Selective Hydrogenation of a,p-Unsaturated Aldehydes

Supported Ionic Liquids Fundamentals and Applications, First Edition. 

Edited by Rasmus Fehrmann, Anders Riisager, and Marco Haumann. 

I Citronellal 3,7-Dimethyl-2-octenal Dihydrocitronellal H Tetrahydrogeraniol Other compounds  

Reaction conditions T = 100°C, p (H2) = 10bar. The selectivities were measured at 100% citral conversion. (Adapted from Ref [13].) 

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The selective hydrogenation of a,P-unsaturated aldehydes to allylic alcohols (desired products) and/or saturated aldehydes is of commercial relevance, as mentioned in the... 

Choppin GR (2003) Actinide speciation in the environment. Radiochim Acta 91 645-649 Claus P (1998) Selective hydrogenation of a,P-unsaturated aldehydes and other C = O and C = C bonds containing compounds. Top Catal 5 51-62 Colon D, Weber EJ, Anderson JL, Winget P, Suarez LA (2006) Reduction of nitrobenzenes and N-hydroxylanilines by Fe(II) species Elucidation of the reaction mechanism. Environ Sci Technol 40 4449-4454... 

Iridium,204,205 together with osmium, has been not widely used in catalytic hydrogenation. Recently, however, iridium or iridium-based catalysts have been shown to be effective in various hydrogenations, such as in selective hydrogenation of a,P-unsaturated aldehydes to allylic alcohols (Section 5.2), of aromatic nitro compounds to the corresponding hydroxylamines (Section 9.3.6), of halonitrobenzenes to haloanilines without loss of halogen (Section 9.3.2), and in the stereoselective hydrogenation of carbon to carbon double bonds (see, e.g., eqs. 3.25-3.27 and Table... 

TABLE 5.1 Selective Hydrogenation of a,p-Unsaturated Aldehydes to Allylic Alcohols over Ir-C Catalyst0 ... 

Selective hydrogenation of a,p-unsaturated aldehydes to allylic alcohols over supported monometallic and bimetallic Ag catalysts... 

As electronic effects of additives have been claimed for the selective hydrogenation of a,p unsaturated aldehydes [9-14], the influence of metal salts was examined in the hydrogenation of acrolein with Co/silica-alumina catalysts. As shown in Table 2, a small amount of Fe (II or III) chloride added into the hydrogenation mixture exerted a favourable effect on the selectivity to allyl alcohol. TTie other metal chlorides examined were less effective on the catalyst performance. Therefore, not chloride anion but Fe cation seems to have positive effects on the hydrogenation of carbonyl group as illustrated by Richard et al.[12j. 

From these findings, it can be concluded that the structure sensitivity in the selective hydrogenation of a,p unsaturated aldehydes such as crotonaldehyde and cinnamaldehyde largely depends on the steric effect of the bulky substituent on P-carbon of the substrate, but that another interpretation, e.g., an electronic effect, should be proposed for the size effect in the hydrogenation of acrolein. 

The results presented here tend to show that H-Pt-Ti02 sites exist even after reduction at low temperature and that they are able to play an important role in selective hydrogenation of a,p unsaturated aldehydes. 

Nevertheless major possibilities for using SAPC in the short term can be foreseen in fine and pharmaceutical chemistry, e.g., for the selective hydrogenation of a.P Unsaturated aldehydes such as retinal [43] and to the production of the commercially anti-inflammatory agent naproxen [44]. 

Figure 15.13 Schematics of gas-liquid-liquid flow patterns observed in the selective hydrogenation of a,p-unsaturated aldehydes. Adapted from 6nal et al. [102],...

Y. Onal, M. Lucas and P. Claus, Application of a capillary microreactor for selective hydrogenation of a, p-unsaturated aldehydes in aqueous multiphase catalysis. Chemical Engineering and Technology, 2005, 28 (9), 972-978. 

Fache, E. Mercier, C. Pagnier, N. Despeyroux, B. Panster, P. (1993) Selective hydrogenation of a,P-unsaturated aldehydes catalyzed by supported aqueous-phase catalysts and supported homogeneous catalysts,/. Mol. Catal.,19,117-31. 

The selective hydrogenation of a,P-unsaturated aldehydes is used as a probe reaction in studying the strong metal/support interaction (SMSI). Ceria is able to form oxygen vacancies and interme-tallic compounds after reduction treatment at relatively high temperatures. 

Scheme 6.8 Selective hydrogenation of a,P-unsaturated aldehydes to unsaturated alcohols in water.

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