Ethyl 3-amino-2-methylpropyl(diethoxymethyl)phosphinate → 3-Amino-2-methylpropylphosphonous acid monohydrate

A solution of 6.0 g of ethyl 3-amino-2-methylpropyl(diethoxymethyl)phosphinate in 30 ml of 36% aqueous hydrochloric acid is heated to reflux for a period of 7 hours. The reaction mixture is then allowed to cool to room temperature, concentrated under reduced pressure and co-evaporated twice with 10 ml water under reduced pressure and co-evaporated twice with 10 ml of water under reduced pressure. The crude product is dissolved in 50 ml of dry ethanol and 5 ml of propylene oxide is added dropwise. The precipitated solid is collected by filtration and dried to give 3-amino-2-methylpropylphosphonous acid monohydrate, m.p. 96°-100° C., 31P=+25.8 ppm (D2O).