Stable polymorph of flibanserin

1. A process for preparing form A of flibanserin 1 having an endothermic maximum at about 161° C. which occurs during thermal analysis using DSC,

said process comprising:

(a) reacting a benzimidazolone 2

 wherein R denotes a suitable amino protecting group, with a piperazine 3

 wherein X is a leaving group selected from chlorine, bromine, iodine, methanesulphonate, trifluoromethanesulphonate and para-toluenesulphonate, in a suitable solvent selected from water, alcohols, mixtures of water with alcohols, polar aprotic solvents and mixtures of polar aprotic solvents with water, in the presence of a suitable base, and

(b) cleaving the amino protecting group R under suitable cleaving conditions.

2. A process according to claim 1 , wherein the reaction of 2 with 3 is conducted at a temperature of at least 50° C.

3. A process according to claim 2 , wherein heating is conducted for about 10 minutes to about 12 hours.

4. A process for preparing flibanserin 1 comprising form A having an endothermic maximum at about 161° C. which occurs during thermal analysis using DSC,

said process comprising:

(a) reacting a benzimidazolone 2

 wherein R denotes a suitable amino protecting group, with a piperazine 3

5. A process according to claim 4 , wherein the reaction of 2 with 3 is conducted at a temperature of at least 50° C.

6. A process according to claim 5 , wherein heating is conducted for about 10 minutes to about 12 hours.