Diphenylphosphine oxide is an organophosphorus compound with the formula (C6H5)2P(O)H. It is a white solid that soluble in polar organic solvents.

[1] Diphenylphosphine oxide can be prepared by the reaction of phosphonic esters, such as diethylphosphite, with Grignard reagents followed by acid workup:[2] Alternatively, it may be prepared by the partial hydrolysis of chlorodiphenylphosphine[1] or diphenylphosphine.

[3] Diphenylphosphine oxide exists in equilibrium with its minor tautomer diphenylphosphinous acid, ((C6H5)2POH: Diphenylphosphine oxide is used in Buchwald-Hartwig coupling reactions to introduce diphenylphosphino substituents.

[1] Thionyl chloride converts diphenylphosphine oxide to chlorodiphenylphosphine.

Organophosphinous acids are deoxygenated with DIBAH.