Preparation of secondary amines from Schiff bases

When noble-metal catalysts are used the secondary amine may reduce the activity of the catalyst, leading often to incomplete absorption of hydrogen. However, the activity of the catalyst is sustained in the presence of acid, which should be strong enough to provide a mixture with pH in the region 2.88-4.64.31 

Catalytic hydrogenation of the C=N double bond as component of a heteroaromatic ring generally requires more vigorous conditions.32 

The following examples illustrate such catalytic reduction. 

In this way were prepared iV-ethylaniline (57-63%), jV-butylaniline (94-96%), and iV-butyl-p-toluidine (88 %), etc. 

Secondary amines from Schiff bases A 2-10 % methanolic solution of sodium tetrahydridoborate (100% excess) is dropped, with stirring, into a 5-10% methanolic solution of the Schiff base. The mixture is heated for 15 min under reflux, then cooled and treated with an equal volume of water, which precipitates the secondary amine produced. Thus were obtained, inter alia, N-benzyl-p-nitroaniline (90%), A -(p-nitrobenzyl)aniline (87%), and iV-benzylaniline (97%). 

---