PROCESS FOR THE PREPARATION OF MONTELUKAST AND ITS SALTS

1 . A process for the preparation of Montelukast free acid and its alkali salts without the formation of unstable or limited stable intermediates comprising:

reacting methyl 2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl-3-halopropyl]benzoate with 1-(mercapto methyl)cyclopropane acetic acid in the presence of alkali hydrides or alkoxides to yield 2-[1-[1(R)-[3-[2-(7-chloroquinolin-2-yl)ethenyl]phenyl]-3-[2-(methoxycarbonyl)phenyl]propyl sulfanyl methyl]cyclopropane acetic acid, which on reaction with a Grignard reagent gives Montelukast free acid or, optionally,

reacting methyl 2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]benzoate with a Grignard reagent to yield 2-[2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]phenyl-2-propanol, which on condensation with 1-(mercaptomethyl)cyclopropane acetic acid in the presence of alkali hydrides or alkoxides gives Montelukast free acid, and

isolating the Montelukast as Montelukast free acid or Montelukast organic base salts.

2 . A process as claimed in claim 1 wherein the term halo in methyl-2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]benzoate or 2-[2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]phenyl-2-propanolrepresents chloro, bromo or iodo.

3 . A process as claimed in claim 1 , wherein the alkali hydride is sodium hydride or the alkali alkoxide is potassium tert-butoxide.

4 . A process as claimed in claim 1 , wherein the reaction of methyl 2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]benzoate (halo ester) with 1-(mercapto methyl)cyclopropane acetic acid is carried out in the presence of a solvent.

5 . A process as claimed in claim 4 , wherein the solvent is dimethyl formamide or tetrahydrofuran.

6 . A process as claimed in claim 1 , wherein the reaction of 2-[2-[(3S)-[3-[(2E)-(7-chloro quinolin-2-yl)ethenyl]phenyl]-3-halopropyl]phenyl-2-propanol with 1-(mercaptomethyl)cyclopropane acetic acid is carried out in an organic solvent.

7 . A process as claimed in claim 6 , wherein the organic solvent is dimethyl formamide or tetrahydrofuran.

8 . A process as claimed in claim 1 , wherein 2-[1-[1(R)-[3-[2-(7-chloroquinolin-2-yl)ethenyl]phenyl]-3-[2-(methoxycarbonyl)phenyl]propyl sulfanyl methyl]cyclopropane]acetic acid is isolated as its organic base salt.

9 . A process as claimed in claim 8 , wherein the 2-[1-[1(R)-[3-[2-(7-chloroquinolin-2-yl)ethenyl]phenyl]-3-[2-(methoxycarbonyl)phenyl]propyl sulfanyl methyl]cyclopropane]acetic acid organic base salt is the dicyclohexyl amine salt.

10 . A process as claimed in claim 1 , wherein the Grignard reagent is selected from methyl magnesium chloride and methyl magnesium bromide.

11 . A process as claimed in claim 1 , wherein the Montelukast organic base salts are selected from Montelukast dipropylamine salt. Montelukast alpha methylbenzylamine salt. Montelukast dibenzylamine salt. Montelukast dicyclohexylamine salt and Montelukast di-isopropylamine salt.

12 . A process for the preparation of Montelukast organic base salts from Montelukast free acid comprising:

dissolving Montelukast free acid obtained by the process of claim 1 in ethyl acetate,

cooling the reaction mass to a temperature of 20° C. to 35° C.;

adding an organic base;

maintaining the reaction mass at this temperature for 10 hrs to 36 hrs;

adding a second solvent;

mixing the reaction mass for 2 hrs to 18 hrs; and

isolating and drying of Montelukast organic base salts.

13 . A process as claimed in claim 12 , wherein the organic base is dicyclohexylamine, dipropylamine, di-isopropylamine, dibenzylamine or alpha methyl benzylamine.

14 . A process as claimed in claim 12 , wherein the second solvent is a C-5 to C-7 hydrocarbon.

15 . A process for the preparation of Montelukast sodium from Montelukast free acid comprising

dissolving Montelukast free acid obtained by the process of claim 42 in methanol;

cooling the reaction mass to a temperature of 20° C. to 35° C.;

adding a sodium hydroxide solution in ethanol;

maintaining the reaction mass at this temperature for 30 min to 2 hrs;

removing the solvents at a temperature below 40° C.;

adding toluene to the residue;

dissolving the residue in toluene by raising the temperature to 40° C. to 60° C.;

cooling the reaction mass to a temperature of 20° C. to 35° C.;

pouring the toluene solution into n-heptane at a temperature of 20° C. to 35° C.;

mixing the reaction mass for 2 hrs to 18 his; and

isolating and drying of Montelukast sodium.

16 . A process for the preparation of Montelukast sodium from a Montelukast organic base salt comprising:

suspending the Montelukast organic base salt obtained by the process of claim 70 in a mixture of water and methylene chloride;

adding an acetic acid solution;

separating the layers;

washing the organic layer with water;

adding a sodium hydroxide solution in ethanol;

removing methylene chloride;

adding toluene;

transferring the toluene solution to n-heptane; and

isolating and drying of Montelukast sodium.

17 . A process as claimed in claim 16 , wherein the Montelukast organic base salt is Montelukast dipropylamine salt, Montelukast dibenzyamine salt, Montelukast alpha methyl benzylamine salt, Montelukast dicyclohexylamine salt or Montelukast di-isopropylamine salt.

18 . A process for the preparation of Montelukast free acid from a Montelukast organic salt comprising:

suspending the Montelukast organic base salt obtained by the process of claim 30 in a mixture of water and methylene chloride;

adding an acetic acid solution;

separating the layers;

washing the organic layer with water;

removing methylene chloride;

dissolving the residue in ethyl acetate;

cooling the reaction mass; and

isolating and drying the Montelukast free acid.

19 . A process as claimed in claim 18 , wherein the Montelukast organic base salt is Montelukast dipropylamine salt, Montelukast dibenzylamine salt, Montelukast alpha methylbenzylamine salt. Montelukast di-isopropylamine salt or Montelukast dicyclohexylamine salt.

20 . A compound 2-[2-[(3S)-[3-[(2E)-(7-chloroquinolin-2-yl)ethenyl]phenyl]-3halopropyl]phenyl-2-propanol.

21 . A compound as claimed in claim 20 , wherein the term halo represents chloro, bromo or iodo.

22 .- 38 . (canceled)