Phosphonium
The phosphonium (more obscurely: phosphinium) cation describes polyatomic cations with the chemical formula PR+
4.[1] Salts of the parent PH4+ are rarely encountered, but this ion is an intermediate in the preparation of the industrially useful tetrakis(hydroxymethyl)phosphonium chloride:
- PH3 + HCl + 4 CH2O → P(CH2OH)4+Cl−
Organic phosphonium salts are common reagents in the laboratory. Those with a P-H bond are produced through protonation of phosphines:
- PR3 + H+ → HPR3+
Many organic quaternary phosphonium cations (P+
R
4) are produced by alkylation of organophosphines. For example the reaction of triphenylphosphine with methyl iodide gives methyltriphenylphosphonium iodide, the precursor to a Wittig reagent:
- PPh3 + CH3I → CH3PPh3+I−
The cation tetraphenylphosphonium (PPh4+) is a useful precipitating agent, analogous to quaternary ammonium salts used in phase transfer catalysis.
See also
- Ammonium (NH4+)
- Hydronium (H3O+)
- Onium compounds
References
- ↑ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam 1995. ISBN 0-444-89307-5.
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