Hydrogenation of unsaturated carbonyl compound

The hydrogenation of unsaturated carbonyl compounds has recently become a research field studied in great detail. The reason is the practical importance of the selective hydrogenation of two different functional groups of these easily accessible compounds. Of the possible products, saturated oxo compounds and unsaturated alcohols are useful synthons in preparative organic chemistry. The increased interest in this field is verified by the appearance of comprehensive works in recent years1,365-367. 

Concept of the synthesis of novel platinum catalysts for the selective hydrogenation of unsaturated carbonyl compounds... 

A new method of synthesis of selective platinum catalysts for the hydrogenation of unsaturated carbonyl compounds is presented. Platinum was deposited on the supports tailored with the monolayer of transition metal oxide. Selectivity of these catalysts strongly depended on the type of inorganic support as well as on the type of transition metal in the monolayer. Catalysts were tested in the hydrogenation of furfural, crotonaldehyde and cinnamaldehyde. Selectivity of the synthesis of the appropriate unsaturated alcohols was enhanced when compared with the reactions performed over classical Pt-metal oxide catalysts. 

In this work, a concept of the modification of platinum catalysts is presented. According to our proposal, the monolayer oxide systems should be the appropriate carriers that can influence the noble metal properties. The monolayer carrier effect depends on its acid-base or electro-nucleophilic properties and the number and capacity of monolayers. This is of great importance in the selective hydrogenation of unsaturated carbonyl compounds. The... 

The results obtained in this work indicate that the selectivity of platinum catalysts for the hydrogenation of unsaturated carbonyl compounds can be markedly improved by doping the carrier with a monolayer of transition metal ion. It is also worth to note that sandwich-type catalysts (ZrC>2/Pt/Zr02/Ti02) are also active and selective in the studied reaction. We believe that on the surface of this system, the end-on adsorption of aldehyde molecule has been forced. 

In this work we have shown that Ziegler type cobalt catalysts are rather selective for the hydrogenation of unsaturated carbonyl compounds into unsaturated alcohols. Nevertheless the selectivity was more important with cinnamaldehyde than with other aldehydes, which showed the eflfect of the aromatic cycle on the stabilization and the adsorption of the conjugated double bond. 

Nevertheless only scare data is available in the recent literature on the application of Group VIII noble metal (M) or rhenium-based mono- and Re-M bimetallic catalysts, in the hydrogenolysis of esters or hydrogenation of acids to alcohols. Recently a few publications, - and patents. have been reported on the transformation of different carbonyl compounds (saturated and unsaturated esters, acids and carboxamides) over rhenium-containing catalysts. In the bimetallic catalysts used for the hydrogenation of carbonyl compounds the rhenium was combined with Pd, or Rh. In the case of catalysts used for the hydrogenation of unsaturated carbonyl compounds the rhenium is usually modified with tin. ... 

Reduction of unsaturated carbonyl compounds to the saturated carbonyl is achieved readily and in high yield. Over palladium the reduction will come to a near halt except under vigorous conditions (73). If an aryl carbonyl compound, or a vinylogous aryl carbonyl, such as in cinnamaldehyde is employed, some reduction of the carbonyl may occur as well. Carbonyl reduction can be diminished or stopped completely by addition of small amounts of potassium acetate (i5) to palladium catalysts. Other effective inhibitors are ferrous salts, such asferroussulfate, at a level of about one atom of iron per atom of palladium. The ferrous salt can be simply added to the hydrogenation solution (94). Homogeneous catalysts are not very effective in hydrogenation of unsaturated aldehydes because of the tendencies of these catalysts to promote decarbonylation. 

On the other hand, hydrogenations under mild conditions, in particular those at ordinary temperature and pressure, are advantageous for monitoring the extent of conversion of substrate exactly and thus achieving selective hydrogenation successfully, as in selective hydrogenation of alkynes to alkenes and in selective hydrogenation of the carbon-carbon double bond of unsaturated carbonyl compounds. 

Taking hydrogenations of C=C and C=0 bonds (and selective hydrogenations, for instance of unsaturated carbonyl compounds) as examples, a method for biphasic catalyses has been proposed [18] and developed [28, 29, 56]. After first reviews by Sinou [79] and Southern [21], Kalck and Monteil - with a focal point on mechanistic backgrounds [17] - and Herrmann and Kohlpaintner - with special emphasis on chemical aspects [16] - reported the state-of-the-art up to 1993. Kalck stated correctly that an important stimulant toward biphasic hydrogenations was the possibility of working under normal pressure, especially for bio-organometal-lic applications. 

The results of unsaturated carbonyl compounds hydrogenation in the presence of metal oxide - monolayer oxide - platinum (Pt loading 2 %) catalysts are collected in Table 3 (Pt from H2PtCl6) and Table 4 (Pt from Pt(acac)2). In all the cases, the selectivity of the platinum catalysts deposited on supports modified with transition metal oxide monolayers... 

The ammonolysis of unsaturated carbonyl compounds in the presence of hydrogen is the most exothermic type. Reaction of phenols, alcohols, and halides with ammonia is only slightly exothermic. Aminolysis of alcohols is much more exothermic than the ammonolysis. Reactions of hydrocarbons with ammonia to form nitriles seem to be special cases in that they are extremely endothermic in nature. 

Vinyl ethers and a,P unsaturated carbonyl compounds cyclize in a hetero-Diels-Alder reaction when heated together in an autoclave with small amounts of hydroquinone added to inhibit polymerisation. Acrolein gives 3,4-dihydro-2-methoxy-2JT-pyran (234,235), which can easily be hydrolysed to glutaraldehyde (236) or hydrogenated to 1,5-pentanediol (237). With 2-meth5lene-l,3-dicarbonyl compounds the reaction is nearly quantitative (238). 

A significant advance in the synthesis of monoorganotin trihaHdes was the preparation of P-substituted ethyl tin trihaHdes in good yield from the reaction of stannous chloride, hydrogen haHdes, and a,P-unsaturated carbonyl compounds, eg, acryHc esters, in common solvents at room temperature and atmospheric pressure (153,154). The reaction is beHeved to proceed through a solvated trichlorostannane intermediate (155) ... 

Cyclic g-haloacetals and -ketals have been prepared by variations on two basic methods. The most frequently used method involves the combination of an a,B-unsaturated carbonyl compound (acrolein, methyl vinyl ketone, croton-aldehyde, etc.) a diol, and the anhydrous hydrogen halide. All possible sequences of combining these three have been used. In most cases the... 

From a mixture of two different aldehydes, each with a-hydrogens, four different aldols can be formed—two aldols from reaction of molecules of the same aldehyde -I- two crossed aldol products not even considering possible stereoisomers (see below). By taking into account the unsaturated carbonyl compounds which could be formed by dehydration from the aldols, eight different reaction products might be obtained, thus indicating that the aldol reaction may have preparative limitations. 

Base treatment of the following ,j3-unsaturated carbonyl compound yields an anion by removal of H+ from the y carbon. Why are hydrogens on the y carbon atom acidic ... 

An alternative strategy for promoting Diels-Alder reaction by proton involves the activation of dienophile by hydrogen bonding [93]. Biphenylene diol 143 (Scheme 4.26) forms doubly hydrogen-bonded complexes with a,j]-unsaturated carbonyl compounds, which strongly accelerate the Diels-Alder... 

Under the principle of vinylogy, the active hydrogen can be one in the y position of an a,P-unsaturated carbonyl compound ... 

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