of an acid on an ionic phosphide. The other method is the disproportionation of white phosphorus with hot concentrated base to produce phosphine and the hydrogen phosphite ion:

Phosphine is a colorless, very poisonous gas, which has an odor like that of decaying fish. Heat easily decomposes phosphine (4PH3⟶P4+6H2), and the compound burns in air. The major uses of phosphine are as a fumigant for grains and in semiconductor processing. Like ammonia, gaseous phosphine unites with gaseous hydrogen halides, forming phosphonium compounds like PH₄Cl and PH₄I. Phosphine is a much weaker base than ammonia; therefore, these compounds decompose in water, and the insoluble PH₃ escapes from solution.