ABSTRACT
The catalytic hydrogenation of substituted benzenes is a classic method for the preparation of substituted cyclohexanes. The ease of ring hydrogenation depends on the substituents present with the order of catalyst reactivity different for each substituent. Most partial benzene hydrogenations use a ruthenium catalyst since it is a good species for promoting the hydrogenation of aromatic systems but not very effective for double bond saturation. Only one ring is generally saturated at a time. This partial hydrogenation is accomplished because the preferred adsorption of the parent polycyclic aromatic precludes the saturation of the partially saturated species until almost all of the parent material has reacted. The stereochemistry of the ring juncture of the decahydro compounds is dependent on the catalyst and conditions used for the reactions. Hydrogenations over nickel catalysts give primarily the trans products and those hydrogenations run in acid medium lead to a predominance of the cis isomer.
