PROCESS FOR THE MANUFACTURE OF MONTELUKAST SODIUM

An improved process for the manufacture of 1-[[[(1R)-1-[3-[(1E)-2-(7-chloro-2-quinolinyl)ethenyl]phenyl]-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropane acetic acid, sodium salt [montelukast sodium(I)]. It consists of converting a vital intermediate 1-(mercaptomethyl)-cyclopropane acetic acid of formula IX, to a quaternary ammonium salt of formula X, using a suitable base in a suitable solvent at 0° C. to 50° C. followed by monometalation to provide an intermediate of formula XI and subsequent condensation of XI with 2-[2-[3-(S)-[3-[2-(7-chloro-2-quinolinyl)-ethenyl]phenyl]-3-methanesulphonyloxypropyl]phenyl]-2-propanol at 0 to -50° C. to afford 1-[[[(1R)-1-[3-[(1E)-2-(7-chloro-2-quinolinyl)ethenyl]phenyl]-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropane acetic acid as the quaternary ammonium salt which is filtered, purified by crystallization from a suitable solvent and finally treated with a sodium base in a suitable solvent to generate montelukast sodium which is isolated by trituration with an antisolvent. The invention provides a convenient process for preparing montelukast sodium (I) in good yields and purities.