SYNTHESIS OF FATTY AMINES - SELECTIVITY CONTROL IN PRESENCE OF MULTIFUNCTIONAL CATALYSTS

Fatty and N-methyl (or ethyl) substituted amines used, for example, fo r the preparation of tensioactive agents are generally obtained from t he reaction of fatty acids (or esters), ammonia, light alcohols and hy drogen or nitriles, light alcohols and hydrogen over copper or nickel catalysts. In these processes, the rate-limiting step is either the li ght alcohol (R'OH) dehydrogenation for the formation of RNR'(2) or the secondary amine formation (R2NH). In both cases the light alcohol and the by-product water have inhibiting effects under the rather severe experimental conditions. Over supported copper-chromite catalysts ther e exists a correlation between the selectivity to RNR'(2) and the pres ence of a well dispersed copper chromite phase stabilized with alkalin e-earth elements. However, over such catalysts the R2NR' amines cannot be obtained with high selectivity. In a second part of our study stim ulated by the fact that environmental legislation will soon mandate re placements of copper-chromium catalysts with non-chromium catalysts, w e investigated promoted nickel catalysts. In order to suppress the inh ibiting effect of light alcohols, hexamethylene tetramine (HMTA) was u sed as methylating agent. Under these conditions, the nitrile is trans formed either into dimethylalkylamine or into methyldialkylamine with a selectivity (or a yield) higher than 90%. Moreover, it was shown tha t HMTA was catalytically converted into monomethylamine (MMA), dimethy lamine (DMA) and trimethylamine (TMA) during the reaction. These reage nts specially MMA, DMA act as methylating agents of primary alkylamine s (RNH2) while the corresponding imines (CH2=NH or CH2=N-CH3) would be the methylating species of the secondary alkylamine (R2NH).