[CH2:1]([OH:5])[CH2:2][CH2:3]C.[OH-].[Na+].[CH2:8]([P:10](CCC#N)(=[O:12])[OH:11])[CH3:9].S(=O)(=O)(O)[OH:18]>O>[CH2:8]([P:10]([OH:11])([CH2:3][CH2:2][C:1]([OH:5])=[O:18])=[O:12])[CH3:9]A stirred apparatus is initially charged with 150 g of butanol, 65 g of water, 150 g (3.75 mol) of sodium hydroxide and 183 g (1.25 mol) of ethyl(2-cyanoethyl)-phosphinic acid (produced as in Example 5). The efficiently stirred mixture was heated to about 120° C. and reacted at that temperature for about 6 hours. Then, 250 ml of water were added and the butanol was removed from the reaction mixture by distillation. Following the addition of a further 500 ml of water, the mixture is neutralized by addition of about 184 g (1.88 mol) of concentrated sulfuric acid. The water is then distilled off in vacuo. The residue is taken up in tetrahydrofuran and extracted. The insoluble salts are filtered off. The solvent of the filtrate is removed in vacuo and the residue is recrystallized from acetone to obtain 203 g (98% of theory) of 3-(ethylhydroxyphosphinyl)propionic acid as a solid material.
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