Hydrogenation of crotonaldehyde and cinnamaldehyde catalyzed by water-soluble palladium complex

The selective hydrogenations of crotonaldehyde and cinnamaldehyde in the aqueous-benzene biphasic system were investigated using water-soluble palladium complex PdCl2(TPPTS)(2) as catalyst. The hydrogenation rate of crotonaldehyde was higher than that of cinnamaldehyde under similar reaction conditions. The palladium complex selectively catalyzed the hydrogenation of C=C bond in crotonaldehyde to form butanal (100%). On the contrary, hydrogenation of both C=C and C=O bonds in cinnamaldehyde occurred simultaneously, with the amount of phenylpropanal only slightly higher than that of phenylpropanol. However, the reduction of C=O bond of cinnamaldehyde could be inhibited by the addition of Na2CO3 solution. Therefore, high selectivity to form phenylpropanal(91%) could be obtained by using Na2CO3 solution at pH 12.2. Other factors affecting the hydrogenation conversion and selectivity of crotonaldehyde and cinnamaldehyde were also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.