[Na:1].[NH2:2][C:3]([P:9]([OH:12])(=[O:11])[OH:10])([P:5]([OH:8])(=[O:7])[OH:6])[CH3:4].[C:13](OC(=O)C)(=[O:15])[CH3:14]>O>[Na:1].[C:13]([NH:2][C:3]([P:5]([OH:8])(=[O:6])[OH:7])([P:9]([OH:12])(=[O:10])[OH:11])[CH3:4])(=[O:15])[CH3:14]22.7 g. (0.1 mole) of the mono-sodium salt of 1-amino ethane-1,1-diphosphonic acid are boiled under reflux in 30.6 g. (0.3 moles) of acetic acid anhydride for about 30 minutes. A clear solution is obtained. On cooling, a viscous yellowish sirup is produced. The sirup can be diluted with water and the aqueous solution can be used directly. In order to recover the crystalline reaction product, the sirup is added with stirring to 40 cc. of glacial acetic acid and the resulting crystalline product is filtered off by suction. After drying, 20.3 g. of the mono-sodium salt of N-acetyl-1-amino ethane-1,1-diphosphonic acid, corresponding to 75.4 % of the theoretical yield, are obtained.
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