Process for the preparation of Gabapentin form-II

1. A process for the preparation of Gabapentin Form-II comprising the steps of:

reacting 1,1-cyclohexane di acetic acid mono amide with an alkali hypo halite solution at a temperature of about −10° C. to about 5° C., followed by acidification with sulphuric acid in presence of a first organic solvent;

extracting the formed sulphate salt into an organic layer with a second organic solvent;

separating the organic layer, followed by drying the layer over dehydrating agents;

adding an ante solvent to precipitate the formed hemisulphate hemihydrate salt followed by its isolation;

dissolving the hemisulphate hemihydrate salt in a short chain alcohol and

separating any insolubles from the salt solution to form a salt solution filtrate;

neutralizing the filtrate with a base at temperature of about 70° C. to liberate free amino acid;

isolating the liberated free amino acid by cooling, leaving formed byproduct base-salt in the mother liquor/solvent;

separating the formed Gabapentin Form-II followed by purification by slurrying in ethanol at temperature of about 60° C.-70° C.; and

recovering the final product by filtering and drying to obtain Gabapentin Form-II having sulphate ions less than 100 ppm with respect to Gabapentin.

2. A process as claimed in claim 1 , wherein the first organic solvent is selected from n-Butanol, MIBIC, methyl ethyl ketone and THF.

3. A process as claimed in claim 1 , wherein the second organic solvent is selected from n-Butanol, MIBK, THF and methyl ethyl ketone.

4. A process as claimed in claim 1 , wherein drying of the organic layer is carried out over dehydrating agents.

5. A process as claimed in claim 1 , wherein the ante solvent is selected from acetone, toluene, n-hexane, and di isopropyl ether.

6. A process as claimed in claim 1 , wherein the short chain alcohol is ethanol and n-Butanol.

7. A process as claimed in claim 1 , wherein the base is selected from di isopropyl ethylamine, and triethylamine.

8. A process as claimed in claim 1 , wherein the neutralization temperature is in the range of 65°C.-75° C.

9. A process as claimed in claim 1 , wherein the purification of Gabapentin is done by slurrying in ethanol in the temperature range 65°C.-70° C.

10. Crystalline Gabapentin hemisulphate hemihydrate characterized by powder x-ray diffraction peaks at 2-theta 6.8, 13.7, 17,0, 18.0, 20.2, 20.6, 24,2, 24.6, 26.2, 26.8, 27.7, 29.9, 30,8, 34.0, and 34.7 degrees.

11. Crystalline Gabapentin hemisulphate hemihydrate characterized by infra-red absorptions having peaks at 686, 757, 901, 917, 986, 1127, 1142, 1200, 1282, 1315, 1430, 1462, 1525, 1580 and 1714 cm −1 .

12. A process for the preparation of Gabapentin hemisulphate hemihydrate comprising the steps of:

reacting 1,1-cyclohexane di acetic acid mono amide with an alkali hypo halite solution at temperature of about −10° C. to about 5° C., followed by acidification with sulphuric acid in presence of a first organic solvent;

extracting the formed sulphate salt into an organic layer with a second organic solvent;

separating the organic layer, and drying it over dehydrating agents;

adding an ante solvent to the organic layer to precipitate a hemisulphate hemihydrate salt followed by its isolation; and

isolating and drying Gabapentin hemisulphate hemihydrate.

13. A process as claimed in claim 12 , wherein the first organic solvent is selected from n-Butane, MIBK, methyl ethyl ketone and THF.

14. A process as claimed in claim 12 , wherein the second organic solvent is selected from n-Butanol, MIBK, THF and methyl ethyl ketone.

15. A process as claimed in claim 12 , wherein the drying of the organic layer is carried out over dehydrating agents.

16. A process as claimed in claim 12 , wherein the ante solvent is selected from acetone, toluene, n-hexane, and di isopropyl ether.

17. A process as claimed in claim 12 , wherein the drying of the Gabapentin hemisulphate hemihydrate is at a temperature range of 50-60° C.