Catalytic partial hydrogenation

A useful alternative to catalytic partial hydrogenation for converting alkynes to alkenes IS reduction by a Group I metal (lithium sodium or potassium) m liquid ammonia The unique feature of metal-ammonia reduction is that it converts alkynes to trans alkenes whereas catalytic hydrogenation yields cis alkenes Thus from the same alkyne one can prepare either a cis or a trans alkene by choosing the appropriate reaction conditions... 

Although these catalytic partial hydrogenations of alkynes may well be regarded as the procedure of choice for (Z)-alkenes,25 other catalytic systems have been explored. These include a sodium hydride-sodium alkoxide-nickel(n) acetate reagent,26 and a sodium borohydride-palladium chloride-polyethylene glycol system.27 Diisobutylaluminium hydride (DIBAL) has also been used for the conversion of alkynes into (Z)-alkenes.28 ( )-Alkenes are formed when the internal triple bond is reduced with sodium in liquid ammonia.29... 

Possible alternatives to cross-linked polymer supports are soluble and colloidal polymers. They would require large scale ultrafiltration for industrial use. Although ultrafiltration is not yet economical for desalination of seawater, it might be for a separation of a more expensive product. One example is the catalytic partial hydrogenation of soybean oil (361 with soluble polymer-bound transition metal complexes. Solid inorganic supports such as silica gel and alumina are usually not subject to these physical attrition and filtration problems. 

In the early 1990s, processes were developed for the production of 1,4-butanediol and y-butyrolactone by gas-phase catalytic hydrogenation of maleic anhydride (131—134). Succinic anhydride is obtained as a partial hydrogenation by-product in these processes. It can be recycled to complete the hydrogenation to the desired products, or be separated and purified. This process could in the future become a significant commercial route for succinic anhydride. 

The presence of other functional groups ia an acetylenic molecule frequendy does not affect partial hydrogenation because many groups such as olefins are less strongly adsorbed on the catalytic site. Supported palladium catalysts deactivated with lead (such as the Liadlar catalyst), sulfur, or quinoline have been used for hydrogenation of acetylenic compound to (predominantiy) cis-olefins. 

Mikroreaktoren sind so klein wie ein Fingerhut, Handdsblatt, May 1998 Steep progress in microelectronics, sensor and analytical techniques in the past transport intensification for catalysis first catalytic micro reactors available partial oxidation to acrolein partial hydrogenation to cyclododecene anodically oxidized catalyst supports as alternatives to non-porous supports study group on micro reactors at Dechema safety, selectivity, high pressure exclusion of using particle solutions limited experience with lifetime of micro reactors [236],... 

The synthesis, structure, and catalytic properties of a Pd11 complex with a partially hydrogenated ligand, shown in Figure 31, are described.393 This study provides the first asymmetric epoxidation of alkenes catalyzed by a palladium complex.393... 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

Rhee and coworkers published the synthesis of bimetallic Pt-Pd nanoparticles [57] or Pd-Rh nanoparticles [58] within dendrimers as nanoreactors. These nanocatalysts showed a promising catalytic activity in the partial hydrogenation of 1,3-cyclooctadiene. The reaction was carried out in an ethanol/water mixture at 20 °C under dihydrogen at atmospheric pressure. The dendrimer-encapsulated nanoclusters could be reused, without significant loss of activity. 

Recently, Chaudhari compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabilized by various polymers (PVP, PVA or poly(methylvinyl ether)) with the one of conventional supported metal catalysts in the partial hydrogenation of 2-butyne-l,4-diol. Several transition metals (e.g., Pd, Pt, Rh, Ru, Ni) were prepared according to conventional methods and subsequently investigated [89]. In general, the catalysts prepared by chemical reduction methods were more active than those prepared by radiolysis, and in all cases aqueous colloids showed a higher catalytic activity (up to 40-fold) in comparison with corresponding conventional catalysts. The best results were obtained with cubic Pd nanosized particles obtained by chemical reduction (Table 9.13). 

Fig. 10.8 Rate constant k2 for the catalytic COD-hydrogenation with [Rh(cyclohexyl-PROPRAPHOS)COD]BF4 as catalyst at various hydrogen partial pressures (normal pressure and commercial argon/hydrogen mixtures (AGA) which contain 9.71% H2). Reaction mixture 15.0 mL MeOH 0.01 mmol catalyst ...

Table 6 Catalysts for the catalytic partial oxidation of ethanol (CPOX/POE) for hydrogen production...

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