6.95 g (0.0184 mol) of unpurified [(4-aminomethylbenzyl)-(4-dipropylaminobutyl)amino]ethyl acetate (14) synthesized in Example 16 and 50 ml of ethanol were charged in a 300 ml recovery flask. 9.8 g (0.066 mol, 3.6 equivalents) of a 25% hydrochloric acid-ethanol solution was added dropwise to the flask under cooling with ice, the mixture was warmed and stirred at room temperature for two hours. The reaction solution was then concentrated. After the addition of hexane to the residue, the mixture was reconcentrated, thereby obtaining foam-like slightly yellow crystals. After dissolving the crystals in 65 ml of IPA at 70° C., 50 ml of ethylene glycol dimethyl ether was added to the solution at 70° C. After stirring the mixture for one day, the precipitated white crystals were recovered by filtration. The crystals were then washed with ethylene glycol dimethyl ether and dried under reduced pressure, thereby obtaining 5.8 g of [(4-aminomethylbenzyl)-(4-dipropylaminobutyl)amino]ethyl acetate hydrochloride (14a) (yield: 64%). [HPLC: 99.0% (HPLC measurement conditions A)] m.p. 105 to 106° C.
