Diphenylphosphine

Diphenylphosphine, also known as diphenylphosphane, is an organophosphorus compound with the formula (C6H5)2PH. This foul-smelling, colorless liquid is easily oxidized in air. It is a precursor to organophosphorus ligands for use as catalysts.

Diphenylphosphine
Names
IUPAC name
diphenylphosphane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.011.447
EC Number
  • 212-591-4
UNII
Properties
C12H11P
Molar mass 186.19 g/mol
Appearance colorless liquid
Density 1.07 g/cm3, liquid
Boiling point 280 °C (536 °F; 553 K)
Insoluble
Hazards
Safety data sheet External MSDS
GHS pictograms
GHS Signal word Danger
H250, H315, H319, H335
P210, P222, P261, P264, P271, P280, P302+334, P302+352, P304+340, P305+351+338, P312, P321, P332+313, P337+313, P362, P370+378, P403+233, P405, P422, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Diphenylphosphine can be prepared from triphenylphosphine by reduction to lithium diphenylphosphide, which can be protonated to give the title compound:[1]

PPh3 + 2 Li → LiPPh2 + LiPh
LiPPh2 + H2O → Ph2PH + LiOH

Uses and reactions

In the laboratory, diphenylphosphine is a common intermediate. It can be deprotonated to give diphenylphosphide derivatives:[2]

Ph2PH + nBuLi → Ph2PLi + nBuH

The preparation of phosphine ligands, Wittig-Horner reagents, and phosphonium salts are commonly accomplished by alkylating diphenylphosphine. The hydrogen atom connected to phosphorus undergoes Michael-like addition to activated alkenes, providing products with which to produce phosphine ligands such as 1,2-bis(diphenylphosphino)ethane (Ph2PC2H4PPh2). Diphenylphosphine and especially diphenylphosphide derivatives are nucleophiles, so they add to carbon – heteroatom double bonds.[2] For example, in the presence of concentrated hydrochloric acid at 100 °C, diphenylphosphine adds to the carbon atom in benzaldehyde to give (phenyl-(phenylmethyl)phosphoryl)benzene.

Ph2PH + PhCHO → Ph2P(O)CH2Ph

Compared to tertiary phosphines, diphenylphosphine is weakly basic. The pKa of the protonated derivative is 0.03:[3]

Ph2PH2+ ⇌ Ph2PH + H+

Handling properties

Diphenylphosphine readily oxidizes.[4]

Ph2PH + O2 → Ph2P(O)OH

An intermediate in this oxidation is diphenylphosphine oxide. The use of the diphenylphosphine–borane complex, Ph2PH•BH3 avoids the problem of phosphine oxidation by protecting the phosphine from oxidation and is available through chemical vendors.[2]

References
  1. V. D. Bianco; S. Doronzo (1976). "Diphenylphosphine". Inorganic Syntheses. 16: 161–188. doi:10.1002/9780470132470.ch43.
  2. Piotrowski, D. W. (2001). "Diphenylphosphine". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rd427.
  3. C. A. Streuli, "Determination of Basicity of Substituted Phosphines by Nonaqueous Titrimetry", Analytical Chemistry 1960, volume 32, pages 985-987.doi:10.1021/ac60164a027
  4. Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_545.pub2.
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