Andreas Dr Freund

New catalytic systems for the selective hydrogenation of halogenated aromatic nitro compounds

Abstract For the selective reduction of halogenated aromatic nitro compounds a new modified supported iridium based catalyst system has been developed. These catalysts are characterized by a high activity combined with an extreme low rate of dehalogenation. Moreover, the formation of other undesired side products such as azo- or azoxy- compounds can be widely avoided. The new modified indium system is an interesting alter-native to existing supported platinum and modified platinum catalysts in this application.

Selective Hydrogenation of Aromatic Aldehydes Using Precious Metal Catalysts on New High Surface-Area TiO2 Supports

Abstract New high surface-area TiO2 extrudates, based on pyrogenic and precipitated TiO2, were used as supports for precious metal (Pd, Pt, Rh) catalysts. The precious metal catalysts were employed in the selective hydrogenation of aromatic aldehydes which have different substituents 1 (R = COOH, CH3, CI). Depending on the choice of catalyst and substrate, the selectivity of the hydrogenation reaction can be directed either toward a benzyl alcohol derivative 2 or toward a methyl-substituted compound 3. The benzyl alcohol is the reaction product obtained using catalysts which have weak or no acidic properties. If acidic catalysts are used, hydrogenolysis to the methyl-compound 3 dominates. Selectivity changes in the order from la to lc. If an alcohol is used as solvent, side reactions, e.g., ether formation or aromatic ring saturation, can be observed. In the case of catalysts on precipitated TiO2, the benzyl ether is obtained at high selectivity in almost quantitative yield. The rate of hydrogenation is determined by the precious metal profile as well as by the electronic properties of the substituents which are effective in the following order: COOH>CI>CH3.

Stereoselective reductions of aromatic compounds

Mono- and bimetallic Rh catalysts were evaluated for the stereoselective reductive amination of alkylphenols to the corresponding alkylcyclohexylamines. Rhodium catalysts as well as bimetallic catalyst formulations with platinum were found to be the most suitable for this one-step hydrogenation. Both the chemo-and the stereoselectivity of that reaction depend on the amount of base added and other parameters such as kind of solvent and/or support.