To a mixture of 1.2 g of 5-(1-piperazinyl)-3,4-dihydrocarbostyril, 1.17 g of potassium carbonate and 20 ml of dimethyl sulfoxide was added 650 mg of 4-aminobenzyl chloride and the mixture was stirred at 80° C. for 2.5 hours. The reaction mixture was poured into a large amount of water and extracted with chloroform. After washing with water, the extract was dried over anhydrous sodium sulfate. Chloroform was distilled off and the residue was purified through silica gel column chromatography. After conversion to hydrochloric acid salt with methanol-hydrochloric acid, the product was recrystallized from methanol-ether to give 0.4 g of 5-[4-(4-aminobenzyl)-1-piperazinyl]-3,4-dihydrocarbostyril dihydrochloride monohydrate, m.p. 224°-227° C. (decomp.), yellow granules.
