Chlorodiphenylphosphine Explained

Chlorodiphenylphosphine is an organophosphorus compound with the formula (C₆H₅)₂PCl, abbreviated Ph₂PCl. It is a colourless oily liquid with a pungent odor that is often described as being garlic-like and detectable even in the ppb range. It is useful reagent for introducing the Ph₂P group into molecules, which includes many ligands.^[1] Like other halophosphines, Ph₂PCl is reactive with many nucleophiles such as water and easily oxidized even by air.

Synthesis and reactions

Chlorodiphenylphosphine is produced on a commercial scale from benzene and phosphorus trichloride (PCl₃). Benzene reacts with phosphorus trichloride at extreme temperatures around 600 °C to give dichlorophenylphosphine (PhPCl₂) and HCl. Redistribution of PhPCl₂ in the gas phase at high temperatures results in chlorodiphenylphosphine.^[1]

2PhPCl₂ → Ph₂PCl + PCl₃Alternatively such compounds are prepared by redistribution reactions starting with triphenylphosphine and phosphorus trichloride.

PCl₃ + 2PPh₃ → 3Ph₂PCl

Chlorodiphenylphosphine hydrolyzes to give diphenylphosphine oxide. Reduction with sodium affords tetraphenyldiphosphine:

2Ph₂PCl + 2Na → [Ph₂P]₂ + 2NaCl

With ammonia and elemental sulfur, it converts to the thiophosphorylamide:^[2]

Ph₂PCl + 2NH₃ + S → Ph₂P(S)NH₂ + NH₄Cl

Uses

Chlorodiphenylphosphine, along with other chlorophosphines, is used in the synthesis of various phosphines. A typical route uses Grignard reagents:^[3]

Ph₂PCl + MgRX → Ph₂PR + MgClX

The phosphines produced from reactions with Ph₂PCl are further developed and used as pesticides (such as EPN), stabilizers for plastics (Sandostab P-EPQ), various halogen compound catalysts, flame retardants (cyclic phosphinocarboxylic anhydride), as well as UV-hardening paint systems (used in dental materials) making Ph₂PCl an important intermediate in the industrial world.^{[1] [3]}

Precursor to diphenylphosphido derivatives

Chlorodiphenylphosphine is used in the synthesis of sodium diphenylphosphide via its reaction with sodium metal in refluxing dioxane.^[4]

Ph₂PCl + 2 Na → Ph₂PNa + NaCl

Diphenylphosphine can be synthesized in the reaction of Ph₂PCl and LiAlH₄, the latter usually used in excess.^[5]

4 Ph₂PCl + LiAlH₄ → 4 Ph₂PH + LiCl + AlCl₃Both Ph₂PNa and Ph₂PH are also used in the synthesis of organophosphine ligands.

Characterization

The quality of chlorodiphenylphosphine is often checked by 31P NMR spectroscopy.^[6]

Compound	^31P chemical shift(ppm vs 85% H3PO4)
PPh3	-6
PPh2Cl	81.5
PPhCl2	165
PCl3	218

Notes and References

1. Quin, L. D. A Guide to Organophosphorus Chemistry; Wiley IEEE: New York, 2000; pp 44-69.
2. 10.15227/orgsyn.094.0313. Catalytic Enantioselective Addition of Diethyl Phosphite to N-Thiophosphinoyl Ketimines: Preparation of (R)-Diethyl (1-Amino-1-phenylethyl)phosphonate. 2017. Lin. Shaoquan. Yasunari. Otsuka. Liang. Yin. Naoya. Kumagai. Masakatsu. Shibasaki. Organic Syntheses. 94. 313–331. free.
3. Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic," In 'Ullmann's Encyclopedia of Industrial Chemistry, 7th ed.; Wiley-VCH: 2008; ; Accessed: February 18, 2008.
4. 10.1071/CH9850111 . Roy . Jackson W . Thomson . RJ . MacKay . M.F. . The Stereochemistry of Organometallic Compounds. XXV. The Stereochemistry of Displacements of Secondary Methanesulfonate and p-Toluene-sulfonate esters by Diphenylphosphide Ions. X-ray Crystal Structure of (5α-Cholestan-3α-yl)diphenylphosphine Oxide . . 1985 . 38 . 1 . 111–18.
5. 10.1021/om9005615 . Stepanova . Valeria A. . Dunina . Valery V. . Smoliakova . Irina P. . Reactions of Cyclopalladated Complexes with Lithium Diphenylphosphide . . 2009 . 28 . 22 . 6546–6558.
6. O. Kühl "Phosphorus-31 NMR Spectroscopy" Springer, Berlin, 2008.