Platinum aromatic ketones

Reduction of carbocyclic rings in aromatic ketones can be accomplished by catalytic hydrogenation over platinum oxide or rhodium-platinum oxide and takes place only after the reduction of the carbonyl group, either to the alcoholic group, or to a methylene group [5S]. 

For aliphatic aldehydes and ketones, reduction to the alcohol can be carried out under mild conditions over platinum or the more-active forms of Raney nickel. Ruthenium is also an excellent catalyst for reduction of aliphatic aldehydes and can be used to advantage with aqueous solutions. Palladium is not very active for hydrogenation of aliphatic carbonyl compounds, but is effective for the reduction of aromatic aldehydes and ketones excellent yields of the alcohols can be obtained if the reaction is interrupted after absorption of one mole of hydrogen. Prolonged reaction, particularly at elevated temperatures or in the presence of acid, leads to hydrogenolysis and can therefore be used as a method for the reduction of aromatic ketones to methylene compounds. 

Catalytic hydrogenation of carbonyl compounds to alkanes is a difficult proposition under normal conditions, although limited success is attainable with aromatic ketones. However, certain enolates derived from ketones have been shown to undergo catalytic reduction to alkanes quite efficiently. For example, enol triflates of ketones are reduced over platinum oxide catalyst to alkanes (equation 56) . Similarly, enol phosphates, conveniently prepared from ketones, can be quantitatively hydrogenated to alkanes (equation 57) . ... 

Cougnon, C., and J. Simonet. Cathodic inunobiUzation of 8-acceptors such as aromatic ketones onto platinum interfaces under superdry conditions. J. Electroanal. Chem. 531 (2002) 179. 

Stability toward reduction makes hydrogen fluoride a good medium for different hydrogenation processes [1, 2] It is a useful solvent for the hydrogenation of benzene in the presence of Lewis acids [f ] Anhydrous hydrofluonc acid has pronounced catalytic effect on the hydrogenations of various aromatic compounds, aliphatic ketones, acids, esters, and anhydrides in the presence of platinum dioxide [2] (equations 1-3)... 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

Aromatic amine-Ketone. The interaction between anihne, the simplest of the aromatic amines with acetone in the presence of various catalysts to yield N-isopropylaniline was examined (Table 17.3). Among the catalysts tested, sulfided platinum catalysts were found to be the most active catalysts for this reaction. 

In contrast to phenolic hydroxyl, benzylic hydroxyl is replaced by hydrogen very easily. In catalytic hydrogenation of aromatic aldehydes, ketones, acids and esters it is sometimes difficult to prevent the easy hydrogenolysis of the benzylic alcohols which result from the reduction of the above functions. A catalyst suitable for preventing hydrogenolysis of benzylic hydroxyl is platinized charcoal [28], Other catalysts, especially palladium on charcoal [619], palladium hydride [619], nickel [43], Raney nickel [619] and copper chromite [620], promote hydrogenolysis. In the case of chiral alcohols such as 2-phenyl-2-butanol hydrogenolysis took place with inversion over platinum and palladium, and with retention over Raney nickel (optical purities 59-66%) [619]. 

Hydrogen and a catalyst.2 0 The most common catalysts are platinum and ruthenium, but homogeneous catalysts have also been used.281 Before the discovery of the metal hydrides this was one of the most common ways of effecting this reduction, but it suffers from the fact that C=C, CssC, C=N and C=N bonds are more susceptible to attack than C=0 bonds.282 For aromatic aldehydes and ketones, reduction to the hydrocarbon (9-37) is a side reaction, stemming from hydrogenolysis of the alcohol initially produced (0-78). 

Ruthenium is commonly used with other platinum metals as a catalyst for oxidations, hydrogenations, isomerizations, and reforming reactions. The synergetic effect of mixing ruthenium with catalysts of platinum, palladium, and rhodium lias been found for the hydrogenations of aromatic and aliphatic nitro compounds, ketones, pyndine, and nitriles. 

There are many examples of the preparation of tertiary aliphatic amines by the reductive alkylation of dialkylamines or secondary non-aromatic heterocyclic amines with ketones using platinum5-13, palladium12"17, mixtures of platinum and palladium18,and nickel12. 13. 9-22 catalysts. 

Unsymmetrical secondary amines are readily prepared in good yields by the catalytic reduction of Schiff bases at moderate temperatures in high-or low-pressure equipment. Many examples have been cited. The intermediate imines are prepared from primary amines and aldehydes—very seldom from ketones—and may be used without isolation (cf. method 431). For the preparation of aliphatic amines, e.g., ethyl-w-propylamine and n-butylisoamylamine, a prereduced platinum oxide catalyst is preferred with alcohol as the solvent. Schiff bases from the condensation of aromatic aldehydes with either aromatic or aliphatic amines are more readily prepared and are reduced over a nickel catalyst. In this manner, a large number of N-alkylbenzylamines having halo, hydroxyl, or methoxyl groups on the nucleus have been made. Reductions by means of sodium and alcohol and lithium aluminum hydride have also been described,... 

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