3,5-Dimethylpyridine → rac-(3R,5S)-3,5-dimethylpiperidine hydrochloride

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Reaction Conditions

Reaction Steps

3,5-Lutidine (6475.0 g.) is hydrogenated under 1000 psi hydrogen pressure in ethanol using 1665 g. of 5% rhodium on carbon catalyst (50% H2O) at room temperature. The catalyst is filtered off and anhydrous hydrogen chloride bubbled into the filtrate at a temperature below 40° C. until the solution is strongly acidic. The solution is then concentrated in vacuo to a thick slurry which is diluted with 40 liters of hexane. The crystalline material is filtered off and dried in the atmosphere to give 8.9 kg. of crude product. The crude 3,5-dimethylpiperidine hydrochloride is dissolved in 14 liters of water and the pH of this solution adjusted to 7.0 with dilute sodium hydroxide solution. The mixture is washed with 7 l. and then with 3 l. of chloroform to remove unreduced 3,5-lutidine. The aqueous solution is then adjusted to pH 12-13 by the addition of 40% sodium hydroxide solution and extracted with 6 l. and then with 3 l. of chloroform. The combined chloroform extract is dried over anhydrous magnesium sulfate and chilled to 5° C. in an ice bath. Anhydrous hydrogen chloride is then injected until the solution is strongly acidic. The chloroform solution is concentrated in vacuo as benzene is continuously added. When most of the chloroform has been replaced, the product is filtered from about 36 l. of benzene. The filter cake is washed with cold benzene and hexane, and air dried, to obtain 4.8 kg. of product, m.p. 222°-224° C.

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