Hydrogenation of acrylic acids

Scheme 8.19 Hydrogenations of acrylic acid derivatives with sugar dithioether ligands.

Quantitative rate measurements under a variety of conditions support such a mechanism [4, 15]. A complete kinetic analysis is available for the hydrogenation of acrylic acid derivatives using the precatalysts RuCl2(PPh3)3 in the solvent dimethylacetamide, although the system is much less active in this more polar and coordinating solvent (e.g., entry 3, Table 3.1). 

Table 21.11 Directive hydrogenation of acrylic acid derivatives. 

The addition of dopants is found to have beneficial effects. However, they are not restricted only to transition metals. The hydrogenation of acrylic acid can be promoted significantly by the addition of neodymium ions onto the palladium particles [142], The selective transformation of 3,4-dichloronitrobenzene to the corresponding aniline has been selected to test pre-prepared Pt hydrosols as heterogeneous catalyst precursors (see Figure 3.9) [143],... 

Zrara-[RuCl2(381-P,A, A, P )]. The complex trans- [RuCl2(380-P, N,N ,P )] catalyzes the hydrogenation of acrylic acid to propionic acid. " ... 

Only limited successful examples of asymmetric hydrogenation of acrylic acids derivatives have included the use of chiral Rh complexes (Scheme 1.17). The diamino phosphine (28) utilizes selective ligation of the amino unit to a Rh center and also exerts electrostatic interaction with a substrate. Its Rh complex catalyzes enantioselective hydrogenation of 2-methylcinnamic acid in 92% optical yield [116], Certain cationic Rh complexes can attain highly enantioselective hydrogenation of trisubstituted acrylic acids [ 1171. 2-(6 -Methoxynaphth-2 -yl)acrylic acid is hydrogenated by an (.S ..S )-BIPNOR- Rh complex in methanol at 4 atm to give (.S)-naproxen with 98% ee but only in 30% yield [26]. 

Enantioselective catalytic hydrogenation. Hoffmann-LaRoche chemists have examined the efficiency of DIOP (1) and a number of related phosphines as ligands for asymmetric hydrogenation of acrylic acids for synthesis of (R)-6-methyl-tryptophan (6), of potential value as a non-nutritive sweetening agent. Of these, 2 and the less available 3 showed the most promise. Thus catalytic hydrogenation of 4... 

Hydrogenation of acrylic acid esters with high enantioselectivity has usually been accomplished with difficulty. The enantioselective reduction of a,p-unsaturated carboxylates with sodium borohydride in the presence of cobalt-semicorrin complexes has been achieved in up to 96% ee (equation 14). The (Eland (Z)-isomers each afford products of opposite configuration, and the isolated double bonds remain un-touched. ... 

Enzymatic hydrogenations generate optically pure isomers attempts to initiate such processes are made on metal-catalyzed hydrogenations. Asymmetric hydrogenation can fill the need for asymmetric compounds of which only one enantiomorph is active, e.g., amino acids such as L-lysine, 1 (indispensable in animal feeds), L-phenylalanine, 2 (a sweet peptide component), L-dopa 3 (a drug for Parkinsonism), are required in the L-form for human or animal consumption. Consequently, most of the examples investigated are related to the asymmetric hydrogenation of acrylic acid or cinnamic acid derivatives. 

The catalyst formed by reaction of these polymer-bound ligands 4 a and 5 with [Rh(nbd)2]S03CH3 (nbd = norbornadiene) was used for hydrogenation of water-soluble (and also water-insoluble) alkenes in aqueous solution. The hydrogenation of acrylic acid proceeded smoothly (TOF ca. 100 h 1 at 25 °C, 1 atm) in water with the PEI-bound catalyst, whereas with the PAA-bound catalyst precipitation of the catalyst occurred due to the change in pH caused by the added acrylic acid [10c], A possible effect of salt formation of acrylic acid with the basic PEI on the reactivity of the unsaturated acid was not investigated. With l-buten-4-ol as the substrate... 

The water-soluble cluster Ru3(CO)9(tppms)3 (tppms = sodium diphenylphosphinobenzene-w-sulfonate) was used as the catalyst precursor for hydrogenation of acrylic acid and styrene. The cluster also catalyzed the hydroformyla-tion of propylene with syngas in water, forming mainly butanal, along with smaller amounts of 2-methylpropanal, butanol, and 2-methylpropanol. Typical conditions were 393 K and 40 atm of 1 1 CO H2. TOFs of 61 mol products (mol cluster h) and product n iso ratio of 15.9 were obtained. Ethylene hydroformylation was also examined. 

The doping of noble metal catalyst precursors is not restricted to the early transition metal series. Toshima has reported significant promotion of catalytic activity in the hydrogenation of acrylic acid by the addition of neodymium ions to palladium particles. Recently, Liu and coworkers have studied the influence of metal ions on the hydrogenation of o-chloronitrobenzene over platinum colloidal clusters, and the metal complex effect on the catalytic performance of metal... 

Table 7 Activation Parameters for Hydrogenation of Acrylic Acid and Cobalt Acrylate...

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