Selective hydrogenation of aldehyde groups in various α,β-unsaturated aldehydes over alumina-supported cobalt (0) catalyst

Selective hydrogenation of aldehyde groups in various alpha,beta-unsaturated aldehydes has been studied over alumina-supported cobalt (0) catalyst (Co/Al2O3) in a liquid phase. The catalyst was prepared by a precipitation method, adjusting the cobalt metal loading to about 37 wt.%. The alpha,beta-unsaturated aldehydes employed in the reaction were 2-propenal (acrolein), (E)-3-phenyl-2-propenal (cinnamaldehyde), (E)-2-butenal (crotonaldehyde), (E)-2-methyl-2-butenal, 3-methyl-2-butenal, (E)-2-ethyl-2-butenal, (E)-2-hexenal (leafaldehyde), and (E)-2-ethyl-2-hexenal. The alpha,beta-unsaturated aldehydes having the substituent at alpha- and/or beta-position of acrolein were converted into the corresponding alpha,beta-unsaturated alcohols over the Co/Al2O3 catalyst in a good selectivity. More than 99% selectivity to (E)-3-phenyl-2-propenol was obtained by the hydrogenation of the (E)-3-phenyl-2-propenal (substituted at beta-position of acrolein with bulky phenyl group). The hydrogenation of (E)-2-butenal (substituted at beta-position of acrolein with methyl group) and (E)-2-hexenal (substituted at beta-position of acrolein with n-propyl group) also gave the corresponding alpha,beta-unsaturated alcohols in 78% and 77% selectivity, respectively. In the hydrogenation of 3-cycrohexene-1-carboxaldehyde, the C=O double bond was hydrogenated preferentially over Co/Al2O3 (97% selectivity to unsaturated alcohol), showing that the conjugation between aldehyde group and olefinic double bond did not affect the selectivity. Co/Al2O3 prepared by the precipitation method is a useful catalyst for the selective hydrogenation of various unsaturated aldehydes to the corresponding unsaturated alcohols. (C) 1999 Elsevier Science B.V. All rights reserved.