School of Engineering and Science - Jacobs University

Fig. 1-19. Three schematically favored adsorbed orientations of cinchonidine on wide
Pt support [76]. Species 1: “π-bonded”, 2: “α-H abstracted”, 3: “N lone pair bonded”.
Hydrogen atoms are omitted.
It is interesting to note, that maximum observed ee values were found at low
cinchonidine concentration, for example, in the works of LeBlond [78] and Bartok [51,
79].
The Fig. 1-20 illustrates dependence of ee on concentration of cinchonidine above the
Pt/Al 2 O 3 catalyst.
Fig. 1-20. Effect of cinchonidine concentration of the ee and the initial rate of
hydrogenation. Filled squares - ee , filled cicles - initial rate in ethyl pyruvate
hydrogenation, open squares - ee and open cycles initial rate in bute-2,3-dione
hydrogenation. Reaction conditions: dichlormethane (12.5 ml), reactant (66 mmol),
catalyst 0.25 g, 50 bar H 2 , 20 C, 1200 rpm stirring. The picture is adapted from [80].
The observed dependence of ee on cinchonidine concentration can be explained in the
following way, in fact, at low concentration of modifier and small part of Pt surface is
modified, whereas on unmodified sites reaction goes racemically (ee =0). When the
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