A mixture of 4-[4-[4-(cis-2,6-dimethylmorpholin-4-yl)phenyl]piperazin-1-yl]benzoic acid ethyl ester (2.46 g) and 1.0 mol/l sodium hydroxide solution (11.6 ml) in a mixed solvent of ethanol (50 ml) and tetrahydrofuran (125 ml) was refluxed for 33 hours, during which period additional 1.0 mol/l sodium hydroxide solution (24 ml) was added to the mixture. After cooling to ambient temperature, the reaction mixture was poured into cold water, and the mixture was adjusted to pH 2 with 1.0 mol/l hydrochloric acid. The resulting precipitates were filtered, washed with water and dried to give 4-[4-[4-(cis-2,6-dimethylmorpholin-4-yl)phenyl]piperazin-1-yl]benzoic acid (1.05 g).
