Patent ID: 8524912

Claim:
A process for preparation of [1-hydroxy-2-(1 H -imidazol-1yl)-ethylidene] bisphosphonic acid monohydrate in a reaction of 1H-imidazole-1-acetic acid with phosphorus trichloride, said process comprising: a) reacting an aqueous solution of 1H-imidazole-1-acetic acid hydrochloride with phosphorus trichloride, wherein the aqueous solution of 1H-imidazole-1-acetic acid hydrochloride is added to phosphorus trichloride, b) removing excess phosphorus trichloride, c) adding water and hydrolyzing reaction products, d) filtering post reaction mixture, e) adding anti-solvent to the filtrate, f) isolating [1-hydroxy-2-(1 H -imidazol-1-yl)-ethylidene] bisphosphonic acid monohydrate from the suspension.