Hydrogenation to Secondary and Tertiary Amines

Hydrogenation of aliphatic nitriles over platinum metal catalysts often results in ex-tensive formation of secondary and tertiary amines. For example, hydrogenation of butyronitrile over Rh-C in water at 100-125°C and 2.76-4.14 MPa H2 gave a mixture of 51.5% of butylamine and 48.5% of dibutylamine, while in hydrogenation with addition of ammonia (167 mol% based on butyronitrile) dibutylamine was formed quantitatively. Under similar conditions the hydrogenations with Pd-C and Pt-C gave tributylamine in yields exceeding 95%.7 

Hydrogenations in methanol tend to be poisoned by ammonia. It is noteworthy that, in contrast to the hydrogenation with nickel and cobalt catalysts, the yields of secondary and tertiary amines even increased in the presence of ammonia over these platinum metal catalysts. 

Hydrogenation of nitriles under conditions favorable for the formation of secondary and tertiary amines can be applied to the synthesis of mixed secondary and tertiary amines. The iV-substituted phenethylamines were synthesized by hydrogenation of a phenylacetonitrile in the presence of an amine an example is shown in eq. 7.45,90 

A mixed tertiary amine is obtained in high yield in copper-catalyzed hydrogenation of an aliphatic nitrile. Thus, the hydrogenation of lauronitrile over a copper catalyst in the presence of dimethylamine gave /V,/V-dimclhyldodccylaminc in a yield of 95%.91 

TABLE 7.2 Hydrogenation of Nitriles to Secondary and Tertiary Amines 

---