Kinetic Analysis of the Asymmetric Hydrogenation of (E)-2,3-diphenylpropenoic acid over Cinchonidine Derivative-Modified Pd/C: Quinoline Ring Modification

The effects of the quinoline ring modification of cinchonidine (CD) on the enantioselectivity of the asymmetric hydrogenation of (E)-2,3-diphenylpropenoic acid over chirally modified Pd/C were systematically analyzed from the kinetic points of view. The substitutions at the 2′- and/or 6′-positions of the quinoline ring of CD by a methyl, vinyl, n-butyl, or phenyl group decreased enantioselectivity over the whole range of the modifier concentration. Kinetic analysis allowed us to estimate the intrinsic enantioselectivity at modified sites and adsorption strength of the modifier. It is revealed that the substitutions reduce both the intrinsic enantioselectivity and adsorption strength of the parent modifier. The intrinsic enantioselectivity is correlated, most likely, to the modifier–substrate interaction strength.