Hydrogenation aromatic carbonyl compounds

Iridium nanopartides also catalyze the hydrogenation of benzyhnethylketone, with high selectivity in reduction of the aromatic ring (92% selectivity in saturated ketone, 8% in saturated alcohol at 97% benzylmethylketone conversion). This preferential coordination of the aromatic ring can be attributed to steric effects that make carbonyl coordination difficult. Therefore, metallic iridium nanoparticles prepared in ILs may serve as active catalysts for the hydrogenation of carbonyl compounds in both solventless and biphasic conditions. 

Knowledge of the variation of electron transfer rate with electrode potential is important for the understanding of electrochemical reactions. The first experiments in this area were prompted by the observation that nitrobenzenes and aromatic carbonyl compounds are reduced in acid solution with little competition from the hydrogen evolution process. This is the case even though the electrode potential is more negative than the value calculated for the reversible evolution of hydrogen in the same solution. The kinetics of hydrogen evolution have been examined in detail. 

Anastasio, C., B. C. Faust, and C. J. Rao, Aromatic Carbonyl Compounds as Aqueous-Phase Photochemical Sources of Hydrogen Peroxide in Acidic Sulfate Aerosols, Fogs, and Clouds. 1. Non-Phenolic Methoxybenzaldehydes and Methoxyacetophe-nones with Reductants (Phenols), Environ. Sci. Techno ., 31, 218-232 (1997). 

Aromatic carbon—hydrogen bonds, catalzyed borylation, 9, 172 Aromatic carbonyl compounds, in samarium pinacol couplings,... 

Aromatic aldehydes and aromatic ketones also can be reduced to hydrocarbons in a completely different manner, namely via the so-called ionic hydrogenation followed by an ionic hydrogenolysis. This kind of reduction is possible only if it can proceed via resonance-stabilized cationic intermediates. This resonance stabilization is readily achieved in a benzylic position, and it is therefore advantageous to employ aromatic carbonyl compounds in this kind of reduction. The carboxonium ion A, formed... 

The condensation equilibrium is displaced to the right by removing the unsaturated cyano ester as it is formed by the addition of hydrogen cyanide The effect is analogous to the single-step formation and hydrogenation of a,/S-unsaturated cyanoacetic esters (method 394). The yields are good with most aliphatic ketones and aldehydes (49 75%), but poor results are obtained with aromatic carbonyl compounds and diisopropyl ketone. 

Whereas aromatic carbonyl compounds having lowest lying (rt, 3t ) triplet excited states are not photorcduced by hydrogen donors such as alcohols and ethers, they are readily photoreduced by electron donors such as arnin and sulphur compounds (5). The electron transfer processes may be generalisoi as follows ... 

The best known hydrogen abstraction reaction of aromatic carbonyl compounds is that involved in the formation Of benzopinacol on ultraviolet irradiation of solutions of benzophenone in ethers and alcohols. 

Initial formation of radicals by photoinduced hydrogen attraction from the substrate is not in dispute and, as noted in Section 1, hydrogen abstraction from alcohols, ethers and hydrocarbons is effected with high quantum efficiencies by aromatic carbonyl compounds in which the lowest lying triplet level is of n—n type, e.g. benzophenone, anthra-quinone (42 -44). 

III. Photoinduced Hydrogen Abstraction by Aromatic Carbonyl Compounds 65... 

Activated hollow spheres have been found to be advantageous for the hydrogenation of carbonyl compounds, nitriles, aromatics, and unsaturated C-C bounds. In the case of carbonyl conqrounds, promoters (e.g.. Mo and Cr) that exist as surface cations were found to be the most effective. In the case of nitriles, the use of promoters to stabilize the residual A1 content of the catalyst so that it can be used with base modifiers was found to be the most useful combination. An example of this was the improved performance of the LiOH treated Cr / Ni promoted Co hollow spheres for the hydrogenation of adiponitrile to hexamethylenediamine. Some reactions were found to be more sensitive to the type of promoter they require. In the case of l,4-dihydroxy-2-butyne, it was found that Mo worked satisfactory as a promoter while the Cr / Fe combination led to worse results. Nonetheless, for all of the reactions studied here it was found that the activate hollow spheres were more active than the activated tablets on both a volume and weight basis, thereby allowing increased flexibility in the use of promoters and other selectivity enhancing additives. 

Schnabel and co-workers have examined the behaviour of aromatic carbonyl compounds in laser flash photolysis. For l-phenyl-2-hydroxy-2-methy 1-propan-1-one (1) in the absence of a hydrogen-atom donating solvent, a-cleavage to give (2) and (3) was the dominant initiating step. 

Reductions of aromatic carbonyl compounds a-substituted carbonyl compounds a-hydroxy ketones p- and y-substituted carbonyl compounds ketones and a- and p-diketones P-keto acids and esters, y-kcto esters masked carbonyl compounds activated double bonds (hydrogenation) acyclic and cyclic ketones reductive amination of keto acids BY BY BY, glycerolDH BY BY, An, Cr, Cu, Gc, Ha, Ks, Mi, Mr, Ns, Pd, Pm, Rn, Y1 BY, Ao, Cb, Cg, Cu, Ct, Gc, Hp, Lk, Mj, Pf, Pm, Pv, Rr, Td, glycerolDH BY BY, An, Gc, Pc HLADH, TBADH, other ADHs, HSDHs AADH, GluDH, PheDH... 

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