What does phosphonium mean?
Phosphonium denotes a positively charged chemical species centered on phosphorus. In organic chemistry, it usually means a phosphorus atom bonded to four groups, often hydrogen, carbon, or other substituents, with a positive charge; salts containing such a cation are called phosphonium salts. The parent ion is PH4+. Phosphonium compounds are useful intermediates because many reactions proceed by forming a phosphonium intermediate and then removing a nearby proton to produce a phosphorus ylide. This makes the term especially important in Wittig and related reactions. Phosphonium compounds can also be stable, isolable solids and may function as ionic liquids or phase-transfer catalysts, giving them applications in synthetic and materials chemistry. Although it is specialized rather than general vocabulary, phosphonium clearly names the positive form of phosphorus and distinguishes it from neutral phosphines and negatively charged phosphate ions.
nounA positively charged phosphorus-containing ion. In organic chemistry, it usually denotes a phosphorus atom bonded to four substituents and carrying a positive charge.
- A positively charged phosphorus-containing ion, especially the parent PH4+ ion or an organic phosphorus cation of the form R4P+.
"The reaction generated a phosphonium intermediate that was converted into the ylide by deprotonation."
"The catalyst was isolated as a phosphonium salt."
"Addition of the electrophile generated a phosphonium intermediate, which then underwent deprotonation to form the ylide."
In technical prose, individual cations are normally called phosphonium ions; phosphonium salts is used when referring to compounds containing them.
"The mass spectrum contained signals from several phosphonium ions."
Phosphonium is the positively charged phosphorus analogue of ammonium.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phosphonium come from?
Phosphonium was formed in the nineteenth century from phosphorus with the New Latin suffix -onium, used in naming positively charged chemical species. The source word phosphorus was coined in the seventeenth century from Greek phōs, meaning “light,” and phoros, meaning “bearing,” in reference to the element's luminous properties. The same phosphorus base underlies cognates such as phosphine, phosphide, phosphate, and phosphite.
How phosphonium is actually used
A specialized term used chiefly in chemistry. The unmodified word generally denotes the cation, while phosphonium salt or phosphonium compound is used for a compound containing it.
Easily confused with phosphonium
Phosphine is the neutral compound PH3, whereas phosphonium denotes a positively charged phosphorus-containing ion.
Phosphate is the negatively charged ion PO4^3−, while phosphonium is a positively charged phosphorus-containing ion.