Tetraphenylphosphonium chloride explained

Tetraphenylphosphonium chloride is the chemical compound with the formula, abbreviated or or, where Ph stands for phenyl. Tetraphenylphosphonium and especially tetraphenylarsonium salts were formerly of interest in gravimetric analysis of perchlorate and related oxyanions. This colourless salt is used to generate lipophilic salts from inorganic and organometallic anions. Thus, is useful as a phase-transfer catalyst, again because it allows inorganic anions to dissolve in organic solvents.

Structure and basic properties

The structure of this salt is . It consists of tetraphenylphosphonium cations and chloride anions . The cation is tetrahedral.

PPh₄Cl crystallises as the anhydrous salt,^[1] which is the normal item of commerce, as well as a monohydrate^[2] and a dihydrate.^[3]

In X-ray crystallography, salts are of interest as they often crystallise easily. The rigidity of the phenyl groups facilitates packing and elevates the melting point relative to alkyl-based quaternary ammonium salts. Also, since these salts are soluble in organic media, a wide range of solvents can be employed for their crystallisation.

Preparation

and many analogous compounds can be prepared by the reaction of chlorobenzene with triphenylphosphine catalysed by nickel salts:^[4]

The compound was originally prepared as the corresponding bromide salt (CAS No. 2751-90-8), which in turn was synthesized by passing dry oxygen through the reaction of phenylmagnesium bromide and triphenylphosphine.^[5] The synthesis probably proceeds via the reaction of the Grignard reagent with triphenylphosphine oxide.

Use in synthesis

Tetraphenylphosphonium salts of inorganic or organometallic anions are often sought because they are easily crystallized. They also tend to be soluble in polar organic solvents such as acetonitrile and dimethylformamide. Examples include the tetraphenylphosphonium perrhenate ^[6] and various thiomolybdates.^[7] Complexes of maleonitriledithiolate are also isolated as their salts.^[8]

Notes and References

1. J. F. . Richardson . J. M. . Ball . P. M. . Boorman . Structure of Tetraphenylphosphonium Chloride . Acta Crystallographica . 1986 . C42 . 9 . 1271–1272 . 10.1107/S0108270186092612. 1986AcCrC..42.1271R .
2. E. E. . Schweizer . C. J. . Baldacchini . A. L. . Rheingold . Tetraphenylphosphonium Chloride Monohydrate, Tetraphenylphosphonium Bromide and Tetraphenylphosphonium Iodide . Acta Crystallographica . 1989 . C45 . 8 . 1236–1239 . 10.1107/S0108270189000363. 1989AcCrC..45.1236S .
3. A. J. . Blake . C. D. . Garner . J. M. . Tunney . Tetraphenylphosphonium Chloride Dihydrate . Acta Crystallographica . 2003 . E59 . 1 . o9–o10 . 10.1107/S1600536802021682. 2003AcCrE..59O...9B .
4. David . Marcoux . André B. . Charette . Nickel-Catalyzed Synthesis of Phosphonium Salts from Aryl Halides and Triphenylphosphine . Adv. Synth. Catal. . 2008 . 350 . 18 . 2967–2974 . 10.1002/adsc.200800542.
5. Dodonow . J. . Medox . H. . Zur Kenntnis der Grignardschen Reaktion: Über die Darstellung von Tetraphenyl-phosphoniumsalzen . Berichte der Deutschen Chemischen Gesellschaft . 1928 . 61 . 5 . 907–911 . 10.1002/cber.19280610505.
6. Book: 10.1002/9780470132623.ch42. Tetrahalo Oxorhenate Anions. 1996. Dilworth. J. R.. Hussain. W.. Hutson. A. J.. Jones. C. J.. McQuillan. F. S.. Inorganic Syntheses. 257–262. XXXI. 9780470132623.
7. Book: 10.1002/9780470132586.ch8. Tetraphenylphosphonium Salts of [Mo₂(S)_n(S₂)_6-n]^2- Thioanions and Derivatives. Inorganic Syntheses. 1990. Hadjikyriacou. A. I.. Coucouvanis. D.. Tetraphenylphosphonium Salts of [Mo2 (S) N (S2)6-N ]2- Thioanions and Derivatives. 39–47volume=XXVII. 9780470132586.
8. Book: 10.1002/9780470132449.ch39. Bis[cis-1,2-Dicyanoethene-1,2-dithiolato(1- or 2-)] Complexes of Cobalt and Iron. Inorganic Syntheses. 1972. Bray. J.. Locke. J.. McCleverty. J. A.. Coucouvanis. D.. Bis[cis -1,2-dicyanoethene-1,2-dithiolato(1- or 2-)] Complexes of Cobalt and Iron. XIII. 187–195. 9780470132449.