Patent ID: 7667071

Claim:
Process for preparation of gabapentin hydrochloride which comprises: (i) converting 1,5-dicyano-2,4-dioxo-3-azaspiro [5,5]-undecane into 1,5-diaminoformyl-2,4-dioxo-3-azaspiro[5,5]-undecane at a temperature of about 78° C. to 82° C. in the presence of a strong acid; and (ii) subjecting 1,5-diaminoformyl-2,4-dioxo-3-azaspiro[5,5]-undecane obtained in step (i) to Hofmann rearrangement under an alkaline condition and acidifying with hydrochloric acid to provide gabapentin hydrochloride, wherein in step (ii), 1 mol of 1,5-diaminoformyl-2,4-dioxo-3-azaspiro,[5]-undecane is dissolved in 3-6 mol of 20-50% sodium hydroxide or potassium hydroxide solution, the reaction mixture is refluxed for about 2.5 to 3.5 hours and then allowed to stand at a temperature of 25° C. to 30° C. for about 24-hours, the alkaline solution is added into sodium hypochlorite solution with the temperature controlled at about −5° C. to 5° C., 35-45% sodium hydroxide or potassium hydroxide solution is then added, and the reaction mixture is heated to a temperature of about 45° C. to 70° C., stirred for about 1-2 hours, and adjusted to pH 1-2 with hydrochloric acid to provide gabapentin hydrochloride.