Hydrogenation Reactors

Syntheses of oligomers of the capsular polysaccharide of the Haemophilus influenzae type b bacteria

“…Therefore it was felt that the ideal spacer would be one derived from a reprcsentative part of the Molecule. Such a spacer will therefore have the structural feature of 50 or 51. The spacer 51 where X is an aldebydc has already bcen dcscribcd by Wangl°. The aldchydic functionality is, we bclieve, ideal as the linking step will he very specific.…”

Hydrogenolysis of Benzylic Alcohols on Rhodium Catalysts

“…In order to achieve C À O cleavage, palladium is employed because, in addition to being a superior hydrogenolysis catalyst, it lowers the risk of hydrogenation of the aromatic ring compared with rhodium or platinum catalysts. [3,4] If CÀO bond scission is not desired, the choice of metal catalyst depends on the functional group of the substrate that is to be hydrogenated. Rhodium is often employed for aromatic ring hydrogenation because it is active at moderate temperature and pressure.…”

“…Platinum is also a good catalyst for aromatic hydrogenation, but it requires higher temperature and pressure than rhodium to achieve comparable activity. [3,5] Although rhodium hydrogenates all the other reducible functional groups of the substrate along with the aromatic ring, it very often leaves the nonreducible functional groups intact. [6] While studying the influence of the nature of the support on diastereoselective induction in the liquid-phase hydrogenation of 1-indanol (1, Scheme 1) over rhodium catalysts, we found a large difference in the chemoselectivity of the carbonsupported and alumina-supported agents.…”

“…[2] The extent of bond scission depends on the nature of the noble metal used as the catalyst, [3] and thus the choice of catalyst therefore depends on whether C À O bond scission is desired. In order to achieve C À O cleavage, palladium is employed because, in addition to being a superior hydrogenolysis catalyst, it lowers the risk of hydrogenation of the aromatic ring compared with rhodium or platinum catalysts.…”

Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

“…Almost all the investigations were conducted with ruthenium and rhodium catalysts, which are excellent for the hydrogenation of aromatic rings under moderate reaction conditions. With these catalysts, the nonreducible functional groups generally remain intact during the reaction [80][81][82]. Nasar et al carried out the hydrogenation of 2-methylanisole over colloidal rhodium modified by a chiral amine but the resulting enantioselectivity was very low ð$1%Þ [83].…”