Enantioselective Catalysis: Influence of Conversion and Bulk Diffusion Limitations on Selectivity in the Hydrogenation of Ethyl Pyruvate

New data on enantiomeric excess versus conversion during enantioselective hydrogenation of activated ketones on a platinum catalyst

“…The phenomenon was later investigated by several research groups and diverse conclusions were drawn depending on the experimental conditions (Table 1). After reviewing the experimental results and completing various novel experiments, Blackmond and co-workers [9,10] and Margitfalvi et al [12], on the one hand, and Baiker and co-workers [13] on the other, proposed explanations for the ITP. According to the former authors [9,10,12], a change in ee versus conversion is an intrinsic feature of the catalytic system, whereas in the opinion of the latter authors [13], the phenomenon is caused mainly by impurities.…”

“…One such problem is the reason for the rapid increase in enantioselectivity (ee) in the initial transient period (ITP) of the conversion. Details of previous studies in this field (Table 1 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]) are reviewed in the Discussion of the present work.…”

“…It was established at an early stage of research that the efficiency of chiral hydrogenation is significantly affected not only by the experimental parameters, which play a decisive role, but also by the methods of execution [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In general, four different methods and their variants [1,2] have been adopted for performing liquid-phase chiral hydrogenation:…”

Enantioselective hydrogenation of ethyl pyruvate in biphasic liquid?liquid media by reusable surfactant-stabilized aqueous suspensions of platinum nanoparticles

“…Nevertheless, we observed a slight agglomeration without consequences on catalytic activities. Hydrogen pressure is also an important factor in enantioselective hydrogenation [26][27][28][29]. The results obtained in ethyl pyruvate after 60 min of reaction time under 1, 20, and 30 bar are summarized in Table 1 (entries [10][11][12].…”

Examination of catalytic behavior and origin of the initial transient period for Pt nanoclusters modified with cinchonidine

“…ITP was observed by Baiker and co-workers [4] and was attributed to an impurity effect (from destructive adsorption of EP and alcoholic solvents on Pt) which could be eliminated by pre-activation with hydrogen. Blackmond and co-workers proposed the ''reaction-driven equilibration'' explanation [5] and demonstrated the significant influence of mass transport (gas-liquid diffusion of hydrogen) limitation on the enantioselectivity [6]. Recently, it was shown that ITP is not only the effect of impurities (lactates in ethyl pyruvate) but could also be a result of competitive adsorption of reactant, modifier and solvent [7].…”