Synthesis catalyst, highly selective

The catalysts derived from supported iron clusters exhibit in Fischer-Tropsch synthesis a high selectivity for propylene. Those catalysts are also selective for the stoechiometric homologation of ethylene to propylene and of propylene to n and iso butenes. The results are explained on the basis of a new mode of C-C bond formation which implies < - olefin coordination to surface methylene fragments or methylene insertion into a metal alkyl bond. 

Although the current industrial methanol synthesis is highly selective to methanol, side products are formed in quantities determined by the specific catalyst used and by the reaction conditions. These side reactions involve... 

We conclude this section by the recent investigations of Lv and Cui. These authors reported on the synthesis and highly selective cis-1,4 polymerization of IP promoted by [CCC ]-pincer bis-NHC rare-earth complexes (Scheme 27) [138]. The presumed active species, containing two Al-(p-H)-Y bridging hydrides, was characterized upon mixing the yttrium precatalyst of type 55 with Al(iBu)3 (10 equiv.) and [PhsC] [B(C6p5)4] (Scheme 27, 56). The binary systems consisting of complexes 55 (Y, Nd, Gd or Dy)/TEA were found to be best suited for IP polymerization (500 equiv. IP, 15-30 min, room temperature, quantitative conversion, 96.3-98.6% cii-1,4-selectivity, 1.73 < PDI < 2.27). It is noteworthy that the isolated active catalyst 56 polymerizes IP with comparable activity and selectivity but with an improved polymerization control vs. the in situ formed catalyst (PDI = 2.83 vs. 3.81). 

A similar process to SMDS using an improved catalyst is under development by Norway s state oil company, den norske state oHjeselskap AS (Statod) (46). High synthesis gas conversion per pass and high selectivity to wax are claimed. The process has been studied in bubble columns and a demonstration plant is planned. 

Homogeneous rhodium-catalyzed hydroformylation (135,136) of propene to -butyraldehyde (qv) was commercialized in 1976. -Butyraldehyde is a key intermediate in the synthesis of 2-ethyIhexanol, an important plasticizer alcohol. Hydroformylation is carried out at <2 MPa (<290 psi) at 100°C. A large excess of triphenyl phosphine contributes to catalyst life and high selectivity for -butyraldehyde (>10 1) yielding few side products (137). Normally, product separation from the catalyst [Rh(P(C2H2)3)3(CO)H] [17185-29-4] is achieved by distillation. 

In the early work on the synthesis of prostaglandins, zinc borohydride was used for the reduction of the 15-ketone function and a 1 1 mixture of epimeric 15(S)- and 15(/ )-alcohols was generally obtained. Subsequent studies led to reaction conditions for highly selective reduction to the desired 15(S)-alcohol. Some of the results are summarized in the following table. The most practical method is E which utilizes borane as the stoichiometric reductant and a chiral, enzyme-like catalyst which is shown. 

The past thirty years have witnessed great advances in the selective synthesis of epoxides, and numerous regio-, chemo-, enantio-, and diastereoselective methods have been developed. Discovered in 1980, the Katsuki-Sharpless catalytic asymmetric epoxidation of allylic alcohols, in which a catalyst for the first time demonstrated both high selectivity and substrate promiscuity, was the first practical entry into the world of chiral 2,3-epoxy alcohols [10, 11]. Asymmetric catalysis of the epoxidation of unfunctionalized olefins through the use of Jacobsen s chiral [(sale-i i) Mi iln] [12] or Shi s chiral ketones [13] as oxidants is also well established. Catalytic asymmetric epoxidations have been comprehensively reviewed [14, 15]. 

The effect of the catalyst composition upon the catalyst activity, selectivity, and reaction pathways was examined using a conventional high pressure fixed reactor and a TAP reactor. Particular emphasis was placed upon the effect of Au and KOAc on the acceleration or impedance of the pathways associated with vinyl acetate synthesis. A summary of the key findings is given below ... 

The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic t3pes of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst that was treated with EDTA (H-EDTA-MOR) showed the highest activity and selectivity for the formation of EA at 603 K, W/F=200 g h mol, and NH3/ =50. The reaction proved to be highly selective for EA over H-EDTA-MOR, with small amounts of ethyleneimine (El) and piperazine (PA) derivatives as the side products. IR spectroscopic data provide evidence that the protonated El is the chemical intermediate for the reaction. The reaction for Uie formation of EDA from EA and ammonia required stronger acidic sites in the mordenite channels for hi er yield and selectivity. 

Interestingly, significant progress has been made for the hydroamination of more reactive substrates such as styrenes, alkynes, dienes, and allenes. Specifically, highly selective catalysts have been discovered for the synthesis of fine chemicals (pharmaceuticals, natural products, chemical intermediates). In this area however, the problem of catalyst stabiUty can also be questioned in several cases. 

The synthesis in Scheme 13.40 features a catalytic asymmetric epoxidation (see Section 12.2.1.2). By use of me30-2,4-dimethylglutaric anhydride as the starting material, the proper relative configuration at C(4) and C(6) is ensured. The epoxidation directed by the (+)-tartrate catalyst controls the configuration established at C(2) and C(3) by the epoxidation. Although the epoxidation is highly selective in... 

Enzymes have several remarkable catalytic properties such as high catalytic power and high selectivities under mild reaction conditions, as compared with those of chemical catalysts. In the field of organic synthesis, enzymes have often been employed as catalyst functional organic compounds were synthesized by the enzymatic selective reactions [1-5]. 

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