A mixture of 4 parts of 3,8-dichlorophthalazine, 4.2 parts of ethyl 4-[2-(4-piperidinyl)ethoxy]benzoate, 4 parts of sodium hydrogen carbonate and 120 parts of ethanol was stirred and refluxed overnight. After evaporation, the residue was taken up in water and dichloromethane. The organic layer was dried, filtered and evaporated. The residue was purified by column chromatography over silica gel using trichloromethane and methanol (98:2 by volume) as eluent. The pure fractions were collected and the eluent was evaporated. The residue was converted into the hydrochloride salt in 2-propanol. The salt was filtered off, washed with 2-propanol and 2,2'-oxybispropane and dried at 50° C., yielding 3.3 parts (46.2%) of ethyl 4-[2-[1-(8-chloro-3-phthalazinyl)-4-piperidinyl]ethoxy]benzoate monohydrochloride; mp. 172.4° C. (comp. 86).
