INFLUENCE OF OXYGEN AND IRON IN THE LIQUID-PHASE HYDROGENATION OF ALPHA,BETA-UNSATURATED ALDEHYDES

The effect of oxygen and FeCl2 additions to the liquid-phase hydrogenation of the two α,β-unsaturated aldehydes, cinnamaldehyde and 2-ethyl-hexenal, was investigated over a Pt/Al2O3 catalyst. The addition of small amounts of oxygen to the feed considerably improved the activity in both the presence and absence of FeCl2. Without oxygen and FeCl2, the hydrogenation of 2-ethyl-hexenal to the saturated alcohol proceeded mainly via hydrogenation of the CC double bond to yield the saturated aldehyde as intermediate. In the hydrogenation of cinnamaldehyde, on the other hand, the C=C and the C=O double bonds were hydrogenated at the same rate, yielding equal amounts of the saturated aldehyde and the unsaturated alcohol as intermediates. Addition of oxygen in the latter case increased the hydrogenation rate of the C=C double bond more than that of the C=O double bond, resulting in a decreased selectivity toward the unsaturated alcohol. The selectivity toward the unsaturated alcohol was in all cases enhanced by the addition of FeCl2. High yields of the unsaturated alcohols were obtained by the addition of oxygen to the FeCl2 promoted Pt/Al2O3 catalyst. The effect of FeCl2 on the hydrogenations over a Pd/Al2O3 catalyst was also investigated. The unsaturated aldehydes were rapidly hydrogenated to the saturated aldehydes in both the presence and absence of FeCl2. The further hydrogenation of the C=O double bond to the alcohols was extremely slow, but was somewhat increased by the addition of FeCl2. No unsaturated alcohols were ever observed using the Pd/Al2O3 catalyst. © 1993 Academic Press, Inc.