Triphenylphosphine oxide

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Triphenylphosphine oxide
Triphenylphosphine oxide
Triphenylphosphine oxide
CAS number 791-28-6 YesY
PubChem 13097
ChemSpider 12549 YesY
ChEBI CHEBI:36601 YesY
RTECS number SZ1676000
Jmol-3D images Image 1
Molecular formula C18H15OP
Molar mass 278.29 g/mol
Appearance white crystals
Melting point 154-158 °C (427-429 K)
Boiling point 360 °C (633 K)
Solubility in water low
Solubility in other solvents polar organic solvents
Molecular shape tetrahedral
R-phrases 22-36/37/38
S-phrases 26
Main hazards slight
Related compounds
Related compounds P(C6H5)3S;

P(C6H5)3; POCl3; PCl5

Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound with the formula OP(C6H5)3. Often chemists abbreviate the formula by writing Ph3PO or PPh3O (Ph = C6H5). This colourless crystalline compound is a common side product in reactions involving triphenylphosphine. It is a popular reagent to induce the crystallizing of chemical compounds.

Structure and properties[edit]

Ph3PO is tetrahedral molecule related to POCl3.[1] The oxygen center is relatively basic. The rigidity of the backbone and the basicity of the oxygen center make this species a popular agent to crystallize otherwise difficult to crystallize molecules. This trick is applicable to molecules that have acidic hydrogen atoms, e.g. phenols.[2]

As a by-product of organic synthesis[edit]

Ph3PO is a by-product of many useful reactions in organic synthesis including the Wittig, Staudinger, and Mitsunobu reactions. It is also formed when PPh3Cl2 is employed to convert alcohols into alkyl chlorides.

Ph3PCl2 + ROH → Ph3PO + HCl + RCl

Triphenylphosphine can be regenerated from the oxide by treatment with trichlorosilane.

Ph3PO + SiHCl3 → PPh3 + 1/n (OSiCl2)n + HCl

Triphenylphosphine oxide can be difficult to remove from reaction mixtures by means of chromatography. It is poorly soluble in hexane and cold diethyl ether. Trituration or chromatography of crude products with these solvents often leads to a good separation of triphenylphosphine oxide.

Coordination chemistry[edit]


Ph3PO is an excellent ligand for "hard" metal centers. A typical complex is the tetrahedral species NiCl2(OPPh3)2.[3]

Ph3PO is a common impurity in PPh3. The oxidation of PPh3 by oxygen, including air, is catalyzed by many metal ions:

2 PPh3 + O2 → 2 Ph3PO


  1. ^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.
  2. ^ M. C. Etter and P. W. Baures (1988). "Triphenylphosphine oxide as a crystallization aid". J. Am. Chem. Soc. 110 (2): 639–640. doi:10.1021/ja00210a076. 
  3. ^ D. M. L. Goodgame and M. Goodgame (1965). "Near-Infrared Spectra of Some Pseudotetrahedral Complexes of Cobalt (II) and Nickel(II)". Inorg. Chem. 4 (2): 139–143. doi:10.1021/ic50024a002. 

Other reading[edit]