Ammonium Hydroxide → Phenylamino-1-(2-phenylethyl)-4-piperidinecarboxylic acid

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A mixture of 60 parts of phenylmethyl 4-(phenylamino)-1-(2-phenylethyl)-4-piperidinecarboxylate and 320 parts of methanol is hydrogenated at normal pressure and at room temperature with 10 parts of palladium-on-charcoal catalyst 10%. Upon the addition of a concentrated ammonium hydroxide solution, the precipitate, which is formed during the hydrogenation, is dissolved. The catalyst is filtered off and the filtrate is concentrated. Methanol is added and the whole is concentrated again. After cooling to room temperature the product is filtered off and dried in vacuo at 120° C, yielding 43.7 parts of 4-(phenylamino-1-(2-phenylethyl)-4-piperidinecarboxylic acid; mp. 268° C.

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