[Na+].[CH2:2]([P:4]([OH:11])([CH2:6][CH2:7][C:8]([O-:10])=[O:9])=[O:5])[CH3:3].S(=O)(=O)(O)O>>[CH2:2]([P:4]([OH:11])([CH2:6][CH2:7][C:8]([OH:10])=[O:9])=[O:5])[CH3:3]In the aqueous solution of 420 g (2 mol) of 3-(ethylhydroxyphosphinyl)propionic acid sodium salt (produced as in Example 12) is rendered acidic with about 196 g of concentrated sulfuric acid and the water is distilled off in vacuo. The residue was taken up in tetrahydrofuran and extracted. The insoluble salts were filtered off. The solvent of the filtrate was removed in vacuo and the residue was recrystallized from acetone to obtain 325 g (98% of theory) of 3-(ethylhydroxyphosphinyl)-propionic acid as colorless solid.
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