VERFAHREN ZUR AUFREINIGUNG VON MONTELUKAST

It relates to a process for the purification of Montelukast, or pharmaceutically salts thereof, or solvates thereof, including stereoisomers or mixture thereof which comprises carrying out a specific set of selective solvent extractions of Montelukast or its impurities in a mixture of an organic solvent and water at specific ranges of pH and temperature which depend on the type of impurities to remove. In particular, it comprises at least one wash of an aqueous phase containing crude Montelukast in salt form with an organic solvent, at a pH comprised between 12.0 and 13.5; and optionally one or more washes of the resulting aqueous phase with an organic solvent at a pH comprised between 8.5 and 10.0. Montelukast is recovered by acidification at a pH comprised between 4.5 and 8.0 and solvent extraction, and is isolated either as acid or in salt form.