Phosphonium

As phosphonium refers to the ammonium ion analog molecular ion in which the nitrogen atom has been replaced by a phosphorus atom. Analogous to the ammonium ion is the phosphonium cation positive charge, the phosphorus atom is in the oxidation number -3 ago. The simplest phosphonium ion is the [ H4P ] . Its salts decompose on contact with water in phosphine and the acid of the anion decays phosphonium chloride in hydrogen phosphide ( monophosphane, PH3 ) and hydrochloric acid (HCl). Because of the elimination of the phosphine phosphonium salts are very toxic. They are used in pest control for the generation of hydrogen phosphide.

Organic phosphonium ions are in the form [ R 4 P ] , where R is an organic radical (for example alkyl or aryl groups ). They are similar to the homologous nitrogen compounds, very stable. They can be prepared by reaction of phosphines with alkyl and aryl halides, wherein, in use of aryl halides, a catalyst is needed (eg NiCl2 ).

Phosphonium salts are of great importance in the Wittig reaction.