Diethylphosphine oxide is primarily used as a key intermediate in organic synthesis, particularly in the production of organophosphorus compounds. It serves as a precursor for the development of flame retardants, which are widely applied in textiles, plastics, and electronics to enhance fire resistance. Additionally, it plays a role in the synthesis of ligands for catalysis, aiding in various chemical reactions, including hydrogenation and polymerization processes. Its applications also extend to the pharmaceutical industry, where it is utilized in the creation of bioactive molecules and drug candidates. Furthermore, it finds use in agrochemical research for the development of pesticides and herbicides.