Triphenylphosphine

Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether. Triphenylphosphine can be prepared in the laboratory by treatment of phosphorus trichloride with phenylmagnesium bromide or phenyllithium. The industrial synthesis involves the reaction between phosphorus trichloride, chlorobenzene, and sodium: PCl3 + 3 PhCl + 6 Na → PPh3 + 6 NaCl Triphenylphosphine crystallizes in triclinic and monoclinic modification. In both cases, the molecule adopts a pyramidal structure with propeller-like arrangement of the three phenyl groups. Triphenylphosphine undergoes slow oxidation by air to give triphenylphosphine oxide, Ph3PO: 2 PPh3 + O2 → 2 OPPh3 This impurity can be removed by recrystallisation of PPh3 from either hot ethanol or isopropanol. This method capitalizes on the fact that OPPh3 is more polar and hence more soluble in polar solvents than PPh3. Triphenylphosphine abstracts sulfur from polysulfide compounds, episulfides, and elemental sulfur. Simple organosulfur compounds such as thiols and thioethers are unreactive, however. The phosphorus-containing product is triphenylphosphine sulfide, Ph3PS. This reaction can be employed to assay the "labile" S0 content of a sample, say vulcanized rubber. Triphenylphosphine selenide, Ph3PSe, may be easily prepared via treatment of PPh3 with red (alpha-monoclinic) Se. Salts of selenocyanate, SeCN−, are used as the Se0 source. PPh3 can also form an adduct with Te, although this adduct primarily exists as (Ph3P)2Te rather than PPh3Te. Aryl azides react with PPh3 to give phosphanimines, analogues of OPPh3, via the Staudinger reaction. Illustrative is the preparation of triphenylphosphine phenylimide: PPh3 + PhN3 → PhNPPh3 + N2 The phosphanimine can be hydrolyzed to the amine.