Hydrogenolysis of Benzyl Esters with Palladiumon-Carbon Catalysts

Abstract

Further studies to demonstrate the possibility of substrate and stereospecific sites on palladized charcoal hydrogenation catalysts have been made. The rates of hydrogenation of the benzyl esters of (+), (−), (±), and meso-tartaric acids, (±) malic acid, d-, l-, and dl-aspartic acids were measured. The rates were observed to be identical for the benzyl esters of the tartaric acids and the malic acid, indicating the possibility that these five substrates can utilize the same catalytic sites for debenzylation. A hydroxy group and the two carbobenzyloxy groups are postulated as being involved in the catalyst–substrate complex. The dibenzyl aspartates when compared to one another undergo debenzylation at the same rates. The rate of hydrogenolysis of dibenzyl succinate was found to be significantly different when compared to the rates of these other substances. Dibenzyl succinate, being devoid of a hydroxy group or an amino group, would not be expected to utilize the same sites as the dibenzyl esters of tartaric, malic, and aspartic acids. Further studies to demonstrate the possibility of substrate and stereospecific sites on palladized charcoal hydrogenation catalysts have been made. The rates of hydrogenation of the benzyl esters of (+), (−), (±), and meso-tartaric acids, (±) malic acid, d-, l-, and dl-aspartic acids were measured. The rates were observed to be identical for the benzyl esters of the tartaric acids and the malic acid, indicating the possibility that these five substrates can utilize the same catalytic sites for debenzylation. A hydroxy group and the two carbobenzyloxy groups are postulated as being involved in the catalyst–substrate complex. The dibenzyl aspartates when compared to one another undergo debenzylation at the same rates. The rate of hydrogenolysis of dibenzyl succinate was found to be significantly different when compared to the rates of these other substances. Dibenzyl succinate, being devoid of a hydroxy group or an amino group, would not be expected to utilize the same sites as the dibenzyl esters of tartaric, malic, and aspartic acids.