A mixture of 4.7 parts of 4-chloro-1,1'-butylidene bis[4-chlorobenzene], 3 parts of 5-chloro-1-(4-piperidyl)- 2-benzimidazolinone, 3.7 parts of sodium carbonate and 100 parts of 4-methyl-2-pentanone is stirred and refluxed overnight with water-separator. The reaction mixture is cooled, water is added and the layers are separated. The organic layer is dried, filtered and evaporated. The residue is purified by column-chromatography over silicagel, using a mixture of trichloromethane and 5% of methanol as eluent. The pure fractions are collected and the eluent is evaporated. The residue is crystallized from a mixture of 2-propanol and 2,2'-oxybispropane, yielding 5-chloro-1-{1-[4,4-bis(4-chlorophenyl)butyl]-4-piperidinyl}-1,3-dihydro-2H-benzimidazol-2-one; mp. 165.4° C.
