SELECTIVE CATALYTIC-HYDROGENATION OF ORGANIC-COMPOUNDS IN SUPERCRITICAL FLUIDS AS A CONTINUOUS PROCESS

We report a new method for continuous hydrogenation in supercritical f luids (CO2 or propane) using heterogeneous noble metal catalysts on De loxan aminopolysiloxane supports. The method has considerable promise both for laboratory-scale hydrogenation and for the industrial product ion of fine chemicals. It can be applied to a wide range of organic co mpounds including alkenes, alkynes, aliphatic and aromatic ketones and aldehydes, epoxides, phenols, oximes, nitrobenzenes, Schiff bases, an d nitriles, Conversion of starting materials, product selectivity, and space-time yields of the catalyst are all high, and the reactors them selves are very small (5- and 10-mL volume). Supercritical hydrogenati on enables the reaction parameters to be controlled very precisely. Re sults are presented for a series of different reactions showing produc t distributions, which are dependent on temperature, pressure, H-2 con centration, and the loading and nature of the catalyst. The hydrogenat ion of cyclohexene has been studied in some detail, and our results ar e related to the phase diagrams of the ternary system cyclohexane + CO 2 + H-2, which we present in a novel way, more suited to continuous re actors. Finally, we report that the supercritical hydrogenation of iso phorone has advantages over conventional methods.