Crotyl alcohol, from crotonaldehyde

Bailie et al. were the first to mention alcohol formation from aldehydes by supported gold-catalyzed selective hydrogenation. The reaction of the formation of crotyl alcohol from crotonaldehyde showed high selectivity (up to 81%) at conversions of 5-10%, with preferential hydrogenation of C=0 rather than the C=C bond [216]. The addition of thiophene promoted this selective hydrogenation. This promotional effect was also observed in similar situations for Cu and Ag, but it was not very common for gold. 

Figure 2A Proposed mechanism for the base-free, aqueous selective aerobic oxidation of crotyl alcohol to crotonaldehyde over PVP-stabilized Au core/Pd shell nanoparticles highlighting the importance of Pd + centers. (Reprinted with permission from Ref [78]. Copyright 2011, American Chemical Society.)...

From the results of this kinetic study and from the values of the adsorption coefficients listed in Table IX, it can be judged that both reactions of crotonaldehyde as well as the reaction of butyraldehyde proceed on identical sites of the catalytic surface. The hydrogenation of crotyl alcohol and its isomerization, which follow different kinetics, most likely proceed on other sites of the surface. From the form of the integral experimental dependences in Fig. 9 it may be assumed, for similar reasons as in the hy-drodemethylation of xylenes (p. 31) or in the hydrogenation of phenol, that the adsorption or desorption of the reaction components are most likely faster processes than surface reactions. 

It is noteworthy that even a separate treatment of the initial data on branched reactions (1) and (2) (hydrogenation of crotonaldehyde to butyr-aldehyde and to crotyl alcohol) results in practically the same values of the adsorption coefficient of crotonaldehyde (17 and 19 atm-1)- This indicates that the adsorbed form of crotonaldehyde is the same in both reactions. From the kinetic viewpoint it means that the ratio of the initial rates of both branched reactions of crotonaldehyde is constant, as follows from Eq. (31) simplified for the initial rate, and that the selectivity of the formation of butyraldehyde and crotyl alcohol is therefore independent of the initial partial pressure of crotonaldehyde. This may be the consequence of a very similar chemical nature of both reaction branches. 

According to Scheme 6.2, the hydrogenation products for crotonaldehyde were butyraldehyde (SAL), crotyl alcohol (UOL), butanol (SOL) and cracking products only at trace levels. Selectivities to UOL, SAL and SOL were maintained from one cycle to the next [20]. 

Catalysts for the selective hydrogenation of crotonaldehyde were obtained by controlled pyrolysis of M40[(CO)9Co3CC02]6 (M=Co and Zn) or M 2 (CO)9Co3CCOO 4 (M =Co, Mo, and Cu). The pyrolyses yield high surface area, amorphous solids. These catalysts are active for the hydrogenation of crotonaldehyde to crotyl alcohol. This differs from conventional metal catalysts, which are selective for the double bond hydrogenation. 

A heterogeneous catalyst derived from the mixed carboxylates [Mo2 Co3(CO)9CC02 4] selectively hydrogenated crotonaldehyde to crotyl alcohol, in contrast to conventional catalysts selective for the hydrogenation of the C=C double bond. " ... 

Figure 2.7 Crotyl alcohol selox over Pd/AI Oj is a strong function of support morphology and Pd oxidation state, with atomically dispersed Pd + centers obtained over mesoporous alumina offering maximum crotonaldehyde production. (Adapted with permission from Ref [35]. Copyright Wiley-VCH Verlag GmbH. Co. KGaA.)...

Promotion by sulfur of gold catalysts for crotyl alcohol formation from crotonaldehyde hydrogenation, J. E. Bailie and G. J. Hutchings, Chem. Common., 1999, 2151. 

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