The parent phosphonium is PH+ 4 as found in the iodide salt,
phosphonium iodide. Salts of the parent PH+ 4 are rarely encountered, but this ion is an intermediate in the preparation of the industrially useful
tetrakis(hydroxymethyl)phosphonium chloride:
Solid
phosphorus pentachloride is an
ionic compound, formulated PCl+ 4PCl− 6, that is, a salt containing the tetrachlorophosphonium cation.[7][8] Dilute solutions dissociate according to the following equilibrium:
Tetrakis(hydroxymethyl)phosphonium chloride has industrial importance in the production of crease-resistant and
flame-retardantfinishes on cotton textiles and other cellulosic fabrics.[12][13] A flame-retardant finish can be prepared from THPC by the Proban Process,[14] in which THPC is treated with urea. The
urea condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to
phosphine oxide as the result of this reaction.[15]
Phase-transfer catalysts and precipitating agents
Organic phosphonium cations are lipophilic and can be useful in
phase transfer catalysis, much like quaternary ammonium salts. Salts or inorganic anions and
tetraphenylphosphonium (PPh+ 4) are soluble in polar organic solvents. One example is the
perrhenate (PPh4[ReO4]).[16]
Reagents for organic synthesis
Wittig reagents are used in
organic synthesis. They are derived from phosphonium salts. A strong base such as
butyllithium or sodium amide is required for the deprotonation:
The compounds Ph3PX2 (X = Cl, Br) are used in the
Kirsanov reaction.[17]
The
Kinnear–Perren reaction is used to prepare alkylphosphonyl dichlorides (RP(O)Cl2) and esters (RP(O)(OR′)2). A key intermediate are alkyltrichlorophosphonium salts, obtained by the alkylation of
phosphorus trichloride:[18]
RCl + PCl3 + AlCl3 → [RPCl3+AlCl− 4
Ammonia production for "green hydrogen"
The main industrial procedure for the production of ammonia today is the thermal
Haber-Bosch process, which generally uses fossil gas as a source of hydrogen, which is then combined with nitrogen to produce ammonia. In 2021, Professor Doug MacFarlane and collaborators Alexandr Simonov and Bryan Suryanto of
Monash University devised a method of producing green ammonia that has the potential to make Haber-Bosch plants obsolete.[19] Their process is similar to the electrolysis approach for producing hydrogen. While working with local company Verdant, which wanted to make bleach from saltwater by electrolysis, Suryanto discovered that a tetraalkyl phosphonium salt allowed the efficient production of ammonia at room temperature.[20]
^Corbridge, D. E. C. (1995). Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology (5th ed.). Amsterdam: Elsevier.
ISBN978-0-444-89307-9.
^Li, T.; Lough, A. J.; Morris, R. H. (2007). "An Acidity Scale of Tetrafluoroborate Salts of Phosphonium and Iron Hydride Compounds in [D2]Dichloromethane". Chem. Eur. J. 13 (13): 3796–3803.
doi:
10.1002/chem.200601484.
PMID17245785.
^
abH.-F. Klein (1978). "Trimethylphosphonium Methylide (Trimethyl Methylenephosphorane)". Inorganic Syntheses. Inorganic Syntheses. Vol. 18. pp. 138–140.
doi:
10.1002/9780470132494.ch23.
ISBN9780470132494.
^Finch, A.; Fitch, A.N.; Gates, P.N. (1993). "Crystal and Molecular structure of a metastable modification of phosphorus pentachloride". Journal of the Chemical Society, Chemical Communications (11): 957–958.
doi:
10.1039/c39930000957.
^Ling-Chung, Sim; Sales, Keith D.; Utley, James H. P. (1990). "Measurement of pKa Values for Phosphonium Salts via the Kinetics of Proton Transfer to an Electrogenerated Base". Journal of the Chemical Society, Chemical Communications (9): 662.
doi:
10.1039/C39900000662.
^S. M. Godfrey; C. A. McAuliffe; R. G. Pritchard; J. M. Sheffield (1996). "An X-ray crystallorgraphic study of the reagent Ph3PCl2; not charge-transfer, R3P–Cl–Cl, trigonal bipyramidal or [R3PCl]Cl but an unusual dinuclear ionic species, [Ph3PCl+⋯Cl–⋯+CIPPh3]Cl containing long Cl–Cl contacts". Chemical Communications (22): 2521–2522.
doi:
10.1039/CC9960002521.
^Dilworth, J. R.; Hussain, W.; Hutson, A. J.; Jones, C. J.; McQuillan, F. S. (1996). "Tetrahalo Oxorhenate Anions". Inorganic Syntheses. Inorganic Syntheses. Vol. XXXI. pp. 257–262.
doi:
10.1002/9780470132623.ch42.
ISBN9780470132623.
^Studies in Organophosphorus Chemistry. I. Conversion of Alcohols and Phenols to Halides by Tertiary Phosphine Dihalides G. A. Wiley, R. L. Hershkowitz, B. M. Rein, B. C. Chung
J. Am. Chem. Soc., 1964, 86 (5), pp 964–965
doi:
10.1021/ja01059a073