Preparation of amines from nitriles

Reduction of nitriles is an important method of preparing amines. It is, however, not always easy to carry out in spite of the unsaturated character of the nitrile group three methods are available (i) catalytic reduction, (ii) reduction by metal hydrides, and (iii) reduction by sodium in an alcohol. 

Catalytic hydrogenation of nitriles to amines had at first little preparative importance since a mixture of primary, secondary, and tertiary amines was always formed. Only when methods were found of conducting the reaction so that primary amines became the preponderant product did the method 

Alteration of nitrogen groups in carbon-nitrogen compounds 

The following methods have proved useful to control the direction of the reaction  

L-Lysine dihydrochloride 23 Diethyl a-(acetylamino)-a-(3-cyanopropyl)malonate (15 g) is dissolved in freshly distilled acetic anhydride (100 ml), platinum dioxide (0.5 g) is added, and hydrogenation carried out at an initial pressure of 3 atm. Absorption is complete in 3 h. The catalyst is removed, and the acetic anhydride is hydrolysed by cautious addition of water (25 ml). The A,A-diacetyllysine is then cleaved by boiling it for 18 h in acetic acid solution containing concentrated hydrochloric acid (d 1.19 100 ml). Evaporation then affords d,l-lysine dihydrochloride (9g, 77%), m.p. 175-180°, which, after dissolution in anhydrous ethanol and precipitation by ether, melts at 187-188°. 

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This process is similar to the Ritter reaction for the preparation of amines from nitriles and olefins. The first step is the regioselective formation of a carbenium ion from the diol 13 followed by addition to the nitrile. The resulting nitrilium ion 15, following attack on the remaining OH group, cyclizes and gives dihydro-1,3-oxazine 14. 

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