Triphenylphosphine - Principal Reactions With Chalcogens, Halogens, and Acids

Principal Reactions With Chalcogens, Halogens, and Acids

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 hot 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 imido analogue of OPPh₃ via the Staudinger reaction:

PPh₃ + PhN₃ → PhNPPh₃ + N₂

The product imides can be hydrolyzed to the amine. Typically the intermediate imidophosphorane is not isolated.

PPh₃ + RN₃ + H₂O → OPPh₃ + N₂ + RNH₂

Cl₂ adds to PPh₃ to give triphenylphosphine dichloride (Cl), which exists as the moisture-sensitive phosphonium halide, This reagent is used to convert alcohols to alkyl chlorides in organic synthesis.

PPh₃ is a weak base, but does form stable salts with strong acids such as HBr. The product contains the phosphonium cation +.