Synthesis, purification, and characterization of phosphine oxides and their hydrogen peroxide adducts

Abstract

Reactions of the tertiary phosphines R₃P (R = Me, Bu, Oct, Cy, Ph) with 35% aqueous H₂O₂ gives the corresponding oxides as the H₂O₂ adducts R₃PO·(H₂O₂)_x (x = 0.5–1.0). Air oxidation leads to a mixture of products due to the insertion of oxygen into one or more P–C bonds. ³¹P NMR spectroscopy in solution and in the solid state, as well as IR spectroscopy reveal distinct features of the phosphine oxides as compared to their H₂O₂ adducts. The single crystal X-ray analyses of Bu₃PO and [Cy₃PO·(H₂O₂)]₂ show a PO stacking motif for the phosphine oxide and a cyclic structure, in which the six oxygen atoms exhibit a chair conformation for the dimeric H₂O₂ adduct. Different methods for the decomposition of the bound H₂O₂ and the removal of the ensuing strongly adsorbed H₂O are evaluated. Treating R₃PO·(H₂O₂)_x with molecular sieves destroys the bound H₂O₂ safely under mild conditions (room temperature, toluene) within one hour and quantitatively removes the adsorbed H₂O from the hygroscopic phosphine oxides within four hours. At 60 °C the entire decomposition/drying process is complete within one hour.