Propylene Oxide → 3-Aminopropyl(isobutyl)phosphinic acid

A mixture of 14.76 g (0.12 mol) of 3-aminopropylphosphonous acid and 96.72 g (0.6 mol) of hexamethyldisilazane is refluxed under an atmosphere of argon with stirring for 16 hours to give a solution. To this solution are added at reflux 60 ml of diethyleneglycol dimethylether and the solution is refluxed for additional 2 hours. The reaction is cooled to 120° and 38.75 g (0.3 mol) of N-ethyl-diisopropyl-amine are added within 20 minutes followed by addition of 54.06 g (0.3 mol) of isobutyl iodide over a period of 20 minutes. The reaction mixture is heated with stirring for 22 hours. After cooling to 10°, the white precipitate is filtered off and the filtrate is evaporated under reduced pressure. The clear solution is cooled, diluted with dichloromethane (300 ml) and extracted three times with 2N hydrochloric acid (3×100 ml). The combined hydrochloric acid-extracts are evaporated in vacuo to dryness, and re-evaporated twice with water (2×100 ml) to give a white solid, which is suspended in 600 ml of acetone and stirred for 1 hour at 20°. 3-Aminopropyl(isobutyl)phosphinic acid hydrochloride (25.3 g),m.p. 149°=155°, is isolated by filtration. After recrystallisation from n-propanol/acetone (200/100 ml) pure 3-aminopropyl(isobutyl)phosphinic acid hydrochloride of m.p. 154°-156°, is obtained. 15.4 g of 3-aminopropyl(isobutyl)phosphinic acid hydrochloride are dissolved in 75 ml of methanol and 300 ml of propylenoxide are added with stirring. After standing overnight at 4°, a white solid precipitates. The precipitate is collected by filtration and recrystallized from n-propanol to give pure 3-aminopropyl(isobutyl)phosphinic acid, m.p. 250°-253° (dec.).