Molar mass 278.29 g/mol Boiling point 360 °C | Formula C18H15OP Appearance white crystals | |
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Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound with the formula OP(C6H5)3, also written as 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.
Contents
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 → Ph3PO + HCl + RClTriphenylphosphine can be regenerated from the oxide by treatment with trichlorosilane.
Ph3PO + SiHCl3 → PPh3 + 1/n (OSiCl2)n + HClTriphenylphosphine 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. One tip for its removal when solving in either toluene or dichloromethane is to add freshly milled magnesium chloride and stir for 20h at 30-35 °C to form a complex, which upon cooling can be filtered off (expect about 95% removal of triphenylphosphine oxide). This is truly a complex as the XRPD of the solid differs from either triphenylphosphine oxide or magnesium chloride and has a solubility in toluene of just 2.1 mg/ml (57 mg /ml for DCM). See WO 1998007724.
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 → 2 Ph3PO