Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula O=P(C 6H 5) 3, also written as Ph 3PO or PPh 3O (Ph = C 6H 5). It is one of the more common phosphine oxides. This colourless crystalline compound is a common but potentially useful waste product in reactions involving triphenylphosphine. It is a popular reagent to induce the crystallizing of chemical compounds.
Ph 3PO is structurally related to POCl 3.[2]
As established by X-ray crystallography, the geometry around P is tetrahedral, and the P-O distance is 1.48 Å.[3] Other modifications of Ph 3PO have been found: For example, a monoclinic form crystallizes in the space group P21/c with Z = 4 and a = 15.066(1) Å, b = 9.037(2) Å, c = 11.296(3) Å, and β = 98.47(1)°.The orthorhombic modification crystallizes in the space group Pbca with Z = 4 and 29.089(3) Å, b = 9.1347(9), c = 11.261(1) Å.[4]
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.[5]
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. Its removal is facilitated by conversion to its Mg(II)complex, which is poorly soluble in toluene or dichloromethane and can be filtered off.[7] An alternative filtration method where ZnCl 2(TPPO) 2 is formed upon addition of ZnCl 2 may be used with more polar solvents such as ethanol, ethyl acetate and tetrahydrofuran.[8]
↑Al-Farhan, Khalid A. (1992). "Crystal structure of triphenylphosphine oxide". Journal of Crystallographic and Spectroscopic Research22 (6): 687–689. doi:10.1007/BF01160986.
↑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.
↑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.