Sodium Hydroxide → Alendronate sodium anhydrous

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Reaction Steps

A one liter flask was fitted with a mechanical stirrer, a thermometer, and a reflux condenser. The flask was charged with alendronic acid monohydrate (25 g, 0.094 mol) and aqueous ethanol. The mixture was heated to boiling with stirring. The aqueous ethanolic sodium hydroxide was added dropwise to the suspension of alendronic acid monohydrate in aqueous ethanol for 3 hours at reflux with vigorously stirring. Then the mixture was stirred at reflux for additional 15 hours. The mixture was cooled to room temperature with stirring. The solid was filtered, washed with absolute ethanol, then with absolute ethyl ether, and dried overnight in a vacuum oven (10-15 mm Hg, 40-50° C.) to give 26.2 g of alendronate sodium, having crystalline Form G.

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