Catalyst asymmetric 430 - mass

As with polybut-l-ene and many other vinyl monomers that contain an asymmetric carbon, isotactic, syndiotactic and atactic stmctures may be drawn. Using co-ordination catalysts such as mixtures of cobalt chlorides, aluminium alkyls, pyridine and water high-1,2 (high vinyl) polymers may be obtained. One product marketed by the Japan Synthetic Rubber Company (JSR 1,2 PBD) is 91% 1,2, and 51-66% of the 1,2 units are in the syndiotactic state. The molecular mass is said to be several hundred thousand and the ratio MJM is in the range 1.7-2.6. 

In a biphasic solid-liquid medium irradiated by power ultrasound, major mechanical effects are the reduction of particles size leading to an increased surface area and the formation of liquid jets at solid surfaces by the asymmetrical inrush of the fluid into the collapsing voids. These liquid jets not only provide surface cleaning but also induce pitting and surface activation effects and increase the rate of phase mixing, mass transfer and catalyst activation. 

Blackmond et al. investigated the influence of gas-liquid mass transfer on the selectivity of various hydrogenations [39]. It could be shown - somewhat impressively - that even the pressure-dependence of enantioselectivity of the asymmetric hydrogenation of a-dehydroamino acid derivatives with Rh-catalysts (as described elsewhere [21b]) can be simulated under conditions of varying influence of diffusion These results demonstrate the importance of knowing the role of transport phenomena while monitoring hydrogenations. 

The effects of added C02 on mass transfer properties and solubility were assessed in some detail for the catalytic asymmetric hydrogenation of 2-(6 -meth-oxy-2 -naphthyl) acrylic acid to (Sj-naproxen using Ru-(S)-BINAP-type catalysts in methanolic solution. The catalytic studies showed that a higher reaction rate was observed under a total C02/H2 pressure of ca. 100 bar (pH2 = 50bar) than under a pressure of 50 bar H2 alone. Upon further increase of the C02 pressure, the catalyst could be precipitated and solvent and product were removed, at least partly by supercritical extraction. Unfortunately, attempts to re-use the catalyst were hampered by its deactivation during the recycling process [11]. 

The high-throughput screening of asymmetric catalysts requires efficient techniques for the determination of enantiomeric excesses. Siuzdak and Finn recently developed a method for that purpose which makes use of kinetic resolution and mass spectrometry [19]. Various chiral secondary alcohols and amines were esterified on... 

Sodeoka et al. have found fhat binuclear /z-hydroxo palladium complex 87 is an efficient catalyst of fhe asymmetric Mannich-type reaction of a-N-arylimino esters with SEE (Scheme 10.80) [226]. Mechanistic studies using NMR and electrospray ionization mass spectrometry suggest that a unique binuclear palladium-sandwiched enolate 88 is involved in fhe palladium-catalyzed reaction. 

Table 7.20 Mass of extracted product, yield, ee-values and osmium content for recycling experiments of osmium catalyst for asymmetric dihydroxylation.

Jessop and co-workers have pointed out that homogeneous catalysis in supercritical fluids can offer high rates, improved selectivity, and elimination of mass-transfer problems.169 They have used a ruthenium phosphine catalyst to reduce supercritical carbon dioxide to formic acid using hydrogen.170 The reaction might be used to recycle waste carbon dioxide from combustion. It also avoids the use of poisonous carbon monoxide to make formic acid and its derivatives. There is no need for the usual solvent for such a reaction, because the excess carbon dioxide is the solvent. If the reaction is run in the presence of dimethy-lamine, dimethylformamide is obtained with 100% selectivity at 92-94% conversion.171 In this example, the ruthenium phosphine catalyst was supported on silica. Asymmetric catalytic hydrogenation of dehydroaminoacid derivatives (8.16) can be performed in carbon dioxide using ruthenium chiral phosphine catalysts.172... 

All the above-mentioned LnSB crystals showed similar mass patterns compared to those of Ln-Li-BINOL complexes, though they contained sodium instead of lithium. The oligomeric structure of the catalysts in the reaction mixture was supported by a slightly positive asymmetric amplification in the asymmetric nitroaldol reaction [9]. In addition, quite recently Shibasaki et al. reported the first X-ray crystallographic structure of a lithium-containing heterobime-tallic catalyst of type LnLB, namely the SmLi3tris(binaphthoxide) complex SmLB [8]. 

In certain applications, the size of the biocatalyst is not suitable for entrapment into the supporting sponge layer of asymmetric membranes. In these cases, the membrane acts mainly as a selective barrier it defines a reactive zone in the vessel, usually the shell, accessible to substrates and products mainly by diffusive mass transfer preventing the catalyst from pollution or inhibition possibly caused by other species in solution.54-69... 

Balazsik, K., Bartok, M. (2004) Heterogeneous asymmetric reactions-Part 40. New data on repeated use of Pt-alumina catalyst during enantioselective hydrogenation of ethyl pyruvate, J. Mol. Catal. A. Chem. 219,383-389. Bartok, M., Bartok, T., Szollosi, G., Felfoldi, K. (1999) Electrospray ionization mass spectrometry in the heterogeneous catalyzed organic reactions unknown compounds in the pyruvate hydrogenation, Catal. Lett. 61,57-60. 

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