摘要

Selective hydrogenation of L-malic acid and L-alanine aqueous solutions, respectively, to L-3-hydroxy-γ-butyrolactone and L-alaninol on a highly dispersed Pt-ReO_x/C catalyst was studied under mild conditions (T = 75°C-110°C). In the low-temperature region, where racemization proceeds by two to three orders of magnitude more slowly than that of hydrogenation, we obtained a chemically (lactone yield > 98%) and optically pure cyclic ester with an enantiomeric excess ee > 99%. In an acid medium (pH < 3.5), L-alanine is in the active state, whereas the carboxyl group is nondissociated and the amine group is protonated. In the region of 3.5 < pH < 7, the structure of the amino acid corresponds to a zwitterion that is characterized by the presence of inactive carboxylate anions. As is the case of malic acid, the appropriate temperature, pH, catalyst loading, and concentration of the acid were found to produce L-alaninol with a yield of 99% and ee > 99%.