Hydrogenation of carbonyl group

Hydrogenation of carbonyl groups occurs readily over most catalysts.144 However, care must be exercised in preventing hydrogenolysis of the resulting hydroxyl group. 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

Ohkuma, T. and Noyori, R. (2004) Hydrogenation of carbonyl groups, in Comprehensive Asymmetric Catalysis, Supplement I (eds. E.N. Jacobsen, A. Pfaltz and H. Yamamoto), Springer, Berlin, pp. 1-41. 

Electrocatalytic hydrogenation of carbonyl groups has been carried out by electrolysis of the ketone (336) in an aqueous Et0H-LiCl04-(C) system in the presence of Rh complexes to yield the alcohol (337) in 95 99% yields (Scheme 124) [459, 460]. 

The hydrogenation of carbonyl groups in compounds containing ethylenic bonds to obtain the corresponding unsaturated alcohols is a very important reaction in the fine chemicals field. Extensive work has been carried out to develop heterogeneous catalysts for these reachons, copper chromite being one of the first systems studied [69, 70]. Transihon metals are widely used catalysts for these reachons. 

Ruthenium alloyed to platinum, palladium, titanium and molybdenum have many apphcations. It is an effective hardening element for platinum and palladium. Such alloys have high resistance to corrosion and oxidation and are used to make electrical contacts for resistance to severe wear. Ruthenium-palladium alloys are used in jewelry, decorations, and dental work. Addition of 0.1% ruthenium markedly improves corrosion resistance of titanium. Ruthenium alloys make tips for fountain pen nibs, instrument pivots, and electrical goods. Ruthenium catalysts are used in selective hydrogenation of carbonyl groups to convert aldehydes and ketones to alcohols. 

Selectivity in the hydrogenation of ,/3-unsaturated aldehydes has become an important topic in heterogeneous catalysis (refs. 1-4). Unsaturated alcohols, important in the synthesis of fine chemicals, may be produced selectively over certain supported group VUI-metal catalysts (refs. 5,6), but the general problem of the selective intramolecular hydrogenation of carbonyl groups remains a challenging task. 

The advantage over most other kinds of reduction is that usually the product can be obtained simply by filtration from the catalyst, then distillation. The common catalysts are nickel, palladium, copper chromite, or platinum activated with ferrous iron. Hydrogenation of aldehyde and ketone carbonyl groups is much slower than of carbon-carbon double bonds so more strenuous conditions are required. This is not surprising, because hydrogenation of carbonyl groups is calculated to be less exothermic than that of carbon-carbon double bonds ... 

Ohkuma T, Noyori R (1999) Hydrogenation of carbonyl groups. In Jacobsen EN, PfaltzA, Yamamoto H (eds) Comprehensive asymmetric catalysis, vol 1. Springer, Berlin Heidelberg New York, chap 6.1... 

Two major areas of research have emerged from studies into asymmetric hydrogenations of carbonyl groups using modified heterogeneous catalysts. The first involves the... 

Smith and Lieber (36) reported that, although the use of alkali activated Raney nickel for the hydrogenation of carbonyl groups, it had a deterring effect on the reduction of aromatic nitro compounds. In particular, alkali retarded the reduction of nitrobenzene and the three isomeric sodium nitrobenzoates, whereas it increased the velocity of reduction of the methyl and ethyl esters of nitrobenzoic acid. 

The technique can also be used for the catalytic transfer hydrogenation of carbonyl groups using formate [34, 35] or isopropanol [36] as the hydrogen donor. It is also worth noting, in this context, that Ru/tppts can be used for the selective hydrogenation [37] or transfer hydrogenation [38] of carbohydrates in a monophasic aqueous system (Fig. 7.8). 

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