C([N:8]1[CH2:13][CH2:12][CH:11]([N:14]2[CH2:18][CH2:17][N:16]([C:19]3[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=3)[C:15]2=[O:25])[CH2:10][CH2:9]1)C1C=CC=CC=1.O.Cl.[H][H]>CO.[Pd]>[NH:8]1[CH2:9][CH2:10][CH:11]([N:14]2[CH2:18][CH2:17][N:16]([C:19]3[CH:20]=[CH:21][CH:22]=[CH:23][CH:24]=3)[C:15]2=[O:25])[CH2:12][CH2:13]111.1 g of 1-(1-benzyl-4-piperidinyl)-3-phenyl-2-imidazolidinone are dissolved in 85 ml of methanol, 34 ml of water and 3.2 ml of hydrochloric acid (chemically pure), and, with the addition of 1.2 g of a 5% palladium on charcoal catalyst, hydrogenated at room temperature and under normal pressure. The calculated amount of hydrogen has been taken up after approx. 15 hours. The reaction mixture is filtered to remove the catalyst and concentrated in a water jet vacuum. The crystalline residue is treated with 2N sodium carbonate solution and extracted with chloroform. The combined chloroform extracts are dried over sodium sulphate and concentrated in a water jet vacuum to yield 7.6 g of 1-(4-piperidinyl)-3-phenyl-2-imidazolidinone as a colourless oil which crystallises on standing; melting point 123°-124° C.
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