Phosphinous acid is the inorganic compound with the formula H2POH. It exists, fleetingly, as a mixture with its less stable tautomer H3PO (phosphine oxide). These species have been generated by low temperature oxidation of phosphine with ozone. H2POH is mainly of pedagogical interest. Many phosphinous acids are known as minor tautomers of stable dialkyl-phosphine oxides; for example diphenylphosphinous acid is the tautomer of diphenylphosphine oxide. Phosphinous acid is the inorganic compound with the formula H2POH. It exists, fleetingly, as a mixture with its less stable tautomer H3PO (phosphine oxide). These species have been generated by low temperature oxidation of phosphine with ozone. H2POH is mainly of pedagogical interest. Many phosphinous acids are known as minor tautomers of stable dialkyl-phosphine oxides; for example diphenylphosphinous acid is the tautomer of diphenylphosphine oxide.