Triphenylphosphine oxide

Triphenylphosphine oxide is the chemical compound with the formula OP(C6H5)3. Often chemists abbreviate the formula by writing Ph3PO or PPh3O (Ph = C6H5). This white 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
Ph3PO is tetrahedral molecule related to POCl3. 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.

As a by-product of organic synthesis
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  &rarr;  Ph3PO  +  HCl  +  RCl

Triphenylphosphine can be regenerated from the oxide by treatment with trichlorosilane.
 * Ph3PO +  SiHCl3  &rarr;  PPh3  +  1/n (OSiCl2)n  +  HCl

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

Ph3PO is a common impurity in PPh3. The oxidation of PPh3 by oxygen, including air, is catalyzed by many metal ions:
 * 2 PPh3 +  O2  &rarr;  2 Ph3PO

Other reading

 * Triphenylphosphine oxide at Chemexper.com