Y. Nitta, T. Kubota, Y. Okamoto
Nov 1, 2001
Citations
1
Influential Citations
26
Citations
Journal
Bulletin of the Chemical Society of Japan
Abstract
The enantioselective hydrogenation of the C=C double bonds in (E)-2-methyl-2-butenoic acid, (E)-2-methyl-2-pentenoic acid, and (E)-2,3-diphenyl-2-propenoic acid has been studied using cinchonidine-modified Pd/TiO2 catalysts with different metal loadings of between 0.5 to 30 wt%. For all of the substrates examined, those catalysts with degrees of Pd dispersion lower than 0.2 have been shown to be rather detrimental for obtaining a high enantioselectivity, as opposed to the tendencies reported for the hydrogenations of keto esters with modified Pt and Ni systems. The hydrogenations of the aliphatic acids are almost structure insensitive with a slight decrease in the enantioselectivity at Pd dispersions lower than 0.2, which is in great contrast to the hydrogenation of the aromatic acid. A similar difference in the structure sensitivity has been observed with catalysts modified by a larger modifier, (−)-dihydroapovincaminic acid ethyl ester. The influence of the substrate structure on the adsorption mode and...