Hydrogenation of isophorone

Highly mesoporous carbon supported Pd catalysts were prepared using sodium formate and hydrogen for the reduction of the catalyst precursors. These catalysts were tested in the enantioselective hydrogenation of isophorone and of 2-benzylidene-l-benzosuberone. The support and the catalysts were characterized by different methods such as nitrogen adsorption, hydrogen chemisorption, SEM, XPS and TPD. 

In the enantioselective hydrogenation of isophorone in the presence of (-)-DHVIN modifier the best optical purity was afforded by small dispersion (<0,05) Pd black catalyst (up to 55%) (7). The influence of the preparation method of Pd black on the optical yield was reported (8). A correlation was found between the oxidation state of the metal surface and the enantioselectivity, the catalyst having more oxidised species on its surface giving higher enantiomeric excess, while the Pd black with lower surface area was more enantioselective. 

In the hydrogenation of isophorone the catalyst type 1 of smaller dispersion resulted in higher enantiomeric excesses especially with DPPM modifier. In the hydrogenation of 2-benzylidene-l-benzosuberone the catalyst type 2 of higher dispersion was more enantioselective. These reverse tendencies or smaller relative difference in e.e. for the latter reaction can be attributed to the use of modifiers with totally different structure and working mode. 

Table 4 Enantiomeric excesses in the enantioselective hydrogenation of isophorone and 2-benzyl- 1-benzosuberone on highly mesoporous carbon supported Pd catalysts.

The hydrogenation of isophorone and acetophenone in the presence of (S )-proline shows some similarities. The effect of Pd-C-(5 )-prohne system is based on the addition reaction of the reactants and (S)-proline in solution and on the chemoselectivity of Pd. Both hydrogenations should be termed diastereoselective rather than enantioselective, since the asymmetric induction takes place in the adduct molecules. 

Table 5 Results concerning hydrogenation of isophorone catalyzed by platinum-stabilized nanoparticles...

The technology has been commercialized, in collaboration with the Thomas Swan company, for the manufacture of trimethyl cyclohexanone by Pd-catalyzed hydrogenation of isophorone (Fig. 7.22) [77]. 

Scheme 10.9 Enantioselective hydrogenation of isophorone over ethyl dihydroapovincaminate-modified palladium black, and the best product ee-value.

Figure 3. Hydrogenation of isophorone with different catalysts and modifiers. Conditions 0.05 mol isophorone, 0.1 g modifier, 0.5 g acetic acid, 25 °C, 0.5 g catalyst, 100 ml MeOH, 40 bar.

Figure 5. Hydrogenation of isophorone over Pd black in the presence of (-)-DHVIN and...

The hydrogenation of isophorone and ethyl pyruvate was carried out in methanolic solution at 25 C and 1-50 bar hydrogen pressure in a conventional apparatus or in a Biichi BEP 280 autoclave equipped with a magnetically driven turbine stirrer and a gas-flow controlling and measuring unit. Before hydrogenation the reaction mixtures were stirred under nitrogen for 10 minutes in the reaction vessel. 

Poliakoff and co-workers developed a catalytic hydrogenation process which has been commercialized by Thomas Swan and Co. for the manufacture of trimethylcy-clohexanone by Pd-catalyzed hydrogenation of isophorone (Equation 4.29) [52],... 

A vinca-type alkaloid, (-)-dihydroapovincaminic acid ethyl ester (Fig. 8) afforded up to 55 % ee in the hydrogenation of isophorone to the corresponding cyclic ketone [46]. The authors assumed that a H-bond between the protonated N atom of the alkaloid and the carbonyl O atom of isophorone was responsible for the enantioselectivity [47]. 

The hydrogenation of isophorone and ethyl pymvate was carried out at 25 °C and under 50 bar hydrogen pressure in a stainless steel autoclave. (Technoclave). 

The apolar toluene and the acetic acid were found to be unfavourable both in the hydrogenation of ethyl pyravate and in the hydrogenation of isophorone. It is interesting that adding water to methanol led to increase in the optical purity of dihydro-isophorone, but resulted in the conplete loss of enantioselectivity in the case of etiiyl pyravate. The possible explanation may be that considerable... 

We have investigated the influence of the water concentration of solvent on the ee in the hydrogenation of isophorone (Figure 1). 

Hydrogenation reactions studied have been those of benzene [92], cyn-namaldehyde [93], and the enantioselective hydrogenation of isophorone and... 

Sipos and co-workers studied enantioselective hydrogenation of isophorone and 2-benzylidene-l-benzosuberone using Pd catalysts supported on mesoporous carbon xerogels [94]. Enantioselective hydrogenation reactions can be strongly affected by the type of support and catalyst [97,98]. A carbon xerogel and its... 

In order to verify the existence of a chiral intermediate with kinetic methods too, we studied the effect of concentration of the chiral auxiliary on rate and enantioselectivity in hydrogenation of isophorone and acetophenone with Pd/C-(S)-proline. 

Farkas and Tungler et al. studied the support effects in the enantioselective hydrogenation of isophorone over Pd catalysts prepared on different carbon supports with different specific surface areas and on activated carbons with different surface chemistries. The Pd catalysts, obtained by different reduction methods of the catalyst precursors had different dispersions, and the... 

Various Pd-black catalysts modified with DHVin differing in then-preparation method showed different ee s fi-om the hydrogenation of isophorone (Farkas and Tungler et al. 

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