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

Selective hydrogenation of aldehyde groups in various α,β-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 α,β-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 α,β-unsaturated aldehydes having the substituent at α- and/or β-position of acrolein were converted into the corresponding a,β-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 β-position of acrolein with bulky phenyl group). The hydrogenation of (E)-2-butenal (substituted at β-position of acrolein with methyl group) and (E)-2-hexenal (substituted at β-position of acrolein with n-propyl group) also gave the corresponding α,β-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.