A mixture of 2 g of 5-(5-chlorovaleryl)-2-benzyloxy-benzamide, 1 g of 1-phenylpiperazine, 0.6 g of sodium carbonate and 10 ml of dimethyl sulfoxide was heated at 90° C. for 6 hours while stirring. After the reaction was finished, water was added to the reaction mixture and the mixture was extracted with ethyl acetate. The extract was washed with water saturated with sodium chloride, dried over anhydrous sodium sulfate and concentrated. The thus produced residue was dissolved in acetone and concentrated hydrochloric acid in an amount of 2 equivalents was added thereto to produce crystals. The crystals were filtered off to obtain 2.3 g of 5-[5-(4-phenyl-1-piperazinyl)valeryl]-2-benzyloxy-benzamide (yield: 73%).
