Phosphine oxides are phosphorus compounds with the formula OPX₃. When X = alkyl or aryl, these are organophosphine oxides.  Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl₃). Such compounds are thermally stable, decomposing only above 450 °C. Phosphoryl refers to a functional group drawn with a phosphorus-oxygen double bond.