Unsaturated aldehydes hydrogenation

Polymeric OC-Oxygen-Substituted Peroxides. Polymeric peroxides (3) are formed from the following reactions ketone and aldehydes with hydrogen peroxide, ozonization of unsaturated compounds, and dehydration of a-hydroxyalkyl hydroperoxides consequendy, a variety of polymeric peroxides of this type exist. Polymeric peroxides are generally viscous Hquids or amorphous soHds, are difficult to characterize, and are prone to explosive decomp o sition. 

In a water/chlorobenzene biphasic system, reduction of aromatic aldehydes by hydrogen transfer from aqueous sodium formate catalyzed by [ RuCl2(TPPMS)2 2] provided unsaturated alcohols exclusively (Scheme 10.7). Addition of 3-CD shghtly inhibited the reaction [13]. It was speculated that this inhibition was probably due to complexation of the catalyst by inclusion of one of the non-sulfonated phenyl rings of the TPPMS ligand, however, no evidence was offered. 

Scheme 36 Epoxidation of a, 3-unsaturated aldehydes using hydrogen peroxide as oxidant...

After hydroformylation, the resulting mixture of saturates, unsaturates, and aldehydes, are hydrogenated over a fixed-bed commercial hydrogenation catalyst. Unreacted olefins are converted to saturates, and aldehydes are converted to the... 

Alkaline condensation of 4-isopropylbenzaldehyde and propanal results, via the aldol, in the formation of 2-methyl-3-(4-isopropylphenyl)-2-propenal. The unsaturated aldehyde is hydrogenated selectively to the saturated aldehyde in the presence of potassium acetate and a suitable catalyst, such as palladium alumina [150] ... 

From a thermodynamic point of view, the hydrogenation of the C=C bond is more favorable than that of the C=0 group. Since there are numerous other important processes to synthesize saturated aldehydes and ketones, the main objective of recent research efforts is to increase the selectivity of hydrogenation of unsaturated oxo compounds into unsaturated alcohols. The results summarized below clearly indicate the significant success achieved in the selective hydrogenation of unsaturated aldehydes. The hydrogenation of unsaturated ketones, in turn, cannot be accomplished yet with similar selectivities. 

To account for the final stage of hydroformylation, Heck and Bres-low a) suggested the intermediacy of coordinately unsaturated acylcobalt tricarbonyls, which are reduced to aldehydes by hydrogen or converted into tetracarbonyls by carbon monoxide. The well known adverse effect of carbon monoxide on die course of the oxo reaction may, therefore, be attributed to this competition. 

Hydrogenation. Carboxylic acids are reduced to aldehydes by hydrogen in the presence of (PhjPl Pd and pivalic anhydride. Alkenoic acids (oleic acid, erucic acid) give unsaturated aldehydes. Diacids are similarly reduced. 

Early attempts to epoxidize simple a,)8-unsaturated aldehydes with hydrogen peroxide in the presence of alkali alforded only acidic products. Payne (Shell Development Co.) found, however, that highly alkali-sensitive aldehydes such as acrolein and methacrolein can be epoxidized successfully by controlling the pH to 8-8.5. Thus acrolein is added to a dilute solution of hydrogen peroxide maintained... 

The activity of the catalysts was tested in the hydrogenation of crotonaldehyde, cinnamaldehyde and furfural at atmospheric pressure. Before the reaction, the catalysts were reduced in a stream of dihydrogen at 623 K. Hydrogenation reactions were carried out in a standard fixed bed vertical reactor. After the catalyst reduction, the reactor was cooled down to the reaction temperature (423, 470 or 523 K) and unsaturated aldehyde and hydrogen were introduced onto the top of the reactor. The first product sample for analysis was taken after 30 min of reaction (period needed to reach reaction steady state). The identification and analysis of the reaction mixtures were performed by means of GC-MS using HP-50 capillary column. 

SOLUTION TO 20a A compound with the correct four-carbon skeleton can be obtained if a two-carbon aldehyde undergoes an aldol addition. Dehydration of the addition product forms an a,)8-unsaturated aldehyde. Catal3aic hydrogenation forms an aldehyde. Some of the a,)8-unsaturated aldehyde might be reduced to an alcohol, but that s all right because both the aldehyde and the alcohol can be oxidized by an acidic solution of Cr03 to the target compound (Section 20.2). 

Marigo M, Franzen J, Poulsen TB, Zhuang W, Jprgensen KA (2005) Asymmetric Organocatalytic Epoxidation of a,P-Unsaturated Aldehydes with Hydrogen Peroxide. J Am Chem Soc 127 6964... 

M. Marigo, J. Franzen, T. B. Poulsen, W. Zhuang, K. A. Jprgensen, J. Am. Chem. Soc. 2005, 127, 6964—6965. Asymmetric organocatalytic epoxidation of a,P-unsaturated aldehydes with hydrogen peroxide. 

Conjugated unsaturated aldehydes are hydrogenated quantitatively to saturated aldehydes with cobalt catalyst under hydroformylation conditions. 

In 1987, Syper studied the oxidation of a,)3-unsaturated aldehydes with hydrogen peroxide, catalyzed by benzeneseleninic acids and their precursors. Bis-2-nitrophenyl diselenide 546 was the best catalyst. Selected results are shown in Scheme 7.86 [357]. 

Scheme 7.86 Baeyer-Villiger oxidation of Cf,jS-unsaturated aldehydes with hydrogen peroxide catalyzed by 546...

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