Preparation of warfarin sodium from warfarin acid

A method for producing warfarin sodium comprising the steps of:

• reacting warfarin acid with sodium carbonate at a temperature of less than about 30° C. in absolute ethanol,
• heating the resulting solution to a temperature of between about 30° C. and about 35° C.,
• removing insoluble salts by filtration at room temperature,
• adjusting the pH to a value of from about 7.8 to about 8.1,
• removing the absolute ethanol by evaporation at a temperature of not more than about 50° C. to form a syrup,
• pouring the syrup into evaporation trays,
• removing additional absolute ethanol in a vacuum at a temperature of less than about 70° C. until a solid forms,
• removing the solid from the vacuum and grinding the solid into a fine powder, and
• removing any remaining solvent in a vacuum at a temperature of less than about 70° C. to produce pure warfarin sodium,
• wherein the ratio of molar equivalents of sodium carbonate to warfarin acid is from about 1.1:1 to about 1.5:1.

A method for producing pure warfarin sodium comprising the steps of:

• step for providing pure warfarin acid, a volatilizable base, and a polar organic solvent,
• step for producing crude warfarin sodium from the warfarin acid and the base in the polar organic solvent at ambient temperature,
• step for removing solid impurities from said crude warfarin sodium, and
• step for obtaining a pH in a range of from about 7.8 to about 8.1, to produce a pure warfarin sodium,
• wherein the inorganic base is selected from the group consisting of sodium carbonate and sodium bicarbonate, and
• wherein the polar solvent contains less than about 10% water and does not produce a clathrate, cause decomposition or promote back-reaction under the conditions for producing crude warfarin sodium.