C1(C[N:8]2[CH2:13][CH2:12][N:11]([CH2:14][CH2:15][N:16]3[C:20]4[CH:21]=[CH:22][CH:23]=[CH:24][C:19]=4[NH:18][C:17]3=[O:25])[CH2:10][CH2:9]2)C=CC=CC=1.[H][H]>[Pd].CO>[N:11]1([CH2:14][CH2:15][N:16]2[C:20]3[CH:21]=[CH:22][CH:23]=[CH:24][C:19]=3[NH:18][C:17]2=[O:25])[CH2:12][CH2:13][NH:8][CH2:9][CH2:10]1A mixture of 79 parts of 1,3-dihydro-1-{2-[4-(phenylmethyl)-1-piperazinyl]ethyl}-2H-benzimidazol-2-one and 320 parts of methanol is hydrogenated at normal pressure and at room temperature with 10 parts of palladium-on-charcoal catalyst 10%. After the calculated amount of hydrogen is taken up, the catalyst is filtered off and the filtrate is evaporated. The oily residue is alkalized with ammonium hydroxide and a small amount of water is added. The product is extracted with trichloromethane. The extract is dried, filtered and evaporated. The oily residue solidifies on triturating in 4-methyl-2-pentanone. The product is filtered off and dried, yielding 1,3-dihydro-1-[2-(1-piperazinyl)ethyl}-2H-benzimidazol-2-one; mp. 122.6° C.
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