text: Dialkylphosphinic acids have the formula RPOH, where R is an alkyl or aryl group. The phosphorus(V) center has tetrahedral molecular geometry. Under the brand names Aerophine and Cyanex, dialkylphosphinic acids are used in extraction and separation of metals as one of the techniques of hydrometallurgy Characteristically the organic substituents are branched to confer solubility and preclude crystallization.
  Formaldehyde and HPO react to give (HOCH)POH.