Hydrogenation of Nitro Compounds to Amines Using Polymer Bound Catalysts

A polymer bound catalyst is a relatively new type of catalyst. The basis of polymer bound catalysis lies in the chemical attachment of a homogeneous catalyst to a solid support, in our case, polystyrene. Applications of polymer bound catalysts started in the late 1960’s, and have been used in several types of reactions. In some cases such a catalyst offers a series of advantages over the classical models of catalysis, homogeneous and heterogeneous. The hydrogenation of various aromatic and aliphatic nitro compounds, such as nitro-benzene and 2-nitropropane, were performed successfully. The hydrogenation activity in most cases was high, and in some reactions the catalyst was able to hydrogenate molecules that the analogous homogeneous catalyst could not. Different metals; specifically palladium, platinum, nickel, and rhodium, were attached to the polymer and the effects of varying the metal on the activity were studied. Palladium supported catalysts with anthranilic acid as a polymer supported ligand were found to be more active and selective than palladium catalysts with a bipyridyl ligand. Substitution on the aromatic ring of the substrate alters the reaction rate. Steric effects have a large influence over the catalytic activity. Electron withdrawing groups do not alter reaction rates greatly, while resonance effects can increase the rate of reaction. Finally the effect of the reaction conditions (temperature, pressure and time) on the catalyst activity were analyzed